Re: Battery switches

[Richard Welty <rwelty@domain.elided>]

On Tue, 14 Jan 2003 12:57:44 +1100 Stuart Thomson <stuart.thomson@domain.elided> wrote:
> Now whilst the engine is running there is no way to cut the power to 
> the coil (as the alternator is earthed through the body), so my battery 
> isolator switch does just that, nothing more, it won't stop the engine 
> running.  I figure that if I've stacked the car seriously enough for 
> someone to pull the isolator switch there's a fair chance the motor 
> isn't going to be running anyway.
 
> Does anyone know how I can make it work for both though??

i've never seen a good solution with the single pole switch.

the mythical "correct" switch is a 3 pole switch. one pole is for high
current, and is the one you connect the battery through. the other two are
low voltage, and are wired thusly:

the one which follows the battery connection (that is, on at the same time
the battery is connected) is used for the low voltage coil wire. when you
cut the battery, you also cut the coil.

the other pole is inverted in sense, it is disconnected when the battery is
connected. you connected it to the positive connection on the alternator,
and the other side connects to a resistor which goes to ground. when the
battery is cut off, it causes a rapid collapse of the field in the
alternator.

richard
--
Richard Welty                                         rwelty@domain.elided
Averill Park Networking                                         518-573-7592
              Unix, Linux, IP Network Engineering, Security
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