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Offline SMPS for 120W maximum in EU, UK, USA ..but with no PFC stage

coffeefet

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We are making an offline 240VAC SMPS which after being installed, will firstly charge up a 24V battery at 5A for 3 hours. Then it will simply sit there for the next 10 years drawing about 2W of standby power, as the equipment continuously monitors some safety valves which should be actuated in case of emergency. The 24V battery also needs to be kept topped up with a “float” charge, but this is only part of the 2W standby power.

As such, is there some clause in the EN61000-3-2 standard which we can invoke in order for us to avoid using a PFC stage?

I mean, our average power draw is so low that surely a PFC stage would not be mandated for this?

I found the below, which is relevant , but not conclusive on this subject….

 

Easy peasy

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Since you are above 75W name plate rating - you have to comply, the good news is a mains choke will get you there.
 

c_mitra

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How about charging the battery outside and then hook-up? Why use a 24V5A SMPS that will be used only once in 10 years (to deliver the full capacity)?
Design your SMPS for the typical load but allow for ruggedness.
 

treez

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Since you are above 75W name plate rating - you have to comply, the good news is a mains choke will get you there.
i believe coffeefet will find there are exceptions though. Eg no guitar amplifiers of power up to 400W have PFC stages....because their average power is peak/8........i have written to all guitar amp manufacturers and they confirm this......also, you can see by looking at open frame smps of 500w for guitar amps that there is no PFC (I am speaking of the new class D guitar amps)
Also, i dont believe coffeefet will be helped by a mains choke alone...but i dont think that is what you meant?......if coffeefet needs PFC, then a full Boost PFC will be needed.......is that what you meant by a "mains choke"?......ie you mean a boost PFC stage with a "mains choke"?

CoffeeFETs case is interesting, because surely it makes no sense for PFC to be mandated for an SMPS with such a low average power draw?
 

treez

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You shoudlnt need PFC....if your product is drawing 2W of power virtually all the time, then it shouldnt need PFC.
 

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