Medium PSU, small UPS, very low power system

[Hakuren]

Hi guys

Would like to inquiry about something I wouldn't normally do. I know how PSU to UPS ratio works. I just want to avoid spending money if it can be avoided. Anyway I asking:

I have small 300W UPS which is purely to support router 24/7/365. I do plan to create one very low power system to also run 24/7/365 for small project I have. I want to plug this system into 300W UPS, but the problem is that all PSUs I have are 500W (I don't deal with small Ws ) and up. Smallest is Enermax Liberty 500W. Would it screw with PFC, OVP, etc...?

Planned system will be based on some SoC (probably Kabini)+ 2 DIMM sticks+ 1 SSD, on-board VGA, all passively cooled. All together will probably draw about 25W (monitor is out of the equation as it will be only for periodical checks) - there will be nothing running except OS & tiny piece of software connecting with external server.

 

[Sith'ari]

I can't understand, what exactly is your question.
As far as i know, it doesn't matter if you plug a 500watt (*or whatever) psu to a 300 watt ups, as long as the pc /psu doesn't exceeds the 300 watt consumption that can be supported by your ups.

 

[Dead Parrot]

Might want to check the PS efficiency at those low power levels. They often get real poor. Even the 80+ ones. You could wind up using 50 or more watts to power that 25W system. Depending on the power needs of your system, might be able to use an old laptop PS. Or for that matter, find an used laptop or netbook.

And yes, PFC and other efficiency things in both PS and UPS can react poorly with each other. The most common failure mode is the 'protected' system will fail when the UPS switches to battery power due to the system PS shutting down when fed the pseudo sine wave from the UPS.

 

[Hakuren]

Might want to check the PS efficiency at those low power levels. They often get real poor. Even the 80+ ones. You could wind up using 50 or more watts to power that 25W system. Depending on the power needs of your system, might be able to use an old laptop PS. Or for that matter, find an used laptop or netbook.

And yes, PFC and other efficiency things in both PS and UPS can react poorly with each other. The most common failure mode is the 'protected' system will fail when the UPS switches to battery power due to the system PS shutting down when fed the pseudo sine wave from the UPS.

Yeah that is my primary concern. I know that APC UPS from Back-UPS series don't like active PFC one iota. Because of that I posted this. I was thinking about used nettop/book or something, the problem is - it has to be totally silent. I will sleep in the same room and last thing I want is 10000rpm mini turbojet fan blowing like mad in the middle of the night (I have old Dell Inspiron with P4 inside and Asus F5U I think, both are idiotically loud). I tested few BRIX and NUCs style of PCs and these are also out of the window because of the noise. Probably best option will be to find small passive PSU for the job... or buy 600W refurbished UPS, LOL.

Thanks, like they say 2 heads are better than one.

 

[FnordMan]

Yeah that is my primary concern. I know that APC UPS from Back-UPS series don't like active PFC one iota.

Other way around. Older active PFC units didn't like stepped approximation. This hasn't been a problem for a while now as I recall. Both of my UPSes are Back-UPS stepped approximation units with fairly recent (3-4 years old) active PFC PSUs. Zero issues on either.