How smart is a computer-type UPS?

I have one of those grey box UPS that is supposed to take over in case of a power outage, connected to the VCR in the lving room. Recently, I replaced the batteries due to problems when the power went out. (The UPS did not keep power top the VCR.)

Since then, I've noticd a peculiarity which I don't fully understand.

If I shut off the circuit at the breaker panel which also feeds the UPS & VCR, the resultant power outage - even if less than 15 minutes, and with nothing being recordrd on the VCR - invariably leads to all power being removed from the VCR, and the clock as well as all programming all go to Electron Pergatory.

But if there is a power outage, lasting about the same time, the UPS does lick in and saves the clock and will continue to record whatever is being taped by the UPS.

As the Ancient Chinese Detective Harry Hoo used to say: "Two Possibilities." Either my UPS wants to see the power drop off in a semi-relaxed slope, and the abrupt slope of the panel breaker opening is just too fast for the thing to respond; or is there another explanation?

HR.

Reply to
Rowbotth
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I vote for another explanation. I don't know what it is, but knowing how UPS work (and having tested many) the explanations you presented do not work.

Charles Perry P.E.

Reply to
Charles Perry

Plug a night light into the UPS along with the VCR. That will cut the backup time a little but you can see if the power is steady. An AM radio would be better.

Reply to
Gfretwell

Lacking sophisticated measurement equipment, a nightlight on the output of the UPS will let you know whether the UPS is actually working. If the light is on and relatively stable (in brightness), the UPS is working.

Charles Perry P.E.

Reply to
Charles Perry

I don't have a full explanation for you, but I noted that my UPS does not kick in unless there is an active load on it at the time of power-loss. In other words; if I plug a lamp into the UPS and then turn the lamp on, and then unplug the UPS from the wall, the lamp will stay on. However, if I leave the lamp off and then pull the plug on the UPS, I can't turn the light back on.

I learned this one day when the power went out and I didn't have a flash light. I thought I could use my UPS as a battery for the lamp, but it didn't work. I later experimented to find out why.

This may not explain your situation, but perhaps a VCR that is not recording does not give enough of a load to keep the UPS active; while a VCR that is recording is enough of a load.

Steve B.

Reply to
Steven Bastien

A lot depends on the UPS that you use. Some are better than others.. Some, like switching supplies, require a minimum load to keep operation in a power fault condition, some do not. Some have a slew rate built in, some do not. A UPS does not "switch" to battery, it is always on battery (keeps a trickle charge on the battery from the DC Link. I suppose there may be some low cost cheapo UPSs that actually do switch, but I'd advise against them for the very reason you had a problem with utility loss v.s. tripped breaker. The ones that actually do switch (very bad design) may depend on a slew factor, provided by a discharge path from a charged RC at the input. If the utility dies faster than the circuit can sense it, the UPS won't work. Personally, you couldn't pay me to use a Slew Rated UPS. Very undependable. You get what you pay for.

A UPS works by rectifiying the utility AC to provide a DC Link which performs two functions. The DC Link provides a trickle charge to the batteries and for the Inverters on the output which change it back to AC. The resulting DC Link is typically 5-10% volts higher than is necessary for the inverters, in order to do both functions. When the input utility drops off, the DC Link continues at battery level, it does not switch, providing sufficient DC from the batteries to the Inverters. When utility power is restored, the rectified utility resumes and the DC Link rises enough to do both functions once again.

In the type that require a minimum load for proper operation, there will be a Current Transformer that provides Load Sensing. In the absence of a load the Inverters are shut off to provide maximum charge to the batteries (in an industrial UPS). In a simple store bought UPS for computers, depending on the brand and model, this may not be true.

I have had great success with all Belkin UPSs. In applications where a load may not be present at all times, I have added a small load bank to guarantee a minimum current draw of 1A to ensure continued operation for very light loads. Check with the manufacturer of your UPS to determine whether a load is required for operation.

Reply to
EEng

Nearly all small UPS (like those sold in office/computer supply stores) are standye, meaning they switch to battery when the power goes off. The short switching time does not effect computers since PC powe supplies will actually ride through a few cycles without a UPS.

Charles Perry P.E.

Reply to
Charles Perry

Right you are Charles, and the very reason I won't use them. Obviously the OP is having a problem with one that doesn't switch fast enough or his load hasn't the input capacitance to hold up the line long enough for the UPS to kick in. I think its a piss poor design. Belkin makes a low cost 1KVA industrial UPS with a Continuance DC link (no switching) that performs beautifully, and is not load dependant. Never had a problem. My UPS experience comes from servicing an 11 state region for Exide Electronics many years ago. We were installing

2.4MKVA UPSs on military bases. Beal AFB had the only 9.6MKVA UPS in existence. I don't know if they've gotten larger since.
Reply to
EEng

It is hard to find small (say less than 1KVA) true double-conversion UPS nowadays since 99% of them are of the "standby" types where inverter only turns on when there is power outage. Short duration (less than 1 cycle or about 17 milliseconds) break in power does not cause problems for switchmode power supplies used in computers & most modern electronic devices. With 97%+ energy efficiency and very low cost ($50 to $300) it is hard to beat at the low end.

Many medium sized UPS's (from 1 to 3KVA) use "line-interactive" or "ferroresonant" designs which can "fill-in" the missing 1 AC cycle and also provide isolation/active voltage regulation all the time. Since only a single AC to AC power conversion takes place, conversion efficiency is around 90%.

Larger UPS's (3KVA and larger) mostly use true double-conversion designs because breaks/makes of 30A + current can damage not only connected equipment but also the UPS. Power conversion efficiency is rather poor at 85% or so since AC to DC and DC to AC conversion must always take place at full power. Air exhaust fan must be on all the time (noisy) and they are rather expensive machines, but this is the best design for larger UPS's.

These different topologies were developed over the past 30 years & each found their sweet spot (optimum performance vs. cost is realized) after millions of units were installed. One cannot compare motorcycles, passenger car and bus engines with a broad, sweeping statement. Each engine was optimized for the application at hand - so were the UPS topologies chosen for the types of equipment to be protected!

Reply to
Nam Paik

OK, the comments about the security and reliability are understood, but as I understood this, they are sort of being ignored. I'm wanting to keep power to a VCR, not keep power to the NSA Computers. There is a difference, you know.

As for why the thing seems to vomit when I open a breaker in the house panel, here's a theory. (I know it sounds silly; then again they used to make stuff that would switch remotely devices, and this system which used a transformer as the demarcation...)

So is it possible that the UPS is looking for a circuit on the feeder - like through a transformer winding - and if it doesn't see this, it responds to an unknown input by staying off? That would fulfill the Shrelock Holmes definition of "Truth", but I don't know if the UPS is that sophisiticated.

(Reply to my email with any answers, please. Vacation! (How would Charles Shultz do a dancing Snoopy here, anyway?)

HR.

Reply to
Rowbotth

Your ni-cad batteries need exercise and they are improving as you cycle them.

Reply to
Gym Bob

Nope. The UPS is not looking for a circuit. Some high end ones will not start up if they are plugged into an improperly wired plug. Your's is not having that problem. Have you tried testing it by simply unplugging it from the wall?

Charles Perry P.E.

Reply to
Charles Perry

You might want to plug in a 100 watt light bulb to the UPS output socket (along with the VCR). Adding such "dummy loads" have been known to improve the stability & waveform quality of low-cost UPS, inverter, power supply products (some units specify minimum load of 10 to 20% before system works properly).

Good Luck!

Reply to
Nam Paik

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