BJ Series Land Cruiser

    Part Sources
    Specs & Stats


Copyright & Terms

Tech Articles

Back | Index | Next

24 Volt Systems

Many cruisers have 24 volt electrical systems, and there are a few things you should know about them if you have one. I'm no electrical expert, but I have gathered a few do's and don'ts. Like how do you jump start a 24 volt system?

The 24 volt system consists of two 12 volt batteries connected in series, instead of in parallel. Canadian BJ60s, for example, have two batteries, but they are connected in parallel: the positives are connected, and each negative goes to ground. This parallel system creates a 12 volt system with a lot more juice than a single battery. Also, both batteries will stay balanced all on their own.

But as I said, 24 volt systems have two 12 volt batteries connected in series: the ground wire connects to the negative, the positive connects to the second negative, and the second positive connects to the starter and everything else. The first battery provides volts 1-12, the second 13-24.

On most 24 volt cruisers, all electrics are 24 volts except the headlights which are 12 volts. This is accomplished by drawing power from the second negative terminal, which is 12 volts. Now you might be tempted to run all sorts of 12 volt accessories this way, but DON'T! The headlights are an exception that works because there are two of them - each headlight draws power from a different battery, thus the batteries stay balanced. Likewise, you could run 12 volt foglights in the same way. But if you hook up a radio (or worse, a winch!), you will draw power from one battery only.

This might not sound so bad, expect unlike in a parallel system, the batteries do not balance each other out. In fact, quite the opposite occurs: when one battery is low, the other one take the excess from the charging system. In other words, if your batteries are unbalanced, one battery will get weaker, and the other will progressively overcharge. Left unchecked, both batteries will need to be replaced.

So here are some basic tips:
  • Install identical batteries at the same time, and make sure they are both fully charged.
  • NEVER tap 12 volts.
  • If you blow a headlight, replace it quickly - and make sure the lights are the same wattage.
  • Swap your right and left batteries at least a couple times of year. If one battery got run down for any reason, swap them more frequently for a while. Or charge both batteries up fully.
So how do you get 12 volts from a 24 volt system? Basically you have two choices: install a second alternator (12 volt one wire); or install a 24 to 12 volt converter. If you plan on many accessories, the second alternator would be best. If you want to run a radio and cb, then a converter would work fine. There are two types of converters, high and low efficiency. The difference is that the low efficiency gets rid of the extra voltage by converting it to heat. This means the unit is larger, with a large heat sink, and that it wastes a lot of energy. A high efficiency unit is more expensive, but better.

So how do you jump a 24 volt system? Well, ideally you do it with another 24 volt system! However, if you're stuck in the parking lot of your local grocery store, you can jump from a 12 volt system - usually. This is because it's usually only one of your batteries that will get run down. So it's a good idea to carry a multimetre with you. Unless your bad battery is really pooched, you can probably just hook the jumper cables up to the bad battery and let the other car recharge your battery for a few minutes.

How do you jump a 12 volt system? Pick a battery and jump. While the system as a whole is 24 volts, each battery is still just 12.