Solenoid-style master kill switches (for race car)

For the rally car we need to add a master kill switch. I would prefer to use a remote-style setup using a solenoid activated via one (or more) remote switches, vice a cable-pull setup like a road-race car would use. I know there are a few off-the shelf kits to do this kind of setup, but they seem ridiculously expensive. Electrical is not really my strong point, but I know some people basically piece this kind of setup together using more "industrial supply" type of parts.

I know it's not rocket science, but would appreciate any thoughts, advice, setups, etc that you all might have for this kind of setup.

Just to clarify, this is the kind of thing I'm talking about: http://www.bimmerworld.com/Safety-Race-Interior/Battery-Electrical/Electrical-Cutoff-Solenoid-Kit.html

I tend to keep it simple when it comes to race cars. What is wrong with a cowl mounted master switch?

Chas_H wrote: I tend to keep it simple when it comes to race cars. What is wrong with a cowl mounted master switch?

This is a rally car. We have to have an interior-mounted switch accessible by both occupants AND "rescuers" reaching through either door. So of course could do a cowl-mounted setup with a pull cable to another switch inside. We also have the issue that these cars get super-dirty, wet going through stream crossings, etc. So something non-mechanical (which will get gunked up, rusty, wed, muddy) is preferable.

irish44j wrote: Just to clarify, this is the kind of thing I'm talking about: http://www.bimmerworld.com/Safety-Race-Interior/Battery-Electrical/Electrical-Cutoff-Solenoid-Kit.html

Biggest part of the cost of that kit is the solenoid and I'm not sure you could find one cheaply that could handle the required load. Assuming that the switches are wired in series you could add extra switches anywhere you want.

Only problem with that is making sure that one doesn't get bumped accidentally. BTDT with a poorly placed and unprotected secondary switch.

yep, I've found that same solenoid online for about $60. Figure just make sure that the switches have covers on them or are a twist-style unlikely to get bumped.

How many amps is your alternator?

I had a car once with one, but I never looked closely at the setup. Basically the solenoid is just a big relay I think.

I'd guess you need to wire it just like a cutoff switch, so the battery is isolated but so is the alternator charge wire.

Maybe you can run two smaller 2 pole solenoids in parallel? One for starter and one for alt? They would switch off the same signal circuits.

What would be really cool would be to use the main fuse as an additional 'switch'. Blow the main fuse, and bang, solenoid cuts all power.

Here may be a couple options...

Solenoid

Relay

Another solenoid

Be sure to get a solenoid that's rated for continuous duty. Some of those cheap ones are intended for short term (starter) duty.

If you're running a starter you may need more than 100a. What are those manual switches rated for?

In this day & age I would probably go solid state relay (look for surplus). Mount it on a heat sink out of the way.

Kendall

irish44j wrote:

Chas_H wrote: I tend to keep it simple when it comes to race cars. What is wrong with a cowl mounted master switch?

This is a rally car. We have to have an interior-mounted switch accessible by both occupants AND "rescuers" reaching through either door. So of course could do a cowl-mounted setup with a pull cable to another switch inside. We also have the issue that these cars get super-dirty, wet going through stream crossings, etc. So something non-mechanical (which will get gunked up, rusty, wed, muddy) is preferable.

The solenoid is just as mechanical and has a lot more wires running to it from the photos of it. Make it and the associated electrics easy to access and repair. Will you carry a spare?

Has ARA clarified that you can run a remote cutoff switch? There have a been several bulletins but none on this.

My preference is to just run two conventional shutoff switches in series and mount on one each end of the dash by the windows

paranoid_android74 wrote: How many amps is your alternator?

80 to 110, depending on which one we're using...

HFmaxi wrote: Has ARA clarified that you can run a remote cutoff switch? There have a been several bulletins but none on this.

I know there are a few high-end teams running them (probably SRT, for that matter). ARA hasn't exactly been clear about much at all. Last I heard this rule actually doesn't apply until NEXT season, but I have a slow summer so figure I might as well get it done.

APEowner wrote: My preference is to just run two conventional shutoff switches in series and mount on one each end of the dash by the windows

I am also trying to avoid having to run heavy-gauge main power wiring behind the dash. I'm not opposed to a conventional setup, just looking to see if there's something better.

irish44j wrote:

APEowner wrote: My preference is to just run two conventional shutoff switches in series and mount on one each end of the dash by the windows

I am also trying to avoid having to run heavy-gauge main power wiring behind the dash. I'm not opposed to a conventional setup, just looking to see if there's something better.

That's certainly a consideration but in my mind (and perhaps no where else) it's better to eliminate complication in systems that can shut the whole car down and a high current continuous duty relay controlled by two switches seems unduly complicated.

The White Rogers relays that are used in a lot of the kits are rated for the current and duty cycle but aren't really designed for the high vibration environment of a Rally car and based on how often continuous duty cycle relays get changed out in other applications I'm just not comfortable with the whole car counting on one.

As you've pointed out there are downsides to running a high current wire all around the car as well but with good craftsmanship and planning they seem manageable.

Having said (or typed) all of that, I've never tried a remote setup and I too would love to know what the experience of others have been.

If I use an NO solenoid or relay, doesn't that take care of my concerns about reliability of the solenoid? If it fails, it cuts the power. If the switch wiring fails, it cuts the power. Is there a scenario where I hit the activating switch and the solenoid fails to cut the power?

I guess I could be driving when an NO solenoid failed, and then the car would coast to a stop. But I already have that risk (and experience) with my track cars, for any number of reasons.

I think a solenoid or relay could fail open or closed either way. NO probably has less chance of failing closed, but you never know in the case of overcurrent - it could weld itself closed.

JBasham wrote: If I use an NO solenoid or relay, doesn't that take care of my concerns about reliability of the solenoid? If it fails, it cuts the power. If the switch wiring fails, it cuts the power. Is there a scenario where I hit the activating switch and the solenoid fails to cut the power? I guess I could be driving when an NO solenoid failed, and then the car would coast to a stop. But I already have that risk (and experience) with my track cars, for any number of reasons.

You'd need to use a NO relay for it to work. They could fail in either open or closed mode but open is the most likely. Actually, I think the most likely failure mode would be that the contacts would get damaged from arcing and the resistance would build giving you weird, intermittent, starting and charging (and with fuel injection drivability issues) like you would with a poor battery connection.

I too have had race cars fail to start and die on the track but to me that's more of an incentive to design for simplicity and reliability not less.

Again, I have no first hand experience with one of these systems. I'm hypothesizing based on my experience with relays in industrial applications and my experiences with race cars. It's entirely possible that there's a relay out there that's provided thousands of hours of reliable operation in rally cars and off road trucks and I've just never seen it.