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Really Strange UPS question

by DerfX / March 21, 2011 8:44 PM PDT

I am a UPS fanatic. Living in Florida, I think we have the "dirtiest" electricity as far as brownouts and other surge problems go. I know surge protectors only filter out the spikes and it requires a UPS to "add" the necessary electricity during a brownout which we get all the time. So I have them on everything including the garage door.

Some years ago, when Circuit City was going out of business, I was able to buy a bunch of 1000VAC UPSs for cheap. They supply about 600 to 650 watts of power for anywhere from fifteen minutes to an hour depending on just how much you are drawing from them.

I actually have a couple more than I really need right now so I was wondering, what would happen if I "daisy-chained" a couple of them? If we had a power outage that lasted a couple hours, which is not all that unusual here, would not the second UPS in line think all was fine while the first one was running down and then the second one would take over and start its cycle of running down? Could you prolong electrical supply for an indefinite period if you daisy-chained an indefinite number of UPSs?

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Not as effective
by Willy / March 21, 2011 11:26 PM PDT

Daisy-chain to me means it would be a "parallel setup". In this regard, it would act on the whole as if it were one unit. While, that appears to seem OK, you may experience some difficulty as the electronics of a UPS while simple or any s/w based one would act sluggish, IMO. Also, I would think the 1st UPS of that chain would get the most punishment and not necessary show as the remaining UPSs, allow it to be so. In the long run, you're defeating the purpose of the UPS. Use the UPS as it was intended for certain devices and allow it to act accordingly. Actually, if you have real bad power issue on a constant basis, get the largest UPS you can afford and plug the same devices you would have on a smaller rated UPS. YPS are intended for a controlled shutdown usually PCs. Any other electronic device maybe better served by a surge protector of a higher rating than simple protectors as they really don't need UPS, though they can be plugged on. Understand, most simple UPS setups are in fact simple surge protector too, many aren't that high rated. Of course, it wouldn't hurt to have direct plug-in surge protector on an AC cord that yet plugs in to a UPS. remember, surge protector do fail if "used", the MOV component breaks down and its done, has to be replaced. A simple surge protector or a cord type can be tossed saving the UPS surge protector circuit if not done in. Check the websites of APC and Tripplite to better understand UPS operation.

tada -----Willy Happy

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Sorry, I didn't make myself clear
by DerfX / March 22, 2011 7:18 PM PDT
In reply to: Not as effective

Operating anything in "parallel" can be dangerous as it is like using fuses or circuit breakers in parallel, it simply defeats the purpose unless you have to allow double the current carrying capability of a circuit.

When I said "daisy-chaining" I meant in "series", one in back of another. So they are all in a line. Then, as the main power went down, the first UPS in line would assume control and maintain power for as long as it could, leaving the UPSs behind it to think all was normal. Then, as the first UPS died, the second UPS would assume control and take over supplying power and so on...

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You don't do that and here's why
by Steven Haninger / March 23, 2011 8:50 PM PDT

When a standard home use UPS goes on battery, it may not output a good sine wave and that can cause damage to some devices. You never connect a surge protector on the input or output of a UPS either and some will warn of warranties being voided for doing this. As well, there is, and albeit a small one, a delay before the "on battery" function triggers. Your daisy chain will contain that delay from one UPS to another. You want minimal delay to the device you're trying to operate. What I'd think you might want, if your pockets are deep enough, is an industrial or hospital grade UPS. It will have a massive isolation transformer and sophisticated circuitry to ensure seamless clean power and will also smooth out the normal transients that occur on raw AC power from your home outlets.

BTW, I install instruments in hospital environments that come with these hospital grade UPS devices. If the hospital has it's own backup UPS power outlets, we are instructed to not plug our UPS into those outlets...not because of redundancy reasons but that they could damage the downwind UPS.

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That makes a lot of sense, thank you
by DerfX / March 24, 2011 8:03 AM PDT

Actually, I do have one of those industrial UPSs but the rest are cheapies. I was just curious and thanks to you, I won't detroy any of them, not that I would have actually tried it anyway, but it's good to know that's it's a bad idea.

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