Matt_Smi

I was wondering if it is bad to have a UPS (which provides surge protection in itself) plugged into another surge protector? I think I remember reading this that this should not be done but am not sure. The reason I ask is because I have an outlet mounted surge protector http://www.newegg.com/Product/Produc...82E16812120214 on the outlet that I want to plug my UPS into. I have three other things plugged into that outlet as well so I need more than two plugs. So I was wondering if I should just get rid of that protector and get a traditional strip style one for the other things I need plugged in and then just plug the UPS directly into the wall, or if it is ok to plug it into my existing protector. Thanks.

Bob McElfresh

There is no problem putting a surge-protector ahead of the UPS.

Most surge-protectors simply clamp any voltage above 120 volts AC to protect electronics.

But it is sometimes a bad idea to plug a analog device (like a audio amp or video display) into a UPS because it can affect the output voltage a bit. This is not a problem for a computer where any rough spots on the input power is ignored by the digital nature of the electronics. But the output of a UPS can look like a "sawtooth" pattern that may affect analog electronics.

Make sure the UPS documentation says it can be used for audio/video/Home Theater equipment. Some of the newer units are designed to NOT affect the power passed through for these devices.

Matt_Smi

Thanks for the reply Bob, actually I am using this UPS on my computer. I was originally going to get one for my HT gear as well, but then I started reading about sine waves and how only very expensive ones put out a pure sine, where as the rest are step sine. Anyway good to know there is no problem in just plugging it into the protector, if anything I figure it gives me an extra layer of surge protection.

David_Rivshin

Plugging an UPS into a surge protector is fine. What you shouldn't do is plug a surge protector into an UPS. I've never seen a great explanation as to why, but what I have read is that the dirty output of the UPS operating on battery will look like many small surges to the surge protector. This in turn will cause the surge protector to shunt power to the ground wire, quickly draining the UPS's battery and destroying the surge protector (most surge protectors are the MOV type, which are degraded every time they activate).

As for stepped sine output being a problem for HT electronics, I have a feeling that's not as big of a deal as some people make it out to be. In most UPS's (read any one you're ever likely to see) power is normally sent straight through from the wall unchanged. It's only when the switch to battery (brownout/blackout/overvoltage situations) that they produce their own power, and that's when you'll get the stepped sine wave approximation. I don't know about you, but when the power just went out I'm not very concerned about my soundstage collapsing, I'm more concerned with getting a flashlight out.
UPS manufacturers might caution against using them for an HT simply because HT's are so power hungry they will very quickly drain the battery. Same reason they say not to plug a laser printer into an UPS.
On the other hand, I don't particularly care about powering my HT for another 10 minutes when the power goes out either, so I don't see much point to an UPS on the HT. A good surge protector seems like a better deal anyways.
BTW, there are UPS's which are always on battery power (and use the wall just to keep the battery continuously charged), but those tend to be very expensive, and probably produce good sine wave output as well.

-- Dave

Chu Gai

Matt said...
Some manufacturers don't recommend it (APC for example) but you'd have to check with them what their reasoning is. There doesn't seem to be a clear consensus on this which suggests to me that you'd be OK with this scenario.

Your explanation David is entirely reasonable and correct especially if the UPS is dirty. You'd have to check with the manufacturer to find out if it's a sine wave, quasi sine wave or something else. THD numbers ought to give you an indication of how good that power coming out is.