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Old 09-21-2011, 11:20 AM
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Dual Battery 12 volt charging and starting

Hello My name is Tim, I am not working on a hotrod at the moment. I am servicing a 1975 80 ton Groves Crane. It has a dual 12 volt battery system with all hot wires going to what i am guessing is an isolator. One battery is reading 13.92 and is grounded to the frame. The other is reading 12.2 and grounds at the isolator. The crane runs fine,alternator has been rebuilt but i have to jump it off every time i start it. i have been trying to figure this problem out for a couple of weeks off and on ....any suggestions would be great!

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Old 09-21-2011, 01:38 PM
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Sounds like the Batt with low Volt reading is gone.
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Old 09-21-2011, 01:52 PM
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If one battery is bad, it will drain the other one. I wonder about the starter though, it may drawing too much and jump starting overcomes the draw.
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Old 09-21-2011, 02:55 PM
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I don't know your system or set up but if it's a 12 volt system you should not have two batteries in parallel. Better to use two 6 volt (golf cart) batteries in series.
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Old 09-21-2011, 03:29 PM
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Quote:
Originally Posted by tburris0131
Hello My name is Tim, I am not working on a hotrod at the moment. I am servicing a 1975 80 ton Groves Crane. It has a dual 12 volt battery system with all hot wires going to what i am guessing is an isolator. One battery is reading 13.92 and is grounded to the frame. The other is reading 12.2 and grounds at the isolator. The crane runs fine,alternator has been rebuilt but i have to jump it off every time i start it. i have been trying to figure this problem out for a couple of weeks off and on ....any suggestions would be great!
I would pull both batteries and have them tested to start with. If it works with the current wiring before it still should. Eliminate the batteries and any bad connections to them first then work from there
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Old 09-21-2011, 05:07 PM
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Chet's tracking X2
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Old 09-21-2011, 05:36 PM
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My Dodge Cummins diesel has 2 big 12v batteries in parallel.....so do several million other factory built Dodge diesel trucks.

No problem untill one battery goes bad then you replace both...standard proceedure with high current systems.

Very good connections and large cables are required. Mine are as big as "pointer finger".
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Old 09-21-2011, 07:42 PM
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If there is an isolator it would be on the positive side.

I am not sure what you mean by having to jump it off, but my guess is that you are having to excite the alternator. If this is so you need to check the isolator as some of them have a wire that comes hot with the key (this is what excites the alternator also) if this is not getting its 12v it will not charge properly. If this voltage is there then the isolator is bad.
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Old 09-22-2011, 04:45 AM
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Some very strange advice on this thread......lol. The good advice would be, as stated above, remove the batts, get them checked and replace if needed.
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Old 09-22-2011, 05:16 AM
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2- batteries

What a dang joke . Two 6-volt golf-cart batteries in a piece of heavy equipment. As suggested,pull both batteries have them checked.Replace if need be. Also make sure both batteries are fully charged before installing. If you jump a piece of equipment off with a dead set of batteries the Alt. will take a long time to charge them up. Install a main disconnect switch on the machine and turn the power off when not in use. This is as bad as the guy at the parts store buying a marine battery to put in his truck cause its cheaper.
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Old 09-22-2011, 07:36 AM
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Isolator ?

A few years ago when you added a second battery to run a camper you added an isolator so it would charge both batteries but the camper electrical would only draw from one battery, saving the charge in the main battery so you could still start the truck the next morning. Today most new factory camper packages come with 2 batteries and the relays to operate the isolation.
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Old 09-22-2011, 07:40 AM
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Yes, do an individual load test on the batteries. Before you get too far, check the starter data plate to be sure it is a 12 volt starter. Some heavy equipment is set up with a 12/24 volt system, where the 'isolator' is a series/parallel switch to allow lights and accessories to run at 12 volts while 24 volts is provided to the starter. The series/parallel switch could be a culprit too.
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Old 11-10-2011, 05:05 PM
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Quote:
Originally Posted by tburris0131
Hello My name is Tim, I am not working on a hotrod at the moment. I am servicing a 1975 80 ton Groves Crane. It has a dual 12 volt battery system with all hot wires going to what i am guessing is an isolator. One battery is reading 13.92 and is grounded to the frame. The other is reading 12.2 and grounds at the isolator. The crane runs fine,alternator has been rebuilt but i have to jump it off every time i start it. i have been trying to figure this problem out for a couple of weeks off and on ....any suggestions would be great!
I think your problem might be the fact the second battery is wired wrong. my guess is that the second battery is wired with out a separate voltage regulator. some thing in the circuit is dragging down the second battery's voltage like the voltage drop on the battery isolator. they are not supposed to drop any voltage but I think that might be the problem! I suggest check the battery isolator.and the secondary battery outside the vehicle.
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Old 11-10-2011, 05:21 PM
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I would have to see the wiring diagram and compare it to the way it is currently wired before I'd try to guess about how to rewire to fix a problem.

Assuming that it worked properly before you had to jump start it, I think checking the batteries is a good start. The battery has a much higher failure rate than the other components in the starting and/or charging circuits. That doesn't eliminate them (after all they may be more than 35 years old).

If it has been rewired or if the batteries are good and you need to troubleshoot the rest of the components, you still need the wiring diagrams.

If you can't get the wiring diagrams try to sketch the circuit as best you can and take some pictues that show the battery wiring, the isolator, and other relevant components.
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Old 11-10-2011, 10:24 PM
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I'm thinking you have a series/parallel electrical system, I not going to try to explain this system because I don't fully understand them. I would try to contact the manufacture or check with a heavy equiptment shop.
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