Latching Battery Relay

[Bitsyncmaster]

I've thought about installing a battery switch mostly for safety if an electrical issue occurred (accident, shorted light switch, engine fire, etc). But I never liked mounting a switch to the battery cover since your using #4 or #2 AWG wires that are not flexible. You could mount your switch to the bottom of the battery "box" but then you need to remove the switch knob to access the battery "box".

So what I did was buy a latching relay which stays in the open or closed position after the control voltage is removed. The "relay" I purchased is really a Ford type solenoid relay used for the starter motor but has a little more mechanics inside to make it latching. I mounted this relay to the floor of the battery box and made up one new battery wire with a fused auxiliary circuit to power the relay even with the battery disconnected. I'm really please with how that layout came out.

You could just use this latching relay with a DPDT center off spring loaded switch which could be mounted anywhere you want. The relay control current is 3 amps so small wiring can be used.

[Bitsyncmaster]

I decided to use a micro to control my battery relay. This would let me use a simple SPST push button. I also monitor the inertia switch so it can also turn the battery power off. Since I turn the battery power of with the inertia switch set, I removed the fuel pump "-" connection and ran it to the frame for ground. That eliminates the high current in the inertia switch and one connection at the washer bottle connectors is also eliminated.

Now you should never disconnect the battery if your engine is running since that most likely will damage the alternator and a lot of electronics in the car. I think your engine will continue to run if you do that anyway since the alternator is still powering the cars circuits. So my micro has an output driving the first AUX relay ground signal that turns off that relay before disconnecting the battery. That AUX relay shuts down the engine and other circuits.

I placed an order for 4 of the circuit boards I designed for this "battery relay" micro. Since there could be a direct short of a battery wire in an accident, I power my micro through a diode and 100,000 uf. capacitor which acts as a battery. I can get 7 relay operation from that capacitor with no battery power.

I mounted that circuit (PCB and capacitor in the drivers side right knee pad.

[Bitsyncmaster]

My micro board is always powered and draws 200 ua. so the software is looping checking both inputs (inertia switch and user control push button). Each of those inputs is sampled every 100 ms. and they need to see 10 valid signals before my board drives the relay. What that does is filter any noise and requires a one second push of the the user push button. It also delays the inertia switch for one second so the doors have time to unlock.

I removed my dash rheostat and mounted my user push button in that location. My micro board also has an LED driver output but I have not implemented that yet since my current push button is not illuminated.