Different UPS, Different output power capacitys, Same battery???

[Anonymous user]

I have several APC UPS units protecting a variety of servers and workstations I'm in charge of. I've discovered over the years that many use the same battery but claim to have a different output power capacity and was hoping someone could give me clarification as to why. For example - the BE650G and BE750G take the exact same battery but claim 390/450 output watts respectively. I always thought of a battery as having X amount of stored power to release and can only theorize that the higher end UPS units are more efficient at converting the stored energy to 110 vac but would appreciate an accurate answer. Thanks.

[Techie_apc]

The two different UPSs which use the same spec battery run time may vary at different power loads. The Same battery does not mean that the these units should provide the same run time at 100 Watts of load because these units output power capacity is not same.

[Anonymous user]

Then I guess a followup question would be - If the exact same load were drawn from the UPS units which use the same battery and are output rated at 650/750 or 390w/450w, would you expect them to have pretty much the same runtime?

[upsguy_apc]

You are correct that a battery only has a set amout of store power. However it comes down to the math of it. A battery has a set amount of amps per hour that it can provide.

And Power (w) = Volts (v) x Amps (i)

Not to go into the dynamics of how inverters work but your two diffrent UPS sizes the 650/750 or 390w/450w output UPS can use the same battery. The only diffrence will be how long the diffrent UPS can run on the same size battery.

For a very simple example this isn't taking into account for fans or other consumed powers of the UPS but.

390w=110v x 3.5a So the battery will have to provide 3.5a to keep the load up.

450w=110v x 4.1a In the larger UPS the battery has to provide more current to keep the load on and will discharge the battery quicker.


Hope this answers your question.

[Techie_apc]

The BE750G and BE650G UPSs runtime is 7 mins if the connected equipment consumes 300 Watts. Click on the below link to compare these units runtime.
http://www.apc.com/products/runtime_for_extendedruntime.cfm?upsfamily=21

The BE650G supports up to 390 Watts / 650 VA, where as the BE750G supports up to 450 Watts / 750 VA on the battery backup outlets. So if the connected equipment exceeds the UPS rated capacity, it will be overloaded. Therefore, I would size a UPS which meets my requirements(Runtime, Output power, etc.,) in order to protect the equipment from Power Problems.

[Anonymous user]

I'm not disputing your advice to get a UPS that meets the need, I'm just trying to understand why different runtime claims are made for different UPS units that use the exact same battery. Yes, the BE750G and BE650G show the same runtime of 7 mins if the connected equipment consumes 300 Watts but why with a 100 watt load will the BE750G run for 38 mins vs the 32 for the BE650G? Same battery, same stored energy...

[voidstar_apc · Accepted solution]

Yeah, it's a little unusual that a higher power UPS is more efficient. Usually they are less efficient due to larger components or more components, but it's certainly possible the designers went with a more efficient design to get more power.