Want to convert 24V SLA system to lithium

[daveola]

I have a 36kWh 24V SLA system in bus (chosen because it matches my bus and my 7kW bus alternator, which is great for charging on the road).

I need to switch to lithium (probably LiFePO4), because SLA is a joke and has endlessly failed to meet it's specs.

I don't need it to be as large, because I don't use the bus as much (and lithium gives me a much bigger discharge range), but here is what I would like.

1) Storage of 3-6kWh
2) Output of 3kW or more (120VAC)
3) Ability to charge off my 1kW solar bank (runs up to 100+V - or I could keep my solar MPPT and charge off 24V output)
4) As high a charge rate as reasonably possible from my 10kW generator (120VAC)
5) Nice to have: The ability to charge off my 24V 7kW bus alternator for charging on the road.
6) Nice to have: Remote panel and/or app control/monitoring

I've been looking at just buying something like the AC500/B300S and dealing with losing 24V input, but I have a feeling that if I knew which components to buy I could get everything I wanted for the same price or better.

I designed and built my current system consists of the 24V battery bank, two Xantrex SW4024 24V 4kW inverters, an 80A 24V MPPT solar charger for my 1kW bank (and a backup charger) - so I'm comfortable dealing with connecting all of this together, but what I *don't* have right now is the time needed to learn about all of the options available in the lithium world to replace all of this. It was a fun project the first time around, but my time is too limited to do all the research *and* do the replace/install, so I was hoping for some pointers

So:

1) Is it easy enough to just get the components to put together a lithium system like this?
2) If not - a suggestion of what I should get, and is it difficult to find a large enough buck/boost that could convert my 24V inputs to charge the bank?

 

[daveola]

And I should probably be clear, specifically I'm trying to figure out a good list of:

Inverter
Charger/BMS
Solar charger (if it needs to be separate)
Way to connect 24V alternator to the battery bank (charger or buck/boost or ??)
Batteries

Looking through Will's Youtube, I can easily find:

But it's not quite big enough, it's out of date, and usually when people increase the size, they just switch to 48V or such

 

[daveola]

Does anyone know someone who can help me find the components for a system like this?

 

[jasonhc73]

Let's start by tempering your expectations of SLA.

SLA is very effective when used properly.

Does anyone know someone who can help me find the components for a system like this?

That is literally what this entire website is about.

This is a DIY website. If you don't have time to learn and to do it, then higher someone and pay them for their knowledge and expertise.

 

[BenQ]

Everything you want is doable, but what’s your budget?

 

[BenQ]

And I should probably be clear, specifically I'm trying to figure out a good list of:

Inverter
Charger/BMS
Solar charger (if it needs to be separate)
Way to connect 24V alternator to the battery bank (charger or buck/boost or ??)
Batteries

Looking through Will's Youtube, I can easily find:

But it's not quite big enough, it's out of date, and usually when people increase the size, they just switch to 48V or such

If you want to connect a 24v lifepo4 battery bank to your 7kw 24 volt alternator you’ll need a 24v 300 amp, fuse, relay, charger, and BMS between them. Or keep a few SLA batteries on the alternator and then put you’re 80 amp 24v charger between the SLAs and LIFEPO4s

 

[daveola]

Or keep a few SLA batteries on the alternator and then put you’re 80 amp 24v charger between the SLAs and LIFEPO4s

Where can I find an 80A 24V charger? I've been trying to find any sort of 24V charger that's over 30A or so, and they seem to be unobtanium, except for the WhisperPower Supreme Pro 80 which I'm trying to get a price on.

 

[daveola]

If you want to connect a 24v lifepo4 battery bank to your 7kw 24 volt alternator you’ll need a 24v 300 amp, fuse, relay, charger, and BMS between them.

The question is whether or not this can be done without a charger - does 27V at least accomplish some charging, or is it going to do nothing, or, even worse, is it bad for the batteries?

If not, where can I find a 24V-24V DC-DC charger that is anywhere close to 7kW??

 

[BenQ]

Where can I find an 80A 24V charger? I've been trying to find any sort of 24V charger that's over 30A or so, and they seem to be unobtanium, except for the WhisperPower Supreme Pro 80 which I'm trying to get a price on.

You already have one. You can plug the battery cables into the solar input of your mppt solar charger and your lithium battery on the battery side.

Alternator -> AGM/SLA Battery -> Solar mppt -> Lithium battery

Check out this video at 15:27

 

[BenQ]

Or a relay isolator should do the trick too. Alternator -> 24v SLA -> relay isolator (on/off with engine) —> 24v lithium batteries -> inverters - house loads

I think using a charger in between the batteries is somewhat safer, but I’ve seen both ways, but no one’s ever compared the two that I know of…

 

[daveola]

You already have one. You can plug the battery cables into the solar input of your mppt solar charger and your lithium battery on the battery side.

Alternator -> AGM/SLA Battery -> Solar mppt -> Lithium battery

That's an interesting idea - I have the 80A solar charger that I could use and have it switch between the alternator and the solar, but then I am limited to only 80A of charge on my lithium and lose the solar input while driving.

 

[BenQ]

So do some math, what will get you more power on a 1 hour drive? Solar panels or alternator? You could do both if you get another charge controller.

 

[daveola]

Does a solar MPPT handle an alternator as an input well? I've heard that I might want things like an alternator isolator and such because of the sudden switching of loads on the alternator. And is this a safe input for the solar MPPT? Does feeding it 300A of 24V cause any problems, or will it just only take 80A from the alternator and ignore the rest?

One of the big questions for me is, when I see a "max charge current", is that the most it will take? Does it just clip at that level? Does it get damaged if fed more than that?

 

[BenQ]

Does a solar MPPT handle an alternator as an input well? I've heard that I might want things like an alternator isolator and such because of the sudden switching of loads on the alternator. And is this a safe input for the solar MPPT? Does feeding it 300A of 24V cause any problems, or will it just only take 80A from the alternator and ignore the rest?

One of the big questions for me is, when I see a "max charge current", is that the most it will take? Does it just clip at that level? Does it get damaged if fed more than that?

I did not advise connecting the alternator directly to the Mppt.

my idea is using SLA batteries (charged by the alternator as an input. With a 100amp fuse in between (I don’t know if there is an 80 amp fuse out there somewhere) it should be good.

 

[BenQ]

Does a solar MPPT handle an alternator as an input well? I've heard that I might want things like an alternator isolator and such because of the sudden switching of loads on the alternator. And is this a safe input for the solar MPPT? Does feeding it 300A of 24V cause any problems, or will it just only take 80A from the alternator and ignore the rest?

One of the big questions for me is, when I see a "max charge current", is that the most it will take? Does it just clip at that level? Does it get damaged if fed more than that?

lol yes if you connect the alternator straight to the mppt w/o a SLA battery as a buffer bad things will happen. Even with a buffer, bad things could happen, so be sure to put a fuse in between there

 

[daveola]

Right - but if the batteries, left to there own devices, will happily take 300A, then I'll just keep blowing the fuse over and over.

So the question in a nutshell is:

Do Lithium batteries take only as much current as they need if everything is working well, or do I need to specifically limit the current to the batteries with something like a DC-DC converter to avoid the Lithiums taking too much current and damaging themselves?

For SLA, you don't have to worry about this - they don't take more current then they need, unless something has gone wrong. But it seems like Lithiums are different with regards to this.

 

[BenQ]

Right - but if the batteries, left to there own devices, will happily take 300A, then I'll just keep blowing the fuse over and over.

So the question in a nutshell is:

Do Lithium batteries take only as much current as they need if everything is working well, or do I need to specifically limit the current to the batteries with something like a DC-DC converter to avoid the Lithiums taking too much current and damaging themselves?

For SLA, you don't have to worry about this - they don't take more current then they need, unless something has gone wrong. But it seems like Lithiums are different with regards to this.

Lithium batteries will take whatever you give them, it’s the BMS that protects them from themselves. But if you try giving them 300 amps you will eventually fry the BMS. Fortunately, in my plan you will have some very resistive SLA batteries soaking up a lot of the amps first, then they will pass on a much reduced # of amps to your charge controller and then your charge controller will pass that safely through a fuse that will blow just in case some outrageous amount of amps makes it that far (unlikely, but ya never know) and then to the BMS which will shut off charging as a last line of defense to keep your precious lithium batteries safe.

 

[BenQ]

With this battery and a 200 amp fuse, you should be just fine, you could just put it in parallel with your SLA batteries without the need for the charge controller between them.

Redodo 24V 200Ah LiFePO4 Battery with 200A BMS Lithium Battery, Max. 5120Wh Energy Capacity, 4000-15000 Deep Cycles & 10-Year Lifetime, Solar System Back-up Power, RV, Trolling Motor etc. https://a.co/d/3QGmETT