Main battery disconnect

[johnneilson]

Wayno,

due to the fact that alternators usually have a pos output wire and the circuit is completed (neg) case ground, you need to control the pos side. The wiring is simple, wire the alternator to the battery side of the switch. This way, the motor and other devices are disconnected from the power source. There are switches (battery disconnect) with two sets of contacts (DPST). I have had them fail mechanically and not function.

Something to consider, I prefer to mount the discon switch as close to the battery as possible. This means it is not at the extremedy of the car. I have used fire system remote cable and handle for this to actuate the switch. It has a couple advantages, single entity to route to location and in case of fire it is not a hot wire that can cause problems (from battery).

J

[MAZDA1807]

On my car I have the alternator exciter wire hooked up to my ingnition switch and the main disconnect on the negative side of the batt. So when the main is turned off the exciter looses its ground which stops the alternator from creating power and everything is dead. Peter

[Queeziryder]

Especially for Dr G

We haven't pad +ve earth for over 50 years 

Neil

PS
Serious point
I prefer solid state double pole disconnect 

[Dr Goggles]

Especially for Dr G

We haven't pad +ve earth for over 50 years 

Neil

PS
Serious point
I prefer solid state double pole disconnect 

Yeah, I know, but read the Midgets sign off line.......

and , you need to understand I have baggage about some of the fine automotive products from the UK...I get the Heebee Jeebees if I watch Inspector Morse..... it's nothin personal, we are on your sideafter all.

[Jon]

Any info on the solid state isolation switch options would be good thanks.


Thanks
Jon

[maguromic]

Jon,  This is the one I use, but you can find others for a lot cheaper that does the same thing.  The offshore boat racers use them and have a plethora of suppliers.  The part is not rocket science, if you are handy, it uses MOSFET transistors and  the whole system could be put together in a weekend.  If there is enough interests I can design and sepec it out. Tony

http://www.motorsportcables.com/battery_isolation.htm

[Milwaukee Midget]

Yeah, I know, but read the Midgets sign off line.......

and , you need to understand I have baggage about some of the fine automotive products from the UK...

Whittling up a Prefect supplied insufficient catharsis?  Okay, then - if I close a deal on an MGB-GT, you can operate the torch and we'll turn it into a ute. 

[gande]

Elmo
There is always the Don and Marty West plan. Mechanical fuel pump and gauges, magneto. No battery, don't need no stinking disconnect.

[fastman614]

The biggest issue in regards to battery shutoff switches or actuators of switches was to standardize the location on the vehicle to where first responders are instructed to go for the purpose of making sure the electricity is shut off.

The "why" of this requirement is also due to the fact that the rules, as presently written, allow for the use of an electrical shutoff to an electric fuel pump as being a positive fuel shutoff. There have apparently been occasions over the years where an engine in an overturned car was NOT running but fuel was being pumped out through the carburetor(s) due to the electric fuel pump remaining in operation. Wrecked cars often seem to have metal that gets bent towards ANYTHING that has the abilty to make sparks - especially if it is electrically live.

We actually played with lighting gasoline on fire with sparks from a single AA cell... and we easily ignited the gasoline (fumes, that is)... so... It has to have been some kind of problem id=f it got wwritten into the rules..... and again, most of us would like to know the reasoning behind or the explanation of the events that prompted the rule in the first place.... and.... the SCTA/BNI is, like most, if not all, sanctioning organizations, rather tight lipped about this sort of stuff....

[Jon]

Thanks Tony, figured it would be MOFSET.

Car is not 100% cold with this, the wiring from the isolator to the control switch is still hot.
It's very cool though and risk of spark is greatly reduced.

Was thinking of running something like this from my tilt switch (bike) to isolate everything & turn off motor when I fall over but I need the power to pull the chutes automatically.

Could build a delay into the tilt switch to isolator circuit but I promised myself that I was going to build by KISS principles.



Thanks
jon

[Elmo Rodge]

OK. Here's what I came up with. What am I missing? By the way, thanx to everyone for their input. It has been quite helpful.  Wayno

[4-barrel Mike]

Run your fuel pump with higher amperage by using a relay: power the relay off/on thru the inertial switch.

Mike

[Elmo Rodge]

Run your fuel pump with higher amperage by using a relay: power the relay off/on thru the inertial switch.

Mike

Mike, I'm nothing on electrics. Is there a particular relay I should look for? Oh, and the battery goes to ground too. Wayno

[4-barrel Mike]

A standard auto parts store 20 (or 30)  amp relay will work.  Wire it thusly:



Pole #30 is the main power, it can come directly off of the starter relay (you will use one, won't you?) or where ever it's easy (short distance) to wire.  Put a 20 (or 30) amp fuse in the line.

Pole #86 will have your inertial switch between the relay and the switch (you will have a fuel pump on/off toggle won't you?).

I assume the "terminal box" will have fuses, right?

Mike

[MAZDA1807]

Wayno, if you're using a One wire alternator, make sure you don't hook anything directly to it (example: fuel pump, msd, ect) because the alt supplies voltage with out an exciter wire. In other words, if the msd and fuel pump were connected directly to it the car would still run with the switch shut off after the car was started. Peter