Use 24v Batteries to run 12v System... Possible?

[furyous68]

Sorry for the long post....

Hi everyone. I am new here. I am an RV greenhorn... don't even own one yet. But, we're in the market & the biggest thing I want out of it is to be as self-sufficient as possible. The very first thing I will be doing (besides checking over the engine, trans, rearend, and general health of the coach) is updating the charging system with a solar system. I do not want to run the generator unless absolutely necessary. I HATE when other campers run their generators for 12 hours out of the day, & I refuse to be one of them.

I'm looking at a 12v/24v solar system w/ a 60A MPPT controller. I know I could use 1 or 2 12v AGM batteries. BUT... I'm really interested in seeing if it's possible to run the RV's 12v system off of 1 or 2 24v batteries. If so, I could use 1 or 2 smaller batteries & due to you only needing to pull 1/2 the amps @ 24v's. I assume you would need a step-down converter between the 24v batteries & the 12v converter in the coach... right?

Somebody school me!

[2oldman]

Boon Docker wrote:
I would say 800 watts of solar is over kill for most people.

For most, probably. Sometimes it's underkill for a couple pots of brew coffee, toaster, a microwave dinner and 6 hours of TV at night, coupled with a couple overcast days or low sun!

[Boon_Docker]

Almot wrote:
Boon Docker, the problem with offgrid camping in Ca is that winter there is better than summer 🙂 - nice weather, not too hot.

However, very low sun, panels harvest much less than in summer. In some places it gets cloudy too. In the night it can get cold enough to need a furnace, this is additional energy draw. IMO, flat 500W is just about the minimum, if they want to avoid generator run.

OK, never thought about winter camping, makes sense now.

[Almot]

Boon Docker, the problem with offgrid camping in Ca is that winter there is better than summer 🙂 - nice weather, not too hot.

However, very low sun, panels harvest much less than in summer. In some places it gets cloudy too. In the night it can get cold enough to need a furnace, this is additional energy draw. IMO, flat 500W is just about the minimum, if they want to avoid generator run.

[Sam_Spade]

theoldwizard1 wrote:

Achieving proper multi-step charging will be the BIGGEST problem to solve !

But not the only one.

This is NOT a project that should be undertaken by a novice.

The OP, and anybody else for that matter, should be able to build a very capable and reliable 12 V system using relatively inexpensive off the shelf parts. One BIG advantage to that is: When you build a "standard" system, then others will know how to test and fix it should the need arise. Including the next owner(s).

[Boon_Docker]

I would say 800 watts of solar is over kill for most people. There are lots of RV'ers out there that have 300 watts or less of solar and do just fine.
I do just fine with 200 watts and a 225 AH battery bank.

[pianotuna]

I would have to lug them into the condo that I'll be moving into in the next year. Not going to happen. I suppose if I had a massive solar upgrade there might be enough capacity to keep the battery bank from freezing.

I'm not comfortable with any battery in my living space.

time2roll wrote:

pianotuna wrote:
LI are useless to me as I need to use the RV in the -30 range.

Bring them inside the RV.

[Almot]

PS: others have commented already, but in case if it wasn't clear, that your idea -

"I could use 1 or 2 smaller batteries & due to you only needing to pull 1/2 the amps @ 24v's"

- this is like using bottles with a wide neck vs narrow neck. It doesn't change the available amount of water.

The only way to have a physically smaller bank with the same amount of energy, is to use Li batteries.

[time2roll]

pianotuna wrote:
LI are useless to me as I need to use the RV in the -30 range.

Bring them inside the RV.

[Almot]

furyous68 wrote:
I am an RV greenhorn... don't even own one yet. But, we're in the market & the biggest thing I want out of it is to be as self-sufficient as possible. The very first thing I will be doing (besides checking over the engine, trans, rearend, and general health of the coach) is updating the charging system with a solar system.

Self-sufficiency has as much to do with energy sources as it does with energy conservation. You need to estimate your energy budget that you (and, most important and not always predictable - your partner) are comfortable with. Buy your RV and go camping with 2*6V batteries, then you will have a better picture.

Very roughly, in Ca, you are looking at 500-800W solar and at least 300 AH battery bank (in 12V terms).

Doing it "the old way", with 12V bank (comprised of either 12V or 6V batteries), means there are fewer parts to fail than with 24V bank (which again can be made of either 12V or 6V units). Just my 2 cents.

It sounds like your RV is going to be a motorhome, rather than a trailer or 5-er. This is different and not familiar to me, so I'll stop there.

Don Piano has suggested a good read.

[Chris_Bryant]

Volta Power Systems uses higher voltage lithium packs, with dc-dc converters for 12 volt stuff. I thought they used 24 volt setup for the Sprinter system, but it looks like they may be running 48 volts, which is supposedly going to be a new automotive standard, but they have been saying that for years...

[pianotuna]

Hi furyous68,

losses going from 24 to 12 are negligible as the 12 volt needs are tiny. It might be good to jump right to 48 volts. I wish I had done so before I got the large hybrid inverter.

2 six volt, 4 six volt, or 8 six volt, but not 6 six volt.

Or you can use 12 volt as I did--particularly if a large inverter may be used.

Wiring is important.

http://www.smartgauge.co.uk/batt_con.html

LI are useless to me as I need to use the RV in the -30 range.

furyous68 wrote:
Ok... back on topic-

It appears that swapping to a couple 24v batteries in parallel with a 24v-12v step-down converter between the batteries & the RV's converter is possible, but not the most efficient system. From what I've read from pianotuna's solar articles... running 4-6 deep-cycle 6v batteries in parallel/series seems to be the way to go. It would probably be a lot easier to set up, & give me way more amp hours in the long run?

[2oldman]

furyous68 wrote:
It appears that swapping to a couple 24v batteries in parallel with a 24v-12v step-down converter between the batteries & the RV's converter is possible, but not the most efficient system.

I'm not sure what you mean by efficient, but losses due to any perceived inefficiencies are tiny compared to your actual use.

furyous68 wrote:
running 4-6 deep-cycle 6v batteries in parallel/series seems to be the way to go. It would probably be a lot easier to set up, & give me way more amp hours in the long run?

4-6v in series = 24v. No difference in ah.

[2oldman]

First time I've ever seen that.

[BarneyS]

Before this thread is closed because it has become quite confrontational, I need to make one comment.

Moderators are members just like everyone else and do NOT give up their right to comment as they see fit on any topic. In fact, we are encouraged by the Admin to participate as much as we care to. We do not choose to put that "Moderator" label next to our name - it comes with the territory.
We mods, as a group, are here because we were asked to help. We volunteer our time to help make the forums a pleasant place to visit and to help enforce the forum rules. We have no particular ax to grind but all have our own personal values and beliefs which may show up from time to time. Non of this however, interferes with our ability to fairly and equally enforce the forum rules that we all agree to when we join.

Sorry to be so long winded but had to clarify about being a mod and making comments in a post. I will leave it open for now but will keep a close eye on it.
Barney

[furyous68]

Ok... back on topic-

It appears that swapping to a couple 24v batteries in parallel with a 24v-12v step-down converter between the batteries & the RV's converter is possible, but not the most efficient system. From what I've read from pianotuna's solar articles... running 4-6 deep-cycle 6v batteries in parallel/series seems to be the way to go. It would probably be a lot easier to set up, & give me way more amp hours in the long run? I wish Lithium batteries weren't so stinking expensive. 3- of these: https://battlebornbatteries.com/shop/12v-lifepo4-deep-cycle-battery/ in parallel would probably be all I'd ever need... only $3000!