Unless I'm wrong, it has to be a mechanical cut off switch. I don't think a toggle switching a relay would pass tech.
All this complication because you get poor charging with a small wire from the Alt all the way back to the battery? Personally I think you are missing the real problem and creating a complicated band-aid that may or may not work. For starters, (LoL) why don't you run the charge wire to the main lug on the starting motor and take advantage of the large cable you have there that does nothing now but start the car? Also, I'm willing to bet you run a generic "1 wire" or perhaps an internally regulated Alternator with the "sense" wire jumped to the output terminal. Doing it either way...numbs...the Alt to the true requirements of the electrical system. A car like your setup is the worst case senario for the potential problems of taking that short cut. The distance from Alt to battery is extreme and without the ability to "sense" voltage output requirements farther back in the electrical harness the output of the Alt is too low to be effective in charging the distant battery. Now...before I get jumped from everyone saying "1 wire etc" works pretty good...yes it does...in most cases. I've built several with jumped sense wire Alternators and my T runs that way right now. No issues. It's just that in extreme setups such as this rear batteried and really long 62, "working pretty good" simply isn't enough.
This is our continuous duty relay wiring on an old race car . The wiring is coming from the inside of car and going to the the kill switch on the back of the car along with a #8 from the 1 wire alternator . This car did pass tech at US131 motorspeedway for a pinks all out event . . yes to this statement many times got cars to run on just alternator ...
I hear what your saying, but wouldn't the alt. charge wire run to the batt. lug on the starter still keep the car running? I mean where does everything else on the car get power from? usually off the starter stud.
All of the different ways of wiring this system are plausible and fine, but I believe the intent is for the ultimate safety in the event of a crash when you don't know what will be damaged or inoperable. So it seems to me the best way would be a shut off on the positive side as close to the battery as possible.
Here is how I wire kill switches to not have a long charge wire. Put a heavy duty relay between the starter solenoid + lug and the alternator, an ignition switched power from the key switch to one of the control leads of the relay and run the ground control side to the rear of the car kill switch (4 post kill switch) small lug and ground the other small lug. PM me and I will fax a schematic if needed.
This Land Speed car (SCTA) is switched on the Positive side through a solenoid like you described. Switching the negative side can be a problem if you attempt to start the car, and your crew forgets to turn the switch on. The electrical system will attempt to find a ground through your electrical components (like the MSD box) and fry them. We have forgotten to energize the system many times with the excitement of strapping the driver in, and different crew members helping. The positive side switch has never caused a problem because the electrical system is dead.
This thread proves that, no matter what the actual question, guys who don't read the post are going to turn it into the same old arguments.
BWWWWAAAAAAAAA!!!!!!!!!!!! That's what I was thinking and hoping would not happen. But I do Appreciate everyones help!!!!! Thanks!!!
I want to speak my mind on this one but am afraid it will cause trouble. I know there are rules. I respect those rules enough not to air out things about knowing the rules and trying find a way to get around them. I would like to get around them and explain the reason for rules in motorsports is for safety; and if a person doesn't care about their safety, rules makers do, and also care about the safety of others. When you participate in a dangerous enterprise with other people and don't want to play by the rules there are many names people will call you because you are a danger to them, and yourself. I know this is a round about way of making my point but I expect y'all understand what I mean. Get a rule book. Do it by the rules. Get a life. No one person is smarter than a group. A person has to take time to sleep, to eat; a group can keep someone on the hunt 24/7. If you think you're above the rules, hubris is a mother.
Not unless the run side of your ignition switch that goes to the coil is somehow wired common with the same part of the power supply. Most modern ignition switches don't have that problem.
Actually...if you're talking about me, I did indeed read all the posts and thru that discovered his reason for wanting to remotely mount the shutoff close to the engine. Poor charging that he experiences on his other ride that is set up the normal way. However...I DID make a boo boo in considering using the starter lug. Not being used to this shut off switch setup (not a drag racer!), I totally forgot that if he runs the charge wire to the starter the car will most likely still run on the alternator output alone if a crew person has to hit the switch in an emergency...thus defeating the whole purpose of the shut off! Sorry about that!!!! I'd still hook up that shut off at the rear as expected and then run a larger size wire for charging the battery. You could also relocate your sense wire pickup location to increase the Alternator output but you would need to experiment to check on just where to put it. If possible it would be good to get some info from a trained automotive electrical person for that...but I'm pretty sure its do-able.
Most cars have redundant grounds and fused power circuits, except for main cables. A crushed chassis can provide the ground path, which is usually set up closer between battery and metal around it, since it doesn't matter when the ground shorts this way. So in a crash, it shorts that way. ....so opening the positive is what they prefer in racing organizations. Posted using the Full Custom H.A.M.B. App!
Don't get me wrong, i'm all for safety, and I respect the rules, My original question was if my idea would pass tech. They want the power killed to the car, and my solenoid would do that. Is there a rule on how far from the battery the "kill switch" has to be? They want a switch at the rear of the car, does it have to be a big ol mechanical switch? Not sayin I'm smarter than the rules, but you have to admit there are some stupid rules. One that pops in my brain is, in my ot chevelle I run in the 11's just on the edge of requiring roll bars. I have thought many times of getting a 5 point harness or at least something better than my 1968 lap belt. Well guess what? if I go with aftermarket belts I need to replace them every 2 years, supposedly they "break down" and are no longer good. But my original 1968 belts are GREAT!!!! And perfectly legal!!! That makes scents.
I think a multitude of tracks utilize the NHRA rules rather than writing their own. I also wouldn't try reading any more into the rules past the text as written. The solenoid kill should work fine and kill the engine when tech does their functional test. If you need more info...you'll get the real word by talking to the NHRA tech director that covers Minn (phone # in earlier post)
I appreciate a good discussion on most anything, especially respectful differences. Trying to build a better "mouse trap" is one of hot roddings foundations, but sometimes better minds spent the time to discover errors and fixes in the simple shit. A negative shut off is ok for that old car you drive around once in a while and want the battery disconnected as it sits around for weeks. A racer that needs to have the power/engine killed in the event of a catastrophy? I think that falls into the simple shit catagory. Leaves the mind clear for where it really counts, like the combination or the weight of the valve train. I think overall this was a good topic, no?
Yes, thanks for all the replies!!! Some times I should stop trying to think so hard, it starts to hurt after a while!!!!
Hey! I pulled my cheat sheet schematic out and realized that what I described above is incorrect. I power both sections of the kill at the battery and run the small wire to the ignition switch which in turn pulls the alternator relay in to connect the alternator to the starter lug (which gets killed through the big side of the kill switch) so there is no way for the alternator to run anything with the kill turned off. The previously mentioned method would work, but, have a chance for a pinch to ground in a crash. Sorry for the misinformation. I always did do better with pictures than words.
Caton, I am trying to read your scematic. I can't read a couple of words but it looks like your kill switch is on the ground side?????
I as responding to a post that made it sound like if the ground was switched off in a crash that the positive could still ground/short out to the frame or anything else metal. I was stating that that would be impossible if the neg side of the battery was nolonger connected to the frame.
No. battery neg grounded to the frame, positive to the kill switch, small kill switch wire to the ignition switch, large kill switch cable to the starter. I know my ground symbols are not drawn as chassis grounds and the battery symbol may have the long and short bars backwards. Battery is at the bottom of the picture, by the way, I did not wright anything by it. Quick sketch I made due to dyslexia issue I often have.
Alternators eat power, of course, so you can also put a switch under your accelerator to cut the alternator out during on the floor operation. Wire it in between the ignition switch and the relay control side.
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