Removing surge protection from power strip

[taste_tester]

I am concerned that some UPS, like the UPS I use in my home office, state not to use surge protectors with it, however I don't know if it's because a statement to prevent end users from overloading the unit with too much plugged into it, or if the surge protection circuit interferes with the UPS' job of monitoring  power.

i know some cheaper surge protectors are simply a plain power strip with the mains routed through some MOV's,  rather than any PCB with the surge protection on there, so i thought maybe remove the MOVs and just direct power to the power strip.

[BeBuLamar]

APC also recommeds not to use a power strip to feed the UPS.

[CaptDon]

Those modified sinewave invertors have a very high peak voltage and very square corners with lots of harmonics. The high peak voltage will disturb the typical 130L10 and 130L20 MOV's. Older MOV's with a lot of hours on them are even more likely to break down. Usually when an MOV fails it does so with a lot of flame and flying pieces and often the only thing left is two tiny nubs of wire where an MOV once resided. When doing sound at the carnivals where power comes from generator trailers I have had lots of MOV's bid farewell with flame and smoke.

[TimNJ]

If you want to retain some surge suppression capability, you can try one or a combination of the below:

If the existing MOVs are rated for 300Vac continuous (which is a very common rating, usually marked ‘471’) on the MOV, increase the MOV clamping voltage rating to ‘561’ or ‘621’. Higher clamping voltage means the MOVs will not get so worn out over time, by whatever heinous spikes the inverter is generating. On the other hand, higher clamping voltage means less surge suppression capability. This is sort of a shot in the dark unless you know exactly what (open circuit, no MOV) peak voltages it is producing.

You can also retain the original clamping voltage, but instead use a thermally protected MOV, such as Littelfuse TMOV. If the inverter does, in fact, wear out the MOV over time, causing total failure of the MOV, it (the MOV) *should* go open circuit instead of creating a hazardous (fire) situation.

You can also try both at the same time, to be extra precautious.

[TimNJ]

Or maybe, just don’t plug it into a surge protector (like they said). 

[taste_tester]

I had actually thought when they said "don't use a surge protector with it" I assumed that meant on the outputs of the UPS.  It didn't even cross my mind someone might try and plug it into a surge protector 

[nfmax]

Those modified sinewave invertors have a very high peak voltage and very square corners with lots of harmonics. The high peak voltage will disturb the typical 130L10 and 130L20 MOV's.

I have encountered this problem! Many such UPS's generate output peak voltages which exceed the maximum allowable, and are high enough to cause damage to switch-mode power supplies connected to them. They actually generate output voltage surges! It is much less of a problem in 110V-land, because the majority of switch-mode supplies are now universal input so can cope, but surge protectors on the UPS output will still trip - correctly, as they should.

If the UPS output is unsuitable for use with a surge protector on its output then it is unsuitable for use, full stop. FWIW I have settled on APC BackUPS 700 for use here in 240V-land, which I have measured do not output excessive peak voltage.

[BeBuLamar]

But it is APC that recommends not to use surge protector.
https://www.apc.com/us/en/faqs/FA158852/#:~:text=Plugging%20your%20UPS%20into%20a%20surge%20protector%20may%20cause%20the,it%20requires%20to%20remain%20online.

[thm_w]

Probably easier to just buy plain power bars, that are <$5, than modifying an existing surge protector?

[james_s]

I frequently remove the MOVs from UPS's and occasionally power strips, after seeing them burn up more than once, in one case burning hole in the carpet at a place I used to work after the building developed a bad neutral connection I just don't trust them. Power surges are rare where I am, I've never had anything damaged by a surge that I'm aware of.

[wizard69]

Those modified sinewave invertors have a very high peak voltage and very square corners with lots of harmonics. The high peak voltage will disturb the typical 130L10 and 130L20 MOV's.

I have encountered this problem! Many such UPS's generate output peak voltages which exceed the maximum allowable, and are high enough to cause damage to switch-mode power supplies connected to them. They actually generate output voltage surges! It is much less of a problem in 110V-land, because the majority of switch-mode supplies are now universal input so can cope, but surge protectors on the UPS output will still trip - correctly, as they should.

If the UPS output is unsuitable for use with a surge protector on its output then it is unsuitable for use, full stop. FWIW I have settled on APC BackUPS 700 for use here in 240V-land, which I have measured do not output excessive peak voltage.

I find this whole discussion a bit funny as we have UPS manufactures suggesting that surge suppression strips should not be used and the reason is the UPS generate excessive spikes.  Maybe what we need is a database of UPS systems that don't do this.   On the flip side shouldn't the UPS be handling any surges that come into the unit anyways?   That is does it make any sense to have down stream surge suppression at all?

[james_s]

I find this whole discussion a bit funny as we have UPS manufactures suggesting that surge suppression strips should not be used and the reason is the UPS generate excessive spikes.  Maybe what we need is a database of UPS systems that don't do this.   On the flip side shouldn't the UPS be handling any surges that come into the unit anyways?   That is does it make any sense to have down stream surge suppression at all?

I think it's fundamental to the fact that the vast majority of UPS's for many years produced a square wave with dead time rather than a sine wave because it was not economically feasible to make them produce a clean sine wave instead. More recently that has been changing, driven primarily by the proliferation of computer PSUs with active PFC. Most consumer UPS's are still the square wave type but sine wave units are steadily becoming more common.