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Auto battery charger for 6 or 12 volt sytems

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Step 4: Wire the rectifier.

Picture of Wire the rectifier.
Of course you can use individual diodes to make a bridge rectifier. I found it easier to get a rectifier ready to use. I bent the input (AC) leads in one direction and the output (DC) leads in the other direction. This made a convenient base or support for the rectifier.

It is a good idea to use a heat sink when soldering diodes to protect them from too much heat. Put a rubber band on the handles of a needle nose plier and clamp the plier jaws on the lead you want to solder.

Watch the output polarity so the + terminal on the rectifier connects to the wire for the red aligator clip. I simply glued the bridge rectifier to the plywood with hot glue. Notice the strain relief for the output cord.

To use: Select 6 or 12 volts with the switch. Connect the red aligator clip to the red battery terminal and the black to the black. Set the base of the charger someplace safe. Plug in the AC cord. Disconnect the AC cord after 12 or more hours. Then disconnect the aligator clips from the battery. This prevents sparking that could possibly ignite hydrogen gas from the charging.

I have also used this charger as a power supply for things like a hot wire cutter. A smoothing capacitor is not necessary because batteries charge better with slightly choppy current.
 
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goldFlake2 years ago
hi .. nice instructable,,
i have a 12volts 3.5 amps regulated smps adapter..
can i use it to charge my motorcycle lead acid battery,,?thats 12volts2.5 AH.?
also i have confusion how much currrent will flow through the circuit..,, i know that the 3.5 amps ooutput of my adapter means that it can supply currents upto this,, but how do i controle the current..?

and at what point do i stop charging ,, i mean at what battery voltae level should i stop.,,, if my battery is unloaded..?
thanks
storre4 years ago
 I have a 1amp 24vDC computer charger. Can I use that directly to charge a 12v car battery? I know it might take longer than usual at only 1amp but is there any reason it would not work? I can monitor the voltage as I charge it but what voltage should I turn it off so I don't fry the battery or is this 1amp charger too weak for that to even be a problem?
No, no, no. Don't put 24V on a 12V car battery. It might explode. Never put twice the voltage on any battery for charging.
Jin77552 years ago
can i connect a capacitor in the output of the rectifier?
Phil B (author)  Jin77552 years ago
You certainly can. If you want some very smooth DC current for a power supply, use 1000 mfd at 15 - 25 or more volts. As I mentioned, I am using this for a charger and slightly choppy current is preferred for charging. Chances are your capacitor will be an electrolytic, which is polarized. Be sure to observe the polarity when connecting it. Thank you for commenting.
Just a quick question. When you said 1000 mFd, are you using the m to represent milli(m) or micro(u)? Not asking to be a jerk just curious, because I have never seen a millifarad capacitor rating.
Phil B (author)  suckafish2 years ago
I was using it to represent microfarads. It is sometimes difficult to do symbols in these comments.
Thank you for clearing that up. I think this is an excellent project. I am currently working on it myself, minus the 6V option. Very well written.
joinaqd5 years ago
phil its joinaqd here. you didnt mention what current it supplies..if you use too much the battery may get hot and be damaged.( i tried to charge my 10v battery with 500mA of current,hoping that it would charge faster,but ever since then it lasted less longer..the proper rating charge for the 10v battery was 300 mA.if the currentis too low battery wont charge
Phil B (author)  joinaqd5 years ago
The output on the transformer is rated at 3 amps. For charging an automobile battery that is a very low current, a trickle. The bridge rectifier I purchased is rated able to handle 4 amps. Usually electronic things should have a bit more margin than that, but it has worked out well over the years I have used it.