Dell hell - I am so mad I could scream!

Started Jan 18, 2009 | Discussions thread
Wayne Larmon Veteran Member • Posts: 9,403
Running a UPS on generator power

mrsfixit wrote:

Wayne Larmon wrote:

I used to not run anything computer related off the generator, but
last year we switched our phone service to VOIP. Because call
service doesn't reach here, now I keep the cable modem running so
VOIP will work. I have the cable modem behind two APC UPSes: a 1400
KVA SmartUPS and a 750 KVA bottom-of-the line APC UPS, daisy-chained
(to attempt to "condition" the AC that the generator puts out.)

I just use the one APC 1200 watt UPS. Can you daisy chain those things?

Only if the first UPS is an APC SmartUPS (or equivalent) that puts out pure sine AC power when it is running on battery power. The cheaper UPSs put out modified square waves. A UPS usually can't run on modified square wave power. Computers can run on square wave power, but UPSs can't. UPSs are finicky. (See below.)

Is the power put out by a generator that much of a problem for
computer equipment? Should I never, ever plug anything in that isn't
connected to the UPS so it can filter the current????

I'm not an expert on this. Here are a few things from Googling variations of "generator UPS" and "generator UPS APC"

Q&A from an APC forum:

Q: ....However, when the generator kicks on, the computer stays on battery back-up and drains the battery. The back-up does not seem to recognize the generator power source....

A: The output of the generator is either not close enough to 50.00 or 60.00 Hz, or it's not sinusoidal enough. BackUPS has higher expectation for input quality than it will ever put out.

If you were to connect a BackUPS to another BackUPS running on the battery, it won't accept the output as clean enough. Generator's output is dirty, but cleaner than the BackUPS's modified squarewave, but the BackUPS won't accept the input power and provides even dirtier power derived from the battery.

3 choices:
Double conversion UPS
Honda EU series sinewave inverter generator

Big generator with clean enough output and heavy enough flywheel to keep frequency swing within BackUPS' liking ;jsessionid=a3YLcLX_491fGbyhWK?messageID=4866

The Honda generators have an extra layer of electronics between the output of the generator and the AC receptacles, solely for the purpose of putting out clean AC power. But they are (of course) more expensive than "contractor's" generators, like we have. One way out would be to keep the contractor's generator for running the house and get a small Honda generator for running computers.

Honda EU series generators§ion=P2GG&category=sq

Ensuring Generator and UPS Compatibility

(A more extensive discussion of how UPSs and generators interact.)

(About needing to adjust a generator so it runs at exactly 60 Hz, before a UPS will work with it.)

I just re-read the manuals for my generator and it doesn't say anything about being able to adjust either voltage or frequency, so I guess I get what I get.

Again, Google for combinations of "generator," "UPS," "problems," etc. After reading the above web pages, along with a few more, I think I'm going back to my old policy of not attempting to run my computers on the generator. (But I'll run the cable modem/VOIP--I tried that last time and it worked with no problems.)

Again, good luck.


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