Check alternator by removing Battery cable?

[BeardedBlues]

I have a 74 EB with battery issues. I just took off the negative battery cable and the engine died. Does that mean that the alternator is dead? Or possibly that the alternator wiring is incorrect?

 

[bluesbish]

that is not really a good way to test the charging system. but yes, the engine should stay running if the alternator is putting out anything. mine always did anyway. I would suspect a problem in the regulator or the wiring. that is where I always found problems on the original style charging system. very seldom had to replace the alternator itself on that style.

 

[bmc69]

It should stay running if you take the positive cable off..but as already noted..its not a good way to test the alternator.

A 10 dollar Chinese voltmeter will tell you if your alternator is charging. Simply measure the voltage on the battery before starting the truck (it won't measure much less than 12.2V if it still has enough capacity to still crank it over and won't be much over 12.6 if fully charged) and then measure the battery voltage after it starts..where you will see it fairly quickly climb on up right on past 13V if yr alternator is functioning.

 

[Broncobowsher]

I have a 74 EB with battery issues. I just took off the negative battery cable and the engine died. Does that mean that the alternator is dead? Or possibly that the alternator wiring is incorrect?

It means you spiked the alternator. Which is an easy way to kill a perfectly good alternator. removing the cable while the engine is running proves nothing. Harbor Freight usually has a digital volt meter on sale for under $5. That will be a better way to figure the charging system (both old and possible new problems)

 

[dlong]

I had a similar issue prior to installing a 3g alternator. With the engine running battery was reading less than 12 vdc. Once I rev'd the engine to around 1600 to 1800 rpm's the alternator will start charging 13.8 vdc. If you have the money do the 3g upgrade you won't be sorry. My battery now charges at idle. There are plenty threads on here just search "3g alternator"

 

[half cab]

Why did old school mechanics do this "Check alternator by removing Battery cable" all the time?I have seen them crank one auto remove the batt from the running one and crank another auto.This was a common thing to do back in the day.Just asking because I have seen it done many yrs and never knew an atl. that went bad from it? I will say this isn't the first time I heard that it wasn't good for the alt. though. Again I'm just asking.

 

[73stallion]

i do it too, never spiked an alternator. but now that someone mentions it, it is possible, and i won't do it again.

 

[half cab]

i do it too, never spiked an alternator. but now that someone mentions it, it is possible, and i won't do it again.

Yep, I hear ya!! I knew a guy about 30 yrs ago was downtown Memphis and had way too much to drink and hit a curb and tossed the batt into the fan and well you know what happened!!He put the batt in the trunk and drove to Tupelo(100 mi.) What did happen was after a few months that battery acid eat the trunk out of the car.Far more $$$ than a new batt and alt!;D

 

[Airmapper]

I was always told that removing the cable was the way to do it, but after the guys on here told me different, and most importantly told me why, I won't be doing it anymore.

I have a digital multimeter, so I should never need to do it the old school way. My '70's battery reads about 14.2V at idle after the 3G upgrade.

 

[deltarat]

My bother-in-law had 3 tractors and only one good battery and he would crank one and put the bad battery in it and move the good one to another one and so on. I told him it would spike the alt and kill it.He said we do it everyday. I ask him how many alts does he replace and he said, "them damn alts aren't any better than the batteries. We have to replace them every month or so. Good thing they are in warranty."

 

[Socal Tom]

Why did old school mechanics do this "Check alternator by removing Battery cable" all the time?I have seen them crank one auto remove the batt from the running one and crank another auto.This was a common thing to do back in the day.Just asking because I have seen it done many yrs and never knew an atl. that went bad from it? I will say this isn't the first time I heard that it wasn't good for the alt. though. Again I'm just asking.

back in the day they probably didnt have the same solid state stuff that alternators do now, and mechanics make money when they sell you things.
Tom

 

[JMurray]

http://www.youtube.com/watch?v=cxNK7N0ZdDs
I use a voltmeter but as you see this is a cheap alternative.

 

[BeardedBlues]

Thanks for the help! I tested with multimeter and with battery at 50% charge the meter showed a constant 12.25 volts with motor stopped, started and revved up. Going to clean connectors and get battery fully charged before I head to Junkyard for a 3G.