How to Use a Truck With a 12 Volt System to Jump-Start a 24 Volt Military Truckby David Robinson
A battery that delivers the correct voltage is essential for almost all vehicles. Deliver too much voltage and components either move or spin too fast, or they overheat and burn out. Deliver insufficient voltage and moving components slow down, or don't work at all. Jump-starting a 24-volt system from a 12-volt system won’t work if only one 12-volt battery is available, but if the 12-volt truck has two batteries, it becomes possible to produce a 24-volt supply.
Position the 12-volt truck as close to the 24-volt truck as possible. Orientate the vehicles so their batteries are as close to each other as possible. For example, if both vehicles have side mounded batteries, park the trucks side by side, and if the batteries are housed in the engine compartment, park them nose to nose.
Access the batteries in the 12-volt truck. They will be linked in parallel to deliver 12 volts, but 24 volts with the combined current capacity of both batteries. Put on strong gloves. Starting with the battery terminal connected to "ground," use a wrench to disconnect the cables linking the two batteries to the truck. When completed, both batteries are isolated from the truck but they remain connected to each other.
Disconnect the battery straps that link the two batteries together. When completed, you have two separate 12-volt batteries, neither of them electrically connected to the truck or to each other.
Using short insulated heavy-duty jump leads, connect the positive terminal of the first battery to the negative terminal of the second one. Two of the four battery terminals remain unused, positive on one battery and negative on the other.
Connect a jump lead from the positive terminal to the positive terminal on the 24-volt truck battery. Connect a second jump lead between the negative terminal and the engine block or other ground connection in the 24-volt truck.
Put the 24-volt truck in neutral and start it following the normal procedure. Once started, disconnect the jump leads from the battery.
- Connect a "memory keeper" device to the 12-volt auxiliary power socket / cigarette lighter in the 12-volt truck before disconnecting the batteries. This protects devices such as radios and GPS units that are designed to stop working when disconnected from a power supply.
- Always disconnect the "ground" side of the battery first. This reduces the risk of electrocution.
- Lead-acid batteries produce hydrogen gas. Keep all sources of ignition well away from them. Hydrogen plus a spark or flame may result in an explosion. )
- The linked 12-volt batteries cannot be recharged while in use, so take care not to drain them in your efforts to start the other truck.
Items you will need
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