KILL SWITCH, AGAIN

#41

A kill switch is recommended to be installed close to the power source, in this case the battery. Remember that e30’s battery cables run from the back of the car to the block in front passenger side, which in case of an accident will remain powered for that distance (almost 7 ft. or more).

Also is important to consider the most basic principle that while racing, cars run in forward motion which increases the probability of a frontal accident. People that located the switch behind the hood, there is the possibility that in a frontal accident the hood moves over the device making it non functional, or covering that area. For these reasons I think the best place is in the license plate area.

Carlos

#42

The best place for a kill switch is where the driver, the corner workers, and EV can reach it during an emergency. Just inside the front driver-side window frame or on the left front dash would be good. An acceptable but less desirable spot is the left front cowl.

I can’t imagine why anyone would want one under the hood or on a rear fender. Is that even legal??

#43

on my e30 M3, mine is in the trunk! (close to the battery) There is a pull wire with a red handle coming out the rear.

The motivations are to have as little wire as possible electrified after a pull, and to install it close the run of the main battery cable.
The only requirement is for it to be accessible externally and to be marked with the lightning bolt sticker.
bruce

Scotty wrote:

[quote]The best place for a kill switch is where the driver, the corner workers, and EV can reach it during an emergency. Just inside the front driver-side window frame or on the left front dash would be good. An acceptable but less desirable spot is the left front cowl.

I can’t imagine why anyone would want one under the hood or on a rear fender. Is that even legal??[/quote]

#44

OK, the wire length concern makes sense. It is possible to move the battery to the tray up front… is that legal in SpecE30?

Of course, that makes for an even lighter rear end. :unsure:

#45

I don’t think there is a perfect location for the kill switch. From a safety perspective, the switch should have the least amount of hot wire and must be easily accessible to corner workers. Given the battery location that suggests the passenger side of the car.

Seems to me that mounting the switch where the harness bar meets the main hoop works well in that regard. The hot section is short, is mostly protected by the rear of the cage, and the switch is easily reached by a corner worker. Unfortunately that puts the switch out of reach of the driver. What I’d like, which I don’t think is allowable, would be to dispense with the ignition switch and have a master switch on the dash that kills all power except that to the starter main lug. I’m not wild about bringing the 4 gauge wire that far into the cabin, but I would like something that is easier to operate in an “exciting moment” than the key.

#46

My kill switch is where you indicated and it can be reached from the drivers seat. It is above the harness bar and on the inside of the main hoop. One of my fire pulls is there as well.

Michael
#36

#47

I came across this one as I’ve been looking at kill switch options since mine is faulty. My thinking is that I can keep the wiring I have already run for the kill switch to the corner of the engine compartment, but run the switch to the interior - probably on the cage at the A-pillar where driver or Emer worker can hit it. Good design if it works, just kind of pricey. Does anyone have experience with one of this design or similar?

http://www.ioportracing.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=BS08&Category_Code=BE

#48

My single pole kill switch used to work. And then it quit working. In between I did fool around with the wiring at the junction box forward of the passenger side firewall. And today I found/fixed the fusible link in the small battery wire.

http://spece30.com/component/option,com_kunena/Itemid,94/func,view/id,44978/catid,9/

After spending a couple hrs playing with my wiring today, I’d have to say that I agree that a 2 pole switch is needed to kill the car because otherwise the generator will keep the car going. But how is it that my single pole kill switch used to work?

Maybe the generator isn’t that good at keeping the car running. Maybe in the absence of the battery to smooth out the voltage curve the DME chokes and kills the car. But maybe it’s a little unpredictable. I dunno.

But I do note that the NASA regs says that the killswitch has to kill all power, except for emergency gear like fire suppression and . And the only way that’s going to happen is with a 2 pole killswitch. So I guess that’s what I’ll be buying.

Near the bottom of the first page of this thread is a pic of my killswitch. I saw that pic and thought “I don’t remember taking that picture”. It’s from the PO. 4 engines ago. Or is it 5? I think it’s 4 engines + 4 heads.

#49

You should use a 3-pole switch. One pole interrupts the main battery lead, another interrupts the DME power lead and the third pole (which has normally closed contacts) is used to shunt a resistor across the alternator output. The resistor will absorb any spikes from the alternator as the engine winds down and avoid damage to the car’s electronics.

Since the alternator output is connected to the starter main lug it will suffice to jumper from the load side main lug of the kill switch to one pole of the normally closed switch. The resistor then connects to the other side of that switch and then to ground.

As an FYI, the separate DME power lead is intended to reduce noise on the DME’s power supply and to avoid the voltage drop that occurs on the main lead during starting.

#50

You are the first I have seen to recommend the use of a 3 pole. I plan to put my kill switch in soon, and I would like to do it properly. Could you describe the color/location of these three wires we need to interrupt. Thanks.

#51

King Tut wrote:

John’s post from earlier in this thread has a good diagram:
http://spece30.com/component/option,com_kunena/Itemid,94/func,view/id,45015/catid,9/limit,10/limitstart,20/#16402

That’s the way I wired mine. I used the switch that Bimmerworld sells.

#52

A three pole kill switch like Bimmerworld and others sell has a pair of 3/8" studs for the main battery cable and four spade connectors. I’m of the opinion that the kill switch, cables, and battery need to inside of the area protected by the cage. The pretty much means that the existing battery and DME power cable won’t be long enough. Since the end of the cable that terminates in the engine bay has a soldered on ferrule, the easy solution is to use the existing cables from the engine bay back to the kill switch and run new cables from the kill switch to the battery. Or you can get a second battery cable from a salvage yard for the aft portion.

A minor complication of running new cables from the kill switch to the battery is the need to include the fusible link in the DME cable. Meaning that you’ll have to splice that section into the wire you run to the kill switch. Or you could get a 50a inline fuse.

Welding cable is readily available in the size needed for the main battery cable. I’m not a fan of clamp-on battery terminals. So I get a solder-on battery terminal from http://www.wiringproducts.com/ and duplicate the OE configuration for the positive battery connection. You can get the solder-on lugs for the main battery cable from a welding supply house or wiring products.com.

The main battery cable connects to the studs on the kill switch and the DME power cable connects to the pair of spade lugs that are open circuit when the switch is off. Then run a small wire, say 12-14ga from the load (engine bay) side of the kill switch studs to one of the remaining spade lugs. The resistor connects to the other spade lug and then to ground.

#53

I feel really stupid. I read all of the prior posts but there is something I just don’t understand. Why don’t we just run the battery power wire and the alternator charge wire to one side of a standard two pole switch. The other side of the two pole switch would then re-connect to the wire that takes power to the main distribution block on the passenger side of the car. When you shut power off, it will kill power to the main distribution block, which would include the engine computer, etc. The car would shut off for sure. Why is not the simple, easy way? I have run a switch just like this on my Factory Five Roadster for 5 years without fail.

Stupid question #2, and I suspect this question is rule driven. Why don’t we just put a simple switch on the negative battery terminal. Switch on, circuit closed, functioning ground, everything runs. Switch off, circuit open, no functioning ground, nothing should run.

Comments on this please?

-Scott

#54

I can’t visualize what you mean by question 1. But as to question 2 disconnecting the battery negative lead while the engine is running will allow the alternator to continue to power the engine. Everything in the car grounds to the chassis, so disconnecting the battery negative just disables the battery.

#55

For my #1:

To visualize, let’s say we mounted a standard two pole switch on the roof of the car, and lets call them pole 1 and pole 2. Take a 2 gauge wire from the positive terminal of the battery and run it to pole 1 of the switch. Take the alternator hot charging wire, extend it with some 2 gauge wire and run it to pole 1 of the switch. You will now have two wires under pole 1 of the switch. Then, off of pole 2, take a 2 gauge wire and run it to the cars power distribution area on the passenger side of the firewall on the car. When you turn the switch off, the power distribution area gets no power, which means the computer and everything else turn off. Seems like it works to me.

For my #2, I might be nuts, but I think it works. If you disconnect the battery negative lead, the chassis is no longer “ground” because it isn’t connected. I wouldn’t do it this way anyhow, but if your car is running and you yank the negative battery terminal, does it stay running?

-Scott

#56

BigKeyserSoze wrote:

[quote]I feel really stupid. I read all of the prior posts but there is something I just don’t understand. Why don’t we just run the battery power wire and the alternator charge wire to one side of a standard two pole switch. The other side of the two pole switch would then re-connect to the wire that takes power to the main distribution block on the passenger side of the car. When you shut power off, it will kill power to the main distribution block, which would include the engine computer, etc. The car would shut off for sure. Why is not the simple, easy way? I have run a switch just like this on my Factory Five Roadster for 5 years without fail.

-Scott[/quote]
I had to rewire my killswitch last week and I was thinking about doing it the way you described. I think that the bottom line is that as long as it kills all power to the car per the NASA CCR, no one is going to care how you do it.

Caveat: Your solution allows 12V to run from the battery to the generator after you’ve opened the killswitch. Not a big distinction, but that is bringing power deeper into the engine bay then other folks are doing.

To wire the killswitch as you describe you will have to remove the secondary wire that goes from the battery to the front distro block and then to the DME.

Ultimately I did it the way most others did…by using a second pole to interrupt the secondary batt wire.

#57

The large and small wires leaving the positive battery post each need their own switch pole. If both are put on the same pole, the car will keep running due to the alternator.

I have heard that it is not favored to interrupt the ground wire because bent metal in an accident can restore a ground path.
thanks
bruce

#58

Scott,

I see what you’re saying for #1. Let me know if it works. For #2, my car keeps running when the neg bat cable is disconnected.

Jason

#59

leggwork wrote:

[quote]The large and small wires leaving the positive battery post each need their own switch pole. If both are put on the same pole, the car will keep running due to the alternator.
[/quote]
I’m with Scott on this one. Although the batt and generator are on the same pole, in his idea, it’s the pole that is isolated by the switch. But that secondary wire does have to be cut for the idea to work.

#60

Anybody know where I can get replacement battery cable? I mounted my cut-off switch near the battery, between the brake lights. My plan is to run the large cable to one post, and the small cable to another post. Then bring them together after the switch right at the battery terminal. Since that run is so short, I’ll probably use either 2 or 4 gauge wire you can get at the parts store. My problem is finding bulk cable locally and to find that weird end on the cable that goes to the power distribution at the front of the car. It kinda looks like a battery terminal post, but slips over the end of the cable. Where do I find this thing?