Converting a 24 passenger bus into a RV and need help with sizing system. Biggest loads: 12k btu mini split, induction cooktop. Looking to charge minimum 800aH of lithium @ 12v or 400 @ 24v from solar, alternator and shore power. Not sure if I should go 12 or 24. Looking to use Victron components with bank of Ampere Time lithium. Also plan to install diesel heater with hydronic water heater option. Also wondering if I should go with 30 or 50 amp service. Will 800aH @ 12v be enough? How much solar? (would prefer not to cover entire roof with panels). Suggestions?
Shuttle bus, 12 or 24 volt
- Thread starter Tom1962
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sunshine_eggo
Happy Breffast!
Link #1 in my signature. Energy audit will essentially answer your question for you.
Rednecktek
Solar Wizard
You're going to need to do a power audit to figure out what you're going to need, especially with the mini-split and induction cooker.
Other than the wire size, you can go either way most likely. Being as that you're using 12v appliances I would stick with 12v so you don't need to worry about converters and secondary wiring systems. The down side of 12v is the thicker wire needed from the batteries to the inverter which in a bus shouldn't be all that big a deal unless you're putting the batteries and inverter at opposite ends of the bus.
As for the panels, laying flat makes a significant hit on panel production so maximizing your panels is ALWAYS a good idea.
With everything being on a single 120v inverter, I'd recommend a 30a plug so you don't have to mess with the wiring as much. A 50a plug just gets you more hot 120v lines, not 240 (without magic parts) so how many 120v circuits are you going to need? Just get an inverter that has hard wire connectors and direct connect it to your transfer switch, the 30a plug to the transfer switch, and the transfer switch to the main breaker panel.
If you get a charge/verter that can take 120v OR 12v and switch automagically that would be the easiest way to go and give you 1 central system.
Also, if you DIY your batteries out of 304Ah cells it'll take up less than half the physical space as all those Ampertimes and save you money per Kwh. They're super easy.
Other than the wire size, you can go either way most likely. Being as that you're using 12v appliances I would stick with 12v so you don't need to worry about converters and secondary wiring systems. The down side of 12v is the thicker wire needed from the batteries to the inverter which in a bus shouldn't be all that big a deal unless you're putting the batteries and inverter at opposite ends of the bus.
As for the panels, laying flat makes a significant hit on panel production so maximizing your panels is ALWAYS a good idea.
With everything being on a single 120v inverter, I'd recommend a 30a plug so you don't have to mess with the wiring as much. A 50a plug just gets you more hot 120v lines, not 240 (without magic parts) so how many 120v circuits are you going to need? Just get an inverter that has hard wire connectors and direct connect it to your transfer switch, the 30a plug to the transfer switch, and the transfer switch to the main breaker panel.
If you get a charge/verter that can take 120v OR 12v and switch automagically that would be the easiest way to go and give you 1 central system.
Also, if you DIY your batteries out of 304Ah cells it'll take up less than half the physical space as all those Ampertimes and save you money per Kwh. They're super easy.
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BobH
New Member
One of the items that pushed me to a 24v sysyem was the expense of the Victron SCC/MPPT's when going with 12V . Using a 24 v system, the use of much less expensive charge controllers was possible. The savings easily paid for the added 24/12 70A Orion converter.
Rednecktek
Solar Wizard
True that, I completely forgot about that. You'll need half the amps on the SCC for the same wattage of panels which saves some money. It'll be something to numbers crunch on the cost of the larger 12v SCC VS multiple smaller 12v SCC's for your system VS the cost of large enough converters to step down from 24v to 12v and all the extra fuse blocks and such to power all your 12v loads. Since converters have absolutely jack squat for surge support you'll need at least 200w of converter for that diesel heater alone because of the power draw at startup on the glow plug. Add in how much wattage for any/all of your other 12v loads (fans, lights, USB-C PD outlets, etc) and find a converter big enough t handle all that at once.
It's a numbers game really on the budget. Going Victron is already going to be a big hit so unless you've got a fat wallet you're likely going to have to find savings somewhere else.
As others have mentioned an 'energy audit' or at least a rough tally of your largest expected energy consumers is a good first step, it'll help you wrap your head around the project and narrow down your options, and it'll help others help you (because without hard numbers it is difficult to give targeted advice).
For a vehicle based system, most DC devices can be found in both 12V and 24V (and many things advertised as "12V" are in fact 12/24V if you look at the tech specs) but it will be easier finding 12V stuff. That is the main upside of 12V. The main upside of 24V is as you get towards a medium to large system, 24V can be more cost efficient (smaller wires and overcurrent protection, cheaper solar charge controller) and allows a larger inverter if need be.
800Ah * 12.8V or 400Ah * 25.6V = ~10 kilowatt-hours
From what I've seen a single burner induction cooktops are usually 1200-1800W, a dual burner is anywhere from 1800 to 3600 Watts. Its a lot of power but generally you probably won't be using it for hours a day, and won't always be using it at max setting. But still your system--at least the inverter--will need to be sized with that in mind. Using the cooktop and A/C at the same time could likely push you past the point of what a 12V system can comfortably handle. And to replenish the power consumed by the A/C you will need a lot of solar, a large solar array + a 12v system = $$$ solar charge controller, moving to 24V cuts that cost in half.
50A = ~12kW (50A * 120V * 2 legs)
For a vehicle based system, most DC devices can be found in both 12V and 24V (and many things advertised as "12V" are in fact 12/24V if you look at the tech specs) but it will be easier finding 12V stuff. That is the main upside of 12V. The main upside of 24V is as you get towards a medium to large system, 24V can be more cost efficient (smaller wires and overcurrent protection, cheaper solar charge controller) and allows a larger inverter if need be.
Something that I find very helpful is to get in the habit of converting to Watt-hours (or kWh) instead of Ah, it makes the math (and comparisons) more straightforward and more intuitive.
800Ah * 12.8V or 400Ah * 25.6V = ~10 kilowatt-hours
Considering these loads, my first impulse would be to go with 24V.
From what I've seen a single burner induction cooktops are usually 1200-1800W, a dual burner is anywhere from 1800 to 3600 Watts. Its a lot of power but generally you probably won't be using it for hours a day, and won't always be using it at max setting. But still your system--at least the inverter--will need to be sized with that in mind. Using the cooktop and A/C at the same time could likely push you past the point of what a 12V system can comfortably handle. And to replenish the power consumed by the A/C you will need a lot of solar, a large solar array + a 12v system = $$$ solar charge controller, moving to 24V cuts that cost in half.
30A = ~3.6kW (30A * 120V)
50A = ~12kW (50A * 120V * 2 legs)
You may not have a choice if solar is to be a primary energy source and A/C is a must. Running A/C and electric appliances like an induction cooktop off of solar can be a challenge for a small-ish vehicle based build even if you do maximize the solar on your roof. Not impossible, but not easy. How much roof space do you have available?
Lots of good info in your comment, but I just want to point out that many common 12V devices used in vehicle based systems can be found in 24V as well. DC compressor fridges, LED lighting, usb chargers, diesel heaters, and so on are available in 24V (one exception to this is the popular roof fans from Maxxair, which are 12v only). That said you are not wrong, that step-down converters will probably be unavoidable for some things.
Rednecktek
Solar Wizard
Absolutely true, but you can get a 12v light bulb or USB charger at any auto parts store in the country. 24v not so much. The 24v diesel heaters are also a little harder to get parts for. I know of 2 places off the top of my head I can walk in to and buy the 12v versions for right off the shelf though.
This is definitely a consideration as well.
justinm001
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you should at least do 50amp 120 using just 1 leg of the 50amp. 6/3 wire. 3600 vs 6000 vs 12000 and youre only getting 80% of that continuous. You can always use dogbone adapters to go smaller but can't go larger.
As much solar as possible.
Are you adding an alternator just for charging? Get a ws500
As much solar as possible.
Are you adding an alternator just for charging? Get a ws500
justinm001
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They make these little things to convert 24v to anything else for small loads. I just found all my bay lighting is 24v (chassis system is 24v) and swapping with led strip lights this weekend using these. Obviously for small loads but they make converters for large loads too.
5V Regulator Module Mini Voltage Reducer Adjustable Direct Current 4.5-24V 12V 24V to 5V 3A Volt Buck Converter Reduced Voltage Regulator Power Supply Transformer Module (20) https://a.co/d/3xrJbf9
Rednecktek
Solar Wizard
Back when I was looking at doing a 24v system for my camp, I grabbed a 720w converter to shift all my 12v loads onto, including 2 diesel heaters, figuring it was about the biggest thing that had decent reviews at the time.
I've since rethought out that plan and changed things around so it's still in a box, but it's a hefty boy with lots of capacity for about $65
I've since rethought out that plan and changed things around so it's still in a box, but it's a hefty boy with lots of capacity for about $65
Thanks for the replies. An audit is underway. But I'm thinking 12v is the way. I doubt I will be using the mini-split very much while boondocking anyways, as it will be used primarily while hooked up to shore power. With that said, I'm looking at 1000w of solar (4x 250w panels), Victron Multiplus 12v 3000a inverter and the 800 aH of lithium. My bus is built on the F550 chassis with a 6.7L diesel and has dual alternators, so I will be using the extra alternator to charge the battery bank. Victron's DC to DC charger is a bit pricey, but Renogy's 60A charger looks reasonable. I hope to have everything completed next Spring in time for a road trip from Alabama's gulf coast to Alaska. The plan is to use a combination of shore power, solar and DC to DC charging to keep the lithium charged. And considering there will only be two of us traveling, I think 12v will work.
justinm001
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Get a wakespeed ws500 for the alternator over dc charger. Not only will it allow you to push all the power but it'll adapt based on alternator temps so you don't overload it.
Pricey! Why not the Renogy 60a charger? Does it not have the same features for a lot less?
12V 60A DC to DC Battery Charger
Compatible with a multitude of alternator types, the DCC12 Series of battery chargers are the most effective way to charge your auxiliary or house batteries from the alternator/starter battery. Easily install the compact yet sturdy DC1212 on RV¡¯s, commercial vehicles, boats, yachts and many...
www.renogy.com
justinm001
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Pricey! Why not the Renogy 60a charger? Does it not have the same features for a lot less?
12V 60A DC to DC Battery Charger
Compatible with a multitude of alternator types, the DCC12 Series of battery chargers are the most effective way to charge your auxiliary or house batteries from the alternator/starter battery. Easily install the compact yet sturdy DC1212 on RV¡¯s, commercial vehicles, boats, yachts and many...
Completely different. What alternators do you have? Likely 200amps or so each. The Wakespeed will give you whatever that 2nd alternator is rated for and pull as much as it can into your battery. When the alternator gets hot it'll ramp down from 200 to cool then ramp up so you're limited to the temp of the alternator. This means you'll be getting 200amps for first 30 minutes then down to like 100amps to cool then back up/down getting at least 100amps constantly. There's no DC to DC conversion loss either its straight power. It also allows you to setup all kinds of features so it doesn't turn on until 2 minutes after startup so engine can warm up and can turn off/down at idle rpms.
The renogy 60a will give you 60amps max and pulls from your engine's batteries/alternator regardless of anything.
Say you have the 800ah lithium and at 50% (400ah) the dc charger will take 6.6 hours the wakespeed would take under 4 hours to fill up. But if you only trip for an hour it'll charge 60a vs close to 200a.
Down the road you can upgrade the alternator to greater amperage and better cooling to get 300amps.
Yes its pricey but its better if you have dual alternators since you can dedicate one to charging. Wakespeed integrates right into Victron's CerboGX so you can see and log it all which is super helpful.
I can tell you this, nothing's better than knowing your batteries are 100% when you pull into camp.
Could also be the difference in being able to charge while driving with AC/heat or still discharging just not nearly as bad
Not sure about the alternators. But the minimum output according to Ford is 175 for the bottom and 157 for the top alternator. There are several aftermarket suppliers that tout as much as 370a at cruising speed and 200 for idle. So I assume the charging time to complete the 400ah deficit would be only 2 hours at 200a?
justinm001
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Correct as long as your bms can handle it or recommend it. 800ah is usually 2x400ah and each bms is usually 200a so you can charge as much as 400a but 200a would be ideal.
Yes there's all kinds of alternators and massive power. Get the model number and you can get the output graph to see how much power at what rpm. Just know it's alternator rpm not engine and it depends on the pulley size.
But even 150a vs 60a is a huge difference. Yes wakespeed is pricey but it's well worth it especially if you drive a lot.
For instance I have a 50dn alternator that pumps out 300a at 12v. My 12v system has 800ah (2x eg4) and the alternator puts out close to 3000w (230a) after traveling 40ft to the front. This let's me run a 15.5k roof AC unit while driving and still massive 100a or so charge to batteries.
That was my next concern... how big do the cables need to be to run 200+ amps from the alternator to the batteries at 30 feet?
justinm001
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Use that as a guide then a loss calc to determine.
Also price wires because they're expensive
Mines a 40ft DP prevost with engine in back and 12v under front bumper. The alt wire was oem so I'm betting 2/0 and needs to be 4/0 so luckily with a wakespeed I can just plug usb into the app on a laptop and turn it down.
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