12v Accessories in 24v Vehicle

by AJ Deysel

With the current surge in Japanese 4WDs being imported to the US market because of age and classic status, especially Toyota Land Cruisers, more and more people find themselves having to deal with 24v electrical systems in the cars. In Japan, many of the Toyota Land Cruiser and Nissan Patrols ran 24v electrical systems. Why?

There is much speculation, with some suggesting that Toyota and Nissan built them at NATO spec, which like all military spec, needs to be 24v. The most likely reason, is based on the climate in Northern Japan where their target market for those vehicles were. Cold and wet. A 24V electrical system, is more efficient than 12V. A 24V starter or heater for instance draws half the current of a 12V for the same power. This mean less current on the wires and less heat generation, in turn providing more reliability in colder environments. This is the reason why most applications that need to be reliable in multiple environments, like military, mining, marine, trucking and heavy duty machinery equipment all use 24V electrical systems.

When comparing two of the same size appliances like a starter or a winch, giving the same current, but one getting 12V and one 24V, the 24V one will be able to provide double the output, so the starter will be able to start a engine easier, and the winch will be able to pull much faster. This is reason why those using a 24V Warn 8274 winch, will have a much faster line speed compared to the 12V Warn 8274 winches. So, if you or your auto-electrician knows how to work and maintain a 24V electrical system, and you can find the accessories and parts you need in 24V varieties, then you will have no reason to have to swap over to a 12V system, and will find quite a few benefits to using 24V accessories.

Luckily, with modern advances in lighting technology and moving towards the LED technology, you will find that LED lights can often accommodate a variety of inputs from 10V to 30V. This coupled with the fact that most of the other heavy current equipment like winches also offer 24V varieties, means you will be well served with a normal off-roader to just leave it 24V.

When using it more as a daily driver or longer distance touring or overland vehicle however, you may find problems trying to find 24V varieties in the interior creature comfort accessories. Compact off-road fridges, two-way radios, GPS systems and other such overlanding equipment often are only available in 12V applications, so in that case, you will have trouble with running a 24V system.

Changing a 24V Vehicle to 12V

Changing the whole 24V electrical system to a 12V system, is often relatively straight forward, but still not easy and can take a lot of time, effort and need a lot to be changed. It would first be recommended to get an experienced auto-electrician to thoroughly go through your vehicle and determine exactly how much of it is 24V and if there is already 12V components or parts of it. Some of the Land Cruisers ran full 12V electrical systems with simply 24V starters and alternators for cranking power for the truck type engines (Toyota 3B, 13B, 14B, etc.). Some of the Land Cruisers ran full 24V electrical systems with a centre-tap 12V headlight system, and then other ran full 24V electrical systems with 24V headlights as well. So making sure exactly how yours is set up, crucial to be able to successfully change or manage it.

If you have a full 24V electrical system, you will most probably have to change every single electricity consuming item in the entire system, everything from the starter and alternator, all the way through to the heater, radio and even the small interior light bulbs inside the dashboard. You should still be able to leave the factory wiring harness in place as it is unlikely that the manufacturers made different wiring harnesses for 12V and 24V varieties of the same vehicle. You also need to remember that your fuses will need to be changed as each item will now use double the Amperage as the 24V item did.

If you have a full 24V system with the 12V centre-tap headlights, then you would again have to change out everthing as above, and then rewire the headlights to run off the full 12V battery and not a centre-tap arrangement anymore.

If you have a 12V system with 24V starting system, then you would simple have to change out the alternator, starter, distributor and glow-plugs / spark plugs.

Running 12V Accessories in 24V Vehicle:

Running 12v Accessories, like audio system, two-way radio, some off-road lights and other auxiliary chargers and system on a vehicle that has a 24v electrical system, is where you have to carefully plan and think through your system. Many backyard mechanics, and inexperienced installers simply tap all 12V accessories to only one of the batteries in a 24V vehicle that runs two 12V batteries in series. This a serious NO, and absolutely not recommended unless you want to jump-start the car weekly and have to buy a new battery for it every few weeks. The reason for this is the unequal charging that will occur, causing premature failure of one or both of the batteries constantly. Your alternator, that is charging your batteries, is not a smart charger, so it does not notice voltage difference between two batteries, it simply picks up total voltage as low (whilst only one battery will be low and the other one at full capacity) and will keep sending a charging current to both. Thus constantly over-charging the battery that is full and has no 12V accessories tapped from it, which then causes it to fail or die completely. This is same reason that a simple dual-battery system in a 12V vehicle, where the charging of the batteries is meant to be done by the alternator or even with a relay regulating it, is not recommended and the incorrect way to do it.

There are two correct ways of running 12V accessories of a 24V electrical system. One requiring a 24V to 12V step-down convertor, and the other requiring an auxiliary battery system, with a separate DC to DC battery charger.

Simply running all 12V accessories from a 24V to 12V step-down convertor, is the faster way to safely do it. Just be sure to add up the total AMPs required by each accessory, and get a step-down convertor with a higher amperage rating than what you will need. Simple. The only drawback here, is that 24V to 12V step-down convertors get quite a lot more expensive as the AMP rating climbs, but here are some good suggestions we would recommend.

The other way of doing it, is running a DC to DC battery charger that can accept a 24V input, straight off your 24V system, and then using it to charge another auxiliary 12V deep-cycle battery. Then run all of your 12V accessories from that auxiliary battery. This is very useful if you will be camping or needing to run some of the accessories or appliances for longer periods of time whilst the vehicle it off. Like for instance running your 12V fridge and lights at your campsite through the night, this will ensure that your main starting battery or batteries are not drained by them, so you can still safely start your vehicle to be on the way again in the morning. The only problem with this set-up, is if you have some of the 12V accessories, that you want to come on with ignition power and go off automatically with it too, like your headlights and possibly your radio too.

Our Choice

For our imported 24V Nissan Patrol / Safari, and our 24V BJ73 Toyota Land Cruiser, we decided to go with a combination of the two. We installed a 24V to 12V step-down convertor running from the Acc, power source on the ignition, so the accessories running of this convertor would come when the ignition is turned to Acc and go off if the ignition is completely turned off, just like the usual accessories on a car (like the radio) that runs off the Acc does. From this convertor we ran the radio and sound system, as well as the two-way radio.

Next, we ran a cable from our main 24V battery power to the back of the vehicle into the loading area with a plug there to plug our portable auxiliary battery box into. The reason we went with a portable auxiliary battery box type setup, is so we can use it not only in one car, but also in any other car we want to go camping with instead, it simply requires a cable with plug installed in each vehicle. Given the fact that we do not camp or go on expeditions the whole year long (as we wish we could), we then do not have to have the unused auxiliary battery in the vehicle the whole time. From this auxiliary battery, we then run the 12V fridge / freezer, camp lights, cellphone chargers and whatever else we need to run from it.

For the headlights, we replaced the front units with these new LED headlights, they are superb and not even close to comparison to the factory old halogen headlights. These light the road up similar to what modern vehicles do, and can run on any voltage from 10V to 30V. We highly recommend them.

Just remember when installing them in a Land Cruiser, Nissan Patrol or other vehicles that use negative switching between high and low beams, you will also need to get one of these module.

For the taillights, to update their intensity and look to match the new front headlights, we simply replaced the globes with LED units capable of handling 10V to 30V, these are what we recommend.

For small USB powered accessories like phone chargers and flashlight chargers, we quickly learned that there is already a multitude of cigarette light port chargers that can accommodate both 12V and 24V, even on of our existing older ones was able to handle it.

If you need a new one, we highly recommend this one as the build quality is really good for the price and it has lasted through our abuse.

Conclusion

If you already have a vehicle with a 24V electrical system, there is really no great need to change it to a 12V electrical system, and getting 12V accessories to work of it is not hard at all, it simply needs some smart planning.

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