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-   -   What’s this resistor for? (http://forums.pelicanparts.com/porsche-911-technical-forum/1180985-what-s-resistor.html)

stubble88 08-01-2025 01:54 PM

What’s this resistor for?
 
X race car.
I see this resistor looking thing that’s grounded and the other end hooked up to this cutoff switch. Any ideas why this would exist?
Thanks
http://forums.pelicanparts.com/uploa...1754085236.jpg
http://forums.pelicanparts.com/uploa...1754085236.jpg

ischmitz 08-01-2025 02:47 PM

Never seen a battery cutoff switch with the 4 spade terminals. What are they for, no idea.

And the resistor looking thing is a 10W or 25W ceramic resistor. Can you make out its value? It should be printed on the ceramic housing. Something like 10R or similar.

It’ll tell you how much power it will turn into heat: For example a 10 Ohm resistor will result in 1.4 Amp at 14 Volt battery voltage (engine running and alternator charging) and this will burn 1.4A * 14V = 19.6 Watt of power and get pretty hot in the process.

If you leave that resistor connected to the battery it’ll drain a fully charged battery in about a day to the point where it won’t crank anymore.

Again, not clear what this is for. In old Kettering ignition systems there was a resistor to prevent the coil from burning up when the points were closed and engine not running. But I can’t fathom what it would do related to the battery cutoff.

TimT 08-01-2025 02:50 PM

Thats basically so you don't fry your alternator if you shut the car down with the cut-off switch

TimT 08-01-2025 02:53 PM

http://forums.rennlist.com/upload/cu...witch_copy.jpg

How it would have been wired

More info linky

stubble88 08-01-2025 03:00 PM

Gotcha. I had to replace that switch because it was glitchy. Got one without the four terminals. How else can I wire this up?

stubble88 08-02-2025 03:09 PM

So this is only beneficial when cutting power via cutoff switch? If one uses the ignition first to cut power then the cutoff, then there is no risk of frying the alternator?


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