SmartUPS 1250 cycles on/off line when AC power is present.

[Anonymous user]

My SmartUPS 1250 has developed a problem. When turning it on, it passes the self test. Batteries are charged to 100%. After a few minutes it starts cycling to battery power for about a second, beeping twice, then goes back to line. In about 2 more seconds, the cycle repeats again. It continues cycling between AC and battery power indefinitely. After a while, the time on AC is just a fraction of a second. It spends a few seconds on battery, switches to AC for just a moment, then back to battery. The AC power is perfectly fine - exactly 120 volts, no glitches. (Other UPS's on the same circuit are not having any problems)

Has anyone heard of this problem? Is there any fix?

Is there any service information or diagnostic procedures available for this model? It has been very reliable, and the batteries are relatively new, so I hate to throw it into the dumpster.

Message was edited by: timg11

[BillP]

Hello:

This does sound strange indeed. Just a few questions, though. Firstly, do you have any type of serial cable attached to this? A dangling cable can often send erroneous signals to the UPS. If not, have you tested the UPS by itself with no load attached, to see if it shows the same symptoms? Have you tried a different outlet on this circuit?

Lastly, there is a "sensitivity" option on this UPS (as well as most APC UPS's) which is worth taking a look at. To lower the sensitivity on this particular unit, you can use the dip switch (Option 1 dip switch...far right) on the back. Setting this switch to the "On" (up) position will lower the sensitivity of the UPS, making it less picky to input line distortion/harmonics. Considering that you have explained that other UPS's on the same circuits are working fine and your input appears clean, this does not appear to be the issue in this case. However, it is always worth a shot for the sake of troubleshooting.

Let us know how it all works out!


Thanks

[Anonymous user]

Thanks for the reply. No there was no serial cable attached. I did connect a serial cable to a terminal program to see if there was any clues. When it goes into the cycling mode, I see a series of !$!$ characters being sent by the UPS.

I am testing it with no load. It has the same behavior.

Very clever idea about the DIP switch. I set switch 1 to On, and so far (within 10 minutes) the UPS has not started cycling. Previously, it started cycling within 2 minutes.
Maybe the internal comparator components have drifted in value enough to make it think good power is bad, but the components in the less sensitive setting have not drifted as far off?

I'll let it go for a day or so and see if it stays up.

Thanks!

[BillP]

timg11 wrote:
Very clever idea about the DIP switch. I set switch 1 to On, and so far (within 10 minutes) the UPS has not started cycling. Previously, it started cycling within 2 minutes.
Maybe the internal comparator components have drifted in value enough to make it think good power is bad, but the components in the less sensitive setting have not drifted as far off?

These were my thoughts exactly. In your situation, obviously your power has not changed any and your other units are operating fine. Considering the age of the unit (we haven't made the 1250's in quite some time, so I'm assuming your's is 10-15 years old) I'm thinking that perhaps the values have caused that to be a bit too picky, thinking power is bad when in fact it is not.

I hope this helps, and I hope your unit continues to work with this setting! I'm sure you've become quite attached to that if you've owned it since it was new. 😉

[Anonymous user]

It's been working OK for a day now with no load, so I think it is a good solution for this problem.
I'll hook the loads up to it again later when I can shut everything down to do the transfer and let you know if that causes any problems.
Thanks for the suggestion!

[BillP · Accepted solution]

Anytime! I appreciate you giving us updates on the situation; the information is helpful.