Help Please. I think I blew my toroidals

[snknby123]

i have searched for over 2hrs. How do I test my 250V 2x25v toroidal transformers for shorts etc?

I had them hooked up with the secondaries open for measurement but had a short in my mains and blew the fuse.

Can I measure the primary's etc and check them? Not sure what they sould be reading ohm wise.

[anatech]

Hi snknby123,
You did the test. Plug in your toroid with all secondaries disconnected. Only the magnetizing current should flow after the initial surge. Your steady state draw should be very low.

To power these up, you could use a variac, light bulbs in series or straight into the outlet. You can not use a dimmer of any kind or you will draw excessive current. Same for running normal transformers off a standard small computer UPS.

-Chris

[Peter Daniel]

Originally posted by snknby123
i have searched for over 2hrs. How do I test my 250V 2x25v toroidal transformers for shorts etc?

I had them hooked up with the secondaries open for measurement but had a short in my mains and blew the fuse.

Can I measure the primary's etc and check them? Not sure what they sould be reading ohm wise.

What do you mean exactly by "having short in your mains"?

Could it be that the fuse was too small or not the right type and it blew because of inrush current at turn on?

See this thread: http://www.diyaudio.com/forums/showt...52#post1710752

[lgreen]

dont panic!

Measure the resistance between blue and gray, should be the same as between violet and brown-- low, say 1 or 2 ohms..probably < 1 ohm. And blue/gray should not connect to violet or brown should be open circuit.

And the resistance between black and red should be the same as between orange and yellow. and black/red should be open circ from orange/yellow.

(using the diagram- http://www.partsexpress.com/pdf/avelspecs.pdf)

Now, these resistance measurements tell you very little. What you have to do to really test the transformer is hook it to a known AC voltage and you know that it converts 115 to 25, so it should convert 11.5 to 2.5 or whatever to the same ratio. Use a variac for this or use a signal generator running about 60 Hz.

then try at wall voltage. carefully.

p.s. having fun yet? hope I didn't cause this?

[MondyT]

Hi snknby123

lgreen has described pretty much all you can check for if all you have is multimeter

If it is in fact one of Avel's 250VA 25+25v toroids (Y236652) then you should measure around 2.8R for each primary and around 0.153R for each secondary (the secondaries are unlikely to be causing the problem however as the wire gauges used here are quite robust) Expect a small difference between the resistances of each pri and sec.

The problem is you could have a few shorted turns in the primary without effecting this resistance much as you are only looking at around 6 to 7mOhms per turn which will not show up too well on a multimeter!

If you can get the primary powered up (watch for the inrush) with the primaries wired in parallel and with 115v 60Hz input, the no-load current (secondaries open circuit) should be in the region of 25mA (12mA with series primaries and 230v 50Hz) and the off load voltages on each secondary should read in the order of 26.7v each (or 0.232 * whatever you have going into each primary)

I hope this helps

Cheers
Ray

[snknby123]

Thanks for all the help.

I think my xformers must be toast. I have a slow blow fuse rated at 250V at 5A with secondaries disconnected.

I'm getting measurements of 1.2 ohms to 3.2 ohms between all of the Primary wires doesn't matter which ones

Disconnect the xformers and the fuse holds. Connect either one of the xformers and "poof" goes the fuse.

This project was really fun. It is really close to being finished. I powered up the xformers to test the secondaries and now I'm $75 in the hole and 3 days waiting for new parts.

Oh Well chaulk it up to being a noobie and being too anxious I guess.

I'll order up another set.

thx -BB

[audio1st]

Hi BB,
I don't understand what you did in the first instance to damage them, you said the secondaries where disconnected? Are we talking two of them??

[pacificblue]

Originally posted by snknby123
I had them hooked up with the secondaries open for measurement but had a short in my mains and blew the fuse.

A short in the mains will not affect the transformer in any way. High current will flow through the short, not through the transformer.

If you bridge those 5 A fuses and connect the transformer directly to mains, does your mains fuse blow or mains circuit-breaker trip? If not, replace the fuses with adequate ones. 250 VA at 110 V are more than 2 A already and the inrush current of a toroid can be many times higher than the nominal current.

Isolate the secondary wires to make sure that they do not accidentally touch each other or PE, when they are not connected.

[snknby123]

I miswired my mains switch where the AC(hot) from the fuse shorted to the neutral when the switch was flipped. I'm a dumbass as I looked over the switch 2 times verifying the correct wiring.

When I flipped the switch with the xformers connected the lights dim, xformers buzz then the fuse blows.

As stated b4 I'm now reading a short (1.5ohms) across my primaries (Blue/Violet ---1.5ohms--- Brown/Grey). Actually any pair of primary wires measure 1.5 to 3.2ohms no matter what combination.

Unfortunately I didn't measure the resistances of the xformers b4 I hooked them up so I had some type of baseline to go by.

This really blows... No way to repair these I guess? I now have 2 very expensive/heavy paper weights

[Peter Daniel]

1.5 ohms is not short, it's normal reading for primaries impedance.

The only problem I could imagine is when you connect single primary to 115V mains and not two in parallel. Then the fuse would blow, but that still shouldn't damage anything.