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Old 2nd October 2013, 02:00 AM   #1
sohan is offline sohan  United States
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Default UPS transformers for Audio amp?

I have two transformers (430-7105) removed from APC ups units. Each of them has 14v output at about 40amps. No center tapping. So i could use two transformers connected together for 14-0-14. My amp is 6 ch of (10watts) chip amps.

I have seen many times ppl use nice toroidal transformers with amp projects. What are the downside of using those huge UPS transformers (in therms of performance, quality and etc..)

Any comment will be appreciated.
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Old 3rd October 2013, 04:54 AM   #2
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not much apart from them being heavy. They use good quality insulation and nice thick copper, so they have very good regulation and low copper losses. They are rated for continuous full load, so both primary and secondary sides are wound with nice thick wire.


The only disadvantage is that if you dont mount them solidly they can buzz.

They can also supply a LOT of current very quickly so a soft start is a good idea because they can easily blow bridge recitifiers. 40 amps continous and they can easily provide 10 times that peak.
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Old 3rd October 2013, 05:07 AM   #3
AJT is offline AJT  Philippines
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just make sure that they are not autotransformer types, that the secondaries are completely isolated from each other...

i have seen Triplette brand ups traffos that are autotransformer types....
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Old 3rd October 2013, 05:09 AM   #4
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Damn thats a dangerous design! Every UPS transformer i have seen is fully isolated, by law i think in australia as the smaller plastic cased UPSes are double insulated, and have user replacable batteries.

The bigger UPS's these days all use high frequency inverters which have no real useful components apart from some nice relays/caps and perhaps mosfets and inductors.
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Old 3rd October 2013, 04:21 PM   #5
sohan is offline sohan  United States
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Thanks all. Its isolated. I checked it. Unfortunately it takes about 18 watts with no load. Pretty high waste of energy.
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Old 4th October 2013, 12:03 AM   #6
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How are you measuring that wattage?
its inductive, so its mostly apparent VA, not real VA.
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Old 4th October 2013, 03:45 AM   #7
AJT is offline AJT  Philippines
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Quote:
Originally Posted by sohan View Post
Thanks all. Its isolated. I checked it. Unfortunately it takes about 18 watts with no load. Pretty high waste of energy.
that means that you have a high capacity traffo, what is its wight in kgs? or lbs?

siince most ups are mostly intended for intermittent duty cycle, that is not so surprising....

building my own traffos, i can say that design considerations for a regular line operated traffos can be different with that for a UPS...
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Old 4th October 2013, 03:59 AM   #8
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AJT they are intended for 24/7 operation maintaining the charge into the batteries.

The models i have pulled apart run that transformer at full load when in "backup" mode until the batteries run out and are rated to 135 degrees. They are pretty hard core components.
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Old 4th October 2013, 04:14 AM   #9
AJT is offline AJT  Philippines
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how do you know? i did not see the OP post an actual model number so we can check...

you mean on-line? i have worked on such installations working for Oil and Gas refinery Projects,
a battery bank in its own room with about 120pcs of 2volt storage cells wired in series,
a transfer switch on another room with the sine wave inverter and distribution boards...
capacity at about 50kva with autonomy time of 12 hours.....
yes i have seen those..
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Old 4th October 2013, 04:17 AM   #10
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At the 14volt output the OP indicated i made a guess at smaller models. like 700va ones.
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