a575@mindlink.UUCP (Michael G. Henders) (10/10/90)
On the subject of jump-starting: I remember seeing a factoid floating about, to the effect that some auto engine control computers were vulnerable to a voltage surge resulting from providing a jump-start. That is, if the car providing the boost had one of these computers, it would be knocked out when the car receiving the boost started up. The explanation was that the terminal voltage of the coupled batteries, under feed from two alternators, would rise above normal levels, killing the computer. Can anyone confirm this effect, or, alternatively, lay it conclusively to rest as an urban myth? (At least I don't need to worry; the only computer in my old beast is the organic one behind the wheel. :-) ) Just curious... -- | Michael G. (Mike) Henders | "The quizzical expression on the face of | | Vancouver, B.C., Canada | the monkey at the zoo is due to his | | a575@mindlink.UUCP -or- | wondering if he is his brother's keeper, | | uunet!van-bc!rsoft!mindlink!a575 | or his keeper's brother."
dunphy@col.hp.com (Dan Dunphy) (11/17/90)
Actually, the phenominom is called "load dump". I am a former Delco EE, and we had to protect against load dump. The alternator, cranking out full tilt, spikes to about 80V for several hundred milliseconds, until it's field current dies. This happens when you disconnect the alternator from a heavy load. The other car starting may have this effect. one way to avoid it is to jump with your engine off, or at least turn it off before disconnecting. Don't forget to connect the - cable somewhere else on the car, no to the battery. Sparks during disconnect can ignite any hydrogen the battery has generated.