12v or 48v system in RV?

@Samsonite801 - I was looking at the 3000EHV-48 ($674)
either that, or using Victron components to piece together a system.

I'd likely be using 6x 250w New Powa panels (1500 w total).
I used the calculator on explorist.life's site, and it's showing array voltage would be around 205v, with output amperage at 26a if I wired all 6 in series. The calculator recommends the Victron 250/60

fpgt72 said:

There is a fuse, the cable is not hot.

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How many amps is your fuse for? So your inverter is pulling over 100amps from the batteries using 4gauge wire and well above the charts but somehow it's OK?

The beauty of parallel systems (48v and 12v), is that the 12v system isn't pulling/supporting any huge loads, so it's componentry is small and dedicated to all the 12v loads that others have listed in this thread.

Many 12v loads in any typical RV setup, and having a parallel 12v system (with or without a 12v inverter) would support all that ... it's doing what 12v does best. Power cables are much smaller, because of small loads ...

The 48v system is doing what it does best, which is supporting huge loads ... keep everything logically together on the 48v side, or even physically together, if RV layout supports or accommodates it. Now your expensive cables are "short", running between battery-bank & inverter, and only the load cables have to go where the big loads are.

The 12v busbar, or bluesea systems' 12v distribution box, are great ideas to run directly off of a 12v battery-bank ...

Finally, you get some redundancy built in, as (unfortunately) the current crop of AIO's might tend to fail on you, and either the vendor or seller could leave you hanging for quite some time in getting repaired/replaced. Being able to run off of 12v, means not everything is dead if the 48v side craps out ...

It's personal choice, of course, but parallel and redundancy don't really prove their worth until you need them (at which point it's too late if you don't have them), so you've got to plan this stuff in ...

sunshine_eggo said:

These typically consume 40-50W continuously even if you don't use any loads.

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Given my system is on and powering other items 24/7/365, it is a non-issue.

sunshine_eggo said:

Additionally the first 200-300W of PV are unusable for loads as they're just feeding the inverter's idle consumption.

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??? this does not compute.

sunshine_eggo said:

Hence, there's a hidden cost to the cheap AiO - you have to buy more battery and more PV

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I do not think so... You are missing a few points ... I live in my RV.. it is always on. I also built a massive battery on purpose, to handle heavier loads down the road. The AIO so many despise replaces $3500 in Victron... I live on SSI, so it was cheap or not at all... so I reject your claims as unrealistic for my situation.

justinm001 said:

One thing to mention is there isn't much 12v to 48v stuff yet

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I found Victron's 48v-12v to be adequate, but will have to double up on mine as it isn't to fond of running the jacks. I do have a deep cycle 12v batt in line to act as a buffer.

Samsonite801 said:

For me, I'd personally prefer to stay with 12v on an RV, and just use two Victron Multiplus 3000 in parallel to get 6000w,

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When I looked at my long term usage, I knew I would be asking for too much power for a 12v system... not that you can't do it with 12v, but it wastes a lot... the other side of that is that you can only pump so much into a 12v battery system at one time. I am starting with 1400 watts of solar but intend to up that to at least 3k or higher in 2-4 years. In order to efficiently absorb this much solar requires a massive 12v system and all that ought wiring. I could easily be running with a 24v system at this time and it would suffice for current needs. When I install the MiniSplit down the road, my consumption will go up. ... but again, I am fulltime, so my usage is different than most I guess.

justinm001 said:

Running the same in 24v is 250a which allows you to

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or at 48v is 125a and even less issues with wiring......

justinm001 said:

to keep it topped off when not on shore

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to clarify my setup, I am never on shore, and use a gen when I have to...

Samsonite801 said:

so each of those loads would require down-conversion solutions,

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I just tapped in the new 12v feed (set to 12.9v on the Victron converter) direct from the 48v battery I built, into the existing 12v battery bay and connected to a 12 deep cycle battery to act as a load buffer. Poof.. no need to do anything else because you didn't change anythign in the 12v system other than disconnecting the existing inverter/controller from the 12 system.

Eggo is saying the inverter will use 50w additional constantly so when calculating your solar there's a few hundred watts that are eaten up. If your solar produces 3kw per day then you have 2.5kw max usable because the extra is feeding the inverters consumption. Probably closer to 2kw.

When I did my trailer, the power distribution was sort of far away from the battery bank. I opted to go with 24 volt so that the main run from the battery bank to the 12v distribution would be smaller gauge. You can get a 24v > 12v converter for pretty cheap. Depending on the loads and length of your wire run, using a higher voltage can save a non-negligible amount of weight and cost.

(I would have gone with 48V, but it ended up being cheaper per watt-hour to buy 8 x 280ah cells than 16 x 100ah cells)

This thread helped a lot i still cant decide whether to go 12, 24 or 48. Trying to talk myself into saying 12v is fine.
If the RV has a large build in generator, do most stick with 12v since they need a 12v starting battery?
Also pretend the batteries can be 3 feet from the inverter and distribution panel, would 24v be silly?

My battery/inverter are in the front of the basement of our 5th wheel. It takes 2 4 foot sections of 6/0 wire to wire up to the 240v system. I went 48v because of efficiency and less cost for wiring. Goid luck.

It is tough to beat a 24 volt system for mobile and DIY.

It is easy to find 24 volt DC rated components and many appliance are dual 12 / 24 volt DC.

There is a large increase in inverter efficiency going from 12 - 24 volt, but going further to 48 volt the gain is much smaller.

The marine industry is full of 24 volt and dual 12 / 24 volt items that are easy to use in a trailer.

I like 48 volt setups but I would not suggest it to a beginner or frankly to the typical DIYer with DIY level tools and skills. This is especially true for mobile.

Mobile and stationary are not the same. The inside of a trailer gets bounced around a lot.

HarryN said:

There is a large increase in inverter efficiency going from 12 - 24 volt, but going further to 48 volt the gain is much smaller.

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Please clarify what you mean by this. Example:



I see 1% gains going from 12 to 24 and another 1% going from 24V to 48V. A 1% gain from 93 to 94% is a 1.07% relative improvement, and a 1% gain from 94 to 95% is a 1.06% relative improvement. Smaller, yes, but it seems contrary to your claim. Sure, this is Victron specific, but I would expect similar ratios from other manufacturers.

If you're referring to the DC side, there's no difference. Going from 12V to 24V for a given power/cabling means a doubling of the voltage and a halving of the current, resulting in 1/4th the losses from wiring. But this is also exactly true for a jump from 24V to 48V.

50ShadesOfDirt said:

The beauty of parallel systems (48v and 12v), is that the 12v system isn't pulling/supporting any huge loads, so it's componentry is small and dedicated to all the 12v loads that others have listed in this thread.

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Does a toyhauler not lend itself well to a parallel system? Because the 12v loads can be quite large? The genny pulls over 100a and ive read my emergency trailer brakes pull 6a each and its a triple axle. So for that example you need to maintain a healthy 12v battery instead of a buffer battery. If you only need 500-1500w of inverter would it be best to have a single 12v battery bank?

Also in this example if i can ditch the 12v lead acid batteries on the tongue i could later put a mini split there. With lithium 12v batteries inside the trailer behind my distribution panel. Its under the fridge so i could put a fan into the fridge duct to expel heat during the summer. (again hope this info can help others and the OP too...down the road will make my own build thread with questions)

Because the 12v loads can be quite large? The genny pulls over 100a and ive read my emergency trailer brakes pull 6a each and its a triple axle. So for that example you need to maintain a healthy 12v battery instead of a buffer battery.

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So, if the 100a were a longer duration i would say you are right, but the starter circuit for the generator should probably never run for more than 5 seconds and the emergency brakes shouldn't be needed for much longer than it takes for the trailer to either come to a stop or crash into something.

For both uses, something as small and cheap as a group U1 'riding lawnmower battery' would be able to meet those short-duration needs and Walmart sells them for <$40. If you look at the small SLA batteries that are usually mounted to trailers for their 'breakaway brakes' system they are WAY smaller than a U1 is! So even then you are really only needing a battery 'as big as a u1' for purposes of cranking the generator, while it could be considered 'overkill' for the emergency braking.

Starting from $29...

Very cool!! I was picturing that in my head after posting. I have some old 3s Lipos i could repurpose but i dont think it would be legal for trailer brakes. If i start the genny using other techniques, would a 24v to 12v converter be legal to use as trailer brake power source?

Probably not a good idea (imo) because of the chance of the converter failing or going into some kind of fault mode and going from 100 to 0 on brakes. At least with a small battery in between the converter and the brakes, you're going to get brakes that gradually fade to nothing but should last the 5-10 seconds you need for emergency braking. I cant imagine a trailer that has left the tow vehicle at highway speeds aka worst case scenario, managing to stay on its wheels for more than 10 seconds without hitting something, even going past 5 seconds would surprise me a little. Considering the size of batteries we're talking about here are $20-40 and a small DC DC converter to keep it maintained is also no more than $20 for the size you'd need, i just don't see a good reason to eliminate the battery from the circuit. It doesn't take up much space, money, or add any real complexity to the circuit and buys you a decent safety factor in return. My .02.

sunshine_eggo said:

Please clarify what you mean by this. Example:

View attachment 169987

I see 1% gains going from 12 to 24 and another 1% going from 24V to 48V. A 1% gain from 93 to 94% is a 1.07% relative improvement, and a 1% gain from 94 to 95% is a 1.06% relative improvement. Smaller, yes, but it seems contrary to your claim. Sure, this is Victron specific, but I would expect similar ratios from other manufacturers.

If you're referring to the DC side, there's no difference. Going from 12V to 24V for a given power/cabling means a doubling of the voltage and a halving of the current, resulting in 1/4th the losses from wiring. But this is also exactly true for a jump from 24V to 48V.

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Thanks for pointing out this chart.

They have definitely narrowed the efficiency difference between 12, 24 and 48 volt over time.

Historically (say 5 years ago) when I looked at the plots of efficiency vs output power, there were some pretty large gaps between 12 vs 24 especially in the 500 - 1500 watt range, but much smaller changes going to 48 volt.

____________

I tend to use US made inverters but also looked at and have done some testing of the victrons.

On this forum 48 volt systems are pretty common and I build them for people - but I am still not comfortable recommending it for a first time DIYer building up a system from scratch.

Anyone who can build a 12 volt system can use mostly the same parts to build a 24 volt system safely. This isn't really true for 48 volt.

With a little bit of care, nearly everything can be found in 24 volt so this makes the number of voltage conversions a very low number.

So I will stick to my suggestion of 24 volt as a base voltage to the OP.

RvNaut said:

I have a 48v/3000w All-In-One Solar Charge Controller/Inverter. There is 1400 of solar on the roof( because of the 48v battery setup I can go up to 5kw of solar on the roof down the road)

Sucking 2500 watts off the batteries to run the microwave and other 120 systems in my coach is no big deal.

Down the road I will be replacing the A/C and furnace with a Mini-Split.

I built my own 48v battery

View attachment 167411

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What size breaker/fuse did you use between the victron 48-12 DC-DC converter and the battery box?

dwwells2 said:

What size breaker/fuse did you use between the victron 48-12 DC-DC converter and the battery box?

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Looks like he used a 30 amp on the 12 volt side converter, so I’d use 10 or 15 amp 48 volt rated fuse or breaker.

48 volt fuses are limiting and get pricey. No longer using ATC fuses.

RvNaut said:

I have a 48v/3000w All-In-One Solar Charge Controller/Inverter. There is 1400 of solar on the roof( because of the 48v battery setup I can go up to 5kw of solar on the roof down the road)

Sucking 2500 watts off the batteries to run the microwave and other 120 systems in my coach is no big deal.

Down the road I will be replacing the A/C and furnace with a Mini-Split.

I built my own 48v battery

View attachment 167411

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What type of breaker fuse did you use between 48V battery bank/box and 48V-12V converter? TIA.
-m

Question if I may, related to this 48V and 12V combination. BTW, I'm using Victron Lynx Distributor in between 48V battery bank (2 EG4 Lifepower) and 48V inverters (2 EG4 3K).

Question > What fuse is suggested between the battery bank (or from Lynx) to a 48V-12V 20A (Victron) converter? This 20A will be to provide 12V power to the existing WFDC distribution center for internal & indirect 12V needs (fridge, lights, water heater, water pump, furnace, … etc.)

I am keeping one 12V AGM battery (and spare) connected for the three external & direct 12V items that don't make sense to use 48V system and conversions (such as:
1- starting the 30A Onan EVAP 4K generator [needing 450 CCA],
2- the electronic RV jack [12V, 30A]
3- the trailer emergency brake [12V, ~14A]

Thanks in advance for your feedback. Other questions on output but will save that for another time/posting.
-m

mikes68505 said:

Question > What fuse is suggested between the battery bank (or from Lynx) to a 48V-12V 20A (Victron) converter?

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I reccomend going above 1.25X the max current. 10 amps on the 48 volt side, and 25 amps on the 12 volt side. That’s the easy part. The harder part is getting a fuse rated for the voltage. Lower amperage 48 volt fuses are hard to come by.

The 12 volt side can have ATC fuses. Since fusing choice is limited at 48 volts, I can’t recommend a 10 amp fuse, but the lowest amp fuse I see for a 48 volt system is MRBF.

I have a 24 volt 35 amp to 12 volt 70 amp Converter. On the 12 volt side I used an 80 amp ANL fuse, and on the 24 volt side, I used a 50 amp ANL fuse. on the DC side. ANLs are rated for 24 volt and less applications.

chrisski said:

I reccomend going above 1.25X the max current. 10 amps on the 48 volt side, and 25 amps on the 12 volt side. That’s the easy part. The harder part is getting a fuse rated for the voltage. Lower amperage 48 volt fuses are hard to come by.

The 12 volt side can have ATC fuses. Since fusing choice is limited at 48 volts, I can’t recommend a 10 amp fuse, but the lowest amp fuse I see for a 48 volt system is MRBF.

I have a 24 volt 35 amp to 12 volt 70 amp Converter. On the 12 volt side I used an 80 amp ANL fuse, and on the 24 volt side, I used a 50 amp ANL fuse. on the DC side. ANLs are rated for 24 volt and less applications.

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Thank you. Now thinking that maybe this 48-12 converter should be directly connected to pos and neg bus bars. Then perhaps inline 30A fuse on pos line to WFDC distribution center. Thoughts?

Remember the fuse is to protect the wire - in case it shorts out. So if you have 12awg wire going to the converter- you should have that fused and the bus bar at 20amps. Because if it shorts out the entire battery bank amps can flow through it.

The 12v wires are limited because the max power that can flow through them is only what the converter can convert.

The way I think about it- anytime your main trunk line uses a smaller wire - that smaller wire needs fused.

mikes68505 said:

Thank you. Now thinking that maybe this 48-12 converter should be directly connected to pos and neg bus bars. Then perhaps inline 30A fuse on pos line to WFDC distribution center. Thoughts?

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I have my converter connected to the main positive and negative line. The 30 amp fuse to the main WFDC distribution could work. I created a 24 volt bus in my trailer that I used a Blue Sea ATC fuse center for, and I fused the line into that with an ANL fuse, that is good to around 33 volts.

The only thing about thing about fusing the line to the WFDC, is sometimes trailers send power to other places. I have two things that have fuses that are not connected to the distribution center. The First is the RV leveling system, and the second is box that controls the lights and awning. That DC power to those two other devices is tapped elsewhere I have not found, I suspect under the floor or behind a wall.

I put my 12 volt fuse right next to the converter, that way all those lines are covered.

mikes68505 said:

What type of breaker fuse did you use between 48V battery bank/box and 48V-12V converter? TIA.
-m

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A dual pole... similar to the PV breaker, so it shut off both legs...