The Stovebolt Site Forums The Shop Area The Electrical Bay Bench charging an 8volt battery?

When the only choices are 12v and 6v on your battery
charger which one should you choose???

The battery is discharged down to around 2.5v so I've
started it out in the 6v mode. It's showing over 9v
draw so I'm assuming that it will charge it to it's
8v potential. Any other observations or thoughts?

Oh, and why do I have an 8v battery when both my
trucks are 6v?? Well when I got the '54 it had an 8v
battery in it, which I promptly took out and cleaned
all the electrical connections, putting it back to
6v. Thought I might be able to use the 8v at the
radio bench for a power supply.

Denny G

Thumbrule is 2.51 volt per cell on standard wet cell batteries. Will be close enough to get it charged and reduce and or back drive sulfation.

Call factory to get their recommended number for regular charge equalizer charge and for temperature correction.

Dan Bentler

Your talking about the charging rate right Dan? Fully charged it
should read about 8.4v correct?
I've already seeing it drop off with the charger on it to 8.68v
so it looks like I should be able to get it pretty close to
it's full charge in the 6v charging mode.
Tks
DG

I would call the charging rate the current.

The charging voltage at 2.51 V per cell on a 4 cell battery (nominal 8V) should be about 10.04 volt.

If you do not have a good voltmeter then pull the cell caps and in the later stage of the charge see if there is bubbling in each cell. One bubble per second or so is fine and indicates you have the battery up to full charging voltage (TVG Temperature Voltage Gassing). It does need to be a rolling boil.

At approx 3 to 5% of battery ampere rating ie say 100 amp hour referanced to 20 hour discharge (4 hr is also common) then you can shut down the charge. This is NOT the cold crank rating.

Watch battery temperature and shut charge down at around 100 F. At this conservative temp you will do no harm to battery. Let cool and restart charge when cooled down to say 80.

Maker of battery will give you all the more accurate values for that particular battery but these numbers are pretty good to use as guidelines.

At rest say 4 hours after charge termination voltage should be about 2.1 V per cell or 8.4 V

Dan Bentler

And that's just about exactly what I've got. I pulled the
battery off the charger last night, put a little load on it to
drain of any surface charge and it measures 8.48v this morning.
Jerry pointed out as we've always been taught by the battery
manufacturers, that the real test for a fully charged battery
is the Specific Gravity. I haven't checked that yet since
because of my move I CAIN'T FIND MY DANG HYDROMETER!

Looks like this little old 10A Sears and Sawbuck charger does
the job on an 8v bat. just fine. Jerry also suggested the I
might use a large pot to drop the voltage in the 12v mode. I
might try that next time it comes up as I've got a few big pots
that I picked up in my years of radio swap meets.

Well, I'm all charged up, and now I know.
Denny G

The best measurement for state of charge is with hydrometer - no doubt about it.

The best test of capacity is a test discharge. PITA takes 4 hours to do but that is the best way to go.

I also like the 25 A discharge done for several minutes. If battery (nominal 12 V) volt stays above 10.5 then should be good. Not the best test but fairly quick and weeds out a bad battery pretty quick.

Dan Bentler