Charging Lead Acid Battery


Thread Starter


I need to charge my car battery. It's very dead at this point. But, I have a variable voltage power supply that's rated for 5A.

I've had it hooked up to the battery at about 15V (if measured without anything hooked up to the power supply) And I've found that around 130mA flows in this configuration. From my measurements, I'm getting about 11-12V.

I've charged the car for 3+ hours, but it hasn't worked.

Should I turn up the voltage? How long do you think this would take? I welcome any other advice you all have as I'm attempting to be both engineer and car repairman here.
I think this is how long it would take:

Starting the car draws around 300A apparently for about 2-3 seconds to start. so at 12V thats (300x12)x3 = 10,800 joules.

While charging I'm providing about 0.13A at 12V (i know the current will vary as it charges but I'm assuming it's constant) so for that to provide 10,800 J it will take at 1.56W about 115 minutes. I'm going to double it which gives about 3h 51m
Higher voltage will probably be best 14.2v will be fine. The current draw will be much higher, supplying the voltage at 12v won't do much.
Turn the voltage up until you get 1A. At 1A it should charge enough for a start in a couple of hours.