OK I really screwed up. I would estimate that I have jump started 50 times in my life and it finally caught up with me. I was helping a Damsel in Distress and I hooked up her battery but when I connected to mine I reversed the polarity but did not realize what I had done (there was a strong arc but I thought it was because her battery was very low). After a minute or so (my truck was running) her battery exploded (case ruptured, acid everywhere). The jumper cables were HOT, the insulation was melted off in places and my negative battery cable terminal (the lead part) was partially melted and puddled on the top of my battery. Everything seemed fine for a couple of days then one day my battery light came on briefly (1994 F-150 XL, 300 straight six, manual tranny M5OD, no bells or whistles, 140k miles, perfect condition, babied it since new, made in Norfolk, VA, I love this truck). No problems since then and my potential gauge (Volts) reads normal. Obviously there was very high current flowing through the jumper cables. Can I expect long term problems?

 

DOH! If it's been fine for a couple of days of regular use, then most likely, everything will be fine. Did you at least replace your cable? Get your battery load tested too. (I'm not even gonna bring up...just to save face, buy her a battery....because that would be wrong of me) Man that sucks! Was she pissed?

 

Actually, you were lucky that you're driving a 1994 vehicle. I stopped carrying jumper cables about 5 years ago when I learned how sensitive newer vehicles are to just that kind of mistake. Yea, it sucks because I like to help folks too, but not at my (huge) expense.) On a newer truck, you might be looking at a serious bill for fried electrical components. Same goes for the jumpee. I'd say you've seen the worst of it though if it's running OK. Remember, no good deed goes unpunished.

 

allways ground the negative cable, don't conect to the - terminal on the battery...alt bracket...bolt on the frame...rad support.. ect work, in the event you do miss natch the boster cables, this prevents blowing up the batt........

 

Recently the battery light came on more often and stayed on for longer durations. The Volt gauge still read in the normal range but I thought I better do something about it before the charging system failed and left me stranded. I replaced the battery but that didn't solve the problem. I took the alternator to a parts store for a bench test and it only made 10 Volts (2/3rds of 15 volts) and the diode light on the test rig came on. I guess hooking up the jumpers backwards fried one of the three diodes. I replaced the alternator and that seems to have solved the problem.

 

It doesn't hurt newer cars in the least. I've jumped off so many pieces of equipment it's pathetic. My battery clamps are so boogered up from arcing that they'll never come loose. I had to replace my alt. at 160,000 miles, but DANG! I've left it hooked to stuff for hours on end. It's no wonder that it finally wore out.

This is just for info.... 99% of the time, when the battery light comes on, it's the alternator. Cause even if the battery was bad, the alternator would still be putting out 13-14 volts. Unless it has a dead short or something.....

Ford was stupid for putting a Battery idiot light in the truck. It really confuses people. It's nothing more than a low voltage light.

 

Not quite true... If the wires are crossed at either end, connecting to the chassis can cause some wierd problems on both ends, and can still lead to a battery explosion.

The primary reason to not connect to the negative terminal on the battery is to minimize the chance of a hydrogen gas explosion (a-la Hindenberg). Dead batteries give off Hydrogen gas. So, always make the final connection (which will spark) to the vehicle with the least discharged battery at a point away from the battery and, therefore, with the least likelihood of exploding in your face.

Just be glad you weren't standing over the battery when it popped. I have. It wasn't pretty. All my clothes went in the trash, and it took a putty knife to scrape my shorts out!

-Joe

 

When you cross connect batteries you are increasing the voltage of the circuit. So you system could see upwards of 18 volts depending on how low the other battery is. Ie. 6v or more from the dead or low battery plus the 12v form your battery. Running this much voltage through a PCM controlled vehicle could cause problems with the PCM. It may alos take out the diods in the alternator as was the case this time.

JMC

 

JMC, I'm not so sure about the 18V issue.... The 'dead' battery is hooked up in series with the other battery if you look at the batteries independently, but they're not independently connected to the load. The second (reversed and half-dead) battery is in parallel with the load on the running vehicle. I think the biggest problem arises from the reversed polarity that tries to back-feed through the PCM, and alternator that way. I think that's what causes the diode(s) to fry.

Also, both batteries are dead-shorted with respect to each other, and anytime you dead-short a battery through a set of heavy-duty cables (i.e. no fusible link) they can easily blow. I've seen them do that in under 2 minutes sitting on a shelf from side-post Delco batteries touching the shelving. (What a mess that was!!)

-Joe

 

This is not true at all, when you hook up batteries in this scenario, it actually appears to be -12V (about). But after connecting the battery they draw so much current, all batteries have some sort of internal resistance, dropping the output voltage. The problem is that what you did is worse than just shorting the two post together. When the two posts are shorted together, there is no resistance. Using ohms law, ANY voltage at 0 ohms, equals infinite current, then the internal reistance of the battery takes over. Since batteries are designed to provide high cranking amps, they have very low resistance. This huge amount of current causes heating in EVERYTHING. The resistance in you booster cables is pretty much negligable even with a meter, but it still manages to melt plastic, this means liteally thousands of amps!

The instant the cables where connected you would only measure 1 to 2 volts at most between the posts of either battery. The explosion comes from the heat but this is not the reason to connect to the frame. As explained before this is becuase of the highly explosive hydrogen gas. The same result would have likely happened connecting to the frame, same current draw, same heat, the only difference would be the slight amount extra resistance between the factory battery connection and where it connects to the body, then the very slight resistance from there to where you placed the booster cable.

Cheers

 

If you have a really good set of jumper cables, I wouldn't connect it to the body. In the event of a "reverse cable" situation, you are gonna melt whatever connects the body to the battery. (in my truck, it's a small wire) Also, electricity follows the path of least resistance. So (for example) it might decide to flow through the PCM, or a bearing or something. (found out the hard way that it will flow through bearings ) So it's a BAD idea to hook a jumper cable to anything other than the battery itself. (not regarding the hydrogen explosion from leaking gas)

Also, if you were gonna weld something on your truck, you HAVE to place the ground on the SAME piece of metal that you're working on. (eg. if welding on exhaust, put the ground on the exhaust, not the chassis) If you put it on something else, you don't know what path the electricity will take. It could go through the PCM or your tranny or a bearing or something.

 

Lets make this simple. Put the Postive (+) on the Positive (+), and the Negative (-) on the Negative (-)! And when you do it be VERY aware of what you are doing! I would NOT want to do what buddy did above.

That is way to many amps to go playing around with!

 

That's not a bad way, but there is a safer way. By grounding the final connection to a chassis ground away from the battery on the running vehicle, you make the exact same connection, and minimize the chance of the spark causing an explosion of the flammable hydrogen gas (and it'll always spark when you make the final connection). + to + and - to - is not a bad alternative if a chassis ground isn't readily available, but again, make the final connection on the running vehicle to minimize the chance of a hydrogen build-up exploding in the engine compartment.

 

That is why I always disconnect the battery before welding. That way it cannot fry the PCM.

JMC

 

My buddy's Escort. She left everything on, and the battery was dead. Good samaritan hooked up the jumper cables wrong. Smoke. Flames. Electrical system was toast. Complete total loss. Insurance company would not pay. Even full coverage does not cover you, when you allow someone to jump start your car, and they cross the cables.