Looking for advice on converting RV to 24v batteries and adding solar

I am currently planning on doing a 24v 280ah battery conversion on my RV. I want to be able to run the microwave and AC for short time periods, possibly add more battery power for longer periods later, so thinking of a 3000w inverter. Most BMS that I have looked at seem to max out at 100a and it looks like i need 125a or more to power this load. I plan to go with DC-DC converter for 12v for now. I am wanting to continue to have the ability to charge with shore power and generator, as well as add solar to the mix. Do people have good recommendations for how to configure a setup like this? I'm still in the planning stage so have not purchased the charger, inverter, panels, or anything other than the LiFePo4 cells yet. I am totally new to this, but have basic electrical experience wiring houses, as well as computer programming experience. Any recommendations would be much appreciated.

You want a BMS that does not have internal low voltage or high voltage disconnects. They usually limit current to 100A. I would go with a Chargery 300A BMS. It provides a 12V signal for low or high disconnects. Purchase an inverter that has the capability to turn off from this signal. The on/off switch on my inverter works well as a disconnect. No need for huge mosfet(s) or relay to disconnect.

@Cal Will did not give a very good review of the Chargery, has it improved since he did the review video?

JTrigger said:

@Cal Will did not give a very good review of the Chargery, has it improved since he did the review video?

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I assume you saw the video? Did any of the criticism resonate with your?

What I recall, he didn't like the dorky display, the fact that replaced shuts must be calibrated, SOC low voltage disconnect scenario. There may be more issues with him?

What he didn't mention is that the BMS does an excellent job at managing the battery. It does do an excellent job and that's the main goal. Issues with the display? I don't really care. The display gives me the info I'm looking for. An artistic look of the display is low on my radar. I don't know what technical background Will has, but performing shunt calibration at three locations is far superior than his idea of just entering a shunt rating. Improved current measurement accuracy is a good feature, nothing to criticize. And it's not like every body need to perform a shunt calibration. The BMS comes with a shunt that's already been calibrated. A replacement shunt requires calibration.

There's something like 24 parameters in setup. Some may think so many parameters are a burden. The more parameters I can modify, the better control I have over battery management operation. That will mean reading the manual before complaining when a 20% SOC value disabled battery discharge. He may have though the Chargery BMS is a plug-n-play unit. With that many parameters under operator control, the user needs to have a firm understanding what the BMS is doing. Granted, the previous manual was not the best. There have been improvements.

JTrigger said:

I am currently planning on doing a 24v 280ah battery conversion on my RV. I want to be able to run the microwave and AC for short time periods, possibly add more battery power for longer periods later, so thinking of a 3000w inverter. Most BMS that I have looked at seem to max out at 100a and it looks like i need 125a or more to power this load. I plan to go with DC-DC converter for 12v for now. I am wanting to continue to have the ability to charge with shore power and generator, as well as add solar to the mix. Do people have good recommendations for how to configure a setup like this? I'm still in the planning stage so have not purchased the charger, inverter, panels, or anything other than the LiFePo4 cells yet. I am totally new to this, but have basic electrical experience wiring houses, as well as computer programming experience. Any recommendations would be much appreciated.

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Looks like you're building exactly what I'm building for my Sprinter van. I have a 24V 280Ah 8S pack made from the Eve 280Ah cells many on this site are buying, and will have solar, shore, and alternator via DC-DC converter. I have a Victron Multiplus 3000/24 inverter/charger and 640W solar. I looked at quite a few options, overthinking it I'm sure, before settling on this setup. It's a high power setup for a van, many get by just fine with half of this or less. Everyone's needs are different.

You will want to think about your energy budget and how you will charge that nice battery bank. One of my design goals is to have 5-7 days of boondocking without charging, which is what drives the large bank. I'm estimating 40-50Ah per day average usage (24V system) with ability to throttle that back to maybe 20-30Ah if needed by modulating usage of high power devices such as microwave and induction cooktop. Not currently planning AC (a big power hog) but may in the future for short evening cool-down but not continuous use. Solar may give me peak ~2kWh/day (about 80Ah/day for 24V system) on bright sunny days but much less at say an overcast NW coast setting. Shore power--not often, but the Multiplus will fully charge a drained 280Ah 24v bank in 4 hours so an occasional overnight in a campground enables dumping and filling everything including an empty battery bank.

On the system design, I'd focus first on selection of an inverter that meets your needs, as I think that will be the biggest driver in your system design. Due to the high current, and also the bi-directional nature of this device if you choose an inverter/charger as I expect you will since you want shore power. Adding solar and alternator/DC-DC charging sources is not difficult, lots of options there, current is much lower and not so much a driver in the design. I'll focus on the inverter here.

Not sure about your level of knowledge on inverters but there is at least one important distinction--HF (high frequency) vs. LF (low frequency). Do your own research on that, lots posted here. In short LF are bigger, heavier, and more expensive, but they have useful, usable surge capability to 2 or 3 times the continuous rating. HF inverters may claim peak power at 2X but that will likely be for milliseconds not seconds or minutes as LF can do. The Victron is LF and the 3000VA version can do 2400W continuous, 3000W for 30 minutes, 6000W for 2 minutes. Since your peak loads may be things like running a microwave in parallel with say an induction cooktop, or an AC motor transient while microwave is in use, that surge is actually useful.

The Victron also has the advantage that it is the only inverter/charger that can have independent enable/disable of the charter and the inverter without any modification. This enables your BMS to control it without needing monster relays, and it enables you to keep your inverter working when your charger is disabled (at high voltage) or vice versa at low voltage--your BMS can shut off the inverter but leave the charger active.

As @Cal said, the Chargery BMS is designed for external control rather than internal FET switches and it would work well for this. I agree with Cal's assessment of Will's review. Will got frustrated trying to do the shunt calibration--not sure why, I thought it was trivially easy to do. But after that he hated it and no turning back. But there are a lot of Chargery users on this forum who like it, and the company is responsive to user feedback.

Also the Electrodacus SBMS0 would work well. I have used both and I'm going with the Electrodacus since it has some additional capabilities I want. But for that matter you could interface a commodity FET-based BMS to drive external switches as well, depending on your goals.

@Airtime, appreciate your thoughts on 24V house batteries. How will you charge from alternator?

@Airtime I appreciate your and @Cal suggestions! It sounds like our setup is closer than you might have thought as my RV is built on a Sprinter chassis. ? @Kev0 you can get a second alternator setup for the Sprinters and have a dedicated 24v alternator, but it's not cheap. It might be possible to use a 24v single alternator with a 12v converter to run the motor, I don't know if something like that would work. For me it seems a generator is more cost effective than adding the second alternator, but I already have the generator.

Kev0 said:

@Airtime, appreciate your thoughts on 24V house batteries. How will you charge from alternator?

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I have a Victron 12/24 DC-DC converter. It puts out 20A at 24V so that means it will draw 40-50A from the alternator. Mercedes BEG (Builder Equipment Guide) specifies 40A and recommends DC-DC as a buffer. That guideline has been there forever and alternators are bigger now, mine is 230A. Plus I've heard that it was actually a wiring limitation to Aux battery and not a factor if you go straight to battery/alternator, but I can't verify that at this point. I believe there is more capacity I could pull, many people do it. But I won't try until I can attach a current sensor and temperature sensor so I can monitor the alternator and not burn it up.

JTrigger said:

@Airtime I appreciate your and @Cal suggestions! It sounds like our setup is closer than you might have thought as my RV is built on a Sprinter chassis. ? @Kev0 you can get a second alternator setup for the Sprinters and have a dedicated 24v alternator, but it's not cheap. It might be possible to use a 24v single alternator with a 12v converter to run the motor, I don't know if something like that would work. For me it seems a generator is more cost effective than adding the second alternator, but I already have the generator.

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Yes a second alternator would be a really nice option, I could fill an empty bank in 2 hours of driving. I'm not sure about using the fast idle option, this is my first diesel and still learning about how to treat it. But anyway it's a couple $k plus installation so I'll see how I get on without it first and add it later if I think I need it.

And I don't know about that idea of one 24V alternator with a 12V converter. Seems like a lot of work including major modification to the vehicle system which I want to avoid for various reasons including warranty. Just stick with factory 12V alternator + 12/24 DC-DC converter, or an independent second alternator that is dedicated to the house battery bank.

I'm still tweaking, but...
My setup is a 6s Telsa module (yes, worth it for the $400 on craigslist. ) It's usable voltages are from 19v to 25 or so. I'm only going up to 24ish.
If you're buying new, I would agree with Prose and suggest going LifePO4. Easier, safer.
My BMS is an Electrodacus. Keep in mind that cutoffs need to be north of the shunts, not between battery and shunt.
Charging is provided by a victron smartsolar controller
A 250a solenoid provides load cutoff and is run by the solar controller - if battery is 19v, this is turned off.
A batterysense provides battery temp data to the solar controller and kills charging below 4c ~39 degrees.
A funky 19v iteration of 3kw inverter provides my inverter needs. I'm still testing this. It will not function at all over 24v.
I will likely upgrade that thing at some point but for $300 vs $1200 I'm willing to mess with it.
I'm probably going to pick up a Victron 3000w 24v inverter charger - these will take care of shore charging and provide the power you're looking for.
I'm also running a 40a 12v converter - it happily drives the 12v systems of my camper.
Don't forget to add soft starts to you A/C or you risk burning the motor up for running off an inverter.
This is all on my 5th wheel camper, which also has a 12v battery for the safety brakes and camper setup systems.

Beyond that, I'm adding a secondary safety control system using arduino and raspberry pi.

Having been building this for a while, I have some thoughts for you.
The only really good reason to go 24v or higher is to get better efficiency for power handling.
Solar charging systems can handle double the power -1200w at 24v vs 600w at 12v.

Ironically, you can acquire 12v inverters, wall chargers, etc much cheaper.
I would price the system out at 12v and 24v. IMO, If you're only going to stick a few hundred watts of solar on it, stick with 12v.
I'm working on 1200 watts for mine, so it's totally worth it.

What solar panels are people going with that have limited roof space? I'm trying to figure out the best option for the most power density. I'm willing to pay more to be able to get more watts on my limited roof space of my Coachmen Prism 2200le.

JTrigger said:

What solar panels are people going with that have limited roof space? I'm trying to figure out the best option for the most power density. I'm willing to pay more to be able to get more watts on my limited roof space of my Coachmen Prism 2200le.

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I went with four Renogy 160D-SS 160W panels for 640W total. Reason was that they best fit my Sprinter roof space. 51.3" length is about perfect for direct mounting on the Sprinter roof rails without overhang past the rails, which I did not want. I will have 2 panels in front, then my Maxxair fan, then two more panels, then a Lewmar hatch/skylight in the back over the platform bed. It will all fit, including allowing for rib locations, with not much room to spare.

JTrigger said:

I am currently planning on doing a 24v 280ah battery conversion on my RV. I want to be able to run the microwave and AC for short time periods, possibly add more battery power for longer periods later, so thinking of a 3000w inverter. Most BMS that I have looked at seem to max out at 100a and it looks like i need 125a or more to power this load. I plan to go with DC-DC converter for 12v for now. I am wanting to continue to have the ability to charge with shore power and generator, as well as add solar to the mix. Do people have good recommendations for how to configure a setup like this? I'm still in the planning stage so have not purchased the charger, inverter, panels, or anything other than the LiFePo4 cells yet. I am totally new to this, but have basic electrical experience wiring houses, as well as computer programming experience. Any recommendations would be much appreciated.

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I wanted the same thing and have it in my fifth wheel. But I went with 12 volt for this reason. Overkill solar has 12 V bms at 120 amps. I run four attached to a central busbar giving me 480 amps for short periods but 200 is constant. I started with 8 cells and that powered it fine but wanted more amp hours. I think this is very important if you don't want to spend big bucks is to go with a low frequency inverter. I went with the aims 3000 watt and have no regrets, Check out the inverter store they carry their products and if you keep checking back they list blems and you can get super deals. if you want to run for long periods you want to get rid of the crap original equipment AC and go with a inverter mini split. As an edit the aims does have a 80 amp shore charger and internal switch