To 48V, or not to 48V?

[Dave01a]

What voltage are you using?

Have a 12V system, and considering upgrading. I'm well versed in the electrical side of things. Smaller wire gauge for higher voltage etc. My question pertains to what you are running off of it inside.

In my current setup, I have a number of things running directly off the 12V, and only use the inverter for 3 kitchen appliances when needed. Microwave, Air Fryer, and Toaster. Almost all of my DC equipment has a 12V/24V input option.

To my understanding of what's out there, if I take the step up to 48V, nearly everything will need to be run through an inverter. There are at least a few 48V AC split units, but everything else will need to be via the inverter to 110V, or a buck/boost transformer down to 12/24V depending on amperage requirements.

 

[Snowy-ClassB]

Like you said, 48v can have some advantages in high current situations like alternator to battery, battery to A/C, and powering today's 120v appliances. Volta's use of 48v allows for a smaller 2nd alternator and smaller wires from the 2nd alternator to the batteries. As you said, the downside is that most appliances are either 120v AC or 12v DC. Inverters and 48v/12v converters add cost, weight, complication, energy waste, heat, and sometimes noise to your rig.

Someday, perhaps we will get native 48v DC appliances. That will be the time to go 48v IMHO.

 

[booster]

Like you said, 48v can have some advantages in high current situations like alternator to battery, battery to A/C, and powering today's 120v appliances. Volta's use of 48v allows for a smaller 2nd alternator and smaller wires from the 2nd alternator to the batteries. As you said, the downside is that most appliances are either 120v AC or 12v DC. Inverters and 48v/12v converters add cost, weight, complication, energy waste, heat, and sometimes noise to your rig.

Someday, perhaps we will get native 48v DC appliances. That will be the time to go 48v IMHO.

Most don't worry about 48v DC things to run as it is easiest to just run the 48v for charging and inverting. Plenty of advantages in smaller wiring, etc. Downside is taking a bit more space for the 48 to 12v converter and some other costs due to higher cost items. Particularly good for high rate charging from the alternator, but those advantages seem to be fading now with the much more conservative charge rates for lithium that have been coming out recently. Right now many are saying .2C rate for best life and .4C max, which is way, way less than the initially touted up to 3C range for lithium. These are 12v speeds though and 48v will be different but my guess is that the wattage means more, but I haven't seen any data on that to this point.


48v lithium batteries are also a lot more cells in series, which appears to increase the balancing issues that have been getting a lot more attention lately by many folks, so care is needed with that.

 

[Dave01a]

Yeah, 48 is doable, but so far, the 24 seems to be the way to go for direct connect devices.

Inverter efficiencies have come way down, but there is still enough loss to justify staying with 24 when you can for small installations. When I get to the diesel pusher conversion, that will probably be 48v, but still on the fence on that one as well.

 

[avanti]

Yes, when we did ours, it felt like 24V was the current sweet spot (no pun intended). I really like that all the 12v stuff runs on regulated 12V from buck converters, rather than fluctuating according to the charger's whims. I have a big 100A converter that runs all the major stuff, and several little ones for scattered small devices, most of which require USB-C. This is more for wiring convenience than any theoretical reason.

Speaking of USB-C: note that many USB-C converters are spec'd at 12-24VDC, but you often won't get full-current for things like laptop or phone charging unless they are running at 24V.

 

[Dave01a]

Avanti, do you have the info on that converter? I don't see many results in searches for higher amp converters, always want to expand my database.

I tend to agree with you on the 12/24 units. I do have a USB charger that I really like that is literally 24V max, so I may have to add a 24V regulator into the mix. I have a fanless brick PC and a pair of 20" LED monitors that use 2A each on 12V, so a small buck/boost dedicated to them is in the works regardless of 24 or 48. The AlpiCool units will take a max of 32V, so they should be good and run better on 24 to boot. I have two 32qt I use as fridge and freezer, and a 9qt I made a special lid for to take between the van and the big trucks I'm delivering.

The lid is made from layers of toolbox foam. Keeps my pop and munchies cool but accessible. Had to add the aluminum angle and strap because the little cooler didn't have a shoulder strap for carrying. Have to carry by hand instead of shoulder, but better one handed than two.

Want a good laugh, just did a quick search on vehicle USB chargers, saw a two port that plugs into the ODBII port.

 

[avanti]

Avanti, do you have the info on that converter? I don't see many results in searches for higher amp converters, always want to expand my database.

https://www.amazon.com/Victron-Energy-200-Watt-Converter-Isolated/dp/B0877ZQZSQ

I tend to agree with you on the 12/24 units. I do have a USB charger that I really like that is literally 24V max, so I may have to add a 24V regulator into the mix.

 

[Dave01a]

Thanks for the link, saved it in my lists

 

[Boxster1971]

I have lived with a 48V Volta system for over a year now in my 2024 Airstream Interstate 19e. Airstream has joined Winnebago, Storyteller and other major B-van builders switching to 48V lithium battery systems. While it is trendy, I’m not sure that is the best solution currently. I agree with @avanti that 24V is probably best at this time since there are many things that can run on either 12 or 24V.

The Volta battery provides 13.2 kW of power. The system has a large 3.2kW inverter with 6000W Surge rating that provides an equivalent to 30A - AC shore power. It also has twin 30A 48V-12V DC converters that provide 60A of regulated 13.8 volts of stable power. The secondary 51V, 6900W Alternator is the big advantage of this 48V system as it will recharge a depleted battery in a few hours of driving with large 4/0 cables running from the engine mounted alternator to the battery mounted in the rear spare tire space. A 12V alternator system would only provide half that much recharging capacity.

I’m not convince that the Volta system is the best solution and noticed that both Winnebago and Storyteller dropped the Volta battery in favor of Lithionics.

 

[Dave01a]

The ideal situation would be for all the ancillary items to be available in 48V, but until it becomes more widely used, I just about have to stick with 24 from what I'm reading.

BTW, I grew up when all the big engine vehicles and equipment was 24V, but as far as I can remember, every big truck I've delivered the last two years has been 12V. I guess I should be thankful the 24V systems have been out long enough to keep the 24V accessories still in production as the RV solar market for them gets up to speed.

 

[Boxster1971]

Just discovered that Tiffin has also dropped the Volta system and gone with Battle Born Lithium in the new Tiffin GH1. Not sure but it looks like they went back to a 12VDC system.

 

[Captain Longbeard]

Something to consider: Solar

I am also planning an upgrade, and going with 24v. I currently have three 110w solar panels on the roof which are in parallel, providing upwards of 17V, but the new battery will need upwards of nearly 30V from the solar to charge. I don't really understand why this is, but my ignorance is of no importance. The point is, if I add another panel, I can run a series-parallel system giving me upwards of 34v for the controller to be able to send the needed voltage to the 24v battery bank.

However, if I were to consider a 48v system (actually a 51v battery), I would have to run all three panels in series, but there is not enough room for a larger series-parallel system. This is less ideal since any partial shading of any panel will affect the entire solar array. With other stuff on the roof, like AC, Starlink, and Maxxfan, potentially shading the panes, along with tree limbs and such, the risk of reduced solar power is real.

On another note, my unit (Coachmen Galleria) has a central 12v fuse panel, and I can easily add a single DC-DC converter to run all of the 12v from the 24v battery bank. While there are space/cost/efficiency considerations to doing this vs a 12v battery, for us, it is more important to reduce charging drive-time, which will be pretty much cut in half with the 24v over 12v. However, even though a 51v battery would cut the charging drive-time in half again over the 24v, the reduced solar charging when boondocking (or siting in a parking lot) negates that benefit, at least for us and our needs.

 

[booster]

Something to consider: Solar

I am also planning an upgrade, and going with 24v. I currently have three 110w solar panels on the roof which are in parallel, providing upwards of 17V, but the new battery will need upwards of nearly 30V from the solar to charge. I don't really understand why this is, but my ignorance is of no importance. The point is, if I add another panel, I can run a series-parallel system giving me upwards of 34v for the controller to be able to send the needed voltage to the 24v battery bank.

However, if I were to consider a 48v system (actually a 51v battery), I would have to run all three panels in series, but there is not enough room for a larger series-parallel system. This is less ideal since any partial shading of any panel will affect the entire solar array. With other stuff on the roof, like AC, Starlink, and Maxxfan, potentially shading the panes, along with tree limbs and such, the risk of reduced solar power is real.

On another note, my unit (Coachmen Galleria) has a central 12v fuse panel, and I can easily add a single DC-DC converter to run all of the 12v from the 24v battery bank. While there are space/cost/efficiency considerations to doing this vs a 12v battery, for us, it is more important to reduce charging drive-time, which will be pretty much cut in half with the 24v over 12v. However, even though a 51v battery would cut the charging drive-time in half again over the 24v, the reduced solar charging when boondocking (or siting in a parking lot) negates that benefit, at least for us and our needs.

The 17v spec on solar panels is normally the maximum power point where the generate the most watts of energy. Maximum voltage spec on them is probably a bit over 21v so your controller would be seeing that amount when at max voltage point. A 24v controller would see 42+v max and would charge the batteries at probably 28.8v is you charge at full voltage or maybe 27.6v is you use the getting more common conservative charge voltage recommendations. An MPPT controller is needed to get max wattage out of the panels.

Unless I am looking at it wrong, for the same size of battery bank in watt hours, your charge time will be very close to same at 12v and 24 and the same "C" rate of charging unless you are going to 24v to reduce the current and get higher watts from the alternator. For instance if you had 4 100ah 12v batteries in parallel 4800wh) and charged at .2C you use 80 amps to charge them and take 5 hours if totally dead to totally full. If you had if you had those 4 batteries as series/parallel 24v (4800wh) each battery would still be charging at .2C but there would only be two strings of batteries at 20 amps each for 40 amps total and would take 5 hours to charge also.

Where you run into a time benefit is when the C rate and battery bank watt hour rating get higher and you run out of alternator capacity with 12v sooner than the 24v system. For instance in the 12v 400ah system if you charged at .8C you would need 320 amps of 12v alternator charging, which gets pretty hard to get from a single second alternator.

If you have the solar on while driving and it is sunny the 24v panels at 440 watts will give 10-12 amps so that adds to your charge rate from the alternator so depending on how carefully you want to control the C rate, you may want to allow for that.

The days of very high charge rates of lithium batteries are fading pretty quickly, it appears, with probably .4-.5C being a common max rate rate and many more starting to have a .2C recommended charge rate. You rarely see the 1C+ rates stated much anymore. Maxing out alternators tended to be the most common lithium charge rate limiter in the past with the high C rate recommendations, but now that is less common unless on larger bank sizes.

Lots of inputs to the equation of how it works out with daily use, days of stay, battery bank size, time driving on drive days, etc. We charge at 120 amps of 12v for our 618ah bank and only about 60ah max under most conditions, plus our stays are fairly long without driving many times. 300 watts of solar covers our use in good sun, or not without got sun. We make up for that with the larger bank/use ratio. If we we using air conditioning off the batteries we would need to charge every day, and our system would not work for that with the rest of our patterns.

 

[Captain Longbeard]

booster, I am looking at installing two Lithionics batteries, which have very aggressive charge rates. The 12v 640ah is recommended to charge at 200A, whereas the 24v 315ah is recommended to charge at 157.5A, therefore providing a faster rate of charge compared to the 12v. If we opt for the premium GTO units (need to check on costs and availability), they charge at 165A. Running two parallel batteries at these charge rates, they can take all the amps that the alternators can put out. Looking around at 12v add-on alternators, I can find up to 280A, but I am looking at installing a 24v alternator that can put out 185A, so that increases the charging capacity and decreases charge time. I know that I am using simple nominal terminology (12v/24v), and that actual voltages might be higher, and charging rates vary based on multiple factors.

But basically, and to the point of this thread, I can get a better charge rate on a 24v Lithionics system than I can on a 12v system. However, going to a 48V battery and 130A alternator would be even more efficient, but solar has a greater potential for lost effectiveness, so that is a trade-off to be decided for each individual. For us, the 24v system seems to be the best balance overall, but that debate continues.

 

[Boxster1971]

Solar is definitely a challenge for a 48V system on a van. The solar that Airstream installed on my van for Volta 48V system is useless. I added a 12V Victron SmartSolar and now use the installed 250 watts of panels to charge the Sprinter chassis battery.

If I want to upgrade solar to something that could charge the 48V Volta system I need a Voc of about 80 volts.

 

[booster]

booster, I am looking at installing two Lithionics batteries, which have very aggressive charge rates. The 12v 640ah is recommended to charge at 200A, whereas the 24v 315ah is recommended to charge at 157.5A, therefore providing a faster rate of charge compared to the 12v. If we opt for the premium GTO units (need to check on costs and availability), they charge at 165A. Running two parallel batteries at these charge rates, they can take all the amps that the alternators can put out. Looking around at 12v add-on alternators, I can find up to 280A, but I am looking at installing a 24v alternator that can put out 185A, so that increases the charging capacity and decreases charge time. I know that I am using simple nominal terminology (12v/24v), and that actual voltages might be higher, and charging rates vary based on multiple factors.

But basically, and to the point of this thread, I can get a better charge rate on a 24v Lithionics system than I can on a 12v system. However, going to a 48V battery and 130A alternator would be even more efficient, but solar has a greater potential for lost effectiveness, so that is a trade-off to be decided for each individual. For us, the 24v system seems to be the best balance overall, but that debate continues.

I just looked at the Lithionics BMS included cased batteries and I think the 640 battery you mentioned, that I didn't look for, may be an outlier that is limiting because of a 200 amp BMS limit.


The similar AH 12v batteries in the 320AH range pretty much all had right around .5C maximum charge rates, as do the 24v ones you list. .5 isn't really a high charge rate by past standards but is probably mid range for a callout now. It is was Victron uses on their cased batteries except for the very lastest version that is higher. Note the specs are rated as an equal to or less than specification, so it highly likely they feel that .5C is not optimum but a level that will not severely reduce life vs going lower. Nobody seems to list predicted life by charge rate, but I have seen some research stuff that indicated .2C or under was best but benefits in life decline quickly below that rate. If everything else is good .5 is probably less of an issue for life expectancy than the going to full charge of 14.4v every cycle and holding there like they do (probably to balance them. Full charging all the time has been shown to shorten life by more sources than charge rate, but I think both do count. Victron does show predicted cycle life at the various depths of discharges from full though, and again compared to the old specs of using 100% discharge and getting 10K cycles, they say 2500 cycles at 80% discharge now.


It sounds like you are looking at similar capacity to what our system is with about 620ah hours or so, and at .5C at 12v you are easily above what a 12v alternator can put out unless you get the really big 320amp units that some have used, but almost no alternators can run at rated for more than a short time so even they would be short. At 24v you would be in the 160 amp range so better that way, but be sure to check and see what the duty cycle is at various alternator temps. It is important because some will be rated at 250 or 260* which is too hot to run continuously for most units. A Balmar regulator will turn down the 280 amp 12v alternators when the get to about 220* and they will heat cycle after that and net only about 165 amps continuously depending on conditions and ventilation they are in. Can't say without seeing a heat vs output graph for the 185 amp 24v alternator you have found, but my guess is that it will net less than that rating as it heats up and runs longer. It is always a good idea to put on a remote regulator that heat senses and reduces output to control temps, as the alternators are too expensive to risk to internal regulators that you can't set, IMO.


Having full voltage and amp settings available on all the charge sources lets you set them to play well together without having to turn them on and off automatically when one or the other is in use. Being able to limit charging amps from the alternator accurately is a great thing to have but only a couple of regulators can do that. You have to remember that the lithium batteries likely will be absorb lots more amps above the max rating and would likely max out your alternator unless you current limit the current to batteries in some way. The solar won't be able to charge to high a rate so no problem and if the shore charger is sized right it would also be fine, plus it would be hard to find one that is 135 amps.


It sounds like you are quite close on having the system set for 24v, but the devil is in the details and equipment capabilities.

 

[Captain Longbeard]

With no intended disrespect to Dave01a of thread hijacking, I think this info is helpful to his initial inquiry, so I will continue. If not, I will pull back.

So far, we are still in the planning phase, working out all of the details, so things may change. The goal is to be able to boondock each night (we tend to be day-drive explorers), and use 12v loads (via DC-DC converter), as well as induction cooktop, microwave, toaster, coffeemaker, and AC (currently 12v, but expect to swap for 120v over summer) without having to think about the power demands through the inverter. Not all loads need to be simultaneous, and not extended usage except for AC, which is the one load we are willing to manage if it absolutely comes down to it. If we do a "camp-day" or two without driving, we want enough bank to power us through, with the solar giving us a little extra, and can always plan to be near a plug if necessary. Another goal is to eliminate the generator for noise elimination, weight savings, and potential plumbing relocation space.

So far, the upgrade package looks like this:
- 24V 185A dedicated second alternator, with smart controller (Wakespeed?)
- 2x Lithionics 24V 315AH (or 330AH) external BIM modules for a total of 630-660AH at 24V
- Victron 24/120V 5000VA/4000W inverter/charger to be able to handle 120v loads
- Hopefully reconfigure solar array to parallel-series 4x110w solar panels through MPPT controller
- 24/12 DC-DC converter powers main 12V distribution panel
- Maybe a 24/12 DC-DC converter to keep chassis battery charged (still pondering this)
- Victron Cerbo GX Controller to Touch screen to monitor everything
- Plus a bunch of wire, connectors, fuses, switches, communication cables, etc.

The solar is a challenge. I don't have room for a fourth 110W panel, but the manufacturer makes 55W panels that are pretty much half of the 110W (specs are NEARLY 1/2), so I hope to be able to parallel the 2x 55W in series with one 110W, and parallel those with the other two 110W in series. It is a bit confusing, but if the two 55's will work the way I want, it will give me the voltage to charge the battery bank, plus offer a little forgiveness if there is any shading on any one panel as opposed to putting them all in series.

This is a big modification (not cheap, either), and most people would say it is overkill, especially the inverter, but it will get us towards being able to travel and use the RV the way we want to, and the point of all of this is to be happy when traveling. Our Coachmen Galleria 24A has a huge garage under the fixed bed, but we don't carry a lot in there, so we can fit all of this in and have room left over.

 

[booster]

With no intended disrespect to Dave01a of thread hijacking, I think this info is helpful to his initial inquiry, so I will continue. If not, I will pull back.

So far, we are still in the planning phase, working out all of the details, so things may change. The goal is to be able to boondock each night (we tend to be day-drive explorers), and use 12v loads (via DC-DC converter), as well as induction cooktop, microwave, toaster, coffeemaker, and AC (currently 12v, but expect to swap for 120v over summer) without having to think about the power demands through the inverter. Not all loads need to be simultaneous, and not extended usage except for AC, which is the one load we are willing to manage if it absolutely comes down to it. If we do a "camp-day" or two without driving, we want enough bank to power us through, with the solar giving us a little extra, and can always plan to be near a plug if necessary. Another goal is to eliminate the generator for noise elimination, weight savings, and potential plumbing relocation space.

So far, the upgrade package looks like this:
- 24V 185A dedicated second alternator, with smart controller (Wakespeed?)
- 2x Lithionics 24V 315AH (or 330AH) external BIM modules for a total of 630-660AH at 24V
- Victron 24/120V 5000VA/4000W inverter/charger to be able to handle 120v loads
- Hopefully reconfigure solar array to parallel-series 4x110w solar panels through MPPT controller
- 24/12 DC-DC converter powers main 12V distribution panel
- Maybe a 24/12 DC-DC converter to keep chassis battery charged (still pondering this)
- Victron Cerbo GX Controller to Touch screen to monitor everything
- Plus a bunch of wire, connectors, fuses, switches, communication cables, etc.

The solar is a challenge. I don't have room for a fourth 110W panel, but the manufacturer makes 55W panels that are pretty much half of the 110W (specs are NEARLY 1/2), so I hope to be able to parallel the 2x 55W in series with one 110W, and parallel those with the other two 110W in series. It is a bit confusing, but if the two 55's will work the way I want, it will give me the voltage to charge the battery bank, plus offer a little forgiveness if there is any shading on any one panel as opposed to putting them all in series.

This is a big modification (not cheap, either), and most people would say it is overkill, especially the inverter, but it will get us towards being able to travel and use the RV the way we want to, and the point of all of this is to be happy when traveling. Our Coachmen Galleria 24A has a huge garage under the fixed bed, but we don't carry a lot in there, so we can fit all of this in and have room left over.

It will be interesting to watch if progress over time,


I think you may want to start a build thread of your own so it stays isolated.


We have a Wakespeed so that could be discussed on the new thread, as there as some worts to them and some of what the claim don't work all that well. There is a new player in it also, Zeus, which claims they are a Wakespeed style regulator with the problems addressed, so you may want to check them out.