I am working on repairing an existing project (arduino controls a charging circuit for a led-acid battery) that has a dead transformer.
The transformer has 4 leads - 2 for primary and 2 for secondary. 110v in and somewhere between 14-18v out on the secondary. About 2" square. It's dead and I want to replace it with a similar sized transformer (it fights tightly in a waterproof housing)
Google was not my friend.
It is probably custom made, and you will need to know the current requirements of the secondary to replace it.
Measure the resistance of the primary and the secondary windings.
Draw a schematic of the transformer showing how many wires and where and what resistance between them.
Dead transformer. Waterproof housing (hot?). Sounds like a blown primary thermal fuse (primary is open circuit).
Sometimes you can pick off the paper to expose the fuse, bridge it, and measure the secondary voltage (under some load).
Don't keep on using the transformer with a bridged fuse. It's there for a reason.
Leo..
Thanks.
I measured the resistance -- blue primary wires (110v) was completely open. The red secondary (let's call it 16v) was 3.5ohms.
I pulled back the tape and found no fuse, but did find a broken wire to what appears to be a center tap on the primary windings.
Scraping back the enamel and reconnecting the wire didn't give me a reading between the two blue/primary wires...
I find it really hard to believe that it would be custom made, nothing else is custom, well; except for the "assembly" of parts.
I'll just get a reasonable transformer & make a new housing... I hoped that the logo would be a clue as to the source.
thank you for your thoughts.
Hi,
It won't be custom made, can you post a picture with a cm ruler in the picture and tell us its dimensions please.
Tom... 
Based on the wire guage, that looks to be a 16V/5A transformer
Can you weigh it ? Transformers tend to follow a predicable relationship between current rating and mass of the metal core the windings are wound on. You wouldn't wind a 3A transformer on a 1A core, so if you know the weight, it is easier to find something comparable.
I'll try -- the scale I have weighs only up to 100g ... I thought we had a kitchen scale but I am not finding it.
"stay tuned"... (Thanks for stickin' with this)
I know you are going to think me crazy to suggest this but if you can get a couple of pulleys and some nylon cord at the hardware store , you can screw a bolt or hook into the wall in the garage and make a cord harness for the transformer and use known weights at the other end (in a cloth grocery bag. Don't laugh, but , fyi, a 1 lb bag of flour weighs 1 lb.... Last time I checked , they had scales at the market to weigh the potatoes. If you weigh each one and label them at the market, then you just add or subtract them the cloth bag suspended by the pulley cord.
It's not exactly rocket science but it should work... (for better resolution, pick smaller vegetables, ha ha)
I am going grocery shopping in a bit; I was just going to weigh it there. it won't be science accurate, but it's better than I have now...
I thought of that but that would be awkward.Maybe you could put it in a brown bag.
I see there is different opinions on that transformer being "custom".
It is. If it was a standard issue transformer, it would be marked other than just a model number.
When building big-scale industrial electronics you use a standard transformer for that event when it needs to be replaced.
In consumer electronics you get the transformer custom made - it's cheaper and you get it exactly like you want.
// Per (Been in the transformer industry)
Hi,
Looks like a 7VA transformer.
Check out 7VA at mouser or some on line supplier that has parametric search, see what 7VA, 220Vac 16Vac transformer comes up with.
Tom.....
Zapro:
........In consumer electronics you get the transformer custom made - it's cheaper and you get it exactly like you want.
// Per (Been in the transformer industry)
You forgot to mention that they can then ask for 3 X the price of a standard transformer for a replacement part.
Weedpharma
A transformer is the only part I have ever had custom made for me. Despite what was said above it turned out to be actually cheaper than a standard one because I was only paying for what I wanted.
You can also get them custom at one off. I once got made a 1kV output at 1A, that was a big bugger, try finding a standard transformer for that spec.
There's a good chance more parts are defective than the transformer. It's probably cheaper and easier to replace the entire 15V power supply.
You can get a 15V, 4A supply for $12 on ebay. It has short circuit and overload protection.
it was 12 ounces as weighed on produce scale.
Everything else is fine. If I supply anywhere from 14-19v it works perfectly...
All that's bad is the transformer.
When I tested the amps; it hovered around .8, and dropped to .4; Max was 1.3amps when I supplied 16v to the circuit...
7va seems small.
I found several transformers, none that would fit existing housing, which is what I was after, hoping the logo would spark someone to recognize it...
Where can I get a custom made transformer for less than $30? I find it hard to believe a custom 1 off project would use custom anything (except maybe a pcb); but I suppose if you were motivated enough to build it; you would customize a lot. I'd be all into buying a custom transformer if it was affordable. but at around $50 it's firmly in the camp of off-the-shelf transformer & new housing...
thanks!
daveyjones:
I find it hard to believe a custom 1 off project would use custom anything (except maybe a pcb); but I suppose if you were motivated enough to build it; you would customize a lot. I'd be all into buying a custom transformer if it was affordable. but at around $50 it's firmly in the camp of off-the-shelf transformer & new housing...
What makes you think the item you have is a 1 off product?
// Per.
because it has an arduino inside & the person who asked me to look at said her husband made it...
FWIW I was at the thrift store today & picked up a wallwart for $2 -- inside is a beefier transformer (slightly bigger and heavier) -- and -- it had a similar "Amc" in a diamond for a logo on the part #.
So I am even more confident that the transformer was made by a company for mass market...
Odd I can't find any hits for "Amc" and "transformer"
