ECN Forum
Posted By: sparkync UPS back up - 04/11/05 10:59 PM
Anyone know what the standard back up time is for a "ups" serving a 3600 wt. load with 120 volts input and output, or maybe know a site that shows some models? I have a customer that has two pieces of equipment in an X ray dept. and he wants "ups" back up. The name plate on each, calls for a 15 amp. circuit. I didn't see the actual amp draw. These machines work together, and are at the present plugged into a 15 or 20 amp. recpt. That's the reason I doubt that they pull 15 amps apiece, because they would have already tripped the breaker. Any help would be appreciated.. Thanks. Steve
Posted By: NJwirenut Re: UPS back up - 04/11/05 11:25 PM
No real standard--it all depends on the UPS, in particular the size of the battery bank attached to it. Could be anywhere from minutes to hours.

One of the "big names" in the industry is American Power Conversion:
Posted By: e57 Re: UPS back up - 04/11/05 11:32 PM

Click on any model, and the enter your wattage at the upper left of the list, and it will give an estimate of run time.
Posted By: SteveFehr Re: UPS back up - 04/12/05 01:36 AM
The up-time isn't linear; half the load will give more than twice the run-time. Rule of thumb is about 5 minutes minimum for a fully loaded UPS, and about 15 for half-load. Long enough to get the generators up and running, and not much more! But as NJwirenut says, it varies wildly from UPS to UPS and use to use. Know the precise draw of the X-Ray equipment would be crucial to a good estimate; for the price they'll pay for 2000+VA UPS, it's worth it to stick a clamp on for a bit so you don't overspend or underestimate.

Also, don't forget to factor the charging circuit of the UPS in, too! If you suspect those two boxes are drawing 14.5A on a 15A circuit, two UPSs on there charging batteries will push it right over the top. I've spoken to engineers at APC who have stated all their Smart-UPS draw 1A while charging. I asked specifically regarding the SmartUPS 1500 and 700, but they said the while line draws 1A while charging. I assume they meant only up through 2000VA or so, as the 15kVA and others certainly draw more!

[This message has been edited by SteveFehr (edited 04-11-2005).]

[This message has been edited by SteveFehr (edited 04-11-2005).]
Posted By: sparkync Re: UPS back up - 04/12/05 02:24 AM
Thanks for the great information. The site is a good site. As far as the back up time; they don't have a back up generator at this clinic, and the supervisor that's having me look into this for him, is just concerned that this piece of equipment will operate til they get through with the patient. I was really looking for something with a longer back up time though. He had a GE representative try to sell him one for $3000.00 that only has a back up time of 7 minutes. He wanted to see if there was another option. Seems awful stout for just 7 minutes of back up. Another question: I went to the APC site. What is the difference between the "run time" and the "back up time"? They give the "run time" in hours and minutes, and it seems they just give the "back up time" in minutes. For the particular model I'm looking at (APC Smart-UPS 3000 VA-120), they have the "back up" time at half load at 19.2 minutes and at
full load at 5.7 minutes, yet on the other page it shows the run time as 8 hrs. and 51 minutes. Don't exactly understand this ?? Thanks for the help.. Steve
Posted By: SteveFehr Re: UPS back up - 04/12/05 09:49 AM
The max run time listed is with a 50W load, I believe. They have the big chart vs/load here:
© ECN Electrical Forums