RF_Burns
New Member
I see a number of references on here showing chassis battery connections (battery charge connection to your trailer battery, DC-DC chargers etc) having the ground connection directly to the negative terminal of the chassis battery. I'm going to make the argument that it should goto the engine block, NOT the chassis battery negative terminal. There should be only one connection to the battery and that is the main ground wire from the battery negative terminal to the engine block.
I spent over 40 years in mobile radio communications systems (Motorola Dealer... Police and Fire Department radios). I've seen lots of burnt wires and damaged equipment from doing this. Side terminal batteries and batteries with a post and stud connection invite issues the most.
Consider this common scenario: You have a large pair of wires run direct from your chassis battery to your new DC-DC charger to charge your new LFP batteries. Normally the chassis engine starter current flows from the positive (we will talk in conventional current flow instead of electron flow) of battery, through the large cable to the starter, which is grounded to the engine block, and back the large ground wire from the engine block to the battery negative terminal. The large wires are designed to carry the hundreds of Amps a starter consumes. The engine starts and all is well.
->But one day... the large negative ground wire from the engine block to the battery gets a bad connection (corrosion, loose terminal etc). Now you try to start the engine and the power flows through the starter to the engine block, but the engine ground is poor, so the current looks to flow in another direction back to ground. The engine block is grounded to the body and frame by smaller ground wires so it finds its way to the House battery negative terminal and back along your DC-DC charger feed supply wires to the chassis battery negative terminal. BUT, none of this wiring was designed to carry the hundred's of Amps a engine starter takes... so things get hot, even burnt and the magic smoke gets out.
Now IF you had the chassis ground wire from your DC-DC charger connected to the engine block, the current would have no where to flow back to the battery as that single wire connection to the battery negative is poor. You would hear a click from the starter solenoid, or maybe not even that. The DC-DC converter would see its power go to near zero volts when you tried the starter, so it would not be harmed.
I know this is a simplification of what would/could and does happen.
So this is my experience and my advice is to never run a ground wire to the negative terminal of your chassis battery. The engine block is the Mother of all Grounds in a vehicle.
So... Only one connection from the chassis battery negative terminal and that is to the engine block.
I spent over 40 years in mobile radio communications systems (Motorola Dealer... Police and Fire Department radios). I've seen lots of burnt wires and damaged equipment from doing this. Side terminal batteries and batteries with a post and stud connection invite issues the most.
Consider this common scenario: You have a large pair of wires run direct from your chassis battery to your new DC-DC charger to charge your new LFP batteries. Normally the chassis engine starter current flows from the positive (we will talk in conventional current flow instead of electron flow) of battery, through the large cable to the starter, which is grounded to the engine block, and back the large ground wire from the engine block to the battery negative terminal. The large wires are designed to carry the hundreds of Amps a starter consumes. The engine starts and all is well.
->But one day... the large negative ground wire from the engine block to the battery gets a bad connection (corrosion, loose terminal etc). Now you try to start the engine and the power flows through the starter to the engine block, but the engine ground is poor, so the current looks to flow in another direction back to ground. The engine block is grounded to the body and frame by smaller ground wires so it finds its way to the House battery negative terminal and back along your DC-DC charger feed supply wires to the chassis battery negative terminal. BUT, none of this wiring was designed to carry the hundred's of Amps a engine starter takes... so things get hot, even burnt and the magic smoke gets out.
Now IF you had the chassis ground wire from your DC-DC charger connected to the engine block, the current would have no where to flow back to the battery as that single wire connection to the battery negative is poor. You would hear a click from the starter solenoid, or maybe not even that. The DC-DC converter would see its power go to near zero volts when you tried the starter, so it would not be harmed.
I know this is a simplification of what would/could and does happen.
So this is my experience and my advice is to never run a ground wire to the negative terminal of your chassis battery. The engine block is the Mother of all Grounds in a vehicle.
So... Only one connection from the chassis battery negative terminal and that is to the engine block.