Tripp-Lite 750VA UPS slow to come on line - Page 1
Forum section: electronics / repair

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 21, 2018, 07:52:20 am
content: This UPS has been in service for a couple of years. It "works", in that it produces output and keeps its battery charged. But if the mains power goes down or flickers, the UPS is just slow enough to come on line that the computer it's powering shuts down and restarts. And we can't have that!Battery removed and tested good but I replaced with known good battery anyhow-- no effect on problem.Visual inspection reveals nothing out of the ordinary on the PCB or wiring.Even when tested with just a small load of a LED lightbulb, I still get a noticeable flicker when shutting off the mains input.Any ideas? I'm stumped as to how to proceed.

author: fourtytwo42
author_rank: Super Contributor
timestamp: May 21, 2018, 05:46:07 pm
content: Sounds a cheap product that doesnt do as it says on the tin, bin job!

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 21, 2018, 09:59:06 pm
content: Well, maybe so, but if I can fix a 100 dollar unit by replacing some little 10 cent part, to restore the function it had for the first couple years of life.... that's preferable to binning the unit, since I don't have the money to buy a new one.So I'd like some advice on troubleshooting and repairing _this_ unit. Thanks for your reply anyway.One could of course extend your philosophy to any broken or malfunctioning bit of apparatus -- like the 1700 dollar guitar amp I repaired last week by replacing a 5 cent resistor. Bin it, it's not doing what it says on the tin, and there are certainly far more expensive units out there on the market that basically do exactly the same thing.

author: BradC
author_rank: Super Contributor
timestamp: May 22, 2018, 12:37:28 am
content: Looking at the problem from another angle, does your PC power supply have the same hold up time it used to?I recently had an issue with a machine rebooting on an APC SmartUPS even when set to highest sensitivity. It turned out the PSU bulk storage caps had degraded and the hold up time was half what it was when new.You'll almost always see a flicker on an incandescent bulb, even on a quick line-interactive UPS.

author: fourtytwo42
author_rank: Super Contributor
timestamp: May 22, 2018, 04:46:23 am
content: Quote from: alsetalokin4017 on May 21, 2018, 09:59:06 pmOMGI am very very sorry, I thought you meant it had always been like that since newI would always elect to repair something, some stuff I have is 40+ years old!!Not knowing the internals of this unit it's difficult to guess but assuming it's output inverter permanantly supplies the load rather than having a transfer switch I would also go for the DCbus reservoir, it cant be a software fault as such so if the grid sense is based on timing unlikely but it could be something to do with the grid sense such as an ageing opto-coupler or voltage divider resistor so it's become slower in sensing failure. Actually thinking about it if the inverter is permanently on it doesnt need to sense failure so it must be a droop in the DCbus as the charger switches off, have you got a scope, maybe you could capture it ?Once again my apologies for my earlier answer

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 23, 2018, 11:42:26 pm
content: Quote from: BradC on May 22, 2018, 12:37:28 amThat was my first thought too, but the PC recently had a hardware upgrade including a new power supply (ThermalTake Smart 500W). But the problem persists.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 23, 2018, 11:46:35 pm
content: Quote from: fourtytwo42 on May 22, 2018, 04:46:23 amNo worries, I know how it is. There comes a point where almost nothing is worth spending more time on, I know. But I'll give this one a little more time before I give up.I don't think the inverter is permanently on, because I can definitely hear a relay clicking when it cuts in, and there is definitely more flickering in the lightbulb I'm using as a test load when running on the inverter.I do have a scope, several in fact. I'll see if I can get a good measurement of the DC bus during a test event.Thanks for not giving up!

author: fourtytwo42
author_rank: Super Contributor
timestamp: May 24, 2018, 05:11:47 pm
content: Ahh if it has a mechanical transfer switch (relay) it could be contact damage causing an initial high resistance connection subsiquently broken down by the arc. I guess it would also flicker badly if the inverter were not phase locked to the grid prior to failure but maybe thats how they are designed anyway, just a free-running inverter and dont care about the phase jump when the transfer switch changes over ? Guess the scope may reveil what is really going onOr again it could be DC-bus droop.........

author: SeanB
author_rank: Super Contributor
timestamp: May 24, 2018, 07:40:46 pm
content: The built in charger for most UPS units has a few high value electrolytic capacitors right next to hot heatsinks, and replacing them, and all the smaller electrolytics around the hot parts, will probably fix the problem. The capacitors will have high ESR from being well toasted over the years, and the smaller ones will also be out of tolerance. As well they often are very much used outside ripple current ratings, often expecting a 1000uF 16V unit to have a 5A ripple current, while the data sheet says max ripple current is around 1A. You wonder which part is making the heat, the capacitor or the 12V battery regulator ( LM317 on a very small heatsink) or the 5W current limiting resistor all next to each other on the well browned board.Do not forget as well the connections for the high current path might also have dry joints as well.

author: Gregg
author_rank: Super Contributor
timestamp: May 24, 2018, 08:23:51 pm
content: My experience is only from larger three phase UPS systems so my input may not be totally correct for your UPS.Any worthwhile UPS should track the input frequency with the inverter running no load and initially switch to inverter via a static switch probably triacs to cover the delay of the mechanical contactors closing thereby negating the need for the static switch when the mechanical contacts carry the load. Timing is critical as the solid state switch can only carry the rated load for a short time until they overheat so their off function is usually by a timing circuit not feedback of the load.Bad contacts in the mechanical relay could be your problem and is certainly the easiest to troubleshoot.The inverter suddenly needing to supply the load requires good capacitors initially, especially since lead acid battery voltage drops immediately and substantially when first loaded. Google “coup de fouet” for more on this.