Power Supply Rectification and Smoothing

[Eeyore]

Daniel Mandic wrote:

Eeyore wrote:

What really annoys me Daniel is that I was doing my best to provide
good info and this guy insisted on preferring the bad info because it
seems he prefers 'folk wisdom' to science.

Hi Graham!

I saw.

You are correct as that. I would like to play a game of Snooker with
you.

Should we meet, I'd be delighted to play a few games with you. It's been a few
years since I last played snooker but it's very enjoyable..

Graahm

 

[John Fields]

On Fri, 19 Oct 2007 20:06:43 +0900, spamfree@spam.heaven wrote:

On Fri, 19 Oct 2007 11:42:13 +0100, Eeyore
rabbitsfriendsandrelations@hotmail.com> wrote:

Daniel Mandic wrote:

spamfree@spam.heaven wrote:

You show by your own intemperate arrogance that you indeed are the
"grade one IDIOT" whose "advice should be taken with a grain of salt."

jack

ah

Your'e hiding information as he does.

And then you wish to attack him, by not answering your questions where
he should have been taken in.



Eyeore blows you away. Give up, before it's too late. (you are
stapling, you have been already caught out. Don't make normality over
that, Moron.)

What really annoys me Daniel is that I was doing my best to provide good info
and this guy insisted on preferring the bad info because it seems he prefers
'folk wisdom' to science.

You simply can't help some people.

Graham

I preferred nothing.
Run your finger under the words again.

I called you on your bullshit and errors and slanging everyone who you
thought disagreed with you.

Things such as your dead wrong assertions about the IEC/NEMA motor
labelling standards, and your woeful ignorance of BDC motor speed
controllers.

And your intemperate outbursts against, for example, the guy who said
the 50V caps were too low. Had you not realised that my transformer,
when lightly loaded, could creep up to 60V or so? Huh?
Who should be taken out and SHOT? Huh?

Face it, you are an arrogant bullshitartist whose advice is
unreliable.

---
Ding! Give that man a seegar!


--
JF

 

[John Fields]

On Fri, 19 Oct 2007 20:06:59 +0900, spamfree@spam.heaven wrote:

On 19 Oct 2007 09:47:50 GMT, "Daniel Mandic" <daniel_mandic@aon.at
wrote:

spamfree@spam.heaven wrote:

You show by your own intemperate arrogance that you indeed are the
"grade one IDIOT" whose "advice should be taken with a grain of salt."

jack


ah


Your'e hiding information as he does.

And then you wish to attack him, by not answering your questions where
he should have been taken in.





Eyeore blows you away. Give up, before it's too late. (you are
stapling, you have been already caught out. Don't make normality over
that, Moron.)



Best Regards,

Daniel Mandic

Huh? That's the second message that makes no sense.
What are you trying to say?

---
Mandic seems to think of himself as a sagacious dispenser of obscure
folksy wisdom and witticisms. Unfortunately, his neophytic command
of written English often reduces his otherwise banal "edicts" to
gibberish.


--
JF

 

On Fri, 19 Oct 2007 08:36:16 -0500, John Fields
<jfields@austininstruments.com> wrote:

Daniel Mandic

Huh? That's the second message that makes no sense.
What are you trying to say?

---
Mandic seems to think of himself as a sagacious dispenser of obscure
folksy wisdom and witticisms. Unfortunately, his neophytic command
of written English often reduces his otherwise banal "edicts" to
gibberish.

Thanks John, I had a look back at some of his posts to see where he
was coming from. All was darkness and obscurity....

jack

 

[Rich Grise]

On Fri, 19 Oct 2007 07:20:02 +0100, Eeyore wrote:

Rich Grise wrote:
On Thu, 18 Oct 2007 11:57:20 +0100, Eeyore wrote:
spamfree@spam.heaven wrote:

Robustness in this context is the ability (strength) to withstand
ripple.

You're talking out of your arse.

There is no such thing.

No such thing as robustness? What color is the sky on your planet?

" the ability (strength) to withstand ripple."

" Withstand ripple" ! ? Are you being deliberately dense ? How do you specify
your circuits' ability to "withstand ripple" ?

"Ripple rejection", "power supply rejection", are a couple of the terms
that I know of.

They guy has a fixation over a
little bit of ripple on a motor supply and thinks it's going to blow things up
or whatever

That's a different question.

It's a damn joke.!

Yes, of course, whatever you say.

FWIW, my objection was to your assertion that "there is no such thing as
robustness".

Cheers!
Rich

 

[Jamie]

Eeyore wrote:

Rich Grise wrote:


On Thu, 18 Oct 2007 11:57:20 +0100, Eeyore wrote:

spamfree@spam.heaven wrote:


Robustness in this context is the ability (strength) to withstand
ripple.

You're talking out of your arse.

There is no such thing.

No such thing as robustness? What color is the sky on your planet?


" the ability (strength) to withstand ripple."

" Withstand ripple" ! ? Are you being deliberately dense ? How do you specify
your circuits' ability to "withstand ripple" ? They guy has a fixation over a
little bit of ripple on a motor supply and thinks it's going to blow things up
or whatever

It's a damn joke.!
^^^^^^^^^^ Stop looking in the mirror! ^^^
Graham

--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[Eeyore]

Rich Grise wrote:

Eeyore wrote:
Rich Grise wrote:
Eeyore wrote:
spamfree@spam.heaven wrote:

Robustness in this context is the ability (strength) to withstand
ripple.

You're talking out of your arse.

There is no such thing.

No such thing as robustness? What color is the sky on your planet?

" the ability (strength) to withstand ripple."

" Withstand ripple" ! ? Are you being deliberately dense ? How do you specify
your circuits' ability to "withstand ripple" ?

"Ripple rejection", "power supply rejection", are a couple of the terms
that I know of.

What's the "ripple rejection" of a motor or mosfet switch ?

Graham

 

[Ross Herbert]

On Fri, 19 Oct 2007 05:38:46 +0900, spamfree@spam.heaven wrote:

On Thu, 18 Oct 2007 08:20:43 GMT, Ross Herbert
rherber1@bigpond.net.au> wrote:

On Wed, 17 Oct 2007 18:16:14 +0900, spamfree@spam.heaven wrote:


Energy content of spikes on the secondary side is a non-issue.
Consider the filter caps as if they were a 36V lead acid battery.
This load would constitute the best output filter with the lowest
internal resistance possible. As far as spikes in the secondary are
concerned the battery is a dead short and the only place they can
then be dissipated is in the secondary winding and the transformer
leakage capacitance. Forget about spikes for your motor run
application.

Thanks Ross. Makes sense. Did you see my question I posed about
turning the mains off and then on quickly with the transformer core
still magnetised, and the phase angle at switchon such that the
transformer goes "boing"?

No, I didn't see that question. However, it is well known that rapid
on-off switching on the mains side of large transformer based power
supplies can result in unintended surges and overloads. Mostly, these
simply cause a circuit breaker to pop but there may be other
consequences depending on the psu design. It is generally accepted
that this practice is frowned upon and belongs in the realm of "worker
vandalism".

To avoid the need of caps, and keep the voltage stable, what about
another suggestion I've had to build "a simple series pass regulator
using a 36V zener like a 1N5936 and a 60A NPN transistor like a
MJ14002. it would be tons cheaper than the humongous capacitors you
would need. Since these need a couple of volts headroom, wind the
transformer to provide a slightly higher voltage say 32V or so. Also
the transistor must be put on a largish heatsink."

You could use this arrangement with a single large electrolytic across
the zener reference as a means of producing a "capacitor multiplying"
effect but you would still need a fairly hefty bulk storage capacitor
across the output to provide for instantaneous current demand due to
sudden load changes. You wouldn't save a great deal if any and in my
opinion it is not required for your application.

I doubt that a single series pass transistor would be suitable either.

Or even "to parallel the outputs of 5 or 6 LM338K 3 terminal
regulators. Since the max output is 32V you would have to float the
regulators above ground using a 3.9V zener like a 1n4730.
Again you would need a big heatsink."

Solid state linear regulators (well designed) for high power DC
supplies have been used successfully as far back as the 60's and are
still used today when the most rugged operational conditions are to be
endured. $ for $ they will withstand almost anything you can throw at
them and while heavy duty switch mode units are also very capable, the
inclusion of safeguards against sudden blow-ups makes them more costly
and complex to design.

A transformer having this capability
for your application will be quite large and very heavy. Since your
transformer is a rehash of a microwave oven unit it is not likely to
have good load regulation.

This one weighs 11 lb, and some others weigh up to 15. Have you a
ball park figure for a reasonably stable load regulation?

It depends to a large extent on how you are going to drive your motor.
If it is going to be running at near full load for several hours at a
time then an 11lb transformer is totally inadequate. For such a
requirement (36V @18A) I would specify a transformer of 1KVA to be on
the safe side. As an example, I have a 1KVA isolation transformer and
this weighs 16Kg (35lb), so your 11lb unit is a pip-squeak by
comparison.

I've just played with the first tranny I came across, but I have an
older much heavier microwave oven to junk. Is bigger the better a
reasonable maxim? The problem is, the price difference between an old
microwave and a large bought one is horrendous

I was only concerened that the margin of error for 50V caps was a bit
fine, especially when a poor tranny might raise that considerably
when lightly loaded. Unfortunately, only the 50V ones are offered at
this cheap price, and so running more in series pairs seemed to be a
compromise. With the balancing resistors, of course.

I mean, I can get 2 dozen of these for around $US18 . Cheapest
capacitance I can find. Even three 12V leadacids would cost much more
and last for much less a time.

It seems to me that you have yet to grasp that your project is not a
simple "use what you can find at the lowest cost" type of project.
What you are trying to do is build a fairly heavy duty transformer
based dc power supply and to do this you have to start out with an
appropriately rated transformer in the first instance. There is no
substitute for an adequate laminated core mass when good load
regulation is required. Grabbing an old microwave transformer and
slapping on a few turns of pvc flex as a secondary is totally
inadequate in my opinion. If you had used something like 10AWG Formvar
insulated magnet wire then you would achieve far greater magnetic
coupling efficiency and get a result closer to what you were looking
for.

You can't use a transformer with poor load regulation AND get by with
the lower voltage rated capacitors - it's that simple. You either use
a good transformer which produces little voltage sag between low load
and full load where lower voltage caps can be used or you cover the
available output voltage range using higher rated caps. It's one or
the other and you have a cost penalty either way.

What is the 30A flex jacket material made of and what is the
temperature rating of the material? 30A PVC insulated flex generally
has a 75C rating and the insulation is quite thick. Operating the
transformer at temperatures over 75C will soften the jacket and
possibly compromise insulation among other things. Ambient temp must
be considered here as well.

This stuff is automotive, I think. It has quite a thin PVC sheath.
Its overall diameter is a whisker over 3mm. Drawn to scale, I can fit
at least 54 turns in the transformers secondary window.
I intend to have a fan blowing continuously over the whole shebang,
caps, transformer, bridge rectifier and motor, and I will monitor the
temps of everything to begin with to make sure that nothing is
getting too hot.

It is a long time since I wound a secondary to get a desired voltage
but from memory I had to wind something between 3 and 5 turns per volt
(240Vac primary) to get what I wanted. Depending upon the number of
turns on your primary will determine your required turns per volt at
the secondary and you should experiment to determine this. 54T sounds
a bit on the low side for a 36V,18A load to me.

From my experience, depending upon the supplier, automotive shops
describe their flex with rather dubious current ratings. If the
overall diameter of your flex is 3mm the wire diameter will be about
half that at best and I would question its ability to conduct 30A for
any appreciable time without drastic losses and severe temperature
increase. See the chart here http://www.powerstream.com/Wire_Size.htm
to get an idea of wire gauge for a nominal current capacity. For
example, 30A power transmission conductor would be in the region of
3.7mm diameter without any insulation.

Thanks for that, Ross. The speed controller is described by my
friendly ee who has experience with them on his bike, as:
"they have big input caps on the supply voltage in the controller,
and the circuit after that can be thought of as a buck switching
supply. All the logic and control runs from a low voltage (14.4v in
Crystalyte) that is internally regulated, so as long as your ripple
does not drop below that or go above the voltage ratings of the fets
or caps, you should be fine."

Since it's a "chopper" type speed controller then a bit of ripple on
the dc output will not be a problem. Your main problem is your
transformer load regulation as I read it.

I've also got a couple of good quality brushless 24V 400W motors
with built in brushless controllers. He rebuilds these to reverse
the rotation. I will ask him about these too.

I've posed the question and await the reply.
These are beautiful machines - black, finned, machined aluminium with
just two heavy power leads emerging and a small control loom for a
pot or a Hall effect twist grip "throttle".
These are too nice for a lathe, best for my trike

I haven't any experience with this type of motor so I can't add
anything.

 

On Sat, 20 Oct 2007 04:16:00 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

What's the "ripple rejection" of a motor or mosfet switch ?

Or even, what's the power output of a 500W motor?

But I digress.

To get back to your appalling logic:

What you are saying is that there is no such concept as "robustness
against ripple"

OK, so far?

Now it logically follows from this, that every electrical machine must
be either totally indifferent to any amount of ripple OR totally
destroyed by any ripple.

If any such machine varied from these absolutes, then it means that a
degree of "robustness against ripple" has been introduced, and you are
claiming that there is no such thing.

So I imagine you are choosing the extreme where every electrical
machine is totally indifferent to any amount of ripple. Afterall, you
have already claimed my motor controller as such.

Thus, if all such machines are totally indifferent to any amount of
ripple, no power supply need ever include smoothing.

Can you therefore explain why so many go to such lengths to smooth
their outputs?

jack

 

On Sat, 20 Oct 2007 05:21:23 GMT, Ross Herbert
<rherber1@bigpond.net.au> wrote:

First up, Ross, let me thank you for your most valuable assistance in
helping me understand these new (to me) concepts. Most appreciated.

I wrote:

Thanks Ross. Makes sense. Did you see my question I posed about
turning the mains off and then on quickly with the transformer core
still magnetised, and the phase angle at switchon such that the
transformer goes "boing"?

No, I didn't see that question. However, it is well known that rapid
on-off switching on the mains side of large transformer based power
supplies can result in unintended surges and overloads. Mostly, these
simply cause a circuit breaker to pop but there may be other
consequences depending on the psu design. It is generally accepted
that this practice is frowned upon and belongs in the realm of "worker
vandalism".

Understood. I guess some important machines are wired with a time
delay to prevent this intentional or unintentional mishap.

We used to get a lot of <1 second power dropoutss which would turn off
some clocks and computers. Seems to have disappeared since we got the
nice underground power. Now THAT is a nice conductor, I wonder how I
could wind my tranny with that

To avoid the need of caps, and keep the voltage stable, what about
another suggestion I've had to build "a simple series pass regulator
using a 36V zener like a 1N5936 and a 60A NPN transistor like a
MJ14002. it would be tons cheaper than the humongous capacitors you
would need. Since these need a couple of volts headroom, wind the
transformer to provide a slightly higher voltage say 32V or so. Also
the transistor must be put on a largish heatsink."

You could use this arrangement with a single large electrolytic across
the zener reference as a means of producing a "capacitor multiplying"
effect but you would still need a fairly hefty bulk storage capacitor
across the output to provide for instantaneous current demand due to
sudden load changes. You wouldn't save a great deal if any and in my
opinion it is not required for your application.

Thanks for that. Understood.

I doubt that a single series pass transistor would be suitable either.

OK

Or even "to parallel the outputs of 5 or 6 LM338K 3 terminal
regulators. Since the max output is 32V you would have to float the
regulators above ground using a 3.9V zener like a 1n4730.
Again you would need a big heatsink."

Solid state linear regulators (well designed) for high power DC
supplies have been used successfully as far back as the 60's and are
still used today when the most rugged operational conditions are to be
endured. $ for $ they will withstand almost anything you can throw at
them and while heavy duty switch mode units are also very capable, the
inclusion of safeguards against sudden blow-ups makes them more costly
and complex to design.

Fair enough. I really want to keep this project fairly inexpensive and
simple. I mean, if all I wanted was a DC variable speed drive for my
lathe, I could just buy a lathe with it on and pay the $2000 extra.
a). I can't afford it,
b). I want the learning and experience gained from homebrewing it and
c). It's not all that important for a LOT of unwanted effort and
expense.

This one weighs 11 lb, and some others weigh up to 15. Have you a
ball park figure for a reasonably stable load regulation?

It depends to a large extent on how you are going to drive your motor.
If it is going to be running at near full load for several hours at a
time then an 11lb transformer is totally inadequate. For such a
requirement (36V @18A) I would specify a transformer of 1KVA to be on
the safe side. As an example, I have a 1KVA isolation transformer and
this weighs 16Kg (35lb), so your 11lb unit is a pip-squeak by
comparison.

Yes, I understand.

It will be driving a hobby lathe, and thus will be used for probably
only a matter of seconds at full load to perhaps a minute or two at
half to three-quarters full load. Otherwise, idling.

This microwave transformer runs at around 1kVA (2000V at about half an
amp) in the microwave, but it is only intermittent use, and is fan
cooled.

I imagine your isolation transformer is rated at 1kVA continuously,
without fan cooling and in possibly hot ambient conditions?

Apparently 1000W output microwave ovens only have a 15lb transformer
and that would have nearly 1500W through it.

I want to run a mere 650W intermittently through the thing, while
blowing air over it and monitoring its temperature.

I first saw these transformers being used in homebrew welding
machines. I've already got two stick welders, so I got to thinking
that it might be nice to put a few more turns around the secondary
core to get 24 or 36 V for a DC motor of which I have a number. The
welding fraternity only wrap a few turns around the trannies to get
their few volts of heavy current. Admittedly, they gang several up
together, depending on how big a bridge they want to weld. They say
they wind them with flex and seem to get around 1 or two turns per
volt.

The primary turns on this one that I happened to have lying about are
either 14 or 15 turns each side of a square window, so around 200 to
220 turns in all. It may be better to use a 15 pounder that I hope is
in the other old microwave I have yet to plunder. I'm saving the
magnets in them to eventually make a wind turbine, multipole
generator.

I'm interested in these projects, partly because it is my nature -
I've been that way for most of my 60 odd years,
(emphasis on the odd .

This lathe motor is not essential. It already has a perfectly good AC
induction motor, but I figured a variable speed drive would be a nice
feature and teach me something in the meantime. You are helping with
that teaching. Thanks again.

I mean, I can get 2 dozen of these for around $US18 . Cheapest
capacitance I can find. Even three 12V leadacids would cost much more
and last for much less a time.

It seems to me that you have yet to grasp that your project is not a
simple "use what you can find at the lowest cost" type of project.

Understood, but if it is expensive, I won't do it, and will understand
why and thus have gained some knowledge and insight

I looked for the most suitable caps at Dick Smith, Altronics and
Jaycar. This seemed to be the 50V 4700uF electrolytics.
As luck would have it, I found at Oatley Electronics, simiar spec
electrolytics at around one sixth the price. Pure coincidence.
I think they only offer 4 different caps.

As apparently little smoothing is required, I was thinking of just
adding $18 worth of these caps wired up as 100V and giving ~28,000uF.
I'm not quite clear whether smoothing caps are of any advantage at all
if in fact no smoothing is required.

Is the upside, a slightly higher effective voltage, and less
likelihood of 100Hz hum, and the downside, perhaps expense?
Are there any other downsides?
Am I wrong in assuming that any smoothing is worthwhile?

I've just had a thought occur to me, and it's probably ridiculous, but
could anything possibly undue occur if the frequency of the PWM of the
controller is a harmonic of 100Hz of any ripple left. It just keeps
nagging me that chopping a variable voltage might have unpredicted
consequences. Seems that no-one I've heard of has ever tried what I'm
doing, so I've had no input from actual experience, just educated
guesses.

What you are trying to do is build a fairly heavy duty transformer
based dc power supply and to do this you have to start out with an
appropriately rated transformer in the first instance. There is no
substitute for an adequate laminated core mass when good load
regulation is required. Grabbing an old microwave transformer and
slapping on a few turns of pvc flex as a secondary is totally
inadequate in my opinion. If you had used something like 10AWG Formvar
insulated magnet wire then you would achieve far greater magnetic
coupling efficiency and get a result closer to what you were looking
for.

So the proximity of the windings to each other is quite important
vis-a-vis output voltage stability? I'm totally clueless about
transformer design, but I'd assumed that if a secondary turn went
through the secondary core windows, it was induced with a voltage
dependent on the primary windings. I'm sure I've seen some
applications where they actually space their windings apart with bits
of cardbord.

See below for a description of this flex..

BTW, according to the current carrying tables, 10AWG can only handle
14.8A for power transmission.

You can't use a transformer with poor load regulation AND get by with
the lower voltage rated capacitors - it's that simple. You either use
a good transformer which produces little voltage sag between low load
and full load where lower voltage caps can be used or you cover the
available output voltage range using higher rated caps. It's one or
the other and you have a cost penalty either way.

I understand. Thanks. That's a clear explanation.

I can of course now see ways of perhaps avoiding or minimising these
trade-off problems you point out. I'm not trying to be argumentative,
but if I am aware of the likely voltage rise on light loads, I can
look out for it, by measurement, and wire my caps in series to make
them safe to 100V.

I will of course be monitoring temp rises when testing.

I'm not trying to manufacture an idiot-proof item for public
consumption, but a Heath-Robinson contraption that I understand fully
and know what to watch out for.

Like some of the old banger cars I used to nurse about the place. If
anyone else tried to drive them, they would fall apart at the first
intersection. They all did me sterling service!
I can remember an RAC breakdown mechanic refusing to help with my
LandRover because it was so non-standard. I got it home without his
help.

This stuff is automotive, I think. It has quite a thin PVC sheath.
Its overall diameter is a whisker over 3mm. Drawn to scale, I can fit
at least 54 turns in the transformers secondary window.
I intend to have a fan blowing continuously over the whole shebang,
caps, transformer, bridge rectifier and motor, and I will monitor the
temps of everything to begin with to make sure that nothing is
getting too hot.

It is a long time since I wound a secondary to get a desired voltage
but from memory I had to wind something between 3 and 5 turns per volt
(240Vac primary) to get what I wanted. Depending upon the number of
turns on your primary will determine your required turns per volt at
the secondary and you should experiment to determine this. 54T sounds
a bit on the low side for a 36V,18A load to me.

Of course I will test it, but as I said above, I believe there are
around 220 turns of the primary windings, so theoretically, 33 turns
should give me 36V across the secondary windings. Gives me some room
for adjustment.

From my experience, depending upon the supplier, automotive shops
describe their flex with rather dubious current ratings. If the
overall diameter of your flex is 3mm the wire diameter will be about
half that at best and I would question its ability to conduct 30A for
any appreciable time without drastic losses and severe temperature
increase. See the chart here http://www.powerstream.com/Wire_Size.htm
to get an idea of wire gauge for a nominal current capacity. For
example, 30A power transmission conductor would be in the region of
3.7mm diameter without any insulation.

It is labelled 41 0.32
That is a 3.3mm^2 conductor.
Nominally rated at 30A

I've measured it at 41 0.30.
That is a 2.9mm^2 conductor.
Nominally rated at 25A.

I will want it to carry 18A
intermittently, and with fan cooling.

BTW, that 3.7mm diameter wire mentioned above is 10.75 mm ^2 or 7AWG.
It is rated at 89A for chassis wiring.

I sometimes run 18A (240V) through a 2.5mm^2 conductor and it gets
perceptibly warm after an hour or so.

Surely that power transmission rating is downrated for extra long
distances where a low maximum voltage drop is specified?

Fig 8 lamp flex of 0.75mm^2 cross section is rated at 7.5A which
multiplied up would mean a 2.9mm^2 conductor would be rated at 29A.
Dick Smith calls it 30A - Jaycar calls it 25A, and charges twice as
much. Altronics don't appear to have anything similar

I think Dick is getting out of the wire business and hasn't bothered
to raise his prices along with the price of copper. Everyone else
seems to have doubled the price of their cables, even though the
doubled price of copper is only relevant to a quarter of the cable
price.

Thanks for that, Ross. The speed controller is described by my
friendly ee who has experience with them on his bike, as:
"they have big input caps on the supply voltage in the controller,
and the circuit after that can be thought of as a buck switching
supply. All the logic and control runs from a low voltage (14.4v in
Crystalyte) that is internally regulated, so as long as your ripple
does not drop below that or go above the voltage ratings of the fets
or caps, you should be fine."

Since it's a "chopper" type speed controller then a bit of ripple on
the dc output will not be a problem. Your main problem is your
transformer load regulation as I read it.

That seems to be the general consensus, now (the ripple) but as I'm
only running an intermittent 18A max through the secondary windings,
perhaps if I doubled up the caps in series for a 100V rating, and
adjusted the secondary windings such that at low load, the voltage did
not creep too high, it is not worth a try?

Of course, it is up to me, along with any responsibility for any
injury, but I would appreciate any learned comment.

I am, BTW, so cautious, checking everything repeatedly, that some say
I'm neurotic. Friends would buy equipment and be so anxious to
assemble it and switch it on, that they would be tripping all over the
packaging, whereas I would take a day or two savouring the assembly
and thinking about every step. So there! ZAP!!! Where did that
bugger come from?

I've also got a couple of good quality brushless 24V 400W motors
with built in brushless controllers. He rebuilds these to reverse
the rotation. I will ask him about these too.

I've posed the question and await the reply.
These are beautiful machines - black, finned, machined aluminium with
just two heavy power leads emerging and a small control loom for a
pot or a Hall effect twist grip "throttle".
These are too nice for a lathe, best for my trike

I haven't any experience with this type of motor so I can't add
anything.

You've helped me enough already, Ross, thanks again, jack

 

[Ross Herbert]

On Sun, 21 Oct 2007 00:27:44 +0900, spamfree@spam.heaven wrote:

On Sat, 20 Oct 2007 05:21:23 GMT, Ross Herbert
rherber1@bigpond.net.au> wrote:

First up, Ross, let me thank you for your most valuable assistance in
helping me understand these new (to me) concepts. Most appreciated.

Not a problem.

Fair enough. I really want to keep this project fairly inexpensive
and
simple. I mean, if all I wanted was a DC variable speed drive for my
lathe, I could just buy a lathe with it on and pay the $2000 extra.
a). I can't afford it,
b). I want the learning and experience gained from homebrewing it and
c). It's not all that important for a LOT of unwanted effort and
expense.

It will be driving a hobby lathe, and thus will be used for probably
only a matter of seconds at full load to perhaps a minute or two at
half to three-quarters full load. Otherwise, idling.

This microwave transformer runs at around 1kVA (2000V at about half
an amp) in the microwave, but it is only intermittent use, and is fan
cooled.

I want to run a mere 650W intermittently through the thing, while
blowing air over it and monitoring its temperature.

The fan is there to cool the klystron but the transformer may benefit
from the airflow as an afterthought.

The primary turns on this one that I happened to have lying about are
either 14 or 15 turns each side of a square window, so around 200 to
220 turns in all. It may be better to use a 15 pounder that I hope is
in the other old microwave I have yet to plunder. I'm saving the
magnets in them to eventually make a wind turbine, multipole
generator.

I'm interested in these projects, partly because it is my nature -
I've been that way for most of my 60 odd years,
(emphasis on the odd

This lathe motor is not essential. It already has a perfectly good AC
induction motor, but I figured a variable speed drive would be a nice
feature and teach me something in the meantime. You are helping with
that teaching. Thanks again.


I looked for the most suitable caps at Dick Smith, Altronics and
Jaycar. This seemed to be the 50V 4700uF electrolytics.
As luck would have it, I found at Oatley Electronics, simiar spec
electrolytics at around one sixth the price. Pure coincidence.
I think they only offer 4 different caps.

As apparently little smoothing is required, I was thinking of just
adding $18 worth of these caps wired up as 100V and giving ~28,000uF.
I'm not quite clear whether smoothing caps are of any advantage at
all if in fact no smoothing is required.

It may be that the controller you are going to use MUST have a ripple
free dc supply since it is designed for use with electric bikes
running from a battery. The brushed dc motor doesn't require a ripple
free supply but the controller might.

In order to run your controller from an unfiltered dc supply it needs
to have an inbuilt dc filter and regulator just to supply its own
electronics.

So the proximity of the windings to each other is quite important
vis-a-vis output voltage stability? I'm totally clueless about
transformer design, but I'd assumed that if a secondary turn went
through the secondary core windows, it was induced with a voltage
dependent on the primary windings. I'm sure I've seen some
applications where they actually space their windings apart with bits
of cardbord.

The most efficient magnetic coupling between primary and secondary
turns is achieved when the maximum lines of flux can cut the secondary
turns. The closer the secondary is to the primary and the closer the
adjacent secondary turns are to one another will ensure the best
magnetic coupling efficiency. Windings in older style transformers may
be separated by a material we used to call Prespan but it probably has
a different name now. It is fairly thin and doesn't affect the P->S
separation too much. Some adequate separation is required for safety
isolation.

BTW, according to the current carrying tables, 10AWG can only handle
14.8A for power transmission.

Yes, I posted the wrong link. I should have posted the one for bare
copper wire http://amasci.com/tesla/wire1.html

I can of course now see ways of perhaps avoiding or minimising these
trade-off problems you point out. I'm not trying to be argumentative,
but if I am aware of the likely voltage rise on light loads, I can
look out for it, by measurement, and wire my caps in series to make
them safe to 100V.

I would first see how your motor performed using a straight
transformer/bridge-rectifier arrangement without filter caps. If it
works ok then you have avoided expense and unwarranted complexity.

This guy has a very comprehensive project site for his DC motor lathe
http://www.bedair.org/9x20camlock/9x20project.html Because he used
110Vac and a 90Vdc motor he doesn't require a transformer, although I
would recommend the isolation even for 110Vac. The internal picture of
the Cycletrol 150 controller he used accepts 110Vac line input and
directly drives a 90Vdc motor. Note that this controller does not
require the dc supply to be filtered for driving the bruished dc
motor.

See Cycletrol info here
http://www.grahammotorsandcontrols.com/products/cyctrldc.php

It is labelled 41 0.32
That is a 3.3mm^2 conductor.
Nominally rated at 30A

I've measured it at 41 0.30.
That is a 2.9mm^2 conductor.
Nominally rated at 25A.

Well you can only give it a go and see what happens.

BTW, that 3.7mm diameter wire mentioned above is 10.75 mm ^2 or 7AWG.
It is rated at 89A for chassis wiring.

I sometimes run 18A (240V) through a 2.5mm^2 conductor and it gets
perceptibly warm after an hour or so.

Surely that power transmission rating is downrated for extra long
distances where a low maximum voltage drop is specified?

Yes, I mistakenly indicated a link to power transmission conductor
gauges. See link I gave above for AWG copper wire gauge data.

Fig 8 lamp flex of 0.75mm^2 cross section is rated at 7.5A which
multiplied up would mean a 2.9mm^2 conductor would be rated at 29A.
Dick Smith calls it 30A - Jaycar calls it 25A, and charges twice as
much. Altronics don't appear to have anything similar

PVC insulated flex for domestic use is not designed for long runs more
than a few meters so it will get hot when carrying 7.5A for any length
of time if it is longer than this. If you use such conductors for a
transformer secondary you will have many meters of wire and because
the transformer gets hot itself I would not like to trust the
insulation. Proper magnet wire is the only suitable conductor type to
use for the secondary as a permannet solution but experiment if you
wish.

Since it's a "chopper" type speed controller then a bit of ripple on
the dc output will not be a problem. Your main problem is your
transformer load regulation as I read it.

That seems to be the general consensus, now (the ripple) but as I'm
only running an intermittent 18A max through the secondary windings,
perhaps if I doubled up the caps in series for a 100V rating, and
adjusted the secondary windings such that at low load, the voltage
did not creep too high, it is not worth a try?

I just took notice of the fact that the controller you refer to is
used for speed control on electric bike motors. As such it is designed
to operate directly from a battery supply and this may be where the
requirement for filtering of a mains powered dc supply is relevant.
While the dc motor doesn't care about ripple the controller you are
going to use may not like it. A controller a-la the Cycletrol 150 is
designed to drive a dc motor from an ac input voltage, not a pure dc
input. This could be overcome if the controller you are using includes
its own dc regulation and filtering.

I hope your experimenting provides valuable information and experience
with dc motor drives and psu requirements.

You can see a whole lot of stuff on motor speed control schematics
here if you are interested
http://www.educypedia.be/electronics/circuitsmotorcontrol.htm

 

[John Fields]

On Sun, 21 Oct 2007 11:35:06 GMT, Ross Herbert
<rherber1@bigpond.net.au> wrote:

The fan is there to cool the klystron but the transformer may benefit
from the airflow as an afterthought.

---
Klystron?


--
JF

 

[Daniel Mandic]

spamfree@spam.heaven wrote:

Huh? That's the second message that makes no sense.
What are you trying to say?

jack

just count Moron



Best Regards,

Daniel Mandic

 

[Daniel Mandic]

John Fields wrote:

Mandic seems to think of himself as a sagacious dispenser of obscure
folksy wisdom and witticisms. Unfortunately, his neophytic command
of written English often reduces his otherwise banal "edicts" to
gibberish.

What a puffy text.

You can't believe that for yourself!?



Best Regards,

Daniel Mandic

 

[Ross Herbert]

On Sun, 21 Oct 2007 08:12:49 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Sun, 21 Oct 2007 11:35:06 GMT, Ross Herbert
rherber1@bigpond.net.au> wrote:


The fan is there to cool the klystron but the transformer may
benefit
from the airflow as an afterthought.

---
Klystron?

Yeah, boo-boo. Of course I meant to type Magnetron.

 

On Mon, 22 Oct 2007 01:55:14 GMT, Ross Herbert
<rherber1@bigpond.net.au> wrote:

On Sun, 21 Oct 2007 08:12:49 -0500, John Fields
jfields@austininstruments.com> wrote:

Klystron?

Yeah, boo-boo. Of course I meant to type Magnetron.

I noticed it, but simply read it as "the thing that produced the
microwaves". I've since looked up the difference. jack

 

On 21 Oct 2007 23:22:53 GMT, "Daniel Mandic" <daniel_mandic@aon.at>
wrote:

John Fields wrote:

Mandic seems to think of himself as a sagacious dispenser of obscure
folksy wisdom and witticisms. Unfortunately, his neophytic command
of written English often reduces his otherwise banal "edicts" to
gibberish.


What a puffy text.

You can't believe that for yourself!?

You would do well to study this excellent English text, Daniel.
It could help you to express what you mean. So far, your choice of
words and syntax has indeed rendered most of your messages as
giibberish.

jack

 

On 21 Oct 2007 23:17:59 GMT, "Daniel Mandic" <daniel_mandic@aon.at>
wrote:

spamfree@spam.heaven wrote:

Huh? That's the second message that makes no sense.
What are you trying to say?

jack

just count Moron

Best Regards,

Daniel Mandic

I don't understand this message, Daniel.
May I offer a few words of advice?

First up, be careful with capitalisation. English native speakers can
get away with ignoring it, but like using much idiom, you should aim
for simple, correctly expressed language. Avoid much idiom and the
jokes of the native speaker until you are much more proficient with
English.

Be careful with punctuation. My "rule" for commas is "when the reading
of the text requires a pause, insert a comma".

Your pithy comment above, has no comma, and so would be read as:

"[J]ust count Moron. (whatever "Morons" are with a capital.)
In other words, "Do nothing else except count the number of Morons."

If you were trying to call me a moron, and trying to tell me to count
(something) then you should have written "Just count, moron."
You could even capitalise the moron then, for emphasis.

You see, the verb "count" can be either transitive or intransitive,
and you have not made it clear which you mean.

BTW, you do leave yourself open to ridicule when you try to insult
with poor language skills. There is nothing sillier than someone
flaming a fellow poster for spelling errors, when the flame contains
its own spelling errors. To criticise, you really should be flameproof
yourself.

Do you come from Austria? Your native tongue would perhaps be German,
or the Austrian version thereof?

German syntax is a little different to English, and what you appear to
be doing, is perhaps using German syntax with a rather limited, but
often inappropriate choice of English vocabulary.

HTH, jack

 

On Sun, 21 Oct 2007 11:35:06 GMT, Ross Herbert
<rherber1@bigpond.net.au> wrote:

I hope your experimenting provides valuable information and experience
with dc motor drives and psu requirements.

Thanks so much for all that wonderful stuff to browse and study, Ross,
you'be been a great help, Cheers, jack

 

[Daniel Mandic]

spamfree@spam.heaven wrote:

On 21 Oct 2007 23:22:53 GMT, "Daniel Mandic" <daniel_mandic@aon.at
wrote:

John Fields wrote:

Mandic seems to think of himself as a sagacious dispenser of
obscure >> folksy wisdom and witticisms. Unfortunately, his
neophytic command >> of written English often reduces his otherwise
banal "edicts" to >> gibberish.


What a puffy text.

You can't believe that for yourself!?

You would do well to study this excellent English text, Daniel.
It could help you to express what you mean. So far, your choice of
words and syntax has indeed rendered most of your messages as
giibberish.

jack

you like the pain in the ass role, do you?

Are you heidnic or more the nazi? I can't see any signs of Right with
you. You are a painful double-thinker.... You should learn from
Eyeore... he can handle that well. He is a strong and nice English Man.



Best Regards,

Daniel Mandic