Need ways to start a car with a dead battery.- 92 Civic Auto.

Automotive alternators can self-excite. Once they are running, some of
their own generated current is used to power the field. So if you
disconnect the battery at that point, the engine keeps running. I don't
think that's the case in every alternator design, certainly not
historically.

 

At which point, the diodes will probably go up in smoke, leaving you
with a dead (if present) battery, *AND* a dead alternator.

Running an alternator no-load/micro-load is a great method of letting
the magic moke out of the diodes.

 

You are 'very' far out of date and way off on this one. GM made a 'one
wire' alternator that will self excite if the rpm get up high enough.
Once running, some alternators can feed off their own power output, but
this isn't 'self excite' at all.

On 'modern' vehicles, if you disconnect the battery, the open ended
alternator surge 'will' destroy the computer, ignition module, stereo if
turned on and any other electronic part active before the alternator
itself smokes out.

That just plain don't work no more, same as push starting a dead or
really low battery car. The battery has to have over 10 volts in it to
turn on the electronics and still have enough to turn the fuel pump on.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
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(More Off Road album links at bottom of the view page)

 

When referring to the parts in automotive applications, the term
"generator" always refers to the fixed-magnet device using a
mechanical commutator, and "alternator" to the one with field coils
and rectifying diodes.

 

If you start a car and disconnect the battery, it will remain running
off the alternator. Once it is running the alternator does not need
_external_ power to its field coil. However, note that the battery
does provide some voltage regulation to the whole system, so
electrical devices may behave erratically if you don't have the
battery in there. (seen it myself)

 

The other electrical accessories are enough to keep the diodes from
going up in smoke. Been there, done that, when a battery wire terminal
corroded all the way through.

 

No, it won't. I've had a battery terminal corrode through and nothing
of the sort happened. Granted, that was not a completely modern car
(electronic ignition, but carbeurated). I've also run a modern car
with a battery which was damaged and not taking a charge; while the
gauges acted erratically and the car idled badly, it was not instantly
damaged.

 

I have seen a mess of newer ones killed like mentioned....

Carb engines are different animals.

Mike

 

Tell that to the alternator that died with a very visible (and
aromatic...) cloud of smoke, a pop that sounded about like a .22 going
off, and a "bacon frying" sound that was easily audible over the normal
engine noise when, instead of just twisting the ground cable on the
battery post as I was trying to do, I managed to lift it off the post
and fumble it instead.

There might have been ten seconds, if that long, of "no battery
connection" involved as I retrieved the cable end, got it lined up, and
stuck it back on the post, but by the time that was accomplished, the
smell of burnt electronics was overwhelming. Testing it on the local
Kragen's machine an hour or so later showed a bad diode trio, and the
pre-rebuild inspection later on revealed that one of them had been
reduced to a lump of char, another was split open, and the third was
just plain GONE - As in no sign of it to be seen other than a scorch
mark in the empty spot where it should have been.

(Yeah, I know... I shouldn't have been dicking with it with the engine
running - We've all got 20-20 hindsight.)

 

Years ago, my 260K miles, 1988 Honda Accord fuel injection
battery cable was cut by the fireman who was at the scene of the
accident. The car idled smoothly for maybe 10 minutes until I'd
shut it off. I still drive it today.

I believe there is a button you can push on these alternator to
go full field. Otherwise, they're self regulated. Last I'd checked,
the voltage never exceeded 15V when idling with the battery
cable unplugged.