Dead Battery

It is a newer Jeep with a 'generator' or 'half an alternator' isn't it?
The regulator is in the computer.

I don't know how they work with no battery, maybe they got excited
before the cable was pulled off, but the only times I have seen that
happen on a Cherokee, the computer toasted right away, the stereo fried
up in smoke and the 'half alternator' died.

Does that 'half alternator' even need an excite?

Mike

Jerry Bransford wrote:
>
> How can the alternator even work with the battery gone? Generators work
> fine with no battery, alternators do not since they need +12 volts from
> the battery for the exciter voltage before they will work.
>
> Jerry
>
> Mike Romain wrote:
> > Now you are talking a dead computer because it got fried from the
> > alternator surging with no battery buffer.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> >
> > curbrider wrote:
> >
> >>91 jeep cherokee 4.0 replaced alternator and it over charge even with the
> >>battery disconneted
>
> --
> Jerry Bransford
> PP-ASEL N6TAY
> See the Geezer Jeep at
> http://members.cox.net/jerrypb/

Well, if you got extremely lucky and didn't fry any electronics, then I
would be chasing cable connections.

The main battery cables need cleaning at 'both' ends, pay close
attention where the negative hooks to the block. Then there is a wire
mesh cable that runs from the rear of the head to the firewall, if
ratty, it can cause the alternator to read all over the place while not
putting juice to the battery.

The case to bracket ground on older Jeeps can go bad too. I test that
by taking a booster cable and run it from the battery negative to the
alternator case to see if the volt readings level out. If they do, then
you have a ground path issue.

Good luck!

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

curbrider wrote:
>
> i only pulled positive cable off for 30 seconds

I know my wife's Grand Cherokee will not even idle after jump starting
it if the battery is totally dead, it dies immediately. Her battery
suddenly went totally dead last week and while I could jump start it, it
would die once I let it idle since there wasn't enough power in the
battery to continue exciting the alternator. I had a hell of a time
even driving it one mile to a battery store to get it replaced, it even
died and literally left me sitting on the railroad tracks at one point,
lucky there were some workmen there that pushed me off the tracks so I
could jump start it again.

Yep, both electronic theory and my recent personal experience says it
won't run without the battery.

Jerry

Mike Romain wrote:
> It is a newer Jeep with a 'generator' or 'half an alternator' isn't it?
> The regulator is in the computer.
>
> I don't know how they work with no battery, maybe they got excited
> before the cable was pulled off, but the only times I have seen that
> happen on a Cherokee, the computer toasted right away, the stereo fried
> up in smoke and the 'half alternator' died.
>
> Does that 'half alternator' even need an excite?
>
> Mike
>
> Jerry Bransford wrote:
>
>>How can the alternator even work with the battery gone? Generators work
>>fine with no battery, alternators do not since they need +12 volts from
>>the battery for the exciter voltage before they will work.
>>
>>Jerry
>>
>>Mike Romain wrote:
>>
>>>Now you are talking a dead computer because it got fried from the
>>>alternator surging with no battery buffer.
>>>
>>>Mike
>>>86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
>>>88 Cherokee 235 BFG AT's
>>>
>>>curbrider wrote:
>>>
>>>
>>>>91 jeep cherokee 4.0 replaced alternator and it over charge even with the
>>>>battery disconneted
>>
>>--
>>Jerry Bransford
>>PP-ASEL N6TAY
>>See the Geezer Jeep at
>>http://members.cox.net/jerrypb/

--
Jerry Bransford
PP-ASEL N6TAY
See the Geezer Jeep at
http://members.cox.net/jerrypb/

Something has changed then from the Cherokee system to the GC's. I have
heard the Grands won't run with a bad battery several times and places.

The Cherokee will run if the battery cable is taken off after starting
like the OP said he did. The one I saw doing it was a 92 and the OP's
is a 91 I think. Not for a long time, but it will run.

I saw the 92 do it twice and burn things up twice after the same shop
left the battery cable loose a second time and it fell off while off
roading once again.....

Well, he saved the stereo because I realized what I was seeing as it
happened so hit the off button fast and the mean green 'alternator' was
just a smokin'.

Mike


Jerry Bransford wrote:
>
> I know my wife's Grand Cherokee will not even idle after jump starting
> it if the battery is totally dead, it dies immediately. Her battery
> suddenly went totally dead last week and while I could jump start it, it
> would die once I let it idle since there wasn't enough power in the
> battery to continue exciting the alternator. I had a hell of a time
> even driving it one mile to a battery store to get it replaced, it even
> died and literally left me sitting on the railroad tracks at one point,
> lucky there were some workmen there that pushed me off the tracks so I
> could jump start it again.
>
> Yep, both electronic theory and my recent personal experience says it
> won't run without the battery.
>
> Jerry
>
> Mike Romain wrote:
> > It is a newer Jeep with a 'generator' or 'half an alternator' isn't it?
> > The regulator is in the computer.
> >
> > I don't know how they work with no battery, maybe they got excited
> > before the cable was pulled off, but the only times I have seen that
> > happen on a Cherokee, the computer toasted right away, the stereo fried
> > up in smoke and the 'half alternator' died.
> >
> > Does that 'half alternator' even need an excite?
> >
> > Mike
> >
> > Jerry Bransford wrote:
> >
> >>How can the alternator even work with the battery gone? Generators work
> >>fine with no battery, alternators do not since they need +12 volts from
> >>the battery for the exciter voltage before they will work.
> >>
> >>Jerry
> >>
> >>Mike Romain wrote:
> >>
> >>>Now you are talking a dead computer because it got fried from the
> >>>alternator surging with no battery buffer.
> >>>
> >>>Mike
> >>>86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> >>>88 Cherokee 235 BFG AT's
> >>>
> >>>curbrider wrote:
> >>>
> >>>
> >>>>91 jeep cherokee 4.0 replaced alternator and it over charge even with the
> >>>>battery disconneted
> >>
> >>--
> >>Jerry Bransford
> >>PP-ASEL N6TAY
> >>See the Geezer Jeep at
> >>http://members.cox.net/jerrypb/
>
> --
> Jerry Bransford
> PP-ASEL N6TAY
> See the Geezer Jeep at
> http://members.cox.net/jerrypb/

I really would not suggest disconnecting the battery on an alternator
based system. The alternator will then put out enough voltage to make
things interesting, if somewhat short lived, for the computers that
don't like somewhere between 40 to 80 volts open circuit. Plus the
battery acts as sort of the filter capacitor for the simple diodes in
the alternator output, so you get a rather rippling waveform.



Mike Romain proclaimed:

> Something has changed then from the Cherokee system to the GC's. I have
> heard the Grands won't run with a bad battery several times and places.
>
> The Cherokee will run if the battery cable is taken off after starting
> like the OP said he did. The one I saw doing it was a 92 and the OP's
> is a 91 I think. Not for a long time, but it will run.
>
> I saw the 92 do it twice and burn things up twice after the same shop
> left the battery cable loose a second time and it fell off while off
> roading once again.....
>
> Well, he saved the stereo because I realized what I was seeing as it
> happened so hit the off button fast and the mean green 'alternator' was
> just a smokin'.
>
> Mike
>
>
> Jerry Bransford wrote:
>
>>I know my wife's Grand Cherokee will not even idle after jump starting
>>it if the battery is totally dead, it dies immediately. Her battery
>>suddenly went totally dead last week and while I could jump start it, it
>>would die once I let it idle since there wasn't enough power in the
>>battery to continue exciting the alternator. I had a hell of a time
>>even driving it one mile to a battery store to get it replaced, it even
>>died and literally left me sitting on the railroad tracks at one point,
>>lucky there were some workmen there that pushed me off the tracks so I
>>could jump start it again.
>>
>>Yep, both electronic theory and my recent personal experience says it
>>won't run without the battery.
>>
>>Jerry
>>
>>Mike Romain wrote:
>>
>>>It is a newer Jeep with a 'generator' or 'half an alternator' isn't it?
>>>The regulator is in the computer.
>>>
>>>I don't know how they work with no battery, maybe they got excited
>>>before the cable was pulled off, but the only times I have seen that
>>>happen on a Cherokee, the computer toasted right away, the stereo fried
>>>up in smoke and the 'half alternator' died.
>>>
>>>Does that 'half alternator' even need an excite?
>>>
>>>Mike
>>>
>>>Jerry Bransford wrote:
>>>
>>>
>>>>How can the alternator even work with the battery gone? Generators work
>>>>fine with no battery, alternators do not since they need +12 volts from
>>>>the battery for the exciter voltage before they will work.
>>>>
>>>>Jerry
>>>>
>>>>Mike Romain wrote:
>>>>
>>>>
>>>>>Now you are talking a dead computer because it got fried from the
>>>>>alternator surging with no battery buffer.
>>>>>
>>>>>Mike
>>>>>86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
>>>>>88 Cherokee 235 BFG AT's
>>>>>
>>>>>curbrider wrote:
>>>>>
>>>>>
>>>>>
>>>>>>91 jeep cherokee 4.0 replaced alternator and it over charge even with the
>>>>>>battery disconneted
>>>>
>>>>--
>>>>Jerry Bransford
>>>>PP-ASEL N6TAY
>>>>See the Geezer Jeep at
>>>>http://members.cox.net/jerrypb/
>>
>>--
>>Jerry Bransford
>>PP-ASEL N6TAY
>>See the Geezer Jeep at
>>http://members.cox.net/jerrypb/

If you have a cheap 0'scope you can find a popped diode if it is failed
to open--the waveform is pretty obvious and the deader the battery the
easier it is to see. If it is failed to short and there is anything
left in the battery, the diode will tend to signal by all the magic
smoke it lets go of. An awe inspiring amount of smoke even on a
presumably dead battery.



L.W.(ßill) Hughes III proclaimed:

> The diode is popped instantly when the battery is disconnected
> while running, you need another rebuilt alternator.
> God Bless America, ßill O|||||||O
> http://www.billhughes.com/
>
> curbrider wrote:
>
>>91 jeep cherokee 4.0 replaced alternator and it over charge even with the
>>battery disconneted