I am going to put the battery in the trunk of my 62 bel air, and I plan on racing it some. I know from my other OT car that the kill switch has to be on the positive side. But what I would like to do is run the pos. cable up to the front near the motor and put in a heavy continuous duty solenoid and run a small switch to the rear bumper. I think this should work BUT... Will it be NHRA legal? and 99% of the time there will be no need to shut it off so by leaving it on would that run the battery down? I would think so. Any advise?
If I am reading this right, you simply want to run the positive cable from the rear mounted battery to a solenoid up front. That wouldn't cause any more drain on the battery than just having no solenoid, so you will be fine there. As for NHRA legality, someone will need to look at their rule book to be sure. I suspect that they want the battery to stop it's power flow right at the rear, not clear up at the front, but only the rule book will say that for sure. Don
I'm not 100% sure (but someone here must know), but it seems that the reason for cut offs is to avoid electrical sparks and heat in the event of a crash---meaning that the wires get crushed to ground. If you run a hot lead the length of the car to a solenoid, then even when the solenoid is shut off there will still be a hot lead running the length of the car. In the even of a crash, that hot lead could crush to ground causing sparks and heat.
Tech has to be able to shut it off from the rear of the car. It has to be clearly marked "ON-OFF" and it has to kill the engine when they flip it to the off position. Ive seen guys stick the on -off decal on a magnet and put it on the bumper by the switch. That way you can remove it for street use.
Well if I do it right, it should kill everything. Just not sure about NHRA liking the little kill switch in the rear of the car and the solenoid shutting it down. But shut off is shut off and that's what they want correct?
No, you are missing the point that there would still be live current all the way up that cable and it wouldn't end until the solenoid. By putting a switch at the very back of the car, the current stops there, and in the event of a crash there is no possibility of a cable being crushed with live juice in it. Don
That's what I was afraid of. I thought it would be easier to mount a small switch in the rear of the car and easier and better to wire the alt. on the other side of the solenoid, rather than run the alt. wire all the way to the batt in the trunk. That's what I did in my OT chevelle and it doesn't seem to charge as well, I think it is too much of a distance for the charge wire.
I have also never under stood the rule of having the kill switch on the pos. side. The Neg. side would be easier and accomplish the same thing.
It doesn't. The kill switch on the neg side still has the potential to accidently ground anywhere else on the car if something goes sideways. Kill switch on the positive = dead is dead.
Um..... if the ground was cut off by the switch there is nothing on the car the positive side could touch that would cause a short. Try this... unhook the neg. side of your battery, then crawl underneath and unhook the pos batt cable at the starter. While holding that "live" pos end in your hand, start touching that end to everything that is metal on the car. Bet nothing happens.
Hey Gus, If you plan on doing a lot of racing at tracks that use NHRA rules, just get a rulebook and do it just like NHRA says. If you're just gonna go fool around once in a while, do whatever but be prepared to be turned away if they look closely at it. My cut-off switches have always been on the negative cable, never thought of doing it any other way.
The rule book says on pos side of battery if its a push pull push will be off and if cable operated has to be at least 1/8 cable no mention if a relay could be used.
If you choose to use a continuous duty solenoid to act as a battery on/off switch, and trigger the solenoid by a smaller toggle switch, that would work fine insofar as cutting battery current at will is concerned. In fact it is exactly what is commonly used in light aircraft and is known as the "master switch". However, I absolutely agree the solenoid should be located immediately adjacent to the battery, NOT the length of car away from the battery with a 'hot' cable running through the body/ch***is. That could result in all sorts of electrical mayhem/fire in an accident. The master switch solenoid draws no current when it is not activated, but the car's electrical system is 'dead' then. Any time the master switch is turned on, the solenoid draws some current. Anyone who has flown light aircraft has experienced a 'dead' battery because after engine shutdown, the master switch was not turned off. A mechanical master switch eliminates that problem unless a mechanical switch does not meet the rules. Ray
I have heard this discussion sooooo many times. As I see it, the shut off in either cable should accomplish the same thing. BUT, If you are going to run NHRA, you better do it their way or you won't p*** tech.
There is a reason the NHRA and the American Boat and Yacht Council say the positive cable is the one to disconnect. Yes, negative functionally does the same thing, but if you don't kill the positive right at the battery you still have a lot of cable that is potentially hot should the ground post touch something. Yes, I know it is unlikely, but why not just do it the way most experts suggest and be done with it ? Don
Okay, the current flows from Negative to Positive. Wherever you open the circuit there is still potential on either side of the switch. To be sure that the battery is completely disconnected from the vehicle, you should put a switch on both sides and control it with one lever. I don't know anyone who has done this, but it could be accomplished quite easily. The question is, "What will p*** tech?" If NHRA thinks the switch should be on the + side, then that is what you have to do to play on their playground. I personally like the negative cable switched, but nobody at NHRA asked me.
One, direct current flows positive to negative two, break either side and the circuit is dead... Posted using the Full Custom H.A.M.B. App!
I've turned off the kill switch to the negative side of the battery on a car equipped with a 1 wire alternator, and guess what happened...nothing. The car kept running. "Oh ******** Highlander!! Can't happen!!" Well, yes it can. The car now had a new electircal source, both positive AND negative coming from the alternator and it's ground to the engine. Now, when you kill the positive side you also kill the 12V needed to "excite" or activate the alternator. There's also a need in some systems to provide a diode in the alt wire. A sort of electrical 'check valve' if you will. It depends on your car and it's system. Oh yeah, that car I "shut off" with the negative kill? Once shut down with the key it was dead. Someone else will correct what I've said here in detail which is fine by me. I openly admit to having a few cobwebs in my memory, and what I mentioned was in the 90s so...
Sorry guys... This was not suspposed to be a question on Pos. or Neg. side cut off. I know that NHRA says it has to be on the Pos. side so that's what I am going to do. Just thinking. On my OT chevelle I have the typical mechanical cut off switch on the Pos. side in the rear bumper. I also have a heavy gauge wire running from the alt. to the Batt. side of the cut off switch. Because of that LONG alt wire, my charging voltage AT the batt. isn't the greatest. So what I would like to do on this car is put a continuous duty solenoid up under the hood on the POS. side run my alt. charge wire to the batt. side of the solenoid. Then loop a small wire from the batt. side cable stud to one of the smaller studs on the solenoid. Then run a smaller wire off of the other small stud (ground side) all the way back to the rear bumper to a smaller switch. Yes I would then have a "hot" cable running the length of the car, but the solenoid is where the power will be shut off. I am thinking the benefit would be better charging and easier to mount a smaller switch in the rear rather than that big ol clunky thing everyone uses.
Gus68, I am glad you brought up the question and I am happy the subject has wondered off course as it often does on the HAMB. I got my question answered without having to make a post or search! I am sorry you have not gotten your answer yet but you most likely will by the end of the day.
8:4 Master cutoff specifies positive side, OFF label, and shutting off all electrical systems. Be sure that it also isolates the alternator from the cars system. My experience has been tech usually makes a functional check to verify that the master switch will kill the engine. If you want this from horses mouth contact West Central Div tech director 816 795-8055
King Ford, Better get out the school books. I don't want a ******* match here, but - to + is electron flow. The guy to blame for the 'Conventional Current' theory is good old Ben Franklin. Old Ben had a 50/50 chance, but turned out he was wrong. Where the confusion comes in, is that most wiring diagrams with negative grounded systems are traced from the + side of the battery to components and to ground. No one cares, or needs to, unless you are one of the little boy electrons trying to hook up with a little girl proton.
No it doesn't. Electrons, (ie, current) flow from negative to positive. Ask any electron, or somebody like me with an EE degree. It's how we remember which way diodes and NPN/PNP transistors need to be configured in electronic circuits. EDIT: Oops, GearheadsQCE already answered the question.
In Road Racing we must have it so when the master switch is off it kills the engine running . Our rules state that the switch must be on the Lower LH or Lower RH of the windshield. This leaves the dangerous situation of having a “live” heavy cable up to the master key. So to get around this we get creative. 1: we put a solenoid on the + side of the battery and run the heavy cable up to the starter. [ this is activated by the starter ****on ] 2: bridge the starter solenoid wire direct to the heavy cable [ some people have this and the rear solenoid both activated by the starter ****on together ] 3: run a + wire up to the master key from the battery [via a fuse near the battery ] then run every thing else off the switched side of the master key 4: run a charge wire to the battery side of the master key [or direct to the battery] ,this prevents a loop back from the alternator through the ignition when switched off. 5: put a diode in the charge wire [as close to the master key or battery ] this will prevent a short circuit through the charge wire.
If the vehicle is not running then electrically it does not matter which side is disconnected. When running it depends on the charging system. I suspect the reason people say "negative side" is because when installing or removing a battery it is safer to remove the negative first in case the wrench contacts the ch***is while loosening the clamps.
To answer the last part of the original question-If you don't turn off the toggle switch to your solenoid when you're not using the car you will run the battery down. It takes current to keep that solenoid energized.
The Jalopy Journal
