anybody wind their own power transformers?

[ALBATROS1234]

i got a few nice sized transformers with useless voltages for tube amps. the EI parts are good sized for what we do but i want to rewind some for amp projects. for instance i have a nice sized working 120vac step down to 12vac, its 180va with a nice thick core, i figure why cant i just take the secondary off and rewind a high voltage 6.3 and 5 volts in place.shouldnt it be that simple or do i have to rewind the primary too if i am changing it to step up?i have the EI pieces removed and if i take off the 12 volt secondary i thnk i can count the windings of the existing primary. if thats the case i just need to know what gauge enamel coated wire to use and get some parafin impregnated transformer paper and figure out my ratio and go to town. i tryed to find an app to calculate what i needed to do but it seems the want way to much info like what type steel are you using,which i get it if you are engineering some tranny for something you want to calculate everything to get max efficiency. i just want a simple calculatore to tell me what guage wire and how many winding on said core to get the voltages i want. i read that years ago hobbyists like us mainly wound their own trannys because off the shelf usually wasnt available. and i have a bunch of perfect sized cores which should theorhetically only need secondaries rewound. anyone know an app or a website which has the basic stuff all in one spot, i really rather not read 15 huge books full of info i dont need if i can get the core info from somewhere. i am an electrician and am confortablle with my skills and attention to detail that i feel good about trying this. thanks guys youre the best.

[PRR]

> i am an electrician and am confortablle with my skills and attention to detail

You are an electrical mechanic. This is a VERY good skill. I see too many others who can't wire-up a paper-bag without shorts.

But you need to think about Electricity.

How does it transform 120V to 12V? There are 10 primary turns for every 1 secondary turn.

But how many turns? Certainly more than 1 or 10.

Those "core type" calculators figure it out for a New Design.

Here you have an Existing Working Design. You assume the maker did it right. (You probably snagged it out of machinery that worked for years and still worked fine.)

You could un-wind it and count turns.

But since you know the specs, and have an electronic AC meter, you can usually determine the turns in a minute. Wrap one turn of fine wire around the existing winding. Energize the 120V winding with 120V. Measure the voltage on the 1 turn. (If your meter bottoms-out, use 10 turns.)

Small doorbell transformers run about 0.05V per turn. Huge cores may run over 1V/turn. I'll guess a 180VA is in the range of 0.2V/turn. So you read 0.2VAC on 1 turn (2V on 10 turns).

So already you can figure the 120V winding must be 600 turns (120/0.2= 600).

And the 12V winding must be 60 turns.

No, wait: there's resistance. The transformer will sag at full load. The rating is for full load. So we typically wind about 10% extra turns. The 13.2V no-load sags to 12.0V at full load. More or less.

Now you want a say 48V winding. At 0.2V per turn this is 240 turns. Round-up for sag, 260+ turns.

The winding-space is fully-packed (5%-20% spare space because slack is much better than too tight to go together). How can you put 264 turns in the space of 66 turns? Obviously each wire must be 1/4 the area. 1/4 area is 1/2 the diameter. You want a wire-table here. You will have to buy new wire.

Put together, instead of 12V 15A you now have 48V 3.75A.

In theory you can re-use the 120V winding. Indeed if it is wound secondary over primary (or separate bobbins) this is what you do. Worst case you have to strip the primary, and you usually can't salvage 500 feet of thin pre-stressed fine wire whipped all over your lab.

The killer fact is that buying magnet wire a 1.4 pound of this and a 1.3 pound of that ends up costing more than a whole pre-wound transformer. More than half the cost is the copper. The tranny factory gets a much better deal per ton than you get for small buys. Including shipping, the balance is unclear.

Do it for fun. Don't expect great savings, especially if your time could otherwise be billed like I was billed for my fusebox. (No complaint, I understood why they charged what they charged, but it makes transformer hacks small potatoes.)

[ALBATROS1234]

Kinda what I was wondering if the cost savings would be that great. There's at least 3 or 4 really perfect sized to make for a tube project. I would think the primary could be saved and the secondary wire is probably 12 gauge for this low volt high amp winding I would guess I would need more like 18 to 22 gauge for the h.v. winding and not many turns of thick wire to get the 6.3 and or 5volt. Was planning on trying to wrap the thick stuff on something and save it for those small voltage windings. I also have a transformer that came on a chassis where the secondary was the inner winding and the primary is fried. I thought that was odd having the primary on top of the secondary. If can found windings the ratios should be simple it's mainly knowing which gauges are used to get what amp ratings on tube gear. Also in a sense it may be easier to Nancy to buy a roll of magnet wire here and there when I get a few bucks rather than drop $70 all at once.  then I can also tailor the transformer to my exact needs rather than try to find an off the shelf that's what I need

[Apexelectric]

I was thinking about the same thing once but came to the realization that in order to do it right, it would require more time, tools and materials than was worth the trouble. Probably wouldn’t sound nearly as good as what was done by someone who does it for a living.

One thing I’ve done recently to get some good transformers at reasonable prices is to buy up some good organ amplifiers and part them out. I’ve been able to buy a working amp with tubes for about 100.00. That’s a 15W-50W PT and OT and tubes for around 100.00 give or take. I’ve got a good enough stock on them now to keep me in low budget projects for a while.

[ALBATROS1234]

i was thinkin cheaply as i thought if i spend $100 i can get the stuff to rewind like 4 large power transformer which are close to $100 for one.

[Joel]

I've done some small transformers (power and output) for my Champ clones - which are now in my Tweed Princeton clone.

There are a couple good books which helped me;

* Electronic Transformers and Circuits, Reuben Lee, 1955
* Radiotron Designers Handbook 4 (otherwise known as RDH4)

Both are available online if you search for them - legitimately I believe.

There are calculators online too, but you can figure out the specs yourself using the books.

I bought a hand winding machine with a mechanical counter on Aliexpress (search for coil winder on the site).  It would probably struggle with a 180VA sized bobbin though. Can't remember what the wire cost me.

Here's a thread of someone who did it much better than me; http://el34world.com/Forum/index.php?topic=22741.0

[ALBATROS1234]

Thank you I will check out the links when I get home tonight. I have a few books about transformers ones quite old called transformer engineering . I am sure it will have ww1what I need bit a quick flip thru indicates there will need to be much time spent digging th p we few pearls out. I was hoping  to find the basic info in one spot rather than have to read 800 pages 780 of which are boring and not relevant