Advice on controlling Alternator to House battery charging?

MrWizard wrote:
solar controller not needed between isolator and battery, won't help anything
and might burn out if battery is really low, when you start the engine

the alternator will NOT over charge your new AGM house battery

OP here, thank you this reassures me!

I’ve replaced those crummy battery isolators with solenoids. It’s a big improvement.
As mentioned, make sure to buy a continuous-duty solenoid.
Another benefit is the options it gives you. I wired a switch on mine to chose either manual both-battery-connect or auto-connect. I used an oil pressure switch to activate my auto-connect so it doesn’t connect the two unless the engine is actually running. Otherwise, if you just wire it to the ignition, if you ever accidentally leave it on you’ll drain both batteries.
Also, if your house battery is dead it puts a strain on your starting battery when you try to start the engine.
It’s easy to do, just remember the oil pressure switch switches a ground wire instead of a “+” wire.

Why don’t you add a panel and upgrade the controller? No supplement will be needed most days. You are already over the general guideline of one solar watt for each battery AH.

MrWizard wrote:

the alternator will NOT over charge your new AGM house battery

This.

IF.....all your batteries are receiving a voltage high enough to charge while going down the road, you probably should NOT mess with anything.

X 2 on getting rid of the diode isolator.

Your issue will be undercharging, not overcharging, as your voltage regulator is likey allowing only high 13v when it and the alternator are hot.

AGMs want to be brough to 14.4 to 14.7ish until amperage tapers to very low numbers. 13.7 will slow amperage the battery accepts by about 2/3, and your diode based isolator knocks off at least 0.5v from whatever the alternator is allowed to make.

Get a continuous duty solenoid and trigger it with the ignition, and hope the solar can hold the battery in mid 14's until the AGm is full after you are done driving. SAve the big finnned heatsink from the diode based isolator, it will be good for something somewhere, but not for isolating your house battery.


The Mopar voltage regulator can be replaced with one that is adjustable voltage. My 89 dodge is modified as such, I can choose any voltage between 12.8 and 15.3 by twisting a dial on my dashboard nect to my digital voltmeter and digital ammeter.

The product below has the voltage dial on its backside:

https://www.ebay.com/itm/NEW-ADJUSTABLE-HD-EXTERNAL-VOLTAGE-REGULATOR-CHRYSLER-DODGE-PLYMOUTH-1970-87/142081547121?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D44040%26meid%3D9122873c24854584a53d2f77cbcad7c2%26pid%3D100623%26rk%3D2%26rkt%3D6%26mehot%3Dpp%26sd%3D142267138079%26itm%3D142081547121&_trksid=p2047675.c100623.m-1

This is basically plug and play^^

If you are really worried about overcharging, or overheating your alternator when your battery is depleted and can suck up everything your alternator can make, set it to 13.8v.

Have a 3 hour drive and need to get as much juice as possible back into it the depleted battery, set it at 14.7v, and drive 30mph plus for underhood airflow, do not idle parked for more than 5 to 10 minutes as alternator can overheat feeding a depleted AGM over adequate thickness copper..

The VR casing needs to be well grounded to battery (-), but you could mount it backwards to the firewall, or put it on some velcro, and have a grounded wire running to battery negaticve from casing, and easily change voltage with a small screwdriver. Especially if you have a helper to rev engine and yell what voltage it is as you twist dial, and tak note of its position for 14.7 and for 13.8.

I would dump the diode based isolator, Not only do you suffer the voltage drop of its diodes but they are terribly unreliable. I was warned and mine started killing my batteries on a trip. Then I was stuck on the side of the road, with family, a trailer and in the dark trying to bypass the stupid thing. Never again.
A 100% solenoid type relay will work better, longer and have no voltage drop.

Example

Hi,

The only reason to isolate the starter battery from the house battery is to prevent the starter battery from going dead.

The biggest issue is getting enough charging while driving to the AGm

solar controller not needed between isolator and battery, won't help anything
and might burn out if battery is really low, when you start the engine

the alternator will NOT over charge your new AGM house battery

I don't think using a solar charge is a good idea, but it is inexpensive and it might work ! The problem is, will that second charger "see" enough voltage from the alternator to charge the battery ? I have no idea how well 2 independent chargers would work charging the same battery.

Read this regarding charging a house battery from a vehicle alternator.

DC-DC battery charging

Put a voltmeter on your AGM and compare to specs. I think the alternator through the diode will be undercharging the AGM. Even on a long 12 hour drive.