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How to Charge 24V Battery From 12V Alternator?
#1
I tried a search but nothing popped up.

I have four 24v Lithium battery modules that I want to install in my camper van. The plan is to run a 24vdc air conditioner.

Each module is 24v at 4KW  Life PO4  3.2v cells.  8S config.

The van has twin 250 amp 12 alternators. 

The AC will consume 400ah ~ per day.

How can I recharge via the alternators ?  I will have solar as well but only 1600 watts .

Thanks in advance.
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#2
Use an adjustable voltage DC to DC boost converter... For an application like this I would use something from a brand name (I like Victron), not those cheap Chinese PCB modules.
https://www.victronenergy.com/dc-dc-converters

For solar, you can use a MPPT charge controller.
https://www.victronenergy.com/solar-charge-controllers

You can use both simultaneously, the DC-DC from the 12v system and solar MPPT on the 24v system to charge your lithium battery bank.
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#3
Thanks Crimp Daddy for the quick reply.

The module can be rewired for 12V but the 24 volt AC unit has more BTU's than the 12V model.

The Victron has a 30 amp max, I guess I would need 4 of them.
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#4
It really depends on how you want to balance that load across your 3 input sources.

You have battery
Supplemental charge coming from alternator via DC-DC to the 24v system.
Supplemental charge coming from solar directly into the 24v system.

You might not need to size the DC-DC so large, but I also don’t know the load calcs from top to bottom. You might have a much easier time during the day with the panels providing the bulk of the supplemental charge.

Is the AC unit inverter/variable refrigerant where it can ramp up/down? Those would be idea as it matches the heating load and does not run at 100% power when on.
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#5
Maybe change one of your alternators for 24v. I imagine by the time you buy a boost converter big enough, its probably cheaper to buy a 24v alternator.

Also beware. Alternators can be damaged when attempting to charge lithium cells due to their low internal resistance.
Korishan and hbpowerwall like this post
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#6
I agree with Geek. I saw a video a few weeks back that showed how the alternator gets abused between lead acid and lithium. To a standard alt, a lithium battery is "almost" a dead short and will cause the alt to run at near 100% output, regardless of rpm of the alt (rpm's does make a different, especially under heavy load; that fan on the pulley needs to cool the alt or it'll burn out). You "can" charge lithium with a standard alt, but you need to have a limiter, like a DC-DC, even if it's 12V-in and 12V-out.
But I think the 24V alt would be a better choice as it's designed to handle a much higher volt/amp output by default. Think of diesels as they run 24V, 2 LA's under the hood. That's potentially 200-300A or even more.
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#7
Diesels run at 24v? Maybe the OTR trucks. Even our fire trucks are 12v systems.

There are smart alternators that are designed for lithium charging. That might be a good place to look. Otherwise the DC-DC converter. You are introducing losses with that. You can stack multiple DC-DCs from victron. They are nice little units but they aren't cheap.
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#8
The two batteries in diesel pickup trucks are usually wired in parallel, not series. It's still a 12V system. There are two batteries so your truck will still start after running the grid heater/glow plugs. I don't know about large tractor trailer trucks, those might be 24V?
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#9
(11-20-2019, 04:31 PM)gpn Wrote: Diesels run at 24v? Maybe the OTR trucks. Even our fire trucks are 12v systems.

There are smart alternators that are designed for lithium charging. That might be a good place to look. Otherwise the DC-DC converter. You are introducing losses with that. You can stack multiple DC-DCs from victron. They are nice little units but they aren't cheap.

No, usually the main system is 12v, but you could have more than one alternator to work a separate 24v system for other needs.
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#10
(11-20-2019, 05:50 PM)Crimp Daddy Wrote:
(11-20-2019, 04:31 PM)gpn Wrote: Diesels run at 24v? Maybe the OTR trucks. Even our fire trucks are 12v systems.

There are smart alternators that are designed for lithium charging. That might be a good place to look. Otherwise the DC-DC converter. You are introducing losses with that. You can stack multiple DC-DCs from victron. They are nice little units but they aren't cheap.

No, usually the main system is 12v, but you could have more than one alternator to work a separate 24v system for other needs.

So its possible to buy/have-installed a 2nd alternator/generator on a standard hauling truck?   For example, if it was a Midnite Solar Classic charge controller, could one get a custom generator for 80v @ 50amp kind of thing powered by the engine?   That would get things up into a much higher level than say 12v @ 100a.
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