DC motors running on batteries

[mjg204]

At the power facility I work at,we have emergency DC equipment that in the event of a power failure,would run off of batteries.Heres the scenario.
3 motors
143 amps
169 amps
22.1 amps
The battery room has 60 cells which are rated from 2.17 to 2.22 volts per cell.How long would these motors be able to run before they would start losing capacity or running down per say?
I found a sticker in the battery room which states 1600 amphr @ 8 hrs or 1400 amphr @ 5 hrs?Could someone try and explain this one to me?It seems that less amps would buy you more time.I am sort of new to this so bear with me.Thanks in advance.

 

[fms]

Ok firstly the 1600 vs 1400 issue is brought about by the fact that most batteries give more of their available capacity when discharged slowly. ie capacity delivered is inversely proportional to discharge rate.

Now for your duration. Assuming that all the motors are running off the full dc voltage (since you havent indicated otherwise) and are wired in parallel, then the situation would be as follows:
The total current drawn by your motors is 143 + 169 + 22.1 amps = 334.1A

So to find the run duration you divide the available ampere hour capacity by the current draw to give (1400/334.1) = 4.19hrs

So you'll get just over 4hrs run time.
PS Ensure that the batteries are deep cycle ones that are designed to be discharged repeatedly to their full capacity.
Hope this helps,
Fionn.

 

[GusD]

Hello mjg204 .

You give the AMP values for your DC motors,but didn't say if this is the actual current drawn by the drives or their nameplate FLC.The amount of total running time is dependent on the motor loads.If loads can be removed during Emergency situations,running time can be extended considerably.The previous post calculations are right on.

GusD