Thread: trunk mounted battery short protection

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Don,

Tried posting this yesterday but the network/website was flaky.

Mike, I like the diagram. I may need to think about this a bit longer, but I think with the cutoff on common between chassis and battery, the car will still run on as the alternator is referenced to the chassis and will continue to generate power to ignition and accessories (fuel pump, coil etc albeit "dirty" power).

In your diagram, I would put the cutoff between the starter and the ignition switch. Although, like I said before, there would be many ways to accomplish the same thing.

I'm pretty sure at this point cutting the battery ground will not stop a running motor if the alternator is still pumping up the positive supply.

I'll concede I know very little about mechanics and cars in general and am very new to hot rodding but I do know a thing or two about electricity as this is my profession.

Another two cents (am I up to a dime yet? )

Chris

Originally posted by skids72
Don,

Tried posting this yesterday but the network/website was flaky.

Mike, I like the diagram. I may need to think about this a bit longer, but I think with the cutoff on common between chassis and battery, the car will still run on as the alternator is referenced to the chassis and will continue to generate power to ignition and accessories (fuel pump, coil etc albeit "dirty" power).

In your diagram, I would put the cutoff between the starter and the ignition switch. Although, like I said before, there would be many ways to accomplish the same thing.

I'm pretty sure at this point cutting the battery ground will not stop a running motor if the alternator is still pumping up the positive supply.

I'll concede I know very little about mechanics and cars in general and am very new to hot rodding but I do know a thing or two about electricity as this is my profession.

Another two cents (am I up to a dime yet? )

Chris

i hate to tell you skids72, but you're wrong. the way I have it is the same as hooking it to the bat. and if you have a sw. between the bat and Ign. (the ign. sw.) then when you cut the sw. off the motor can't run. if you ran the alt wire to the Ign. side of the sw. then you couldn't cut it off. the cut off sw. is just there to cut the bat. off when the car is sitting. if you put all of your wires, acc. ign. ect. on the out put side of the ign. switch and the alt. on the input side of the ign. sw. then when you cut the key off nothing can work.

Mike,

If I'm reading this correctly, I think I agree with your logic and I don't think it contradicts my logic. The point I was trying to make is that cutting ground at the battery will not stop the motor.

Please pardon my lack of artistic ability, but here are some diagrams of what I am suggesting:

And another:

Denny,

The alternator takes no juice, it generates it by the action of the motor spinning it through electromagnetic induction. You have one wire on the alternator and that one wire will keep everything running (poorly) even with no battery in the system at all.

Just try pulling the black cable off your battery with the engine running and let me know what happens.

I guess the controversy is between 3-wire vs. 1-wire alternators. Regardless, a 3-wire alternator can keep itself alive for a period of time if it's battery output is still electrically connected to the + input. We are looking at a way to kill the motor with the ignition switch on (the stator field in the alt is energized through the ign switch).

Agreed, they do make 2-pole kill switches for separate batt and alt cutoff.

But they also make 1 pole switches (that I use) and if you are to use a 1 pole switch, the alt must be on the battery side of the switch to kill the engine

That last sentence sums up my position.

denny the blue wires are hooked to the big bat. wire. + alt. and +ign. hot all the time.

skids72, you're saying thats the same as pulling the neg. cable off of the bat. to see if your alt. is charging, and you might be right there, but why would you want to cut the motor off with the cut off sw. with the motor running and the ign. sw. on? if you're planning on doing that much, then you'll need the dioded. if you cut the "ign. sw. off," then the motor want be turning, so it cant produce elec. so the motor can't run. the only reason i put a cut off sw. in a st. car is to cut the bat. out of the system while its sitting still, with the ign. off. they use them at the drags mostly to cut the fuel pump off, not cut the motor off, and it dont make no dif. where you put the cut off sw. at.

Mike, the point of all this is to have an emergency cutoff switch on the back of the car for emergency situations at the strip as required by NHRA in situations where the battery is relocated to the rear of the vehicle. If you're just looking to prevent the car from being started, cutting ground will work just fine as well as many other options. In fact, for that application (theft deterrent, etc.) cutting the ground is the best solution.

Sorry, Denny. I don't think I understand what you're doing in Mike's picture.

Well, I hope Don got his question answered. And I don't want to argue any more than necessary. I know I'm a newbie here and I don't want to irritate so many knowledgable folks cause I'm going to need all your help in the future. I'm just trying to help with what I think I know about.

Peace, all...

danny, my blue wire from the starter to ign. sw. is the same wire you put in there.

denny,i dont know why you couldnt understand what i was doing, i did.

"Like the guy that uses red cable for the ground." you haven't used red wire for a ground before? i have. i've wired cars with all one color wire before to, who needs color coding.

about a yr. down the rd. its a bitch when you have a problem and you go to check the car and you have all black wires. that dont make no dif. though, i can still fix it.

Thanks guys, I was at a one day conference today but it looks like you were working hard on the circuit. By the time I check this all out I should get something to work. It's going to be very cold here for a day or two (after two days in the 60 F range last week) so I plan on hunkering down and studying the TPI circuit, Sweeden's book and your diagrams till I am sure I got it figured out. Lt1s10 has it right though as to the difference between theft protection and NHRA requirements. Maybe I can get the theft protection mainly but also make the motor cutoff built in too. Thanks again. Any other comments are welcome while I figure this out.

Don Shillady
Retired Scientist/teen rodder

Originally posted by Don Shillady
Thanks guys, I was at a one day conference today but it looks like you were working hard on the circuit. By the time I check this all out I should get something to work. It's going to be very cold here for a day or two (after two days in the 60 F range last week) so I plan on hunkering down and studying the TPI circuit, Sweeden's book and your diagrams till I am sure I got it figured out. Lt1s10 has it right though as to the difference between theft protection and NHRA requirements. Maybe I can get the theft protection mainly but also make the motor cutoff built in too. Thanks again. Any other comments are welcome while I figure this out.

Don Shillady
Retired Scientist/teen rodder

just keep in mind Don, if you're gonna be cutting the motor off with the ign. sw. then it dont make no dif. how you hook the bat. cut off sw. up. the only thing you have to be sure of it having the alt. wire hooked to the bat. side of the ign. sw.