Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!mintaka!streeter From: streeter@theory.lcs.mit.edu (Kenneth B. Streeter) Newsgroups: sci.electronics Subject: Re: Car Battery Rechargers Message-ID: <1990Oct16.025415.22005@mintaka.lcs.mit.edu> Date: 16 Oct 90 02:54:15 GMT Sender: daemon@mintaka.lcs.mit.edu (Lucifer Maleficius) Reply-To: streeter@im.lcs.mit.edu (Kenneth B. Streeter) Distribution: na Organization: Laboratory for Computer Science, MIT Lines: 34 In article <1990Oct15.202407.13654@mthvax.cs.miami.edu> wb8foz@mthvax.cs.miami.edu (David Lesher) writes: >NEVER disconnect the battery on a running car. This is referred >to as a "load dump" and generates the worst possible transient >voltages. The battery is an essential low impedance element at >frequencies above DC. Without it, the inductance of the field is >such that the electronics will be history before the voltage >regulator can get things down to where they belong. >The best way to avoid problems is patience. Hook up the cars. >Sit and let the weak one charge for a while. (10 minutes maybe) This will give better results, and is practically essential in very cold weather. The jumper cables will simply not carry enough current to start a car -- a typical jump works by charging the "dead" battery somewhat so that the "dead" battery assists in the starting. >Once the other car is running, you can let the good car idle >down, and maybe if you want, turn on all of its loads: headlights, >heater, etc. Then disconnect the cables. It is best to disconnect the jumper cables shortly after the "dead" car has been started. Leaving the jumper cables connected when both cars are running makes the alternators "fight" one another for the correct voltage. This is generally best avoided, but it won't do any harm for short periods. -- Kenneth B. Streeter | ARPA: streeter@im.lcs.mit.edu MIT LCS, Room NE43-350 | UUCP: ...!uunet!im.lcs.mit.edu!streeter 545 Technology Square | (617) 253-2614 (work) Cambridge, MA 02139 | (617) 225-2249 (home)