Accidentally Shorted Battery

[MP_R33]

I recently had to charge my flat battery ( not using car very much at the moment) and when I attached the neg lead back to the battery (with pos obviously already connected) I accidently (and clumsily) touched the ratchet used to tighten the nut between the neg and pos terminals of the battery resulting in big spark and me jumping quite high.

The car has been used since then and everything seems normal, but my question is could there have been damage to the electrics and/or the battery?

Many thanks.

[Badgaz]

probably not the first to do that.... i don't think you will have damaged anything...most things are fused...probably just damaged your ratchet with the little arc welding.

[MP_R33]

I have heard that you can fry odour ECU and sensors by doing this though? My ECU is fine given that the car starts. Sensors going into the ECU though, how would you even know? Would it generate the engine light to come on.?

[Simon-S14]

The fact that everything runs means that is fine. You'd have to hold the ratchet across the two terminals for a longer period of time to do real damage

[GTSBoy]

And the ratchet would glow bright yellow and then melt before the battery went flat anyway. And in the meantime, the only effect at the ECU would have been removal of power.

The real problem you have heard about (although obviously not correctly) is reverse polarity connection. Hook up a jumper battery or car backwards and see what happens to the ECU (which may be nothing, depending on how good the RP protection is).

Edited February 25, 2014 by GTSBoy

[GH05T]

haha did that once on an r31. plenty of smoke, but no damage to anything electrical somehow.

[MP_R33]

Ah I see, Nah I heard you could fry the ECU from shorting it as long as the battery was in the car. Wasn't aware of the reverse polarity but that makes sense.

[dopey]

they say welding with out rmoving the battery termanals can also damage the electrics and yet there are shops the don't do it that way with brand new corvettes with no problem, so I think a lot of it is just talk.

[GTSBoy]

Realistically, the welding thing is perfectly true. Or at least it used to be. And it isn't the battery terminals you need to remove. The ECU needed to be unplugged from the loom to prevent it from getting nasty zaps up through the earth connections.

More modern cars and ECUs have much better protection against this sort of thing so you can get away with it. But back when all this was new, many ECUs and other vehicle electronics were damaged by welding.

[MP_R33]

Well it shorted through my ratchet, so it should be fine, only thing would be the ECU that would be damaged if left on long enough and I would have known by now if it was wrecked. Are there any other components besides the ECU that can be damaged?

[GTSBoy]

In a Skyline? Of course. Auto controller, if present. HICAS controller, if present. ABS controller, if present. Even the air conditioner controls, the radio, various other electronic boxes. But, and I must restress this, NOT from what you did.

[MP_R33]

Ye in a Skyline, aren't those things protected by fuses?

[GTSBoy]

Fuses take a moment to blow. Very high voltages can destroy sensitive electronics in tiny fractions of that time.

[89CAL]

Think about it, Your shorting a battery accross the terminals. Basically you are bypassing everything between the positive and negative circuit in the battery. The only damage will be to your ratchet.

Unplugging sensitive electrics when welding is a good practice to do, in theory if you have the earth lead close to where you are welding (and provided it isnt near an ECU etc) then the chances of damaging it are minimised Because the circuit wants to take the shortest route to the earth lead. So if the earth lead is at the back of the car and you are welding on the front reo bar, you can imagine that the circuit is much more likely to join with the ECU circuit then if you have the Earth lead closer to the welding area. Having said that, I would never weld on a car without unplugging ECU's etc because its alot of current to pass through the chassis

Shorting across the battery terminals is not much different to shorting from the positive to the chassis (because the Battery negative goes to a nearby Chassis earth anyway)

The most likely thing you will damage is the battery. This is a bit more of an issue if the battery is in the boot, has been through some charging cycles and there is hydrogen gas around. Arcing the terminals can result in battery explosion. I've seen plenty of horrible photos of people messing with batteries in dump trucks/dozers where this has happened and the battery is a mangled wreck.

Summary:

Shorting battery terminals, not advisable but generally doesnt end in disaster

Welding with ECU's plugged in: No

Edited February 26, 2014 by 89CAL

[Badgaz]

its not usually voltage...its current that blows things up...12 volts is 12 volts.. unless you are talking about static discharge voltages.

[89CAL]

Remember that some ECU's require a 5V power source for sensors and dont generally like higher voltages then that.

OHMS law proves that voltage is proportional to current. Voltage goes up, current goes up

Edited February 26, 2014 by 89CAL

[iruvyouskyrine]

Extremely high voltage can kill things like diodes etc. Cyrrent most certainly does kill things, but massive voltage spikes will also do it.

[GTSBoy]

its not usually voltage...its current that blows things up...12 volts is 12 volts.. unless you are talking about static discharge voltages.

Welding........much more than 12v.

[89CAL]

Welding........much more than 12v.

And much more current then you will find in your fuse box in your car

Some people are lucky and get away with welding with everything still connected, but for the small amount of effort it takes to unplug stuff, its not worth the risk

[Badgaz]

no shit.