ekingsting there are some very cheap ($25) watts up clones on Hobbycity, seems like great value, price of a few cups of coffee.
Kevin wrote:I'm a newbie to electronics. I have the same motor as you. My battery is 36V 20amps. So how do I calculate how many watts my battery should be able to supply? Do I sound like a moron? Is this really simple algebra?
That depends on battery chemistry - what C rate the battery can discharge at reasonably.
Volts x Amps = Watts
eg If you have cheap 36 V 20 Ah LiFePO4 that can do 2C you can safely draw a max continuous 40Amps (2C x 20Ah).
So you could draw 36V x 40 A = 1440 W.
LiPo can do much higher C rates so supply higher watts.
Remember what a battery can PEAK discharge is very different to what battery, BMS, controller or motor may be able to handle for sustained periods, which is why watt ratings are generally understated by manufacturers. Ping rates his 36V20Ah battery for 800W which looks conservative, but will go easy on the pack (it's rated at only 1C continuous, 2C Peak).
Not sure if there is a rule but I consider Peak is 10sec to 1 minute, burst is 1 sec.
Volts x Amp hours = Watt Hours, which if you know how many Wh you use can estimate run time. You have 720 Wh (less if you run lead acid batteries which sag). If you average 15 Wh per kilometre you might go 48 km.