UPS inrush current in battery mode - can it kill the battery/UPS?

I’ve been reading up on the combination of UPS and Active PFC power supplies, as they are common here in the EU. Seems you need to take 2 things into account. First, some A-PFC PSUs cannot work with the modified square wave output of some UPSs. You need a pure sine wave version. Though it may work (as Seasonic says in their FAQ, just try it out).

Secondly, A-PFC PSUs have a high inrush current up to their specced capacity (i.e. a 1000W PSU can pull that 1000W briefly at startup)

I tried my workstation, with a Seasonic Prime Ultra Titanium 1000W on an Eaton Ellipse Eco 800VA (550W). It works, when I pull the plug during a 450W load, the Eaton switches to battery power, and the workstation just keeps working. Seasonic says it should not be a problem and the PSU cannot be damaged by the modified sine wave output of the Eaton.

However, using the monitoring software from Eaton, I do see a very high inrush current peak when switching to battery mode (I could briefly see 650W but it may be higher as it’s just a very brief peak). I planned on a higher capacity UPS anyway, I just had the 800VA lying around and wanted to see if its wave output form would work on the Seasonic.

But I am still worried, as the highest Eco type can handle 1000W, so barely the max inrush peak of the workstation. And I’d like to add a few small devices to the UPS as well (not much extra load).

So I asked Eaton, and they kinda danced around the inrush current subject and advised to buy a pure sine wave UPS from the 5P line. These are twice as expensive and also bloody loud. Not something I want on my desk. Seems they just want to make a sale (as the 5P tower models only go up to 1000W too)

So my question is: can the inrush current peak damage the UPS or battery, or is the worst that can happen just the UPS overcurrent protection kicking in and shutting down? It seems the protection of the Eco did not activate in my test, even if it went into the red zone for a very brief moment. Not sure if that means it’s OK, or if the Eco’s overcurrent protection is crap.

Any insights would be much appreciated.

Did you ever get an answer to this? Running into something similar but with straight utility power. Short version is a “conditioner” was installed upstream which is supposed to normalize the power but does so by constantly changing voltages upto +/- 10v. Power can fluctuate normally but isn’t supposed to by such drastic amounts.

End result is system instability. I can literally see the power dips (120v->110v for example), coincide with micro freezing. 110v is of course within range but it shouldn’t be dropping 10v at once.

No, unfortunately no replies as you can see. Nor did I find other places with information that was useful. I suspect that UPS these days are all crap, from all the reviews I’ve found, pictures of internals I saw, the component quality is rock bottom for everything below $800 and maybe above that. Doesn’t matter what brand, APC, Cyberpower, Eaton, Bluewalker, Emerson Liebert,… it’s all crap these days, most are built by just a few Chinese OEMs and not worth the money.

Since there’s very few proper reviews out there (gamers don’t seem to need UPS, so the consumer press doesn’t bother) there’s no pressure to make decent stuff either.

To answer your question, yes the inrush can damage the UPS but not the battery*.

UPS have a limited life in terms of how many times it can thunk it’s relay’s over. Passive UPS’s can also damage connected devices, as when inlet power drops they switch. Which can brown out connected devices and also cause another inrush current draw.

Active UPS’s tend to last much longer as they are inline and actively conditioning power and also don’t suffer as drastic current inrush as they’re inline and won’t cause brown outs to connected devices.

Some UPS are marked with a surge limitation (APC tend to mark this as Joules). Which is in addition to what the UPS is rated to.
Eg. If you have a 1000W rated UPS with 100J surge it can momentarily, for 1 second, draw an additional 100W without damaging the UPS.

As for over current protection, it varies from brand to brand. Some may trip the internal fuse (should trip ideally) others may brown out (cheaper ones).

TL:DR. Yes inrush (above spec) will damage the UPS. As long as you’re within spec of the UPS, then you’ll be fine. Also avoid Passive UPS’s.

*The battery can be damaged if on battery power at the time of inrush. (likely with passive UPS) Usually there’s no damage, but the time remaining on battery may not be accurate until the battery has recharged and/or self tested.

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