Hey

Is it possible to discharge a lead-acid battery, and then charge it up again the wrong way around(poles reversed)?

I'm wondering because i just put a battery into a friends car, his old battery was shot, however, the pole marked plus, was actually minus, and the same for the pole marked minus. I'm guessing this battery is either a production fault, or the above mentioned has happened.

The car was an old corolla, so not a lot of electronics to fry luckily..

I must say that I really don't think it seems likely that a factory made a battery the wrong way round, but you never know.

Daniel

 

Yes, it is entirely possible to do that.

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It would totally wreck the battery though.

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Yeah, that's what I thought. I'm just glad I didn't try it on a newer car with more fragile electronics.

Daniel

 

So are you saying that when you went to remove the old battery the red lead was connected to the minus terminal? Seems curious that someone knew the poles were swapped when it was first installed.

 

That is not what i'm saying. At least not what i'm trying to say.
The old battery had the black lead connected to the minus pole, and the red lead to the positive pole.

The battery was really tired, and wouldn't hold a charge very well, so we decided to change it out with one I had laying around in the garage.

When i put the "new" battery in, I connected it the same way as the old one, but since someone has probably charged it with the polarities reversed, the pole marked with a plus was actually the negative terminal of the battery and vice versa.

Things obviously didn't work very well like this. The car wouldn't start, the lights wouldn't come on etc, so I started measuring around to see what was happening. I switched the leads on the battery and now it works like a charm. But i guess it might wear out rather quickly

Daniel

Edit: Typo

 

That is strange. I wonder if it was a recycled battery.

 

Check the alternator if it is charging. A reversed polarity battery with enough charge left in it, will fry the rectifier diodes.

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As kids we were illegally driving an old car on the road

And we found the faster we went, the dimmer the lights got - we had put the battery on the wrong way round. The series wound starter motor still turned the correct way of course, and because it had a dynamo it didn't have any electronics to fry.

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Yeah, very strange indeed. Don't really know where it came fram. I think my dad bought it a few yeas ago, but not sure if anyones ever used it.

I wonder who would try to charge a battery the wrong way in the first place..

And i would think it would need to have been really deeply discharged, or else it would probably overload the charger?

I already checked. It just blew a fuse, so no harm done.


Aaah, the simpler times... I guess some electronics were a bit more sturdy back in the day.

 

No 'electronics' involved, dynamo's produce DC directly, and the control boxes were just mechanical relays - in fact by pushing one of the relays manually (without the engine running) you could re-polarise the field coil of the dynamo and make it negative earth instead of positive earth.

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Positive earth is crap because it can result in corrosion problems.

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It's how all cars were at one time, negative earth came later - and required the introduction of car radios that could be switched to either.

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@Hero,
Yeah, Ford was positive ground until 1956, relatively recent, so to speak.

@Nigel,
Ah, the days when you could start a car with a simple paper clip. At least you could tell whether the generator was working. My Honda died a couple of years ago from a bad alternator. No idiot lights, nothing. First thing that went was the speedometer, then only a few seconds later, the engine stopped cold in rush-hour traffic on a freeway. By "dynamo," is that a magneto ignition or generator in American?

John

 

A dynamo 'may' be called a 'generator' in America, but dynamo is the correct term - it produces DC directly, where an alternator (which could also be called a generator) requires rectification.

Interesting Ford changed from positive earth in 1956, the car in question was an old Ford, probably slightly predating that.

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