2nd Boiling Battery - Input needed (1 Viewer)

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You can always run the batteries in parallel without the isolator. That's how I run my batteries as its the stock Dodge/Cummins method. One day I will isolate them but it's been running fine for years now except for the time I boiled the batteries due to over voltage. I did install a new external voltage regulator that has a fail safe for when I loose ground.
 
With my dual battery setup here’s what I did for an isolator

I wired ( 2 gauge wire )batteries in parallel with a continuous duty rated solenoid and fuse / circuit breaker .
The solenoid is controlled via a 12 v relay which gets its signal from an engine oil pressure switch. Here’s a rough ladder diagram and solenoid I used.
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Here are a couple of pics on my battery isolation scheme
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That dual battery solenoid is a good part. We use them all of this time in Limos with dual battery setups. Use a voltage suppressor
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between the top two posts so that you cannot get any backfeed of power. We use a cole hersee 24119
They are inexpensive and last for a long time
 
That looks like a fly back diode on the coil terminals . It prevents the excessive sparking on the control relay contacts .

“A flyback diode is a diodeconnected across an inductorused to eliminate flyback, which is the sudden voltage spike seen across an inductive load when its supply current is suddenly reduced or interrupted. It is used in circuits in which inductive loads are controlled by switches, and in switching power supplies and inverters.”
 
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My BJ60 was stock with two batteries in parallel. One battery would always over charge and one under.

The issue must be your isolator. I'm not a fan of dual batteries joined together. Most certainly not in parallel. Todays batteries are more powerful than when my cruiser was new. So I run one battery now.

My second battery is going to fully independent. It will be a deep cycle and used for power in cabin, running electronics and additional items, maybe even the winch. I will only have a chagrinning circuit for it. If I need to use it to start it will only be emergency and that's what booster cables are for, or you can have a boat style switch, battery A or B, or Both. Physically turn it. No demon drains and weird cross overs.
 
Nice work sleuthing out the problem. I'm certain it's your existing isolator. That type is known to have a voltage drop internally and to fail long-term. I had one on my 80 that failed after a few years.

I am a big fan of the Blue Sea marine products. Here's a chart to help you figure out which ACR you need.

http://assets.bluesea.com/files/resources/reference/ChooseACR.pdf

I went with the 7610, as it meets all my needs. Though I already have wiring and switch to manually combine both batteries if I need. The 7620 has that feature built in, which is convieient, but as I recall it's quite a bit more expensive due to the much higher amp capacity.
 
My BJ60 was stock with two batteries in parallel. One battery would always over charge and one under.

The issue must be your isolator. I'm not a fan of dual batteries joined together. Most certainly not in parallel. Todays batteries are more powerful than when my cruiser was new. So I run one battery now.

My second battery is going to fully independent. It will be a deep cycle and used for power in cabin, running electronics and additional items, maybe even the winch. I will only have a chagrinning circuit for it. If I need to use it to start it will only be emergency and that's what booster cables are for, or you can have a boat style switch, battery A or B, or Both. Physically turn it. No demon drains and weird cross overs.
Yes this is how it should be done. My dual batteries are assigned to different tasks
The starting battery just serves the starter circuits , glow plug circuits , ignition circuit and the electric fan circuits.
The accessory battery runs everything else.
The only parallel circuits are the bond/ ground and the positive , connected only when the engine has oil pressure . So when pulling heavy loads on the start battery( such as glow plugs and cranking motor ) there is no excessive current draw between batteries. I’ve used this on other vehicles without issue for years.
 
Hellroaring Technologies has good products. Pricey, but solid. They have several diagrams for different ways to isolate. Even if you choose a different device, the website is an education.

I like simple. Blue Sea does it well. Solenoid is simple if you want automatic.

Rather than run house loads on a 2nd battery, I recommend running everything off your main batt. Don't run anything off the spare to have it as a true reserve.
 
@EasternYeti I personally am not knowledgeable enough on electrical stuff to offer my own thoughts, but my electrical friend (who you met in Moab) has been following this thread and agrees with you/majority that everything is pointing to your isolator as the culprit.
 
Wanted to close the door on this issue and let everyone know it was indeed the isolator. We re-wired the dual battery setup to tide me over until we can clean it up over the summer.

Fabricated a base plate and mounted the fuse block, breaker, and isolator. This kept the install pretty clean and much less cluttered. Overall I’m quite pleased and blue sea has a lifetime warranty on everything.

A big thanks to everyone here who helped me narrow this down. - fun fact - O’Rileys doesn’t log the battery warranties in the system so if your a dope like me and boil one a week after you replaced it, they have no way of knowing unless you tell them :hillbilly:

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