Using 24v starter on 12v

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Hello everyone electrical question here.

I currently have a jap spec 1996 hdj81 land cruiser with 24 volts starting 12 volts running.

I am wanting to convert it to run at 12v all the time with Lifepo4 cells (lithium battery) charging straight from the alternator.

Now I would like to take out the 24v starter system and run it all at 12v but my question is whether I need to buy a new starter or not, my current one is 24v 4500 watts and the 12v equivalent is 2500 watts that the Australian market got. What I need to know is whether the 24v starter will have enough grunt at 12v to start the truck. I won't be starting it in super cold weather maybe -3 will be absolute worse but most of the winter it won't be in the negatives. I tend to leave camp after 10.00 am

Another consideration is the Lifepo4 cells I'm using has a max current draw of 1360 amps and don't have much voltage sag, unlike the lead-acid batteries. If I was drawing let's say 300 amps my voltage will only sag as low as 13v whereas you'll need a very good lead-acid battery bank to sag above 11v at that current.

Currently, my 24v starter draws 190 amps at 11v per battery. If the voltage was now 13v from the Lifepo4 cells would the amps increase to accommodate the drop in voltage to maintain starting capacity. I don't think it will need the full 4500 watts just the standard 2500watt starter capacity I would imagine will be sufficient as it seems to start instantly now, don't mind it turning over once or twice.

My other concern is if it has the torque to run at 12v will it have the speed to get the engine up to a starting RPM.


and lastly, if it won't work what is the difference to allow the 2500 watt one to work.
 

NLXTACY

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You need to swap out the starter. I used an ML-ACR to convert the 24v to dual batteries.
LiFePo isn’t designed as a starting battery. I would reconsidered that as only the aux battery.

just make sure the 12v starter you get isn’t internally damaged like ours was.

This is what I recently did for a customer (I’ll post schematic later):

19D3B1E7-1E05-4BF4-8891-79F3FDBFF382.jpeg


FAA01238-0566-4BD2-94D6-B0E5DFD7D906.jpeg


B995EC1E-0FEF-4DAA-A2D3-FDD77B857AC2.jpeg
 
Joined
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You need to swap out the starter. I used an ML-ACR to convert the 24v to dual batteries.
LiFePo isn’t designed as a starting battery. I would reconsidered that as only the aux battery.

just make sure the 12v starter you get isn’t internally damaged like ours was.

This is what I recently did for a customer (I’ll post schematic later):

View attachment 2778122

View attachment 2778123

View attachment 2778124
These
You need to swap out the starter. I used an ML-ACR to convert the 24v to dual batteries.
LiFePo isn’t designed as a starting battery. I would reconsidered that as only the aux battery.

just make sure the 12v starter you get isn’t internally damaged like ours was.

This is what I recently did for a customer (I’ll post schematic later):

View attachment 2778122

View attachment 2778123

View attachment 2778124
These Lifepo4 cells will be fine for starting, actually will be a lot better than lead acid. The whole point of it is to save some space and weight and only have 1 battery as starter and aux with a cut off so only can drain down to 30 giving me enough capacity to still start it. So how come you need to change the starter, is it because it cranks to slow or pushes to much current through?
That schematic would be awesome thanks.
 
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The other option is having 2 12v lifepo4 batteries in 1 battery pack and extend the cables over but it gets a bit more complicated keeping the cells balanced and designing the pack also gets a bit complicated and will need 2 jumper packs if I manage to accidentally drain them.
 
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I would think you'll have to use 12 volt starter.
Having had a hdj81, when one battery was weak, you get nothing more than a clicking solenoid on attempted starting
yeah that is because the current needs to go through the flat battery in order to start it which the flat battery has a lot of internal resistance.
 
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Its an amperage thing:
Watts=Volts X Amps
4500W/24V=187 amps
1200W/12V=100 amps

You straight up just arn't pulling enough amps to drive a 24V starter with a 12V system.
To drive a 4500Watt starter at 12V you'd need to draw 375Amps. The wiring might become the fuse.
 
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Its an amperage thing:
Watts=Volts X Amps
4500W/24V=187 amps
1200W/12V=100 amps

You straight up just arn't pulling enough amps to drive a 24V starter with a 12V system.
To drive a 4500Watt starter at 12V you'd need to draw 375Amps. The wiring might become the fuse.
Yeah so thats what i'm wondering factory 24 volt starter right due to voltage drop its more like
4500 watts / 22v = 205 amps,
in practice I get 190 amps but not sure how accurate my amp meter is or not pulling full capacity out of the motor.
but the 12v equivalent is only 2500w
so with Lifepo4, I'll get 13v starting so lets say it needs a minimum of 2500w to start the truck will the starter draw just what it needs to start it?
so 2500w/13v = 192 amps.
even if it takes 3000w that's only 230 amps at 13v which isn't too far over the rated amperage capacity of the starter. The problem I'm having is understanding if this is what the motor will do. I know winch motors draw current based on how much load is on the motor so thinking it will be the same here.

I know it will be slower too but just need to know if it will be fast enough to start it.
 
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You need a 12V starter if you want it to operate at 12V.

24V starter as has been started will barely engage at 12V (if at all) and it certainly won't spin worth a damn to start a diesel even in hot weather.

It would be like trying to run a 12V starter when the battery is at 6V - dead as a door nail mate.

cheers,
george.
 

mudgudgeon

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I also don't mind rewiring with appropriate sized wire to further reduce voltage drop

I would expect very little voltage drop over a few feet of cable.

If your engine is in good shape, you only need a momentary current draw.

A 1HD-T (FT) should fire on the very first compression stroke, unless you are in extreme cold conditions, which is what the 24 volt system was for.
Any HD-T I've had anything to do with, starting was "turn the key to start, and release virtually immediately".
 
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I would expect very little voltage drop over a few feet of cable.

If your engine is in good shape, you only need a momentary current draw.

A 1HD-T (FT) should fire on the very first compression stroke, unless you are in extreme cold conditions, which is what the 24 volt system was for.
Any HD-T I've had anything to do with, starting was "turn the key to start, and release virtually immediately".
yup that's what it does fires on the first compression stroke which is why I was thinking it'll be okay to drop some starting capacity.
 

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