Power transformer rating

rsumperl · 29th September 2010, 05:28 PM

Greetings all,
If I have a power transformer that states the secondary as 440vac @ 150va, is that telling me I can draw 340ma?

Thanks,
Ray

20to20 · 29th September 2010, 05:41 PM

Quote:

Originally Posted by rsumperl

Greetings all,
If I have a power transformer that states the secondary as 440vac @ 150va, is that telling me I can draw 340ma?

Thanks,
Ray

Yes, but I'd look real close at that 150"v"a to see if it isn't actually 150"m"a.

rsumperl · 29th September 2010, 05:53 PM

Checked twice, definitely 150va

paulb · 29th September 2010, 06:06 PM

But it doesn't mean you can draw 340mA DC after rectification.

TheGimp · 29th September 2010, 06:18 PM

It may also be the input VA rating of the transformer so figure 90% of that for safety sue to core losses, IR loss, etc.

Capacitive input filter will get you near 622V with SS rectification. So figure 217mA max.

Inductor input filter will give lower voltage at higher current.

rsumperl · 29th September 2010, 06:22 PM

So, if I do a choke input, do you think 300ma possible?

TheGimp · 29th September 2010, 07:09 PM

At what voltage?

Sim it in PSUD II and see what you get.

Merlinb · 29th September 2010, 07:25 PM

For ordinary rectifiers (capacitor input) the RMS ripple current will be about 1.5 times the DC load current. You shoudl be safe up to 230mA continuous DC.
If its a class AB amp then you can design for higher maximum currents if you think it won't be continuous.

Tom Bavis · 30th September 2010, 12:47 PM

What's the DC resistance of primary and secondary?

rsumperl · 1st October 2010, 10:42 AM

Tom, the resistance of the primary is 2 ohms and secondary is 30 ohms.

29th September 2010, 05:28 PM	#1
rsumperl diyAudio Member Join Date: Oct 2009 Location: Binghamton, NY	Power transformer rating Greetings all, If I have a power transformer that states the secondary as 440vac @ 150va, is that telling me I can draw 340ma? Thanks, Ray

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29th September 2010, 05:53 PM	#3
rsumperl diyAudio Member Join Date: Oct 2009 Location: Binghamton, NY	Checked twice, definitely 150va

29th September 2010, 06:06 PM	#4
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	But it doesn't mean you can draw 340mA DC after rectification.

29th September 2010, 06:18 PM	#5
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	It may also be the input VA rating of the transformer so figure 90% of that for safety sue to core losses, IR loss, etc. Capacitive input filter will get you near 622V with SS rectification. So figure 217mA max. Inductor input filter will give lower voltage at higher current.

29th September 2010, 06:22 PM	#6
rsumperl diyAudio Member Join Date: Oct 2009 Location: Binghamton, NY	So, if I do a choke input, do you think 300ma possible?

29th September 2010, 07:09 PM	#7
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	At what voltage? Sim it in PSUD II and see what you get.

29th September 2010, 07:25 PM	#8
Merlinb diyAudio Member Join Date: May 2006 Location: York	For ordinary rectifiers (capacitor input) the RMS ripple current will be about 1.5 times the DC load current. You shoudl be safe up to 230mA continuous DC. If its a class AB amp then you can design for higher maximum currents if you think it won't be continuous.

30th September 2010, 12:47 PM	#9
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	What's the DC resistance of primary and secondary?

1st October 2010, 10:42 AM	#10
rsumperl diyAudio Member Join Date: Oct 2009 Location: Binghamton, NY	Tom, the resistance of the primary is 2 ohms and secondary is 30 ohms.

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