Transformer parts

[Stevie342000]

I am pretty certain that his has been asked before but too lazy to do a search. I have a little knowledge on transformers and coils etc. I am looking to expand my knowledge what books should I read.

I have a copy of Radio designers handbook and Babani book on coils, the latter covers the fundamentals.

But if I were to make my own transformers where would I go to get the laminations, insulating materials, coil formers (aside from making them). I have seen some Youtube clips on rewinding field coils, I have a couple of designs for a coil winder and have seen Youtube clip on audio transformers.

[ms660]

Originally Posted by Stevie342000

But if I were to make my own transformers where would I go to get the laminations, insulating materials, coil formers (aside from making them). I have seen some Youtube clips on rewinding field coils, I have a couple of designs for a coil winder and have seen Youtube clip on audio transformers.

Ed Dinnings the man on the forum for transformer info, I think he usually checks in most days, he might answer some specific questions you may have or point you in the right direction for suitable links/books etc.

Lawrence.

[Stevie342000]

Yes I thought he was the go to person and that he might answer some of the more specifics. There is a neat YouTube clip by a Japanese guy who winds an audio coil but says nothing, not even on his home built 3 motor servo controlled winding machine.

Plus I thought he would have enough knowledge of the forum and the various threads to pull the information together. Hence the question, just reading some Crowhurst papers now, apparently he did the bits in the Big Red Book.

I have seen him referred to and I thought he might sign post me towards suppliers/supplies/parts in anything less than a ton(ne) order size in 100s minimum order, working my way through the link above, useful thanks.

[paulsherwin]

Six posts deleted. Please keep this thread civil or it will be deleted. We don't allow pointless squabbling here.

[Ed_Dinning]

Hi Stevie, Wires and tapes are no problem and can be found on e-bay/ scientific wire company.

Lams are a bigger problem; try Googling them and you may get some manufacturers catalogues to down load that show shapes and sizes. Metric and Imperial types can still be found. Materials are usually Stalloy or Unisil (grain orientated steel). There are also special nickel steels but these are specialist and expensive.

Try Milles Platts for bobbin details

Then look in local area for a small transformer winder and go and see him with details of what you require in the way of lams and bobbins; he may agree to supply you small quantities if you are lucky. They will be quite pricy as is the way of things !

Failing that get some old transformers to dismantle/ re-use.

Ed

[joebog1]

I have the same problems !!! I used to buy australian made laminations, but that company is gone.
The replacement company wont sell less than 100 kgs of laminations!!! Thats a LOT of iron of only one size. Its made in India ( of excellent quality however).
Copper in the "average " sizes come on 30 kg reels, and at present its about $500 a reel
depending on copper tax on the day, and the wire guage.
Thin wire ( <.6mm ) is even more expensive but comes in 6 kg reels.
Beware the cheap chinese nylon bobbins !!! they distort if you try and make a "nice tight" winding. Just removing the drive hub can be a REAL pain. ( I also doubt its temperature ratings)
I commonly use old PCB material that I etch the copper off for one offs and specials.
All in all its becoming a more and more " specialised trade".
To make really "nice" transformers they will need varnishing ( either vacuum or even cold dipping) and then baking. There are air drying varnishes however.
I havent tried it, but varnishing might be do-able by spraying each layer when you wind it.
I am not trying to dissuade you at all, but perhaps advising, as Ed has suggested, to do some pricing checks before you start.
Joe

[jonmiller]

A Google search for "transformer laminations"
came up with

http://ascocomponents.co.uk/

Birmingham.

[Stevie342000]

Thanks Ed and Jon that is all use full much appreciated. What are the usual materials for insulation or the modern equivalents of old materials. I have an old project I would like to build I have the winding details for all the transformers and chokes including the output transformer.

It comes as no surprise that we all struggle to get the laminations in a pricing/quantity that is acceptable to us. Everything is based on thousand units of this thus driving the price down, it seems industry is not set up for the smaller end user not at an affordable price?

[jonmiller]

Hi there
http://www.wes.uk.com/products/elect...adhesive-tapes

They sell the tapes and the lacquer.

Kr

Jonathan

[Ed_Dinning]

Hi Stevie, the Asco site has some good cross references as to lam sizes etc. I've not used them as yet.
Modern wires are normally double insulated so do not need tissue between layers, but should obviously have it between windings. Type 56 polyester tape is normally used.

Note that some modern bobbins are double section. One side for the Pri, the other for the sec. This makes it easier to get the required safety creepage and clearance distances as required for commercial transformers. It does, however, give much worse transformer regulation with load.

I have used spray varnish between layers on an EHT transformer before and it worked quite well.

Ed

[FrankB]

If you want to wind your own transformer, how about salvaging microwave oven transformers?
I just picked up 10-15 of them for free, just haul them off. Most primary windings are separate, and there is plenty of salvageable wire on the secondary to rewind about anything you might need. With a bobbin core too!
Just cut the welds with a grinder and then you can do the "E&I" thing or just use the laminations "as-is" and tack weld them back on.
I am going to build a spot welders out of 2 of mine. A 110V version, and a 220V version.

[Radio Wrangler]

Aren't microwave oven transformers designed with a lot of leakage flux to make them act more like current sources than voltage sources?

Just what you need for a spot welder, of course. The classic 50Hz iron-transformer arc welder boxes use a screw thread to move a flux shunt as their current control.

David

[Ed_Dinning]

As RW says, not the best of transformers those from microwaves, but great for rough and ready stuff such as spot welders etc.
Note that a lot of these have an implied duty cycle, so may well overheat if used for long periods of time.

Ed

[dominicbeesley]

For mains transformers and non-hi-fi audio transformers I managed to collect a good number of old switch gear transformers by skip diving (with permission). A good source were any industrial sites that were being upgraded. There are usually a good number of very good quality transformers for converting various voltages. The ones I found were nearly all autotransformers for converting between 400/240/24/36 volts. A bit of time with a hammer and vice to dismantle and you get a pile of lams, a nice strong bobbin and quite often a big tag board.

The other source, when I used to have the time to attend, were Radiophile auctions. There was usually a sorry looking box of old transformers that nobody wanted in the auction as they were non-standard or out of low-value radios. In one box I got a bonus of half a dozen Danbury kits which I've used in various projects.

It all depends on what you need them for. I've now started stockpiling old linear wall warts as they seem to be coming rare now.

I'm not sure how kosher it is (i.e. does it damage the wire coating) but I've used anti-corona lacquer on a low frequency transformer to stop it buzzing. A couple of squirts every now and then when winding made for a less raspy finished item.

I'm interested in the vacuum impregnation idea. I have a pair of 20VA mains transformers on one of my amplifiers that buzz horribly and was wondering if I could make my own vacuum impregnation setup. How much of a vacuum would be needed to be effective? vacuum cleaner, backing pump?

[joebog1]

I use an ordinary single cylinder cheap chinese air compressor in reverse.
By reverse I mean I connect my "vacuum tank" ( holds the transformer in the varnish) to the inlet of the compressor.
I remove the air filter and I have made an adaptor ( its 1/2" BSP thread ) to couple an air hose onto the inlet port of the compressor. I open the drain valve on the air tank all the way so that it never gets any pressure in the tank. I suppose the vacuum is not that great, but it removes a lot of air that would normally be retained within the windings.

I generally run it for a couple of hours after heating the varnish and the transformer to ensure its thin enough to expel the air easily. You of course MUST make sure that your "vacuum tank" containing the varnish and transformer doesnt leak air. I use an old round transformer case that used to drive a large neon sign. Its about 12" diameter and 15" deep. The top cover is held on by 20 or so screws with a rubber gasket between the "pot" and the "lid". I removed one of the big insulators that were for connections to the windings, and fitted a standard Nitto air coupler nipple. As all my air tools are clip on I use my standard air hose to clip onto my bodged up adaptor, and then to the vacuum pot. I cant do pictures untill next year, but I hope Ive explained it well enough.

To return the compressor to normal, just remove the adaptor and refit the air filter.

The actual compressor is a "toy" that I origionally purchades to clean PC cases out. It was $100 and came with a brad nailer, so I guess the compressor by itself would set you back about 50 quid. Its small enough to carry into a clients shop/house/building so its not large.

Joe

[mark_in_manc]

I've been wondering about using an aluminium domestic pressure cooker as a vacuum vessel. Pretty sure ours could handle (-) 15 psi, and I could evacuate it through the spigot where the weights usually sit which regulate the internal pressure. No need to tighten the handle which normally keeps the lid on its seal

[TrevorG3VLF]

The seal on my pressure cooker is 'one way'. I have not tried to turn it inside out to seal a vacuum. Perhaps a simple O ring would do.

Beef stew will have an interesting taste.

[dominicbeesley]

Compressor, good idea. When I go up to my garage tomorrow I'll have to take a look at that, I have a 3hp job. I've never looked at the inlet so no idea how easy that would be to fettle something up...

[joebog1]

Tis easy !!!
remove the air filter and associated metal/plastic parts untill you have "just the inlet manifold" its usually a screw in fitting!. almost every air compressor ( little ones) that I have worked on have 1/2" BSP threaded inlet adaptors.
By "little" I mean single phase 3HP or less. Big compressors are mostly screw types these days and are a completely different kettle of fish.

I have been "dabbling" with the idea of using an automotive air conditioner compressor.!
For the last 10 years or so these are also screw compressors, albiet to start with on "expensive posh" cars, but today is normal.
INSTANT vacuum and huge pressure difference is easily abtainable.
Its another "gonna-do". so dont hold yer breath

Joe

[Radio Wrangler]

The ordinary piston compressors have lightly-sprung inlet valves opened by air pressure difference. They seriously limit the amount of vacuum you can achieve. Purpose designed vacuum pumps are usually rotary vane jobs and don't need valves for just this reason. I've been looking into pumps with a view to building a vacuum chamber to simulate very high altitudes. Inevitably, there's a lot of Chinese ones to be found in the usual places.

David