[TowerTalk] OT: Generators and UPS's

William P. J. Bressette wpj at 8inchfloppy.net
Fri Aug 25 08:13:15 EDT 2006

I work in TI and have ran into this situation many times while trying temp setups the generator is producing a digital signwave or square sinewave and the APC products need to have a very smooth square sine or they think the power is bad and switch over to battery, the only very expensive gensets like cat etc designed for comp rooms usually produce this for the smaller side check out the honde computer generators never had an issue with them.


From: towertalk-bounces at contesting.com on behalf of K8RI on TowerTalk
Sent: Fri 8/25/2006 12:52 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] OT: Generators and UPS's

I have 9500 Watt gas powered generator and use a manual transfer switch.  By
the time I can make the switch the generator has stabillized.

> I have a generator with an automatic transfer switch. In the event of grid
> failure, I have more than enough capacity to run the house, shack, and
> office (all co-located). I have numerous computers in my office; each has
> a
> line conditioner (primarily useful for over/under voltage events) and a
> plugged into the line conditioner.

Do you have real line conditioners or the plug strips they call line
conditioners which really aren't.  Typically with computers a line
conditioner is basically a UPS that runs off the battery all the time.  They
are considerably more expensive than most UPSs and have a very clean wave

> Yesterday, the grid went down for about an hour. The generator came on
> after
> about 30 seconds; the UPS's carried the computers during this interval.
> Some
> of the UPS's began to switch on and off. The generator was running at
> around
> 40% average load; the voltage fluctuation couldn't have been very much, as
> the line conditioners were not reacting at all. While I didn't monitor the
> frequency, in the past I haven't seen it change much.
> I always set the UPS's for maximum tolerance of noise and voltage. The UPS

I have mine set for minimum although suprisingly the computers can handle a
really ratty wave form and are not really sensitive to much unless it's a
really big voltage excursion or spike.

> on my primary computer was one of the ones cycling on and off. It was
> reporting noise as the reason. That UPS, along with all of the others that
> were cycling, died after around 15 minutes.

Sounds like battery replacement time.
It depends on the UPS, but I use APCs. When the original batteries died I
replaced them with external Lead Acid batteries with a much higher capacity.

> Interestingly, the three UPS's that weren't cycling were Belden
> 350VA/500VA
> models that I would consider cheaper units. The more expensive APC units
> and
> some cheaper Conext units all cycled and failed.

As I said above, it sounds like the batteries are ready for replacement.
Have you run the self test?

> The generator is well grounded and connected to the single point ground
> with
> 2" copper strap.
> It is pretty certain that the cycling culprit is noise and I doubt I could
> clean the line sufficiently to make the sensitive UPS's behave- especially
> since the line conditioners have noise filters in them already. (There are
> a
> lot of posts similar to this in the Usenet, but I couldn't find any
> solutions.)

I'd have to see those line conditioners, but I doubt they are really
"conditioners", but rather just filters using MOVs,

> I need to replace about 7 or 8 UPS's, from 500VA to 1500VA. Has anyone
> been
> down this road before and found a reliable UPS model and/or brand for use
> with a generator?

I use APCs in the 750 VA range and they now have over 120 hours while on the
generator. So far I have no complaints. The batteries seem to last about 4
years although the program complains when the 3 years is up.

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com (Use return address from home page)
> Tnx,
> Doug
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