Battery replacement issue (big one)

It wasn't backwards - that was just the 8 track drive taking the opportunity
to
get rid of an extremely obnoxious tape. ;-)

Ted

 

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.

 

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 www.car-part.com - 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.

 

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

 

Joe wrote:

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...)