How to Charge 24V Battery From 12V Alternator?

Jim-C

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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.
 

Crimp Daddy

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Jim-C

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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.
 

Crimp Daddy

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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 dont 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.
 

Geek

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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

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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.
 

gpn

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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.
 

Crimp Daddy

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gpn said:
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.
 

OffGridInTheCity

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CrimpDaddy said:
gpn said:
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.
 

LithiumSolar

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OffGridInTheCity said:
CrimpDaddy said:
gpn said:
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.

Yes, there are kits out there to install 2 and 3 alternators in one car/truck. You would just need the kit and an appropriately-sized belt. There are people doing it for their crazy subwoofer audio systems lol.
 

Crimp Daddy

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OffGridInTheCity said:
CrimpDaddy said:
gpn said:
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.

Its pretty common in the car stereo world... it drives off a belt, so creating a separate 24v system should be pretty easy.


image_rihlhr.jpg
 

OffGridInTheCity

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CrimpDaddy said:
OffGridInTheCity said:
CrimpDaddy said:
gpn said:
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.

Its pretty common in the car stereo world... it drives off a belt, so creating a separate 24v system should be pretty easy.


image_rihlhr.jpg

WOW! Fantastic - I Love It! I'm looking at starting a custom cargo trailer project in 2020and of course I'd like to set it up with massive battery and PV array andinverter and... A little tiny Victron12v -> 24v 50a just won't cut it. I... want.... power... and this picture looks exactly like the right approach :)
 

Jim-C

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I considered installing a 24v alternator. I would still need a DC to DC converter to maintain the proper steady output voltage.
I'm going to get 4 Orion 12 to 24 with 30 amp output.

Thanks for the replies.
 

camthecam

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I wonder if you had a custom regulator to just lift the field windings and trick the alternator to put out what you want. Rectifier pending of course.
 

OffGridInTheCity

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Based on above I found 12v and to a lessor degree 24v 'second alternator' kits and it looks like they need some kind of regulator. And I'd really like to stay with a 48v lithium ion battery bank so its compatible (my packs are transferable) between my home version and my custom RV.

A while back, for my home battery bank, I bought several 750watt 48v (lithium-ion voltage oriented) chargers from ebay.com. They are on a power strip to turn on 1 or 2 or 3 or 4 etc... (I can control the wattage devoted to charging) and output hooked directly to the battery bank. This lets me use my home generator to charge my battery bank to feed power into my system.

So maybe a similar setup for a 12v or 24v alternator -> 120v inverter and then run a standard 120v based 24v or 48v chargers. I understand there are losses - maybe as much as 20% ? in this scheme - but it might simplify trying to find specific battery bank regulators etc and this would scale up to max the alternator can put out.
 

Yandina

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Yandina now manufactures automatic Lithium compatible series/parallel switches for charging 12, 24 and 36 volt batteries from a 12 volt alternator at up to 100 amps.
www.trollbridge.info
 

CarelHassink

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