winding a torroid ??

Minion · 21st October 2011, 11:06 PM

Hi , I have a torroid that has a short in the secondary , I came to this conclusion because the torroid isn"t putting out any voltage and the secondary has a 0.2 ohm resistance while the primary has a 1.8 ohm resistance ......

What I wanted to do is unwind the secondary and rewind it with some new wire but I had a few questions that I was hopeing someone might be able to answer .....

Is there a formula to estimate how many turns equals how much voltage and what thickness wire will handle how much current ??

It is a pretty huge core , maybe 5 inches across so it will be fairly easy to feed wire through the hole .....

Thanx

indianajo · 21st October 2011, 11:58 PM

Vin*turnsin=~ Vout*turnsout
You should measure the wire that was on it with a micrometer and buy more.
Don't expect a bargain on magnet wire at the current time. Even the surplus houses are charging a lot for it.
I tried rewinding a 36V golf cart transformer secondary once. It was an E-core. I had a shorted turn to core before I was halfway done. I hope you have better luck. I had a metal core, which made an easy check. I don't know how you would check quality on a toroid core.

DSP_Geek · 22nd October 2011, 05:06 AM

Quote:

Originally Posted by indianajo

Vin*turnsin=~ Vout*turnsout

The above equation is incorrect.

Vout/Vin = turnsout/turnsin.

AndrewT · 10:34 AM

turnsin/turnsout gives the open circuit voltage for the secondary related to the mains supply voltage.
The secondary will drop by the transformer regulation when fully loaded by a resistor/s

That may mean, for a 5" toroid, that you need ~5% more secondary turns to achieve the correct secondary loaded voltage.

Check the primary insulation very carefully. Check what you can of primary winding without taking off any insulation.

That insulation is what isolates the mains from your project.
That insulation saves you from potentially fatal accidents.

barrymagrec · 22nd October 2011, 06:18 PM

Double check your diagnosis. If you had some shorted turns you would still get some voltage out. If the whole secondary was shorted on atransformer of that size you would expect to blow the primary fuse, assuming there is one, if not the whole transformer would get very hot quite quickly.

Barry

Minion · 22nd October 2011, 06:48 PM

Well , The Day before the Transformer worked fine (it is used for the power amp section of my 2 channel guitar amp) but the next day I turned on the amp and the power amp section didn"t work ...

So I opened up the amp and checked the fuse (1amp slo blo) and it was fine so then I tested that the Transformer was getting the 120v from the mains and it was .....
So then I tested the output voltage and I was getting about 0.3v on each side of the center tap ...... it doesn"t seem to be getting hot it visually looks fine .....

It isn"t the amp either because I replaced the transformer with another one I had and the amp works fine ......

Do you know of any other things that could cause this ??

Thanx

aandy · 22nd October 2011, 10:34 PM

best check the transformer is getting power

barrymagrec · 22nd October 2011, 10:58 PM

If the transformer is giving the same (wrong )voltage either side of the centre tap it suugests the problem is in the primary. Is there a thermal fuse embedded in the transformer?

21st October 2011, 11:06 PM	#1
Minion diyAudio Member Join Date: May 2006	winding a torroid ?? Hi , I have a torroid that has a short in the secondary , I came to this conclusion because the torroid isn"t putting out any voltage and the secondary has a 0.2 ohm resistance while the primary has a 1.8 ohm resistance ...... What I wanted to do is unwind the secondary and rewind it with some new wire but I had a few questions that I was hopeing someone might be able to answer ..... Is there a formula to estimate how many turns equals how much voltage and what thickness wire will handle how much current ?? It is a pretty huge core , maybe 5 inches across so it will be fairly easy to feed wire through the hole ..... Thanx

21st October 2011, 11:58 PM	#2
indianajo diyAudio Member Join Date: Jan 2010 Location: Jeffersonville, Indiana USA	Vinturnsin=~ Voutturnsout You should measure the wire that was on it with a micrometer and buy more. Don't expect a bargain on magnet wire at the current time. Even the surplus houses are charging a lot for it. I tried rewinding a 36V golf cart transformer secondary once. It was an E-core. I had a shorted turn to core before I was halfway done. I hope you have better luck. I had a metal core, which made an easy check. I don't know how you would check quality on a toroid core. __________________ Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,SP2-XT's, T-300 HF Projs, Steinway console, Herald RA88a mixer, Wurlitzer 4500

22nd October 2011, 10:31 AM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	turnsin/turnsout gives the open circuit voltage for the secondary related to the mains supply voltage. The secondary will drop by the transformer regulation when fully loaded by a resistor/s That may mean, for a 5" toroid, that you need ~5% more secondary turns to achieve the correct secondary loaded voltage. Check the primary insulation very carefully. Check what you can of primary winding without taking off any insulation. That insulation is what isolates the mains from your project. That insulation saves you from potentially fatal accidents. __________________ regards Andrew T. Last edited by AndrewT; 22nd October 2011 at 10:34 AM.

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22nd October 2011, 06:18 PM	#5
barrymagrec diyAudio Member Join Date: Apr 2010	Double check your diagnosis. If you had some shorted turns you would still get some voltage out. If the whole secondary was shorted on atransformer of that size you would expect to blow the primary fuse, assuming there is one, if not the whole transformer would get very hot quite quickly. Barry

22nd October 2011, 06:48 PM	#6
Minion diyAudio Member Join Date: May 2006	Well , The Day before the Transformer worked fine (it is used for the power amp section of my 2 channel guitar amp) but the next day I turned on the amp and the power amp section didn"t work ... So I opened up the amp and checked the fuse (1amp slo blo) and it was fine so then I tested that the Transformer was getting the 120v from the mains and it was ..... So then I tested the output voltage and I was getting about 0.3v on each side of the center tap ...... it doesn"t seem to be getting hot it visually looks fine ..... It isn"t the amp either because I replaced the transformer with another one I had and the amp works fine ...... Do you know of any other things that could cause this ?? Thanx

22nd October 2011, 10:34 PM	#7
aandy diyAudio Member Join Date: Mar 2007 Location: middle earth	best check the transformer is getting power

22nd October 2011, 10:58 PM	#8
barrymagrec diyAudio Member Join Date: Apr 2010	If the transformer is giving the same (wrong )voltage either side of the centre tap it suugests the problem is in the primary. Is there a thermal fuse embedded in the transformer?

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