Estimating UPS run-time?

RT(hrs) = 0.8 * 20 * 24 / 950 = 0.4

What's the prize?

John

Insufficient data - what's plugged into it? The rating does not patter, the actual load is what matters.

If at full load, 20 x 24 / 950 gives the time you'll never actually get, due to both inefficiency and the fact that the 20AH batteries only give

20 AH of it's withdrawn over 20 hours. Suck it out in half an hour and you get much less, so you would not get half an hour even with 100% efficiency.

So, you won't get 30 minutes and 30 seconds. 15 min might be a good practical guess, but of course the batteries in a UPS are usually so abused (cheap charging circuits designed to kill batteries and make you buy new ones) that 5 minutes would be doubtful after a year or two.

--
Cats, coffee, chocolate...vices to live by

Insufficient data - what's plugged into it? The rating does not patter, the actual load is what matters.

If at full load, 20 x 24 / 950 gives the time you'll never actually get, due to both inefficiency and the fact that the 20AH batteries only give

20 AH of it's withdrawn over 20 hours. Suck it out in half an hour and you get much less, so you would not get half an hour even with 100% efficiency.

So, you won't get 30 minutes and 30 seconds. 15 min might be a good practical guess, but of course the batteries in a UPS are usually so abused (cheap charging circuits designed to kill batteries and make you buy new ones) that 5 minutes would be doubtful after a year or two.

--
Cats, coffee, chocolate...vices to live by

1. Connect intended load to UPS.

1. Unplug UPS.

2. Start stopwatch.

1. When UPS shuts down or load no longer works properly, stop stopwatch and read backup time available.

That's the best case estimate. It's an estimate because the battery life will not be the same the next time the UPS is used. Inexpensive UPS units often trade quick charging of the batteries (to have full UPS power available again as quickly as possible) for battery life (a properly controlled charge takes longer but preserves battery life).

See the discharge chart on page 2 or this document

for info on discharge rate versus power available. A 26AH battery (20 hour rating) can only provide 15.6AH when discharged in one hour. That's only 60% of the 20 hour rating. At an equivalent discharge rate, your

20AH battery can only provide 12AH. 24V * 12AH = Watt hours - that's perhaps 15-20 minutes. Most UPS units are designed to take a load until

1. the load can be shutdown properly or
2. a slower backup device (generator) can be brought online.

If you want long-term power from batteries, you need BIG batteries and an inverter than can run at full power for days without overheating. Your UPS is probably only rated for some minutes of power and will overheat and shutdown (or die) if you try to run it at 950VA for several hours.

I have a 180 watt APC UPS that powers my home network (wireless router and a 16 port switch). It's good for something over an hour with a load of less than 50 watts. This is normally adequate, as outages are infrequent and usually short.

How do I know it runs an hour plus? A windstorm took out power to the area for 16 hours last July. I have an 80AH car battery that I could connect to this UPS, but I think the UPS generates too much heat to allow it to run for 8 hours and I can live without the internet for a few hours ;-)

I fired up the smaller of my two generators intermittently - just enough to keep the fridge and freezer cool. I used a 12 volt fan connected to an 8AH gell cell battery (good for about 24 hours use) instead of the ceiling fan in the bedroom for people cooling and I cooked on the grill outside to avoid heating the house.

John

Can u plz tel me Why the power in UPS is measured in VA instead of WATTS? i'm a begineer,Plz help me out?

I cn hrdl rd/ndrst wt y mewn?

It's about reactive power factor; if it's a capacitive or inductive load instead of a pure resistance, the reactive power can exceed the real power, and the rest is dissipated in the source. Battery capacity is measured in Amp-hours; even if you're driving a pure inductance or pure capacitance, which draws no "real" power, the battery still has to provide the current.

And, since this isn't the twitland, please speak English rather than twitspeak.

Good Luck! Rich

How much are you paying for this school? We generally don't do other people's homework for free.

Good Luck! Rich

24 950 WATT / 24 VOLT =3D X AMPS

t =3D 20 AH / X =3D 20 * 24 / 950 =3D 480/950 =3D .505 HOURS

Considerably shorter than that. The 20 AH rating is what the battery can provide over 20 hours - 1 amp x 20 hours. When you discharge it at a higher rate, in this case at about 39.6 amps or ~ 40 times the nominal 20 AH rate, it cannot provide anywhere near the full 20 AH rating.

Ed