12V vs 24V pros and cons

[Re-Pete]

I've been hearing that 24V may be superior to 12V for an RV. I'm in the process of rebuilding my 1992 Excella and I'm looking for input on this if anyone has anything to offer. I will be installing 400 to 600W of solar and approximately a 300 to 400A LiFePO4 battery system. My 120V AC system will be 30A. I will be installing a 12V or possibly a 12V / 24V Danfoss compressor Electric Fridge/Freezer. Anyway, I'd sure appreciate some knowledge based guidance.

[GMFL]

Here is a few right off the top of my head.
I’m looking at possibly running a 24V system in my new trailer also.

12 volt pros
Simple system to design
Most of your RV is already set up for it (lights, furnace ect...)
No special equipment needed

12 volt cons
Need to run bigger wire
12volt appliances will run sluggish as battery voltage drops

24 volt pros

Can run smaller wire for larger inverters
Less amps
With 24-12 volt converter your 12volt appliances will run crisp and clean.

24 volt cons
You gotta learn a new system
Solar Array must be larger To be able to run series pairs to increase voltage for higher charge voltage.

[Re-Pete]

Originally Posted by GMFL

Here is a few right off the top of my head.
I’m looking at possibly running a 24V system in my new trailer also.

12 volt pros
Simple system to design
Most of your RV is already set up for it (lights, furnace ect...)
No special equipment needed

12 volt cons
Need to run bigger wire
12volt appliances will run sluggish as battery voltage drops

24 volt pros

Can run smaller wire for larger inverters
Less amps
With 24-12 volt converter your 12volt appliances will run crisp and clean.

24 volt cons
You gotta learn a new system
Solar Array must be larger To be able to run series pairs to increase voltage for higher charge voltage.

GMFL,

Thanks so much for your input. Can you advise me of a book/s or website/s where I can get some additional edumakation?

[AKNate]

Originally Posted by GMFL

...
12volt appliances will run sluggish as battery voltage drops
....
With 24-12 volt converter your 12volt appliances will run crisp and clean.

He is planning on using lithium batteries, so low voltage will not be an issue. Lithium’s have an essentially flat voltage curve all the way until they are nearly dead.
24 V is great because you halve your current and can use much smaller wires. Unfortunately everything is designed around 12 V. Your 24 V system will just likely run a converter to make it 12 V, adding conversion loss. The amount of wiring between the batteries and DC bus and inverter is minimal anyway, so you’re not really saving a lot. If you do happen to find 24 V devices to use, some day when they break, it is going to be much harder to find parts/replacements when you’re on the road.
In short, 24 V is better. I’d go with 12 V.
Once you get into far bigger systems than yours, then it can start to make sense to go 24 V.

[uncle_bob]

Hi

One other gotcha:

Your brakes are 12V. You *must* have a battery to run the breakaway system. Relying on a 24 to 12 converter may not be a real good idea for this part of things. One would have to do a bit of research into just what is "legal" state by state and country by country.

The same issue applies if trying to charge from your TV. You will need a 12 to 24 converter for that side of things. If you are going heavy lithium this may not be a concern. ( = doing significant charging from the TV may or may not be in your plans).

12V gizmos are made for the RV market. 24V stuff is made mainly for the boat market. Ask any boat owner what he thinks of the prices on the spares for his "treasure" .... do it with the kids out of range unless you want them to learn a lot of new words

Consider that you aren't just buying a fridge. The list of things in a modern trailer goes on for a while:

A/C (maybe two)
Vent fans (maybe two)
Water pump
Tongue jack
Power stabilizers
Kitchen fan
Inside lights
Outside lights
Stereo
TV
DVD player
Power to computer(s)
WiFi
Cell booster
Cable TV box from the campground people ....
Satellite TV box
and on and on and on .....

You can say that you will run most of this off of a 24V to 12V converter. Once you do that, you are right back to a 12V system. Since you have both 24 and 12V wiring, getting things crossed up ... yikes ....

Solar wise, you can run a 72V panel setup into 12V batteries or into 24V batteries. It's just a matter of how you wire this or that. Pick the right parts and it all works fine. There is no practical impact on the solar side of things *unless* you want it to be so.

What do you gain? Well, that depends ...

1) If you re-size the wire ( cut the weight in half) when you go to 24V, the voltage drop for a given power level will be same / same as it was at 12V. You will loose half the power you would have otherwise.

2) If you keep the same wire ( it's heavy but it's already in the trailer ) the voltage drop will be 1/2 of what it was ( current is half, drop is half).

What does this mean? If you had a loss of 1% in the wire at 12V, in case 1, you would save 0.5%. In case 2 you would save 0.75%. Yes you *can* measure these sort of losses with the right sort of test gear. Noticing a sub 1% change on a real RV in real use .... good luck.

If you want to set up to run your A/C off of your battery bank full time / mid summer then sure, 24V probably makes sense. The sort of solar and battery you would need is way past what you are talking about. How you would fit a few KW of solar on an AS .... no idea.

An AS has a *tiny* power system in it. Much of what you see here or there is targeting much larger systems. The "advantage" of higher voltage is mainly on a larger system.

Bob

[daleyocum]

24v is also less efficient than 12v since you’d need to run everything through a regulator in order for it to be used by the vast majority of RV devices. That costs you about 10%-15%.

I just don’t see doing all that just to have smaller wires near the batteries.

[kidjedi]

If you're reading what people are saying, then you're hearing the unfortunate truth: 24v is better, but 12v is drastically easier. Just like so many things in this world, the "best solution" doesn't always win the initial contest, and then the inferior solution becomes the standard (and thus, the inferior solution propagates itself until it's the only way to go). Everything you can buy to live life in your RV or automobile is set up for 12v DC or 120v AC (AC being another possibly inferior contest winner, but that's a conversation for another thread).

[BobnGayl]

From an engineering perspective, higher voltage is a better option -- 24 volt vs 12 would be more efficient in a RV. 240 vs 120 in a house. 440 vs 220 in factories. The US is one of the few countries that uses 110-120 volt power in homes. Europe has been 220-240 forever. 220-240 has many advantages over 110-120, not the least is better conductor and motor efficiency. The downside of course is that 220 is more dangerous in terms of electrocution potential than 120. That is why European 220 volt outlets usually have switches, so they can be turned off prior to plugging or unplugging an appliance. That said, I have never seen any statistics that say more people are electrocuted in 220 volt countries than here although that may be the case. Nevertheless, 110-120 is what we have and I doubt it will ever change and 220-240 is what Europe has and I doubt that will ever change either. Things start with one system and it's nearly impossible to change it.

[RWitherspoon]

I like this man's approach to testing and explaining things

https://www.youtube.com/watch?v=Vi7eswWwosk

I almost never use manuals as a video shows how to DIY much better.

[Re-Pete]

Guys,
Thank you, thank you, for such great and detailed advice and links. Based on what I've seen, researching on my own, I was pretty sure that what all of you have recommended would be the correct way to go, but mine was a gut feeling. What I wanted was facts and that's exactly what you have all provided. Much appreciation. Please stay safe.