Making a battery tab welder with an old car battery

Thread Starter


Joined Sep 17, 2016
I want to make a simple battery tab welder using an old 12 V car battery, a car solenoid and an Arduino to control the duration of the pulse, similar to devices I've seen on YouTube.

I bought a 12 V solenoid that claims to be rated for 200 A, although I don't know whether that's accurate. The pulses will only be short duration, like 200-300 ms. so it's probably fine. The car battery, fully charged, has about 14.4 V open-circuit voltage and when I use 14.4 V to close my relay, 180 mA flows. The Arduino pins can output 20 mA so I'd like to put 20 mA into a 2N2222 transistor (just what I have knocking around) to enable ~180 mA to flow through the coils in the relay. The output of the relay will connect through a fuse (not sure what value fuse to use yet; something like 200 A) to some copper nails which be the electrodes to do the tab welding.

My previous experience with transistors says that they sometimes don't like being partially-opened, right? I think I had a transistor overheat even though I think it was operating at less than its maximum rated current and I think I was told it was because it was partially-open. So I'm wondering whether someone could help suggest a resistor value to use between the 5 V output pin on the Arduino and the base of the 2N2222 transistor.

The Arduino will be powered from the car battery as well - would it be okay with the input voltage dropping when the welding happens? I'm not sure how much the voltage sags. Maybe that's a better question for the Arduino forum, anyway?

I will use a potentiometer to allow the duration of the pulse to be fine-tuned.

Thanks in advance for any help.