Thread: trunk mounted battery short protection

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Don,

I ran the single wire (8 gauge) back from the alternator directly to the battery, then I've got the beefy positive cable from the battery through the kill-switch to the rest of the car. This way, when the switch is opened, energy from alternator is cut off from everything but the battery.

Tech, can you comment on this setup. I assumed it was legal and it works like a charm.

My two cents,

Chris

skid72, Thanks that sounds like something I can do but let's hear what Tech1 says since that may still allow the engine to run? Sorry to be so dense but the Sweeden book "How to Wire your Street Rod" is very good but offers several optional circuits and I need to get this "in my head" before I start cutting wires since I have a history of making mistakes even when I think I have been careful.

Don Shillady
Retired Scientist/teen rodder

Originally posted by Don Shillady
Sorry to ask more dumb questions, but if the cutoff switch is in the rear of the car accessible, but hidden maybe with a screen door spring-loaded flap, with a cutoff on the alternator as well as the battery that means the single wire from the alternator has to go all the way back to the cutoff switch? And of course there has to be enough slack in the wires to the cutoff switch that the flap can move up and down. I have sweated out circuits a lot before and burned up quite a few with micro-amp applications but here we are talking hundreds of amps so I need to get it right the first time! The TPI guy boasted that their harness has an 8-gauge alternator wire compared to a 10 in the Painless kit, but I will have to unravel the harness to figure out if the alternator wire is long enough to go to the back of the car. If not I guess I can use No. 8 welding cable; my local supplier had quite a range of sizes and the welding cable is really flexible.

Don Shillady
Retired Scientist/teen rodder

hope you don't mind me asking don, but why are you so worried about being able to cut the alt. out? that's one wire I wouldn't run no further than I had to. the less cut off and switches you have the better off you'll be. as far as the drags go(cutting the alt. out) its only good for a few HP, and if you're bracket racing it wouldn't make no dif, but that 8-gauge alt. wire sounds like over kill to me also. where are you picking up the 12 V for the IGN. switch? just wondering. look like to me the (big starter wire, at the starter) would be the best place to pick up the alt. and Ign. 12V . with the cut off at the bat. I dont see what the NHRA has to do with it. you need the cut off for when you're not driving the car, but for safety is no good to you, because no one will know where its at.

I can vouch the engine does not run-on with this approach. I just had to re-wire it last fall because I failed tech the way it was set up when I bought the car. You just need to make sure there's nothing else on the circuit between the alternator and the battery - one wire. Everything else is energized through the kill-switch.

Good luck,

Chris

Denny,

True. Alternator wire is hot all the time which is why you need to separate it out from ignition circuits etc if you want to kill the engine with a switch. There are a couple ways to do that: buy a two pole switch which cuts alternator and primary circuits separately or buy a one-pole switch and run alternator alone to the battery (no switch).

There are always multiple ways to achieve a desired result. I'm just sharing the approach I've used successfully. FWIW....

Now we're getting somewhere! DennyW I see Skid72's idea should work al long as there is a hefty diode in the wire from the alternator to the battery, any suggestions for a diode? The PIV should be at least 30 V in my mind allowing for swings in polarity which should be easy to find but the amp rating would have to be at least 100 amps for my alternator. lt1s10 put his finger on the whole problem that is a racing setup has to be visible and easy to get at, but a street situation is to hide the cutoff. Tech1 suggests a swing up flap like the hidden license plate idea. I had hoped to get a few 1/4 mile times but I do NOT intend cometitive racing with the little cam I have in the engine and an 8" rear so I guess I will set up a hidden cutoff. Lt1s10, you know the tracks in the area here, is there any class to just get a recorded time without an external cutoff and a roll bar; a run-what-you-brung class? Thanks Skid72, that idea is looking good with the addition of a diode if someone has any suggestions fo the source of the diode.

Don Shillady
Retired Scientist/teen rodder

I hear ya, denny. It is good to have a clue before you dive into something. My flaw is I often jump then look. Make more mistakes up front --> more mistakes = more lessons learned Of course, there's the balance: do-think-do vs. think-do-think.... I usually prefer the former.

Don, good to come up with a solid plan with lots of info. All I have to offer should be taken with a grain of salt as probably anything you read on here should be

Don,

I would suggest there is no diode required. Personally, I just ran a solid wire..... alternator has bridge rectifier diodes built in. As always, your mileage may vary

Chris

this will work

Originally posted by Don Shillady
Now we're getting somewhere! DennyW I see Skid72's idea should work al long as there is a hefty diode in the wire from the alternator to the battery, any suggestions for a diode? The PIV should be at least 30 V in my mind allowing for swings in polarity which should be easy to find but the amp rating would have to be at least 100 amps for my alternator. lt1s10 put his finger on the whole problem that is a racing setup has to be visible and easy to get at, but a street situation is to hide the cutoff. Tech1 suggests a swing up flap like the hidden license plate idea. I had hoped to get a few 1/4 mile times but I do NOT intend cometitive racing with the little cam I have in the engine and an 8" rear so I guess I will set up a hidden cutoff. Lt1s10, you know the tracks in the area here, is there any class to just get a recorded time without an external cutoff and a roll bar; a run-what-you-brung class? Thanks Skid72, that idea is looking good with the addition of a diode if someone has any suggestions fo the source of the diode.

Don Shillady
Retired Scientist/teen rodder

12 sec. or slower all you need is a helmet, and seat belts. think you gonna run faster than that? thats around 120 mph.

Don, I think Denny and Mike have you covered, but if you're still interested in the diode you might try Mouser Electronics at www.mouser.com

Thanks all. The circuit shown by lt1s10 looks simple and DennyW agrees. Lt1s10 by "acc." you mean accessories like lights and gauges I guess? I will study that a lot. You even drew in the 1/0 red and 2/0 black wires so I guess you are visualizing it pretty good. I was going to get right back but the Forum went down for several hours and then my son is taking an on-line course so he had the PC phone line for a few hours while you guys were working it out. I was going to ask about the double-pole switches. The scheme suggested by Skid72 looked like I could get the Moroso switch Tech1 suggested and that is a maybe. As of now I will study the simpler circuit Lt1s10 and Dennyw suggest AFTER I study the harness I got from TPI. I need to make sure that circuit is compatible with the harness. I sincerely cross my fingers and hope that the multiplug on the base of my '83 Camaro column has a corresponding plug in the harness, but first I need to sit in the garage and spread out the harness. Believe me I know I am talking to several hundred years of combined experience here and I really appreciate the advice. Lt1s10 also solved my problem in that I won't have to worry about the dragster setup Tech1 inspects since I will be lucky to ever make it into the 14s with the little cam I have in the 350. I would like to be better than 15 in the 1/4 and if all I need is a helmet and seat belts I will be able to get a thrill or two. I recall in some Rod Magazine they reconstructed the AMBR No1 with a flathead Merc built to 1950s specs and it did not break 15 even with a very light body so I guess my memories are calibrated on something like what would be a 17-18 quarter mile time with the old 59AB setup. Since I have been playing with VWs and MGs for the past 15 years I probably have not been under 20 for a long time! I never got a timed run for my VW with the Judson supercharger, but it seemed to me that the huffer only helped top speed and did not do much for the torque. Anyway I remember my Dad's '70 Chevelle with a 350 and it was a wild ride as I recall. Thanks again for the help, I'm not out of the woods yet but getting there with your help.

Don Shillady
Retired Scientist/teen rodder

WTF????

A short is a short...
WTF does 8 foot of battery cable have to do with it?
Just curious...
Jeff

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.