12v to 6v charging

[LarryCopper]

My factory 12 volt batteries bit the dust. After a lot of research I have decided to go with 6 volt batteries instead. Not really for the cost, but I dry camp a lot since I use my camper at my hunting lease much of the year. I'll keep my existing good 12 volt battery around as a backup in case one of the 6 volts go down.

So I have a couple questions regarding charging:
1. I'm under the impression I can use the existing on-board 12 volt charger as long as I hook it up to opposite terminals on both batteries (instead of both on the same battery like the 12 volt parallel). Is that right?
2. I have a 12-Volt 20-amp solar charger that I used to leave connected to the old batteries to keep them topped off. Can I use this same system by doing the same thing - connecting it to both batteries?

I don't wanna make any assumptions...

Thanks,
Larry

[BarryD0706]

The batteries have to be in-series in all cases. That means positive of one connected to negative of the other, and RV connections made to the two remaining (unwired) terminals.

[Iggy]

YES. You are correct. You c an use your 12 volt charger as well as your 12 volt solar. As Barry said hook the two 6 volt batteries in series and you will have one positive terminal on one batter and the Negative will be on the other battery.

[Lynkage]

X2 for Barry's hookup!

Edit: and the diagram!!

Are you sure your solar charger is 20 amps? That would cook your batteries pretty quick unless you were using that much power and it would be pretty big.

Is it maybe 2 amp instead?

[BarryD0706]

I'm sure it's 20-amp capacity, regulated to produce the amount of charge the batteries need.

[LarryCopper]

Originally Posted by Lynkage

Are you sure your solar charger is 20 amps? That would cook your batteries pretty quick unless you were using that much power and it would be pretty big.

Is it maybe 2 amp instead?

LOL, now y'all know why I'm asking!

It is 20 watt, not amp. I picked up one of these (with the controller) at Cabela's for $60 on sale last year.
Amazon.com: Sunforce 50123 20W Solar Battery Charging Kit: Automotive

I have a generator I use to charge with and this to trickle while I'm gone. I'm also considering a battery disconnect so I shut down all the drain while I'm gone for a while. Can I get one like this or is there something more specific I need?
Amazon.com: NOCO ID220S 6V-24V 125 Amp Battery Disconnect Switch: Automotive

Thanks again!
Larry

[Lynkage]

Originally Posted by BarryD0706

I'm sure it's 20-amp capacity, regulated to produce the amount of charge the batteries need.

A 20amp (2500w) solar panel would cost about 3+ grand. That is why I asked, but as we see it is a 20watt.

[Lynkage]

BTW Larry

The 6v batts work really well!!

[BarryD0706]

Originally Posted by Lynkage

A 20amp (2500w) solar panel would cost about 3+ grand. That is why I asked, but as we see it is a 20watt.

12v x 20a = 240 watts

[LarryCopper]

Originally Posted by Lynkage

BTW Larry

The 6v batts work really well!!

That's what I hear, especially for my needs. Notice how I stuck in the "keeping my good 12v around in case" comment to try to keep this thread from spiraling out of control?

[1A Camper]

Originally Posted by LarryCopper

That's what I hear, especially for my needs. Notice how I stuck in the "keeping my good 12v around in case" comment to try to keep this thread from spiraling out of control?

Larry, Larry, Larry, so you think you can control a post.

After all you are talking about Battery, All someone has to post is.

You do a lot of dry camping and you can not have too much battery and now that you have a spare 12 volt battery laying around, why not put it to use. With the 2, 6 volts battery tied together to make a 12 volt battery tie the spare 12 volt battery in parallel with the 2, 6 volt batteries.
You can even charge them in that configuration.

[Lynkage]

Originally Posted by BarryD0706

12v x 20a = 240 watts

Yes that is right. I had 120v on the brain.

The 240 watt panels have come down in price and are around $500 for ones that will last some time and not burn itself out.

Sorry for the thread jack!

[LarryCopper]

Originally Posted by 1A Camper

You do a lot of dry camping and you can not have too much battery and now that you have a spare 12 volt battery laying around, why not put it to use. With the 2, 6 volts battery tied together to make a 12 volt battery tie the spare 12 volt battery in parallel with the 2, 6 volt batteries.
You can even charge them in that configuration.

Hmmmm, makes my head hurt...

So a question about that setup. From what I've read an advantage of 6v in series you get the cumulative output, but from 12v in parallel the output is limited by the weaker battery. If that is true, wouldn't I potentially be limiting the output in that configuration since it would essentially emulate 12v in parallel?

Again, forgive me if I'm way off base. Just thinkin' here and I don't know a lot about this stuff.

[RPAspey]

Originally Posted by LarryCopper

Hmmmm, makes my head hurt...

So a question about that setup. From what I've read an advantage of 6v in series you get the cumulative output, but from 12v in parallel the output is limited by the weaker battery. If that is true, wouldn't I potentially be limiting the output in that configuration since it would essentially emulate 12v in parallel?

Again, forgive me if I'm way off base. Just thinkin' here and I don't know a lot about this stuff.

you are correct. One shouldn't parallel a set of 6v with a 12v. One reason is that the batteries would have different impedances thus charge and discharge at different rates. Also, by paralleling the batteries, you would essentially halve the impedance thus causing the charger to over charge both sets of batteries. possibly damaging the charger as well.

[1A Camper]

" From what I've read an advantage of 6v in series you get the cumulative output, but from 12v in parallel the output is limited by the weaker battery."

In my world the main advantages of the two 6 volt batteries is that they are normally made for Golf Carts and have a more robust construction. Other may add lower internal resistance, ( read less power lost inside the battery under heavy loads ).

Now lets take a look at a lead acid battery. Each cell has an output of about 2.1 volts. So your 6 volt battery has 3 cells and an output voltage of 6.3 volts, stack the two 6 volt battery you get 12.6 volts. That is the same as a 12 volts battery that has 6 cells. No different. Now cells can be bigger and you get more power but the voltage will stay at 2.1 per cell.

Now getting to your question. You have 2 battery one strong and one weak. Which would it be better Serial or Parallel? I am not sure, but I kinda of like the 2 batteries in Parallel ( never had 6 volt batteries so no surprise there ). Here my thinking. When a load is placed on the Parallel battery the strong battery will supply most of the power, and the voltage out will stay at 12 volts. If I look at the Serial battery as I place a load on them the weak battery will start dropping in voltage and my 12 volts will start dropping, that may be a problem depending on what kind of load. The thing I like about the Serial setup is it is much easier to see a weak battery (battery going bad), the voltage should be the same on each battery under load. (6 volts). Still not sure which I would get the most usable power out of.
I have seen it said that all battery must be the same size and same age, to be tied together, but in my world I have not found that to be true. we live on a boat 4 to 6 months a year and 75% of that time we do not have shore power. The house bank was a group 27 and 4D and a 8D battery hardwired in Parallel, and after 3 years the group 27 went bad. Charging is done with 250 watts solar with a 30 amp solar controller and engine driven alternator.

I think when you have enough battery you can break some rules and still be happy with your system. When I have not had enough battery I have never found a rule that I was breaking that would make a enough different and give me enough power.

[1A Camper]

Originally Posted by RPAspey

you are correct. One shouldn't parallel a set of 6v with a 12v. One reason is that the batteries would have different impedances thus charge and discharge at different rates. Also, by paralleling the batteries, you would essentially halve the impedance thus causing the charger to over charge both sets of batteries. possibly damaging the charger as well.

Why is it bad if the batteries charge or discharge at different rates?
That is like saying I cannot fill a swimming pool at the same time with 2 different size hoses or 2 different size drains that they must be the same size.

I can not think of any way tying two battery together that they would trick a charger into overcharging the batteries. Most battery charger put out around 14 volt to charge a battery. If you have 1 or 20 batteries the voltage is not going to get higher so no over charge.

Now for the half impedance damaging a battery charger. Very unlikely. Most battery charger are made knowing that bad battery will have cells that can be shorted and not damage the charger and that is a lot less impedance then 2 battery tyed together. Also most battery charger are design to only deliver only so much current and then current limit at that level and not self destruct.

[LarryCopper]

Originally Posted by Iggy

YES. You are correct. You c an use your 12 volt charger as well as your 12 volt solar.

I also asked this question on the Cabela's website where I bought it. Here is the "expert" response:

The SunForce 12-Volt Battery Solar Charger, item # IK:524702, cannot be used to charge two 6v batteries connected in series.

Maybe I should contact the manufacturer directly. I'll let ya know what I find out.

[1A Camper]

Quote:
The SunForce 12-Volt Battery Solar Charger, item # IK:524702, cannot be used to charge two 6v batteries connected in series.
End Quote:

I can not think how you got an answer like that, There is no different between a 12 volt battery (6 cell in one case) and 2 6 volt batteries (6 cells in 2 cases) connected in series as far as charging.

All I can come up with is he saw a 6 volt battery and said no way which would be true.

[raspivey]

Originally Posted by 1A Camper

I can not think of any way tying two battery together that they would trick a charger into overcharging the batteries. Most battery charger put out around 14 volt to charge a battery. If you have 1 or 20 batteries the voltage is not going to get higher so no over charge.

The charger will only see the "bank" as a whole, not the individual batteries. Setting aside charging rates for a second, think about it in terms of capacity instead (I'm pretty sure the single 12V doesn't have the same capacity as the 6V's). Let's say the 12V has 80 AH capacity and the 6V pair has 225 AH. Let's also say they're both 50% discharged. The charger sends set amperage to them until they read....usually around 14.4V then tapers the amperage off. If the cells in the 12V hit full charge first and the bank as a whole is at, say 12.9V, the charger is still putting power to both sets full blast and could possibly start to boil the smaller battery.

[RPAspey]

Originally Posted by 1A Camper

Why is it bad if the batteries charge or discharge at different rates?
That is like saying I cannot fill a swimming pool at the same time with 2 different size hoses or 2 different size drains that they must be the same size.

your analogy is not correct. your pool is your battery. the hoses are the cables. a proper analogy is you would have two pools of different sizes. one hose drains both. the higher pool will drain first, most likely into the lower pool. you then essentially have only the water in the lower pool. to fill the pools, they would both fill at the same rate, but can only hold as much water as the lower pool, any more and the water would spill out. same with the batteries, the better battery may never be charged fully.

I can not think of any way tying two battery together that they would trick a charger into overcharging the batteries. Most battery charger put out around 14 volt to charge a battery. If you have 1 or 20 batteries the voltage is not going to get higher so no over charge.


not true. battery voltage rises with the charge state, that is how much current the battery has absorbed. the charge rate is determined by the state of the battery AND its internal resistance, ie impedance. if the impedance is too low, the charger will keep pushing current even when the voltage is at 2.27v per cell.



Now for the half impedance damaging a battery charger. Very unlikely. Most battery charger are made knowing that bad battery will have cells that can be shorted and not damage the charger and that is a lot less impedance then 2 battery tyed together. Also most battery charger are design to only deliver only so much current and then current limit at that level and not self destruct.

huh. short out a common battery charger lead and watch what happens. the charger may self destruct.

dang it, I replied to individual statements but they appeared in the quotes.