Battery Grounding issue HDJ80

[toadshade]

I am installing new battery boxes and in a hurry to get on the road I temporarily connected the old terminals and did not realize my terminal screw was too high and arced on my hood when I went to start the truck. It actually welded itself to the hood and I had to hammer on a rod through the hood opening to open the hood. I know, stupid. But what surprised me is it was the negative terminal. I would have thought that would happen on the positive side but I need to know if I am missing a ground to the chassis or something. As far as I know it is factory wired. When I went to start, there was a one second hesitation and a small white puff of smoke when I went to start. The truck ran fine grounded to the hood but scared the hell out of me. Especially when I could not get the hood open. Do I need to run a ground to the body? For clarification, it is battery B which is the drivers side battery on a LHD. I am not completely familiar with the 24V system so I just assumed any grounding on the A battery would also be grounding the B battery.

 

[kevin in okinawa]

on my 24v 12ht, the second battery is grounded to the body

 

[erics]

not having specific experience with 24v vehicle but some engineering studies in my past, you need to think of the two 12v batteries in series as one 24v battery all together

pos terminal on first 12v battery is pos of the "entire" 24v battery (which goes to vehicle load) , neg on first goes to pos on 2nd, neg on 2nd is ground of "entire" 24v battery (and goes to system ground)

but even if they are connected correctly like this, each individual 12v battery can supply another circuit composed of path between its pos and neg terminals... I'm thinking this is what happened when you shorted one 12v to the hood and the puff of smoke was something in that new path burning to open (thus eliminating that path). The truck would then go back to running fine because new path was gone and old path was not damaged (or damaged enough to open it).

I would find what got smoked!

 

[toadshade]

The puff was the weld to the hood. But what I have found out is exactly what you said. The negative terminal should be treated like a positive terminal on the B battery. I just didn’t realize that the switch went back to the battery itself. I thought the switching mechanism isolated the batteries.

 

[Squash]

If this is an 80*s series with the 24 volt starter your system is all 12 v except for the starter.

Connect terminals as a 12 volt system. Do not use the body as a positive post ground.

 

[toadshade]

No I’m not. Misunderstanding. I just meant the negative post on the B battery should be considered a positive terminal. Or rather treated like one only while starting.

 

[Squash]

Yes!
I believe you got that right.
Lesson is to always check terminal clearance. Be sure to check battery hold downs as rough roads can throw a battery out of the tray.
In our underground mines we cover the batteries of all equipment with a stout piece of rubber. Historically people would stand on the hoods/roofs as a mobile ladder which occasionally resulted in your dilemma.

 

[toadshade]

Yep. Learned that the hard way. This whole thing started because I was building new trays for two Group 31 batteries. Ironically I set up the battery quickly so I could go to the auto parts store for a terminal connector that fit better. . But now I am going to get one that has a really nice cover. My positive terminals have a TH Marine Hydra with a cover. Don't think they make a single. The covers are only positive not that it matters.