EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: wardenclyffe on September 05, 2013, 05:22:35 pm
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Hey guys,
I was doing some simple efficiency testing on this off the shelf AC-AC power supply the other day and I noticed that the power consumption with no-load connected (standby) was up over 5 watts! I know the current federal standard says it has to be lower than 0.5 watts and I think ENERGY STAR is around 0.3 watts. I was wondering if someone could tell me why the consumption is so high and what could be done to lower it. I cracked it open and its nothing but a transformer and some input filtering. Any ideas?
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I would recommend the GOPS.
Good old power switch.
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I would recommend the GOPS.
Good old power switch.
Haha, fair enough. Anyone got something more elegant?
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AC-AC adaptors are exempt from the regulations because small mains frequency transformers are inefficient so it's impossible to achieve such a low standby power.
If the device being powered just rectifies it to DC then replace the adaptor with a modern switched mode power supply based adaptor. If it needs AC then you're stuck with an inefficient mains transformer and need to turn the power off when possible.
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5W sounds high even for a bad transformer. Were you measuring true power, or just VA?
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If the unit was a switched type, look at how you were measuring the power. It might be that it was producing a lot of noise that was upsetting the power measurement and causing it to read high.
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5W sounds high even for a bad transformer. Were you measuring true power, or just VA?
True power measurement