12v to 6v charging

[1A Camper]

Originally Posted by raspivey

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.

"The charger sends" a max "amperage to them until they read....usually around 14.4V". I added "a max" to your line. I think we are both say the same thing up to this point.

"then tapers the amperage off". If you are saying that the charger is controlling amperage? Then I disagree. If 14.4 volts are applied to a 50% charged battery. I agree that the controller/charger will most likely go to max set point on the current. Until the battery voltage come up to the point that the voltage of the controller is at 14.4 voltage. Then the controller just sit at 14.4 voltage and no longer control current as it is below the max current. but as the battery gain more charge the current drop because the battery will draw less. Again we may be saying the same thing. But the battery is controlling the current at this point base on it charge.

"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."
This is the part that I know we are not saying the same thing. OK we have 12V battery fully charged and the 6V bank not so much. The charger sitting at 14.4 volt, Now the battery are controlling how much current they will draw. The 12V would be drawing something like 1 amp and the 6V bank could be drawing like 15 amp.
Let say we have a swimming pool that is 14.4 inches high. Let say we have a 1 gal container and a 5 gal container and the top of each container is at 14.4 inches. Then let say we have a small hose to each container. When hoses are first turn on a lot of water flow in the 2 hoses as the water rises the flow become less and when the water hit 14.4 inches the flow stops.
In real life I come back from camping and I will have one battery discharge and one charged. I will connect the charger and switch both battery on the charger. The discharge battery will warm up a little but the charged one stay cool and does not boil off any fluid.

[garbonz]

NOOOOOOOOOO. DO not wire disimilar batteries together. The weakest one or ones will drain the life out of the others. You could keep it around as a backup tho.

[raspivey]

We were pretty much saying the same thing...I just mis worded that a little regarding amp draw. I just checked my charger instructions and it SAYS it runs max amps until it reads 14.4 then holds 14.4 until it's below a certain amp reading. That tells me it's actually controlling current for part of the cycle but, having really thought about it, I actually believe it runs 14.4V at 7A until the amps drop to around 2. Makes more sense anyway. That being said, you're probably right about not overcharging one but I'd still be careful with it.

[garbonz]

Originally Posted by 1A Camper

"The charger sends" a max "amperage to them until they read....usually around 14.4V". I added "a max" to your line. I think we are both say the same thing up to this point. "then tapers the amperage off". If you are saying that the charger is controlling amperage? Then I disagree. If 14.4 volts are applied to a 50% charged battery. I agree that the controller/charger will most likely go to max set point on the current. Until the battery voltage come up to the point that the voltage of the controller is at 14.4 voltage. Then the controller just sit at 14.4 voltage and no longer control current as it is below the max current. but as the battery gain more charge the current drop because the battery will draw less. Again we may be saying the same thing. But the battery is controlling the current at this point base on it charge. "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." This is the part that I know we are not saying the same thing. OK we have 12V battery fully charged and the 6V bank not so much. The charger sitting at 14.4 volt, Now the battery are controlling how much current they will draw. The 12V would be drawing something like 1 amp and the 6V bank could be drawing like 15 amp. Let say we have a swimming pool that is 14.4 inches high. Let say we have a 1 gal container and a 5 gal container and the top of each container is at 14.4 inches. Then let say we have a small hose to each container. When hoses are first turn on a lot of water flow in the 2 hoses as the water rises the flow become less and when the water hit 14.4 inches the flow stops. In real life I come back from camping and I will have one battery discharge and one charged. I will connect the charger and switch both battery on the charger. The discharge battery will warm up a little but the charged one stay cool and does not boil off any fluid.

Frankly your argument and experience is unconvincing against the overwhelming professional information in the literature that unanimously recommends NOT grouping dissimilar batteries together, either voltage, or size or age. It is not even smart to use cables of different lengths to connect batteries in parallel. There are completely irrefutable scientific reasons for this that I will not go into. Look it up on Battery University, or any solar off the grid journal.

As always your experience may vary, but that is not a reason to recommend it to others without caveats.

[1A Camper]

Originally Posted by garbonz

professional information in the literature that unanimously recommends NOT grouping dissimilar batteries together, either voltage, or size or age. It is not even smart to use cables of different lengths to connect batteries in parallel. There are completely irrefutable scientific reasons for this that I will not go into.

As always your experience may vary, but that is not a reason to recommend it to others without caveats.

I agree with the above 100% but if you know the reasoning of the statement you can decide if the trade off is worth it.
Lets take the cables lengths, being the same lengths. I think that is the most straight forward, it is all about resistance of the wire.
On my trailer the battery are using 10 gauge wire, If the web site I looked at is correct the resistance of the wire per foot is .001588 Ohms.
I have 2 battery but the wire run to one battery and then run 3 feet to the next. Lets say the ground wire are the same length.
That means that the longer run of wire has .004764 Ohms more then the shorted wire.
I have a 30 amp charger that means when charging at a 30 amp rate ( worst case) the voltage drop is going to be 0.142892 V on the 3 foot wire. ( actually only about half that as the first battery is getting 15 amp so only 15 amp in the longer wire). So if I am charging the first one at 14.4 V the other is being charged at 14.257108V. Now the professional do not seem to agree what the charging voltage should be. I have seen anything from 13.2V to 14.6V.
So do I care no, but other may since the professional tell you are charging your battery at a different rate and you are.

[BarryD0706]

You have 10 gauge wire in a primary battery circuit? That sounds way wrong.

[1A Camper]

Question asked:
Can I charge a 12V bank of 6V battery and a single 12V battery at the same time.

I say Yes.

The set up.
I dry camp. I have a switch on each bank of battery. I run my 6V bank to 50% then use my 12V to 50%.
What do I do, I have a generator and charger.
Do I charge the 6V bank for 2 hours and the run the generator for another 2 hours charging the 12v battery, or can I charge both at the same time. They will end up at different charged point say one at 80% the other 70% but I can get another day out of each.

The professional say not to do it but I can not see the harm in charging both at the same time.

[1A Camper]

Originally Posted by BarryD0706

You have 10 gauge wire in a primary battery circuit? That sounds way wrong.

Yes I do, It is an A-Frame. Our highest current is charging the battery. So 10 gauge is OK

[LarryCopper]

Originally Posted by 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.

Well, turns out it was a typical "expert" at Cabela's.

This is what the manufacturer said:

Thank you for your email.
There are no issues with running your battery system in series for 12V. You
can connect the controller the way you described below.

I had mentioned running 6v in series connecting the charger to opposite poles of each battery.

[garbonz]

Originally Posted by 1A Camper

Question asked: Can I charge a 12V bank of 6V battery and a single 12V battery at the same time. I say Yes. The set up. I dry camp. I have a switch on each bank of battery. I run my 6V bank to 50% then use my 12V to 50%. What do I do, I have a generator and charger. Do I charge the 6V bank for 2 hours and the run the generator for another 2 hours charging the 12v battery, or can I charge both at the same time. They will end up at different charged point say one at 80% the other 70% but I can get another day out of each. The professional say not to do it but I can not see the harm in charging both at the same time.

That's kinda what I was encouraging, use the batteries separately. Charging together is not optimum, but for an outing or two and eventually charging the batteries fully and separately, I don't see a problem.

The other piece in the drycamping scenario, is that the charger will start to taper the charge at about 80% of full and so you can waste a lot of generator time getting the battery(s) fully charged. I run my battery bank from 50% to 80% in about an hour with a temp compensated charger that pumps a lot of amps (55) right up to the 80% point and that way I get 60 amps of usable power out of a 200 amp battery pack with one charging episode with the generator. If I use more than 60 amps, I just use a second charge cycle in the evening before dark.

My generator is SO QUIET, you really can't hear it.

[BigBaron]

Just a comment on the charger voltage. I saw another person who does a lot of boondocking mention that golf cart batteries like 14.8 volts for charging.
http://popupbackpacker.com/2014-mila...-solar-system/
Anyone else hear this info before?

[1A Camper]

I have not heard of any different number for 6 volt battery banks. I have heard number as high as 16 volt for charging 12 Volt battery. I like around 14.2V to 14.4V. The higher the voltage the faster the charge and the shorter the battery life. If I was charging at 14.8 volts, I would watch fluid level and feel the battery to see if it is getting warm and if neither is happening I would think all was good.

[raspivey]

Some types of batteries like a little higher voltage. I'd have to dig out my manual again, but I know my charger has settings for AGM and gel and I believe it uses 14.8 as a setpoint instead of 14.4 . I think it does the same in cold weather mode.

[RPAspey]

Originally Posted by BigBaron

Just a comment on the charger voltage. I saw another person who does a lot of boondocking mention that golf cart batteries like 14.8 volts for charging.
http://popupbackpacker.com/2014-mila...-solar-system/
Anyone else hear this info before?

yup. My Trojan T-145 are supposed to charge at 14.8V, but only during the bulk portion of the charging cycle. Then 13.8V for absorption, finally 13.2V for float.

[garbonz]

Originally Posted by RPAspey

yup. My Trojan T-145 are supposed to charge at 14.8V, but only during the bulk portion of the charging cycle. Then 13.8V for absorption, finally 13.2V for float.

Actually the absorption voltage should be the same as the bulk charge, with decreasing amperage to hold it there till the charging rate drops to a low rate (like 2-5 amps) whence to will go to float.

I have not heard of such a low abs voltage, that more like a high float.


Hmmmm?

[garbonz]

Don't forget the temperature of the battery itself, which effects the charging voltage at all stages. None of the OEM (or PI for that matter) have temperature compensation, so normally keep the voltage down a bit to account for this.

Really good external charges can have temp comp and different setting for different batteries..

Here is one for example.

New Xantrex Truecharge 2 20amp Battery Charger 3 Bank 12v Temperature Compensated Charging
by Xantrex

Temp vs voltage curve in this link.

http://www.tekrispower.com/pdfs/xant...20Charging.pdf

[Netcomdude]

Batteries in a parallel banks should always be of the same voltage and amp/hr. rating.

Two six volt batteries across a 12 volt battery in parallel is just a bad idea.

Just get two identical 12 volt batteries if you want to double your total amp rating of the bank.

Internal resistance of a battery does matter.
Especially when hooked to a charger.

[RPAspey]

Originally Posted by garbonz

Actually the absorption voltage should be the same as the bulk charge, with decreasing amperage to hold it there till the charging rate drops to a low rate (like 2-5 amps) whence to will go to float.

I have not heard of such a low abs voltage, that more like a high float.

Hmmmm?

you're right. I'm not sure why I said that. (I'm getting old I guess)

After checking my notes, its 14.8v until the current drops to 1.04A or times out at 3 hours, then go into float at 13.2v. According to Trojan, daily charge is 14.8, absorption is 14.1-14.7, float is 13.2, and equalize I'd 15.5.

[Netcomdude]

This is great. Everything you ever wanted to know about batteries, but were afraid to ask. LOL