Yikes... Reversed Jumper Cables!!!

Since you DIDNT blow a fuseable link or fuses in the fusebox, you may have gotten lucky and the battery sank all the voltage. The resistance of the jumper cables saved your ass by dissipating the power as heat. Watch for telltale signs, alternator whine in the radio, watch the voltmeter for strange readings. Check your alarm system and see if it survived. The reverse current was also dissipated by the 6 diodes in the alternator and the stator. Also hit the "Keep-alive" circuit in your radio and alarm system.Check the electronic clock too. If you didnt turn the key you probably saved yourself a LOT of money. You got your Christmas present early..... Problems might not surface for a while.

Sounds to me like you got lucky...Why worry?

That's my take on it, too. Sometimes it is better to be lucky than to be good ;-)

If you have access to a digital voltmeter, measure the AC voltage across the battery with the engine running. Damage to the diodes in the alternator will show up as AC voltage above about 0.1 volts.... typically 0.5 VAC or more. If that's good it's time to stop worrying about anything but the battery.

I haven't seen delayed damage from reversed cables (except to the battery life) like I have seen with lightning damage. You should be okay - except I wouldn't trust the battery that was already discharged and then jumped backward. I predict it won't last the winter.

Mike

You got lucky. There was probably enough resistance in the jumper cables, and the charged battery was probably old enough that it couldn't push enough amps to burn anything up.

I seriously doubt there will be any long- term problems. I'm glad for you...

Kewl info!

...if you were showing >.1 VAC, could you throw an external bridge rectifier on it and get by that way, or does the condition actually cause other stress to the alternator, that eventually kills it (excess heat, etc)?

I looked at that years ago when I had a shorted diode on my Datsun's alternator. The alternator puts out 3 phase AC requiring

6 diodes to convert to DC. It's pretty much impractical to kludge something up to do that.

Back then, you could buy a new bridge assembly and solder it in yourself. I think it cost less than USD 20 and took about 1/2 hour to do it.

Whether they are available now, I don't know.

Exactly so. The AC is a symptom of the diode bridge being damaged. I also don't know if the diodes are available separately any more. They are inside the alternator, on two plates (3 per plate; one for each phase at each end of the windings.) I've never changed any myself. In all the bad alternators I've seen the AC voltage was at least 0.5 volts, and the most recent one was reading 1.7 VAC!

In modern cars a damaged diode bridge tends to get worse within a few days or weeks, as the high current demanded by all the electrics and electronics is pulled through two phases instead of 3. But if the AC is low now - indicating all three phases are working - there is no reason to worry about it getting worse from the jumper incident.

Mike

IMHO

to the car, connecting the batteries in series would just look like you shorted across the battery. there would be no excessive currents in the cars' circuits to blow fuses or links. with the batteries in series you are taking power out of the car (out of both cars) not putting it in.

to the jumper cables, it would look like you connected them to a battery and then shorted the other ends, times two.

that said, if you were to jumper your 12v battery to a 24v battery, either in series or parallel, bad things would happen.

it is unlikely that shorting the battery for a short period would damage the alternator. this short would simultaneously reduce the current available for the alternator's field. the alternator rectifiers do not burn up when you drive on a low battery. a lead acid battery has a low internal resistance, this is what allows it to dump the large currents required for starting. when a battery is in a low state of charge, say below 10 volts, it is going to draw pretty much the same current from the alternator as if it were a dead short. in addition, I believe alternators are designed to operate into a dead short, that is, the field current is limited to a maximum that will not allow fire to occur in either the field or stator windings. it is only logical to install rectifiers with a rating that can readily handle the maximum output.

and finally, when you engage your starter motor, this is probably only a few ohms resistance. in other words nearly a dead short. so again, it is unlikely you caused any damage to either battery, either.

You REALLY need to re-read the statement AND learn simple electrical theory!!! Connecting a healthy charged 12 volt battery to another vehicle BACKWARDS results in a lot more then *YOU* think. Re-read it again and think about what was asked and done....

Also..you know nothing about alternators.......

>

My God, you are INCREDIBLY smart. Could you please take a few minutes and tell us EVERYTHING you KNOW about ALTERNATORS.

Hey Chuck!!! some BOZO named Norm thinks I am you! Amazing.... If you really DO want to know about the "innards" of Alternators..I used to rebuild them :) Would be happy to share the info if you need it.

I know Norm and while he doesn't know much about alternators he does know usenet jerks. If he says that you are me then that is good enough for me. By the way Mortimer I have been having trouble with my esophagus, how about you?

Has been fine! ate a whole pizza without chewing it last night.

Try a lighter weight oil. If that doesn't do it you might need new seals or a rebuild. Or you could check a wrecking yard for a low mileage one. (Actually, I do have trouble with my esophagus, and it really hurts when the spasms get going!)

Mike