BE425M UPS faults with PC plugged into battery backup

[Anonymous user]

I have a brand new BE425 UPS, which has been plugged in (charging) for 24 hours.  My intent is to use this for a home PC, which will be up 24/7.  My initial testing with the PC causes the UPS to fault.  That is, it flashes red/green and has a constant loud tone. 
Measured with a kilo-watt device, the PC draws 100 watts during power up and draws about 70 watts after. The UPS is rated for 200+ watts.
I have isolated the fault behavior, and it seems to happen when I do this:
- I set in the PC BIOS to automatically turn on the PC when it has power.
- The PC is plugged into a battery backup AC socket on the UPS.
- The UPS is plugged into my house AC socket, which has power.
- I turn on the power on the UPS by pressing the button. The UPS powers on, clicks, and then the fault occurs (red/green flashing with constant tone).
The fault does NOT occur in these scenarios:
- if I power up the UPS with a single low wattage (5W) device plugged into one of its battery backed AC sockets
- if I power up the UPS with the PC plugged into a non-battery AC socket on the UPS
- if I power up the UPS, let it do it's self test, and then I manually switch on the PC (plugged into battery backed AC socket).
So to summarize, the UPS faults when it is powered up and there is a 100 watt load on its battery-backed AC socket.
Is the fault scenario above normal behavior or do I have a bad unit?

[Anonymous user · Accepted solution]

I would suggest testing with a simple resistive load, like a lamp.

Outside of a defective unit, the only thing I can figure would be your computer's power supply having a very poor power factor. This could cause the UPS's microcontroller to believe it is overloaded when it is not.

I would actually suggest a larger UPS for your computer, such as a 750 VA unit or larger. This is for a few reasons: it gives you more headroom for future expansion, it's easier on the battery and the unit's electronics, you'll have more runtime during a power failure (especially as the batteries age) and the larger models can handle certain power disturbances without having to use up the battery.

I am quite surprised by the BE425 not having a user replaceable battery. (I'd almost buy one just to crack it open and see how "non serviceable" the battery really is.)

[Anonymous user]

Thanks, I appreciate the reply.

On 1/27/2017 1:16 AM, William said:

I would suggest testing with a simple resistive load, like a lamp.

I will try a lamp later and report back.

On 1/27/2017 1:16 AM, William said:

Outside of a defective unit, the only thing I can figure would be your computer's power supply having a very poor power factor. This could cause the UPS's microcontroller to believe it is overloaded when it is not.

I guess your theory on the power factor is plausible.  What seems weird is that the fault only occurs if the load is there during the UPS self-test at power up.  The fault doesn't occur if the same load is applied AFTER the self test.  What would explain that?

On 1/27/2017 1:16 AM, William said:

I would actually suggest a larger UPS for your computer...

I appreciate the advice, but I'll probably stick to what I have. I've been running an ES350 for 4 years now (until it died), and that has been fine.  The older UPS never had any issues with my PC.  The only reason I went with the 425 was that it was only a few dollars more than a new 350.

[voidstar_apc]

What sometimes happens is in the brief period between loss of power and the UPS intervention, some power supplies draw full power. This is very brief but can overload a small UPS. Usually the max power draw is labeled on the power supply near the power cord.

[Anonymous user]

OK, I did the lamp test and the UPS did NOT fault.

The comments about the issue potentially being the power supply got me thinking... I took a look at it and it is an Antec BP550 80+, with active PFC.  I've read that there can be compatibility issues between UPSs and active PFC power supplies.  What the incompatibilities are I'm not sure, but I'm guessing that's the problem here.

[voidstar_apc]

The simpler non-PFC power supplies could be relied on not to do anything stupid, but it's not relevant these days since all computer power supplies are now the PFC type.

As for compatibility, I'd say some supplies will not allow you to under-size your UPS relative to the power supply's watt rating. Likewise, older UPSes with heavy transformers were a bit more tolerant of overload. Both are unfortunate but within spec.

[Anonymous user]

Have you looked to see what the sensitivity is set to in the software?

[Anonymous user]

I didn't look at the sensitivity settings because they didn't seem relevant.  Since you point it out though, it probably doesn't hurt to adjust those settings and see if it helps.  I'll give it a try later and report back.  Thanks!

[Anonymous user]

I've now done my test scenario with the PC using all 3 sensitivity settings.  No matter the setting, the UPS still faulted.  Good thought though!

[Anonymous user]

I am accepting William's answer because he had some spot on advice about what to do. If I could also accept voidstar's I would as well.  However, I can only accept one. Both gave answers, but from different angles.

William was spot on with his advice - the lamp test was important in establishing that the UPS does work. His advice on upgrading to a 750 is probably what most people with a PC should do. If I wasn't so cheap that would probably be the route I'd take, although I suspect that if I bought another ES350 (old style UPS) that it would work for my use case.

voidstar kind of talked me through the whys... why the new UPS won't work with today's PCs.

Thanks for everyone's help!