Battery overcharge?

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Jim Hilburn

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Jun 13, 2017
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Hi, I wrote sometime ago about connecting 2 batteries in parallel. I have that done and everything is working well. I just installed a dc meter so I can easily see what the state of the batteries is and what voltage my chargers are bringing them to.
I just started the engine and saw it was reading 14.6v. Pretty sure it isn't a smart charging system. So the question is can you overcharge during a long days drive?
 
Jim Hilburn said:
Hi, I wrote sometime ago about connecting 2 batteries in parallel. I have that done and everything is working well. I just installed a dc meter so I can easily see what the state of the batteries is and what voltage my chargers are bringing them to. I just started the engine and saw it was reading 14.6v. Pretty sure it isn't a smart charging system. So the question is can you overcharge during a long days drive?
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You will probably find the voltage to drop if you drive longer. Your vehicle regulator should take care of it.

I find in my Chevy vehicles, the battery voltage is highest when I first start the engine and then it starts to drop as I drive.

But keep on eye on it. You don't want it to go much higher than that 14.6 VDC.  But see what it is after a 20 minute drive while the engine is still  running.

-Don-  Yuma, AZ
 
I think I'd let the engine run 20 minutes or so and then check it again.  Should drop off as the batteries charge up.

I think that's a good idea to permanently attach a DC voltmeter right at the batteries.
 
Vehicle alternator charging systems don't use charge regulators, but they do vary the voltage between about 13.5 and 14.6. Doesn't seem to bother the vehicle (chassis) batteries, so I expect the house batteries won't mind much either. It is yet another variable in the life of a battery, though, and yet another reason not to get too hung up on the finer points of battery care & feeding. 
 
Gary RV_Wizard said:
Vehicle alternator charging systems don't use charge regulators, but they do vary the voltage between about 13.5 and 14.6.
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I guess that depends on what you're calling a charge regulator.

Usually, the voltage regulators are built into the alternators these days. 

GM has been doing that for many years.

I think of that as a charge regulator, but not nearly as good as it could be for a RV house battery. But it gets the job done.


-Don-  Yuma, AZ
 
Alternators have a built-in system voltage regulator, but that is NOT at all equivalent to the voltage and amperage regulation of a dedicated battery charging system such as you would find in most any modern battery charger. The alternator just maintains system voltage using a voltage feedback circuit. Since it has to service multiple power needs such as headlights, HVAC fans, interior lighting and so on, it cannot attend solely to battery management. The power sucked by a low battery is just one of many amp loads on the alternator, and not even a priority one.  The alternator cannot tell what the batteries are doing, e.g. accepting bulk charge or floating, and doesn't care. If the system voltage begins to fall, it increases output and drives the voltage up. Whether that voltage change stemmed from the headlights or an internally shorted battery.
 
Thanks everyone. Question answered.
This should probably be a new topic, and one that is often debated but I ended up with a new flooded marine group 27 (Carquest) and another new group 29 (Walmart) and was told it would be OK to parallel them. However, looking to the future, I want to get the most amp hours I can, mainly to be able to run the furnace at night in summer but in high altitude Colorado where it can get pretty chilly. I think these will do that but on to the question.
I have a 23' BT Cruiser and while so many suggest the 2 6v GC solution, my compartment works better with the Group 27 size. So I'm still trying to understand why 2 12v true deep cycles in parallel like a Trojan 27TMH isn't just as good of a solution.
 
while so many suggest the 2 6v GC solution, my compartment works better with the Group 27 size. So I'm still trying to understand why 2 12v true deep cycles in parallel like a Trojan 27TMH isn't just as good of a solution.
Click to expand...

It is just as good, but may be more expensive on a per amp-hour basis. It's not 6v vs 12v that makes the difference - it is the quality of the battery internals, i.e. the deep cycle design.

The two GC2 6v solution is, however, superior in battery life (longevity) than your two 12v marine/RV type batteries. Those batteries are not in the same league in terms of quality.
 
I just did the run the engine test. Went 30 minutes and the voltage went from 14.6 to 14.2 Don't want to use anymore gas to find out if it keeps dropping but it did drop.
Sorryu about the battery question. i realize it's a quagmire.
 
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