Battery replacement issue (big one)

I fried the diodes in an alternator of a friend's old car when I replaced the battery. I connected the red battery lead to the +ve terminal and the black to the -ve -- only to find out later that the red lead on this vehicle was the ground; I assume that's not the way it came from the manufacturer.

Perce

Actually, all kidding aside, you SHOULD appreciate that.

It's tough to protect the vehicle. The master fusible link needs to pass so much current in normal operation that it can't be expected to protect the vehicle components from something like a reversed battery.

What it does is protect you.

Seriously, a shorted battery very often WILL explode. The least of your worries at that point would be cleaning acid off from everything in the engine compartment. You should be more concerned with at least your eyes (battery acid in the eyes is almost instantly blinding, and pretty much usually permanently) and the explosion could be fatal to leaning right over hooking up the thing.

Years ago I had a 1950 Willy's. Now, I didn't do it, but someone I know said they actually had their Willys try to turn over backwards when things got reversed. Allegedly there was no damage.

pic of the cables in general including the thick black one I replaced> that I connected to negative.>

Auxiliary cable that got severed>

Picture of the positive battery terminal on the positive side of the> battery.

Heck - I might as well pile on with everybody else.

The big cable in your first photo that you connected to the negative terminal - that is your positive lead. The red block that it goes to is the point to which you would clamp the positive lead of a jumper cable if you were to jump it from another vehicle. BTW - that is the point from thru *all* power from the positive terminal of you battery gets to the rest of the vehicle (with the exception of the hot wire to the alternator). Notice there are three cables on that junction - one from the battery (the positive lead), one that is the hot wire to the starter, and the third is power to *everything* else. That third wire goes to that fusible link that Joe P. mentioned, again - it's red, and it is the positive power supply.

And - BTW - I do see a "Plus" sign ("+") in your third photo (partially hidden) at the tip of the battery clamp bolt. So at least the pretty red felt donut is on the right post (Again - red for positive). Unfortunately the electrons don't pay attention to color. :)

Your hope is that the reverse-voltage protection designed into your electronics was robust enough to protect them until the fusible link had time to open. If you come out unscathed in the electronics, count your blessings. If not, get familiar with

- it will save you lots of money.

Stick to computers (your day for sarcasm) :) - except be aware that UPS batteries use the same wire color convention: Black is neg., red is pos. Also - inside the computer, on your power connectors, black is ground, other voltages are colors - one of which is red.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Oops - Should have read "BTW - that is the point thru which *all* power from the positive terminal of you battery gets to the rest of the vehicle (with the exception of the hot wire to the alternator)."

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Nobody has mentioned this, and it would have been helpful to the OP, to mention the one thing that does actually short out when you apply voltage backwards. It's diodes that do that. From all the ignorant comments about this costing "thousands" to fix "everything" it appears nobody actually thought about that, or maybe as a group we're too dumb to bring it up. That current flow went through the alternator diodes. The actual voltage was applied everywhere, but 12 volts the wrong way isn't going to hurt anything. It's too wimpy.

So before alternators were put on cars, they didn't have any diodes in them. You could take a postive ground vehicle and convert it over to negative ground with no big deal. The generators had permanent magnets in them, so you'd have to rewire that to get it to work at full output, but again, that was no big deal. A motor with no permanent magnets will work either way, and obviously all the lights and other resistance loads like that don't care.

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Hi Bill...

Arghhh, now that UPS's are in play, it's probably worth mentioning to the OP (who confesses to being a newbie) that the AC supply to the UPS throws another twist into it, with the black being the "dangerous" one.

It's a plot.

Take care.

Ken

Very true. Diodes don't like reversed voltage. A co-worker put the battery in backwards on a ThermoKing refrigeration trailer, loaded of course......Guess who got to fix his screw up? Yep, me.

That unit never did work right after that, even after replacing nearly $1,000 in parts. So, yeah, depending on what you do it to, it can be expensive. Sometimes though not always in parts, but the time (also expensive) to find what else got fried.

12 volts wimpy? Here's an experiment.....lay your sweaty arm across the leads of a 12 volt automotive battery. Please report back. When there 700 amps available at 12 volts, somethings gonna give.

That's the point we're making. Duh! ;-) (humor mode here).

There were even older cars that had positive to earth voltage setups, if I recall. I'd ask my Uncle Bob, but he died long ago.

You are quite incorrect on that assumption. Reversed 12v will easily take out the main control module, transmission control module, body control module, stereo and anything else electronic in the car. I hope that he was lucky and didn't cook anything. I have seen several show up at the junk yard that were hooked up backwards and the cost to repair was so high that the cars were junked.

Steve B.

Hi...

Think I might be wandering far off topic here, and I apologize to those of you who it might offend, but for what little it may be worth...

Lifelong love of cars. Lifelong hobby of photography.

Now we virtually all have digital cameras, which has a per picture cost of zero (if we don't print paper pictures)

Put the two together, as you all can, and take pictures of everything you take apart - just leave them all in the camera - and if necessary you can easily refer to them when you're re-assembling.

Do it to everything. Build a rec room and covering up water pipes and electrical wiring and telepost screw locations? Take pics before the drywall goes up. Running pipes and wires at the lake that are going to be buried? Take pics that include reference points before you bury them.

And tons more opportunities, but to kinda cover my you know what for topic... taking vac lines off? Take pics from every angle first :)

Take care.

Ken

Now you are showing *your* ignorance - on several points.

You are correct about the alternator diodes - there are three pairs with each pair connected in series from positive bus (diode cathode) to ground (diode anode) - reverse biased. Reversing the voltage will forward bias those diodes. It's a toss up as to whether the fusible link (which is in parallel with those diodes) or the diodes would be destroyed first - perhaps they designed the fusible link to go first since the alternator is the only thing it protects.

Also, any electronic module intended to be powered by d.c. will be destroyed if reverse-voltaged if the designers didn't specifically design to protect from that happening.

12 volts is too wimpy to hurt anything? Did you see the photo of the OP's fusible link?

As an electronics designer of over 20 years I honestly don't know if the auto mfgrs. take the extra steps (probably some do, and some don't). But I can tell you that to do so adds some minor cost and operational ineffiencies, so, with both of those being at a high premium in today's cars, it's a good bet that they left out such "non-essentials" from some modules (unless it's company policy not to).

But not the electronic modules (of which there are more of on this car than you have fingers). At best they simply don't work until the right voltage polarity is applied. At worst, they get seriously damaged.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Go back and read the original post, pay attention to the part about his wipers running and not being able to turn them off.

Do you know what component has control over the wiper motor?

"Just like the old battery had them on" doesn't mean jack squat, not all batteries have the terminals in exactly the same locations. You MUST look at the battery labels before connecting.

I suspect you've got a whole lot of fried electronics due to hooking it up backwards.

That doesn't even make sense.

The negative cable should NEVER connect to anything "red." The convention is that red=positive, black = negative.

Unless of course your dealing with home wiring, in which case there's neither "positive" or "negative," just "hot" and "neutral." Unfortunately, the convention THERE is that black=hot :-/

Then WHY bother with a new battery? The old one was obviously fine.

Actually, they don't mind reverse voltage at all. When you turn the car off, the diodes are reverse-biased and conduct no current. With the car running, they are forward-biased because the alternator is producing a higher voltage than the battery, and therefore they carry the charging current produced by the alternator. Unfortunately, what happens when you put the battery in backwards is that the alternator diodes are FORWARD biased, and create a short circuit. They then burn out trying to conduct the full current provided by the battery.

Why sarcasm? He was stone-cold serious. If the fusible link hadn't popped, you'd have had a pretty good sized conflagration in your face. Conservation of energy, y'know- all that energy in the battery has to go SOMEWHERE, and it turns into heat. Lots of heat.

Hi...

Once upon a time when I was very young and foolish (now I'm very old and even more foolish) I was working on my car after dusk... had a metal clad flashlight. Put it down on the battery, shorting the top posts.

Huge portions of the flashlight instantly disappeared. But it was very very bright for a millisecond or so :)

Take care.

Ken

All batteries are marked next to the post with the polarity. To match up the cables when in doubt, ignore colors - someone else may have worked on it - and follow the cables. All "current" cars I am aware of (enough disclaimers?) are a negative ground system. (I have heard of some old foriegn cars with positive ground but I don't believe there are any now - bloggers please advise). In a negative ground, the negative cable will always have a thick strap to bare metal of the engine block, and usually an additional strap to the metal of the frame or body. The positive will never have a strap to metal. It will have a thick cable to the starter. Various systems have additional cables, but the main thing to look for are connections to bare metal of the engine/frame/body=negative.

The best advice I ever got when I first started playing with motorized vehicles was to "look at what you're seeing".

In fairness, sometimes it's awfully hard to realize that what you're seeing doesn't look right. Checking all your assumptions is always good advice, but the assumptions that are most embedded are so subconcious you don't realize you're making them (there are a few readers of this newsgroup who know me from other contexts, who will remember some unbelievably ignorant questions I asked the first time I did a tuneup on a car with an automatic transmission...)