I need a transformer with 24V primary and secondaries of 200-0-200 and 15-0-15. I can't seem to find any oddball thing like that, so I was thinking of making one myself. I've seen what appeared to be hand wound transformers on old prototype boards I pulled out of e-waste. They consisted of either a PCB mount "barrel" or PCB mount square core, with magnet wire wound onto it. I can't seem to find these empty cores for sale either. What keyword do I need to use in order to find these things?

 

Transformer stampings and transformer laminations.

 

E-Cores ?

What power levels are you looking at? What frequency? It may be cheaper (and way faster) to have one custom wound.

 

Hello,

You could look for E I lamination cores:
http://en.wikipedia.org/wiki/Magnetic_core

More info on how to use the E I lamination can be found here:
http://sayedsaad.com/fundmental/index_transformer.htm

Bertus

 

Look in the 'phone book, most decent sized cities have tranformer rewid shops, they can just make the windings to your spec. Doing multiple windings is a pain, and 200-0-200 will also be a pain to do yourself due to the very large turns.

 

I would be interested in how to do it with a toroid sometime, just to see if it is safe. I remember seeing a technique using a split ring that was a spool. You feed the ring through the donut hole of the toroid while it is open, close the split ring, and then wind the wire on the now closed spool. This in turn is used to wrap the wire around the toroid. When the spool is empty you open the spool ring and pull out your new completed toroid. It was mechanized, using specialty built fixtures, and so was very fast. It was on a You Tube video I saw many years ago, I have no clue where it is.

 

I can't disagree. I used to be the design engineer at a power supply corporation and the things I saw in the transformer shop told me that, much like most other skills, the people that do it every day can put the rest of us to shame...before morning coffee break.

If you can find a place that will make a one-off and treat you fairly on the price(unlike my previous boss), it's worth the price to not have to learn everything from core sizing to vacuum impregnating...or end up using 3 or 4 single output transformers in a single product.

You need to know how the mfg specs their product, too. If you say, "200-0-200 at 3.4 amps and 15-0-15 at 350 ma, that's what it will load down to in RMS at such and such a line voltage. You need to get your rectification factors in before you make up your specs.

 

Probably not the same video, but I got a lot of hits on You Tube's search...

https://www.youtube.com/watch?v=6lvm3FGTHSI

 

That video reminded me of a story from my transformer guy. He said engineers think transformers are made of iron and copper, but they have more pieces of tape and paper than pieces of iron and copper put together. (He was not winding toroids like that video.)

PS, the bigger the watts, the less turns of wire!

 

I would be interested in how to do it with a toroid sometime, just to see if it is safe. I remember seeing a technique using a split ring that was a spool. You feed the ring through the donut hole of the toroid while it is open, close the split ring, and then wind the wire on the now closed spool. This in turn is used to wrap the wire around the toroid. When the spool is empty you open the spool ring and pull out your new completed toroid. It was mechanized, using specialty built fixtures, and so was very fast. It was on a You Tube video I saw many years ago, I have no clue where it is.

It's an interesting process - I haven't seen it before,
Here are some YouTubes
http://www.youtube.com/watch?v=6lvm3FGTHSI
http://www.youtube.com/watch?v=53VKxQSvJ7Q (home brew)
http://www.youtube.com/watch?v=DgJUBLYQfpA
http://www.youtube.com/watch?v=5S_G0lnQnaA

 

I use 240/24 volt transformer with the primary and secondary reversed for my valve amps and pre amps.

 

I found a Hammond for my 3 tube guitar amp.
The experimental amp I built was the one that wound up with 4 transformers

 

So what I'm gathering is that there's a lot more to making a transformer than wrapping some wire around a piece of iron. Well darn, I was hoping it would be easy.

I don't know exactly what specs I need. What I really need is 24VDC in, +/-200VDC and +/-15VDC out. A DC/DC converter fits the bill better than a transformer but the 200V ones cost a lot. the +/- 15V will power a couple of opamps and the 200V is a signal to another circuit that I don't know the particulars of, but I imagine it's a high impedance input. I don't think I need much current at all. As far as the frequency, not sure. I was looking at some generic switching circuits.

If I'm going to pay for a custom transformer then I might as well just shell out for the DC/DC converters. I was hoping to take this route to save a couple hundred bucks.

 

I have done this. It is not impossible, though tedious as all <snip>

Stripping the coils off a E-I frame, that was close to specs for the result I wanted. Actually had to chop up a few, before I found a suitable nylon bobbin for the windings.
Frames that have the E's & I's interlaced, are a <snip> to dismantle without distorting the 'leaves'.
You must also tediously scrape or soak all the original varnish off the leaves.
Look at some transformers, the E frames are simply side by side, with the I's forming a laminated closing bar...
Interesting Hysterisis and eddy currents live in these, and you must put a layer of electrical hardboard between the e's and the closing bar.

It is a good idea to wrap plumbers teflon tape between layers of your coils, and wind them almost as tight as you think you can get away with. Uniform layers... I have never been able to get 'jumble' winding to work.

Normal Thermal Expansion of the windings, can pop several adjacent coils insulation, or in extreme cases causing a simple 'open coil' or a flaming short if you wind too tight. Better let varnish soak into the tiny voids between layers and coils, and immobilize them.

 

It would be interesting to make a toroid winder. Only really weird nerds need apply.

 

Sewing notion supply people make a nice little tool called a " Tatting Shuttle " which works nicely on larger toroids, and will carry quite a nice amount of - say - .010 magnet wire...
Much larger than that gets to be a <snip> to deal with.

 

It would be interesting to make a toroid winder. Only really weird nerds need apply.

Are all the weird nerds thinking the same thing? When I saw your video, my mind instantly went to my scrap junk in the garage, putting things together in my mind to make one of these things. I thought was just me.

 

If you don't have enough time to reinvent the (toroid winding) wheel, you can use a stick with a notch in each end.

 

You didn't say what power rating and frequency. At least I didn't see it.
I assume 60Hz?

I would try to find something with the ratio 24V / 2x200V (or the other way around) or something that comes near to it and add windings for the 15V.

 

So what I'm gathering is that there's a lot more to making a transformer than wrapping some wire around a piece of iron. Well darn, I was hoping it would be easy.

I don't know exactly what specs I need. What I really need is 24VDC in, +/-200VDC and +/-15VDC out. A DC/DC converter fits the bill better than a transformer but the 200V ones cost a lot. the +/- 15V will power a couple of opamps and the 200V is a signal to another circuit that I don't know the particulars of, but I imagine it's a high impedance input. I don't think I need much current at all. As far as the frequency, not sure. I was looking at some generic switching circuits.

If I'm going to pay for a custom transformer then I might as well just shell out for the DC/DC converters. I was hoping to take this route to save a couple hundred bucks.

You could use a battery charger as a core. Peel the windings off counting the secondary turns. That will give you the turns per volt. Measure the wire size, and do your calculations from that. I have an article here with a good description on how to build a converter. It's got lots of good info on the transformer. I've done this for a larger electronic battery charger. Also a street light ballast is a good source for a core.