[TowerTalk] OT: Generators and UPS's

Alan NV8A nv8a at att.net
Fri Aug 25 08:59:34 EDT 2006

On 08/24/06 09:55 pm Doug Rehman wrote:

> I realize this is off topic, but I can't find an answer elsewhere and
> TowerTalk has the best technical resources I can think of. (OK, I guess I
> can tie it to towers, because the generator will run the tower winch in the
> event of a power failure and the computer in the shack has a UPS and will
> eventually control the rotator...)
> 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 UPS
> plugged into the line conditioner.
> 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
> 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.
> 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. 
> 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 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 have APC UPS units of various sizes (biggest is a Back-UPS Pro 1100) 
for our computers and DirecTiVos). I've never seen any cycle as you 
describe, but I've never tried feeding them from a generator: the 
computers monitor the UPS state and shut down cleanly within 5 min of a 
mains power failure; if the DirecTiVos run the UPS batteries down and we 
miss recording part of a program, that's just too bad.

But our UPS units are very basic. I don't think they make any attempt to 
clean up "bad power." Perhaps yours are just too smart for their own 
good when it comes to feeding them from a generator.


Alan NV8A

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