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Weird PC PSU Capacity (feddit.it)

submitted 2 months ago* (last edited 2 months ago) by mattreb@feddit.it to c/askelectronics@discuss.tchncs.de

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Bought a new PC, and I was measuring its consumption out of curiosity. I noticed something weird (to me): when the PC is off (in fact, I completely disconnected the PSU and did the same test), there is quite some current running in the power cable to the PSU (0.15A).

Further measures showed a power factor of (almost) zero, and I can actually measure a capacity of 2uF across the PSU ac input.

I did the same thing on an older PC I have, and there is no current / capacity. So what would the reason of a capacitor across the mains on the input be in a PSU?

PS: the PSU is a Thermaltake Toughpower GF A3 1050W

Edit: I found some official measurements for this specific PSU: https://www.cybenetics.com/evaluations/psus/2249/ that have 40W standby apparent-power by design

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[–] Fermion@feddit.nl 3 points 2 months ago* (last edited 2 months ago) (1 children)

I don't know the answer, but I found this discussion which seems relevant.

https://electronics.stackexchange.com/questions/69666/atx-power-supply-front-end-how-does-this-work

The explanation given says it has to do with the functionality allowing the psu to be used with either 110VAC or 220VAC mains.

Does the psu you measured without input capacitance have a physical switch for selecting 110V or 220V?

[–] mattreb@feddit.it 3 points 2 months ago

Thanks, I'll have a look. It's an universal mains power supply with no voltage switch.