1982 Chevy P30 454 overcharging engine battery

[Ped8015]

Hey all. My new alternator is overcharging my engine battery.  I read about 16V on they battery with my meter and my dash indicates about 16V. Even if I charge my battery with an external charger it still reads 16V when I start the engine. It still reads 16V after driving.

I have a 1982 Chevy 454 P30 Winnebago Chieftain.  This started a few months back when the engine battery was not charging so I replaced the alternator with a new unit from Oriellys. Found the bad alternator by swapping battery and by checking voltages. After replacing the alternator the battery would charge but it would be over 16V. I thought over time it would go back to normal... Wishful thinking.

After a month of use the old battery quit working.  I am thinking it is due to overcharging or maybe it was 6 years old.  I replaced it with a 860CCA and everything works fine but I still have about 16V on the battery and meter when connected to the battery.

The RV still starts and still charges both engine and house batteries.  I know 16V is too much.  How should I troubleshoot this and f[/size]ix this?  I was thinking of simply placing a voltage regulator on the main wire coming out the alternator but I am sure there are better ways.Thank you and please ask any question. Will not hurt my feelings.Phill

[BrandonMc]

Is the battery 16V or 12V while the engine is off?
Your alternator may run 16V while the engine is running and charging the battery.


I think you are only supposed to see the alternator charge the Coach battery if the Dual switch is active

[tmsnyder]

It sounds like you got a bad rebuilt alternator.  Was there any warranty on it? I would take it back.


Also check to make sure the ground at the alternator is equal to the ground at the battery.  0V between the "-" terminal on the battery and the ground at the alternator.

[BrandonMc]

I had to go looking for some more specific information, maybe this can help

14.2 volts

A car alternator needs to be putting out at least 13-14 volts (ideally between 13.8 and 14.2 volts) to effectively charge a 12 volt car battery. If the alternator is putting out too much voltage (15+ volts), it is likely your battery acid will boil over out of the battery.

http://www.todayifoundout.com/index.php/2010/01/how-to-test-a-car-alternator/

[Ped8015]

Did some testing today.  Went through all connections.  Replaced the ground cable from the batter to the frame.  Used a better multimeter and the battery is 12.6 with engine off.  14.6 with it running.    It is a 12V battery. 

I am wondering if the alternator needs to be replaced. I do not think there is any other electrical hardware that regulates the voltage on this P30.

[Ped8015]

Thank you for the replies!!!  Any help is much appreciated. 

[DRMousseau]

Did some testing today.  Went through all connections.  Replaced the ground cable from the batter to the frame.  Used a better multimeter and the battery is 12.6 with engine off.  14.6 with it running.    It is a 12V battery. 

I am wondering if the alternator needs to be replaced. I do not think there is any other electrical hardware that regulates the voltage on this P30.

12.6V on the fully charged resting battery is good. Without starting engine, turn on the headlights,... good battery shouldn't drop much. Anything that quickly drops below 10V from that 12.6V, is usually evidence of a bad cell and need of a new battery. If lights are dim or don't work, yet battery reads good voltage,... then ya have a bad cable connection and it won't start either. With a good battery and connections, you should be able to start engine WITH the headlights on,... if not, then a weak battery (if lights dim) or bad connection (if lights go out) can quickly help you look for problems.




That 14.6V while running, is a normal charging voltage from alternators at running speed, and should NEVER be more. And certainly not anywhere even near that 16V you mentioned in your opening post!!! I wondered of a faulty alternator when I saw that. It WILL cause batteries to boil and swell, and will cause excess hydrogen that can ignite with the spark of a slightly loose battery cable when starting and,... BOOM! New battery needed! Careful around these conditions. At a slow idle, charging voltage from alternator is usually less on a fully charged battery, about 13.6V and often less,... because of slower engine RPM. Rev it up, and it should increase and settle solid at that 14.6V and never more.


Battery condition AND those connections can affect this. A battery hydrometer is cheap, and if your battery ISN'T one of those sealed maintenance-free ones, you can easily assess it's charge and condition with a hydrometer. Otherwise it's mostly a guess relative to voltage readings in various manner. While battery terminal connections and cable ends MIGHT be cleaned and tightened occasionally,... they're usually neglected until problems occur. WORSE for other ends and connections that might never even be seen. These problems don't show up till battery or system failure. Changing weather can have an instant impact on these connections, usually in sudden damp or wet weather, or sudden cold conditions. You can drive all summer, unaware of a problem,... then the first week of autumn rains or an overnight freeze and suddenly, it appears. This can also show up after a long period of storage or disuse. "It was fine when I parked it last month,.. now it won't start!"

[Rickf1985]

14.6 is the top end of the normal scale. It is a far cry from the 16 volts you were mentioning in the beginning. The new ground cable may have solved the problem since a bad engine to body ground would give a voltage differential at the alternator as someone else mentioned. I prefer to see 14.5 volts but right now you can be out of panic mode and not be afraid to drive it. You are lucky that at a constant 16 volts it did not blow the battery, I have seen that more than once. Acid boils out and then battery shorts out and BOOM! A short circuit in a hydrogen gas environment is usually pretty exiting. What I would do now is visit a couple different Advance or Auto Zone stores and have them do a free charging system check and see what they come up with. Get a couple different opinions. As long as they are all in the 14.6 and down range you are good but anything above 14.6 get the alternator replaced, the regulator is bad.

[Mike_Rosoft]

I had a similar problem, I also dried out my main and coach batteries and was going down the replace alternator route. My friendly alternator rebuilder suggested I test / replace the mechanical regulator with a new electronic one as the alternator I gave him did not have a regulator built-in and seemed ok!  (I replaced my old mechanical one with a sterling products marine regulator). Not had a problem since and the voltage is kept at a steady 14.2V on charge. (different type of batteries have different charge voltages and currents none of them are 16V!!!!)

[Rickf1985]

I have not seen a GM product with a mechanical regulator since the 60's! Other than very high amperage alternators in the 200 amp plus range. All 10si and 12si alternators have internal regulators.