Battery Kill switch

[Bitsyncmaster]

Just thought of a possible problem with a battery kill switch (or relay). If you hit the kill switch with the engine running, then your alternator will still provide power to all the cars electrical systems. I am thinking of some ways to kill the ignition when the battery is disconnected.

In case of an electrical fire, you may not think to turn the key off first.

[Silverbullet]

Get the negative side of the coil to go to ground....

Craig

[dmc]

The good switches nowadays have a separate set of contacts that you wire the alternator through.
They will have two large studs and two smaller ones.
They are available from painless wiring among others.
Not your typical Chinese stuff.

[David T]

I would hope in the case of a fire you would shut the motor off to shut the fuel pump off. A lot easier than going for the battery switch. Let the Fire Department worry about the battery!

[Bitsyncmaster]

I thought of a fix. I'm building a circuit board to run my battery kill relay so I just added a driver to connect to the AUX relay ground. I will keep that driver on so the relay is normal (grounded) if the battery is still connected. Then I can turn that ground off (which will kill the ignition ECU power) before I energize the kill relay.

[DMC5180]

I thought of a fix. I'm building a circuit board to run my battery kill relay.

Of coarse you are! :biggrin:

[Exolis]

What about a relay that will cut Rotor Field current? Then a switch to disconnect B+ on the Battery.

[Bitsyncmaster]

What about a relay that will cut Rotor Field current? Then a switch to disconnect B+ on the Battery.

There are lots of ways to really "kill" the engine but using the existing AUX relay ground control pin seem to be simple. You just need an MOSFET to drive ground so that takes no power driving the gate of the MOSFET.

[David T]

Go ahead make it complicated. Now when nothing works you have a lot more to try to figure out! Before you go nuts with this see how they handle the problem in small aircraft. They use a remote switch to run a relay. The remote switch is a special 2 part switch so you can still run the motor without the alternator. Clever little circuit but they are using a magneto (actually 2) for ignition.

[Ron]

What about a relay that will cut Rotor Field current? Then a switch to disconnect B+ on the Battery.Once the voltage regulator has kicked in, killing the field's supply will not do any good (self-exciting regulator or not).

[Exolis]

Once the voltage regulator has kicked in, killing the field's supply will not do any good (self-exciting regulator or not).

Not sure if I understand clearly or if the Alternators made in the 80s were vastly different then today. If there is no current going to the Field rotor, then it won't charge since there is no opposing magnetic field. The Voltage Regulator simply acts as a PWM to keep the voltage at no more then 15V when the speed changes.