Moparts

Power Cut Off switch Question.

Posted By: 451Guy

Power Cut Off switch Question. - 03/28/14 06:20 PM

Last summer I finally got my car back to the track to make some passes. I had done a ton of stuff to it over the winter and one of the upgrades I made was installing an alternator for the first time. When I went through tech the inspector turned off the main power switch and the car kept running. I have since been told that I need to put a diode in the excite wire to solve this. I am getting ready to do this but I have no idea what size of diode I will require. The alternator is a 55 AMP Denso unit. Any input will be appreciated.
Posted By: BobR

Re: Power Cut Off switch Question. - 03/28/14 07:18 PM

Quote:

Last summer I finally got my car back to the track to make some passes. I had done a ton of stuff to it over the winter and one of the upgrades I made was installing an alternator for the first time. When I went through tech the inspector turned off the main power switch and the car kept running. I have since been told that I need to put a diode in the excite wire to solve this. I am getting ready to do this but I have no idea what size of diode I will require. The alternator is a 55 AMP Denso unit. Any input will be appreciated.



I used to run a switch on my alternator that I could control from inside the car.
Posted By: Cab_Burge

Re: Power Cut Off switch Question. - 03/28/14 07:37 PM

Another option is to run the big battery charging wire from the alternator to the battery side of the switch so the alternator will charge the battery when the motor is running but it will not supply voltage to the electrical system when the cut off switch is turned off My car is that way, I used a #10 wire from the alternator ran directly to the battery + post connection
Posted By: challenger1320

Re: Power Cut Off switch Question. - 03/28/14 07:41 PM

Just put the disconnect on the ground cable
Posted By: an8sec70cuda

Re: Power Cut Off switch Question. - 03/28/14 07:48 PM

Quote:

Just put the disconnect on the ground cable


If I'm not mistaken, the NHRA and IHRA rulebooks both state the cutoff has to be on the positive side.
Posted By: Polarapete

Re: Power Cut Off switch Question. - 03/28/14 07:50 PM

Sorry, NHRA rules require the cutoff switch be in the positive cable, not negative. It would seem to work the same, if the wreck caused no body damage, but if it did and the negative cable was grounded before the switch by being cut the circuit would still be live and the switch would have no effect
I wanted to run it through the ground, too. It would have been easier, but you have to consider all possibilities or there is no point to doing it at all.
Posted By: MR_P_BODY

Re: Power Cut Off switch Question. - 03/28/14 08:15 PM

The simplest way is to just run the alt output wire
to the battery side as Cab said.... there are other
ways to do it but thats the easiest and the best way
Posted By: 68 HEMI GTS

Re: Power Cut Off switch Question. - 03/28/14 08:16 PM

Quote:

Another option is to run the big battery charging wire from the alternator to the battery side of the switch so the alternator will charge the battery when the motor is running but it will not supply voltage to the electrical system when the cut off switch is turned off My car is that way, I used a #10 wire from the alternator ran directly to the battery + post connection



thats how i did my dart, works good.
Posted By: Cab_Burge

Re: Power Cut Off switch Question. - 03/28/14 08:22 PM

Quote:

Just put the disconnect on the ground cable

The alternator will continue to supply voltage to the motor through the various engine to body grounds so shutting the switch off will not kill the supply of electrons to the ignition, trust me on that All electron flow from batterys is from the negative post through that cable to the to the motor and returns to the positive post of the battery, not from the positive to the negative like most people think That makes the negative cable not a good idea to hook up to the cut off switch
Posted By: MR_P_BODY

Re: Power Cut Off switch Question. - 03/28/14 08:28 PM

Quote:

Quote:

Just put the disconnect on the ground cable

The alternator will continue to supply voltage to the motor through the various engine to body grounds so shutting the switch off will not kill the supply of electrons to the ignition, trust me on that All electron flow from batterys is from the negative post through that cable to the to the motor and returns to the positive post of the battery, not from the positive to the negative like most people think That makes the negative cable not a good idea to hook up to the cut off switch



Wouldnt matter anyways... after you start the car you
can take the battery out and it'll run fine.. it has
to open the alt output circuit
Posted By: 383man

Re: Power Cut Off switch Question. - 03/28/14 09:02 PM

Most I know do what Cab says and run the alt output wire to the battery side of the cutout switch. Another option is like I did years ago on my bracket car and that was I put a toggle switch on one of the field wires and ran it inside the car so I could kill the charging system when I made a pass and you can also just kill the charging circuit when going thru tech with that toggle switch in the car so it dies when the kill (cutout) switch is turned off. It is alot less wire to run if you just tap into a field wire and run it in the car within the drivers reach on a toggle switch. I burned out a rotor on my bracket cars alt so thats one reason I would kill the charging system when making a pass. Ron
Posted By: MR_P_BODY

Re: Power Cut Off switch Question. - 03/28/14 09:12 PM

Quote:

Most I know do what Cab says and run the alt output wire to the battery side of the cutout switch. Another option is like I did years ago on my bracket car and that was I put a toggle switch on one of the field wires and ran it inside the car so I could kill the charging system when I made a pass and you can also just kill the charging circuit when going thru tech with that toggle switch in the car so it dies when the kill (cutout) switch is turned off. It is alot less wire to run if you just tap into a field wire and run it in the car within the drivers reach on a toggle switch. I burned out a rotor on my bracket cars alt so thats one reason I would kill the charging system when making a pass. Ron



Dont let the tech guy see you with a separate switch
set up like that... its a no no .. if you forgot and
had it on during a pass it wont kill the ignition
if needed and your knocked out
EDIT
I use to have a switch on the panel just to kill the
alt during a pass but I seen ZERO difference in et
or mph but that was with the output still on the
battery side of the switch... so when I rewired the
car I left that switch out of it
Posted By: 383man

Re: Power Cut Off switch Question. - 03/28/14 09:22 PM

Quote:

Quote:

Most I know do what Cab says and run the alt output wire to the battery side of the cutout switch. Another option is like I did years ago on my bracket car and that was I put a toggle switch on one of the field wires and ran it inside the car so I could kill the charging system when I made a pass and you can also just kill the charging circuit when going thru tech with that toggle switch in the car so it dies when the kill (cutout) switch is turned off. It is alot less wire to run if you just tap into a field wire and run it in the car within the drivers reach on a toggle switch. I burned out a rotor on my bracket cars alt so thats one reason I would kill the charging system when making a pass. Ron



Dont let the tech guy see you with a separate switch
set up like that... its a no no .. if you forgot and
had it on during a pass it wont kill the ignition
if needed and your knocked out




I run the alt output wire to the battery side of the cutout switch on my 63. I also put a voltmeter in the car since the stock ammeter wont read correctly when you run the alt output wire like that. On my old 340 bracket car in the late 70's and early 80's I burnt out two alt rotors so I thought taken power away from the rotor on the 6500 rpm passes may help to not damage the alt rotor circuit. Did it help ?? Well it did not burn out any more alt rotors but I did roll the car about 1-1/2 years later. Course with the alt output killed the car will die when the cutout switched is turned off even if the alt is not wired right but like you said if you forget to hit the toggle switch and would crash then it wont kill the car so I do agree with NHRA on that rule that you still have to run the alt output wire correctly. Ron
Posted By: rickraw

Re: Power Cut Off switch Question. - 03/28/14 11:09 PM

Does anyone have a fuse on their alt wire to the battery?
Posted By: CHAPPER

Re: Power Cut Off switch Question. - 03/28/14 11:28 PM

Quote:

Does anyone have a fuse on their alt wire to the battery?



I do.
Posted By: plycuda

Re: Power Cut Off switch Question. - 03/28/14 11:38 PM

I have one on the alt and the starter wire
Posted By: StealthWedge67

Re: Power Cut Off switch Question. - 03/29/14 12:03 AM

Quote:

Quote:

Does anyone have a fuse on their alt wire to the battery?



I do.



Lets go over this.... What size fuse, and where exactly is it?
Posted By: plycuda

Re: Power Cut Off switch Question. - 03/29/14 12:30 AM

I have 150 and 300 amp

Attached picture 8092265-20140328_180958-Copy.jpg
Posted By: 383man

Re: Power Cut Off switch Question. - 03/29/14 12:44 AM

My original harness uses the fuseable links to protect the alt output wire from a short. I added a 70 amp large type bolt on fuse at the battery on my 63 with the battery in the trunk as it has eyelet terminals so I bolted it to the battery cable end and then bolted the wire from the alt to it as I put an eyelet terminal on the alt wire at the battery end. Ron
Posted By: Bigcube

Re: Power Cut Off switch Question. - 03/29/14 02:07 AM

I don't like running the alternator wire to the battery because that wire will be hot all the time. I set mine up with a relay. I use a continuous duty relay, similar to a Ford starter relay. See attachment.

Attached picture 8092372-2519432-KILLSWITCHRELAY.JPG
Posted By: MR_P_BODY

Re: Power Cut Off switch Question. - 03/29/14 02:37 AM

Quote:

Does anyone have a fuse on their alt wire to the battery?



Yes.. I have a 100 amp on it
Posted By: rickraw

Re: Power Cut Off switch Question. - 03/29/14 02:47 AM

How many amp alt?
Posted By: racerx

Re: Power Cut Off switch Question. - 03/29/14 05:11 AM

for this.
Posted By: MR_P_BODY

Re: Power Cut Off switch Question. - 03/29/14 05:14 AM

Quote:

How many amp alt?



Its a 85A Denso
Posted By: racerx

Re: Power Cut Off switch Question. - 03/29/14 05:34 AM

Quote:

I have 150 and 300 amp

Where do uall purchase these fuses from?
Posted By: MR_P_BODY

Re: Power Cut Off switch Question. - 03/29/14 05:43 AM

Quote:

Quote:

I have 150 and 300 amp

Where do uall purchase these fuses from?



I get them from a local electrical ware house near me..
its a larger fuse like the mini flat bladed ones in
the cars about 8 years ago... its just bigger with
its own holder
Posted By: Just-a-dart

Re: Power Cut Off switch Question. - 03/29/14 06:11 AM

Quote:

Quote:

I have 150 and 300 amp

Where do uall purchase these fuses from?



Good car audio shops have them.
Posted By: racerx

Re: Power Cut Off switch Question. - 03/29/14 01:13 PM

Quote:

Quote:

Quote:

I have 150 and 300 amp

Where do uall purchase these fuses from?



Good car audio shops have them.

Thax.
Posted By: rbj

Re: Power Cut Off switch Question. - 03/29/14 03:44 PM

Quote:

I don't like running the alternator wire to the battery because that wire will be hot all the time. I set mine up with a relay. I use a continuous duty relay, similar to a Ford starter relay. See attachment.



X2 ran mine same way , they run the constant duty on golf carts a lot got mine of eBay cheap and easy. Dvw recommend this idea and works well.
Posted By: TruPerformance

Re: Power Cut Off switch Question. - 03/29/14 06:00 PM

Rather than running the alt power wire all the way back to the kill switch, I found it easier to run the field wire through a relay. I just ran a small 12 ga wire back to the switch for power, when the switch is off, car dies. I thought that was better than running the higher voltage the length of the car.
Posted By: RobX4406

Re: Power Cut Off switch Question. - 03/29/14 06:57 PM

You can fuse all you like, BUT, that line is still live until the fuse blows. Plenty can go wrong until that happens.

I do the CD relay and kill the line. Rather not have any live wires to the front when the master switch is thrown.
Posted By: StealthWedge67

Re: Power Cut Off switch Question. - 03/29/14 07:46 PM

Quote:

I have 150 and 300 amp



Sorry to be an electrical idiot.... but that's what I am, and I want to be certain of what I think I'm seeing: We're talking about a 300 amp fuse on the pos. cable, and a 150 amp fuse on the neg, correct? Then, following Mike & Jim's outlines, a 100 amp fuse on the alternator wire, along with running that wire through the continuous duty relay....

Am I straight on this?
Posted By: Bigcube

Re: Power Cut Off switch Question. - 03/29/14 08:10 PM

Yes, you wire per the diagram AND use the fuse. I should put a fuse in mine.

My alternator is very close to the frame. I would forget to take the battery cables off and saw sparks when I was pulling the motor. I wired it in before I put it back together a few years ago. The Solenoid is the silver thing under the tail light behind the battery.I have it wired into the cut off switch.





Posted By: 383man

Re: Power Cut Off switch Question. - 03/29/14 08:32 PM

On mine I use a Ford type starter solenoid in the trunk since I ran my starter cable under my carpet I did not want it hot all the time so its only hot when cranking as I have it going thru the solenoid. The smaller red wire is my 12 volt feed which is the wire my cutout switch controls as it goes to the starter relay on the firewall where the car picks up it hot 12 volt feed to the fuse box , ign switch , headlite switch and so on. I have a 70 am fuse with eyelets on it on the red wire as its bolted to the battery cable end and then hooked to the wire. The black wire is my alt output. I like the idea of putting the field circuit on a relay that would kill the field when you turn the kill switch off and stop the charging system from working. That would work as long as the relay control turns the relay off when the cutout switch is turned off. Ron

Posted By: Todd

Re: Power Cut Off switch Question. - 03/29/14 08:32 PM

Did mine the same way. That way the power at the alt is off when the kill switch is off.

Attached picture 8093352-DSC00788(Large).JPG
Posted By: RobX4406

Re: Power Cut Off switch Question. - 03/29/14 08:45 PM

On a race car the way that s605 is wired is fine if you turn the master off.

Street car, if you leave the master on, the S605 will be a constant draw and drain the battery. It needs to be switched with something from a keyed source in the on position.

There's a minimum standard, then there are improvements.
Posted By: StealthWedge67

Re: Power Cut Off switch Question. - 03/29/14 09:20 PM

Quote:

On a race car the way that s605 is wired is fine if you turn the master off.

Street car, if you leave the master on, the S605 will be a constant draw and drain the battery. It needs to be switched with something from a keyed source in the on position.

There's a minimum standard, then there are improvements.



Uhggg...... Why must there always be problems?! Are there relays available that would work like this, but not need to be switched? I generally break the master cutoff whenever I leave the car. But if I were to add this, I would want to do it correctly and not expose myself to potential dead battery issues. Wiring it all the way from the key switch seems like a hassle and lots of added wiring, which I don't want.

PS: sorry to hi-jack, but this is good info. and I think its relevent to the OP.
Posted By: RobX4406

Re: Power Cut Off switch Question. - 03/29/14 09:56 PM

Quote:

Quote:

On a race car the way that s605 is wired is fine if you turn the master off.

Street car, if you leave the master on, the S605 will be a constant draw and drain the battery. It needs to be switched with something from a keyed source in the on position.

There's a minimum standard, then there are improvements.



Uhggg...... Why must there always be problems?! Are there relays available that would work like this, but not need to be switched? I generally break the master cutoff whenever I leave the car. But if I were to add this, I would want to do it correctly and not expose myself to potential dead battery issues. Wiring it all the way from the key switch seems like a hassle and lots of added wiring, which I don't want.

PS: sorry to hi-jack, but this is good info. and I think its relevent to the OP.



Find a wire that is hot when key is in run position and wire it to trigger the CD relay, pretty simple.

What's a 16ga wire weigh... not much and have it mirror route of the taillight wiring.
Posted By: 383man

Re: Power Cut Off switch Question. - 03/29/14 11:04 PM

Quote:

Quote:

Quote:

On a race car the way that s605 is wired is fine if you turn the master off.

Street car, if you leave the master on, the S605 will be a constant draw and drain the battery. It needs to be switched with something from a keyed source in the on position.

There's a minimum standard, then there are improvements.



Uhggg...... Why must there always be problems?! Are there relays available that would work like this, but not need to be switched? I generally break the master cutoff whenever I leave the car. But if I were to add this, I would want to do it correctly and not expose myself to potential dead battery issues. Wiring it all the way from the key switch seems like a hassle and lots of added wiring, which I don't want.

PS: sorry to hi-jack, but this is good info. and I think its relevent to the OP.



Find a wire that is hot when key is in run position and wire it to trigger the CD relay, pretty simple.

What's a 16ga wire weigh... not much and have it mirror route of the taillight wiring.



Rob is right as it is simple just make sure you use key on powered wire as I would not use a hot all the time wire for much of anything so you dont have a draw. I leave my switch on most of the time on the street and have no drain at all. But I run my alt output back to the battery side of the master switch and only use a solenoid for my starter cable. I do turn it off if I park the car where I cant see it all the time. Ron
Posted By: plycuda

Re: Power Cut Off switch Question. - 03/30/14 01:15 AM

Quote:

Quote:

I have 150 and 300 amp



Sorry to be an electrical idiot.... but that's what I am, and I want to be certain of what I think I'm seeing: We're talking about a 300 amp fuse on the pos. cable, and a 150 amp fuse on the neg, correct? Then, following Mike & Jim's outlines, a 100 amp fuse on the alternator wire, along with running that wire through the continuous duty relay....

Am I straight on this?




300 amp on the starter cable and 150 on the alternator cable. not the neg cable
Posted By: Scott58

Re: Power Cut Off switch Question. - 03/30/14 02:33 AM

Another option that I don't think has been mentioned in this thread is the use of a double pole / 4 terminal cutoff switch like a Longacre 45780 or 45782 (for higher output alternators). It solves the problems of a constantly "hot" alternator wire / solenoid drain.

http://www.longacreracing.com/products.a...amp;prodid=7581
Posted By: MR_P_BODY

Re: Power Cut Off switch Question. - 03/30/14 02:41 AM

Quote:

Another option that I don't think has been mentioned in this thread is the use of a double pole / 4 terminal cutoff switch like a Longacre 45780 or 45782 (for higher output alternators). It solves the problems of a constantly "hot" alternator wire / solenoid drain.

http://www.longacreracing.com/products.a...amp;prodid=7581



If I were to change over I would go with this switch..
I always like the KISS way of doing things
Posted By: RobX4406

Re: Power Cut Off switch Question. - 03/30/14 02:47 AM

Quote:

Another option that I don't think has been mentioned in this thread is the use of a double pole / 4 terminal cutoff switch like a Longacre 45780 or 45782 (for higher output alternators). It solves the problems of a constantly "hot" alternator wire / solenoid drain.

http://www.longacreracing.com/products.a...amp;prodid=7581



Decent solution. It is more money than a CD and 180 amp master switch
Posted By: MR_P_BODY

Re: Power Cut Off switch Question. - 03/30/14 02:59 AM

Quote:

Quote:

Another option that I don't think has been mentioned in this thread is the use of a double pole / 4 terminal cutoff switch like a Longacre 45780 or 45782 (for higher output alternators). It solves the problems of a constantly "hot" alternator wire / solenoid drain.

http://www.longacreracing.com/products.a...amp;prodid=7581



Decent solution. It is more money than a CD and 180 amp master switch



But with way less stuff that can fail... I'll take
the KISS way every time
Posted By: RobX4406

Re: Power Cut Off switch Question. - 03/30/14 03:11 AM

Quote:

Quote:

Quote:

Another option that I don't think has been mentioned in this thread is the use of a double pole / 4 terminal cutoff switch like a Longacre 45780 or 45782 (for higher output alternators). It solves the problems of a constantly "hot" alternator wire / solenoid drain.

http://www.longacreracing.com/products.a...amp;prodid=7581



Decent solution. It is more money than a CD and 180 amp master switch



But with way less stuff that can fail... I'll take
the KISS way every time




And if one side of that component fails...

It's two components built into one switch. It's still controlling two circuits. You can still wire around one side in an emergency.

Pick your parts, pay your money.
Posted By: MR_P_BODY

Re: Power Cut Off switch Question. - 03/30/14 03:20 AM

Quote:

Quote:

Quote:

Quote:

Another option that I don't think has been mentioned in this thread is the use of a double pole / 4 terminal cutoff switch like a Longacre 45780 or 45782 (for higher output alternators). It solves the problems of a constantly "hot" alternator wire / solenoid drain.

http://www.longacreracing.com/products.a...amp;prodid=7581



Decent solution. It is more money than a CD and 180 amp master switch



But with way less stuff that can fail... I'll take
the KISS way every time




And if one side of that component fails...

It's two components built into one switch. It's still controlling two circuits. You can still wire around one side in an emergency.

Pick your parts, pay your money.



I understand that its basically 2 switches but from
the guys that I know running it they havent had any
failures in at least 6 years( and still going)..
I had a failure in a constant duty solenoid in a
matter of a few weeks on my Rampage.. I replaced it
but bought a spare to carry with me
Posted By: 70HemiGTX

Re: Power Cut Off switch Question. - 03/30/14 06:09 AM

Quote:

Another option that I don't think has been mentioned in this thread is the use of a double pole / 4 terminal cutoff switch like a Longacre 45780 or 45782 (for higher output alternators). It solves the problems of a constantly "hot" alternator wire / solenoid drain.

http://www.longacreracing.com/products.a...amp;prodid=7581




I have a similar switch on my Dart. Two poles are large and two are smaller. The larger ones have the + cable running over that side of the switch. The smaller ones have 3 wires coming off the switch going to three different relays. 1 for a relay that supplies current to the MSD box and 2 wires go to the relays at the fuel pumps. Flip the switch and the engine and both fuel pumps shut down immediately. Very simple and not much current in the three wires going to the relays. Plus I have a 300A fuse in the + cable before the switch and a 5A fuse for the smaller wires. Pretty simple and effective.
© 2024 Moparts Forums