Can two 6V and one 12V be charged by rv system?

[nickdarr]

I searched and could not find answer that did not involve using large solar setups. Since obtaining new neck hardware, I have a CPAP. We have used our two 6v batteries and camped, but not since my new CPAP friend travels with us. We are getting a separate 12 volt for the CPAP. Can I place this inline (parallel) with the two 6v and charge through the TT wiring system? Or, am I better served to run a separate charger for that battery? We have a small solar panel and hope to add more as cash allows. We run the generator to fully charge each day.

[LScamper]

"where does the energy go? well, the 12V with lower AH will discharge faster than the 6V combo. so the 6V will be charging the 12V as well as supplying part of the load with the 12V."

So after the 6V charges the 12V will the 12V then supply that energy given to it by the 6V to the load?

[D_E_Bishop]

Lwiddis wrote:
How small a solar panel? Standard is one solar watt per battery AH. Then you adjust for location, type of controller, expected daily use etc. Idaho is a state where more solar watts may be needed in the fall and winter months.

He said DID NOT involve solar.

[1SAST]

nickdarr wrote:
We like our 27dbhs. We have drug it all over the US and through Canada to Alaska. We had a 23 bhs and loved it. I prefer the smaller slide. My two qualms with with the 27dbhs are it is unusable when the slide is in. The bathroom is closed off and the bunks are separated from the front room. When open, there is a nice sized amount of space. My kids like all the room. The second is we have had a lot of trouble with our tongue jack. It is an EZ lift. We are on our second one and it is making the same grinding noise as the first. A little nit picky complaint, but our TP holder is in a cabinet. I don't know if that has changed, but it is inconvenient. I like the bed and the overall layout is nice. Now that we are done potty training the little one, the bathroom issue is not as big a deal.

Thank you. My children are 8 and 11. On paper it seems to be a great fit for our family. Thank you for the reply.

[BFL13]

Two dissimilar batteries in parallel where one is 85AH and the other is 150AH will be at the same voltage. Their bank capacity is now 235AH.

When a load is put across the pair, each will be drawn down equally according to its proportion of AH size. Each will reach 50% SOC at the same time and their voltages will still be the same.

IE their voltage will be 12.2, and capacities now will be 42.5AH and 75AH.

So you can camp with these no problem. You can do 50-90 recharges with them connected no problem. Where you have a problem is charging them back to 100%

So at home you separate them and get each up to 100% by its own specs. Now you can put them back in parallel and float them at 13.2 or so and they will both stay fully charged.

You cannot put them back in parallel and just let them sit with no float voltage or else they will self-discharge with one battery eating the other and all that bad parallel stuff. You could leave them separated and just sitting there for a while--longer when it is cold out.

Time2roll has always said leaving them on a float will make up for all that because there is enough voltage to keep them both up even if they each want a different amount and there is some action going on between them.

[ktmrfs]

brulaz wrote:

MudChucker wrote:
I did thjs once...you will suck down the bank faster than if they are seperate. Yes you can charge together but the 12 will pull down nearly twic as fast as the sixes and most of the power of the sixes will go into topping up the twelve. I dont knkw or care what the theory is here, in my case i bet the bank lost about a third of its run time.

Heard this before, and I believe you and the others here, but I've never understood it.

So the combined bank loses maybe 1/3 of its Ah during discharge. Where does that energy go?

Perhaps because battery charging is not 100% energy efficient, the re-charging of the smaller bank by the bigger bank loses some energy. But a third?

EDIT: just read the 2010 link Oldman2 provided above and it provides a lot more info. Maybe I'm beginning to understand ... maybe. A lot depends upon battery type I guess.

where does the energy go? well, the 12V with lower AH will discharge faster than the 6V combo. so the 6V will be charging the 12V as well as supplying part of the load with the 12V.

Now if all the batteries are the same AH rating and similar construction, not an issue.

and when charging, probably not as much an issue either. It's the discharge cycle and different capacity and battery chemistries that gets ya.

[wa8yxm]

I have often been flamed for saying "There are no six volt batteries in RV's"

Now.. the reason for this is simple.. When you use GC-2's (Six volt batteries when in the store) you wire two of them in series, this makes a bit 12 volt battery.. So what you have is a 2 piece 12 volt battery.

Looking at it this way the question becomes
Can I charge two 12 volt batteries in parallel at the same time

The answer of course is YES.. IN fact that is EXACTLY how my RV worked when delivered... Two Six Volt GC-2's in series for the house and one 12 volt Gorup 70somethign for the engine in parallel.

Now it has some additional 12 volt batteries in parallel several hundred amp horus.

[Dusty_R]

nickdarr wrote:
Thank you for all the answers. I will separate and use a small charger for the 12V off the generator. The two 6V are used by the rest of the family when not on the generator, i.e. lights, phone charging, TV, etc.

Or you could run the CPAP off the RV 12 volt system.

Dusty

[brulaz]

MudChucker wrote:
I did thjs once...you will suck down the bank faster than if they are seperate. Yes you can charge together but the 12 will pull down nearly twic as fast as the sixes and most of the power of the sixes will go into topping up the twelve. I dont knkw or care what the theory is here, in my case i bet the bank lost about a third of its run time.

Heard this before, and I believe you and the others here, but I've never understood it.

So the combined bank loses maybe 1/3 of its Ah during discharge. Where does that energy go?

Perhaps because battery charging is not 100% energy efficient, the re-charging of the smaller bank by the bigger bank loses some energy. But a third?

EDIT: just read the 2010 link Oldman2 provided above and it provides a lot more info. Maybe I'm beginning to understand ... maybe. A lot depends upon battery type I guess.

[MEXICOWANDERER]

Mudchucker, yours is where reality is the cruel taskmaster. Like a professor with a birch pointer. A third battery can be wired-in by using a automatic operation voltage triggered relay like a Sure Power.

You ought to see the War Zone when a calcium/calcium battery is left connected to 5% antimony batteries like GC220s or L16s. I've seen the former last a whole week.

[MudChucker]

I did thjs once...you will suck down the bank faster than if they are seperate. Yes you can charge together but the 12 will pull down nearly twic as fast as the sixes and most of the power of the sixes will go into topping up the twelve. I dont knkw or care what the theory is here, in my case i bet the bank lost about a third of its run time.

[nickdarr]

We like our 27dbhs. We have drug it all over the US and through Canada to Alaska. We had a 23 bhs and loved it. I prefer the smaller slide. My two qualms with with the 27dbhs are it is unusable when the slide is in. The bathroom is closed off and the bunks are separated from the front room. When open, there is a nice sized amount of space. My kids like all the room. The second is we have had a lot of trouble with our tongue jack. It is an EZ lift. We are on our second one and it is making the same grinding noise as the first. A little nit picky complaint, but our TP holder is in a cabinet. I don't know if that has changed, but it is inconvenient. I like the bed and the overall layout is nice. Now that we are done potty training the little one, the bathroom issue is not as big a deal.

[1SAST]

nickdarr wrote:
I searched and could not find answer that did not involve using large solar setups. Since obtaining new neck hardware, I have a CPAP. We have used our two 6v batteries and camped, but not since my new CPAP friend travels with us. We are getting a separate 12 volt for the CPAP. Can I place this inline (parallel) with the two 6v and charge through the TT wiring system? Or, am I better served to run a separate charger for that battery? We have a small solar panel and hope to add more as cash allows. We run the generator to fully charge each day.

I am so sorry to hijack your thread but I have to ask how you like your CREEKSIDE 27dbhs. We are literally days away from pulling the trigger on one. Thanks so much for your time.

[MEXICOWANDERER]

Fine to charge them as a gang but destruction incorporated after the music stops. When charging stops separate the six cell from the three cell batteries. It's a pain but a bigger one is replacing those that got et...

[nickdarr]

Thank you for all the answers. I will separate and use a small charger for the 12V off the generator. The two 6V are used by the rest of the family when not on the generator, i.e. lights, phone charging, TV, etc.

[naturist]

Don't claim to be an expert, and have never tried this, but in a perfect world, it should work. The problem is that this is not a perfect world, and how you wire them up is only a small part of that imperfection. The two 6s likely have a different capacity than the 12, and since even copper wire has some small resistance no matter how large that wire is, I can forsee lots of problems with keeping such a system operating well. But what do I know, other than that common wisdom suggests one ought to only hook up well matched batteries in parallel, and do so with careful attention to not overcharging one while undercharging the other, or discharging one excessively relative to the other. I think you need to do a lot of reading on the topic before you try it, not merely pop off a query to an internet forum, where you are guaranteed to get lots of advice on both sides of the issue from lots of people with no real knowledge of the topic. Like me.