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I plan a conversion with heavy electrical needs, and I am trying to figure out whether to do a parallel connected 12V battery system, or series connected 24V or 48V?

I can put 2, 3 or 4 12V batteries in parallel:
  • Can use 3 batteries for capacity
  • Can power 12V fridge, 12V lights, 12V fans directly.

I can put 2 batteries in series (or 4 batteries as 2 + 2) for 24V:
  • Smaller wiring for lower current
  • No self-discharge
  • Some fridges work on 24V, but most would need to run on 110 through the inverter
  • Lighting would need 24V - 12V stepdown.
  • No way to use 3 batteries if I need ~3kWh total capacity

I can put 4 batteries in series for 48V:
  • Not sure I need 4 batteries for capacity (3 should be enough)
  • Even smaller wiring.

Any advice?
 

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24 volt systems are pretty common in boating and trucks, so 24 volt components are wide spread. IMHO it is a substantial advantage over 12 volt at the 2+ kW inverter size range. A 2 kW inverter needs 4 batteries of most types used in conversion vans anyway to support the power, so 3 really isn't a factor.

I build both 24 and 48 volt based systems for customers, mostly 48 volt for heavier setups. It is quite different to build a 48 volt system than 12 and 24 due to components availability.

As an example, many van electrical systems use blue sea electrical parts and fuse blocks. 100% of them are compatible with 12 and 24 volt systems, so you can use them the same exact way that you would build a 12 volt system.

0% of the blue sea components are 48 volt compatible, so it is a much deeper / more intensive engineering effort to find parts.

AFAIK, there isn't any difference in self discharge between 12 vs 24 vs 48 volt systems.

100% of your 12 volt components can run from a DC - DC converter / distribution panel. I do it all of the time. You can build your own or buy them pre-made.
 

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What you plan to power is a big factor. For me, I don't use much power. A cooler type fridge, lights, 300 watt inverter, radios to play with. So sticking with 12V was an easy choice. The wiring isn't too large and it is easy to use the vehicle charging system.

At home, I have a 48V system. I am off the grid and so if I need to use the welder while the laundry machine is running I would need massive cabling. You really can't run 12V inverters above 2-3000 watts due to the wire size required. So if you need moderate to a lot of power a higher voltage system makes sense.

So as is always the case, before doing any planning or purchasing equipment, do a thorough energy audit and figure out what your loads are. Then you can design a system that will do what you need it to.
 

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If I were to do it again, I'd probably go 24 V rather than 12V, and source as many 24V components as possible. Note that there are plenty of LED light strips and other lighting options (rock lights, overhead lights, etc) that will run straight on 24V, besides the fridges and other components mentioned above.

One more nerdy battery thing to consider--series batteries will almost certainly be fine for a long time. But, they can theoretically get out of balance with each other, especially if you use lower-quality or unmatched batteries. That is after discharging, in a 2-series "24V" string, one battery might be a lot lower voltage than the other, which leads to even more uneven ageing and un-balancing of your pack. So, good quality (matched, of course) batteries and a BMS that monitors individual battery voltage might be advised for any arrangement that relies on series configurations, though it is certainly not required. Manually checking individual battery voltage (balance) on a regular basis would probably be just fine, and I'd bet that most people don't even do that. LiFePO4 batteries will have a much longer life than most of the campervans and RV's that they're installed in; so, premature failure due to an unbalanced series pack is probably not an issue for most situations.

But, something to consider--with my all-parallel 12V system, I would feel pretty comfortable adding a not-perfectly-matched additional battery in parallel to my pack if I wanted an extra 100Ah capacity at some point. That wouldn't be an option with any series config.

Best of luck
 

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I'm in a somewhat similar place of still trying to figure out whether to go with 12V or 24V for my battery bank. I had a thread going a couple of weeks ago that had some input from various people on which direction to go, but I'm still undecided. My main struggle/indecision comes from the following...

For an inverter around 2500-3000 watts 24V makes more sense then 12V - So 24V makes more sense for my inverter/load needs

however...

Charging from my alternators is much easier with 12V than 24V since there are very few 12V->24V high output chargers. Best case it seems is to spend about $1000 running multiple chargers in parallel, pulling about 120 amps at 12V to get around 50ish amps at 24V (10% or so conversion losses).

So my electrical system is currently on the back-burner until I come back to the design and think it through more.

Most of my loads will be 110V, so the 12V/24V choice there doesn't matter much, and as mentioned by others it's easy to have 12V distribution center in your design if you have 24V.

How many watt hours do you need each day? And what is your peak watt load that you'd encounter under normal usage?
 

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I can put 2, 3 or 4 12V batteries in parallel:

I can put 2 batteries in series (or 4 batteries as 2 + 2) for 24V:

I can put 4 batteries in series for 48V:
You have to calculate watt-hours of the proposed pack to see which has best output.

Ah are added together in parallel arrangement.

Ah are not added together in series arrangement.

Watt-Hours = Amp-Hours x Battery Voltage

Pros for high voltage: reduced current and wire size, usually greater watt-hours capacity.

Cons for all multiple battery banks: many more connections and opportunity for failures.
 

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I never even considered 12V, and spent most of my time researching 24V versus 48V. I was intrigued by 48V for a time, but not anymore.

I've recently settled on 24V because nearly everything that I need is 24V, including the batteries themselves, so most of my components can be powered straight from the batteries with no efficiency loss or fan noise. My shurflo revolution 4008 is 24V (I couldn't find a 48V shurflo or any other brand for that matter but maybe they exist), my dometic cfx3 75dz only takes two voltages: 12 or 24 but can only make ice if using 24V, so that's a no-brainer, my carbon heater tape to run a heat trace on my uponoor pex-a plumbing and pump/tanks isn't rated for 48V, and at 24V it already outputs 4x the heat versus 12V so consequently I can use long runs and reduce the number of parallel strips to just 2, I've easily found good quick-charge phone and tablet chargers that accept 24V (but not 48V), and there are LED lights galore in 24V so that's easy peasy lemon squeasy, but above all, the single most powerful 2nd alternator I can source and safely install in a Transit that has the toughest mounting bracket around to handle all that torque demand is 24V (275A, although I've settled on the 250A version for its better handling in high heat when it'll be needed most).

There are 48V alternators but no one that I know is running one on a Transit, and the one guy I know running it in a Sprinter de-rated it significantly based on real-world constraints (heat, always heat) to about the same output as the 24V 275A. The only company that sells a 48V alternator that I would even consider does not yet have a mounting solution for it, and is merely hoping that the bracket for the upcoming 24V 275A alternator just might work on theirs too.

So 48V gets me one thing only: thinner wire. That's it. But now I can't recharge because there's very little hope of imminently purchasing and installing a 48V alternator, so I have to buy an expensive high output boost converter that isn't 100% efficient and wastes energy in the form of heat to make a 24V alternator charge a 48V battery bank. And I also have to purchase a high capacity buck converter to get down to 24V, and if it ever fails, I'm dead in the water. No fridge/freezer, water pump, lights, etc from the moment it fails. At least if/when the boost converter fails I can drive to a local place to get it replaced. So that means I have to purchase two high capacity buck converters so I can carry a spare. Between the cost/space/weight of boost converter to charge the 48V bank, and the two buck converters, and all the wire to hook those up, and the increased system complexity by virtue of two new failure points, any gains from thinner wire start looking like a bad joke.

Besides, the inverter/charger I want accepts either 24V or 48V. Granted a higher voltage feeding the inverter/charger means that theoretically you can drain the batter bank lower and still keep the inverter up and running when powering large loads, but the reality is no one discharges lithium down to 5% anyways because it prolongs battery life if you charge at 20-30 or even 40%. At those levels a 24V LFP pack's output voltage is still plenty high enough to sustain the rated capacity of the inverter. So once again, no advantage to 48V other than thinner wire. Yet many disadvantages.

Cheers.
 

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What is the benefit of a 24 volt system? Smaller wire diameter is not important. Very few dollars saved in wire cost.
It mostly has to do with whether or not you want air conditioning, and not just a few hours of it, but essentially on-demand 24/7 climate control. You just can't get a 12v alternator that cranks out 6.6kW, and the closest one at 5.1kW runs at a whopping 430A, so cabling to reach the mid-point, or worse the rear of the van finally does become an issue, especially if you're also paralleling 4+ packs to build something like a 20kWh bank.

Once you're at 24V, cabling is still a fair amount of work and cost to handle that kind of current, but it's all manageable; 48V makes it even easier, but then you need boost/buck converters, which outweigh the benefit. 12V, 430A means even 4/0 isn't really enough for hot climates or if your battery bank is anywhere beyond jammed up right behind the driver's seat, so no swiveling captain's chair, and even then, you'll probably get too much voltage drop at 12V for it to be worthwhile, which is another advantage of 24V: the Vdrop due to cable heating becomes smaller, and your inverter has to work a lot less to maintain a constant output. It's smaller yet at 48V, but that still doesn't outweigh all the boost/buck complexity.

Beyond those issues, if you don't just want a/c, but you want ultra-efficient cooling and heating (heat pump) to minimize driving or high-idling hours to recharge the battery bank, then you really need 240V to power something like a 42 SEER Carrier minisplit. You can get 30 SEER on 120V, which is still good, but 42 SEER is 40% more efficient, which is huge. I haven't found a 12V inverter with the kind of specs I like that delivers 240. I want so much headroom that the inverter never runs beyond 50% of capacity, even 33% would be great to help it remain ultra-efficient with the fan running slow and quiet.

Cheers.
 

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It mostly has to do with whether or not you want air conditioning,

Cheers.
You answered my question. Fully understand

I am not in a climate that requires air conditioning so 12 volts works fine. The longest cable length in my installation is about 18" because all the high amperage 12 volt electrical components are located next to each other.

Since I have a vehicle powered inverter and do not charge directly from the vehicle battery/alternator I have a 12/3 cord from the inverter back to the house inverter. One string of 120 volt AC outlets that can be powered by shore power, the vehicle powered inverter or the house inverter.
 

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You answered my question. Fully understand

I am not in a climate that requires air conditioning so 12 volts works fine. The longest cable length in my installation is about 18" because all the high amperage 12 volt electrical components are located next to each other.

Since I have a vehicle powered inverter and do not charge directly from the vehicle battery/alternator I have a 12/3 cord from the inverter back to the house inverter. One string of 120 volt AC outlets that can be powered by shore power, the vehicle powered inverter or the house inverter.
That sounds like a workable setup, although if you're inverting to power devices that could otherwise just run on DC current, you're also generating heat and sacrificing efficiency, thereby increasing the need to run the engine more often. I know that's a debate you've already had, so no need to re-hash it, I get the pros and cons. For the sake of driving range and maximizing time spent off-grid, I'm against idling anymore than I absolutely have to, but that's just my priority list, and doesn't have to be yours. And the extra heat from inverting to power devices really isn't a problem for cold climates where that heat might actually be desired.

But it mostly is about climate. If I didn't like hot places so much, light casual clothing, beaches, lakes, river sports, pools, and wasn't trying to maintain perpetual summer (southern hemisphere during northern hemisphere winters), I'd have a much simpler setup. We just went from 90 degree weather to 23F and 2 days of snow here in the desert southwest, and in those 2 days I went from feeling like a champ to feeling miserable. I can't wait to get down south. If covid wasn't disrupting things I'd be readying the trip to Australia or a return to southern Mexico, or Chile. There's nothing like leaving a freezing cold dark wet climate bundled up in burdensome heavy clothes and ending up somewhere you can drop into shorts, a t-shirt and flip-flops, then go swimming with beautiful ladies walking along the beach in increasingly non-existent swimsuits.

Cheers.
 

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thereby increasing the need to run the engine more often.
With my electrical usage I almost never need to run the engine to charge the house battery. Charging from the vehicle powered inverter is my backup when weather conditions force its use. The 300 watt solar panel and MPPT controller almost always provide enough power.

Last couple of days during a power outage I used the van to power our home refrigerator and freezer. Once had the house inverter shut off due to low voltage so had to run the engine and use the vehicle powered inverter instead of the house inverter. Did drive the van between each day and used the vehicle powered inverter to charge the house battery.
 

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With my electrical usage I almost never need to run the engine to charge the house battery. Charging from the vehicle powered inverter is my backup when weather conditions force its use. The 300 watt solar panel and MPPT controller almost always provide enough power.

Last couple of days during a power outage I used the van to power our home refrigerator and freezer. Once had the house inverter shut off due to low voltage so had to run the engine and use the vehicle powered inverter instead of the house inverter. Did drive the van between each day and used the vehicle powered inverter to charge the house battery.
I love the concept of solar, especially in hot dry sunny places I frequent, but there just isn't enough surface area to deliver enough power to keep a high-efficiency a/c heat pump running. I saw one guy who spent thousands to build motor driven expanding panels and even he tacitly admitted in one of his videos that the panels were really only delivering 70-80% of spec and were just enough to run his smaller a/c unit for 6-8hours at night (no hot afternoon/evening a/c), and worse yet they required cleaning all the time (what a hassle that must be). And even then, you still need a backup system for cloudy weather, and the backup system is usually an alternator.

I may use some of the new roll-out stick-on solar panels, but mostly as a battery keeper, and won't plan for it as any kind of primary power source. But again, that's largely climate driven. For cold places and less efficient setups it may be a reasonable way to go. But having ultra-efficient 24/7 on-demand climate control with frozen foods, ice-cream/ice-pops and making ice cubes in a 100-110F+ climate is a very different power requirement than keeping some eggs and bacon cool in a 70-80F location. It's apples to oranges. Or to be more exact, ice-cream to milk.

Cheers.
 

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I love the concept of solar, especially in hot dry sunny places I frequent, but there just isn't enough surface area to deliver enough power to keep a high-efficiency a/c heat pump running. I saw one guy who spent thousands to build motor driven expanding panels and even he tacitly admitted in one of his videos that the panels were really only delivering 70-80% of spec and were just enough to run his smaller a/c unit for 6-8hours at night (no hot afternoon/evening a/c), and worse yet they required cleaning all the time (what a hassle that must be). And even then, you still need a backup system for cloudy weather, and the backup system is usually an alternator.

I may use some of the new roll-out stick-on solar panels, but mostly as a battery keeper, and won't plan for it as any kind of primary power source. But again, that's largely climate driven. For cold places and less efficient setups it may be a reasonable way to go. But having ultra-efficient 24/7 on-demand climate control with frozen foods, ice-cream/ice-pops and make ice cubes in a 100-110F+ climate is a very different power requirement than keeping some eggs and bacon cool in a 70-80F location. It's apples to oranges. Or to be more exact, its ice-cream to milk.

Cheers.
With my climate and electrical usage the single 300 watt panel supplies enough power without needing to use the backup vehicle powered inverter to power the charger. The system just works without any attention.

The vehicle powered inverter is used to heat shower water or to power a electric air heater but seldom used for charging. In our recent 2 day power outage I used the van to power the home refrigerator and freezer. Used both the van house inverter and once had to run the engine and use the vehicle powered inverter.
 

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As Van Gogh said in #14, it is your use case that drives what is best for you. I agree w/ Harryn in #3 that above 2k W+ or so sustained loads make 24v much more desirable than 12v.

My rooftop AC pulls 1.5 k W from the house bank or alternator and my instant HW heater pulls 2k W. That is about the limit for me at 12v thru single strand 4/0 and the associated terminals and switches.

I have found solar more of a novelty than a significant contributor to charging. Its real use, in my application, it keeping my 400AH of AGM topped off. It is quite noticeable on the roof (only 180w). If I was to switch to Li batts, I'd probably remove it or go to a very small (not obvious) panel since I have the infrastructure already.
 

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As Van Gogh said in #14, it is your use case that drives what is best for you. I agree w/ Harryn in #3 that above 2k W+ or so sustained loads make 24v much more desirable than 12v.

My rooftop AC pulls 1.5 k W from the house bank or alternator and my instant HW heater pulls 2k W. That is about the limit for me at 12v thru single strand 4/0 and the associated terminals and switches.

I have found solar more of a novelty than a significant contributor to charging. Its real use, in my application, it keeping my 400AH of AGM topped off. It is quite noticeable on the roof (only 180w). If I was to switch to Li batts, I'd probably remove it or go to a very small (not obvious) panel since I have the infrastructure already.
I view solar as a way to run the refrigerator and modest loads, although in my own van I run all of my tools from the van electrical system, including power saws.

Sub 200 watts is really just a trickle charger. Once you hit 500 - 600 watts it starts to really make a difference, and that can be done fairly easily with 24 and 48 volt systems. That is the path that I would suggest - increase vs decrease your solar.

I stock 24 volt / 1100 watt inverters and 48 volt / 2 kW inverters, so that is what I use in builds when ever possible. For one off DIY though, 24 volts makes a lot of sense.

To some extent it depends on where your back ground is. I started out with 270 vdc systems so moving down to 48 was tough enough. I couldn't bring myself to go to 24 volt for significant amounts of power. Also 48 volt alternators are easier to implement on sprinters than Transits (at least so far) so that was an influence.

AFAIK there are no existing 24 volt alternators for Transits so no matter what battery pack voltage you choose (12 / 24 / 48) you have to use a DC- DC charging method to charge the pack correctly.

People ask what is the key advantage to 24 / 48 volt systems. My answer - system stability. It will run appliances when a 12 volt system won't.
 

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RVing quote
"I have found solar more of a novelty than a significant contributor to charging.
Its real use, in my application, it keeping my 400AH of AGM topped off. It is quite noticeable on the roof (only 180w). If I was to switch to Li batts, I'd probably remove it or go to a very small (not obvious) panel since I have the infrastructure already."

I'm curious with what you would replace it with ?
Thanks
 

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Every single time i read one of these threads I learn something! Mostly that a Generater solves all lifes problems. I guess if your living on city streets and being stealth Gens are not ideal, but the rest of the time? I'm sorry, coming from the boating world i do not understand the ( for lack of a better word) , "Obsession", with hi dollar electrical systems.
 

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Every single time i read one of these threads I learn something! Mostly that a Generater solves all lifes problems. I guess if your living on city streets and being stealth Gens are not ideal, but the rest of the time? I'm sorry, coming from the boating world i do not understand the ( for lack of a better word) , "Obsession", with hi dollar electrical systems.
Why a generator? Why not just use the generator that is already built into the van (the alternators)?
 
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