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diy solar

Cons of 48v setup for RV?

Firstascent

Solar Enthusiast
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Mar 7, 2020
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I’m going to do either a 24v or a 48v setup for a 5th wheel toy hauler. I have 16 x 3.2v/280ah cells on the way so I can either run 16s or 8s2p.

i haven‘t purchased anything else yet until I decide. I know I’ll be starting with 4 residential panels around 350W each, I know I’d need a 48v to 12v converter for running my 12v components, I’d prefer to have some charging capacity from the alternator, because why not get some charging while driving.

im not necessarily looking for specific items for my build, just general thoughts on pros/cons first.

thanks for any tips, excited I finally placed my battery order which now makes it official!
also, in case it matters, I’m in the U.S., so 120vac inverter would be used. I’d like to use as much Victron as possible pending final costs.
 
I have 16 of those batteries as well and ended up going 24 volt. I would of liked to do 48 volt, but couldn't come up with an inverter I liked (need something quiet and in the 4000 watt range). From my understanding, 48 volt can be dangerous and shock you, while 24 is pretty safe. Other than that, I would do 48 volt if you already have an inverter in mind due to the savings on wire, fuses, busbars and the need to run only 1 bms vs 2.

From my research, 48 volt inverters were more expensive, but again you do save a few dollars on wires and such. If Victron made a 4000 watt, 48 volt inverter that does 120 AC (they have one that does 230 AC in this range) I would of spent the extra money and went that way...
 
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I have 16 of those batteries as well and ended up going 24 volt. I would of liked to do 48 volt, but couldn't come up with an inverter I liked (need something quiet and in the 4000 watt range). From my understanding, 48 volt can be dangerous and shock you, while 24 is pretty safe. Other than that, I would do 48 volt if you already have an inverter in mind due to the savings on wire, fuses, busbars and the need to run only 1 bms vs 2.

From my research, 48 volt inverters were more expensive, but again you do save a few dollars on wires and such. If Victron made a 4000 watt, 48 volt inverter that does 120 AC (they have one that does 230 AC in this range) I would of spent the extra money and went that way...

thanks for the input! Good point on the safety factor as well. I am aware of that but thanks for mentioning it.

i did notice that as well on what victron offers. They had some nice inverters I was looking at until I saw it was only for 230 :( so nope, currently do not have a specific inverter in mind. However, a 3000 would be sufficient for my needs so still considering them.
 
A few thoughts off the top of my head, take em with a grain of salt:

You could make either work and probably not regret either. 16 cells makes 48V more compelling for the simplicity of a single BMS and/or no paralleling of cells.

I think the biggest con of 48V in a mobile context is a lack of compelling pro's. The reasons that make 48V shine in off-grid/stationary applications are often not the case with mobile builds (but this is case specific).

48V makes the most sense for off-grid systems where:
  1. The system is usually PV Array --> Battery Bank --> Inverter --> AC distribituion --> Appliances. Meaning the only real relevance of the DC voltage is battery bank configuration and wiring between the charge controller, battery, and inverter. The availability of 48V DC appliances doesn't really matter because all the wiring will be AC anyways.
  2. Wire runs can sometimes be much longer so higher voltage makes a big difference
  3. PV array sizes can be quite substantial a 48v controller helps keep the amperage down
  4. More likely to have larger loads requiring a bigger inverter pulling more amps,
With a mobile system
  1. PV array size is probably small to medium, 24V would be fine
  2. A lot of wiring and appliances are DC, most DC appliances are 12 or 24 volt but 48 volt is much less common
  3. Wire runs generally aren't that long, advantage of higher voltage becomes less important
  4. 48v is more geared towards residential / stationary, 12 and 24 are the standards for mobile and marine, its possible that in some case features relevant to your use case would be more common with lower voltage components (this is total speculation) and you would have more selection.
  5. The efficiency gains in your DC wiring might be negated or worse by the DC-DC converter (however if you would need a dc-dc converter to go from 24-12 maybe this is a wash--but there is much more available in 24v)

Safety and code requirements are also a factor.
 
+1 on DZL comments.
Also leveling jacks, if you have them, are usually high draw 12V. (Mine on 38k lb bus coach draw 170A). So can’t run them from inexpensive dc to dc converters. Maybe yours doesn’t have them or don’t draw as much?
Issue comes down to your use case. If you use a ton of AC appliances (oven, AC units, coffee makers, IR heater, electric water heater, house fridge) then it might make sense. If most of your loads are 12V then 48V seems less optimized.
 
A few thoughts off the top of my head, take em with a grain of salt:

You could make either work and probably not regret either. 16 cells makes 48V more compelling for the simplicity of a single BMS and/or no paralleling of cells.

I think the biggest con of 48V in a mobile context is a lack of compelling pro's. The reasons that make 48V shine in off-grid/stationary applications are often not the case with mobile builds (but this is case specific).

48V makes the most sense for off-grid systems where:
  1. The system is usually PV Array --> Battery Bank --> Inverter --> AC distribituion --> Appliances. Meaning the only real relevance of the DC voltage is battery bank configuration and wiring between the charge controller, battery, and inverter. The availability of 48V DC appliances doesn't really matter because all the wiring will be AC anyways.
  2. Wire runs can sometimes be much longer so higher voltage makes a big difference
  3. PV array sizes can be quite substantial a 48v controller helps keep the amperage down
  4. More likely to have larger loads requiring a bigger inverter pulling more amps,
With a mobile system
  1. PV array size is probably small to medium, 24V would be fine
  2. A lot of wiring and appliances are DC, most DC appliances are 12 or 24 volt but 48 volt is much less common
  3. Wire runs generally aren't that long, advantage of higher voltage becomes less important
  4. 48v is more geared towards residential / stationary, 12 and 24 are the standards for mobile and marine, its possible that in some case features relevant to your use case would be more common with lower voltage components (this is total speculation) and you would have more selection.
  5. The efficiency gains in your DC wiring might be negated or worse by the DC-DC converter (however if you would need a dc-dc converter to go from 24-12 maybe this is a wash--but there is much more available in 24v)

Safety and code requirements are also a factor.
Thanks! And you bring up some great points, some which I’ve considered.

the single BMS is definitely a PRO. I do like to keep things as minimal as possible to keep it clean, but not at the expense of function.

I will admit that I know for my specific setup, a 24v system would still be more than capable. I’m only going to have 1.5kw of panels, if I ever expand, it wouldn’t be substantially.

I know I have no specific “need” for a 48v system, I kinda just want to because it’s less common for mobile systems and that interests me :) but of course it can be efficient so it’s a win-win, or so my initial thoughts lead me to believe haha.

one thing I didn’t think about is efficiency between 24 and 48v converters, I’ll need to research that and look at the numbers to see how that plays out. If they are similar, it would still be worth it due to one BMS. but as there is definitely 12v items on board I’ll need to just make sure sure it makes sense.

being able to get by with smaller wires is always nice though as well, from a cost standpoint but also just install as well with wire routing. I enjoy custom projects, electrically and mechanically, but this will be my first solar setup.
 
+1 on DZL comments.
Also leveling jacks, if you have them, are usually high draw 12V. (Mine on 38k lb bus coach draw 170A). So can’t run them from inexpensive dc to dc converters. Maybe yours doesn’t have them or don’t draw as much?
Issue comes down to your use case. If you use a ton of AC appliances (oven, AC units, coffee makers, IR heater, electric water heater, house fridge) then it might make sense. If most of your loads are 12V then 48V seems less optimized.
Yes I will have leveling jacks. But to be honest the trailer is actually being built right now (delays due to covid) so I’ll definitely want to verify how much those pull. I’ll also need to confirm which appliances are 12vdc vs 120vac. I recall most being 120Vac except for lighting but I could be wrong.
 
I have done some experimenting over the years with a two inverter setup.

Buy a 24 volt 3000 watt Victron MultiPlus inverter and a Victron Solar Charge Controller.
This inverter will let you limit the 120 volt input current to as low as 7.5 amps.
This 7.5 amps can be combined with the battery power in what Victron calls PowerAssist.

These are super cool features no mater if the shore power is coming from your friends house while moochdocking or pulling power from a second cheap pure sine wave inverter located in your pickup truck.

That's right install a 12 volt 2000-3000 watt inverter behind the divers seat. Use a temperature gun to check the temp of your large single or two mid-sized alternators or install a alternator temp gauge in the pickup. You will be able to control the amp draw on your alternator via Bluetooth on your phone by adjusting the Victron Multiplus back in the 5th wheel.

You will have to check on the capabilities of you alternator. 7.5 amps x 120 volts is 900 watts available to your MultiPlus.
900 watts / 13 volts is 69.2 amps + truck inverter losses. Probably 75-80 amps to your alternator.

This setup gives you the most flexible way of charging from your truck without overheating your alternator(s).
Your LFP Batteries will only get charged from two very high quality Victron charging sources (Solar & MultiPlus).
You will also have 120 volt ac power in your truck when you are away from your 5th wheel. (who wouldn't want that)

And by the way you will need a 200 amp breaker & 200 amp continuous duty relay under the hood controlled by your truck ignition to disconnect the truck inverter when the truck is not running. Skipping the breaker could result in a fire if you have a short on the way to the inverter behind the drivers seat. Skipping the relay will result in many dead truck batteries.

Rick
 
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I have done some experimenting over the years with a two inverter setup.

Buy a 24 volt 3000 watt Victron MultiPlus inverter and a Victron Solar Charge Controller.
This inverter will let you limit the 120 volt input current to as low as 7.5 amps.
This 7.5 amps can be combined with the battery power in what Victron calls PowerAssist.

These are super cool features no mater if the shore power is coming from your friends house while moochdocking or pulling power from a second cheap pure sine wave inverter located in your pickup truck.

That's right install a 12 volt 2000-3000 watt inverter behind the divers seat. Use a temperature gun to check the temp of your large single or two mid-sized alternators or install a alternator temp gauge in the pickup. You will be able to control the amp draw on your alternator via Bluetooth on your phone by adjusting the Victron Multiplus back in the 5th wheel.

This setup gives you the most flexible way of charging from your truck without overheating your alternator(s).
Your LFP Batteries will only get charged from two very high quality Victron charging sources (Solar & MultiPlus).
You will also have 120 volt ac power in your truck when you are away from your 5th wheel. (who wouldn't want that)

Rick
Interesting setup, and something I definitely haven’t thought of. I have just one alternator in my truck, but of course want to keep an eye on heat, so the idea of a temp sensor is good. And yes 120 in the truck is always nice to have, but thankfully I already have that from the factory :) I have a 120vac outlet in the cab as well as in the truck bed. One of my favorite factory options!
also, the power assist feature sounds cool, I hadn’t heard of that before.


@DW SD didn’t think about that, that would make sense if I go with a 24v system.
 
I’m going to do either a 24v or a 48v setup for a 5th wheel toy hauler. I have 16 x 3.2v/280ah cells on the way so I can either run 16s or 8s2p.

i haven‘t purchased anything else yet until I decide. I know I’ll be starting with 4 residential panels around 350W each, I know I’d need a 48v to 12v converter for running my 12v components, I’d prefer to have some charging capacity from the alternator, because why not get some charging while driving.

im not necessarily looking for specific items for my build, just general thoughts on pros/cons first.

thanks for any tips, excited I finally placed my battery order which now makes it official!
also, in case it matters, I’m in the U.S., so 120vac inverter would be used. I’d like to use as much Victron as possible pending final costs.
I’m going to do either a 24v or a 48v setup for a 5th wheel toy hauler. I have 16 x 3.2v/280ah cells on the way so I can either run 16s or 8s2p.

i haven‘t purchased anything else yet until I decide. I know I’ll be starting with 4 residential panels around 350W each, I know I’d need a 48v to 12v converter for running my 12v components, I’d prefer to have some charging capacity from the alternator, because why not get some charging while driving.

im not necessarily looking for specific items for my build, just general thoughts on pros/cons first.

thanks for any tips, excited I finally placed my battery order which now makes it official!
also, in case it matters, I’m in the U.S., so 120vac inverter would be used. I’d like to use as much Victron as possible pending final costs.
Ruth and I have been living on solar in our school bus for a few years. As the system has evolved it has become quite robust. We were off grid starting in 2011 with a system that had no budget constraints. So we went 48 volts. Our 5KW split phase inverter ran about four grand. In 2016 while we were away, thieves got us and stole the whole ranch, power system and all. On a much tighter budget we started with this inverter: https://www.ebay.com/itm/20000w-sur...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649, and 8 sunpower 320W solar panels with a single 60A MPPT solar controller.
Our battery system was 6 walmart RV batteries connected 2S4P.
As we grew our system the one thing that has not had to change is our inverter. We have had it for 4 years and it has absorbed all the abuse we could throw at it. Has no problem handling loads like our 15,000BTU AC unit, Microwave, Deep freeze, Toaster over and coffee maker, sometimes all at once.
Big benefit to 24V is availability of devices such as, inverters and charge controllers at decent prices. The reason I put the link to that particular inverter is you cant beat the price for the product. It is efficient and robust. The seller was really cool when we sank it in 2 feet of water under power and fried the MOSFETS. By then we had it for 2 years and I contacted him about parts. He was frustrating to communicate with because of the language barrier but after many messages back and forth he sent me the MOSFETS and control boards free of charge. We originally paid 289 for this unit with a 24V UPS built in. I think the UPS version now runs about 450.00 Still amazing compared to what I paid for the 48V Xantrax 5KW inverter in 2011. JUst a note if you are looking for split phase 110/220 this guy has a 3KW continuous, 3500W 3mins, 12KW momentary LF Pure sine inverter for 309.00. Heck I sound like a commercial.
Good luck with your build.
 
Ruth and I have been living on solar in our school bus for a few years. As the system has evolved it has become quite robust. We were off grid starting in 2011 with a system that had no budget constraints. So we went 48 volts. Our 5KW split phase inverter ran about four grand. In 2016 while we were away, thieves got us and stole the whole ranch, power system and all. On a much tighter budget we started with this inverter: https://www.ebay.com/itm/20000w-surge-power-5000W-LF-pure-sine-wave-power-inverter-DC-24V-AC-110V-60HZ/264578846391?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649, and 8 sunpower 320W solar panels with a single 60A MPPT solar controller.
Our battery system was 6 walmart RV batteries connected 2S4P.
As we grew our system the one thing that has not had to change is our inverter. We have had it for 4 years and it has absorbed all the abuse we could throw at it. Has no problem handling loads like our 15,000BTU AC unit, Microwave, Deep freeze, Toaster over and coffee maker, sometimes all at once.
Big benefit to 24V is availability of devices such as, inverters and charge controllers at decent prices. The reason I put the link to that particular inverter is you cant beat the price for the product. It is efficient and robust. The seller was really cool when we sank it in 2 feet of water under power and fried the MOSFETS. By then we had it for 2 years and I contacted him about parts. He was frustrating to communicate with because of the language barrier but after many messages back and forth he sent me the MOSFETS and control boards free of charge. We originally paid 289 for this unit with a 24V UPS built in. I think the UPS version now runs about 450.00 Still amazing compared to what I paid for the 48V Xantrax 5KW inverter in 2011. JUst a note if you are looking for split phase 110/220 this guy has a 3KW continuous, 3500W 3mins, 12KW momentary LF Pure sine inverter for 309.00. Heck I sound like a commercial.
Good luck with your build.
Thanks for your input especially with experience from both sides! Sounds like you had a decent setup, super crappy what happened to it though :(

if you were to start from scratch, today, would you stick with 24v? For argument sake, assume 24v and 48v parts are same price and readily available.
 
The primary advantage to a 48 volt system VS a 24 volt system does not apply to the bus because the wire runs from the panels to charge controllers and batteries are as short as they can be. Voltage drop due to internal resistance of the wire runs is negligible. We could use one less charge controller and inverter efficiency would be slightly better, however the number of batteries required to achieve the same storage capacity that we have now doubles with a 48v system. That's twice the battery cost. Twice the battery weight and twice the battery space.
If I had it all to do over I would stick with 24 volts for the mobile system. One thing I would do different is I would go 100 percent LiFePo4 batteries. We started with 6 lead acid RV batteries 2S3P. About 540 lbs. They are still in use as a 12v backup system. We evolved to 48 18ah AGM cells configured into 3 24v batteries, about 540 pounds. Then added two BYD 24v LiFePo4 battery packs, minus the huge heat sinks, about 300 pounds. They added an additional 400ah to our capacity. And because of their chemistry most of that additional 400ah is useable, where, with the AGM batteries, due to never wanting to exceed 50% depth of discharge, only 1/2 of that 400ah of storage is accessable.
If I started from scratch with the budget to do it, I would build an 800 ah, 24v LiFePo4 bank with 16 100ah cells configured 8S2P. Save the weight and space. And have all the capacity I desire even if the sun doesn't shine for 3 days straight.
We are very happy with our hodge podge system though. We can run our 15000 BTU portable a.c. all day on hot days and even into the evening. Our deep freeze is set at max cold and never has to be on a timer. We never fixed the bus alternator because the solar keeps the 12v system charged, which has 8 deep cycle batteries in it. Our 50 inch tv can run day and night. And we still are not consuming all that our 12 panels can produce.
I would go mini split for my AC as well but that's for another thread.
 
The primary advantage to a 48 volt system VS a 24 volt system does not apply to the bus because the wire runs from the panels to charge controllers and batteries are as short as they can be. Voltage drop due to internal resistance of the wire runs is negligible. We could use one less charge controller and inverter efficiency would be slightly better, however the number of batteries required to achieve the same storage capacity that we have now doubles with a 48v system. That's twice the battery cost. Twice the battery weight and twice the battery space.
If I had it all to do over I would stick with 24 volts for the mobile system. One thing I would do different is I would go 100 percent LiFePo4 batteries. We started with 6 lead acid RV batteries 2S3P. About 540 lbs. They are still in use as a 12v backup system. We evolved to 48 18ah AGM cells configured into 3 24v batteries, about 540 pounds. Then added two BYD 24v LiFePo4 battery packs, minus the huge heat sinks, about 300 pounds. They added an additional 400ah to our capacity. And because of their chemistry most of that additional 400ah is useable, where, with the AGM batteries, due to never wanting to exceed 50% depth of discharge, only 1/2 of that 400ah of storage is accessable.
If I started from scratch with the budget to do it, I would build an 800 ah, 24v LiFePo4 bank with 16 100ah cells configured 8S2P. Save the weight and space. And have all the capacity I desire even if the sun doesn't shine for 3 days straight.
We are very happy with our hodge podge system though. We can run our 15000 BTU portable a.c. all day on hot days and even into the evening. Our deep freeze is set at max cold and never has to be on a timer. We never fixed the bus alternator because the solar keeps the 12v system charged, which has 8 deep cycle batteries in it. Our 50 inch tv can run day and night. And we still are not consuming all that our 12 panels can produce.
I would go mini split for my AC as well but that's for another thread.
Thanks again for your detailed insight. Weight and space is a concern to me as well, why take up more if I don’t need to :)
My cells I’m waiting on are all LiFePO4, and should put me around 180lbs for a 14kwh battery bank.

min jealous of your SunPower panels! Haha. I’ll be starting with 4, been looking at SunPower or LG panels in the 350W range. But luckily that’s an easy addition if I ever add more panels later on.

ill have a decent battery bank, and will wait until I have some hard data on my usage in this new living environment. Since the trailer is still being built all I can do is guess and continue planning the basics of my system. Should have the trailer around mid-end of July.
 
I’m going to do either a 24v or a 48v setup for a 5th wheel toy hauler. I have 16 x 3.2v/280ah cells on the way so I can either run 16s or 8s2p.

i haven‘t purchased anything else yet until I decide. I know I’ll be starting with 4 residential panels around 350W each, I know I’d need a 48v to 12v converter for running my 12v components, I’d prefer to have some charging capacity from the alternator, because why not get some charging while driving.

im not necessarily looking for specific items for my build, just general thoughts on pros/cons first.

thanks for any tips, excited I finally placed my battery order which now makes it official!
also, in case it matters, I’m in the U.S., so 120vac inverter would be used. I’d like to use as much Victron as possible pending final costs.
Don't know how far you are from Phoenix but there is a guy there selling new old stock Sunpower 340wpanels for .30 per watt.
 
Don't know how far you are from Phoenix but there is a guy there selling new old stock Sunpower 340wpanels for .30 per watt.
Pretty good deal! I’m in Oregon, so not terribly far. I go down to SoCal often for work too so in the general direction
 
+1 on DZL comments.
Also leveling jacks, if you have them, are usually high draw 12V. (Mine on 38k lb bus coach draw 170A). So can’t run them from inexpensive dc to dc converters. Maybe yours doesn’t have them or don’t draw as much?
Issue comes down to your use case. If you use a ton of AC appliances (oven, AC units, coffee makers, IR heater, electric water heater, house fridge) then it might make sense. If most of your loads are 12V then 48V seems less optimized.
How have you resolved the high current requirement of the leveling Jack's?? I have the same concern for my RV installation plan.
 
How have you resolved the high current requirement of the leveling Jack's?? I have the same concern for my RV installation plan.
Maybe the question was targeted for me?

I kept my system 12V native. An alternative might be to find 24V hydraulic motors.
I don't run Air Con via inverter. I can run a convection oven, but won't often nor for long.
DC to DC converter is another option. But likely pricey for something to deliver high current (>30A) 12DC.

Doug
 
@BrianG another option I saw someone else do that had a 24v system was they had a separate 12v battery just for their electric/hydraulic jacks. You’d have to charge them separately somehow but it’s an option. Their reasoning was that their current dc-dc converter was only 30A or so which wasn’t enough to handle the load of their jack.


i will have electric/hydraulic jacks that come with my trailer as well but I don’t know how much the load is. Once I know that I’ll figure out the best path forward for me. I’m leaning toward dc-dc converter though
 
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