If the power supply had a power factor of 1 then the 24VA would = 24W. That's the best case. Any power factor less than perfect would yield fewer Watts. I'm not the EE, so I may be confused, but my feeling is that unless the specs are mis-stated on the sticker it's impossible for this power supply to provide the device's stated maximum of 24.3W. Apparently, it's enough with normal usage under normal conditions, but it must not have much margin for anything abnormal.
-Adam ________________________________ From: AF <af-boun...@af.afmug.com> on behalf of Ken Hohhof <khoh...@kwom.com> Sent: Wednesday, December 11, 2024 7:49 PM To: 'AnimalFarm Microwave Users Group' <af@af.afmug.com> Subject: Re: [AFMUG] Sizing DC Power Supplies Insufficient information. VA vs watts I think involves power factor? I think they are the same only for resistive (non reactive) loads. Then does load have an initial inrush current? And what does the power supply do in an overload situation – current limit, go into foldback, or supply more than rated power for a short period? The max of 1A might be some kind of safety or UL rating thing, not actual power consumption. Or max startup current for purposes of determining fuse size. From: AF <af-boun...@af.afmug.com> On Behalf Of Chris Fabien Sent: Wednesday, December 11, 2024 4:39 PM To: AnimalFarm Microwave Users Group <af@af.afmug.com> Subject: Re: [AFMUG] Sizing DC Power Supplies Would be easy enough to bench test this with a variac. The specs on the power supply are a bit suspect too. Max of 1A at Min 100V = 100 watts to put out 24W of power? On Wed, Dec 11, 2024 at 5:30 PM <ch...@go-mtc.com<mailto:ch...@go-mtc.com>> wrote: Looks like you nailed it to me. From: Adam Moffett Sent: Wednesday, December 11, 2024 3:09 PM To: AnimalFarm Microwave Users Group Subject: [AFMUG] Sizing DC Power Supplies So riddle me this: Let's say you have this 12V device which needs a maximum of 24.3 Watts. [cid:ii_193b7df04b0cb971f161] What amperage of 12V switching power supply would you spec for this device? Personally, I'd go for around 2.5 - 3.0 Amps so I have a safety margin. Nokia supplies a 12V 2.0 Amp. [cid:ii_193b7df04b0cb971f162] So 24VA to supply up to 24.3W. If those numbers are real, then isn't that undersized to start with? I would never have looked except that we have 3 of these on the same street all rebooting every few minutes, and they all started doing it at the same time this morning. It so happens they're all getting electric service off the same transformer, so I'm imagining there's low voltage or some other condition making the DC power supply a little less efficient and now it ain't got the juice to keep the device running. In which case someone at Nokia is an idiot. Please tell me if I'm the crazy one here. -Adam ________________________________ -- AF mailing list AF@af.afmug.com<mailto:AF@af.afmug.com> http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list AF@af.afmug.com<mailto:AF@af.afmug.com> http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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