TECH TIPS
RESPECTFUL DISAGREEMENT
Q: To Steve Turchet and the Tech Tips in concerning a pervious question covered in the October 2021 issue of the military vehicles magazine. In a 24 volt system consisting of two 12 volt batteries, you can’t draw off just one 12 volt battery alone to get 12 volts. However you can draw off both batteries with equal 12 volt loads. In the late 1950s John Deere came out with a 24 volt system for their diesel tractors using all 12-volt accessories. To achieve this John Deere (and very early M135 trucks) generators at that time had two 12 volt outputs. 12 volt positive ground and 12 volt negative ground. (For example two lights on one side, had to be equalled by two lights on the other side) The light switch and the ignition switch we’re split down the middle. Each side had their own equal 12 volt input battery. Battery A and Battery B. By hooking your CB radio up to just one 12 volt battery the 24 volt system can’t detect a single 12 volt draw and won’t charge the two batteries correctly. Thus a much better approach would be a converter box. I have seen them on eBay for very affordable prices. Or a resistor to bring 24 volts down to 12. Be careful to test the voltage under load for an accurate reading. Speaking with over 45 years experience as a John Deere dealer certified mechanic, by drawing off only one battery severely shortens the life of that battery. Many fire departments have been disappointed using repurposed military trucks by adding a 12-volt fuel pump to only one battery. Don’t let yourself be caught on the side of the road.
— Joe Ackerman
A: I have to respectfully disagree… not in theory, but from practical experience. In the late 1970s I had an M37 with its stock 24 volt electrical system using two 12 volt batteries in series. I
