Question about alternator/Battery

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Coryduran

Coryduran

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I was driving home today when my car died in the middle of the road. I was able to get it off to the side and I realized that I hadn't put my battery cables back into the terminal tight enough when after I was done installing the new starter. Well I fixed that problem and got home without a hitch, but I have a question now, that may just be due to the fact that my belief was incorrect.

It was my understanding that once the car was starter, the alternator took over all power duties, and the battery wasn't needed for any power. This belief would lead me to believe that if my battery had become disconnected while I was driving, my car should have continued on down the road. Am I just incorrect in this?
 
There is an old wives tale I'd like to kill. It is a uh, um, gag......"troubleshooting procedure" where you are supposed to yank one cable off. If the car keeps running, the alternator is "good."

There are several things wrong with this, and the newer the vehicle, the worse it gets.

First, if you yank off a cable while the car is running, a tremendous instantaneous voltage spike can be over 100 volts!!!!! I proved this to some non--believers years ago.

This spike can fail solid state components in your car.

The second thing is, IF THE ENGINE IS RUNNING SLOW ENOUGH the alternator may not be charging (enough) 'specially if the lights, heater, etc are on, so the alternator may not be "putting out" enough to keep the thing going.

If it shows charge OK now that you have the cables fixed, it's OK. One good thing is to check charging voltage---battery up and recharged, engine at "low cruise", voltage after warmup at the battery should be about 13.5-14.5, depending on who's book you read.
 
Thanks. That makes sense and after i talked to some of my family they basically said the same things, so thanks a lot.
 
67Dart273 said:
There is an old wives tale I'd like to kill. It is a uh, um, gag......"troubleshooting procedure" where you are supposed to yank one cable off. If the car keeps running, the alternator is "good."

There are several things wrong with this, and the newer the vehicle, the worse it gets.

First, if you yank off a cable while the car is running, a tremendous instantaneous voltage spike can be over 100 volts!!!!! I proved this to some non--believers years ago.

This spike can fail solid state components in your car.

The second thing is, IF THE ENGINE IS RUNNING SLOW ENOUGH the alternator may not be charging (enough) 'specially if the lights, heater, etc are on, so the alternator may not be "putting out" enough to keep the thing going.

If it shows charge OK now that you have the cables fixed, it's OK. One good thing is to check charging voltage---battery up and recharged, engine at "low cruise", voltage after warmup at the battery should be about 13.5-14.5, depending on who's book you read.
Click to expand...
You are absolutely correct. This is one bad trouble shooting myth that won't die. I have seen a lot of damage from this, even burnt out headlights.
 
The myth is one thing, but I don't think this addresses what happened to you. I still think you have another issue.
 
I dunno I think it does address my issues. My battery cable came loose because it wasn't tight enough and that caused the car to die because there wasn't enough power. The alternator alone isn't enough to power the car, the new stereo in the glovebox and the speakerbox in the back. Makes sense to me.
 
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