Overcharging house battery with van battery

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Virgil Jones

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I really appreciate the video on installing a solenoid between the van and house battery.
  I am in the process of building a campervan (just bought the van). 
I have watched the video and searched the forums and (maybe I am missing it)  cannot find the answer to...

If driving a long day, can I overcharge the house battery with the van battery.  In the video the van battery power is being routed directly into the house battery with only fuses and solenoid between.
Thanks
 
Virgil Jones said:
I really appreciate the video on installing a solenoid between the van and house battery.
  I am in the process of building a campervan (just bought the van). 
I have watched the video and searched the forums and (maybe I am missing it)  cannot find the answer to...

If driving a long day, can I overcharge the house battery with the van battery.  In the video the van battery power is being routed directly into the house battery with only fuses and solenoid between.
Thanks

Possible yes. Likely, no.

The vehicle's voltage regulator is timid, designed to insure the hot battery is not constantly overcharged.

They usually drop to a safe 13.7ish volts prematurely, as they simply never were expected to recharge depleted house batteries which would want 14.4v for hours.

If you are concerned by this possibility, put a Voltmeter on your dashboard whose voltage sense lines are on the house battery, and after driving for 4 hours, and seeing  of 14.2 volts or higher the whole time, then you might be in the full charge nearing overcharge arean.

But it is far far more likely your house battery will be chronically undercharged as opposed to overcharged.

Battery temperature plays a big part too.  Without knowing that variable on a longer drive, guesses are entirely meaningless

The overcharging concern when driving is 'Almost' a non issue.  The actual voltage allowed, its duration,  and battery temperature would need to be known to declare it to be an issue.

And if it were a major issue, every car driven through the desert, would need a new battery at the other end.
 
No one has yet reported encountering something like that.

When the house battery is fully charged, it will reach a state of equilibrium with the engine battery, and no more current should flow.  The voltage regulator will cut the alternator output back to just what is needed to run the vehicle, and neither battery will continue to charge.
 
More likely your alternator will burn up before the house bank is fried.
 
Also, the assumption is that the vehicle charging system is just topping off your house battery, and that you have some other method -- solar, shore power, whatever -- doing most of the charging. Unless you're driving a lot every day, the alternator doesn't have enough time to recharge a house battery that's down to, say, 70% charge.
 
MrNoodly said:
Also, the assumption is that the vehicle charging system is just topping off your house battery, and that you have some other method -- solar, shore power, whatever -- doing most of the charging. Unless you're driving a lot every day, the alternator doesn't have enough time to recharge a house battery that's down to, say, 70% charge.

I'm putting 400 watts of solar panels on the roof.  This is part of what brought the concern.
 
Virgil Jones said:
I'm putting 400 watts of solar panels on the roof.  This is part of what brought the concern.

If your charge controller is like mine, it disengages itself when it senses an another charging source.
 
MrNoodly said:
If your charge controller is like mine, it disengages itself when it senses an another charging source.

Can't speak for every product, but usually charging sources will work together until the battery voltage, or the voltage seen at the charging source output terminals, on one of the charging sources, reaches or exceeds its programmed setpoint.

For example, if my solar controller is set for 14.4v absorption and battery is depleted and I then start engine, the solar and alternator combine their current until that 14.4v threshold is reached/exceeded, and only then the solar controller stops providing current.

Now the alternator can provide huge amperage and can quickly bring the  only minorly depleted battery voltage upto and past 14.4v, so it would appear the solar controller instantly shuts off, but if the battery were well depleted, and the vehicles voltage regulator decided to only go to 14.2v, while the solar was still seeking 14.4v, then both should combine their current for a period of time until the high amperage of the alternator and the Solar,were able to bring the well depleted battery to or above the 14.4v absorption voltage setpoint of the controller.

The voltage regulation of the alternator and solar controller and any other possible charging sources can all play a weird game when all have slightly different setpoints.  usually it is of no consequence to recharge time as the battery is up in the 80% range when they all start trying to confuse each other, and one then does not require multiple charging sources as the acceptance rate of the battery is limited at that point.

How much amperage is required to instantly, or nearly instantly bring a 50% depleted battery to absorption voltage varies greatly, with battery capacity, and battery health, and the cabling between alternator and battery all playing a huge part in the variability.

When new my group27 AGM maxed out my alternator at ~106 amps before voltage 
Now with ~400 deep cycles on it 3 years later it only takes about 85 amps to instantly bring it to 14.5v 

My vehicle takes 8.2 amps to run the engine at idle, and 12.2 amps at 2000 rpm.  I can lower my vehicles voltage regulator to the mid 13's, and if the Sun is high, my solar panel can power a portion of my Van engine electrical needs.

It runs amazingly smoothly and is quicker revving when the alternator is not having to make any/little juice, compared to when it is cranking out 64 amps to power the engine and recharge a depleted battery.

each ~25 amps the alternator makes requires ~ 1 engine HP.
 

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