Re: Any point in knowing the charge left in the battery?
Originally Posted by SVOboy
I found a little write-up showing how to make a meter for this and I was wondering if there was really any practical reason for doing this in terms of gas mileage xor anything else.
Do you mean a volt meter or a meter to determine the state of charge of the battery? Normally you wouldn't care much about this unless you plan of shutting your engine off at a stop light or coasting with headlights, stereo, windshield wipers on, and then starting up again with the starter. All of those things will drain your battery. If your trips are relatively short, your alternator may not be able to charge your battery sufficiently. Day after day the charge drops until you can not longer crank it over. In that case, you might find a voltmater handy. If you drop between 12V with no load, you really should charge your battery.
It's just a schematic, almost exactly like the afr thing but it reads the range of voltage of the battery rather than 0-1.
Post up the schematic. It would be very beneficial to those who want to do an EV conversion someday. EV fuel gauge.
IMHO (in my honest opinion), a voltmeter wouldn't make a very good EV fuel gauge. Batteries in general, and NiMH chemistries in particular provide most of thier capacity in a fairly tight voltage range, typically 1.25 to 1.0 volts per cell. The perfect analogy would be a narrowband O2 sensor. A voltmeter would really only show full charge, charge but not fully charged, and dead battery. Perhaps the new Lithium ion chemistry is different. I don't know much about LI except that they can get very hot and are very explosive if charged or discharged properly.
SOC State Of Charge in pb lead batteries 13.5 float voltage 12.9-12.8 full 10.4 dead when measured no load resting for several minutes. Li-Ion 4.25-4.20 full 3.0 dead pretty linear again measured no load. The Li-Ion often use an alcohol based electrolyte DUH Flamable!! and Lithium reacts with water.