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.

[pnichols]

Wow BFL .... you must have a good back with all that battery swapping.

My RV batteries are ~72 lbs. each and are mounted low, so they are not only heavy ... but one has bend over and down to remove or replace them.

(I put em' in a couple of years ago and hope to never have to take them out myself.)

[BFL13]

Balancing is better, but hard to get exactly. Unless you are camping for months, it won't matter that much. You will be back home in time to "recover" your batts properly before going out again.

I my case with the two RVs and six batts (two 12v T-1275s, two- GC2 6v Wets, and two 12v AGMs) the drill is to keep the two AGMs in the truck camper and the two GC2 Wets in the trailer. The two T-1275s get swapped back and forth as needed, so the trailer has four batts normally- two 12s and two 6s. (Done up as two big 12s in parallel)

The truck camper has its two AGMs plus if needed the two T-1275s get added in as a big 12 in the truck bed wired into the camper to the two AGMs as another big 12.

It all works great. I just have to keep on top of who is doing what to whom battery wise and make sure they all get to their individual 100%s once we are home before returning them to their Floats. (AGMs get their own float)

Have no fear of mixing and matching. Use what you have and get your money's worth. Just stay on top of things. Batteries are not fire and forget.

[wa8yxm]

As I said for the BIG load (1500 watt inverter) Balanced may well be an advantage.

But for most of the RV. if you are interconnecting with 4GA starter cable.. It won't make much difference.. I'd say you support that since in your case they did NOT balance the big inverter

[grizzzman]

wa8yxm wrote:
I do agree connecting Wet with AGM, not the best idea

As for "Balanced configuratrion"
"
Assuming you use common 4GA starter cable, which is super good for batteries in parallel (or series) unless you are using major power (in which case upgrade to multi-zero) the imbalance will not be anything you can measure.

Now if you are sucking MAJOR amps (IE: the 200+ of my 2,000 watt inverter) THEN balancing may be important... But for "normal" RV use.. not.

That has not been my experience. I had a MH that had a 1500 Watt inverter. The batteries were balanced for the RV but whoever installed it hooked it up on one battery. Care to guess what battery failed first? How about a Ford powerstroke? The battery on the passenger side fails first? another example of an unbalanced battery system.

Oh and the inverter in the RV ran a 5 channel DVD stereo and 19" LCD
So it never saw a high load.

[RJsfishin]

Quote:

but then I've never run a combo like this so I don't have any first hand experience.
-----------------------------------------------------------
That was not hard to determine !!
At least a few here know what their talking about.
But still trying to figure out why the OP ever asked the question here, knowing that he was going to do it his own way no matter what !

[wa8yxm]

I do agree connecting Wet with AGM, not the best idea

As for "Balanced configuratrion"
"
Assuming you use common 4GA starter cable, which is super good for batteries in parallel (or series) unless you are using major power (in which case upgrade to multi-zero) the imbalance will not be anything you can measure.

Now if you are sucking MAJOR amps (IE: the 200+ of my 2,000 watt inverter) THEN balancing may be important... But for "normal" RV use.. not.

[MEXICOWANDERER]

Charge together
Discharge together

Rest, apart

[pnichols]

Another issue not talked much about that may exaggerate the effects of different types of combined batteries is - "are any of them that are connected in parallel connected in a balanced parallel configuration".

Even if matched and/or new identical batteries are connected in parallel wrong, then they can over time age differently such that one battery or set of batteries eventually becomes weaker than the other battery or set of batteries due to unequal sharing of load and charging currents. This applies to 6 volt batteries where dual sets of them wind up in parallel with other 6 volt dual sets of them and it applies to 12 volt batteries where any quantity of them wind up in parallel with each other.

[BFL13]

There is a wrinkle when you parallel a Wet with an AGM where the voltage vs SOC of an AGM is different (higher with AGM) so they are not quite at the same SOC per voltage, but it still doesn't matter while camping for a while.

You still have to get them back to 100 as soon as you can separately. In this case I would also float them at home separately since they are likely to have different float voltage specs.

The main thing is to use whatever batts you can for camping and get the most AH. Then sort it all out later at home. We are not talking full-timing here obviously.

[wa8yxm]

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.

I have heard this many times and always shake my head and ask "how can people believe this"

BFL13 wrote:

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.

This basically has it. Once the batteries have gone througn ONE charge or discharge cycle they will be in lock step..

If they were out of sync.. Then the battery with the higher state of charge will provide nearly all the current till the voltage drops (Voltage and state of charge are related) then they share according to capacity

And when charging the batter with the LOWER voltage, and thus the lower state of charge, will take nearly all the charge till they sync up.

And from that point on they are basically ONE battery, always in sync

"So the "One will charge faster" or "One will discharge faster" folks..

Well, They need to go back and study more

NOTE: This applies to batteries in parallel
And the pair of six volt .. For this discussion are ONE 12 volt battery

For batteries in series.. (The two sixes) Identical is necessary.. but even with multiple pairs.. It only applies WITHIN THE PAIR, the other pairs can be different.


BATTERY--BATTERY--12 volt..Works, they are identical
Battery-Battery-12 volt.. works, They are identical

Put those two pair in parallel even though they are different.. Still goood

BUT
BATTERY-Battery 120 volt.. Not good,

[BFL13]

I have mixed and matched various combos and it does work out ok while camping. The high draws are just for a short time and as you say, the low draws are not much of an issue. In between the batteries "middle" as best they can. Actually that is a slow process with its tiny voltage difference between batts, the AH exchange is glacial.

With the extra batts, even when dissimilar, you do get way more AH and need to recharge less frequently, which is the object of course. Also the inverter does not hit its 11v alarm so soon with the extra AH on the job.

It does not matter if on a recharge one gets higher than the other because after you stop at imagined 90% they will middle sort of and start a new cycle downwards. Nobody is measuring exact numbers.

As mentioned it really matters after you get home and need to get each batt to 100% true. Got to separate them for that.

[grizzzman]

I agree with BFL13. As an example my GC2 batteries have a rested voltage of 12.93 and my group 31 batteries have a rested voltage of 12.66. The lower voltage battery will bring the higher voltage battery down. Do that enough and the higher voltage battery will head down a sulfating death spiral.

[ktmrfs]

BFL13 wrote:
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.

as long as the batteries are similar construction and similar internal resistance your analogy makes sense. but a GC has much much higher internal resistance so when in parallel with a 12V marine battery unless the discharge and charge currents are reasonably low not sure the analysis holds. on discharge, the GC under even moderate load will have more internal voltage drop than the 12V causing the 12V to share more of the load and discharge faster, then having the GC charge the 12V when the load is removed.

but then I've never run a combo like this so I don't have any first hand experience.

[ktmrfs]

LScamper wrote:
"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?

yes, but remember charging efficiency is not 100 percent.
and 6V have much higher internal resistance than 12V so there is also an imbalance under discharge load, especially if the draw is very high.

250AH GC starting current near a few hundred Amps, 12V 80AH marine battery starting current 600 to 800 Amps. quite a difference as the load increases.
not a good combo.

the lower the current draw, the better the situation is.