48v RV install - possibly omit 48v to 12v converter?

[AustinBlazer]

Hello All,

I'm planning and designing a 48v system for a 31 foot motorhome install;
Victron Multiplus-II 48/3000
48v 100AH battery
Solar ground deployed - additional added to roof in phase2

I see nearly all 48v installs have a 48v to 12v converter to power the stock RV 12v systems. However at 48v there aren't any good options like the 24v non-isolated 70amp Victron module, so a 12v battery may be required anyways to operate slides/etc.

I'm considering just leaving the stock 120v > 12V DC charger in the motorhome with the 12v battery and omitting the 48v>12v converter for these reasons;
1. Few good 48v>12v converter options available to buy today
2. Eliminate needing to wire additional 48v component
3. Leave 120v breaker to charger 12v system as is - I don't like the "put tape warning leave off" solution especially if others may use the RV.
4. Simplifies system design in that 48v is only tied to 120v.
5. Allows flexibility to turn off 48v system and remove battery for some trips, reducing 80lbs of battery weight and reclaiming that storage space. All electrical systems would still function in stock manner without 48v system running.

The primary downside I thought of was the loss of efficiency going from 48v>120V>12v with two steps vs a direct 48V>12V. But even that doesn't seem like an actual loss when I calculated it
Multiplus II Efficiency 48v>120v is 95%
Victron Charger 120v>12v is 94%
Combined is .95*.94= 89%
Victron Orion is 48v>12v = 87% (2% worse)

I don't think the 12v load will be significant so the efficiency probably doesn't matter.

What do people think about omitting a 48v>12v converter?

 

[hidiyguy]

I'm contemplating doing the same thing for a future build using the same logic.

 

[time2roll]

The real efficiency loss is keeping a flooded lead-acid battery top charged 24/7 while in use.

Are there any large loads on the 12v such as hydraulic slides or leveling?

Give it a go. Can always update if needed. Consider a 12v LFP battery with a small charger that only runs when the battery gets low.

 

[hidiyguy]

Agree, at these prices I'd use a 12v LFP for no worry about drain during storage. If I have roof space I may install a solar panel just for the 12v LFP.

 

[Aussieguy]

just wondering why bother to even go 48v

plenty good 12v inverters and solar controllers
can understand doing it on a larger "tiny home" or a house

31 foot motor home won't have room for enough panels to make the effort worth while



savings going to 48v is negligible especially since you need to have higher voltage for charging

12v controllers can be better with the poor solar conditions often found in campgrounds

 

[AustinBlazer]

just wondering why bother to even go 48v

plenty good 12v inverters and solar controllers
can understand doing it on a larger "tiny home" or a house

31 foot motor home won't have room for enough panels to make the effort worth while



savings going to 48v is negligible especially since you need to have higher voltage for charging

12v controllers can be better with the poor solar conditions often found in campgrounds

There are numerous advantages and disadvantages with either choice of 48v vs 12v.

I prefer 48v for all of these reasons;
1. Much smaller wires in the whole system, which is lower $ but primarily for me much easier to work with as I want an extremely clean looking install. I hate working with big 4/0 type wires and hate how they look.
2. Less voltage drop and more efficient
3. Much smaller/cheaper MPPT needed (ie 150/45 can do 650watt @12v or 2600watt @ 48v)
4. Simpler smaller lighter battery (5.1kWh in single 48v 100ah 80lb battery with one BMS) - equivalent to 12v 400Ah which would likely be at least 2x batteries. If I ever want to increases capacity I would have two 48v batteries for 10kWh... again this would need to be many more batteries at 12v with tons of bulky 4/0 wires.
5. Much smaller amp/fuses needed - can use little 30A-125A MIDI fuses for the entire system
6. Anything lower than 50V is still considered "low voltage" so although more dangerous than 12v doesn't have a stop your heart shock risk. The amps being 25% make the system less dangerous and cumbersome than 12v IMO. 400amp fuses and the like is just a crazy amount of current.

 

[AustinBlazer]

The real efficiency loss is keeping a flooded lead-acid battery top charged 24/7 while in use.

Are there any large loads on the 12v such as hydraulic slides or leveling?

Give it a go. Can always update if needed. Consider a 12v LFP battery with a small charger that only runs when the battery gets low.

Yeah I can eventually measure more of the 12v loads and consider some of those 12v changes after better understanding that. But I can also just leave the 12v chassis and 12v house batteries as is. Might not have ideal efficiency as you say if the battery top charging is 24/7. But could focus on the rest of the system first, and just change that segment at a later time if needed.

 

[AustinBlazer]

just wondering why bother to even go 48v

plenty good 12v inverters and solar controllers
can understand doing it on a larger "tiny home" or a house

31 foot motor home won't have room for enough panels to make the effort worth while



savings going to 48v is negligible especially since you need to have higher voltage for charging

12v controllers can be better with the poor solar conditions often found in campgrounds

The poor solar conditions is a good consideration, thanks. Yes I would need enough panels with enough overhead over 48v with my PV voltage.

 

[rustythorn]

There are numerous advantages and disadvantages with either choice of 48v vs 12v.

I prefer 48v for all of these reasons;
1. Much smaller wires in the whole system, which is lower $ but primarily for me much easier to work with as I want an extremely clean looking install. I hate working with big 4/0 type wires and hate how they look.
2. Less voltage drop and more efficient
3. Much smaller/cheaper MPPT needed (ie 150/45 can do 650watt @12v or 2600watt @ 48v)
4. Simpler smaller lighter battery (5.1kWh in single 48v 100ah 80lb battery with one BMS) - equivalent to 12v 400Ah which would likely be at least 2x batteries. If I ever want to increases capacity I would have two 48v batteries for 10kWh... again this would need to be many more batteries at 12v with tons of bulky 4/0 wires.
5. Much smaller amp/fuses needed - can use little 30A-125A MIDI fuses for the entire system
6. Anything lower than 50V is still considered "low voltage" so although more dangerous than 12v doesn't have a stop your heart shock risk. The amps being 25% make the system less dangerous and cumbersome than 12v IMO. 400amp fuses and the like is just a crazy amount of current.

when folk ask why use a 48v system it reminds of when my students ask me why they should learn math. regardless of my response, they are never satisfied with the answer.

 

[justinm001]

This is basically what I do. I have 200w of 12V solar as a trickle charge to handle the idle loads then have a Victron charger to pull more. Have it hooked up to a kasa smart switch and run home assistant so it turns the charger on when 48V SoC is above 80% and off when below 30%. This way if the 48V is charged it'll charge the 12V. still need to program so if on shore it'll turn on the charger.

I also have a Victron Quattro inverter on the 12V as a backup but it broke so bypassed it for now.

 

[dcg9381]

I'm doing a 48V battery system and will be using a 12V step down converter to do everything 12V.. Simply because it's much easier to find things that are rated for 12v in the RV space. Converter is 30A max, so not using a lot of that power, but just keeping everything 12v simple.

I'm going to use the same inverter as you've selected.

 

[MakeMePower]

I'm confused victron makes a 48/12. what do you mean there are no good options?

https://amzn.to/3zxi1k5

 

[AustinBlazer]

I'm confused victron makes a 48/12. what do you mean there are no good options?

https://amzn.to/3zxi1k5

Well your right there are options, the issue is those options are much worse. Here is one at 24v that's over double the power (amps) almost half the cost, and much smaller footprint too https://a.co/d/9ZAEIBr

 

[HRTKD]

3. Much smaller/cheaper MPPT needed (ie 150/45 can do 650watt @12v or 2600watt @ 48v)

This is the only valid argument. All the rest are fluff. You're making your system more complicated than it needs to be

In an RV, most of the wire runs are so short that using 2/0 awg cable versus 2 awg cable isn't that big of a deal.

That said, I am putting in an 48v system. The ONLY reason I'm doing so is because of the amount of PV that I'm putting on the roof (2550 watts). If you're not putting more than 1,000 watts on the roof, you don't need a 48v system. I will be using the Victron Orion 48-12 to power the 12 volt system in the camper. However, I have no high amperage loads in my camper. No hydraulic jacks, no slide-outs, etc.

The Victron 48-12 (by itself) isn't a good solution for an RV with high amp 12v loads (loads greater than about 25 amps). This is a huge hole in Victron's product offering. Using a small lead acid battery is a good solution as a buffer for those high amp loads. I'm doing something similar to handle starting the generator and running the tongue jack.

 

[Rocketman]

Also, verify where the generator gets is start from - chassis or house battery. They can be ran on either side.

 

[HRTKD]

Also, verify where the generator gets is start from - chassis or house battery. They can be ran on either side.

Agreed. That's something my system will be taking into account.

 

[WarmPepsi]

There are numerous advantages and disadvantages with either choice of 48v vs 12v.

I prefer 48v for all of these reasons;
1. Much smaller wires in the whole system, which is lower $ but primarily for me much easier to work with as I want an extremely clean looking install. I hate working with big 4/0 type wires and hate how they look.
2. Less voltage drop and more efficient
3. Much smaller/cheaper MPPT needed (ie 150/45 can do 650watt @12v or 2600watt @ 48v)
4. Simpler smaller lighter battery (5.1kWh in single 48v 100ah 80lb battery with one BMS) - equivalent to 12v 400Ah which would likely be at least 2x batteries. If I ever want to increases capacity I would have two 48v batteries for 10kWh... again this would need to be many more batteries at 12v with tons of bulky 4/0 wires.
5. Much smaller amp/fuses needed - can use little 30A-125A MIDI fuses for the entire system
6. Anything lower than 50V is still considered "low voltage" so although more dangerous than 12v doesn't have a stop your heart shock risk. The amps being 25% make the system less dangerous and cumbersome than 12v IMO. 400amp fuses and the like is just a crazy amount of current.

All very valid points, despite the claim they're not. 4x less amperage on everything you do has a large effect on things. I know I have no interest in a dozen 12v batteries, I'll opt for my 48v server rack batteries that have the option to be swapped out to my home setup if ever needed.

But as far as the initial question about the converter, I use my entire inverter/battery system like a "secondary generator". Most Rv's will have a transfer switch to swap from shore power to generator power any time the generator is running (normally a 30-40 second delay). I simply installed a second one. So my power priority goes Generator/Inverter/Shore power. I just use the stock converter, and regardless of what power is feeding it, the converter runs the 12v stuff and keeps the single 12v battery topped up.

It means there's no interaction between my whole solar/inverter/battery setup at all with the factory 12v systems. It's just another way to provide 110vac.

 

[HighDesertOffgrid]

The ONLY reason I'm doing so is because of the amount of PV that I'm putting on the roof (2550 watts). If you're not putting more than 1,000 watts on the roof, you don't need a 48v system.

The only reason I am considering 24-48v is the options for 240 split phase for the 18kbtu minisplit that is replacing the roof unit.
Will still retain the 12v system and battery for the 4 slides and 6000# landing gear (although I may research if they can use 24v).
Putting 5kwh on the roof and could easily do it in 4s2p 12v.

 

[corn18]

OH Lord how I wish I had went 48V from the start. I have my batteries under the bed and it is a 10 ft run to the MPII 12V 3000. I doubled up the 4/0 cable to the inverter because I did not like 160 deg F cables. That is 40 ft of 4/0 cable. Ugh. If the inverter were 48V, I could use single 2ga cable and have the same voltage drop as my 12V system with 2x 4/0 cables. Having 325A running around my camper is not the way.

 

[Dave in AZ]

Having 325A running around my camper is not the way.

I hope you're quoting The Mandalorian. You might like to know, when he rebuilt his spaceship, he DEFINITELY went 48V, I zoomed in and could tell
This is the Way.

 

[time2roll]

OH Lord how I wish I had went 48V from the start. I have my batteries under the bed and it is a 10 ft run to the MPII 12V 3000. I doubled up the 4/0 cable to the inverter because I did not like 160 deg F cables. That is 40 ft of 4/0 cable. Ugh. If the inverter were 48V, I could use single 2ga cable and have the same voltage drop as my 12V system with 2x 4/0 cables. Having 325A running around my camper is not the way.

Or put the inverter in with the battery and pull some #10 romex. That is a lot of copper...

 

[corn18]

Or put the inverter in with the battery and pull some #10 romex. That is a lot of copper...

I could but I didn't want to sleep on a humming inverter. Actually, I can sleep through anything. My wife cannot.

 

[MakeMePower]

I could but I didn't want to sleep on a humming inverter. Actually, I can sleep through anything. My wife cannot.

are you running a residential fridge? otherwise why not turn off overnight?

 

[corn18]

are you running a residential fridge? otherwise why not turn off overnight?

Yup, running residential fridge. I might try it out, though. Sure would be nice not having all that 4/0 cable running everywhere.

 

[corn18]

Just redid my diagram moving the MPII under the bed with the batteries. The beauty and simplicity makes me want to do this. No more 325A running everywhere. Pretty easy to make this move, too.

Now:



Move: