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klugesmith

Wed Apr 04 2012, 10:50PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

ben123324 wrote ...
... it can theoreticaly put out a few kw without overheating(1-3 depending on awg).

How can you expect to get more power than the original design, without running even hotter? The OEM design was cost-reduced by experts. Wire AWG choice does not matter -- as the wire gets thicker (for more A), fewer turns will fit (for less V).

Do you have any techniques to increase power, other than:

1. Include windings in the window area formerly occupied by core shunts. That's offset by the lower packing density of your hand-wound coils.

2. Better cooling ( stronger forced air? oil? ) to allow more power loss in the transformer.

and perhaps less practically...
3. Use wire whose insulation can operate at higher temperature.
4. Operate at higher frequency.
5. Operate at extremely low temperature, to reduce the copper resistivity and I2R power loss.

Newton Brawn

Thu Apr 05 2012, 01:44AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi !
Here some notes based on what I learn winding tranformers;
1- all calculation shall be in the ISO sistem (meter, tesla, square meter, ohm, henry, weber, amper turn per meter )

1-a MOT typical core witout secondary or no secondary load after 1 hour reaches 48C when working at 1.2T at 60Hz. 43C when working at 1.0T, 38C when working at 0.8T. No fan or forced ventilation

2- the table from Philips Lab is very useful to calculate the number of turns in a window area, resistence o the coils, weigt of th coils, etc .

]tabela_de_fios_ibrape.pdf[/file]

3-The bobin form: Curt a block of wood with the same measurements of central core leg. Rub parafin on all surface. Cut long ribows of craft paper with the same wide of the block and apply carpenter gloe on one side ogf the ribow. Wind 10 turns of the paper on the wood block, Leave to dry, remove the block, insert the core in the form to verify if is nescessary some adjustment in the form.

4- insulation between form first wire layer and between turn layers - For 60Hz I use polyester film, 0.1 mm (for #20 AWG and thicker) and 0.05mm (for #22 AWG and thinner) I buy in the same place that sell wire for transformers. Eventually I have bought in a store for art articles. - Mylar paper for drawings . Polyester/ Mylar is good insulation used up to 130- 150C.

5- keep a margin of 5mm between the extremes turms of a layer and the border of insulation film.

6- The insulation impregnation is a alkyd vernish (the classical G.E Glyptal). you can find some spar clear varnishe in Home Depot, or even a alkyd varnishe. It keeps the hole coil as a block and prevent the colapse of winding.

I will be back soon.

Regards

Newton

Newton Brawn

Thu Apr 05 2012, 02:16AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

7- Here is the parafernalia that I use to wind coils for tranformers and inductors. Despite the picture is showing a small transformer, the same device have wound coils for MOT and welding transformers. Just make the wood block bigger. Attached to the end of crankcase is a turn counter.

Ben Solon

Thu Apr 05 2012, 02:27AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

Klugesmith: I said theoreticly. I don't want or need anywhere near 1kw. At 5v that is 200A, 12v @ 80A, 24v @ 40A, etc. when have you ever needed 200A continuos from 5v? At any voltage really. If you had the window space and your windings where big enough then you could have infinite power at the limitation of the breaker. XD
And btw, nice job with those small iron cores. I do similar stuff with ferrite chokes, but without the nice looking wire.

And Newton: most of this has already been said, and even magnet wire doesn't need extran insulation at low voltages like these. I alreays said I was using wax/oil paper for the primary.

Newton Brawn

Thu Apr 05 2012, 03:53AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi Forty !

Congratulation for the advice of " Easiest MOT Savage Reuse " site . It is a really detailed instruction for projects that use MOT.

I have cut the core welding by hand using a arc saw, hss.

When I cut the the magnetic core in order to separate the I and E cores, I do not cut exact in the midle of the core welding.

The saw open a slot 1mm out of the welding center, in such way that the E core is not damaged. only the I core receive 1.5-2 mm deep scratch. When reasembling the E core with the I core invert the I core leaving the scratch out of the main magnetic flux.

If the cut is locate in the center of the welding, both E and I cores will be scratched, resulting in a reduction of area of magnetic flow (increasing the induction in that location)

Regards

Newton

Newton Brawn

Thu Apr 05 2012, 04:04AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi Ben !

I agree with you that in this case the insulation of magnetic wire do not requies extra insulation between layers. Todday all comercial transformers are made with no insulation between turns.
However, for only one tranformer, and IF I DO NOT HAVE THE PROPER BOBBIN, I feel more confortable using film insulation between layers, for mechanical purposes.

Regards

Newton

Steve Conner

Thu Apr 05 2012, 07:06AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Welding a stack of Es to a stack of Is is a cheap and nasty trick for cheap and nasty transformers, such as MOTs. They're supposed to be interleaved, for more metal-to-metal contact and higher magnetising inductance.

Having said that, if the transformer is run at a very high flux density, the tiny air gap between the E stack and I stack might help it run a bit cooler.

Ben, you'd be surprised, if you have a high end computer the CPU probably draws nearly 100A and the GPU the same again. Of course this is supplied by DC-DC converters, not a MOT, but it's an example of a household appliance that needs an assload of current at low voltage.

Ben Solon

Thu Apr 05 2012, 02:14PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

Wow. Must be a pretty nice computer. Atx supply's only put out around 25A at 5 volt levels. What voltage is it supplied at? And I know of a few high current household apliences, but nothing like that!

And for the rest, my friend just got a 3d printer, so you will like the bobbin when I print it. A lot better than paper.

teravolt

Thu Apr 05 2012, 04:37PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

how much power, voltage, amprage are you looking for?

Ben Solon

Thu Apr 05 2012, 10:08PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

various taps for various needs. low voltages at ~10A and higher ones at around 1-5A.

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