Is this water in the toroidal trafo ?

[Chris Jones]

hihihi wrote:

Chris Jones wrote:

I think that heating to low temperatures (40 deg C) for a long time will
not necessarily dry the transformer well, especially if the humidity of
the
environment is high (e.g. in an outdoor greenhouse or a gas oven). Also,
the warm temperature may accelerate the corrosion cause by the water
(e.g. the iron core).

I just opened one trafo to the core.
There was water in the secondary and primary windings.
I have no way of knowing how long the trafos have been wet.

There is rust on the metal core.

This is a normal webcam picture of the core with rust.
http://home.wanadoo.nl/vroemm/temp/snapshot-20070821-101731.png

This is the same picture, but improved with gthumb -> image -> equalize
http://home.wanadoo.nl/vroemm/temp/snapshot-20070821-101731-eq.png

I must assume the other 15 trafos can have the same or more rust.

My trust in the trafos is getting low.
It looks wise to me NOT to use the trafos.
Unless someone has a good reason why it is safe to use them for the long
term.

I think that a small amount of rust on the core is not likely to be a
problem. The only thing that I would be concerned about is if the
insulation on the wire were to fail, and that can even happen in new
transformers.

Once the transformer has been completely dried out, then I think that it
will not suffer any significant further deterioration.

Chris

 

[Lostgallifreyan]

Chris Jones <lugnut808@nospam.yahoo.com> wrote in
news:13cmndj4ca54n8e@corp.supernews.com:

Most of your other points were already made before you posted.
Yes, though sometimes it can be useful to know whether several people
agree that something is a good idea. Perhaps I should have take the
extra time to explain explicitly that someone had suggested the ideas
and that I was agreeing with them, but I didn't think that was
necessary because it is plain for all to see where other people posted
things first, and I don't pretend otherwise.

The main thing is that not all posts propagate to all people, so anything
that looks like a possibility they didn't can be frustrating. Acknowleging
one shows a chain of events that rules that problem out neatly.

I'm not talking about turning it into an icepack, just creating a
strong temperature difference across the tape layer for a few minutes
to test for dryness after an 80°C bake.

What you say here makes sense to me, though I did misunderstand some
of your previous posts on the subject, for example, you wrote:
"Vacuum and cold are closely related, so you could try a peltier.
Best not though, far too awkward, and the cold trap will just cool
your box..."

I could not quite understand what you were suggesting with the
peltier. That is why I made the point that I did not think freezing
would be a good cure for the moisture. Your suggestion of using
cooling as a way of testing whether the transformer had been dried out
did sound sensible to me.

Fair. My point was a sort of thin joke really, on the face of it a small
Peltier is actually good, it locks down the water in a separate location,
avoiding the need to use vacuum to constantly draw vapour out to maintain
low pressure. The joke is that to do that with any strong effect, the
secondary (entirely unwanted) effect is to cool the entire setup. Although
I guess you could pass the hot side waste heat back to the transformer
somehow. Pointless complexity, perhaps...

I realise that using a vacuum had already been suggested. The OP then
said :
"Problem is, i do not have a vacuum box."
so I suggested a couple of ways of obtaining vacuum pumps.

Sometime I ought to get one actually, my old fridge compressor is a tad
crude. Thing is, while you might easily put a vaccuum pump into service to
dry something in a sealed chamber, it's only easy from the standpoint of
pressing into service a bit of kit that is already there. Analogy: It's
easy to use a car to get the shopping done, unless you have no car, in
which case it's far easier to carry the shopping than to buy the car.

Also I don't think anyone else has commented on the relative merits of
drying at say 40 degrees C and drying at say 105 degrees C. The
vapour pressure of water is rather different in the two cases and so
the time required would be rather different. If anyone has tried this
and has experiences to share then that would be useful.

Agreed. I see no problem with 105°C on toroidal transformers. I let it go
at 80 because it will work, and it's just below a much lower risk standard
rating. The only part I can imagine might protest at 105°C is the little
PVC sheaths on the wire ends. And maybe the sticky tape that stops the
outer tape unwinding.

 

[Chris Jones]

Lostgallifreyan wrote:

Most of your other points were already made before you posted.
Yes, though sometimes it can be useful to know whether several people agree

that something is a good idea. Perhaps I should have take the extra time
to explain explicitly that someone had suggested the ideas and that I was
agreeing with them, but I didn't think that was necessary because it is
plain for all to see where other people posted things first, and I don't
pretend otherwise.

And if
you're suggesting my advice on use of a freezer is wrong, forget it, I'm
not talking about turning it into an icepack, just creating a strong
temperature difference across the tape layer for a few minutes to test for
dryness after an 80°C bake.

What you say here makes sense to me, though I did misunderstand some of your
previous posts on the subject, for example, you wrote:
"Vacuum and cold are closely related, so you could try a peltier. Best
not though, far too awkward, and the cold trap will just cool your box..."

I could not quite understand what you were suggesting with the peltier.
That is why I made the point that I did not think freezing would be a good
cure for the moisture. Your suggestion of using cooling as a way of
testing whether the transformer had been dried out did sound sensible to
me.

If you read more, and decide less that all other posts before you arrived
are wrong, irrelevent, or not even there, you might have made a better
post.
I realise that using a vacuum had already been suggested. The OP then

said :
"Problem is, i do not have a vacuum box."
so I suggested a couple of ways of obtaining vacuum pumps.

Also I don't think anyone else has commented on the relative merits of
drying at say 40 degrees C and drying at say 105 degrees C. The vapour
pressure of water is rather different in the two cases and so the time
required would be rather different. If anyone has tried this and has
experiences to share then that would be useful.

Chris

 

[hihihi]

Lostgallifreyan wrote:

A better idea is to buy a cheap paper bag of granulated sugar and seal
that in the box with the transformers.

I put a kilogram granulated sugar without the bag in a plastic bag.
With a hygrometer, which pointed to 90 % humidity at startup.
Not much air in the bag.
All at room temperature.

After 2 days the hygrometer still points at 90 % humidity.

Does not seem to work.

--
hihihi is the username, wanadoo the domain, nl the country.

 

[Lostgallifreyan]

hihihi <See@signature-at-the-bottom-of-the-message.invalid> wrote in
news:46cbfa14$0$3885$dbd41001@news.wanadoo.nl:

Lostgallifreyan wrote:

A better idea is to buy a cheap paper bag of granulated sugar and seal
that in the box with the transformers.

I put a kilogram granulated sugar without the bag in a plastic bag.
With a hygrometer, which pointed to 90 % humidity at startup.
Not much air in the bag.
All at room temperature.

After 2 days the hygrometer still points at 90 % humidity.

Does not seem to work.

Ok. Was just a thought... A paper bag or dish full of salt might work
better. I just didn't want to recommend salt as it's very corrosive if any
gets onto metal.

Sugar (or salt) will definitely take up water, but the best way is to heat
the transformers to drive off water and let unrestricted airflow carry it
away. Nothing is going to work better than that. One single exception might
be viable if you have it, a portable dehumidifier. If you have that you can
do this in a closed cupboard with no source of heat other than the
dehumidifier itself. That can dry a pair of wet jeans overnight so it
should be useful.

 

[hihihi]

Lostgallifreyan wrote:

I just didn't want to recommend salt as it's very corrosive if any
gets onto metal.

My thoughts exactly

The sun has not shown itself for days, and is not expected to the coming
days.

I am now looking for a suitable secondhand mini oven at ebay and such
places.


--
hihihi is the username, wanadoo the domain, nl the country.

 

[Lostgallifreyan]

hihihi <See@signature-at-the-bottom-of-the-message.invalid> wrote in
news:46cc1fae$0$12207$dbd4b001@news.wanadoo.nl:

I am now looking for a suitable secondhand mini oven at ebay and such
places.

Look for a laboratory block heater with temperature control (Labline, for
example), those go for astonishingly low cost at times. I got one for about
Ł15 (most of that was postage), and it's a very useful thing to have.

 

[Dave Platt]

I put a kilogram granulated sugar without the bag in a plastic bag.
With a hygrometer, which pointed to 90 % humidity at startup.
Not much air in the bag.
All at room temperature.

After 2 days the hygrometer still points at 90 % humidity.

Does not seem to work.


Ok. Was just a thought... A paper bag or dish full of salt might work
better. I just didn't want to recommend salt as it's very corrosive if any
gets onto metal.

How about using the sort of silica-gel dessicant beads that are used
to dry flowers and (ahem) protect electronic equipment against humidity?

A craft store might be a good place to start looking - look for a
product like Flower-Dri (tm) or a competitor. These are small-bead
silica-gel dessicants, with some amount of a moisture-indicator added
(likely cobalt chloride or something containing it).

The dessicant can be reactivated, once it's saturated with moisture
and its indicator loses its blue color, by warming it in a vented
electric oven for a few hours (temperatures from 240 to 325 degrees F
seem to be used for this).

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[hihihi]

Lostgallifreyan wrote:

Use heat.

How about this heat method :

Put a 220 volt lightbulb of X watt in series with the primary side of the
trafo.
To prevent high short circuit current, in case of disaster.

Then put a load on the secondary side.

Balance the wattage of the light bulb and the secondary side load so that
the trafo gets nicely warm, like 80 degree Celsius.

Put a old smoke detector above the trafo, just in case it starts smoking.

This way the trafo will dry itself )

Are there any problems with this method ?


--
hihihi is the username, wanadoo the domain, nl the country.

 

[hihihi]

hihihi wrote:

How about this heat method :
Put a 220 volt lightbulb of X watt in series with the primary side of the
trafo.
To prevent high short circuit current, in case of disaster.
Then put a load on the secondary side.

How about this :

Put no load on the secondary side.
Short circuit the secondary side with a ampere meter, to monitor the
secondary current.
And then adjust the wattage of the lightbulb in series with the primary
side, to get the maximum secondary current.

Trafo A is secondary 28.7 volt 3 ampere.
220/28.7=7.66
3/7.66= 0.391 ampere primary side.
220 x 0.391 = 86 watt lightbulb in series with primary side ????
In the real world this would be a 75 watt lightbulb ?

Trafo B is 34.6 volt 3 ampere.
220 / 34.6 = 6.358
3 / 6.358 = 0.471 ampere primary side.
220 x 0.471 = 103 watt lightbulb in series with primary side ?
In the real world this would be a 100 watt lightbulb ?

Trafo C is 22.2 volt 4 ampere
220 / 22.2 = 9.9
4 / 9.9 = 0.404 ampere primary side.
220 x 0.404 = 88 watt lightbulb in series with primary side ?
In the real world this would be a 75 watt lightbulb ?

Any problems with peak current when switching ON ?
Any problems other with this ?


--
hihihi is the username, wanadoo the domain, nl the country.

 

[Chris Jones]

hihihi wrote:

hihihi wrote:

How about this heat method :
Put a 220 volt lightbulb of X watt in series with the primary side of the
trafo.
To prevent high short circuit current, in case of disaster.
Then put a load on the secondary side.

How about this :

Put no load on the secondary side.
Short circuit the secondary side with a ampere meter, to monitor the
secondary current.
And then adjust the wattage of the lightbulb in series with the primary
side, to get the maximum secondary current.

Trafo A is secondary 28.7 volt 3 ampere.
220/28.7=7.66
3/7.66= 0.391 ampere primary side.
220 x 0.391 = 86 watt lightbulb in series with primary side ????
In the real world this would be a 75 watt lightbulb ?

Trafo B is 34.6 volt 3 ampere.
220 / 34.6 = 6.358
3 / 6.358 = 0.471 ampere primary side.
220 x 0.471 = 103 watt lightbulb in series with primary side ?
In the real world this would be a 100 watt lightbulb ?

Trafo C is 22.2 volt 4 ampere
220 / 22.2 = 9.9
4 / 9.9 = 0.404 ampere primary side.
220 x 0.404 = 88 watt lightbulb in series with primary side ?
In the real world this would be a 75 watt lightbulb ?

Any problems with peak current when switching ON ?
Any problems other with this ?

You idea sounds sensible, but the wattage of the lightbulbs might need some
experimentation because the filament resistance is not constant with
different supply voltages, and there will be some voltage dropped across
the transformer.

You could get the same amount of heat into the transformer windings without
having to dissipate as much heat in the light bulb if you start with a
lower AC supply voltage (from another transformer), and then limit the
current using a low voltage light bulb (e.g. from a car indicator light),
adjusted to get the same current as you already calculated above.

E.g. of you need 0.471 Amperes, probably you only need less than 20 Volts
across the primary with the secondary shorted in order to get this much
current to flow. You would have to measure and adjust the series
resistance.

If you intention is to make the transformer get quite warm then you might
have to exceed the rated current, which will be safe to do as long as you
monitor the temperature carefully.

Chris

 

[hihihi]

Chris Jones wrote:

You idea sounds sensible, but the wattage of the lightbulbs might need
some experimentation because the filament resistance is not constant with
different supply voltages, and there will be some voltage dropped across
the transformer.

I just did a experiment.
200 Watt 220 volt lightbulb in series with primary side.
Gives 43.3 volt on primary connectors.
And 4.6 ampere secondary, this is 50 percent overload.
Temperature went up to 60 degree Celsius and was still rising.
It is late, 01:00 at night, so i ended the experiment.

You could get the same amount of heat into the transformer windings
without having to dissipate as much heat in the light bulb if you start
with a lower AC supply voltage (from another transformer), and then limit
the current using a low voltage light bulb (e.g. from a car indicator
light), adjusted to get the same current as you already calculated above.

I will think about it, and see if i have suitable trafo.

What about this idea.
I have 4 trafos of 34.6 Volt 3 ampere.
All have to be dried.
What if i connect the secondary of the first trafo to the secondary of the
second trafo ?
And then the primary of the second trafo to the primary of the third trafo.
Then the secondary of the third trafo to the secondary of the fourth trafo.
And the short circuit the primary of the fourth trafo.
Oeps..
Is this crazy ? To unpredictable ?
Would be nice if it worked, could dry 4 trafos at the same time.

If you intention is to make the transformer get quite warm then you might
have to exceed the rated current, which will be safe to do as long as you
monitor the temperature carefully.

Yes, good suggestion.


--
hihihi is the username, wanadoo the domain, nl the country.

 

[ehsjr]

hihihi wrote:

Lostgallifreyan wrote:


I just didn't want to recommend salt as it's very corrosive if any
gets onto metal.


My thoughts exactly

The sun has not shown itself for days, and is not expected to the coming
days.

I am now looking for a suitable secondhand mini oven at ebay and such
places.

I see microwave ovens thrown out often. Get one free,
put a bulb inside of it and let the bulb supply the heat.
You could even use a dimmer on the bulb and put a small
oven thermomenter inside to control the max. temperature.

Ed

 

[Hal Murray]

You idea sounds sensible, but the wattage of the lightbulbs might need some
experimentation because the filament resistance is not constant with
different supply voltages, and there will be some voltage dropped across
the transformer.

Why not just put the right size light bulb (aka heater) under the
thing you want to heat.

--
These are my opinions, not necessarily my employer's. I hate spam.

 

[hihihi]

ehsjr wrote:

I see microwave ovens thrown out often. Get one free,
put a bulb inside of it and let the bulb supply the heat.

Toke me some time to realize, you mean, do NOT switch the microwave ON.

A not working microwave as heat isolating box, good idea.



--
hihihi is the username, wanadoo the domain, nl the country.

 

[hihihi]

ehsjr wrote:

I see microwave ovens thrown out often. Get one free,
put a bulb inside of it and let the bulb supply the heat.

Can the inside of a microwave take 80 degree Celsius for many hours ?
No melting roof panel ?

--
hihihi is the username, wanadoo the domain, nl the country.

 

[Lostgallifreyan]

hihihi <See@signature-at-the-bottom-of-the-message.invalid> wrote in
news:46cd3c81$0$24496$dbd4f001@news.wanadoo.nl:

I see microwave ovens thrown out often. Get one free,
put a bulb inside of it and let the bulb supply the heat.

Can the inside of a microwave take 80 degree Celsius for many hours ?
No melting roof panel ?

Don't bother, you'd have to get the water out, and the only practical way
is to alter the oven so the fan works, but not the magnetron drive.

I think your self-heating idea is good. Chain primaries together, four or
more in series, and short each secondary separately. That way you won't
have to calculate loads, if the primaries are enough in number to drop the
input voltage for each transformer, the right proportions of energy per
transformer will be easy enough to get even if different types are there in
one chain. Try at least 4 primaries in series so the temperature rise isn't
too fast, and set a temperature regulated switch to open the supply circuit
if they get too warm, if you're not going to watch over them. But watch
over them anyway till you're very sure what response you're getting.
Monitor the smallest transformer's temperature.

 

[Lostgallifreyan]

Lostgallifreyan <no-one@nowhere.net> wrote in
news:Xns9995627CA59ABzoodlewurdle@140.99.99.130:

the right proportions of energy per
transformer will be easy enough to get even if different types are
there in one chain.

NO. Scratch that... Forgot to consider that there would be different
primary currents! It will work if each chain has the same type though.

 

[ehsjr]

hihihi wrote:

ehsjr wrote:


I see microwave ovens thrown out often. Get one free,
put a bulb inside of it and let the bulb supply the heat.


Can the inside of a microwave take 80 degree Celsius for many hours ?
No melting roof panel ?

No problem - 80 C is way lower than it can take.

Ed

 

[ehsjr]

Lostgallifreyan wrote:

hihihi <See@signature-at-the-bottom-of-the-message.invalid> wrote in
news:46cd3c81$0$24496$dbd4f001@news.wanadoo.nl:


I see microwave ovens thrown out often. Get one free,
put a bulb inside of it and let the bulb supply the heat.

Can the inside of a microwave take 80 degree Celsius for many hours ?
No melting roof panel ?



Don't bother, you'd have to get the water out, and the only practical way
is to alter the oven so the fan works, but not the magnetron drive.

"Don't bother" ?? How much stuff have you experimented with
this way to arrive at that conclusion? For the record, I've
done it many times - although I've never dried toroids.

As to running the fan if he wants to - we're talking about
a microwave oven that was thrown out. What's the problem
with modifying that?

Ed

I think your self-heating idea is good. Chain primaries together, four or
more in series, and short each secondary separately. That way you won't
have to calculate loads, if the primaries are enough in number to drop the
input voltage for each transformer, the right proportions of energy per
transformer will be easy enough to get even if different types are there in
one chain. Try at least 4 primaries in series so the temperature rise isn't
too fast, and set a temperature regulated switch to open the supply circuit
if they get too warm, if you're not going to watch over them. But watch
over them anyway till you're very sure what response you're getting.
Monitor the smallest transformer's temperature.