HDJ81 12/24v system

[TuffMudder]

I’m buying an hdj81, and I’m trying to get some specifics on how the dual batteries are set up. My current understanding is accessories have a dedicated battery and the starter uses both batteries.

That main two things I’m trying to figure out is:
Is the starter the only thing that is 24v?
If the accessory batteries does, will the truck still start?

Any other information would also be appreciated

I know some people convert it all to 12v so I’m curious as to what the original logic was in having the starter 24 and everything else 12v

Thanks

 

[Dork]

Starter is the only 24v in the vehicle. When starting, the second battery is put in series to temporarily provide 24v. The first battery (right side) stays at 12v all the time so all electronics and accessories connect to that one.

If one battery dies they both will since they are connected in parallel when off or running. You can't start with only one. I had to jump mine when I first picked it up by having two other batteries connected to it with cables. If they are just dead batts, you can charge both at the same time.

Makes the truck fire up instantly, even in the bitter cold , so I'm considering keeping it in place on mine.

 

[TuffMudder]

Thanks @Dork . Any idea what happens if the battery responsible for the 12v side dies?
I’m thinking of times camping and running accessories without the truck running.

 

[Douglas S]

I removed mine and replaced with a 12v starter so I could isolate one battery. The 24v starting system worked well while I had it.

 

[bug616]

Very common to convert 80 series diesels to a 12 volt starter thereby freeing up the accessories battery to be for leisure only. I just did mine last weekend, took me a morning going slow. Some good info here on doing the conversion 12 volt starting conversion on a 1997 24 valve manual 80 series LandCruiser

The 100 series was 12 volt start in all configurations. 24 volt start is simply not needed. Maybe if you live above the Arctic circle but even then, 100 series diesels don't have starting problems. It's likely a good example of the 80 being over engineered.

 

[TuffMudder]

Thanks for all of the great information huys

The one thing I’m still curious about is, if I’m camping and running accessories with the vehicle off, and the accessories battery dies, will the vehicle still start on the remaining good battery.

Alternatively, is this situation impossible, because running the accessories uses 12v but still drains the 2 batteries equally?

 

[slow95z]

Get a battery isolation device. You can run accessories off one and save the other for starting.

 

[TuffMudder]

Get a battery isolation device. You can run accessories off one and save the other for starting.

So if I’m interpretting that correctly, your saying, accessories draw from both batteries equally, but with a battery isolation device, accessories only draw from on battery and the second battery is only used for the starter in conjunction with the accessory battery?

 

[Dork]

If you run in the stock configuration, your batteries are parallel when vehicle is off. Therefore, both batteries are running your accessories and dying at the same time. If a battery just fails or falls apart, you can't start the vehicle, and the failed battery will likely pull the good one down with it.

If you had an isolation device as mentioned, you could theoretically run one down, then connect them together and use the good one to charge the low one up to 50% or so, then hope it starts? I wouldn't.

 

[bug616]

Thanks for all of the great information huys

The one thing I’m still curious about is, if I’m camping and running accessories with the vehicle off, and the accessories battery dies, will the vehicle still start on the remaining good battery.

Alternatively, is this situation impossible, because running the accessories uses 12v but still drains the 2 batteries equally?

My understanding is that it is impossible to drain just one battery with the 24 volt start left in situ, as the batteries are always connected in parallel except when starting, when they connect in series. So yes, if you're running accessories with the vehicle off, you are draining both batteries equally. It is however a fact that with the 24 volt start, if one battery dies, the vehicle will not start.

By converting to 12 volt start, you effectively build in a level of redundancy as you can wire one of two ways: one is where you can select which battery you start from; the other, as I have done, is where you join the batteries in paralllel but with a battery disconnect (i.e. an isolator). That way, if the starter dies, you simply turn your switch and jump start from the leisure battery. Alternatively, you could keep it really simply and just carry jump leads.

 

[Douglas S]

Get a battery isolation device. You can run accessories off one and save the other for starting.

This won't work with a series/parallel switching system.

 

[TuffMudder]

Ok, now I think I’m on the right page and understand why the options are limited to living with it as is, a third battery with the original 2 batteries confined to starting or converting to 12v starter. I was hoping there were other options, but I can work with this. Trying to have a protected start may be excessive, but i am so that guy that will leave accessories on and end up with a dead battery

 

[mudgudgeon]

Dork is correct.
Batteries are connected in parallel. BOTH batteries run the 12 volt stuff.
When starting, the switching solenoid drops the parallel connection, and connects both batteries in series.

The big down fall of this system is that batteries aren't isolated. If one battery goes bad, it very quickly drags the other one down too.
If you replace one, you need to replace both.
Buying two batteries to replace one gets old fast!
The OEM terminal layout means you need two different batteries too, the POS/NEG terminals are on opposite sides on each battery.

 

[TuffMudder]

Yeah, I plan to do either go 12v conversion or if i go with rear drawers, i can hide a deep cycle accessories only battery in the back.