Building a full-time vanlife retired-ambulance — 48V system for mini-split, induction cooktop, Starlink, hot water, TV — looking for advice :)

[EvergladesRoamer]

Hey everyone — I just bought a retired ambulance on a 6.7L Cummins diesel and I’m converting it to full-time vanlife. I want a 48-volt house system that can run a ductless mini-split, an induction cooktop, Starlink, hot water heater, lights, TV, and other typical loads — and I’d like the battery bank to last a couple days without charging. I can weld and will build the battery enclosure (leaning aluminum for weight).

What I’m hoping to get from this thread: real-world sizing advice, recommendations on Victron (or equivalent) components, tips on alternator upgrades / DC-DC charging, and any gotchas (BMS, ventilation, wiring, soft-start for the mini-split, generator/shore integration).


What I have / constraints

• Vehicle: retired ambulance with 6.7L Cummins diesel (running and mobile).
• Prefer 48V house system (weight/efficiency reasons).
• Goal: battery bank to comfortably run critical loads for ~2 days off-grid.
• Loads I’ll run (typical): mini-split A/C, induction cooktop (intermittent), Starlink, hot water heater (TBD: electric vs propane), TV, lights, water pump, fridge, and electronics.
• Prefer Victron ecosystem (inverter/charger, DC-DC, Cerbo GX, BMS) but open to alternatives.

Initial questions

1. Is 48V the right call for a rig this size vs 24V? (I’m leaning 48V for lower current / smaller busbars.)
2. Recommended battery capacity and maybe best bang for buck in which batteries to look into (kWh / Ah at 48V) for 2 days for the loads above?
3. Inverter sizing — MultiPlus II 48/5000 enough, or should I go larger to cover induction + A/C start loads?
4. Best approach to charge from the vehicle alternator (DC-DC vs direct)? Alternator upgrades you’ve used on a 6.7 Cummins?
5. Recommended Victron models and any alternative parts (BMS, contactors, shunt, Cerbo GX, remote panels).
6. Real world tips: soft-start device for mini-split, wiring gauge, fusing, ventilation for battery box, achieving Shore+Alternator+Solar seamlessly.
7. If you’ve done a similar ambulance → vanlife conversion, please post photos and wiring diagrams.

Appreciate any advice and links to model numbers or wiring diagrams — thanks!
I’m glad I found this community

 

[justinm001]

Solar? This will be the biggest benefit for 48v and also help last multiple days.

5kw inverter sounds perfect. A dual burner 120v/1800w induction cooktop works really well. A/c mini split shouldn't have easy start or large startup so should be ok, so depending on size that's usually 1500w. A 5kw inverter is 40w idle loads so 1kw per day just being turned on.

DC DC converter you'll only get 400w each with the Victron 12/48 and they aren't smart so you will only get like 70-80% charge. You can stack a bunch though.

For shore id suggest using 50a and using 1 leg (3 of 4 wires). One thing is with a 5000w Victron inverter the minimum charge is like 13amps so just enough not to trip a 15a breaker when moochdocking

One thing I'm about to do is use a marine water heater 11gal. It's electric but has a loop so I can run a diesel fluid heater with a pump, and/or use engine coolant.

You probably want 10-20kwh of batteries. 2-4 rack batteries. They make those huge 15kw wall batteries which might be easier to login.

 

[HRTKD]

I have a 48v 280Ah LiFePO₄ battery in my trailer. It is very heavy at over 225 lbs for just the cells. It takes up a pretty good size footprint too. I suspect your rig can handle the weight, but do you have the room?

Take a look at the energy audit spreadsheet in the Resources section of the forum. It can help you get a handle on how much battery you really need.

System Energy Audit and Sizing Spread Sheet

Apr 20, 2020

Tool for estimating power usage and estimating system size

• FilterGuy
• Planning and Sizing Tools

If possible, cover every square inch of the rooftop in solar panels. I have enough solar that I don't need - or use - any alternator charging.

There are a couple of other ambulance builds here on the forum. Look them up and see what they did.

 

[EvergladesRoamer]

Solar? This will be the biggest benefit for 48v and also help last multiple days.

5kw inverter sounds perfect. A dual burner 120v/1800w induction cooktop works really well. A/c mini split shouldn't have easy start or large startup so should be ok, so depending on size that's usually 1500w. A 5kw inverter is 40w idle loads so 1kw per day just being turned on.

DC DC converter you'll only get 400w each with the Victron 12/48 and they aren't smart so you will only get like 70-80% charge. You can stack a bunch though.

For shore id suggest using 50a and using 1 leg (3 of 4 wires). One thing is with a 5000w Victron inverter the minimum charge is like 13amps so just enough not to trip a 15a breaker when moochdocking

One thing I'm about to do is use a marine water heater 11gal. It's electric but has a loop so I can run a diesel fluid heater with a pump, and/or use engine coolant.

You probably want 10-20kwh of batteries. 2-4 rack batteries. They make those huge 15kw wall batteries which might be easier to login.

I was thinking of setting up the system to connect solar a bit later , I’m trying not to drill holes on the ambulance since it’s marine grade aluminum fully welded .

I really appreciate your feedback
Thank you so much

 

[EvergladesRoamer]

I have a 48v 280Ah LiFePO₄ battery in my trailer. It is very heavy at over 225 lbs for just the cells. It takes up a pretty good size footprint too. I suspect your rig can handle the weight, but do you have the room?

Take a look at the energy audit spreadsheet in the Resources section of the forum. It can help you get a handle on how much battery you really need.

System Energy Audit and Sizing Spread Sheet

Apr 20, 2020

Tool for estimating power usage and estimating system size

• FilterGuy
• Planning and Sizing Tools

If possible, cover every square inch of the rooftop in solar panels. I have enough solar that I don't need - or use - any alternator charging.

There are a couple of other ambulance builds here on the forum. Look them up and see what they did.

Yes I have plenty of space it has a few large boxes that can fit easily .
I’m going to look into the energy audit spread sheet that sounds like a great tool .
I appreciate you taking your time to help out

 

[EvergladesRoamer]

does anyone recommend a battery ?
That’s the best bang for buck in a 48v system ?

 

[justinm001]

does anyone recommend a battery ?
That’s the best bang for buck in a 48v system ?

Ecoworthy seems to be the best option. You also can get a CerboGX (not S) and plug them in directly then no need for a shunt.

If you can fit 2000w of panels on the roof you'll be able to make 5+kwh per day which is 1 100ah LFP battery. Its free power thats there so you charge during the day and discharge at night. If properly sized you can last forever.

Drill a few holes and use brackets to hold all the panels. Then you're only worried about 6 or so bolts going through the roof. Cover in that eternalbond or whatever and it'll last forever too.

 

[chrisski]

I’d do a good power audit and come up with a good battery bank size.

My guess is you’re asking for 20 kWh of power to run an AC about 14 hours a day for two days. This is a 400 lbs battery bank that could be waste high 2’ wide and 3’ deep. My power is just a guess actual AIR CON draw is more important, which finding planning data is a needle in a hay stack. Adding a hot water heater and electric fridge will add more power.

Solar to charge that in an ambulance build is not realistic, mostly because of the 2 kWh to 5 kWh array needed. 1 meter square of panels equals 180 watts of power so a minimum of around 12 meter squared. This is likely your whole roof and ground mount the same size.

You can make it easier by running a generator a few hours a day to cover what the panels don’t produce for battery charging.

 

[RvNaut]

Appreciate any advice

Your roof will not hold a lot of solar. I have a 48v 15kwh battery that I have been living off of for 1.5 years in a class A RV. It weighs close to 275#s.
I had 1250 solar up top, and knew it was insufficient, but money.. this summer I bought and am now putting up 4250w ( 8 535w panels)

In order to run your AC 24/7 you will be running the engine and that converter a lot.

Look at mini-splits to save power. Consider a small inverter genset supplemental charging.

What @chrisski said is spot on...

 

[S Davis]

I have 13.5kwh of batteries (225lbs) on my crew cab that runs my a/c, refrigerator, aux diesel fuel pump, MDVR, lighting, battery heat and ventilation, work tool charger, all 12 volt. I have a victron 12/3000 for microwave and other non battery tools. No solar, I charge at 100 amps from the 220amp alternator or shore power.

 

[HRTKD]

My guess is you’re asking for 20 kWh of power to run an AC about 14 hours a day for two days. This is a 400 lbs battery bank that could be waste high 2’ wide and 3’ deep. My power is just a guess actual AIR CON draw is more important, which finding planning data is a needle in a hay stack. Adding a hot water heater and electric fridge will add more power.

EvergladesRoamer said he's going with a mini-split, which I suspect will use a lot less power than the typical RV rooftop air conditioner. So it may be doable.

Like I said already, put as much PV on the roof as possible. If it isn't enough, add more on the ground.

 

[chrisski]

EvergladesRoamer said he's going with a mini-split, which I suspect will use a lot less power than the typical RV rooftop air conditioner. So it may be doable.

Like I said already, put as much PV on the roof as possible. If it isn't enough, add more on the ground.

Definitely doable, but a bit of work. I wish I could find the video that was popular here a few years ago which was an ambulance build or similar. That ran at 500 W. He filled his roof up with panels and then slid an equivalent from underneath.

I would picture a 2 day supply of electricity to look like this after build



Depending on how low the sun is to the horizon and the actual kWh requirement that could cover running the appliances and a two day reserve.

It’s a bit of space to give up in an ambulance build. Also several thousand dollars.

 

[EvergladesRoamer]

Thanks for the great feedback gentlemen i truly appreciate it.
My boat electrician friend who’s going to do the install says I should see batteries we are going to build the system off so we can build a comfortable housing to be able to slide out and work on .
My questions are should I look into the rack batteries and if so which ones?
And what else should I purchase first to start installation?
I’m looking into 15kw-20kw
And if possible can I get a list of what to get to make system complete
And ready for some solar in the future?
I’m worried I may under order or over and get stuck w electronics I can’t return.

Any advice would be greatly appreciated

 

[chrisski]

Done over again, ii would consider these eg4? server rack batteries at 5 kWh each:

EG4 LifePower4 48V v2 - EG4 Electronics

Discover the EG4 LiFePOWER4 48V v2 battery, designed for durability and high performance with enhanced features.

eg4electronics.com

Or

EG4® LL-S 48V 100AH Lithium Iron Phosphate Battery

The EG4 LL lithium battery 48v boasts a lifespan exceeding 15 years, over 7000 deep cycles, along with safety features and BMS monitoring.

eg4electronics.com

Id stack three or four. Intent would be to put them on a server rack sized for the three or four batteries I’d purchase.

Please keep in mind these are not designed for a mobile installation, but I doubt you’d find a mobile battery bigger than 1200 Wh or perhaps 3 kWh.

I ordered my 13 kWh battery cells from China and assembled myself. That takes days of work. Getting a server rack with pre made busbars and wiring would save a lot of time, and not be much more than I paid.

 

[justinm001]

Done over again, ii would consider these eg4? server rack batteries at 5 kWh each:

EG4 LifePower4 48V v2 - EG4 Electronics

Discover the EG4 LiFePOWER4 48V v2 battery, designed for durability and high performance with enhanced features.

eg4electronics.com

Or

EG4® LL-S 48V 100AH Lithium Iron Phosphate Battery

The EG4 LL lithium battery 48v boasts a lifespan exceeding 15 years, over 7000 deep cycles, along with safety features and BMS monitoring.

eg4electronics.com

Id stack three or four. Intent would be to put them on a server rack sized for the three or four batteries I’d purchase.

Please keep in mind these are not designed for a mobile installation, but I doubt you’d find a mobile battery bigger than 1200 Wh or perhaps 3 kWh.

I ordered my 13 kWh battery cells from China and assembled myself. That takes days of work. Getting a server rack with pre made busbars and wiring would save a lot of time, and not be much more than I paid.

I'm about to swap all out for a pair of those new Jixing (or however it's spelled) 15kwh batteries.

 

[chrisski]

I'm about to swap all out for a pair of those new Jixing (or however it's spelled) 15kwh batteries.

Is this the one?

China 15KWH Lithium Battery Manufacturers Suppliers Factory - 15KWH Lithium Battery Price

We're well-known as one of the leading 15kwh lithium battery manufacturers and suppliers in China. Please feel free to buy or wholesale high quality 15kwh lithium battery in stock here from our factory. For price consultation, contact us.

www.jingsun-power.com

It fits what I’d consider with the compact size and pre built and says it’s for EVs.

Also, are you using this in a mobile build?

 

[justinm001]

Is this the one?

China 15KWH Lithium Battery Manufacturers Suppliers Factory - 15KWH Lithium Battery Price

We're well-known as one of the leading 15kwh lithium battery manufacturers and suppliers in China. Please feel free to buy or wholesale high quality 15kwh lithium battery in stock here from our factory. For price consultation, contact us.

www.jingsun-power.com

It fits what I’d consider with the compact size and pre built and says it’s for EVs.

Also, are you using this in a mobile build?

This one that will reviewed. Yes for my RV. 5kw solar , 10kw inverters. I have 2x100ah sok racks now and right at max 100a BMS for both charge and discharge. So not only will I triple my size but will have plenty to charge faster with chargeverters

 

[chrisski]

This one that will reviewed. Yes for my RV. 5kw solar , 10kw inverters. I have 2x100ah sok racks now and right at max 100a BMS for both charge and discharge. So not only will I triple my size but will have plenty to charge faster with chargeverters

Thanks. That is a good size to place in an RV.

 

[EvergladesRoamer]

I’d do a good power audit and come up with a good battery bank size.

My guess is you’re asking for 20 kWh of power to run an AC about 14 hours a day for two days. This is a 400 lbs battery bank that could be waste high 2’ wide and 3’ deep. My power is just a guess actual AIR CON draw is more important, which finding planning data is a needle in a hay stack. Adding a hot water heater and electric fridge will add more power.

Solar to charge that in an ambulance build is not realistic, mostly because of the 2 kWh to 5 kWh array needed. 1 meter square of panels equals 180 watts of power so a minimum of around 12 meter squared. This is likely your whole roof and ground mount the same size.

You can make it easier by running a generator a few hours a day to cover what the panels don’t produce for battery charging.

I did the audit and you were spot on with about 20 kWh
Do you have any batteries you would recommend?

 

[chrisski]

It’s difficult for me to recommend something I have not used in a mobile app.

I have built my mobile battery with cells from China, but I would wish that experience on no one.

I like the three batteries listed in post #14 and on. I would like the EG4 batteries the best and would contact them about mobile applications and if they sell a four place server rack and if not the could give a recommendation on what to buy.

Whatever you decide, look at the max heat and se if you can avoid using in those conditions. I’m not sure EG4,has low temp protect.

 

[robby]

It’s difficult for me to recommend something I have not used in a mobile app.

I have built my mobile battery with cells from China, but I would wish that experience on no one.

I like the three batteries listed in post #14 and on. I would like the EG4 batteries the best and would contact them about mobile applications and if they sell a four place server rack and if not the could give a recommendation on what to buy.

Whatever you decide, look at the max heat and se if you can avoid using in those conditions. I’m not sure EG4,has low temp protect.

Why would anyone buy EG4 batteries when Eco Worthy 48V 100Ah batteries are about 80% cheaper and from my experience work a lot better.

 

[justinm001]

Why would anyone buy EG4 batteries when Eco Worthy 48V 100Ah batteries are about 80% cheaper and from my experience work a lot better.

OP is wanting 12v... How is ecoworthy better than the EG4 48v counterpart?

 

[chrisski]

Why would anyone buy EG4 batteries when Eco Worthy 48V 100Ah batteries are about 80% cheaper and from my experience work a lot better.

I know nothing of the ecoworthy battery, so can’t say anything.

Would you recommend it?

I’m not really partial with ecoworthy since I cancelled two orders from them after a bait and switch five years ago.

 

[robby]

OP is wanting 12v... How is ecoworthy better than the EG4 48v counterpart?

The Passive Balancer in the Eco Worthy BMS actually works very well while the Eg4 sucks.
The Cells in the Eco Worthy stay well balanced while the EG4 drift all over the place.
I have both in use right now and there is no comparison.

 

[Nef003]

You can make it easier by running a generator a few hours a day to cover what the panels don’t produce for battery charging.

Very true. Yet
Add as much panels as you possibly can.

Also - why not convert the alternator to 48v to charge your batteries as you drive ? That would also help a ton.