5

I've installed an extra 12V source in my car and everything is working.

While installing it I removed the positive terminal from the battery and left the negative connected. (Resting the positive on the plastic cover on top of the terminal) Once the work was done I just reconnected the positive side of the battery.

I've been reading up saying there could have been issues if I had accidently touched the spanner to a metal part of the car and created a short circuit. I didn't have any issues (Didn't touch any metal with the spanner) and the only thing that happened was the terminal sparked a bit while I was pushing it down while re-connecting everything.

The car is all working but I just wanted to make sure it wouldn't have any adverse effects on the electronics in the car as I've read I was meant to remove the negative terminal first, then positive; reconnecting the positive first.

(which i obviously didn't do just disconnecting the positive while doing work)

Randomstingray
  • 51
  • 1
  • 1
  • 2

2 Answers2

5

Ah yes, those pesky little battery terminals. They ain't the same. The one labelled "+" (usually red) is connected to everything electrical in the car, while the one labelled "-" (usually black), only goes to a couple of bolts here and there. It would make sense, one would think, to disconnect the one connected to all the stuff, wouldn't it?

Well, it doesn't. Good practice is actually to disconnect the negative one for the following reason:

  • when the positive terminal is disconnected, it will arc when it comes into contact with just about any unpainted metal part of the car. The terminal doesn't have to touch a metal part directly, it can (and will) go through metal tools (like a spanner, screwdriver or pliers). The reason this arcing occurs is that, as stated above the negative terminal is connected to the body of the car (through a few bolts). Therefore, touching the positive terminal to the body of the car completes the circuit.
  • when the negative terminal is disconnected, it can't arc, only the negative battery post itself can (that's where the juice is coming from).

As for the sparks you saw, those are normal when reconnecting a battery and the battery charge has changed a little bit since the connection was broken. This does no harm to the battery.

tlhIngan
  • 12,200
  • 8
  • 38
  • 71
1

I think the other answer is a bit misleading when it talks about arcing,

The battery positive terminal is usually connected to the fuse box via a thick cable and the starter motor by another thick cable.

The battery negative terminal is usually connected to the car’s bodywork by a single thick cable.

If the positive terminal is being disconnected first using a spanner/wrench the tool is then electrically connected to the positive terminal. If you accidentally touched the bodywork or any other metal part with the tool at the same time you will cause a short circuit capable of carrying hundreds of amps which can literally melt the tool, cause a fire and burn your hand.

If the negative terminal is being disconnected first using a spanner/wrench the tool is then electrically connected to the negative terminal. If you accidentally touched the bodywork or any other metal part with the tool at the same time you will only be connecting to the negative terminal of the battery, so no danger. As long as you don’t touch the battery positive terminal at the same time you will be OK and since the battery positive terminal usually has a red cover on it there is little risk.

Once the battery negative is disconnected, accidentally touching the battery positive to the cars bodywork using a tool is no longer dangerous.

If only the positive terminal is accessible at first, then you just need to be extra careful,

HandyHowie
  • 25,681
  • 3
  • 40
  • 76