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Old 12th July 2006, 09:56 PM   #1
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Default how to id transformer VA

I have a number of center tap 120v transformers and while secondary voltage is easy to determine how does one determine the current limit? Second does each channel of say a chip amp require a dedicated PS? and in my case with active x-over can i supply the three amps for that single channel with a dedicated power supply, I would hate to have to build 17 seperate powersupplys for this project! Third all chips being used require +-15 v, need i replicate these for each chip or channel. thank for any help
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Old 12th July 2006, 10:44 PM   #2
phn is offline phn  Sweden
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No need for dedicated PSU. Most would prefer it, but cost gets in the way.

Do you know the watt rating of the trafo? W/V=VA.

Edit: It's good practice using a (or two, +/-) voltage regulator for each chip and mounting them close to the chip. The filter caps before the regulator(s) can still be shared.
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Old 13th July 2006, 03:06 AM   #3
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regretfully the transformer came out of an old amp. large toroid rectified to + -45 volts but no markings to suggest wattage?. on the ps for the chip amps i had a brain fart am using the +-15 v to power the crossover section sorry.
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Old 13th July 2006, 08:09 AM   #4
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The weight is a good first indication of the VA capability.

You can load the transformer, determine iron and copper losses by measuring outgoing and ingoing power. The efficiency will generally be the highest at the nominal power rating.
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Old 13th July 2006, 11:45 AM   #5
AndrewT is offline AndrewT  Scotland
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+-45Vdc sounds a bit high for chipamps?
regards Andrew T.
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Old 13th July 2006, 12:02 PM   #6
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If you go to the Plitron site, click Standard Toroids, then select Mechanical specifications you can get the dimensions vs. VA rating. You would still have to measure the voltage, but VA will help you determine the current capability.

Here's the direct link:
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