English flagGerman flagFrench flagSpanish flagDutch flagCzech flagDanish flag

New Cruiser: Expeditions

The travels of an all aluminum Land Cruiser and its owners…

Canada Flag South Africa Flag

24 Volt Issues

Written by Robin on Wednesday, January 5, 2000

Over time I have had nothing but problems with the 24 volt systems in the Landcruisers I have owned. Other 24v cruiser owners will identify with this. Batteries drain, they die, you purchase a better warranty, try Optima, and still you have problems. Finally, I came upon the solution.

Why do you keep having to replace your batteries in a 24 volt Landcruiser? Over time, different batteries will vary slightly in their charge, just by their nature. The 24 volt alternator in the Landcruiser makes sure that there is always 24 volts, but it doesn’t care how that volatage is achieved. Since the system is made of two 12 volt batteries in series, the assumption is that each battery will be receiving an equal charge from the alternator. However, in reality, if one battery has a slightly higher charge, say 13 volts, then the other battery will only be receiving 11 volts. This overcharges the one battery, and undercharges the other. If this continues, eventually both batteries will be fried.

The solution is to use a charge equalizer. This is a unit that constantly works to ensure that both batteries are equal. It works on a voltage differential – if it senses a voltage difference between the two batteries, then current is directed from the higher battery to the lower battery. As the differential approaches zero, so does the current.

Some people suggest that a charge equalizer will drain the batteries if it is left for an extended period of time. Though there is about a 4% loss through the equalizer, this loss only occurs when there is a voltage differential, i.e. the batteries do not have equal charge. As soon as the charges are equalized, no current passes through the equalizer, and hence there is no energy loss, except for 0.017 amps drawn by the unit from the 24 volt side. This is equivalent to the draw from the clock on a car stereo. However, if you had one bad battery (one that doesn’t maintain its charge) and one good one connected with an equalizer, the good battery would be constantly working to charge the bad one. If the vehicle was sitting for a long time, then eventually the good battery will be drained since its charge was directed to the bad battery.

A charge equalizer works especially well if you are tapping 12 volts to run accessories such as a radio, fridge, or laptop. With the vehicle turned off, the accessories can run, draining the 12 volt battery. Meanwhile, the charge equalizer supplements the drain by taking charge from the high side battery to the low side one.

Where to Find One

An excellent equalizer can be purchased from Level 42-Landcruiser work, run by from Greg Bowie. This unit is made by Solar Converters, who offer excellent support. Greg Bowie is their distributor. I paid $220 CAD for the 20 amp model (20 amp @ 12 volts), though I am not sure of the current pricing.

Install

There are 4 wires coming out of the box: black (grnd), white (12 volt), and red (24 volt), and an LED light that indicates the internal fuse health. The red one gets connected to the 24 volt terminal of the high side battery (where the starter lead is connected). The white one gets connected to the 12 volt terminal of the low side battery, and the ground is connected to the negative terminal of the low side battery. Connect the wires directly to the battery terminals – for example, do not connect the ground to the frame. The unit needs to see the actual voltages coming directly from the batteries. I used small disconnect plugs to connect them to the battery terminals.
The equalizer with the 4 wires and some toggle switches I insatlled.

There are two internal fuses in the unit. One blows if the amperage going through the equalizer is too much. The other one blows if the ground wire is disconnected from the battery while either of the two hot wires are still connected. Any time I do any work on the truck, and have to disconnect a battery, the hot wires (white and red) must be unplugged from the charge equalizer. I found the disconnect plugs to be too cumbersome, so I drilled into the side of the equalizer box and installed two toggle switches – one for the red 24v lead and one for the white 12v lead. This is simple to do, as the box the equalizer comes in has a lid that is easily unscrewed. Make sure the holes are well siliconed up, as water must not enter into the box!
Inside the equalizer with the toggle switches installed. The side of the equalizer with the toggle switches installed.

The unit should be installed in the engine compartment at a convenient location. Inevitably the fuses will blow at some point, and you need to be able to remove the top of it to change them. I put mine on my drivers fender apron. I cut the LED wire and lengthened it to run back to the dash. I drilled a small hole (I can’t remember the size) and the light is a press fit into it.
A Note on the LED Light:
There are two fuses, but the LED only indicates one of the fuse’s health. This fuse is the one that blows if the ground wire is disconnected while the 12v or 24v lead are still connected to the batteries. When the LED light is off, then this fuse is blown. If the other fuse blows due to an overload of amperage there is no indication. If you suspect that it has blown, you can confirm it by turning the unit off, putting a voltmeter across each battery and measuring the voltage. Turn the unit back on, and re-check the voltage. You will likely see a small change with the unit on, and if so then the fuse is ok.

Setting the Voltage

There is a potentiometer inside the equalizer. (A potentiometer is a variable resistor, with a set screw that is used to vary the resistance). You can change the balance of the equalizer by setting the potentiometer: connect the 12v lead and measure the voltage of the 24v lead. It should be around 24-26 volts. Set the potentiometer to around 25. Disconnect the 12v lead, and connect the 24v lead. Measure the 12v lead’s voltage. It should be half that of the 24v lead. If not, set it so that it is. You need to iterate this a few times until the 12v lead is half the voltage of the 24v lead. Do this with fully charged batteries in good condition.

Further Reading on The Truck:
1
Comment by Stancil
March 5, 2011 @ 10:00 am

Just wanted to say that for the past 24 years of owning my 24volt BJ70 Land Cruiser, I have never had a moment’s trouble with the electrical system not the imbalances between batteries that you describe. Maybe in another 24 years, they might create some trouble. Will keep you posted.

2
Comment by Keith
July 30, 2014 @ 7:50 am

I love my 1987 HJ60 but have experienced battery issues twice. My last batteries lasted me seven years so I am not complaining. I am installing Optima batteries this time but I just ordered the Solar Converter’s equalizer and really appreciate the article on your website. Thanks and nice truck and nice to read about your adventures.

Post a Comment