Quote:
Originally Posted by Chris is me
That being said this is a valid concern - does anyone know how I could predict battery discharge rates using math? I have no idea how to do it.
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Looking at the spec. sheet for the batteries:
http://www.alliedelec.com/Images/Pro...A/610-0002.PDF
The last graph gives discharge characteristics. The C-rate or CA on the graph can be roughly calculated as Current Load/Rated Amp Hours so at your quoted 60 amps
CA~3.4
Visually extending the curve; you're right on the edge.
If you current usage rises to 80 amps with a greedy manipulator you'll almost certainly run of battery life.
Disclaimer: I'm not an expert on batteries and am only ~70% sure my interpretation of the C-Rate is correct.
Another method you could try is using Peukert's law.
Where the time to full discharge is approximated by:
t=H(C/(IH))^k
Here t is time to full discharge, C is the rated capacity, I is the current, H is the rated discharge time and k ranges between 1.1-1.5 for lead acid batteries (it is generally empirically determined, but we can use the discharge curves to estimate it)
Using the spec sheet again:
C=17.4 H=20 hours I=60 amps k~1.34
t~4.1 minutes
For 80 amps
t~2.8 minutes
So it all comes down to how much you want to trust the math. To me it looks like a very border line case especially if you have a high current (always on rollers, heavy lifting etc.) manipulator.
For more information:
http://en.wikipedia.org/wiki/Peukert's_law