I tried to jump start my truck incorrectly. What was going on electrically speaking?

The other day, I went to start my pickup and the battery was dead. My wife was getting ready to head to work in her car so I rushed to hook up jumper cables to my truck. I got them right on her car but brain-farted on my truck. I hooked the red cable up to the negative post. I blame the fact that our battery posts are opposite each other. Also, I’m a idiot. I hooked the black cable to a metal post near the engine block that says “Ground”. I went to start the truck and my before I could even get in, my wife informed me that the “Ground” on my truck was starting to smoke. Sure enough, I got it disconnected and then realized what I had done. :smack:

What was going on that caused it to get so hot so fast?

A short circuit from her battery’s positive post, through the cable to your battery’s negative post, through your battery’s negative cable to the grounding post, through the other cable to her battery’s positive post. The jumper cables and your negative cable would have glowed red it they didn’t have insulation.

The grounding post was glowing. Is this how a welder works?

the batteries short circuited.

if you would have made good battery to battery contact then you would have seen massive sparks instantly on contact and you would have melted metal on the cables or battery post connectors.

Fixed my mistake.

Essentially, yes.

Sort of.

What you did was similar to a resistance welder, which is not the same as most welders that you typically see. The most common welders are “stick” welders or “Wire-feed” welders, where an arc is created to make a lot of heat (enough to melt metal), and to have the current carry the molten metal to the object to be welded. If you had carefully pulled the connection apart, and let it arc, then you would have made a welder!

This, by the way, is also an excellent way to make a battery explode. Excessive current from the short can cause the electrolyte to boil and the battery explodes from the pressure.

This could have potentially damaged quite a few things. Consider yourself lucky.

ETA: Be glad that you made the other connection to the truck’s frame and not to the battery. That could have exploded both batteries and/or fried much of the entire electrical system of one or both vehicles.

You can actually use batteries to weld in a pinch. I’ve seen people do it when offroad but I never examined the end result.

How long might it typically take for batteries to explode under such circumstances? Like, would it happen nearly instantly, including your face among the damaged goods? Or would it take several seconds, or several minutes?

The most common way battery’s explode is from the hydrogen gas that is created inside a battery especially a discharged or discharging battery. When connecting jumper cables making the final connection on a discharged battery there is always a spark! That is why the final connection is made away from the battery, and battery’s are vented (some vented through a vent tube to outside of vehicle like battery’s mounted under the back seat in some cars) anyway the spark can ignite the volital hydrogen gas. Even with cables connected properly there can be sparking when the starter is engauged.
As for cables becoming red hot, even correctly connected jumpers especially a discount store El-cheepo set will heat up to the point the insulation will melt and catch on fire while the starter is cranking. To prevent this, good quality cables and short cranking cycles are key.
I have been just a few feet from several battery explosions in the past and luckily nobody was seriously hurt. Most battery’s seem to blow out through the side’s.

while batteries might have an embossed plus or minus, it is not a bad idea with a paint pen or nail polish to put a big + near the positive terminal.

I’ve done it. Sometimes it comes out good, other times it’s brittle and breaks easily. Definitely an emergency use only type of fix.