I just installed an ampedbike hub motor on my bike, and the throttle has a 3 LED meter that is supposed to gauge battery level, but so far, as long as the power is on, all 3 lights are lit. The way it's supposed to work is that the green shows full charge, the yellow means the battery is getting weak, and the red indicates empty. They're not all supposed to be lit at the same time. The motor and controller came as a kit, and the battery was a separate purchase, but everything is 36V. I'm wondering if the problem has something to do with the fact that I'm running a pingping 36V 20AH lifepo4 instead of lead-acid.
I would eventually like to get a Cycleanalyst, but it's not in the budget for a while. In the meantime, Harborfreight is going to be putting their cheap volt-ohm meters on sale next weekend for $1.99. That I can afford!
My question is; how can I rig up a VOM as a dedicated "fuel gauge" to monitor the state of my battery, as opposed to idiot LED lights that don't function properly anyway? Would I want to monitor voltage or amperage, or could I get 2 VOMs and monitor both?
Thanks in advance for your shared genius.
"I'm wondering if the problem has something to do with the fact that I'm running a pingping 36V 20AH lifepo4 instead of lead-acid."
I think so. lead acid batterys lose voltage almost proportionally to depth of discharge, LiFePO4 have an almost flat discharge curve (the voltage is close to the same for almost the whole capacity of the battery)
I don't think a volt meter will work for you. Your "idiot lights" effectively read voltage. you need a Ahr meter. I have no idea where you could source what you are looking for
"I think so. lead acid batterys lose voltage almost proportionally to depth of discharge, LiFePO4 have an almost flat discharge curve (the voltage is close to the same for almost the whole cappacity of the battery)"
But wouldn't that make the green light stay on all the time instead of all 3?
You said:
It would depend on how the led meter was wired.
You could check the behavior of the LED meter with a VOM and a voltage divider, or you could just use the VOM as your battery meter. You would have to be pretty sharp-eyed to spot when the pack was running out of juice, since the voltage drop at that point is pretty fast. The Harbor Freight meters have enough precision to spot the small Lion voltage drop.
You said:
It would depend on how the led meter was wired.
You could check the behavior of the LED meter with a VOM and a voltage divider, or you could just use the VOM as your battery meter. You would have to be pretty sharp-eyed to spot when the pack was running out of juice, since the voltage drop at that point is pretty fast. The Harbor Freight meters have enough precision to spot the small Lion voltage drop.