speedyebikenoob said:
I'm running a 60 volt battery on my e bike, and fully charged it's about 67 volts. My battery meter does read in percentage but it also reads out the battery voltage, and I think I would prefer to calculate my range based on that. Does anyone know how I could calculate the amount of watt hours left for a given voltage, for example 62 volts?
You can do it but it's not easy.
First get the discharge curve for your battery at a few standard loads (say, .25C, .5C, 1C.) Then do the same at a low rate but at different temperatures (three temperatures that represent lowest, highest and average temperatures.) With that data you should be able to do a linear interpolation at each point to synthesize a discharge curve for your current temperature and discharge rate.
Then you measure temperature, current and voltage, plug them into your curve, and look up remaining energy from the curve.
You may also want to add an ESR and a total-capacity variable, since ESR increases and capacity declines with time. Then you tweak them as the battery ages. Alternatively repeat the tests again.
I've gotten within about 5% of coulomb counting using the above method.
Also, my battery has 24 amp hours in it, so 60 x 24 should give me 1440 wh right? But what about if it's completely charged? Shouldn't it be 67 x 24 which is 1608 wh?
To get an accurate number, integrate the area under the discharge curve. A simpler way is to just use the average voltage and you'll be close.