I'm about three quarters of the way through my FED build, and starting to tie down some of the details. My home track is IHRA sanctioned. I'm trying to minimise anything electrical on this thing (and no electronics) to make it as era-correct as the IHRA regs will allow. The IHRA rules require a master switch to shut down all electrical power on the vehicle. This makes sense... I could readily see myself doing something like this: INSANE CRASH! NITRO DRAGSTER! MELTDOWN DRAGS! BYRON DRAGWAY! (youtube.com) (though truth be known it would be a brave track official who would step up to two smoking slicks to turn off the master). The battery on the FED is only running the starter (no push starts in IHRA ) and a water temp gauge. Wiring in the master switch for that was easy enough. It got me thinking though - turning off the battery will do very little given that I am running a magneto. I figure that a simple solenoid will do the job. When the master is off, the solenoid closes and earths the magneto P terminal (in parallel to the ignition on/off switch in the cockpit). When the master is on, the solenoid opens and the magneto is free to run. Thought I would check in here to see how others have done this. Open to suggestions too please on a high-quality 12V solenoid that will handle the magneto primary back voltage (around 200V or so) and a lot of vibration. Would need to be power-to-open type. Cheers, Harv
Use a 5 pole relay. Connect magneto to normally closed side to ground. When you switch on master have it energize relay and break ground to mag. When you shut master off it will apply ground to mag and kill it.
im thinking if ya use the regular battery/kill switch that has the 2nd circuit for alternator , that 2nd circuit could be used as a mag ground miss you dad fabricator john
Isnt a magneto grounded when ON? Consider the relay orientation vs acceleration. Look at what g load the relay will take.
Right, this will work, use a standard Bosch type relay: Connect 87a and 85 to earth/ground. Connect 30 to the magneto kill wire. Connect 86 to the wire from the hot side of master switch.
No. When a magneto is grounded, all power is to the ignition is gone. Just like the ground strap on a Briggs & Stratton lawn mower engine, It kill's all ignition power.
That would make for an open circuit when switch is off. That’s why 4 pole switch’s say not for mag use.
Thanks all. You can use a 4 pin relay, but it has to be "NC" (i.e. turn the power on and it opens, whereas most relays are "NO"). This is an example of a 4-pin NC: 4 PIN NORMALLY CLOSED RELAY WITH PRE WIRED HOLDER 12V DC 20 AMP NEW N/C | eBay Anyone recommend a manufacturer of either a 4-pin NC or a 5-pin relay please? Looking for something good for up to 200V, and robust enough to survive FED vibration. Prefer something that uses ring terminals, but that might be pushing my luck. Locally the best I know of is NARVA, but open to suggestion. .NARVA does a heavy duty 4-pin NO version, but not a 4-pin NC or 5-pin. Narva HD Relay Normally Open 12V 4 Pin 200A 68022 9314464680229 | eBay Cole Hersee do a nice range of heavy duty relays, but they are high-amp starter solenoids. Cheers, Harv
I was referring to the suggestion that this switch alone by a few is all you need. But yes, adding a relay would solve the problem. What I don’t know. Is this common practice by racer’s and or acceptable?
All good... that's the exact switch I am using That's what I don't know either. I figure there are some guys here who have done it before, and probably smarter than I would have made it. Cheers, Harv
No need to make it over complicated with relays and what not. You can get switches specifically design to kill all electrical power and the magneto, https://www.flamingriver.com/batter...0-combination-magneto-and-battery-kill-switch
Hey Harv, have you checked with IHRA regarding using a magneto? If they are allowed, doesn't the cut off have to be accessable by track staff? Not trying to dampen your enthusiasm, just don't want you to have to change a load of stuff later.
Aha! that's the solution. Many thanks. Looks like the wiring runs would be near identical to using my existing switch and a relay, so no harder than what I was thinking of doing. Just need to get over the $350 Aussie Peso pricetag I started out with the IHRA rulebook, copy and pasted it, then deleted everything that did not relate to a FED. As the build has progressed, I've been deleting the stuff that complies from the list. Not much to go now. The rules allow magnetos, with not much guidance: Each car in competition must have an ignition switch or magneto “kill-switch” in good working order, located within easy reach of the driver. Magneto “kill-switch” wiring must either be routed outside the frame rail or enclosed in a 16-inch length of thick walled steel tubing in the flywheel bell housing area. I'm all good there - magneto kill switch wiring is nowhere near the flywheel, and switch is located on the dash. The rules also require: MASTER CUTOFF: Mandatory if the battery is relocated or is specified by class requirements. It must be located on the rear of all entries and must break the positive side battery supply to the competition vehicle. If the switch is mounted to facilitate a push or pull activation, it must be positioned in a way where “off” is in the push position. If the switch is mounted in any other fashion, it must be labeled in a way that is clearly identifiable as to which way off is positioned. Plastic or keyed switches are prohibited. I meet this requirement as written, but I'm not comfortable with the intent... it aims to cut all power to the motor. Without a magneto earth, I'm still running. I could Smokey Yunick the rules (only comply with what is written, not the intent) but feels right to comply in this case. Cheers, Harv
I see, said the blind man who couldn't really see at all. Sorry, couldn't resist using that old chestnut. They only magneto I've had anything to do with was in an old timber 'putt- putt' launch with a single cylinder Clae 2 stroke. To shut it down there was a switch that would earth out the magneto so you need a switch that kills power but also earths out the magneto. You'll work it out.
Yes, I thought the switch that was posted would do the job, I have a habit of thinking out loud when posting. It's how I suss things out to myself and also to anyone reading that doesn't understand why a particular part is required. It's not much use to those that don't know why they need a particular part.
Top Fuel and some Top Alcohol cars, amongst others, don't have that electrical shut down provision. They have a removeable ground wire at the coil that they pull off at start-up. They shut down the engine by the fuel injector 3 way shut-off valve.
In an emergency they still have an electrical shut off that’s cuts ignition, along with a number of other things including deploying chutes. It was a failure in John Force’s recent accident. The electrical trigger went off but because the chassis was bent the distance between the chute and solenoid decreased and there wasn’t enough throw to release the chute.
You're absolutely correct ..... I forgot about the Electrimotion system that is now mandatory for these classes.
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