UPS options - Page 1
Forum section: electronics / general

author: PaulAm
author_rank: Frequent Contributor
timestamp: August 13, 2021, 11:10:01 pm
content: I'm in the midst of a multiple day power outage and my UPS decidedly does not like my backup generator. I thought that was because this is an old generator with a mechanical speed govenor which starts at 62Hz dropping to 60Hz once you get to about 30% load. Having not much else to do, I tried running the UPS when the generator was under load and it still didn't like it. It kept switching on and off battery.Power outages are not uncommon and, since I'm in a rural area, I'm often at the bottom of the priority list. One and two day outages happen a couple times a year.Because this is a multiple day outage, I bypassed the UPS so the server rack could come up, but I'd rather just let the UPS carry over the systems until the generator is up and running.So what are my options here? A double conversion UPS? Some kind of power conditioner? Replacing the generator is not an option (this is a 16KW generator, 66A, 240V at 60Hz)

author: gnif
author_rank: Unknown
timestamp: August 13, 2021, 11:25:51 pm
content: If your UPS is capable of 100% duty a stopgap might be to convert it to be a fully online UPS if you have a power supply of the right voltage and high enough current to power it in parallel with the batteries.

author: David Hess
author_rank: Super Contributor
timestamp: August 14, 2021, 04:19:56 am
content: I have used 4 different online UPSes over the years with my 3 kilowatt inverter generator and they all worked fine. I have heard that various offline UPSes are much more picky.

author: bdunham7
author_rank: Super Contributor
timestamp: August 14, 2021, 04:31:26 am
content: You probably should have a careful look at the output of the generator. There may be a reason the UPS doesn't like it. My line-interactive and off-line UPS boxes all work find with my sub-$1K inverter generator. Mid-to-low grade regular backup generators can have some awfully brutal outputs, especially if you have a poor power factor load with harmonics. If you really want your stuff to have clean power you may need a full double-conversion, aka online UPS.

author: nctnico
author_rank: Super Contributor
timestamp: August 14, 2021, 03:35:36 pm
content: You also need to oversize the generator otherwise it can't deal with non-resistive loads. Rule of thumb I got told is a factor of 2. But this may not be applicable to 'inverter generators'.

author: PaulAm
author_rank: Frequent Contributor
timestamp: August 14, 2021, 04:00:16 pm
content: The UPS is a 3KW, I load it about 20% for a 40+ minute runtime. The generator is 16KW, so size is not the problem. It's an old generator, so 100% mechanical, not an inverter.I do have a 40KW monster, but that's a pain to drag out.OK, I put my scope on it and the trace and the fff look ugly

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 14, 2021, 04:15:00 pm
content: What battery voltage is the UPS? If it's 48V, a telecom rectifier can be used to float charge them.

author: PaulAm
author_rank: Frequent Contributor
timestamp: August 14, 2021, 04:16:28 pm
content: It's an APC Smart UPS with 24V batteries. The line frequency is pretty close, but there may be an option in the UPS to desensitize it to that amount of distorsion.edit:Ha, I looked up up the APC faq and their rec is to get a different generatorWell, let's see if I can twiddle the UPS paramaters a bit.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 14, 2021, 04:35:10 pm
content: A pair of 12V server power supplies in series tweaked for about 13.8V each will work well.

author: Red Squirrel
author_rank: Super Contributor
timestamp: August 14, 2021, 05:19:05 pm
content: Some UPSes seem to be better than others at handling bad power, I find brownouts can be especially bad as I've seen situations where a UPS does not trip fast enough to battery and the equipment ends up seeing the brownout and locks up. Having a laser printer on the same circuit can cause weird things because the voltage drops on the circuit but not enough to trigger UPS to kick on,but enough for PCs to lock up. I always make sure to put laser printers on a separate circuit. Online UPSes are the best but they are very hard to find as a consumer and are very expensive. Best bet is to basically set up your own. Power supply -> battery bank -> pure sine inverter. Everything runs on inverter all the time. The power supply is setup to supply a voltage of 2.25v per cell assuming lead acid batteries. This is the hardest part to find as a consumer unless you build it yourself. They are typically called rectifiers in telco world.For my servers I use an inverter-charger but it's standby like most UPSes so it's not perfect, but it seems to handle dirty power well, and is also not aggressive at switching back to AC immediately when it comes back. So if there is a series of very fast flickers it will stay on UPS until the AC has come back stable. APCs are notorious for trying to switch back to AC immediately and if there is multiple flickers often time the load will see the brunt of it.Been meaning to upgrade my setup to a 48v dual conversion but then I kinda took a different approach with my money and instead I'm upgrading my shed's solar setup and plan to run feeds throughout the house including to the server room that way I can cover more things like fridge etc in an emergency. From there I just need to decide how to incorporate the solar into the server rack. I'm thinking just an A/B switch that uses relays to switch the power feed to the UPS from hydro or solar. In fact I may design an A/B switch device (basically a box with two power cords and one output) and create multiple for other loads around the house too. For now I will just have separate outlets and manually move the loads though. If I automate it I can run loads off solar based on the actual output though and save on my hydro bill, so that's the end goal.

author: PaulAm
author_rank: Frequent Contributor
timestamp: August 14, 2021, 05:20:50 pm
content: I cut down the sensitivity setting from high to medium and it's now happy with the power, so that was an easy fix. Might have to widen the vultage trip points or drop sensitivity to low if things start getting flaky under a higher load, but that takes care of the immediate problem.I was considering a 1KW AC->DC->AC sineware converter in front fo the UPS to be used during outages, but that doesn't look necessary now. Might be necessary if things get really flaky under higher loads; we'll see.thanks for the responsesI do have an 8KW medical online UPS I grabbed at a surplus auction but I didn't want to dedicate it to the server rack, that's way overkill.

author: james_s
author_rank: Super Contributor
timestamp: August 14, 2021, 07:35:48 pm
content: Conventional generators are notorious for having nasty waveforms. I have a Honda inverter generator that puts out a nice clean sine wave and none of my UPS's have any trouble with that. IMHO the drastic reduction in noise and enormous fuel savings make it an easy choice for me, having had an inverter type I would never go back to one of those 3600 RPM screamers.At least your UPS has a sensitivity adjustment, that's probably all you can do. The generator produces dirty power and you can't change that, the UPS is just doing what it's meant to do, sensing the dirty power and switching to battery.

author: PaulAm
author_rank: Frequent Contributor
timestamp: August 16, 2021, 06:29:47 pm
content: Outage finally ended 3 hours short of 4 days. That was fun.The default sensitivity setting is somewhat paranoid, but easy enough to change once you know about it. I swapped the UPS back in when I had the generator down for maintenance and everything was fine.