Divide voltage by 2

[Buckeye_Jim]

As an electrical engineer, I should point out a few more problems with the series resistor idea. First you want to see about 7 volts across the battery. If the charger is putting out 14 volts, then the series resistor would need to drop 7 volts. If the battery is really discharged then it may accept as much current as your 12 volt charger is capable of providing. Let's say that is 20 amps. Then the resistor needs to be 7/20 = .35 ohms. The power that this resistor will dissipate is the volts times the amps or 7 times 20 or 140 watts. It will get hot. Maybe an electric hot water heating element might be around .35 ohms, but you would need to have it immersed in a bucket of water.

Now, when the battery accepts less current, the voltage drop across the resistor will drop, increasing the voltage across the battery.

So, Radio Shack probably has a 1/4 amp 7 volt DC wall wort that will charge you battery, it will just take a while. Auto parts stores should have 6 volt chargers or can order them for you.

Good Luck,

Jim

 

[gemini5362]

get a 6 volt zener diode and put it in paralel with the battery. get one good for about 20 amps

 

[DieselPower]

Have to agree with the rest. The easiest way to charge a 6V battery is buy a 6V charger. Last time I checked there are still alot of 6V chargers available at the store. I know I must have 8 or more that do 6 and 12 volt systems and two that do 6, 12 and 24 volt.

 

[Buckeye_Jim]

get a 6 volt zener diode and put it in paralel with the battery. get one good for about 20 amps

Gemini,

Good idea about the zenner diode, as it will solve the issue of a variable voltage drop across the resistor. But you would not connect it in parallel with the battery, but in series. Then you still have that 20 amps times 6 volts or 120 watts of heat. Probably difficult to find one that big though.

jim

 

[stumpfield]

As an electrical engineer, I should point out a few more problems with the series resistor idea. First you want to see about 7 volts across the battery. If the charger is putting out 14 volts, then the series resistor would need to drop 7 volts. If the battery is really discharged then it may accept as much current as your 12 volt charger is capable of providing. Let's say that is 20 amps. Then the resistor needs to be 7/20 = .35 ohms. The power that this resistor will dissipate is the volts times the amps or 7 times 20 or 140 watts. It will get hot. Maybe an electric hot water heating element might be around .35 ohms, but you would need to have it immersed in a bucket of water.

Now, when the battery accepts less current, the voltage drop across the resistor will drop, increasing the voltage across the battery.

So, Radio Shack probably has a 1/4 amp 7 volt DC wall wort that will charge you battery, it will just take a while. Auto parts stores should have 6 volt chargers or can order them for you.

Good Luck,

Jim

I'm an electrical engineer myself and undertanding the theoretical complexity. I was hoping there's an off the shelf gadget for this purpose. Anyway, I asked my 78 year-old father. Guess what he said?
"go to the junk yard to see if you can find a 6v voltage regulator... Look for cars in the 50's."

 

[gemini5362]

Jim

It has been a long time since I have done any basic electronic work now all they let me do is replace cards. But for some reason i was thinking that you could use a zener in parralel. Once you got above the rated voltage the zener would start conducting and basically clamp the voltage at that level. I seem to remember a million years ago in college they made me do some equations with some strange name like Laplace Transform to compare filter components and I could not believe how well zeners worked. although i guess you are right they would be put in series for voltage regulation. I probably knew that but time and the ability to recall is a inverse proportional relationship.

Now that I have said all of this I would just go out and spend 20 or 30 bucks and buy a 12/6 volt battery charger if it was me

 

[smitesmash]

I will bow down before the EEs here.

In theory though, can't you run 2 6v chargers in series using a 12v charger?

My advice is to find some 6v wall wart charger (you probably have several hanging around already)

 

[gemini5362]

I will bow down before the EEs here.

In theory though, can't you run 2 6v chargers in series using a 12v charger?

not sure what you mean by that statement is it a mistype ?




actually go to somewhere like sam's they have good chargers with 6 volt charge mode and start mode, it also has 12 volt charge and 12 volt start mode. They are less than 100.00 and you will have seveal good options to work with

Not a EE I went to school for BSEET they design stuff we fix it

 

[smitesmash]

sorry, brain not in gear.

In the same way that 2 1.5v batteries (cells) create a 3.0v potential, couldn't you charge two 6v batteries in series off of one 12v source.

 

[tallyho8]

sorry, brain not in gear.

In the same way that 2 1.5v batteries (cells) create a 3.0v potential, couldn't you charge two 6v batteries in series off of one 12v source.

You could, but in his very first post, he says he doesn't want to, as they would be in various states of charge.

This would be similar to me charging my golf cart batteries. I have six 6 volt batteries in series and use a 36 volt charger. Sometimes mine are in various states of charge also because I have lights and accessories wired to 2 of them, but they still all seem to charge ok.