We had another pretty good lightening and wind storm Wednesday night. Took down our main power line at work and we were without power all day and the electric company wasn't very optimistic and having it repaired by this morning. We have a big 35kw generator for running most of our big equipment to keep everything going, but there's nothing to run the small office. I normally do payroll on Thursday and print our checks off the computer and was quickly running into an "oh shit" scenario of not having paychecks ready today.

I figured this was a good chance to check out my Champion 3500 watt generator. I hooked it up to three refrigerators we have for the employees to make sure everything was working normal. They all started up and ran fine. I let them run for about an hour while I attended to some other pressing issues and they were all cooling nicely when I returned.

So I unplugged all the refrigerators and started hooking up the computers, printer, router, etc. that I needed to run payroll. The main server runs off a couple of Belken 375 ups units. They seemed fine.

I had two APC units for my computer, an ES 550 and ES 350. When I plugged them in and turned on my computer, all they did was scream every few seconds. 3 beeps, then pause, three beeps and pause. Then maybe 10 to 15 seconds of nothing, then 3 beeps again.

I was like wth? Both these computers are plugged into the same cord on the same circuit. I pulled out my killawatt meter to check the hz. Anywhere from 62.1 to 62.5. Voltage was similar. 121.1 to 121.5 volts steady.

After farting with it in a hot office for 30 minutes, I gave up on the APC's, plugged my PC straight into the cord, did payroll, printed checks, filed payroll taxes, and shut the whole thing down.

My security camera system runs off an APC ES 750 unit and I wanted to see if it had any electrical damage from the storm. I plugged the ES750 into the generator and it ran fine. Never chirped once. I pulled up all the security cameras and they ran fine.

As luck would have it, the electric company repaired the line about 9 hours sooner than they claimed was possible. We plugged everything back into today and it all runs fine.

So... What's the difference between the UPS? The Belkins were fine, the ES 750 was fine, but the ES 550 and ES350 where almost playing music and you would have sworn we had shit power, but we metered out and ran fine. Today the ES550 and ES350 are plugged into wall and running perfectly. Wall power is coming out at 59.9 hz and 119.2 volts.

APC UPSes are usually more sensitive to dirty power. That is, if the sine wave isn't clean, running in a narrow Hz and voltage range they complain and click over to battery or do a double conversion on the input power to clean it up.

This can usually be changed via a setting on the UPS (at least with the smart-ups).

This.^ Tornado hit town a few years ago and I hooked up the reefer, freezer, TV , and the PC UPS to my generator. UPS acted the same way. Inexpensive (relatively) generators evidently don't put out clean power. Apparently, low-medium cost UPSes can't handle it, more expensive ones can.

Some UPS brands accept generator power better than others, Its a crap shoot to say that the more expensive ones are better with generator power. I have an assortment of 1/2 a dozen different brands, and most which do ok with the genny depending on the load and extension cord. Additionally, the generators play a role in this UPS acceptance of its power, for instance the 5k Coleman generator does great with the UPS, while the harbor freight 800watt and another small chinese 1500 watt do terrible.


most of my UPS are modified, I buy them cheap at a couple of different computer junkyards in the area. By modified I mean that I have replaced either the small 7amp hr 12v battery, or on the larger models the one or two 12amp hr batteries with much larger batteries. The smaller ones run off some 20amp hr SLA and the largers off of some 35amp hr SLA, and one 1500 watt model runs off golf cart batteries (in series). All in battery boxes with extensions added to the UPS battery terminals.

You could buffer the "dirty power" with a battery charger, I have a large one capable of charging at 50 amps continuous and a few cheap small ones that charge at 15 amps. On a sealed system this is not so feasible, because the battery and battery terminals are self contained within the UPS...but if you wanted to hack together a system to keep your security cams running for sometime (or whatever else), it would work.

Reading the specs on the APC ES350, looks like it's only configured to run on 60hz +/- 1. So 62 hz puts it out of spec. There's an adjustment for voltage, but not hz.

The sad part is the output on battery, which is 60hz +/- 3. So it technically provides worse power than what I had available.