Ok guys now I know that I should have a better grasp on this stuff by now, but I’m still trying to figure these battery ratings out and how they relate to my expected range, so here goes. My pack is made up or the crown GC 225 ( which by the way I’m very happy with they don’t gas much and I’ve found no weak cells!) their rating is 20ah 225, 5ah 175 with a RC of 115 minutes at 75amp. So if the RC =143 amps and if I’m toolin down the road drawing around 100 amps could I expect around 100 minutes running time, conversely if I’m drawing 200 amps could I expect 50 minutes, 300 amps =25 minutes ect? I know that there exist an inverse proportion between current draw and current availability with the traction pack but I just can’t seem to get it. Major, if your there be gentle not all of us are engineers! By the way I did move my ampmeter shunt to the batt. Side and it doesn’t spike at takeoff anymore but I still tend to draw between 100-200 amps with gentle acceleration and speed. Any help?
Hi ace,
I'll try to be gentle
Do you know about Peurket's Law?
http://en.wikipedia.org/wiki/Peukert's_law
As the rate increases, the battery's available capacity decreases.
Or in other words: The higher the current drawn from the battery, the less Ampere hours (AH) you can get from it.
It would appear your batteries are rated at 225Ah at the 20 hour rate which would mean you can draw 11.25 Amperes (A) from them for 20 hours. When you draw more current, you get less Ah. The other spec is RC (reserve capacity) and that figures to 143Ah at 75A. A lot less than the 225AH rating, right? And then add into the mix that you really do not want to fully discharge your batteries to keep them from early demise.
So to keep it simple, and avoid doing the Peurkert math, let's just say you can use 120 Ah at an average battery current of 75A. That would be 75A for 1.6 hours (96 minutes). Now then, if your average speed is 30 mph at the 75A, you could travel 48 miles.
This is not an exact calculation, but meant to show you what is involved in estimating your range. Gentle enough?
major
