“The tractor (or swather, or insert any other self-propelled implement) won’t start? No problem. Just go bring the pickup truck around, and grab the jumper cables as you pass by the shop.”
Before you connect to those terminals, let’s take inventory of some important considerations that may save you some money and could very well save you from serious injury.
The first thing you want to consider is what are the starting amps required by the engine and battery that are failing? Many diesel engines require 900 CCAs (cold cranking amps) or much more in order to properly spin the starter bendix. You can find the CCA rating of your battery on top of the battery’s casing.
So what’s that got to do with jumping the battery? Knowing the ampere needs of the system will allow you to select the correctly sized jump cables to transfer the power between the “jumper and the jumpee.” Aren’t all jumper cables the same? Hardly.
Many inexpensive automotive jumper cables you can pick up at the local discount store simply won’t hold up to the strain of starting a diesel motor. When you jump from a stalled vehicle and retrieve your cables, are they hot to the touch?
It doesn’t even have to be a jumper cable; many cables found on battery charger/starters are simply gauged too light to transfer the amount of power needed by the down battery. The result of all that heat is the same effect as that of heat on any metal – it weakens it, usually to the point of failure.
Failed cables can short out and spark a fire – or worse, cause a battery to explode. Unfortunately, I know this firsthand. We were jump-starting a tractor with a diesel pickup, and luckily, we were out in an open field behind the farm shop so no other equipment was around. We knew the cables were weak, so we left them to build the battery slowly. That was lucky because that meant no person was around either. The positive side of the jumper cable failed and grounded the positive post on the truck battery.
I can’t remember how loud the sound was when the battery blew. I can’t say it was a blast, but it was loud enough for us to come running to find the front of the truck ablaze. Luckily, even the truck suffered only superficial damage. It needed a new grill, some paint and of course, a new battery.
I recount this for you so you understand that carrying capacity of a cable is no different than a pasture; overdo it, and you will pay the price. So what size jumper cables do you need? Like sheet metal and shotguns, the size of cable is expressed as a gauge. The lower the numerical gauge, the bigger or heavier the cable.
Generally speaking, the lower the gauge, the more power the cable will transfer without excessive buildup of heat. On most farms, a 2- or 1-gauge cable will start most engines. It is also advisable to have 20 or 25 feet of cable in order to reach batteries that are less accessible. You may also find the heavier gauge will have longer cable lengths, which will allow you to go battery to battery more easily in more and varied situations.
While the cost of cables goes up as the wire gets thicker, you’ll also notice the quality of clamps get better as well. Cheap wires have cheap clamps, which are a pain in the butt to use, and they are less likely to stand up to time. Cheap clamps are copper-plated. Better clamps will be solid copper, which will transmit electricity much better. After utilizing a plated set a few times, the copper can be worn off down to the steel substrate, which does not transmit the electricity nearly as well, meaning your cables won’t work very well.
Insulation is no different as to the gauge of wire. The thicker the wire, the better the insulation. If you live in a cold climate, cheaper insulation will usually crack very easily. Better insulation will retain its pliability while you uncoil and recoil it during and after use. Cheap insulation will not want to straighten out, making them very hard to use.
Self-contained battery boosters can be very handy. Their portability and convenience make them a great addition to any shop. Some can be quite powerful, peaking out at 1,500 amps; however, once again, lighter cable thicknesses and clamps can lower the effectiveness of these otherwise handy tools. While it may not be very prevalent, avoid using a hybrid vehicle to jump-start a standard battery. Hybrids can carry voltages that overwhelm and damage the disabled machine’s battery and charging system.
Of course, having the correct jumper cables is only helpful if the running engine’s battery is up to the task and you connect the battery correctly. Always make sure you are connecting positive to positive, and ground the final negative cable up away from the battery, fuel or oil. The final connection will most likely cause some sparks, and a fire or explosion may result.
Finally, consider the battery that will not start the machinery may have issues that cannot be solved by any set of jumper cables. Always check age and condition of the battery before you begin to try to recharge it. 
Andy Overbay holds a Ph.D. in ag education and has more than 40 years of hands-on dairy and farming experience.
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Andy Overbay
- Extension Agent
- Virginia Cooperative Extension
- Email Andy Overbay
