Kill switch on a generator car (Page 1 of 2)

It's really easy. One side gets the positive battery cable going to the battery, and the large wire from the alternator. The other side gets everything else. The large starter wire, ignition wires, the fuse box, literally everything else. No need for resistors.

Easy peasy, and Bob's your uncle.

The generator will be able to dump it's power to the battery as it's winding down, which will be fine. Just be aware the output post of the generator will be hot at all times, so cover it appropriately.

Lots of alternator/generator and starter posts are hot all the time. I isolate my starter with a remote relay but the alternator post is hot all the time.

At first I thought you were talking about like having a gas generator separate from your engine. Doing like locomotive hybrid thing.
Then realized you were talking about the alternator.

By rules its not kosher to keep alternator bypassed the kill switch. aka keeping post hot.
But with computers, you dont really want to cut battery per rules. The spike will kill all microelectronics.
So best per rules connect the alternator though that secondary switch, so when you trigger it, alternator and battery cut off. Just have a resistor on the alternator at all times. so when you do flip the switch, energy is dissipated.

This only works if secondary circuit can handle 30+ amps, cause alternator can put out that much. Specially if battery is low.
Alternatively, if you can cut the field coil to the alternator, that will work nicely too. that be better solution. Just run field coil through the switch.

The only thing other than the points/coil will be gauges. Not sure if they will be damaged.

Will the resistor setup for a generator be the same as the resistor setup for an alternator?

OMG, are you saying you have an actual generator/dynamo not alternator in your hooptie?
On those the regulator is the issue. So need to cut between the generator and regulator.  You can clamp the generator output. Just dont go too crazy with the resistor.

As I read it, everything running on electrical power must be interrupted by the switch, but nothing directly about the alt except a warning about the car being able to run off the alt after the battery is disconnected if the wiring is set up wrong.

3.G ELECTRICAL & MECHANICAL REGULATIONS 

3.G.1 Master Electrical Kill Switch. All cars must have a racing-type master electrical kill switch easily turned both off and on by the belted-in driver. The control for this switch should be red; the OFF position should be clearly indicated; the switch should be easily accessible from outside the car; and the switch should be clearly marked by a three-inch or larger lightning-bolt symbol. All electricity must be interrupted by the kill switch (if you don't do that, the engine may still run off the alternator even after the battery circuit is disconnected). Don't put the switch where it's likely to be hit by another car in traffic or crushed in an accident.

This is how I wired our car based on how I read the rules. The battery is connected to the alt, but the alt 'shuts off' with the master switch and the engine dies when the master is switched off.

Bill

If you want to make sure the car will shut down interrupt the coil source. No spark no run!  Just interrupting the field wire won't necessary work.  I can unplug my alt and it will keep the car running once it gets the field signal it's on till you shut the car off.

Unless the disconnect switch is actually IN the battery shutting down the positive post, then there will be power in a wire/cable routed somewhere in the car, and even if that were the case, one could still have the alt running everything with said post 'off'.

Again, the way we read it, as long as the engine and every electrical item will be 'shut off' with the master (pumps, fans, lights, alt, radio, GPS, doomsday device, Kerig,....) then all is well with the world. 

Yes, some way to buffer the load would work too, but just adds one more thing to fail.

We could be wrong on this.......

Bill

We don't see the grey, maybe others do.

There is no requirement for the battery to be inside the main cage area, so it could be balled up in the front or rear crumple zone, so a cut off switch will be of no use to stop a short.

In our opinions, with proper cable and terminal protection, the risk is minimized and with less things on the car that could fail causing the car to stall on the track. 

The question is has anyone failed tech because the battery and alternator were directly connected but in a way that the car still shut off with the master disconnect?

Bill

Just to be clear, I understand you can't cut all power. I did write that in my second post in this thread.

As far as the Lemons rules go it isn't clear. If you race in some other series, they want the alt disconnected. If you're doing a new kill switch and considering other series seems it's a simple choice to me.

If you do the battery right, the battery, cable and kill switch are all inside the crash/safety cell and protected.

3? years ago at njmp I was told (by someone helping run the event)  the alternator power had to be cut by the kill switch. Our car was wired keeping the alt hot. They were rushing and we flew through safety inspection. I don't know who it was. I'm not sure they'd go around checking if your alt has power with the switch off or even if he was right.

Rule clarification would be nice, though I don't want rulebook page creep either.

My thoughts are usually what I can come up with as worst case scenario. I put the battery in as far as comfortable to keep it safe in a crash. I've been telling people not to switch on their fuel pump for safety reasons. There have been some fuel pump feeding the fire stories because they forgot to hit the kill switch or turn the fuel pump off. Maybe seems stupid or isn't given a second though at the time.

Another year we were racing we had a battery cable short out over bumps. It killed one of the diodes in the alt. It could have been much uglier. That's in big part why I'm considering the battery circuit breaker. If the car gets stuffed in a crash and the battery is shorting I'd want a way for it to trip. BMW has battery cables with charges in them that can be popped in a crash...I don't think I'm way out in left field here.

If doing small things can make the car safer I'm all for it.

Sorry for the sorta hijack fpr.

Dont forget to add start bypass, cause you will have a bad time if you dont.

Alternatively you can wire relay to the alternator sense. So if alternator not putting out energy, then relay is off.
Also need start bypass