smiles@ferrari.nmc.ed.ray.com (Kevin Ruddy) (11/06/90)
I'm sorry if this isn't the appropriate group for this kind of query, but I just didn't know what group to use instead. If there's a better group available, please tell me so I can direct myself there ... I'm looking for a UPS for my A/V equipment. I saw one for sale in Crutchfield's for $350. It's a unit that does 20 minutes at 450W. That's more than enough for my uses, as I'm purchasing it primarily to keep all my equipment from forgetting the stuff I store in it, not actually run the equipment. However, I understand that there is more than one kind of UPS technology, and that some types fail when they actually need to be used. What are the different types of UPSes? As an aside, how can I find other manufacturers of small(ish) UPSes that cost less? Any help in this matter would be greatly appreciated. (I don't want to spend that kind of money for the use I have, but I lose power so frequently that it's driving me bananas having to reset all of my equipment.) Oh -- and if the UPS can only handle a 450W throughput, does that mean that I can't pull more than 450W through the box at any given time, or that's just all it'll support if it doesn't have any juice being sent to it? Thanks again. Kevin Ruddy smiles@ferrari.nmc.ed.ray.com
grege@gold.gvg.tek.com (Greg Ebert) (12/01/90)
I know of 2 types of UPS's (Uninterruptible Power Sources).
Standby - As the name implies, it kicks-in when the power drops below spec.
The only problem is that it takes a finite amount of time to
determine if a failure has in fact occurred, and then it has to
start-up and switch from the line to the inverter. I have seen
many UPS's specifying 1/2 cycle switchover (8.3msec).
For very sensitive loads, this may be unacceptable.
Continuous - Always running. The AC line constantly recharges (if necessary)
the battery pack, and the inverter drives the load. Although the
switchover time is zero, thus no glitching, you are always burning
some kWh in the inverter/charging circuit due to circuit losses.
The other thing that might be unsettling is that a failure in the
UPS can disrupt power to the load even though the AC line is OK.
[This happened here a few months ago. Not very funny].
Power ratings are MAXIMUM, and usually apply to resistive (ie unity power
factor) loads; you will need to derate for inductive loads and probably
most power supplies. Trying to squeeze a few extra watts might cause the
beast to shut down or 'fold back' (ie, lower Vout to reduce Pout).
My $0.02: Get a standby UPS for a PC. Price is usually $0.80/watt, or
$350-$400 for 450 W.
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