24V for vehicle specific systems (cheaper/more efficient(?), but how much)

[Dzl]

It seems to me a lot of the discussion/conventional wisdom of "24/48 volt systems will always be cheaper/more efficient compared with 12 volt systems" is in the context of stationary systems, cabins, homes, etc. And that for us mobile folks (land based, marine is a different story), the equation is a bit different.

Here are a few of the reasons I see the equation being different for (small to medium) mobile systems:

1. We don't just feed everything through an inverter and wire everything in 110. So the voltage we choose isn't just a 'storage voltage' its ideally the voltage we will be using for most of our wiring, so it follows that the voltage we use will have a larger effect on the system and the appliances/electronics/products available to us.
2. We generally are talking about smaller spaces ~40-300 square feet at most. So the cost of wiring should be a smaller part of our budget than with a larger stationary 'whole house system.' Or maybe I am thinking about this point backwards, maybe the wiring cost is greater for mobile systems since more of our wiring is lower voltage higher amperage wiring when compared with wiring in 110?
3. We are also talking about smaller square footage available for PV so in contrast to stationary setups where space is often plentiful and big panels are cheap, the charge control is somewhat less likely to be the bottleneck in our system (one of the major reasons to consider 24vdc).
4. For many of us, mobile power requirements/draws will be much much lower than the draws required for all the creature comforts of a house. So like point 2 this should in theory reduce the cost of wiring as % of total system cost by allowing the use of smaller gauge wire.
5. 12 volt appliances appear to be much more plentiful (especially used) and often substantially cheaper than 24 volt alternatives. You could easily use a dc-dc converter, but there is a conversion loss of 4-6% iirc (?) when converting 24vdc to 12vdc, not major but also not ideal.

For all these reasons, the conventional wisdom of 24v/48v will be cheaper/more efficient for a given system size doesn't seem well calibrated to mobile systems, where the variables are much different and seem much more complicated than a stationary off grid system (where the conventional wisdom of use a high voltage, minimize losses, convert to AC, makes sense).

I'm not arguing that 24v doesn't make sense for mobile applications, I think in many cases it probably does, but I think there are more tradeoffs and factors to consider for those of us with mobile setups. I am admittedly just beginning to wrap my head around PV, battery storage, etc, so there is probably a lot I am missing, or misunderstanding. That is sort of what this post is about. I'm 'thinking out loud' and hoping to instigate a productive conversation on the topic, and hopefully learn a thing or two. Other than wiring and charge controller wattage, what other benefits and efficiencies does 24vdc bring to the table. Tell me where my thinking is wrong (or right)?

 

[OyOv-MBC]

I’m attempting to jump start a hockey stick leaning curve as well for my mobile application. You’ve summed up many of the questions jostling around in my head as well. What I have picked up on in terms of eeking up a bit to say 24 v storage there may be more varied inverter/converter and alternator charging options than 48v and up.

 

[coachgeo]

slightly off topic..... in my situation have existing 12v wiring (former ambulance) as power feed to 12v power outlets. My refrigerator is 12 to 24v power.

If my understand is right 24v requires lower guage wire than 12v.... so can I utilize a section of the former 12v wiring as 24v feed to this refrigerator? (plan to have 24v house battery banks. Truck uses 24v alternator (mostly 24v that is / its complicated)

 

[coachgeo]

...

1. 12 volt appliances appear to be much more plentiful (especially used) and often substantially cheaper than 24 volt alternatives....

if you look close you will find many devices advertised (even used devices) as 12v.... are actually in the specs said to be ok to be powered anywhere between 12 to 24v. Only can guess that this to be the case cause there is market outside of usa where. 24v is the norm. Overseas the same thing may be advertised as 24v (with different plug though)

So look at specs close.

 

[Dzl]

slightly off topic..... in my situation have existing 12v wiring (former ambulance) as power feed to 12v power outlets. My refrigerator is 12 to 24v power.

If my understand is right 24v requires lower guage wire than 12v.... so can I utilize a section of the former 12v wiring as 24v feed to this refrigerator? (plan to have 24v house battery banks. Truck uses 24v alternator (mostly 24v that is / its complicated)

An ambulance build, cool. I was looking into that a few years back, its a good solid platform to begin with. Built strong, high output alternator, usually diesel engines, and a good form factor to convert. What chassis, E-450? Are you over on expedition portal as well?

As to your question about wiring, I think you are on the right track, if the 12v wiring could power your fridge at 12v, it should be able to easily power it at 24v. Are you planning to get a second alternator rated for 24v or are you saying that your current alternator is 24v? If you don't have or don't want to install a dedicated 24v alternator but want to be able to charge your batteries, consider a DC-DC charger/isolater, it (1) makes it safe to charge lithium batteries from an alternator and (2) allows you to charge 24v batteries from a 12v source or vice versa. The companies that make a product like this are Victron, Redarc, and Sterling Power (Renogy makes 1 but only for 12v to 12v).

if you look close you will find many devices advertised (even used devices) as 12v.... are actually in the specs said to be ok to be powered anywhere between 12 to 24v. Only can guess that this to be the case cause there is market outside of usa where. 24v is the norm.

Yeah, I've found this to be the case. But not uniformly so, part of the appeal of 12v is that (in the US at least) you can always count on finding a 12v compatible product, and usually at a cheap price point. Most everything is available in 24v, you just have to look harder and sometimes pay more or order online. Its not really a dealbreaker (as you could easily just use a converter) but more of a convenience and provides some peace of mind if you need to make a repair/get a replacement in some small town. And to be honest, I don't really know how much of a factor this would be, but if I needed a replacement part in some smalll town, it would be nice to be able to count on finding it at the hardware or autoparts store as opposed to having to order off amazon or special order something. A couple examples of things I haven't foudn available in 24v are chargers for my powertool batteries (available in 12 or 120) or a roof fan (fan-tastic fan/maxxfan). That said, I'm drawn to the efficiency of 24v as well. Its hard to know what is right, there are pros and cons to both and its likely either would be fine.

 

[coachgeo]

An ambulance build, cool. I was looking into that a few years back, its a good solid platform to begin with. Built strong, high output alternator, usually diesel engines, and a good form factor to convert. What chassis, E-450? Are you over on expedition portal as well?

welllll no... its a PL bodies ambulance box... but mounting it on an LMTV military truck

As to your question about wiring, I think you are on the right track, if the 12v wiring could power your fridge at 12v, it should be able to easily power it at 24v. Are you planning to get a second alternator rated for 24v or are you saying that your current alternator is 24v? If you don't have or don't want to install a dedicated 24v alternator but want to be able to charge your batteries, consider a DC-DC charger/isolater, it (1) makes it safe to charge lithium batteries from an alternator and (2) allows you to charge 24v batteries from a 12v source or vice versa. The companies that make a product like this are Victron, Redarc, and Sterling Power (Renogy makes 1 but only for 12v to 12v).

trying to figure that out see my thread on this..

24v sorta alternator(s) , 24v truck sorta , 1000w solar panels and lithium

complicated and looking for advice. . 28v/14v 200* amp/50amp alt. on engine (yes dual voltage) will use 28v side for charging probably to primary 24v wet battery bank on engine first and house lithium battery second (yup military truck based camper) Yes truck has 12v accessories and lighting...

www.diysolarforum.com

Yeah, I've found this to be the case. But not uniformly so,.... That said, I'm drawn to the efficiency of 24v as well. Its hard to know what is right, there are pros and cons to both and its likely either would be fine.

since my truck is already 24v it just makes since

 

[Dzl]

since my truck is already 24v it just makes since

Oh yeah, no question, if you've got a native 24v system, that makes the most sense.

welllll no... its a PL bodies ambulance box... but mounting it on an LMTV military truck

Right on! I was looking into those as well (LMTV's) a while back. Those are some badass trucks if you can stomach the MPG's, low top speed, and lack of creature comforts. Love the CTIS system. Great truck for a great price if you are willing/able to do a lot of the work yourself. Do you have the truck yet or still looking?

 

[coachgeo]

Oh yeah, no question, if you've got a native 24v system, that makes the most sense.



Right on! I was looking into those as well (LMTV's) a while back. Those are some badass trucks if you can stomach the MPG's, low top speed, and lack of creature comforts. Love the CTIS system. Great truck for a great price if you are willing/able to do a lot of the work yourself. Do you have the truck yet or still looking?

got one.. few years later and now two are in my back yard..... aggggggg..

 

[Wellydex]

For me 12 or 24 was a close decision. These were the main points that swung me.
I had calculated I needed 5kw hr of battery.
I could get a good price on 200 ah cells and was more comfortable configuring these in a single 24v battery than 2x 12 in parallel.
I needed a 35amp MPPT ($ 500 NZ) at 24v but would need 70A (850$) at 12V.
I wanted a 3000 VA inverter. And at 12v this would pull 250A. At 24v this is way more manageable at 130A.
And finally, as we are 240v AC in New Zealand, the maths is easier to do power conversions!!!

 

[Merlmabase]

I'm also at an early stage of learning the principles of solar/mobile power system design, and also wrestling with the 12V/24V question. Based in Canada. For me, these seem like the biggest pros for each one, although some of them might be based on incorrect assumptions.

12V pro - I'm very interested in the Redarc Manager30, the all-in-one MPPT solar charger, 110VAC charger, and alternator charger. From what I understand, unless you have a vehicle with a 24V alternator (or install one), charging a 24V system is a no-go, and the Manager30 can't charge a 24V system in any case. I'm working on a camper build that can manage Canadian winter conditions, so I can't count on ample solar, and want to be able to go places where AC charging isn't likely to be available.

24V pro - it would be cool to have the capability to run high-draw AC devices on this system. I'm thinking power tools specifically. If my system is 12V, I believe I'll need to heavily up-spec on cable diameter and inverter capacity.

If anyone is able to tell me if this is analysis is at least basically correct, I would greatly appreciate it!

 

[Supervstech]

I'm also at an early stage of learning the principles of solar/mobile power system design, and also wrestling with the 12V/24V question. Based in Canada. For me, these seem like the biggest pros for each one, although some of them might be based on incorrect assumptions.

12V pro - I'm very interested in the Redarc Manager30, the all-in-one MPPT solar charger, 110VAC charger, and alternator charger. From what I understand, unless you have a vehicle with a 24V alternator (or install one), charging a 24V system is a no-go, and the Manager30 can't charge a 24V system in any case. I'm working on a camper build that can manage Canadian winter conditions, so I can't count on ample solar, and want to be able to go places where AC charging isn't likely to be available.

24V pro - it would be cool to have the capability to run high-draw AC devices on this system. I'm thinking power tools specifically. If my system is 12V, I believe I'll need to heavily up-spec on cable diameter and inverter capacity.

If anyone is able to tell me if this is analysis is at least basically correct, I would greatly appreciate it!

A decent 1200 or larger 12v inverter will operate most any power tool out there...
My pickup has an old LF 1200 inverter, and it handles all my shop tools easily... not all at once, obviously... but starts my 6.5hp shop vac, my sawzall, my chop saw, and 3/4” chuck hammer drill through concrete block and concrete easily...

 

[Dzl]

12V pro - I'm very interested in the Redarc Manager30, the all-in-one MPPT solar charger, 110VAC charger, and alternator charger.

This sounds like a very cool product, I'm surprised I haven't come across it before. I'll definitely be looking into it!

From what I understand, unless you have a vehicle with a 24V alternator (or install one), charging a 24V system is a no-go, and the Manager30 can't charge a 24V system in any case.

Victron and Sterling Power make DC-DC chargers that allow you to charge a 24v battery bank from a 12v alternator (and vice versa)

I'm working on a camper build that can manage Canadian winter conditions, so I can't count on ample solar, and want to be able to go places where AC charging isn't likely to be available.

I have similar design goals as you (though I'll be avoiding the cold as best I can). What sort of camper are you building out (trailer? truck? RV? custom?)

24V pro - it would be cool to have the capability to run high-draw AC devices on this system. I'm thinking power tools specifically. If my system is 12V, I believe I'll need to heavily up-spec on cable diameter and inverter capacity.

If anyone is able to tell me if this analysis is at least basically correct, I would greatly appreciate it!

More than just 'up-speccing' the wiring, Fuses, Breakers, Busbars, Shunts, Relays, BMSs, SCCs etc will also all need to be rated for 2x the amperage. With a simple system this may not be a big deal, with a complex system it can add considerable cost.

A pro for 12v that shouldn't be discounted is that there is virtually always a 12v version of any product and way more selection, way less (but still a decent amount) available in 24v, and exponentially less available in 48v.

 

[Dzl]

A decent 1200 or larger 12v inverter will operate most any power tool out there...
My pickup has an old LF 1200 inverter, and it handles all my shop tools easily... not all at once, obviously... but starts my 6.5hp shop vac, my sawzall, my chop saw, and 3/4” chuck hammer drill through concrete block and concrete easily...

Just to clarify the terminology:

LF = Low Frequency

Low frequency inverters can handle a significantly higher startup surge for a substantially longer period of time. This is especially important with appliances/tools that are motor driven.

 

[Supervstech]

Just to clarify the terminology:

LF = Low Frequency

Low frequency inverters can handle a significantly higher startup surge for a substantially longer period of time. This is especially important with appliances/tools that are motor driven.

True.
Low frequency

 

[Merlmabase]

My pickup has an old LF 1200 inverter, and it handles all my shop tools easily... not all at once, obviously... but starts my 6.5hp shop vac, my sawzall, my chop saw, and 3/4” chuck hammer drill through concrete block and concrete easily...

Cool, thanks for sharing your experience. The dream would be to power my Ridgid jobsite table saw. Big load, but it's the previous gen with a built-in soft start, so peak amps might not be SO bad.

I have similar design goals as you (though I'll be avoiding the cold as best I can). What sort of camper are you building out (trailer? truck? RV? custom?)

Have my eyes on a box truck. Something pretty specific actually - where I live, there's one type that regularly pops up in the provincial fleet vehicle auctions. The transit company outfits these box trucks as mobile maintenance workshops. Each one that comes through is a bit different, but most have some specific features that I'm really looking for: easy passage between box and cab, well-sealed fairing over the cab with lots of storage space, ample standing height in the box, barn doors at the rear rather than a roll-up. Usually larger-engine chassis with duallies, and many even come with their own alternator-charged AGM batt with a little inverter/breaker box setup. I'd change all that over to a custom power system eventually, but if I have a modest power system built-in, at least I can put off that expense for a year or two. I've also seen a couple of them with some pretty cherry stainless drawers/cabinetry, that I could flip to offset vehicle cost. Generally low miles and good condition.

I'm a pretty big guy, 6'4", and all the popular trade vans folks like to convert are just a little on the claustrophobic side for me. Besides, as a former contractor, I much prefer the idea of insulating/outfitting a square box than the curved interiors of those vans. Seems like a huge headache, and wasted space.

Anyway, thank you both for the input!

 

[Merlmabase]

LF = Low Frequency

Low frequency inverters can handle a significantly higher startup surge for a substantially longer period of time. This is especially important with appliances/tools that are motor driven.

I see. And you can still find them on the market? I assume they have to output 60Hz AC, what exactly does the "low frequency" refer to?

 

[Dzl]

I see. And you can still find them on the market? I assume they have to output 60Hz AC, what exactly does the "low frequency" refer to?

I don't have the depth of knowledge to explain the technical difference beyond that LF inverts use big transformers whereas HF inverters use FETS,

The two major benefits of LF are (1) much better surge/peak power handling (2) better durability/reliability and a longer service life, and downsides (1) heavier and bulkier (2) upfront cost.

Yes you are correct the Low frequency does not refer to output AC frequency. IIRC it has something to do with the DC to AC conversion.

Here is a discussion on LF and HF I started a while back when I had the same questions as you. And here is a short explanation and comparison from a company that makes both LF and HF inverters. I have found that frequency is rarely advertised, but learned that size/weight + continuous to peak power ratio is a decent metric.

And yes they are still on the market, though someone on this forum, I cant remember who (Craig maybe?) says that true low frequency inverters are almost non-existant these days (I'm not sure what that means though).

 

[Merlmabase]

Here is a discussion on LF and HF I started a while back when I had the same questions as you. And here is a short explanation and comparison from a company that makes both LF and HF inverters. I have found that frequency is rarely advertised, but learned that size/weight + continuous to peak power ratio is a decent metric.

This is great, thanks!

 

[BiduleOhm]

I don't have the depth of knowledge to explain the technical difference beyond that LF inverts use big transformers whereas HF inverters use FETS,

The two major benefits of LF are (1) much better surge/peak power handling (2) better durability/reliability and a longer service life, and downsides (1) heavier and bulkier (2) upfront cost.

Yes you are correct the Low frequency does not refer to output AC frequency. IIRC it has something to do with the DC to AC conversion.

Here is a discussion on LF and HF I started a while back when I had the same questions as you. And here is a short explanation and comparison from a company that makes both LF and HF inverters. I have found that frequency is rarely advertised, but learned that size/weight + continuous to peak power ratio is a decent metric.

And yes they are still on the market, though someone on this forum, I cant remember who (Craig maybe?) says that true low frequency inverters are almost non-existant these days (I'm not sure what that means though).

The HF ones are basically a boost DC/DC converter to have a high voltage DC followed by a H-bridge driven with high frequency PWM to create the 60 Hz AC.

The LF ones have a H-bridge driven with high frequency PWM to create 60 Hz at the battery voltage and then a good old transformer to elevate the voltage.

The names comes from the fact HF ones use a high frequency DC/DC converter while LF ones use a (low frequency) 60 Hz transformer to do the conversion.

 

[Delmar]

I see. And you can still find them on the market? I assume they have to output 60Hz AC, what exactly does the "low frequency" refer to?

New low frequency inverters are available but expensive. Used industrial UPS units are low frequency, and units with bad batteries are inexpensive and readily available. Look for external battery connectors indicating the UPS is capable of continuous operation. However the larger ones are typically 48V powered.

Edit: the UPS will also include an automatic transfer switch for shore power, and battery charger. Good deal for an all-in-one system. i have mine back-feeding my breaker panel for backup power.