24v or 48v, Which way to go?!?

[breadtrucker]

Hi all. This is my first post. I am about to build my main solar power system and I’m gathering parts right now. It will be in my 28 foot BlueBird School bus. I think I can fit about 8 450w panels on the roof. We are about to build a small cabin so I want to power the cabin from the bus as well. I used to have a breadtruck that I built into a tiny home on wheels. You may know me as the Breadtrucker on YT. I just sold the breadtruck and replaced it with this skoolie.

So far, I know I will have 4 12v 200AH GoldenMate LIFEPO4 batteries. 800AH total. With these batteries, I have to option to build a 12, 24, or 48v system. I need all the other parts. Looking for affordable options. Is my best bet to build a 48v system? Should I get an all in one like an EG4 or Victron Multiplus?

I am also going to be running a 12v 8000BTU rooftop AC from Velit. Would it be feasible to run the AC on a 48v to 12v converter?

I’m leaning towards a 48v system but I would like the opinions of the experts here on this forum. I’ve been lurking for years but I just registered today! tia

 

[BenFromSignatureSolar]

If you are going to use those batteries for sure, I would probably go with something like a 12V Victron Phoenix.

 

[yodamota]

do you already own the velit ac system? It looks like it can handle 24v input?

 

[pollenface]

48v

higher voltage = more solar per charge controller amp

My Victron 100/20's
290w @ 12v
580w @ 24v
1160w @ 48v

I only need 6awg cable for my 6kw inverter

I would only use a lower voltage is there was a specific reason to do so.

 

[KITROBASKIN]

But Btrucker says he has 4 12V batteries. Series connection will need to be balanced. Extra expense to down-convert voltage? Already has a 12V AC. DC wire runs are not going to be that long on a bus. Looks like he will not be getting more panels.

Where is member 12 Volt Installs?

 

[Warpspeed]

I suppose it depends what you eventually plan to run off this.

Don't overlook installing a dual system, 110/220v ac (from 48v) and a separate straight 12v dc system from a fifth battery.
You could then switch off the inverter when not needed and run lighting and low power stuff direct from 12v.
Being able to charge the 12v system from the engine might also be useful sometimes.

That also offers some redundancy if something does go wrong, you are not left completely in the dark.

 

[chrisski]

I am also going to be running a 12v 8000BTU rooftop AC from Velit. Would it be feasible to run the AC on a 48v to 12v converter?

IME no, a converter hound not be used to run a load that high. Based off my 15k BTU, I expect an 8000 BTU AC to be pulling 1000 watts from a battery, or about 100 amps.

If the specs on the AC say less perhaps it can, but again you’d be the first on the block to try this and even with a soft start the surge can be huge. This may not be a factor if this is an inverter AC.

So far, I know I will have 4 12v 200AH GoldenMate LIFEPO4 batteries. 800AH total. With these batteries, I have to option to build a 12, 24, or 48v system.

Having done a 12 volt build and a 24 volt build, my recommendation for high wattage loads would be 48 volts, with as much as possible on the AC inverter. There are some “unavoidable” 12 volt loads that a low amperage 48 volt to 12 volt can handle.

-The higher voltage DC has less amps and keeps the busbars and fuses less amps

-For accessories, the automobile and boating has tons of 12 volts available, but step that up to 24 volts, becomes a bit harder to find but you can still get USB charging ports and lights, but step that up to 48 volts there are very, very few accessories available.
—IMO, a 10% to 15 % loss to go with 120 VAC higher wattage accessories makes finding and replacing and maintaining them so much easier.

I looked at going to 48 volts, and what stopped me was I was upgrading from 12 volts was some of the already installed SCCs and fuses etc was rated to handle 24 volts, but not 48 volts. That would have been hundreds of dollars to replace.

I don’t have many 24 volt products, and those that I do have would have easily been left 12 volts. I would not be able to fast charge my USB devices at 12 volts, but I could have easily used a regular 120 VOC charger to do so.

 

[breadtrucker]

do you already own the velit ac system? It looks like it can handle 24v input?

I already have the 12v AC. It comes in either 12 or 24v but it doesn’t handle both. I would have had to order the 24v one if that is what I wanted. But 12v is what I have

 

[breadtrucker]

I suppose it depends what you eventually plan to run off this.

Don't overlook installing a dual system, 110/220v ac (from 48v) and a separate straight 12v dc system from a fifth battery.
You could then switch off the inverter when not needed and run lighting and low power stuff direct from 12v.
Being able to charge the 12v system from the engine might also be useful sometimes.

That also offers some redundancy if something does go wrong, you are not left completely in the dark.

I have definitely been thinking about this option too!! I have about 310AH of lithium laying around. It would be nice to have a separate 12v system for the small stuff. It would work well for videos to be able to test 48v and 12v equipment on my channel.

 

[Mattb4]

.

So far, I know I will have 4 12v 200AH GoldenMate LIFEPO4 batteries. 800AH total.

Just in case there is a misunderstanding but that 800ah is only if you run the batteries in parallel at 12vDC. If you arranged them in 2S2P for 24vDC it would be 400ah and in 4S for 48vDC it would be 200ah. 800ah at 12vDC = 9600wh worth of power to play with. Concerning connecting LiFePO4 batteries in series. Not all can handle it. (Some folks simply do not want the additional BMS's in series.) You want to check the specifications.

 

[breadtrucker]

Just in case there is a misunderstanding but that 800ah is only if you run the batteries in parallel at 12vDC. If you arranged them in 2S2P for 24vDC it would be 400ah and in 4S for 48vDC it would be 200ah. 800ah at 12vDC = 9600wh worth of power to play with. Concerning connecting LiFePO4 batteries in series. Not all can handle it. (Some folks simply do not want the additional BMS's in series.) You want to check the specifications.

Yes that is correct. 4 200AH 12v batteries. So in 4s at 48v would be 200AH. It seems like 12v 4p is out of the question. I do not want to run these batteries in 12v configuration.

 

[Tomthumb62]

Yes that is correct. 4 200AH 12v batteries. So in 4s at 48v would be 200AH. It seems like 12v 4p is out of the question. I do not want to run these batteries in 12v configuration.

Running those four batteries in parallel is far less problematic than running in series. You got that backwards.

If you do go for a dual system, I’d setup your 12v side with your 800Ah of batteries. You have a 12v air conditioner so that is going to suck a lot of juice in the low sun of evening or dark of hot nights. Then build or buy a real 48v battery, you’ll have less problems and complexity than if you try to wire multiple batteries in series.

 

[KITROBASKIN]

Why do you not want to run your batteries in 4P?

 

[Tomthumb62]

Since you have some YouTube fame, you could just get one of those sparkly paint markers and sign each piece of equipment you wish to sell, then auction them off. Of course don’t ship anything, make it known they have to come pick it up. Then invite them in for a beer or coffee or a meal to make it worth their while.

Then you’d have some fresh cash to start over with a 48v system. 48v mini mini split, inverter, battery, charge controller, etc. you’d be so much better off. Small 48/12 converter for light DC loads

If this was just your bus, you could get away with a 12v or 12/48v dual system. A dual system would allow your redundancy so if the 48v side goes down, you could possibly rewire the 12v to limp along until you could fix the 48v side. But since you’re planning on using your bus to power a cabin, man, it would be so much easier to just go straight with a 48v system.

 

[breadtrucker]

If money wasn’t an object and since you have some YouTube fame, you could just get one of those sparkly paint markers and sign each piece of equipment you wish to sell, then auction them off. Of course don’t ship anything, make it known they have to come pick it up. Then invite them in for a beer or coffee to make it worth their while.

This is a nice thought but I’m afraid that I don’t have that level of fame. It’s not like I’m Will Prowse or something!

 

[dougbert]

@breadtrucker with the bus, maybe the cops will leave you alone more.

with that amount of space, I would vote for a dual system as well. 12v and a 24 v

 

[breadtrucker]

Running those four batteries in parallel is far less problematic than running in series. You got that backwards.

If you do go for a dual system, I’d setup your 12v side with your 800Ah of batteries. You have a 12v air conditioner so that is going to suck a lot of juice in the low sun of evening or dark of hot nights. Then build or buy a real 48v battery, you’ll have less problems and complexity than if you try to wire multiple batteries in series.

Running those four batteries in parallel is far less problematic than running in series. You got that backwards.

Are you certain that is true? I was watching this video from Will Prowse.
12 volts VS. 24 volts for Off-grid Solar Power Systems
He seems to think series connecting more than 3 batteries at 12v is a bad idea. Check it out and see what you think.

 

[Tomthumb62]

This is a nice thought but I’m afraid that I don’t have that level of fame. It’s not like I’m Will Prowse or something!

You might be surprised. I mean, just be humble and human about it. You don’t need to be Will Prowse. Just be you. YouTubers are built upon donations. I notice when my wife is away, I want to use my dollars to support others in growth. I mean I’m still supporting her financially, but since she’s away visiting family, I’m here on the webs wanting to be helpful. I’ve donated to Google chrome extension developers and YouTubers in the past week. Not more than $25, but it feels good to do. You might have more supporters than you think. You just have to ask. Worst that happens is it hear crickets. In such a case, your self esteem takes a hit? Who’s damaging your self esteem, others or you?

I’m no social media expert but I do know a bit about marketing. Marketing not to manipulate people into giving you money, but to connect to them as real people and inspire them to be a part of your journey. Your success becomes part of their success. I know this sounds like glass half full sort of stuff, but I find this more true than not. If you stop watching the news or get off Facebook or even Reddit, you might find that there’s way more humanity in the world than the 1% will have you believe through their manipulation of what you see through their platforms.

Anyways, I’d be happy to take a quick look and suggest a path forward of asking for donations or auctioning off your gear. I want nothing in return except the experience of doing it. I can’t get in there with boots on as I’m pretty busy with life now, but perhaps I can be of service enough to get you started.

 

[Tomthumb62]

Are you certain that is true? I was watching this video from Will Prowse.
12 volts VS. 24 volts for Off-grid Solar Power Systems
He seems to think series connecting more than 3 batteries at 12v is a bad idea. Check it out and see what you think.

Yeah he does think that. And it’s supposedly true to a degree. But parallel connections are way less problematic than series. In either case, you should have an active balancer. Victron has one. I know nothing about them other than they’re pretty much essential if you have multiple batteries in series or parallel. It adds expense and complexity.

 

[Crowz]

Even if the 12v ac causes issues if your going to do much in the way of ac stuff especially powering the cabin I would go 48 volts and look to replace the 12 ac if needed. The savings on wire alone will work out pretty nicely. Plus you will be able to run much larger ac loads with 48 volts.

Ive run 12 volts systems and run a house on 24 volts in the past. 48 volts I have now taught me 48 volts rocks