Van build - run 48v, drop down locally to 12 volt?

[chrisstratton]

I'm considering another van build and wonder if I might run 48volt lines to different locations, such as to a diesel parking heater or heat pump, then put a 48v to 12v converter (sized correctly for wattage)?

 

[pollenface]

The world is your oyster

 

[Rednecktek]

Do you need so much power that you need a 48v system or can a 12v system fulfill your needs?

You can absolutely use multiple step down converters if that's easier for you than having a single larger step down and central fuse block for everything.

 

[chrisstratton]

I had a system w/ 24v @150ah (3600kwh). That was not adequate to run the A/C overnight (12kbtu, which, in our FLA weather, drew about 900w). I'm thinking to double the 3600 to about 8kwh.

 

[Dzl]

I'm considering another van build and wonder if I might run 48volt lines to different locations, such as to a diesel parking heater or heat pump, then put a 48v to 12v converter (sized correctly for wattage)?

Is this question whether you *can* do this or whether you *should* do this?

• If can, than yes
• If should, than it depends.

Also, don't forget about 24V, for many people, its a good compromise between the two. But it really depends on your goals and your system. Every standard voltage has its place.

 

[chrisstratton]

Do you need so much power that you need a 48v system or can a 12v system fulfill your needs?

You can absolutely use multiple step down converters if that's easier for you than having a single larger step down and central fuse block for everything.

I've been looking for a 48v fuse block and haven't found yet

 

[chrisstratton]

Is this question whether you *can* do this or whether you *should* do this?

• If can, than yes
• If should, than it depends.

Also, don't forget about 24V, for many people, its a good compromise between the two. But it really depends on your goals and your system. Every standard voltage has its place.

Thanks for a very helpful answer.

 

[Rednecktek]

I had a system w/ 24v @150ah (3600kwh). That was not adequate to run the A/C overnight (12kbtu, which, in our FLA weather, drew about 900w). I'm thinking to double the 3600 to about 8kwh.

Gotcha! Yup, a 48v system seems right up your alley. You'll have to get large enough converters to handle any startup surges and such from motors and pumps and the like, converters don't surge like inverters do so if you need to supply a 12a startup draw from a diesel heater (I know those very well and you want 12a for the startup with pump, fan, and glow plug) then you need a 12+ amp/150+ watt converter all the time.

Repeat for each step down instance. Most often it's cheaper to buy a 600w converter than it would be to buy 4 of the 150w converters. When you're pulling wires for all the 12v stuff it's easier to go from a single 48v breaker to a fuse block where you can use simple easily available automotive fuses rather than having to source a 48v rated fuse or breaker for each converter and have to track down a 48v replacement if 1 of your converters pops.

Having said that, there's no reason you can't do a step down at each load, just plan all the parts accordingly.

 

[justinm001]

I've been looking for a 48v fuse block and haven't found yet

Wouldn't any 12v fuse block handle 48v?
Would a 48v to 12v converter at each location be cheaper than just thicker wire?

 

[chrisstratton]

Wouldn't any 12v fuse block handle 48v?
Would a 48v to 12v converter at each location be cheaper than just thicker wire?

Perhaps - the listed ratings I see limit to 32v. Re: you second question - maybe.

 

[Dzl]

My 2c, a van is relatively small, and most van builds make heavy use of 12v or 24v appliances/devices. For these reasons, the upside to 48V will be a bit more limited and the downsides will be a bit more of a bother.

Many of the popular brands and parts people use for vehicle and marine systems are 12/24v. I'm not just speaking of popular appliances like DC compressor fridges, I'm also talking about things like fuse blocks, circuit breakers and fuses, switches, lighting etc. Of course you can usually find alternatives online but it can still be a limitation, and takes more research/effort, alternatively you could get around this with DC-DC converters as you have proposed but then that comes with a conversion efficiency penalty and added costs. My feeling is until you are pushing up against limits of the lower voltages it makes sense to stick to them (not everyone shares this logic though).

What are the reasons you desire 48V over 24V (or 12V)?

 

[chrisstratton]

My 2c, a van is relatively small, and most van builds make heavy use of 12v or 24v appliances/devices. For these reasons, the upside to 48V will be a bit more limited and the downsides will be a bit more of a bother.

Many of the popular brands and parts people use for vehicle and marine systems are 12/24v. I'm not just speaking of popular appliances like DC compressor fridges, I'm also talking about things like fuse blocks, circuit breakers and fuses, switches, lighting etc. Of course you can usually find alternatives online but it can still be a limitation, and takes more research/effort, alternatively you could get around this with DC-DC converters as you have proposed but then that comes with a conversion efficiency penalty and added costs. My feeling is until you are pushing up against limits of the lower voltages it makes sense to stick to them (not everyone shares this logic though).

What are the reasons you desire 48V over 24V (or 12V)?

No especially good reason compared to 24v other than smaller wiring.

 

[justinm001]

My 2c, a van is relatively small, and most van builds make heavy use of 12v or 24v appliances/devices. For these reasons, the upside to 48V will be a bit more limited and the downsides will be a bit more of a bother.

Many of the popular brands and parts people use for vehicle and marine systems are 12/24v. I'm not just speaking of popular appliances like DC compressor fridges, I'm also talking about things like fuse blocks, circuit breakers and fuses, switches, lighting etc. Of course you can usually find alternatives online but it can still be a limitation, and takes more research/effort, alternatively you could get around this with DC-DC converters as you have proposed but then that comes with a conversion efficiency penalty and added costs. My feeling is until you are pushing up against limits of the lower voltages it makes sense to stick to them (not everyone shares this logic though).

What are the reasons you desire 48V over 24V (or 12V)?

I agree with this but things are changing and a lot more 48v systems are coming. For instance jeep/ram uses 48v alternators for their etorque (like MB). Tesla is also switching to 48v. It just makes more sense across the board as electronics are needing more power.

 

[Dzl]

No especially good reason compared to 24v other than smaller wiring.

My guess is that any cost savings from smaller wiring would be offset by the added cost of the per device dc-dc converters, but I could be wrong. I suppose you could/should price out both (and take into consideration cost and availability of, BMS, overcurrent protection, etc which could tip the scales towards 48V or not depending on the details).

 

[chrisstratton]

I agree with this but things are changing and a lot more 48v systems are coming. For instance jeep/ram uses 48v alternators for their etorque (like MB). Tesla is also switching to 48v. It just makes more sense across the board as electronics are needing more power.

I, too, think that 48v is the coming thing. These systems are more easily changed to a more efficient standard. Consider our 110-120VAC residential standard - the 208vac European standard must save a bunch in resistance loss and wiring. Changing that US standard would be very painful.

 

[Rednecktek]

I've been looking for a 48v fuse block and haven't found yet

I don't think they exist outside certain marine and industrial usages. At that point you would just be flexing your budget more than anything else.

Wouldn't any 12v fuse block handle 48v?
Would a 48v to 12v converter at each location be cheaper than just thicker wire?

Nope, unless you have a really high draw 12v appliance you can get away with 14awg pretty much every time.

 

[Dzl]

I agree with this but things are changing and a lot more 48v systems are coming. For instance jeep/ram uses 48v alternators for their etorque (like MB).

Some years down the road, that might change things as the industry adapts (I hope so at least), but as it stands right now my experience is there aren't as many 48V options in comparison to 12V or even 24V, and vehicles with non-12V charging systems are rare.

Also since much of the equipment used in vans and vehicle builds comes from the marine world, not the automotive industry, its important for that industry to change as well. Probably more important.

 

[HarryN]

I build both 24 volt and 48 volt power systems for vans and have for years.

In both cases I have DC - DC converters for the 12 volt loads and of course inverters for the 120 vac loads.

What happens in practice is that with a 24 volt system, you can readily find >90% of the DC appliances such as heaters, refrigerators, lights, etc in either 24 volt or dual 12 / 24 volt. So if you plan to mostly use it for moderate power level DC loads and occasional 120 vac loads, then 24 volt is a really good path. About the only thing that is hard to find in 24 volt are roof top fans so you will need to be creative about that aspect or use a converter.

With 48 volt, it is a LOT harder to find components that are actually rated for both "mobile use" and "full 48 volt range use". As an example, with 12 and 24 volt systems, you can use pretty much everything listed on the blue sea web site without issue. With a 48 volt system, almost nothing on that site is usable except for a few specialized parts.

So the big advantage of 48 volt is mostly in making things more compact and if you plan heavier power loads / especially 120 vac air conditioners and fast charging via secondary alternator.

Essentially committing to 48 volt means that the bulk of your DC loads will end up being nominal 12 volt loads. It works just fine, but it is what it is.

My suggestion is to use 24 volts if you are building it yourself.

 

[HarryN]

Battery wise, for running the air conditioner, very roughly it takes about 1 kW average to keep comfortable in your location.

So to run for 8 hrs, it will take roughly ( 8 hrs ) x ( 1 kW ) ~ 8 kW-hrs of usable battery storage capacity. It does not matter if it is 24 or 48 volt based.

To go longer, just increase the hrs number in the calculation - or turn on a charging source in the middle of the night.