Battery overcharging?

Three times this summer I have had to add water to my 1987 Goldwing's
(GL1200A Aspencade) battery. I understand that this is often due to the
battery being overcharged and boiling the electrolyte. The bike's previous
owner installed a volt meter that I observe to indicate between 11 and 12
volts when idling and between 12 and 13 volts when above about 2000 RPM.
With sustained crusing above about 2500 RPM, the meter will rise to just
short of 14 volts and stay there until I have to come to a stop when it
then returns to the idling and mid-RPM levels previously described. I
never observe more than 14 volts indicated.

This seems to say that the voltage regulator is working properly, or does
it? On sustained cruise, should the battery become sufficiently charged
that the regulator no longer needs to supply more than the battery's
nominal 12 volts?

In short, does the described behaviour indicate overcharging that is the
likely cause of the battery boiling off water?

Other than a leak, which I am certain is not occuring, is there another
explanation for the water loss?

 

I am not a battery expert...

It *is* normal for conventional batteries to boil off _some_ water
under normal conditions. How much, I don't know. I'd say having
to add water three times in a season does indicate overcharging,
unless you ride exclusively in very high temperatures.

Here is a simplified chart from Yuasa's technical manual for batteries,
note full charge voltage varies between different battery chemistries:

Battery Voltage Reading Using a Voltmeter
State of Sealed CX &
Charge VRLA YuMicron Conventional
100% 13.0v 12.7v 12.6v
75% 12.8v 12.5v 12.4v
50% 12.5v 12.2v 12.1v
25% 12.2v 12.0v 11.9v
0% 12.0v or less 11.9v or less 11.8v or less

You can find this excellent manual (and other valuable info) at:

http://www.yuasabattery.com/literature.asp

My guess is either the voltmeter isn't reading the true battery voltage
due to voltage drop from being hooked up somewhere other than directly
to the battery, and/or there are some high resistance connections
that need to be cleaned up, and/or the voltage regulator is defective.

Yes, once the battery is fully charged, in an ideal system, the
charging system would deliver (at the battery terminals) exactly the
same voltage as a fully charged battery sitting on the bench with
no load on it. However, due to the fact that battery voltage varies
with temperature, and unless the regulator has a remote temperature
sensor glued to the battery, the reasonable thing to do is to set
the charging voltage to be slightly higher than the exact break
even point. This does mean that some water will be boiled off,
but hopefully not so much as to ruin the battery. The alternative
would be to set the voltage lower than what is needed for full charge,
which would eliminate the problem of boiling off water, but it would
make the battery have less capacity and not last as long.

You are to be commended for actually looking at your battery more
than once per season. I would check all wiring connections carefully
and use a precision voltmeter to check the true charging voltage.
If everything checked out, I'd probably just continue to add water on
a regular basis, or depending on the voltage readings I was seeing,
I might just spring for a sealed VRLA battery, which likes a slightly
higher charging voltage.

 

I think you shouldn't be seeing anything below 12 volts.
You ought to check this with a voltmeter connected directly
to the battery terminals but unless there's a large drain
at the point where the voltmeter's hooked up, those readings
are too low. Check the battery voltage with the bike shut off.
It should be somewhere around 12.5 .

There's a good chance the battery's shot and operating with one cell
completely shorted out and the charging system's working its ass
off to bring 5 cells to a state of charge that would be appropriate
for 6.

You could test the specific gravity of the individual cells with a
hydrometer to confirm this. If you have a friend with a similar bike,
borrowing his battery and checking the behavior would also confirm
the problem. If it were me, I think I'd test and probably replace the
battery.