Lighten front axle load by changing batteries on Mitsu/Isuzu?

[Jfet]

In my quest to take some weight off of our front axle I had the idea of replacing the twin 12V AGM starting batteries on our Isuzu NRR with something else. The desire is to take 80 pounds off the front axle by replacing the 120 pounds of batteries with something more like 30 pounds (figuring the battery position is so close to the front axle it is supporting about 80% of the weight).

a) What amount of amps is really needed to start this 4 cyl diesel? The current configuration is paralleling two 12V AGM or Gel batteries.

b) Is there a reliable Lithium Iron Phosphate or Lithium Manganese battery that could do the job at 25% of the weight?


Anyone changed their battery configuration to something different?

 

[LeishaShannon]

Just to see if I could i've started our truck using very small (8.4ah) hobby sized LYP batteries, the current available from small lithium batteries are incredible. We're replacing the start batteries ( 2 x 12v wet cells in series) with 40ah LYP batteries which weigh just 6 kg each and because they're physically smaller we've been able to fit them in between the chassis rails, avoiding the need for the ~10kg battery L bracket. Total weight saving is ~30Kg. You will want to fit at minimum a low voltage disconnect to protect the batteries and ideally some sort of SoC monitor like the Victron BMV series.

 

[Jfet]

Just to see if I could i've started our truck using very small (8.4ah) hobby sized LYP batteries, the current available from small lithium batteries are incredible. We're replacing the start batteries ( 2 x 12v wet cells in series) with 40ah LYP batteries which weigh just 6 kg each and because they're physically smaller we've been able to fit them in between the chassis rails, avoiding the need for the ~10kg battery L bracket. Total weight saving is ~30Kg. You will want to fit at minimum a low voltage disconnect to protect the batteries and ideally some sort of SoC monitor like the Victron BMV series.

Excellent information. I am unsure what chemistry I should use since we get colder weather here than probably typical for Australia. I had been thinking LiFePO4 because they are extremely safe but they don't work well in freezing temps. Well, let me amend that. You can warm them up by running something like the headlights for a few minutes then when you go to crank they will be able to put out the amps.

Another consideration is charging since they can take in a lot of amps from your alternator (which may not be up to the task).


The other possibility is to try and go with just one lead acid battery instead of two. The Isuzu uses 2 x 12V in parallel but I don't know that it is really needed to have two.

 

[Gatsma]

Where you will see the need is on your coldest mornings. As an experiment, on a really cold morning in the next couple of months, disconnect one battery and see what happens. If after the first few cranks it slows too much for your taste, connect the other one. At least you will have your answer, with no damage done

 

[Jfet]

Yes. It has not gotten cold yet, but when it does, one experiment I want to do is to measure how much current it actually takes to crank the engine. Is it 400 amps, 600 amps, 800 amps?

This would help me determine what if any Lithium solution would work. The Winston LYP cells say they can handle continuous 3C discharge and 10C discharge for 5 seconds. If you used 100AH cells, that would be 300A continuous and 1000A for 5 seconds (probably could supply something inbetween those figures for 15 to 20 seconds). Four of those cells would be about 28 pounds.

 

[SkiFreak]

I had been thinking LiFePO4 because they are extremely safe but they don't work well in freezing temps.

The latest lithium batteries also have yttrium (LiFeYPO4) which are meant to be significantly better than the standard LiFePO4 batteries when it come to working at low temperatures.

 

[Gatsma]

You definitely want to get a worst-case scenario, at least as best you can. You mention they can take a lot of charging amps, but were wondering if the alternator was up to it. I doubt it would be a concern; you just know that the battery will TAKE a certain charge load; doesn't mean you have to "feed" it that fast. I would think that as long as the alternator was in good enough shape to charge lead-acid batteries, Lithium ones shouldn't be a problem. You just know it'll take whatever you throw at it.
Keep us posted!

 

[LeishaShannon]

Lead batteries are somewhat self regulating.. as they get to ~80% they naturally slow down the charge rate. LYP batteries will accept ridiculously high currents until they are completely full and this may be too much for the stock alternator. I'd suggest using one with over-temperature protection and ideally a remote shutdown so you can stop it when the LYP batteries are full. You probably also want to use a lower charging voltage than the stock alternator will provide.
With LYP there is no reason why you couldn't use your house bank as the start bank too, perhaps the house bank could be inside and somewhat protected from the cold?

 

[Jfet]

Well, uhm, the house bank is at the back of the camper, over the rear wheels of the 176" wheelbase Isuzu. Running 800 amps through 15 to 20 feet of copper wire would mean 00000000 gauge wire at a cost probably exceeding the GDP of Botswana.

 

[westyss]

I experimented using one start battery for a while and two are needed for starting in the winter, summer was okay but as temps neared 0'C it didn't have enough to turn it over.

While I only had one start battery during that winter I needed to hook up the house batteries to it for starting which seems like it might be a viable option to drop one start battery, with maybe a remote switch to connect the house batteries when needed for winter ops.

 

[LeishaShannon]

Ahhhh! Our Isuzu NPS 300 is 24v... only needs ~150A to start so 50mm2 cable does the job quite nicely. 12v would need a tad thicker

 

[Jfet]

I am looking at the Odyssey 65-PC1750T AGM battery right now. $289 US with free shipping from factory.

58 pounds (heavier than a Lithium for sure but not as heavy as twin batteries)

1325A in hot weather
950A at minus 18 C

Sounds like that might be the way to go. If weather is colder than minus 18, use jumper cables or something to hook up a temp starting battery.

 

[dlh62c]

I am looking at the Odyssey 65-PC1750T AGM battery right now.

Is the Odyssey close to the form and fit of the battery your replacing?

Will you have to make modifications to the tray and/or holding clamps to secure it?