I know, done to death, but one more kill sw question...

[Spinnetti]

My switch isn't wired right (doesn't shut down the alternator), so I need to fix it. I understand about needing a fancy switch to not blow the diodes, but couldn't you just interrupt the wire from the key (in addition to interrupting the main battery cable) to shut it down?

TIA..

 

[JoshS]

That's exactly what the fancy switches do. When you move the switch from on to off, two circuits open (the main battery circuit and the ignition circuit from the key) and a third circuit closes (to dump the alternator output as it spins down to ground through a resistor, to protect the alternator.)

 

[Spinnetti]

That's exactly what the fancy switches do. When you move the switch from on to off, two circuits open (the main battery circuit and the ignition circuit from the key) and a third circuit closes (to dump the alternator output as it spins down to ground through a resistor, to protect the alternator.)

Ok, but what doesn't make sense is, why the resistor? Every time you shut your car off with the key, the existing circuit manages that - why not just put the key wire through the cut off switch? That's what's got me confused. I don't see why the ballast resistor is needed when the stock systems handle it already ?

 

[pfcs]

You're absolutely right about switching off the ignition circuit thru the secondary kill swx circuit, however a better more reliable approach is to use the secondary swx to ground the switched (-) terminal of your coil if you have one. This results in a much simpler circuit (only one grounding wire running to the coil) instead of running the ignition power supply circuit to the kill switch and back to the ignition. This leaves all consumers loading the alternator while it coasts down and stops supplying voltage, peoperly protecting it. And we all know how unreliable and susceptible to the elements kill switches can be-any misfiring or electrical gemlins with switched ignition being thru a kill switch would make me paranoid about the switch.

 

[JoshS]

Ok, but what doesn't make sense is, why the resistor? Every time you shut your car off with the key, the existing circuit manages that - why not just put the key wire through the cut off switch? That's what's got me confused. I don't see why the ballast resistor is needed when the stock systems handle it already ?

Because normally, the battery and the alternator are still connected to each other when you shut the car off, and the battery acts as the sink for the alternator.

However, when you shut the car off with a kill switch, the battery and the alternator are no longer connected to each other. So the alternator has absolutely no place to drain when the power is cut, without such a ballast system.

 

[Spinnetti]

Because normally, the battery and the alternator are still connected to each other when you shut the car off, and the battery acts as the sink for the alternator.

However, when you shut the car off with a kill switch, the battery and the alternator are no longer connected to each other. So the alternator has absolutely no place to drain when the power is cut, without such a ballast system.

<lightbulb turns on> Ok, I get it finally! Battery is sink. Gotcha -thanks! How about PFCS's idea about just grounding the coil side? that would be handy since its only about 12" from my kill switch.