1 KVA 240 v transformer output 6v,8v,12 v AC how to test if

[Bob Eldred]

"Rob" <Rob@rob.co.uk> wrote in message
news:u5jl51l8u1tsa1j2is8o0h52p66l6mmoal@4ax.com...

Hi
well since last time i asked for advice i have had a few
problems...First problem was i had ordered some 400A 30V low Vf
Schottky diode rectifiers i won them on ebay

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=3877178672&ssPageName=STRK:MEWN:IT
...But never got them through the post so that delayed me a week or
so..Then i Bought from a Surplus shop 8 x 110 amp Rectifiers..they
were only a about 3$ each ...used but untested..I got them from Cpi
surplus in the USA ..very fast service...Unfortunatley the diodes i
bought were Silicon controlled rectifiers...Which my Radio Ham friend
told me they are no use for what i wanted...So i was realy pissed
off!!...So i decided to spend even more money on another PSU rated at
5 Volts at 325 amps..I won it on ebay a week orso ago..

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=7501227612&ssPageName=STRK:MEWN:IT..

http://www.abex.co.uk/sales/electronic/psu/rack/p10/p_series.pdf

Its made by Power Ten INC.. its a 19 inch rack mounted PSU with
variable Voltage and Current control..First impressions were WOW!!
when i turned it on it sounded like a jet taking of lots of noise from
the internal fans...However my Smile was soon wiped of my face when i
tried to test the power output...

I connected it up to a short length of nicrome wire and set the
voltage to 5 Volts and slowly turned up the current .. all i could get
was 20 amps the wire glowed white hot ..Now i have done this test
before on my old 400watt computer PSU and it went off scale on my 25
amp analoge meter.. and melted the nicrome wire...

I then tried a very crude electrolyisis of my Lead Nitrate solution,
using my old 400 watt PSU i can get 15 amps thru it ..But with this
PSU i only managed a poxy 2 amps... i am now totaly pissed off!!!?

Have i wasted even more money?...How can i test my PSU?.. will it
damage the unit if i make a dead short on the connections.. and slowly
turn up the current ?...The control for the current works by setting a
limit on the power supply...I hope some one can put a smile back on my
face...

Dont forget i want to use the power supply for electrolysing Sodium
Chloride solution..I have read several patents and the cells run at
about 4.75 volts at several hundred amps....

So i assumed that a 5V supply should be able to do the job... I have
got several amp meters to read the current..


http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=4534893020&sspagename=STRK%3AMEWN%3AIT&rd=1


http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=7500828509&ssPageName=STRK:MEWN:IT

But at the moment i have no power supply that can give me the current
i require..

Is the PSU faulty?...or is it something else i am overlooking?..

Hope some one can help ....

Cheers

Rob

"I connected it up to a short length of nicrome wire and set the
voltage to 5 Volts and slowly turned up the current .. all i could get
was 20 amps the wire glowed white hot ..Now i have done this test
before on my old 400watt computer PSU and it went off scale on my 25
amp analoge meter.. and melted the nicrome wire..."

How do you know it will only put out 20 Amps? What is the "droop" on the
five volts as you increase the current? What is the current sensing scheme
in the PS? At 325Amps, you can be sure there is an "ample" shunt some where
in the unit. Be sure the right shunt is in place. Double up on the nichrome
test resistor and cut its lenght in half. Better yet, put the nichrome in a
pan of water and measure the voltage and current. The water should keep it
cool enough that the resistance stays more or less constant. You need to
make a resistor you can rely on that is about 0.125 ohms for 40 Amps @ 5
Volts. Be sure the leads and connections don't add to your resistance. It
wouldn't take much to degrade the current to 20 Amps.

On another subject, why couldn't you use the SCRs as rectifiers. All you
have to do is trigger them on each half cycle with some simple circuitry.
Bob

 

[John Popelish]

Rob wrote:

Hi
well since last time i asked for advice i have had a few
problems...First problem was i had ordered some 400A 30V low Vf
Schottky diode rectifiers i won them on ebay
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=3877178672&ssPageName=STRK:MEWN:IT
...But never got them through the post so that delayed me a week or
so..Then i Bought from a Surplus shop 8 x 110 amp Rectifiers..they
were only a about 3$ each ...used but untested..I got them from Cpi
surplus in the USA ..very fast service...Unfortunatley the diodes i
bought were Silicon controlled rectifiers...Which my Radio Ham friend
told me they are no use for what i wanted...So i was realy pissed
off!!...So i decided to spend even more money on another PSU rated at
5 Volts at 325 amps..I won it on ebay a week orso ago..
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=7501227612&ssPageName=STRK:MEWN:IT..

http://www.abex.co.uk/sales/electronic/psu/rack/p10/p_series.pdf

Its made by Power Ten INC.. its a 19 inch rack mounted PSU with
variable Voltage and Current control..First impressions were WOW!!
when i turned it on it sounded like a jet taking of lots of noise from
the internal fans...However my Smile was soon wiped of my face when i
tried to test the power output...

I connected it up to a short length of nicrome wire and set the
voltage to 5 Volts and slowly turned up the current .. all i could get
was 20 amps the wire glowed white hot ..Now i have done this test
before on my old 400watt computer PSU and it went off scale on my 25
amp analoge meter.. and melted the nicrome wire...

I then tried a very crude electrolyisis of my Lead Nitrate solution,
using my old 400 watt PSU i can get 15 amps thru it ..But with this
PSU i only managed a poxy 2 amps... i am now totaly pissed off!!!?

Have i wasted even more money?...How can i test my PSU?.. will it
damage the unit if i make a dead short on the connections.. and slowly
turn up the current ?...The control for the current works by setting a
limit on the power supply...I hope some one can put a smile back on my
face...

Dont forget i want to use the power supply for electrolysing Sodium
Chloride solution..I have read several patents and the cells run at
about 4.75 volts at several hundred amps....

So i assumed that a 5V supply should be able to do the job... I have
got several amp meters to read the current..

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=4534893020&sspagename=STRK%3AMEWN%3AIT&rd=1

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=7500828509&ssPageName=STRK:MEWN:IT

But at the moment i have no power supply that can give me the current
i require..

Is the PSU faulty?...or is it something else i am overlooking?..

Hope some one can help ....

Cheers

Rob
Either of the shunt meter combinations you bought will drop some of

the supply voltage as they read current. For the experiments you have
done so far, have the external current meters read about the same as
the panel meter on the supply? If so, eliminate the external meter
and just read the current of the panel of the supply.

It sounds like you are voltage limited, but it would be a good idea to
put a volt meter across any dummy load to verify that the load voltage
equals the panel meter on the supply.

You can parallel several chunks of nichrome for the load test. Make
sure you clamp them into heavy terminals (like split bolt clamps used
to bond ground wires) and use heavy wire (something with copper about
as fat as a pencil) from the supply to avoid voltage loss.

 

[Rob]

Ok let me explain a little bit more.. on the front panel i have 2
control knobs each one controls voltage and the second one is used to
set a limit on the current...the digital display, displays the actual
voltage and thel current in use..

Today what i have done is the following .. The rear Positive and
negative terminals i connected a piece of copper welding rod about a
foot long its about 2 mm thick.. To me this is a dead short and i
expected to be able to turn up the current so as to melt the copper
rod... However all that happend was that at about 30 odd amps it
glowed red and then the current gradually dropped to about 25 amps...I
admit i am a total novice at electrics but i was sure it would have
took more current than 30 amps...i was sure it would glow white hot
and pop like a fuse?...I then cut the welding rod and tried it at
about 3 inch long this time it glowed whiter at about 80 amps...at 5
volts..Now i have to say im getting very pissed off!!!..So next i
added to the rear terminals a 10mm bolt about 3 inch long .. turned up
the current and i stopped as it went over 150 amps???.... didnt want
to break anything so i stopped increasing the current...Now i am
totaly baffled the PSU can supply at least 150 amps to a big bolt?...
so why isnt it giveing that type of amperage thru my electrolyitic
cell?...

My final test was to use a car battery tester.. this consists of a
large strip of bent metal in between 2 metal prongs.. which has a amp
meter in between it can test 12 v and 6 v car batterys...you normaly
hold the prongs on the battery terminal and the heavy metal strip
gets very hot you can read the ammeter readings to see how good the
battery is..the bent metal strip is coverd with asbestos sheet to stop
getting burnt..

Well i connected this battery tester to the positive and negative
connection while my Dad turned up the current control..we stopped the
experiment at about 250 amps.. it was obvious the PSU was working?....

So i am totally gutted have i just wasted a lot of money... on a PSU..

Why ? wont the PSU supply lots of amps to my Cell?....I have read
several patents...the Voltage on the cell ranged between 3.9 v and 4.5
v? at several 100 amps?.. the electrolytic solution is a super
saturated Salt solution..?... I have replicated the exact experiment
yet it wont work?..So surley the PSU is faulty?... but yet if it is
why did it supply 250 + amps in the battery test?.. is there some way
i can force the amps out of the unit?...

If the answer is yes I have wasted even more money .. what power
supply do i actualy need?...I have had several knock backs with this
project.. but this one as knocked me of feet..My friend's say i have
to stop wasting money...but i will get another power supply if i have
to...i wont be beaten...i will just go bankcrupt ..

Hope you can advise?...

 

[John Popelish]

Rob wrote:

Ok let me explain a little bit more.. on the front panel i have 2
control knobs each one controls voltage and the second one is used to
set a limit on the current...the digital display, displays the actual
voltage and thel current in use..

Today what i have done is the following .. The rear Positive and
negative terminals i connected a piece of copper welding rod about a
foot long its about 2 mm thick.. To me this is a dead short and i
expected to be able to turn up the current so as to melt the copper
rod... However all that happend was that at about 30 odd amps it
glowed red and then the current gradually dropped to about 25 amps...I
admit i am a total novice at electrics but i was sure it would have
took more current than 30 amps...i was sure it would glow white hot
and pop like a fuse?...I then cut the welding rod and tried it at
about 3 inch long this time it glowed whiter at about 80 amps...at 5
volts..Now i have to say im getting very pissed off!!!..So next i
added to the rear terminals a 10mm bolt about 3 inch long .. turned up
the current and i stopped as it went over 150 amps???.... didnt want
to break anything so i stopped increasing the current...Now i am
totaly baffled the PSU can supply at least 150 amps to a big bolt?...
so why isnt it giveing that type of amperage thru my electrolyitic
cell?...

My final test was to use a car battery tester.. this consists of a
large strip of bent metal in between 2 metal prongs.. which has a amp
meter in between it can test 12 v and 6 v car batterys...you normaly
hold the prongs on the battery terminal and the heavy metal strip
gets very hot you can read the ammeter readings to see how good the
battery is..the bent metal strip is coverd with asbestos sheet to stop
getting burnt..

Well i connected this battery tester to the positive and negative
connection while my Dad turned up the current control..we stopped the
experiment at about 250 amps.. it was obvious the PSU was working?....

So i am totally gutted have i just wasted a lot of money... on a PSU..

Why ? wont the PSU supply lots of amps to my Cell?....I have read
several patents...the Voltage on the cell ranged between 3.9 v and 4.5
v? at several 100 amps?.. the electrolytic solution is a super
saturated Salt solution..?... I have replicated the exact experiment
yet it wont work?..So surley the PSU is faulty?... but yet if it is
why did it supply 250 + amps in the battery test?.. is there some way
i can force the amps out of the unit?...

If the answer is yes I have wasted even more money .. what power
supply do i actualy need?...I have had several knock backs with this
project.. but this one as knocked me of feet..My friend's say i have
to stop wasting money...but i will get another power supply if i have
to...i wont be beaten...i will just go bankcrupt ..

Hope you can advise?...

The patents you read talk about the voltage at the load, but you have
to get that current to the load with almost no voltage drop if your
supply has only the voltage needed for the load. What diameter copper
are you using to connect the supply to your salt load? The conductors
inside the salt bath also have to be very heavy to keep voltage loss
to a minimum, of you have to make up that extra voltage with a higher
voltage supply.

 

[John Fields]

On Tue, 12 Apr 2005 12:32:51 +0100, Rob <Rob@rob.co.uk> wrote:

Ok let me explain a little bit more.. on the front panel i have 2
control knobs each one controls voltage and the second one is used to
set a limit on the current...the digital display, displays the actual
voltage and thel current in use..

Today what i have done is the following .. The rear Positive and
negative terminals i connected a piece of copper welding rod about a
foot long its about 2 mm thick.. To me this is a dead short and i
expected to be able to turn up the current so as to melt the copper
rod... However all that happend was that at about 30 odd amps it
glowed red and then the current gradually dropped to about 25 amps

---
Yes. what happened is that the resistance of the rod was greater than
you thought, initially, and then as it got hotter and hotter its
resistance got greater and greater and increased to the point where
with 5 volts across it the power supply could only push 25 amps
through it.
---

...I admit i am a total novice at electrics but i was sure it would have
took more current than 30 amps...i was sure it would glow white hot
and pop like a fuse?...I then cut the welding rod and tried it at
about 3 inch long this time it glowed whiter at about 80 amps...at 5
volts..Now i have to say im getting very pissed off!!!..

---
Why? You're starting to get at the root of the problem! A shorter
piece of rod would have less resistance than than a longer one so, for
the same voltage across it, the PSU would push more current through
it, exactly what happened!

Since you cut the rod to 1/4 the length of the one foot one you stared
out with, the resistance would drop to 1/4 the resitance of the first
one, so with the same voltage across the short one you could expect
four times the current through it. Since you got 25 amps through the
long one, that means you should have been able to get 100 amps through
the short one, but since the short one got hotter than the first one
its resistance would increase to the point where you'd get something
less than 100 amps, which is what happened; you got 80 amps. Pretty
close, though!
---

So next i added to the rear terminals a 10mm bolt about 3 inch long ..
turned up the current and i stopped as it went over 150 amps???....
didnt want to break anything so i stopped increasing the current...
Now i am totaly baffled

---
The bolt had less resistance than the copper rod, so the PSU pushed
more current through it.
---

the PSU can supply at least 150 amps to a
big bolt?... so why isnt it giveing that type of amperage thru
my electrolyitic cell?...

---
Could be lots of reasons... The resistance of your electrolytic cell
is too high, the cables connecting it to the PSU are too long or have
a diameter that is too small, the connections from the PSU to the
cables and from the cables to the PSU have a resistance that is too
high...
---

My final test was to use a car battery tester.. this consists of a
large strip of bent metal in between 2 metal prongs.. which has a amp
meter in between it can test 12 v and 6 v car batterys...you normaly
hold the prongs on the battery terminal and the heavy metal strip
gets very hot you can read the ammeter readings to see how good the
battery is..the bent metal strip is coverd with asbestos sheet to stop
getting burnt..

Well i connected this battery tester to the positive and negative
connection while my Dad turned up the current control..we stopped the
experiment at about 250 amps.. it was obvious the PSU was working?....

So i am totally gutted have i just wasted a lot of money... on a PSU..

Why ? wont the PSU supply lots of amps to my Cell?....I have read
several patents...the Voltage on the cell ranged between 3.9 v and 4.5
v? at several 100 amps?.. the electrolytic solution is a super
saturated Salt solution..?... I have replicated the exact experiment
yet it wont work?..So surley the PSU is faulty?... but yet if it is
why did it supply 250 + amps in the battery test?.. is there some way
i can force the amps out of the unit?...

---
Lower the resistance of whatever is between the PSU and the cell or
get a PSU with a higher voltage output.
---

If the answer is yes I have wasted even more money .. what power
supply do i actualy need?...I have had several knock backs with this
project.. but this one as knocked me of feet..My friend's say i have
to stop wasting money...but i will get another power supply if i have
to...i wont be beaten...i will just go bankcrupt ..

---
You refuse to quit, huh? EXCELLENT!!!
---

Hope you can advise?...

---
If you crank it to the max with no load on it, what kind of voltage
can you get out of it?

Your PSU obviously works, so the trick is going to be to get as much
of that 5V it can put out to the cell.

If we look at the worst case input voltage for the cell, you say that
that's 4.5V, so that means that if the most you can get out of the
power supply is 5.0V and the cell needs 4.5V to work, you can only
lose 0.5V in the wiring between the supply and the cell. If you want
to put 250 amps into the cell, that means that 250 amps also has to go
through the wiring, so the maximum resistance you're allowed is:

E 0.5V
R = --- = ------ = 0.002 ohms
I 250A

which isn't a lot of resistance, so the first order of business will
be to select the size of cable which will pass 250 amps without
dropping 0.5V. If we arbitrarily say that the PSU will be located so
that there will need to be ten feet of cable from the PSU to the cell,
and then ten feet of cable from the cell back to the PSU, then that
means that the cable we choose will have to have a resistance of less
than 2 milliohms per 20 feet, or 100ľohms per foot.

Consulting a wire table, we find that #0 AWG has a resistance of 0.098
ohms per thousand feet, so that will work. With a diameter of 0.325",
it won't be that hard to work with, either. To get the lowest
resistance connections you should solder lugs on the ends of the
cables and make sure the connections to the power supply and the cell
are good and tight.

One final trick, your power supply has remote sensing, which means
that instead of keeping the voltage regulated at the output of the
supply, you can set it up to keep the voltage AT THE CELL regulated
and compensate for the cable resistance, within limits. I'd still go
with the #0 and the soldered lugs and all, but I'd use remote sensing
to compensate for cable heating and changes in the cell resistance
when it's running, etc. Check 3.5 on page 36 of the manual for how to
do it.

--
John Fields
Professional Circuit Designer

 

[Rob]

On another subject, why couldn't you use the SCRs as rectifiers. All you
have to do is trigger them on each half cycle with some simple circuitry.
Bob

Is it easy to make a circuit to make to use of the SCR diodes? ? were
would i find such a circuit diagram?

 

[Bob Eldred]

"Rob" <Rob@rob.co.uk> wrote in message
news:9dan519v051c2s45ji12aui8eolqatpcqt@4ax.com...

Ok let me explain a little bit more.. on the front panel i have 2
control knobs each one controls voltage and the second one is used to
set a limit on the current...the digital display, displays the actual
voltage and thel current in use..

Today what i have done is the following .. The rear Positive and
negative terminals i connected a piece of copper welding rod about a
foot long its about 2 mm thick.. To me this is a dead short and i
expected to be able to turn up the current so as to melt the copper
rod... However all that happend was that at about 30 odd amps it
glowed red and then the current gradually dropped to about 25 amps...I
admit i am a total novice at electrics but i was sure it would have
took more current than 30 amps...i was sure it would glow white hot
and pop like a fuse?...I then cut the welding rod and tried it at
about 3 inch long this time it glowed whiter at about 80 amps...at 5
volts..Now i have to say im getting very pissed off!!!..So next i
added to the rear terminals a 10mm bolt about 3 inch long .. turned up
the current and i stopped as it went over 150 amps???.... didnt want
to break anything so i stopped increasing the current...Now i am
totaly baffled the PSU can supply at least 150 amps to a big bolt?...
so why isnt it giveing that type of amperage thru my electrolyitic
cell?...

My final test was to use a car battery tester.. this consists of a
large strip of bent metal in between 2 metal prongs.. which has a amp
meter in between it can test 12 v and 6 v car batterys...you normaly
hold the prongs on the battery terminal and the heavy metal strip
gets very hot you can read the ammeter readings to see how good the
battery is..the bent metal strip is coverd with asbestos sheet to stop
getting burnt..

Well i connected this battery tester to the positive and negative
connection while my Dad turned up the current control..we stopped the
experiment at about 250 amps.. it was obvious the PSU was working?....

So i am totally gutted have i just wasted a lot of money... on a PSU..

Why ? wont the PSU supply lots of amps to my Cell?....I have read
several patents...the Voltage on the cell ranged between 3.9 v and 4.5
v? at several 100 amps?.. the electrolytic solution is a super
saturated Salt solution..?... I have replicated the exact experiment
yet it wont work?..So surley the PSU is faulty?... but yet if it is
why did it supply 250 + amps in the battery test?.. is there some way
i can force the amps out of the unit?...

If the answer is yes I have wasted even more money .. what power
supply do i actualy need?...I have had several knock backs with this
project.. but this one as knocked me of feet..My friend's say i have
to stop wasting money...but i will get another power supply if i have
to...i wont be beaten...i will just go bankcrupt ..

Hope you can advise?...

For openers, your cell resistance plus all of the other resistances of the
wires, connections, etc., add up to more than 0.05 Ohms required to get 100
Amps at five volts. A power supply of this current capability will 'always'
have remote voltage sensing that allows you to sense the voltage at the
load bypassing the voltage drops of wires, terminals, shunts, etc. At the
output terminals of the P.S. look for a second connection on both the
positive and negative points labeled "sense" or "voltage sense" or some such
wording. Disconnect these wires from the output terminals and re-connect
them with extension wires directly to your load, resistor, welding rod or
cell making it a four wire connection. That way the power supply will
maintain five volts at the load and not somewhere else, up stream as it now
does. In doing this, I think you'll find much better performance with the
ability to deliver much greater current.

Another point: Any metal that gets hot, especially red hot, increases
markedly in resistance. This limits the current to some lower than expected
value. Light bulbs work this way. When cold, the resistance is low and it
increases to a high value when the lamp is operating which limits the
current keeping the lamp from blowing. I suspect that is why you had trouble
delivering higher currents into your rod resistances. This is the reason why
I suggested placing the resistance elements in water, to keep the increase
in temperature, and therefore resistance in check.
Bob

 

[Fritz Schlunder]

"Rob" <Rob@rob.co.uk> wrote in message
news:u5jl51l8u1tsa1j2is8o0h52p66l6mmoal@4ax.com...

I then tried a very crude electrolyisis of my Lead Nitrate solution,
using my old 400 watt PSU i can get 15 amps thru it ..But with this
PSU i only managed a poxy 2 amps... i am now totaly pissed off!!!?

As others have suggested either indirectly or directly stated, your power
supply is almost certainly perfectly fine. The problem lies in your
implementation and/or understanding of the physics and chemistry of what you
are doing.

The answer to why you only got 2A versus 15A through your lead nitrate
solution lies probably in your words "very crude." Something differed
between your two tests, and I would bet it was more than just the PSU you
employed. The chemistry behind the electrolysis cell is very important in
dertermining what your results will be. Not only does the chemical reaction
have a built in voltage (below which possibly very little current will flow
at all regardless of voltage applied), but other physical factors are very
important as well. The electrode material and geometry can be very
important. The spacing between the electrodes may be important. Addionally
the molarities and other chemistry aspects (ex: temperature, prescence of
impurities, etc.) will play a major role.

You most likely altered something you weren't aware of between the two tests
that made a major impact on the cell's performance.

It is also conceiveable the 400W PSU (presumably from a computer) output
something more than 5V on the 5V rail (which I what I assume you used).
Given that they have multiple rails to regulate, they often end up not
regulating any of them very well, so it isn't that hard to find computer
PSUs that output say 5.5V on the 5V rail. The new PSU probably is better
regulated since it has only one rail and is a high end device. If it only
outputted say 4.8V (which is acceptable for most 5V specifications), then
that might also play a role in producing your differing results.

Dont forget i want to use the power supply for electrolysing Sodium
Chloride solution..I have read several patents and the cells run at
about 4.75 volts at several hundred amps....

What exactly are you trying to do? Can you tell us what patent numbers you
are looking at and/or provide us with links so we can read for ourselves?
As I understand it sodium chloride has a melting point of 804 deg. C. As I
understand it sodium metal vapor can possibly catch fire or maybe even
explode at this temperature when in contact with air. Even so you have to
keep the sodium away from air to prevent it from extreme rapid oxidation at
these temperatures. So normally something like 60% by mass of calcium
chloride is added to the cell to lower the melting point down to around
575-600 deg. C. Is this what you are planning to do?

As I understand it commercial production of sodium is typically done in
Downs cells operating at many thousands of amps with an applied voltage of
up to maybe 8V or so even though basic chemistry might lead you to believe
4.07V is adequate. At high current it is crucially important to keep
parasitic resistances down both inside and outside of the cell.

In addition to using your power supply's voltage sensing at the load
feature, you might also consider changing the calibrated 5V reference
voltage. The manual also has a section detailing this. If you adjust the
potentiometer to set it at the maximum you may be able to coax somewhat
higher voltage out of the device, but it may have adverse side effects such
as making the readouts on the front somewhat inaccurate. I would consider
this as a last resort.

Have you actually tried hooking your new supply up to an NaCl electrolyser?
I'm guessing you haven't. I'm guessing you haven't constructed that part
yet. You might be suprised, it may actually work better than you are
currently convinced it will. Molten sodium chloride isn't the same stuff as
some kind of crude lead nitrate solution.

You may find something like this wire gauge specifications calculator useful
in helping you with obeying V=IR in your design.

http://www.mogami.com/e/cad/wire-gauge.html

 

[Rob]

Sorry to be a pain..

But can some one explain this to me ?


If i had good connections big thick wire , a Anode and cathode of say
stainless steel...surface area of 500 square cm and placed it in a
saturated salt solution( sodium chlordie dissolved in water) and
connected a PSU that was rated at 5 V 300 amps.. what current would
flow thru the cell?.. should it be like a dead short?. Is a DC psu
all the same ? are plating rectifiers different ?? I am sure than it
if i had a plating rectifier i would get my 100 amps thru the cell?


..I have just looked at some plating rectifiers... and saw a term
called "constant current" Does this mean the Plating rectifeirs can
be set to give out a fixed say 100 amps? current..thats is force the
amps thru the solution?...My PSU you set the Max limit that can be
drawn.. but a plating rectifier if you set 100 amps will it force 100
amps thru?.. in which case i think my dc PSU is not up to the
job..ARRRGGHHH...

To confirm this i have just won a 140 amp bridge rectifier on ebay.. i
will use this to get DC cuurrent from my 83 amp AC
transformer..hopefully when i connect this transformer to a salt
solution i will get more amps flowing thru?..i will use the 15 amp
Variac tocontrolnthe current?..

To be continued....

 

[John Fields]

On Wed, 13 Apr 2005 13:00:49 +0100, Rob <Rob@rob.co.uk> wrote:

Sorry to be a pain..

But can some one explain this to me ?


If i had good connections big thick wire , a Anode and cathode of say
stainless steel...surface area of 500 square cm and placed it in a
saturated salt solution( sodium chlordie dissolved in water) and
connected a PSU that was rated at 5 V 300 amps.. what current would
flow thru the cell?.. \

---
That depends on the resistance of the circuit. See below.
---

should it be like a dead short?.

---
Well... 0.017 ohms, which is a fairly small resistance, but it's not
quite a dead short.
---

Is a DC psu all the same ?

---
No.
---

are plating rectifiers different ??

---
They're usually full-wave rectified AC with no smoothing.
---

are I am sure than it
if i had a plating rectifier i would get my 100 amps thru the cell?

---
If it could put out enough voltage to overcome the circuit resistance,
yes.
---

.I have just looked at some plating rectifiers... and saw a term
called "constant current" Does this mean the Plating rectifeirs can
be set to give out a fixed say 100 amps? current..thats is force the
amps thru the solution?...

---
Yes, if it can generate the voltage necessary to drive the 100 amps
through the resistance of the circuitry.
---

My PSU you set the Max limit that can be
drawn.. but a plating rectifier if you set 100 amps will it force 100
amps thru?..

---
Yes, if it can generate the voltage necessary to drive the 100 amps
through the resistance of the circuitry.
---

in which case i think my dc PSU is not up to the
job..ARRRGGHHH...

---
Your PSU will get the job done if you can get the circuit resistance
down low enough. If you can't, then you'll need a supply with higher
than a 5V output in order to overcome that resistance. See below.
---

To confirm this i have just won a 140 amp bridge rectifier on ebay.. i
will use this to get DC cuurrent from my 83 amp AC
transformer..hopefully when i connect this transformer to a salt
solution i will get more amps flowing thru?..i will use the 15 amp
Variac tocontrolnthe current?..

---
That will get more current through, but you need to make sure that you
don't exceed 83 amps for anything other than short intervals,
otherwise you'll damage the transformer. ISTR there was also
something about the fuse in the primary which limited the secondary
current to something less than 83A???
---

To be continued....

---
You need some electricity 101, so stop spending money for a while and
read this:

In the circuit you're talking about you need to be concerned with only
three things: voltage, current, and resistance.

If you were to look at it like plumbing, voltage would be like
pressure in a pipe, current would be like how much water would flow
through the pipe when the faucet was opened, and resistance would be
like the diameter of the pipe or how far the faucet was opened.

Let's say that you had a pipe with a faucet on one end and with the
faucet closed there was 100PSI of water pressure in the pipe.

Now let's say that with the faucet opened up up all the way you'd get
100 gallons per minute flowing out of the faucet. If you upped the
pressure to 200 PSI what would happen? You'd get 200 gallons per
minute flowing out of the faucet.

Same with electricity. If you had a power supply with a pressure of
100 volts which was causing 100 amps to flow through a wire and you
upped the voltage to 200 volts, what would happen? The current would
go to 200 amps.

Now, looking at the pipe, if its diameter was decreased but there was
still 100PSI of pressure in the system, what would happen? The flow
would _decrease_ because the resistance of the pipe would increase.

Same with electricity. For a given voltage, if the diameter of the
wire is decreased, the current in the wire will also decrease because
the wire will offer greater resistance to the flow of current.

We relate voltage, current, and resistance to each other using Ohm's
law:

E = I*R

Where E is the voltage difference between two points in a circuit,
R is the resistance between those points, and
I is the current in the circuit.

Just like water is made up of water molecules, electricity is made up
of electrons, and just like the quantity of water flowing past a fixed
point in a given amount of time depends on how many water molecules
flow past that point, the current in a conductor depends on how many
electrons move past a fixed point in a given amount of time.

If you want to get into it any deeper than that we can do that later,
but for right now you need to understand that, at a given voltage, the
current which a power supply can force through a resistance will
depend on that resistance.

In the case of your 5V supply, to determine how much current the
supply can force through the resistance we can rearrange:


E = I*R (1)


to:

E
I = ---
R


Now, if we have a 5 ohm resistance, we can write:


E 5V
I = --- = ---- = 1 ampere
R 5R


If we drop the resistance down to 1 ohm we'll have:


E 5V
I = --- = ---- = 5 amperes
R 1R


so you can see that the lower the resistance, the more current the
power supply can force through the resistance.


In order to determine what the resistance needs to be in order to
allow, say, 250 amps to flow from a 5V supply, we'll rearrange (1) to


E 5V
R = --- = ------ = 0.02 ohms
I 250A

Which is a pretty small resistance and is the reason you can't get
much current through your cell. Also, that's the _total_ resistance,
which includes the cell, the cables, and all the fittings between the
cell and the supply, so a high resistance anywhere in that chain can
spell failure.

--
John Fields
Professional Circuit Designer

 

[Fritz Schlunder]

"Rob" <Rob@rob.co.uk> wrote in message
news11q51l1inm0n2n2kpbtd1k5daaeeu71bn@4ax.com...

Sorry to be a pain..

But can some one explain this to me ?


If i had good connections big thick wire , a Anode and cathode of say
stainless steel...surface area of 500 square cm and placed it in a
saturated salt solution( sodium chlordie dissolved in water) and
connected a PSU that was rated at 5 V 300 amps..

Okay well I got curious enough to try this out. I used an 8oz plastic
yogurt cup mostly filled with water and some (though not necessarily fully
saturated) table salt (I used iodized salt, so not quite pure NaCl). One
electrode was the back plate for an ATX computer case (where all the
connectors on the motherboard exit to the real world). I'm sure this is
some kind of steel though perhaps not stainless. The other electrode was a
standard nail used for nailing 2"x4" wood together for making houses and
things.

I used the 5V rail of a computer power supply (measured at 4.88V output). I
managed to get somewhere between 3A-7.5A depending upon the exact time. The
wiring resistance used to the cell was fairly small (~0.1 ohms), so the
primary current limiting effect was provided by the electrolysis cell. The
nail was hooked to +4.88V while the other electrode was hooked to ground.
After maybe around half an hour the nail had pretty much totally disappeared
into the solution. The other electrode was largely unchanged. During
operating a gas was observed to be bubbling up from the grounded electrode.
The other electrode did not bubble (at least not significantly). After the
nail was used up I replaced it with a large iron bolt and resumed the
reaction. Eventually the water turned into a dark grey thick sludge. If I
placed a small rare earth supermagnet on the exterior of the cup it would
stick. I could move the magnet around and move small amounts of the sludge
around with it.

My theory of the observed reaction is this (however it is only my theory and
I am no expert in electrochemistry):

2H2O(l) + 2e- --> H2(g) + 2OH-(aq) E=-0.83V
and
Fe(s) + 2OH-(aq) --> Fe(OH)2(s) +2e- E=0.88V

Adding these two half reaction potentials together gives 0.88V - 0.83V =
0.05V. I'm not sure but I think this reaction actually produces energy,
unlike making sodium metal and chlorine gas which takes lots of energy.

So in other words the gas that was observed to bubble up from the negative
electrode was most likely hydrogen gas.

If your objective is to make sodium metal, or even chlorine gas from your
sodium chloride, this method will not work. As I understand it whatever
chemical reaction that requires the least voltage will be the one that
dominates in your electrolysis cell. Since making sodium metal and chlorine
gas takes 4.07V while the above mentioned reactions may actually produce
energy (??) no sodium is produced. Electrolysis of plain water only takes
1.23V, so in the absence of any other possible reactions sodium would still
not be produced. Even if you could make sodium metal, it would instantly
react with the water in your cell to make something else (sodium hydroxide
maybe?). Some people like to throw sodium metal into pools of water for fun
since it makes quite a violent/explosive reaction.


What is your objective? What are those patent numbers you are looking at?

 

[Rob]

The Cell is going to be used to produce Sodium Pechlorate..you need a

anode made of Platinium or Lead dioxide.. ..its a two stage process
first you need six coloumbs of electricity to convert the chloride in
to chlorate >>>then a further 2 coloumbs of electricity to convert it
in to perchlorate..assuming 100% efficiency..in real life more like
50% to 60%..

I will post some patent numbers if you are intrested in how it
works..

One patent with lots of examples is 002945791 the page to look at is
page 6 example III and IV this gives all the info...you need to run
the cell...Notice the voltage is 4.75 Volts and current is 285
amps..in this example the current density is 1 amp per square
inch..total surface area of the lead dioxide anode is 285 sqaure
inches..My cell has approx 110 square inches hence i want to run the
cell at around 110 amps?..

All the patents i have read mention 4 to 5 volts... to run the cell
with leadioxide anodes ... you need higher voltage 6.5 v if Platinum
is used ..

I have tried everything with my power supply cannot deliver anywhere
near the currnet i require

Even tho its rated at 325 amps at 5V?..

So i am experimenting with 180 amp Arc welder..

I am sure that i need higher voltage power supply to get the current
needed.
..The Arc welder is AC so i will rectify the current with 140 amp
rectifier...so here is my theory...

i measured the voltage of the Arc welder it was 50V off load.. then i
measured it while it was welding(under load) the voltage was 30V..So i
belive this will happen..

i will connect it to my cell using a 15 amp variac to control the
current?..i reckon the Arc welder will drop voltage down to 4 V? on
the cell? whilst passing 100 orso amps?..

The only concern is my duty cycle? on the welder its rated at 5 KVA i
hoping this means it can supply 100 amps at 5V?..

If this doesnt work i will be errrr... stuck...

i have copied the following from a forum i post too...it has some
pictures of my anodes i will had pictures of my cell wents it
finshed....



Ok i think i have cracked making Large Graphite Substrate Lead Dioxide
Anodes (GSLD)..If you want to make Chlorate(ClO3) or Perchlorate(ClO4)
you can use various Anodes Platinum is the probably the best ...Lead
Dioxide (PbO2) is next best...

I have gone for the PbO2 anode because you can run the cell right from
Chloride(Cl) to Perchlorate(ClO4)..if you used Platinum to do this
then you will get excessive corrosion on the Platinum Anode due to the
low Chloride concentration stage..

I tried plating PbO2 on to 13 mm Carbon Gouging rods because they were
very cheap and looked like graphite!!.but i found it didnt take the
coating very well so i Binned the idea..Graphite works realy well..
I got some Fine grained 10 mm Graphite 500mm long rod
http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Graphiterods.JPG

Also after making Good 10mm Anodes i got some larger 32 mm x 500mm
graphite rod
http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Graphiteend.JPG

You need to treat the graphite so that the PbO2 adheres well.. To do
this you simply electolyse the anode in a 10% Sodium hydroxide
solution i applied 3 volts at about .0.05 Amps per square
Decimeter..that works out at about 1.5 to 1.75 amps For the 10 mm
Anode and about 6 to 7 amps for the 32 mm Anode..

Anode being etched
http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Etchedanode.JPG

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Etchingintank.JPG

When electroplating the PbO2 tiny oxygen bubbles form,If theses
bubbles are allowed to stay on the coating these bubbles will form
pits which will allow the corrosive salt solution through and thus
destroy the substrate which in turns destroys the Anode..
In industry surficants are used which eliminates this problem..I spinn
the electrode the centrifugal force throws off the bubbles leaving a
nice smooth coating...

The plating tank was a 3 litre pyrex beaker .the plating solution was
333 g a litre Lead Nitrate + 50 g litre Copper Nitrate ..To spin the
electode i used a Small 240v electric motor from a Fan..Mounted on
plank of wood..To lower and raise the electode i used my camera tripod
...

The plating tank operated at approx 60 centigrade i used an electric
hotplate with magnetic stirrer to agitate the solution..

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxide/Anode1intank1.JPG

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxide/Anode1intankcloseup3.JPG

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxide/Anode1intankrealclose4.JPG

Here is a close up of the finished product
http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxide/Anode1outoftankcloseup7.JPG

I tried the electrode in a Sodium Chloride solution and it took 9 amp
with no sign of errosion or heating.. So i Started making 32mm
anodes..
I had to use a larger electric motor the Small fan motor siezed up
when spinning the larger electode..Because the motor wieghed much more
i had to use Aluminium bar to mount the motor on ...the extra weight
helped reduce vibration..

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Anode4intank1.JPG

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Anode4intank11.JPG

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Anode36mmcloseup1.JPG

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Closeupanode4out17.JPG

After plating the tank is replenished with the addition of Lead
Dioxide (PbO) a bright yellow powder
...Plating
tank with an excess of PbO added i leave it stirring over night
then filter the solution.. and leave it to stand for a few days before
use so that any nitrites formed (which lowers the plating tanks
efficiency).are oxidised back to nitrate..I acidify the solution to PH
1 with Nitric acid and its ready for use.

..I could have used a surficant to eliminate the bubbles, but continued
use of the plating tank ends up that the breakdown products of the
surficant makes a poor PbO2 coating...and to eliminate the breakdown
products required the use of amly alcohol and distillation
equipment...
Here are a few more pictures


http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Anodesvarious.JPG

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Ptmesh.JPG]

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/13mmPbO2anodenumber1.JPG

http://www.saspyro.pwp.blueyonder.co.uk/Leaddioxidebig/Anode.JPG
36 mm Anode made to take at least 27 amps[/url]

 

[John Fields]

On Fri, 04 Mar 2005 10:47:06 +0000, rob <sasman@sasman.com> wrote:

Hi

I am a total novice in electrics and am not sure were to post this
question?.. i hope some one can help me...I need a transformer that
can supply aprrox 6 Volts Dc at 75 amps..
I have just purchased a 240 v ac input 1 KVA rated transformer its AC
output is 6v ,8v and 12 V..Now i understand that i need to rectify
the current and have just got off ebay a dozen MBRP40030CTL 400A 30V
schottky diodes with low Vf.. i assume that these will be able to
supply a 75 amp current.. at 6 v?..I got them because there rated at
400 amps..and were very cheap!
http://www.onsemi.com/pub/Collateral/MBRP40030CTL-D.PDF

My other question is that there is label on side of the transformer
which is hand written saying that it is rated at 83 amps?..
Label pic
http://www.saspyro.pwp.blueyonder.co.uk/label.JPG

yet when i looked inside i found a large fuse holder with 63 amps at
550v printed on it.?
http://www.saspyro.pwp.blueyonder.co.uk/fuse.JPG

yet the fuse thats attached to it says 40 amps at 550VAC..


http://www.saspyro.pwp.blueyonder.co.uk/Fuse2

Now i am confused ? if the fuse is 40 amps does that mean i have only
transformer that can supply 40 max?..

Inside the transformer there is a board with 1KVA printed on it

http://www.saspyro.pwp.blueyonder.co.uk/inside.JPG

i hope this makes some sense?

Is there any way i can test to see if it can supply 75amps ?

First things first...

1. If the transformer is rated at 1kVA with a 240V input, then that
means it's designed to operate with 240V on its primary, and should be
able to supply a total of 1kVA to a load connected to the secondary.
From your photos it appears that the transformer has a single primary
and a single, tapped secondary, so at 1kVa the currents which should
be available from the secondary at the various taps will be:

VA 1000
I = ---- = ------ = 166.6A for the 6V case,
E 6

1000VA/8V = 125A for the 8V case, and 1000VA/12V = 83.3A for the 12V
case, so it looks like the secondary was wound with wire designed to
supply a maximum of 83A out of the secondary, no matter which tap you
use, and that's what that "83" on the label means.

2. The voltage and current written on the fuseholder is what the
fuseholder is rated for, which is no more than 660V across it (at
least it _looks_ like 660V to me) with no fuse in it, and no more
than 63 amps through it with a fuse installed. That means you
shouldn't put anything bigger than a 63 (60) amp fuse in it.

3. The 40 amp fuse that's in there means that the last person who used
the transformer fused it for 40 amps. If you want to fuse it for a
different current you'll need to change the fuse, but if you want to
run it at 75A you'll need to change the fuseholder as well.

4. Since you're allowed 83 amps out of any tap on the secondary you'll
be able to take 75 amps, no problem, but if you need 6VDC there might
be a problem if you use the 6V tap, since you'll be dropping some of
the voltage available from the secondary in the diodes when you
rectify the AC to get DC. On the other hand, if you used the 8V tap
you could still get 75A out of it, but if you wanted 6V out you'd have
to get rid of the extra volt or so with about a 100 watt regulator.

Then there's the question of the filter capacitor. That is, whether
you need one or not. What's your application?


5. Finally, to test it at 75 amps, what you'll need to do is put a
resistance across the 6V tap which will allow 75 amps to flow through
it with 6V across it. That resistor will need to be:

E 6V
R = --- = ----- = 0.08 ohms
I 75A

and it'll dissipate:


P = IE = 75A * 6V = 450 watts while it's connected, and you
should measure the current and the voltage out of the transformer _at_
the transformer while it's being exercised.

--
John Fields

 

[rob]

On Fri, 04 Mar 2005 10:43:17 -0600, John Fields
<jfields@austininstruments.com> wrote:

From: John Fields <jfields@austininstruments.com

Thanks John for that fantastic reply..I am much more confident now
that i have more information on my PSU...

I am using the PSU to power an electrochemical cell for making
Chlorate/Perchlorate.. Unsmoothed Dc current will work ok for this
purpose....The voltage is not critical ..

You mention that i will need a 0.08 Ohms resistor to produce a 75 amp
load...
I have purchased some 18 gauge Nikrothal 80 wire with a .040"
diameter, 0.4062 ohms per foot..

Am i correct in thinking that i can divide 0.4062 (foot ) by 12 to
get the Ohms per inch?.. which = 0.03385 Ohms (per inch) so i would
need 2.37 inches ?...I intend to use this as a variable resistor to
increase/decrease the current flowing in to the cell..

Thanks

Rob

 

[Rich Grise]

On Sat, 05 Mar 2005 15:53:54 +0000, rob wrote:

On Fri, 04 Mar 2005 10:43:17 -0600, John Fields
jfields@austininstruments.com> wrote:


From: John Fields <jfields@austininstruments.com


Thanks John for that fantastic reply..I am much more confident now
that i have more information on my PSU...

I am using the PSU to power an electrochemical cell for making
Chlorate/Perchlorate.. Unsmoothed Dc current will work ok for this
purpose....The voltage is not critical ..

You mention that i will need a 0.08 Ohms resistor to produce a 75 amp
load...
I have purchased some 18 gauge Nikrothal 80 wire with a .040"
diameter, 0.4062 ohms per foot..

Am i correct in thinking that i can divide 0.4062 (foot ) by 12 to
get the Ohms per inch?.. which = 0.03385 Ohms (per inch) so i would
need 2.37 inches ?...I intend to use this as a variable resistor to
increase/decrease the current flowing in to the cell..

Yeah, use 2 3/8" of wire if you want to start a fire.

6V * 75A = 450 watts. Your wire will disappear, and splash molten
Nikrothal all over the bench and your lap and your face.

Get some fat wire with a R of about 0.01 ohms per foot, and use 8 feet
of it.

Or shop around for a 6V, 450 watt electric heating element.

And fuse the primary at about 2 amps, for the 75 amp test.

Good Luck!
Rich

 

[The Phantom]

On Fri, 04 Mar 2005 10:47:06 +0000, rob <sasman@sasman.com> wrote:

Hi

I am a total novice in electrics and am not sure were to post this
question?.. i hope some one can help me...I need a transformer that
can supply aprrox 6 Volts Dc at 75 amps..

Rob,
Do you have any instruments that can measure currents of ~75 amps
AC? Of 5 amps AC?

Do you have an AC voltmeter?

The tests that others have proposed so far require you to dissipate
power on the order of .5 kw.

The standard method for testing the capability of a transformer
without actually dissipating a power equivalent to the rating of the
transformer is the short circuit test.

You need a variac for this. You dead short the 6 volt output of the
transfomrer. You connect a variac capable of about 5 amps output to
the power line. Turn the output of the variac all the way down to
zero output (THIS IS VERY IMPORTANT). Connect the variac output to
the 240 volt winding of the transformer with an ammeter in series to
monitor the current. SLOWLY turn up the variac until the ammeter
reads the rated current for the 240 volt winding (about 4 amps AC in
this case). You may need to put a (power) resistor of a few ohms in
series with the 240 volt winding of the transformer if the current
comes up too fast (which it undoubtedly will) when you SLOWLY turn up
the variac. (If you don't have any suitable power resistors, use an
electric heater or some light bulbs as resistors). (An even better
alternative would be to follow the variac with a small step-down
transformer. Something with about 5 amps output at 6 or 12 volts.
The variac would power the line-voltage winding and the low voltage
winding would power the 240 volt winding of the 1kva transformer you
are testing.)

When you have the current into the 240 volt winding set to 4 amps AC,
you just wait around and see how hot the transfomer gets. The current
in the shorted 6 volt winding should be about 160 amps. Ideally you
should short the 6 volt winding into a suitably rated shunt and then
you could directly measure the current there.

Without knowing the details of the transformer insulation system, I
can't say what the maximum allowable temperature rise is, but if the
transformer doesn't start stinking too much, you're probably ok. So
far, we would be testing the transformer at its full rated power.

Since you only want 75 amps from the 6 volt winding, you could set the
primary current in this test to 1.875 amps AC. This would correspond
to 75 amps in the 6 volt secondary. Just let it run for a few hours
while monitoring the temperature rise. This will provide a test of
the transformer at the actual current which you will be using.

Rectifying the output of the transformer will cause the current to be
non-sinusoidal which will increase the copper (I^2*R) losses.

You could also connect your rectifiers in whatever configuration you
will use, and short the output from the rectifiers. This will give
you a method of testing the heatsinking of the rectifiers. As before,
turn the variac which is supplying the 240 volt winding ALL THE WAY
DOWN before you start the test. Turn up the variac SLOWLY while
monitoring the current in the 240 volt winding until you reach 1.875
amps AC. You should use a true RMS ammeter when the rectifiers are in
circuit for best results. I wouldn't turn the current up to 1.875
amps right away with the rectifiers in circuit; turn it up gradually
while monitoring the temperature of the rectifiers. If the rectifiers
sizzle when touched with a wet finger, you probably should use some
more heat sinking.

The advantage of the short circuit test method is that you only
dissipate a power equal to the losses in the transformer which should
be under 100 watts for a transformer of this size. (light bulbs or
electric heaters extra) It does not include the core loss, but that
shoud be a negligible part of total losses at nearly full power out of
the transformer.

 

[Lord Garth]

"Rich Grise" <richgrise@example.net> wrote in message
newsan.2005.03.05.19.15.17.509359@example.net...

On Sat, 05 Mar 2005 16:08:34 +0000, Lord Garth wrote:


"rob" <sasman@sasman.com> wrote in message
news:71jj2156rh6tbuuhqpf89s40opa253auhr@4ax.com...
On Fri, 04 Mar 2005 10:43:17 -0600, John Fields
jfields@austininstruments.com> wrote:


From: John Fields <jfields@austininstruments.com


Thanks John for that fantastic reply..I am much more confident now
that i have more information on my PSU...

I am using the PSU to power an electrochemical cell for making
Chlorate/Perchlorate.. Unsmoothed Dc current will work ok for this
purpose....The voltage is not critical ..

snip?
Rob

Take care with this substance...it is a contact explosive.

According to a current thread on news:rec.pyrotechnics, you don't even
need an electrolytic cell - with the right mixture of reagants, the KClO4
precipitates out of solution on its own.

And, on its own, it's not explosive. It's a very strong oxidizer, but it
still needs fuel. You might be thinking of ammonium perchlorate - that's
pretty nasty stuff.

Good Luck!
Rich

You're right Rich, I was thinking of ammonium perchlorate. Sorry!

 

[John Fields]

On 5 Mar 2005 21:29:04 -0600, The Phantom <phantom@aol.com> wrote:

On Fri, 04 Mar 2005 10:47:06 +0000, rob <sasman@sasman.com> wrote:

Hi

I am a total novice in electrics and am not sure were to post this
question?.. i hope some one can help me...I need a transformer that
can supply aprrox 6 Volts Dc at 75 amps..

Rob,
Do you have any instruments that can measure currents of ~75 amps
AC? Of 5 amps AC?

Do you have an AC voltmeter?

The tests that others have proposed so far require you to dissipate
power on the order of .5 kw.

The standard method for testing the capability of a transformer
without actually dissipating a power equivalent to the rating of the
transformer is the short circuit test.

---
AFAIK, the short test is used to measure the copper losses, not the
"capability" of a transformer, whatever that means.
---

You need a variac for this. You dead short the 6 volt output of the
transfomrer.

---
NO!!! If you do you will exceed the current rating of the secondary
and, possibly, damage the transformer. The transformer is rated for
1kVA out of the _entire_ secondary which, at 12VRMS out comes to the
83.3 amps noted on the transformer's faceplate. That is, the
transformer secondary is wound with wire which is designed to carry
83.3 amps no matter which voltage tap is used.
---

You connect a variac capable of about 5 amps output to
the power line. Turn the output of the variac all the way down to
zero output (THIS IS VERY IMPORTANT). Connect the variac output to
the 240 volt winding of the transformer with an ammeter in series to
monitor the current. SLOWLY turn up the variac until the ammeter
reads the rated current for the 240 volt winding (about 4 amps AC in
this case). You may need to put a (power) resistor of a few ohms in
series with the 240 volt winding of the transformer if the current
comes up too fast (which it undoubtedly will) when you SLOWLY turn up
the variac. (If you don't have any suitable power resistors, use an
electric heater or some light bulbs as resistors). (An even better
alternative would be to follow the variac with a small step-down
transformer. Something with about 5 amps output at 6 or 12 volts.
The variac would power the line-voltage winding and the low voltage
winding would power the 240 volt winding of the 1kva transformer you
are testing.)

When you have the current into the 240 volt winding set to 4 amps AC,
you just wait around and see how hot the transfomer gets.

---
That's not really a valid criterion, since the core losses are only
going to be a fraction of what they would normally be with 240VAC on
the primary. Moreover, if you're going to do it properly you need to
monitor the temperature rise of the transformer over ambient and make
sure it doesn't exceed the spec.
---

The current in the shorted 6 volt winding should be about 160 amps.
Ideally you should short the 6 volt winding into a suitably
rated shunt and then you could directly measure the current there.

---
The shunt's an OK idea, but it needs to short out the _entire_
secondary, for the reason given earlier.
---

Without knowing the details of the transformer insulation system, I
can't say what the maximum allowable temperature rise is, but if the
transformer doesn't start stinking too much, you're probably ok. So
far, we would be testing the transformer at its full rated power.

---
No, you'd only be exciting the copper, not the core. To determine the
core losses, you'd need to do the open circuit test.
---

Since you only want 75 amps from the 6 volt winding, you could set the
primary current in this test to 1.875 amps AC. This would correspond
to 75 amps in the 6 volt secondary. Just let it run for a few hours
while monitoring the temperature rise. This will provide a test of
the transformer at the actual current which you will be using.

---
This isn't a good test either, because the core losses will be even
less than they were previously and won't reflect the conditions under
which the transformer will be expected to function in real life.
---

Rectifying the output of the transformer will cause the current to be
non-sinusoidal which will increase the copper (I^2*R) losses.

---
Yes. Conversion efficiency is about 81% for a full-wave bridge.
---

You could also connect your rectifiers in whatever configuration you
will use, and short the output from the rectifiers. This will give
you a method of testing the heatsinking of the rectifiers. As before,
turn the variac which is supplying the 240 volt winding ALL THE WAY
DOWN before you start the test. Turn up the variac SLOWLY while
monitoring the current in the 240 volt winding until you reach 1.875
amps AC. You should use a true RMS ammeter when the rectifiers are in
circuit for best results. I wouldn't turn the current up to 1.875
amps right away with the rectifiers in circuit; turn it up gradually
while monitoring the temperature of the rectifiers. If the rectifiers
sizzle when touched with a wet finger, you probably should use some
more heat sinking.

The advantage of the short circuit test method is that you only
dissipate a power equal to the losses in the transformer which should
be under 100 watts for a transformer of this size. (light bulbs or
electric heaters extra) It does not include the core loss, but that
shoud be a negligible part of total losses at nearly full power out of
the transformer.

---
As Fritz Schundler pointed out earlier, an optimum transformer design
will yield core losses equal to copper losses.

--
John Fields

 

[John Fields]

On Wed, 09 Mar 2005 18:10:24 +0000, rob <sasman@sasman.com> wrote:

Well thanks for all the help and advice..I have took Johns advice and
this morning the post man delivered a Claude Lyons Regavolt 715-E 240V
15Amp Variac...
http://www.saspyro.pwp.blueyonder.co.uk/Variac.jpg

http://www.saspyro.pwp.blueyonder.co.uk/Variacrating.jpg


Will this variac work as a variable resistor? so that i can control
the current going in to my electrochemical cell?.. or will it just
control the voltage?..

---
Good move! It will do both. What will happen is that the variac will
control the voltage into the primary of the transformer, therefore
controlling the output voltage from the secondary, and as the voltage
into the cell changes, so will the current. The higher the voltage,
the higher the current.
---

Phantom I have a Digital Multimeter a 2 amp panel meter and a 25 amp
panel meter that is all the measuring equipment i have .. i am looking
for a 0 -100 amp DC panel meter + shunt..I cant do much more until my
Diodes arrive..i will let you know how i progress ..

---
OK. Good luck!

--
John Fields

 

[Rob]

Hi
well since last time i asked for advice i have had a few
problems...First problem was i had ordered some 400A 30V low Vf
Schottky diode rectifiers i won them on ebay
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=3877178672&ssPageName=STRK:MEWN:IT
....But never got them through the post so that delayed me a week or
so..Then i Bought from a Surplus shop 8 x 110 amp Rectifiers..they
were only a about 3$ each ...used but untested..I got them from Cpi
surplus in the USA ..very fast service...Unfortunatley the diodes i
bought were Silicon controlled rectifiers...Which my Radio Ham friend
told me they are no use for what i wanted...So i was realy pissed
off!!...So i decided to spend even more money on another PSU rated at
5 Volts at 325 amps..I won it on ebay a week orso ago..
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=7501227612&ssPageName=STRK:MEWN:IT..

http://www.abex.co.uk/sales/electronic/psu/rack/p10/p_series.pdf

Its made by Power Ten INC.. its a 19 inch rack mounted PSU with
variable Voltage and Current control..First impressions were WOW!!
when i turned it on it sounded like a jet taking of lots of noise from
the internal fans...However my Smile was soon wiped of my face when i
tried to test the power output...

I connected it up to a short length of nicrome wire and set the
voltage to 5 Volts and slowly turned up the current .. all i could get
was 20 amps the wire glowed white hot ..Now i have done this test
before on my old 400watt computer PSU and it went off scale on my 25
amp analoge meter.. and melted the nicrome wire...

I then tried a very crude electrolyisis of my Lead Nitrate solution,
using my old 400 watt PSU i can get 15 amps thru it ..But with this
PSU i only managed a poxy 2 amps... i am now totaly pissed off!!!?

Have i wasted even more money?...How can i test my PSU?.. will it
damage the unit if i make a dead short on the connections.. and slowly
turn up the current ?...The control for the current works by setting a
limit on the power supply...I hope some one can put a smile back on my
face...

Dont forget i want to use the power supply for electrolysing Sodium
Chloride solution..I have read several patents and the cells run at
about 4.75 volts at several hundred amps....

So i assumed that a 5V supply should be able to do the job... I have
got several amp meters to read the current..

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=4534893020&sspagename=STRK%3AMEWN%3AIT&rd=1

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=7500828509&ssPageName=STRK:MEWN:IT

But at the moment i have no power supply that can give me the current
i require..

Is the PSU faulty?...or is it something else i am overlooking?..

Hope some one can help ....

Cheers

Rob