Battery replacement issue (big one)

Steve wrote:
> Henry Bemis wrote:
>
>> Very true. Diodes don't like reversed voltage.
>
>
> 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.

Unless the fusible link - which is in series with the diodes and nothing
else - opened in time to keep the diodes from being destroyed.

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

exiledtiger wrote:

> 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,...

On this particular car, no. Cable goes directly to the negative jump
post/main body ground on the right front strut tower (and is clearly
labeled as the negative jump post). There is a heavy cable going off of
that neg. jump post that - I think - goes to the starter. There are
some braided grounding straps from the right fender well (approx. 6 or 8
inches from the neg. jump post) going to 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...

But, in this car, not directly. There is a main cable going to the
positive jump post - the red thing shown in the OP's first photo. There
are two other cables from that pos. jump post - one goes to starter, the
third goes to everything else (except alternator/generator). The second
(smaller) wire coming off the battery cable clamp is the hot wire to the
alternator/gernator.


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".

FWIW, the OP's replacement battery has the same post arrangement as the
original battery - but he has it rotated 180°. Perhaps the previous
battery had been installed backwards *OR* he made the change when he put
this battery in, but failed to re-arrange the cables to the opposite end
of the battery compartment.

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

On Sat, 14 Jul 2007 22:44:39 +0000, afx wrote:

> On Jul 14, 5:43 pm, afx > wrote:
>> Thats exactly what I thought it sounded like, but the thing is I put
>> the battery cables on just like the old battery had them on, the weird
>> thing I was thinking of was the negative cable connected to the left
>> side of that red post that the positive connects to the other side, is
>> that correctly done? Maybe the old battery just didnt have enough juice
>> to give this reaction?
>
> And would you know why the windshield wipers wont turn off? is that
> because the auxiliary wire was severed? Thanks for the help!

The wiper controller is fried.

Most of the electronics in the car will need DC-DC converters, 12V is
much to high to high for modern electronics so the voltage has to be
converted to something usable (in the mid 90's that was probably 3.3V).
The DC to DC converter modules should be diode protected so most of your
electronic modules are probably OK. However the fact that the wiper
module is busted is a worrisome sign. It may be that the wiper module is
a relic of the 60s that ran directly off of 12V which is why it didn't
have any protection. The microprocessors in the car can't possible use
12V so I would guess that they are OK. However I'm a computer engineer
not an automotive electronics engineer so it's possible that I'm wrong.


For future reference Red means HOT, Black means GROUND.

On Sun, 15 Jul 2007 21:47:26 -0600, Joe Pfeiffer wrote:

> exiledtiger > writes:
>>
>> 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...)

Nothing concentrates the mind like the prospect of being hanged in the
morning.

Dr. Johnson


Shorting a car battery can be fatal, the OP is very lucky that he got off
with only a burned hand. When something is a life or death matter you
check and the check again. I can see how a professional mechanic might
get blase about batteries because they do it every day, but an amateur
should treat the thing like it's a landmine. I've always gotten my
replacement batteries at Sears, you leave the car for an hour, go to the
food court and get an Orange Julius, and come back when it's done.

Joe Pfeiffer wrote:

> exiledtiger > writes:
>
>>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...)

Hmmmm.... sounds like I may have forgotten a good story... ;-)

Steve > writes:

> Joe Pfeiffer wrote:
>
> > remember some unbelievably ignorant questions I asked the first time
> > I did a tuneup on a car with an automatic transmission...)
>
> Hmmmm.... sounds like I may have forgotten a good story... ;-)

It started with, "it has to be in Drive when setting the idle speed,
right?" and went downhill rapidly from there.

"Henry Bemis" > wrote in message
. net...
> 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.
>
>> The actual voltage was applied everywhere, but 12 volts the wrong way
>> isn't going to hurt anything. It's too wimpy.
>
> 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.
>
>> 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.
>
> 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.
>

lol...beat me to it...it's not the volts that kill you, it's the amps. i was
working on a 24 volt (2 12volt batteries) electric wheelchair once and i
hadn't noticed the owner had put a non-standard plug on the charger cable.
it had exposed prongs and it touched the metal frame....wow....fireworks
and the plug welded itself to the frame while burning a hole in it...and
this was heavy gauge chromed steel...and that was only a 100 amps system...

as you say, 700 amps can create quite a show.

Simon wrote:

> ...it's not the volts that kill you, it's the amps...

Since areas of the body have a characteristic resistance, because of
Ohm's law (for a given resistance, voltage and current are
proportional), I've always thought that was an extremely ignorant cliché
- a way for semi-technical people to try to impress non-technical
people, when in reality it shows ignorance (to the truly technical
person). Either the person making the statement is ignorant of Ohm's
law or its implications, or hasn't thought the meaning of the statement
thru before making it. In reality it also comes down to what the
impedance of the source of the voltage and current is (resistor divider
effect), but on its face, the cliché shows ignorance.

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