Runs fine w/o battery?

[skeeters_keeper]

I was always under the impression that in order for the alternator to produce current it needed a steady 12v reference from the battery etc. Recently, however, I have had my batteries negative cable come disconnected a few times (cheap terminal; i got a new one now) and the car would run fine until shut down, then obviously nothing.

Any thoughts? I don't have a voltage gauge so I'm not sure how much the alt is putting out when there is no batt. Is it bad for the voltage regulator or anything?

[ckiesman]

idk, but my parts car (93 festiva) and my old s10 did the same thing

[LoneManWolf]

I don't know how true this is
but i was told this can be very bad for electronics on a car, stereo, computer and such.
Which would depend also i suppose on how those things are grounded i guess...
as for it running when the negative battery cable is taken off that's how i was taught to test a alternator

[JoDan]

The car will run w/o battery but its pushing hard to produce enough current to run everything which will eventually ruin an alternator... thats why its better to charge a battery instead of jumping so the alternator doesn't have to make up for the lost battery voltage

[Grey Vw]

I don't know how true this is
but i was told this can be very bad for electronics on a car, stereo, computer and such.
Which would depend also i suppose on how those things are grounded i guess...
as for it running when the negative battery cable is taken off that's how i was taught to test a alternator

Thats also how I was taught.

[Pu241]

Anyone got a good explanation as to why this is so?

I was under the impression that the field had to be "excited" by the battery in order for the alternator to produce current.
In this case once the electric field in which the armature is rotating is "excited"(built, established, generated whatever term you want to use) the 12 volt source/battery is removed. At this point could the alternator be considered "self-exciting" and continue to produce output?

[speedoholic]

To check to see if you have a bad alternator, I have always unhooked the battery while running. If the car ran with the battery unhooked, the alternator was good but if it died as soon as you unhooked the battery, the alternator was bad.

[TominMO]

I thought the battery only spun the starter, then the alternator's rotation via the belt ran the motor, and therefore kept the alternator running too.

And John, let's have no more talk about self-exciting, OK? Unless you want to take it to the Arena.

[speedoholic]

The car also draws power from the battery while it's running but it's constantly getting replenished by the alternator.

[LoneManWolf]

Anyone got a good explanation as to why this is so?

I was under the impression that the field had to be "excited" by the battery in order for the alternator to produce current.
In this case once the electric field in which the armature is rotating is "excited"(built, established, generated whatever term you want to use) the 12 volt source/battery is removed. At this point could the alternator be considered "self-exciting" and continue to produce output?

it does it b/c it does it lol
that's the only explanation i have for you
i also know that if u have a bad battery that won't hold a charge the car will run once u get it started... say from rolling down a hill and popping clutch until u stop it
i drove 80 miles home like that one day
battery was dead as a doornail but as long as i didn't cut the car off i was fine

[gauge_half_inch]

the car will run without a battery but without a charged battery, the alterators regualtor sees a dead battery and fields the coils in an effort to recharge the "dead" battery. this causes voltage spikes when running, when the engine idles it causes alot of drag on the poor little engine and the alternator can not keep an even voltage.

[skeeters_keeper]

Thank you, gauge! That is exactly what I was looking for.

I was pretty sure that it worked something like that, just not exactly. I figured the alternator would probably be running at full output (trying to 'recharge' the non-existent battery). I guess if run for too long like this it could damage some components due to the voltage spikes, but probably not the regulator itself.

[gauge_half_inch]

its good to see 30K in education isnt going to waste. im a auto tech at toyota right now.

[AlaskaFestivaGuy]

I believe that Speedoholic's explanation is correct. The battery is a "middleman" between the alternator and devices that consume current, including the ignition system.

Airplanes are different -- the battery is used ONLY for starting (after turning on the "battery master" switch) and for emergency power after the alternator fails. The switch can be turned off anytime after starting with no ill effects, though most people leave it turned on to be ready for an emergency restart. The ignition system, however, is separate and driven by something called a "magneto," which also incorporates a distributor. For safety, there are two independent ignition systems, each with its own magneto and spark plugs. Either ignition system can be disabled to check that this other one is working; this check is always performed before takeoff so you know you have a backup available and for the little bit of extra power that comes from having both spark plugs firing in each cylinder.

[AlaskaFestivaGuy]

$30K in education going to waste? I've got two engineering degrees and 30 years of industrial hardware/software engineering experience working what's classified as an entry level job, but is far from that. Nobody wants to hire experience any more, or they want it, but don't want to pay for it. Think about that the next time you board a 737 and notice the youthful person in the "right seat" in the cockpit. In all likelihood, that first officer is making only 1/3 to 1/2 of what your average UPS truck driver makes. And airplane mechanics top out at around $20/hour with 30 years of experience.