Battery "State of Charge" meter vs hydrometer (long winded techie rambling)

[mike davis]

....I thought I would bring it up again to seek some opinions from the "techies"....
Speaking to you now is an electrical engineer with electric vehicle and off grid experience.
....The background is that battery state of charge is almost impossible to determine with a voltmeter...

From a practical standpoint a volt meter is the most useful tool in the kit.

I have a line powered 4 - 40 Volt digital meter (alliedelec.com #527-0050) continuously monitoring the Bus 'bus' voltage which I can supply from the house battery, the starting battery, both, or nothing.

When the Bus is siting in my drive unused both batteries are connected to the bus in parallel and in parallel with a 3 Amp 25.5 Volt (my Bus is a 24 Volt system) ac line powered power supply.  Thus a quick glance at the meter tells me battery health.  When fully charged the reading will be 25.5 +/- about 0.4 Volts depending on temperature.  A different reading may mean the batterys are not yet charged or you have a problem.

When I'm driving I should see somewhat more than 27 Volts.

When off grid and using only the house battery the voltage will decline from about 25.5 Volts down to about 24 Volts, which is as low as I'll allow it to go for battery lifetime considerations.

I don't care what % of charge remains because I don't know how many Amp hours are in the fully charged battery to start with.  Every time you cycle the battery it looses some if its full charge capacity.  In my particular case a new house batery will drop from 25.5 to 24 Volts over a weeks time.  An old battery will make that plunge in a couple of days.

I recommend you place a volt meter someplace where you can take a glance at it every time you walk by.  You will soon learn the ebb and flow of your battery system without having to fuss around with messy, hard to interpret hydrometers.

-RickBrown in Reno, NV

here is a link to 2 cheep and easy inline volt meters

http://www.cetsolar.com/cigplugs.htm

look down the page

                     mike

[Fred Mc]

Rick, on the voltmeter that you use are the wires connected directly to the batteries or can you connect into the house wiring system (24 v) anywhere?

Thanks

Fred Mc.