it says under MYTHS about batteries: "10.6. Test the alternator by disconnecting the battery with the engine running.
A battery as like a voltage stabilizer or filter to the pulsating DC produced by the charging system. Disconnecting a battery while the engine is running can destroy sensitive electronic components, for example, emission computer, audio system, cell phone, alarm system, etc., or even the charging system itself. These damages can occur because the voltage can rise to 40 volts or more. In the 1970s, removing a battery terminal was an accepted practice to test charging systems of that era. That is not the case today. Just say NO if anyone suggests this."
So like I said, old vs new. The alternator puts out a rectified DC signal. That means it was AC but the diodes rectified into DC. there is still a small amount of ripple on the output. with the battery in place, the battery acts like a shock absorber which mellows the ripple out. This ripple can ruin electronics in NEW vehicles. Old stuff like ours aren't affected because the technology is more resistant to the ripple.
Ok this shows it fine. notice it says 40 volts or MORE!!!!! not peak at 18 or 40!
now all you have to do is realize that anything with electronics, and this means your old car with electronic ignition, electronic tachometer, electronic voltage regulator are succeptible to the damage caused by the prehistoric diagnostic method. This also includes any stereo thats been installed, and many many other possibilities.
If you look at a chrysler regulator, does it not say right on it "ELECTRONIC VOLTAGE REGULATOR"???? why is it so hard to accept that it has sensitive components in it??
This also mentions it can damage the alternator as well!!!
so lets see, how old are these cars that dont have alternators?? 62 ish???? wow thats old!! Older than any car I own, so a person shouldnt do this on anything newer than 62 ish , how about that.
when did Chyrco come out with electronic ignition? I think it was 72?? so this includes anything newer than 72, plus anybody that has upgraded to electronic ignition.
when did Chyrco come out with the electronic voltage regulator?? Im not sure on this one, around 70? hmmm but also. most replacement regulators for the pre electronic ones are actually electronic ones inside the old mechanical style casing!!
so its plain to see that anything new enough to have an alternator, or ELECTRONICS, it is NOT ADVISEABLE TO DISCONNECT THE BATTERY WITH THE ENGINE RUNNING!!!
now check back to my original post. tell me its a good idea to remove the battery cable! the arcticle above states just to say NO to this suggestion!, and thats from a boat site!
oh and stumpy, what type of voltmeter are you using?? is it an analog type or a DVOM. An analog type will actually pass the current across a shunt and read closed circuit voltage. A DVOM will read the actual voltage. I suspect youre using some type with a shunt. They are not all the same.
