| Electronics > Beginners |
| nobody talking about switching PS wasting power on input filter caps? |
| (1/21) > >> |
| stefon:
They say like PS are 80-90% efficient, but they all have filter capacitors on input. So if I calculate correctly 5W cellphone charger (230V/50Hz) with 220nf X2 filter cap, just plugged to wall will waste 3.5W of power... Some power supplies have like mains filter with dual 0.47uf cap... so just this fitler is wasting 16W??? But also this cap is not getting hot at all... so I'm calculating something wrong? But I measured current and it matches calculations.... |
| BravoV:
--- Quote from: stefon on August 22, 2019, 12:09:08 pm ---.. so I'm calculating something wrong? --- End quote --- How do we know if its wrong or not ? Show us the calculation. |
| capt bullshot:
This is called reactive power. The current is 90° phase shifted to the voltage, energy flows forward and back with each cycle of the mains frequency. You can measure this current, and it will match your calculation, but you won't get billed for it ;) No one talks about it in public, but yes, it's there and it loads the utilities and creates losses along the distribution network. |
| ArthurDent:
I believe you're wrong blaming the capacitors. If you check RC charging circuits and formula you will see that the current drops to zero when the capacitor is fully charged. For capacitors in a SMPS to dissipate 3.5 watts they would have to be defective. The voltage across those filter capacitors is still connected to the inverter circuit that could draw some current but with no output load, that is close to zero in small SMPSs. I Just checked the supply for my laptop and my wattmeter registered 0 watts or voltamps. I think the efficiency you mention is generally for a fully loaded supply and there are lots of components in a SMPS that contribute to losses under full load. |
| themadhippy:
--- Quote ---You can measure this current, and it will match your calculation, but you won't get billed for it ;) --- End quote --- yet,once there's a 100% enforcement take up of smart meters the energy suppliers will have the ability to start charging for it ,as they already do with large power users. |
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