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#73960 by nn5i
Sat Jan 29, 2011 5:00 pm
Bear207 is quite right; and besides, he ably identifies great posts. Staying below the rated capacity of UPSs and other power supplies is a good idea, not particularly for the reasons he states, but (it seems to me) mostly because most of the things you plug into it impose startup loads much larger than their running loads. For example, when you turn on an electric light it will briefly consume up to ten times the power that it uses while operating steady-state. Almost everything that's electric does this, especially if it's got lamps or motors in it. Electronics is not quite as bad (usually), but the ratio can still be large.

Me, I maintain a large Onan generator and don't worry much about power failures. It weighs 800 pounds and occupies a lot of floor space, but it can supply the startup load of the central air conditioning system while also drying clothes in the electric dryer. That's nice, especially in hurricane season.
#74160 by murphy
Tue Feb 01, 2011 10:24 am
Shawn wrote:How to figure out how long an UPS can keep the system alive during a blackout? Is that something on the box or the manual of the UPS unit?

The graph on this page will give you an idea of how it works.

http://www.apc.com/products/resource/in ... _watts=200

Basically the higher the load the quicker it goes dead.
If you put a very light load on a large UPS you can get some reasonably long run times.
#129935 by lbmofo
Fri Jun 19, 2015 5:46 pm
I got my modem, router, ooma, phone base all plugged into the UPS.

I've had issues with the modem knocking itself offline periodically; every time this happens, all my neighbors would still have internet. A lot of times, unplugging the coax, power and plugging back up would have worked (modem gets back online). Often times, I had to wait a few hours or even overnight for this method to work. Later, I found that if I touched the center conductor of the coax cable and then hook up again, the modem goes online right away.

I recently took modem off the UPS and plugged directly into power outlet. Seems to have fixed this issue.

Likely the UPS putting out non sinusoidal power wave causing issues? Not sure.
#129959 by thomasm
Sun Jun 21, 2015 5:28 am
Some devices don't like the momentary interruption when a cheap UPS detects a power problem and turns on its inverter (the circuit that changes the battery voltage to 120 Volts AC). Other devices don't like the square wave produced by cheap UPS's. To solve this problem, professional telecom and computer equipment require a 48 volt DC power source. This standard came from the telephone company which used huge lead-acid batteries to run their central offices. (and still do)

However new devices (cell phone chargers, internet modems, and Ooma) use small plug transformers that use a tiny inverter themselves. This was done originally for cost saving, as the major expense was the heavy copper-laden transformer that was required. But as these devices became more sophisticated, they were able to handle wide variations of input voltage and frequency making them usable anywhere in the world without an adapter. You may notice that some of these devices say they can use any voltage from 100-250 volts! As a side advantage, these devices can get away with much smaller filter capacitors because the output of the inverter is much higher than the 60 Hz line frequency.

These new plug transformers can take a momentary power outage or spike or even the "dirty" AC that the current cheap UPS' deliver. But some can't and those are the ones that cause the device they are powering to lock up when the power fails. Fortunately, the Ooma transformer seems to work fine with my cheapie UPS.

If you have one of the fussy transformers, the answer is to buy a better UPS. The professional models have a ferroresonant transformer which eliminates the momentary outage when switching to battery power. They also have higher quality inverters that produce nearly a perfect sine wave output. But they are expensive!

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