Wiring question: battery cutoff and magneto

[Don Elzinga]

Anybody have a link to a wiring diagram for an F5? I'm wondering how the engine is turned off via the emergency battery disconnect switch. Do you use a solenoid that grounds the killswitch wire when it loses battery power?
Thanks,
Don

[kea]

You need the master switch made for vehicles with an alternater. The Mag needs to be grounded to shut the engine down.
This switch has extra connections on it, more then just the two large poles.
When the battery is disconnected (key turned to off position), at the same time a connection is opened that you use to "kill" the magnito output.

[Don Elzinga]

Keith,

OK, that will be easier than wiring up a relay. Do you have that 6J1051 in stock?

Don

[kea]

Yes, in stock.

[B17overhead]

Hi there Don and friends. I hope ur solo car is coming along Don.

I saw this idea first on Bob Fox's DSR years ago:

Use a circuit breaker instead of a manual-only disconnect sw.

With a 2-stroke, add a relay to kill the ignition to gnd. Cheap and light to add a relay.

If one uses about a 60 Amp breaker for the main disconnect it will help keep the wiring from catching on fire if there is a short and you don't get to the kill switch in time. The beaker will react near instantly BEFORE the wires heat up. Using a breaker should allow you to more safely run smaller gauge starter wires also- like #12.

I bought a couple of dual breakers from an electronics surplus store in San Jose for about $10 each. Reason for getting 2 was so I would always have a spare that perfectly fits the tiny little panel I made for it.

I have a pair of 18 Ampere-hour sealed AGM batteries on board that need to both be disconnected at once to be legal: one bat for data recorder and starter and the other bat for the O2 sensor heaters and giant electric fans plus electric water pump.

The reason for 2 bats is that if I ever run the fans too long and discharge the battery, I can still start the car. It also increases the total capacity on board to about 36 Amp-hour so I am go much longer before charges.

This solved a problem for me that I could not solve without Mickey Mousing using a conventional "kill" sw with both bat returns tied together(may satisfy the rule but not 100% safe).

Incidentally, I designed this system before the advent of affordable and safe Lithium-lead batteries for racing. I just bought a 34 A-hr equivalent single battery for another car that weighs less than 1/2 of one of my lead acid 18 A-hr bats..

In any case, using a circuit breaker is cheap and offers one level of added protection, especially for cars that typically have no fire system, as in solo.
-Chuck

[rickb99]

Just grab a 6j1051 and be done

[B17overhead]

Agreed that a manual disconnect is quick and dirty, but with a tiny bit of extra work, a breaker will gain you extra protection.
Also, remember that we are considering the case of formula and sports racers with no fire suits or fire systems.

The ever popular manual switch only buys you legality with little practical protection from damage with real world faults.

You will probably never ever be fast enough in a crash or even standing in your garage with your hand already on the manual discon switch to prevent melted insulation or welded connections/switch contacts if any of the battery supply wires go to ground somewhere.

A dual breaker as I showed with trip levers linked together is also about the only way to properly deal with 2 batteries on board.

He might not be the first, but I think Bob Fox was brilliant to use this other approach.

[10rmotor]

These are the breaker type switches that I and others have used in DSR for years with no problem. Available in many different amp ratings and can be easily panel mounted just like any other switch.

http://www.aircraftspruce.com/catalo...clickkey=32749

[rickb99]

.....but I think Bob Fox was brilliant to use this other approach.

A name to respect and consider what he uses.

[Rick Brannon]

These are the breaker type switches that I and others have used in DSR for years with no problem. Available in many different amp ratings and can be easily panel mounted just like any other switch.

http://www.aircraftspruce.com/catalo...clickkey=32749

Good choice additional information about D.C. breaker application http://www.miniature-circuit-breaker...ou-never-know/