Divide voltage by 2

[stumpfield]

Anyone know a simple and inexpensive way to divide the output voltage by 2?
I want to charge a 6v battery. My battery charger is 12v only. I don't want to connect 2 6v batteries in series each time I want to charge them because each have different state-of-charge. Any ideas? Thanks.

 

[RavensRoost]

I think the only real answer is to use a 6 volt charger. Any other scheme will likely only over or undercharge the 6 volt battery. I don't think there is an easy way out....

RavensRoost

 

[randy41]

seems to me that you could put a resistor in the + line to cause a 6v drop. but i dont know what size.
hmmmm....there is a relationship between volts, amps, and ohms. but i think the amperage output of the charger is not constant.

 

[RavensRoost]

seems to me that you could put a resistor in the + line to cause a 6v drop. but i dont know what size.
hmmmm....there is a relationship between volts, amps, and ohms. but i think the amperage output of the charger is not constant.

Randy, you nailed it. You could choose a charging voltage and current and select a resistor to give the 6v battery what it wanted.....for a very brief time until it chatrged up more and now wants less current/higher voltage. I am sure there are "intelligent" devices that will do this. I bet they also cost more than a "dumb" 6 volt charger ;-)

 

[czechsonofagun]

seems to me that you could put a resistor in the + line to cause a 6v drop. but i dont know what size.
hmmmm....there is a relationship between volts, amps, and ohms. but i think the amperage output of the charger is not constant.

yes, this is correct. If you have an electrical heating element I would connect it in series with the battery and check for the voltage on. 6V battery could be charged by something like 8V (12V is charged by 14.8V in a car).

my $0.02 only

 

[Highbeam]

V=IR or P=IE

Voltage (potential) = current * resistance

You've got to get the units right but that's the relationship.

 

[Ken_CT]

Whenever I try to do something like that, the most expensive part in the arrangement gets ruined. Kinda like a $300 picture tube blowing to protect a 10 cent fuse.

 

[heehaw]

i've occasionally needed to do something like your talking about, and wired a light socket in series with whatever i'm tryin to burn up, oops, i mean charge or operate: anyway, the more current you want, the bigger the bulb you screw into the socket. actually this does work "fairly" well for a cheap motor speed control on small AC motors. what the heck, light bulbs are cheap, and "maybe" it won't cook the battery or charger.
heehaw

 

[AndyM]

By the time you rig up whatever it will take to drop the voltage in your charger, it would probably be easier to buy a cheap six volt charger.

 

[ericinmich]

V=IR or P=IE

Voltage (potential) = current * resistance

You've got to get the units right but that's the relationship.

It was stated in another post, but I'll try to clarify.

The V=IR is true, but the problem is that the I (current) would be changing during the charging. You've all seen that when you hook up the charger to a battery it reads high (10, 15, ?) amps right away, then starts coming down over the next minutes and hours. You would need to have a variable resistor and a volt meter across the battery (or resitor if you like to subtract) to keep the correct voltage for charging.

Much easier to get a charger that has a 6V setting like my 20 year old one does...

 

[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.