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Old 29th September 2010, 06:28 PM   #1
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Default 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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Old 29th September 2010, 06:41 PM   #2
20to20 is offline 20to20  United States
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Quote:
Originally Posted by rsumperl View Post
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.
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Old 29th September 2010, 06:53 PM   #3
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Checked twice, definitely 150va
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Old 29th September 2010, 07:06 PM   #4
paulb is offline paulb  Canada
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But it doesn't mean you can draw 340mA DC after rectification.
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Old 29th September 2010, 07:18 PM   #5
TheGimp is offline TheGimp  United States
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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.
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Old 29th September 2010, 07:22 PM   #6
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So, if I do a choke input, do you think 300ma possible?
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Old 29th September 2010, 08:09 PM   #7
TheGimp is offline TheGimp  United States
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At what voltage?

Sim it in PSUD II and see what you get.
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Old 29th September 2010, 08:25 PM   #8
Merlinb is offline Merlinb  United Kingdom
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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.
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Old 30th September 2010, 01:47 PM   #9
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What's the DC resistance of primary and secondary?
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Old 1st October 2010, 11:42 AM   #10
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Tom, the resistance of the primary is 2 ohms and secondary is 30 ohms.
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