Transformer question

tubesmuggler · 17th November 2009, 02:47 PM

I have a quick noob question about a PT I have. It's secondaries are labeled like this:

250V/100mA - 0V - 250V/100mA

I'm not certain what this means the current rating is. I'm guessing another way to show this is 500VCT/200mA, correct?

Or is it 500VCT / 100mA ?

TIA!

Tom Bavis · 17th November 2009, 04:07 PM

500VCT @ 100 mA. DC output capacity will be about 100 mA as well. DC current could be more with choke input, but voltage would be too low for most applications.

tubesmuggler · 17th November 2009, 04:07 PM

Thank you sir!

hemgjord · 17th November 2009, 11:32 PM

On the same subject, I never got this really clear.
If I for example have a 500VCT @100mA TX what can I expect it to handle if used for bridge rectification instead of the (I suppose) expected full wave rectification.
Can I actually pull 100mA @ 500V?

/Olof

Tom Bavis · 18th November 2009, 03:47 AM

No, you can't get 100 mA since you have to supply capacitor ripple current as well as dc current - 60-70 mA would be more like it. With choke input you could get 90 mA or so. Duncan Amps PSU designer can give a good idea of the RMS transformer current for a given DC current.

hemgjord · 18th November 2009, 08:37 PM

Quote:

Originally Posted by Tom Bavis

No, you can't get 100 mA since you have to supply capacitor ripple current as well as dc current - 60-70 mA would be more like it. With choke input you could get 90 mA or so. Duncan Amps PSU designer can give a good idea of the RMS transformer current for a given DC current.

Hi there
Yes I am aware of this, it was late and I did not express myself very clear. I refered to actual AC current to be drawn from the secondary.
What I really wonder is; if a TX is spec'd at 500VCT@100mA, is this for use in a full wave circuit where you actually can draw approx 60-70 mA at 350VDC?
Or can it be used in a bridge circuit to supply 60-70mA @ 700VDC?

It is quite a difference.

/Olof

Tom Bavis · 18th November 2009, 10:24 PM

About 100 mA in a full-wave center-tap circuit, maybe 130 mA with choke input. About 60-70 mA at 700V in full-wave bridge. About 90 mA at 500V with FWB and choke input filter. Any of these result in about 100 mA RMS AC current in the transformer secondary.

17th November 2009, 02:47 PM	#1
tubesmuggler diyAudio Member Join Date: Apr 2005 Location: Ontario	Transformer question I have a quick noob question about a PT I have. It's secondaries are labeled like this: 250V/100mA - 0V - 250V/100mA I'm not certain what this means the current rating is. I'm guessing another way to show this is 500VCT/200mA, correct? Or is it 500VCT / 100mA ? TIA!

17th November 2009, 11:32 PM	#4
hemgjord diyAudio Member Join Date: Apr 2007	On the same subject, I never got this really clear. If I for example have a 500VCT @100mA TX what can I expect it to handle if used for bridge rectification instead of the (I suppose) expected full wave rectification. Can I actually pull 100mA @ 500V? /Olof __________________ I'm not allowed to do magic, union rules...

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17th November 2009, 04:07 PM	#2
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	500VCT @ 100 mA. DC output capacity will be about 100 mA as well. DC current could be more with choke input, but voltage would be too low for most applications.

18th November 2009, 03:47 AM	#5
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	No, you can't get 100 mA since you have to supply capacitor ripple current as well as dc current - 60-70 mA would be more like it. With choke input you could get 90 mA or so. Duncan Amps PSU designer can give a good idea of the RMS transformer current for a given DC current.

18th November 2009, 10:24 PM	#7
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	About 100 mA in a full-wave center-tap circuit, maybe 130 mA with choke input. About 60-70 mA at 700V in full-wave bridge. About 90 mA at 500V with FWB and choke input filter. Any of these result in about 100 mA RMS AC current in the transformer secondary.

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