Car Battery Charger from Spare Parts in Mint Tin

I needed a trickle charger for a seldom-used vehicle. Not wanting to spend money, I slapped this one together in about 30 minutes from parts lying around:

Bill of materials:
- Mint tin box or other enclosure
- LM317T regulator in TO220 package
- Heatsink for TO220
- Spare Notebook charger with 14V or more output
- 1 ohm, 2W resistor (I used 5W because that is what I had)
- #4-40 x 3/8" screws and 2 #4 nuts
- Wire
- Cigarette Lighter plug
- Solder
- Hot Glue Gun
- Soldering iron
- Dremel tool with abrasive cutoff wheel
- Drill with 1/8" bit
- Wire cutters n strippers
Remove these adsRemove these ads by Signing Up

Step 1: Prepare the box

Drill at least 2 holes in the lid to attach the heatsink and LM317T regulator

Gently bend the LM317 leads to a right angle

Align the mounting hole on the LM317 to one of the mounting holes for the heatsink

Mark a slot for the leads to pass through the lid. Cut this slot out with an abrasive cutoff wheel in a Dremel tool (High Speed rotary)

Use the rotary tol to cut a slot in both ends of the box bottom, and fold down. Close lid and make sure there is enough clearance for the cables to pass through the slots when the lid is indeed closed.
agis689 months ago
since you use the LM317 why don't make the specific ciruit for this job provided in the manufacturer datasheet?
ARJOON4 years ago
my question is. how much power input does the battery need to be input to charge.

i used a computer power supply but it did not work
-12v + +5v   make +17v which help u for charge battery
PLEASE do not use this circuit, it will ruin your battery, or worse. Use the circuit from the LM317 datasheet on page 21 titled "12V battery charger" (duh). The input voltage needs to be at least about 17V.
This is stupid. Why did you wire the LM317 as a constant current source? How about reading the freakin data sheet? How about actually using it as a 13,8V regulator, that you could leave hooked up to the battery indefinitely for float charging? If you ran the circuit in the schematic from a standard 19V laptop power supply, the output would be >16V, and the battery would produce LOTS of gas (hydrogen + oxygen). Nice way to blow up your house.
matstermind3 years ago
so, a. can this be used to charge a 12 volt electric scooter battery? and b. can i use a 1.2 ohm resistor?
Sethro4 years ago
" If the battery is 12V, then OUT pin of the LM317 is 1.2V greater, or 14.2V. " 14.2V? shouldn't it be 13.2? if the input for the LM317 needs to be 1.5V greater than the out (which is 13.2 or 14.2), The computer charger needs to be around 16 - 17 V. Mine puts out 19V. I have an extra 18V cordless drill charger that puts out 19V 2.2A, would this work in place of the comp cord?
FeedTheGrid5 years ago
lemonie5 years ago
Do you actually need to regulate the voltage? What would happen if you just connected the notebook charger? L
. If you did that to a discharged battery, things would probably overheat. According to the author, the regulator is actually being used to control current (see Step 4). A schematic would probably go a long ways toward explaining it.
The Speaker Guy (author)  NachoMahma5 years ago
there is a crude schematic in one of the pictures
. Oops. Didn't notice that. And it's hard NOT to see.
The Speaker Guy (author)  lemonie5 years ago
A very high quality charger would provide a temperature-compensated regulated float voltage of about 13.6V. That however is somewhat difficult, and not necessary considering that 1.2A is really just a trickle. The idea was cheap and simple. Note this charger should not be left on indefinitely, as noted in the instructable.
Do you need the voltage to be regulated, or would the notebook charger work anyway? I'm asking because I don't know. L
guerroloco5 years ago
If you're not supposed to wire anything to the box, how come your schematic shows a wire connecting negative to "case"? And, the picture shows two wires soldered to the box. This matches your schematic but not your written instructions.
The Speaker Guy (author)  guerroloco5 years ago
Good catch, I did make the mistake of soldering to the box, and I should know better. I subsequently unsodlered the wires from the box. That was easier than locating an isolating washer for the TO220 tab on the LM317.

Get More Out of Instructables

Already have an Account?


PDF Downloads
As a Pro member, you will gain access to download any Instructable in the PDF format. You also have the ability to customize your PDF download.

Upgrade to Pro today!