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Perhaps a previous user of the truck jumped it backwards

On today’s show, a caller asked if she should be responsible for charging the battery backwards on her friend’s truck. She described that her friend loans the truck to people and that it needed to be jumped. Since it sounds like the friend loans the truck to people, it is possible that a previous borrower jumped the truck with the cables reversed causing the damage. Then the caller and her partner (the electrician), tried to jump the truck, which didn’t start because the damage was already done.

The Brothers Grim were quite certain that a battery cannot be reverse charged but that is not correct. If a wet cell battery is severely discharged a battery charger will charge it in reverse. I have seen it done twice. But the shop that repaired the truck struck me as overly dramatic when they billed for replacing the diode in the AC clutch circuit. After hearing that I questioned everything they said.

I too was puzzled when C&C said a battery could not be reverse charged.

As to Butternc’s question, yes it’s very possible the previous borrower hooked the jumper cables up backwards. That would would have made them the previous-attempted-borrower.

I’ve never seen it happen myself, but my auto-shop instructor years ago told me a battery can indeed be charged up backward. The plus and minus gets reversed. Then if you put the battery in and didn’t know it was reversed, it would likely damage the car’s electrical system.

For the reverse charging to happen, it would probably have to be dead to begin with, and then reverse charging would be an easy mistake if the charger leads weren’t carefully checked for polarity. If it was partially charged and you hooked it up backwards, the charger probably would complain and blow its circuit breaker. But that comment from my shop instructor was a couple decades ago. Maybe the current auto batteries are different and can’t be reverse charged.

It seems like it would be simple enough to determine if a battery was reverse charged or not though. A simple DVM test on the battery in question would show it straight away, yes or no.

Whatever happened, either the battery was reverse charged, it was put in backwards, or it was jumped backwards, it seems to me that whoever had control of the car when the mistake was made should reimburse the owner. If that simply cannot be determined, then in my opinion, like C& C say, the borrower should split the cost with the owner. It might be that the borrower was not at fault. But it’s just the chance one takes when borrowing something.

I bought a 1948 Dodge where the battery was put in backwards. The Dodge was a 6 volt positive ground. I discharged the battery by purposely leaving the lights on for 24 hours. I then brought the battery back up with the correct polarity with a battery charger. With the reversed polarity, the ampere gauge showed charge when the car wasn’t running and discharge when the car was running. Except for the radio, everything worked with the backward hook-up. After I connected the battery the correct way, I repolarized the generator which only took a second. I don’t remember the procedure–there was one procedure for an externally grounded field coil and another for an internally grounded field and I don’t remember which system was used on the Dodge generator.
There was also a story in an old Popular Science magazine from the early 1960s in its running serial “Tales From the Model Garage”. Gus Wilson, the master mechanic and proprietor had a customer bring in a 1957 Plymouth. Apparently a corroded connection had caused the polarity to flip flop. Gus diagnosed the situation and did exactly what I did with my 1948 Dodge.

How about instead of reversed polarity, a destroyed computer via electrical transients? I don’t know a ’92 Ford Ranger from Tom’s face, but it was certainly into the era of electronics and computerization. Recall that the caller Bridget said that her partner the electrician had “never owned a car newer than 1998” (yes, that’s a quote… just re-played that segment). The guys didn’t ask what kind of vehicle was providing the jump. What if it was some 1950s or early ’60s beast with a generator and a mechanical voltage regulator? Spikes a-plenty! The older vehicle won’t care, but something of a more recent decade loaded with electronics well might. True, the battery of the jump-supply vehicle will be acting as a filter capacitor, but over at the other end of a set of jumper cables (inductance and series resistance) with a dead battery (and thus no filtering at that point), there could easily be IC-killing spikes. And/or the regulator might be regulating poorly or too high, possibly supplying 16+VDC to the Ranger.

I think the guys dropped the ball not investigating the nature of the vehicle supplying the jump.

Those wanting to stay with the reverse polarity theory may have some evidence: what if the guy (the electrician) was tired? At work when he’s wiring a building, black is hot. In the car, black is ground. Normally he would remember the difference, but if he was tired?

Whatever the case, this call would be good for Stump The Chumps or at least some flavor of follow-up, if any new recordings are still being made.

These are my theories and i’m sticking with ’em!