Power Cut Off switch Question.
#1599655
03/28/14 02:20 PM
03/28/14 02:20 PM
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Joined: Feb 2006
Posts: 474 Alberta, Canada
451Guy
OP
mopar
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OP
mopar
Joined: Feb 2006
Posts: 474
Alberta, Canada
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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.
Thanx 451 Guy
512 cu in 71 Demon Super Street Car - NO LONGER - Broke Crank Best ET 9.57 @ 139.96
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Re: Power Cut Off switch Question.
[Re: 451Guy]
#1599656
03/28/14 03:18 PM
03/28/14 03:18 PM
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Joined: Oct 2004
Posts: 8,165 Left Coast
BobR
master
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master
Joined: Oct 2004
Posts: 8,165
Left Coast
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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.
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Re: Power Cut Off switch Question.
[Re: challenger1320]
#1599659
03/28/14 03:48 PM
03/28/14 03:48 PM
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Joined: Jan 2003
Posts: 13,375 Marion, South Carolina [><]
an8sec70cuda
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 13,375
Marion, South Carolina [><]
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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.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Power Cut Off switch Question.
[Re: challenger1320]
#1599660
03/28/14 03:50 PM
03/28/14 03:50 PM
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Joined: May 2003
Posts: 1,751 Graham, WA
Polarapete
top fuel
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top fuel
Joined: May 2003
Posts: 1,751
Graham, WA
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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.
1986 Dodge Ramcharger 440 2wd, Bracket Racer Under Construction 1998 Ram 2500 QuadCab, new daily driver. 2008 Honda Element 2014 Carry-On 7x14 Cargo Trailer
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Re: Power Cut Off switch Question.
[Re: 451Guy]
#1599661
03/28/14 04:15 PM
03/28/14 04:15 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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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
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Re: Power Cut Off switch Question.
[Re: Cab_Burge]
#1599664
03/28/14 04:28 PM
03/28/14 04:28 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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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
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Re: Power Cut Off switch Question.
[Re: MR_P_BODY]
#1599665
03/28/14 05:02 PM
03/28/14 05:02 PM
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Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,421
Balt. Md
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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
Last edited by 383man; 03/28/14 05:03 PM.
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Re: Power Cut Off switch Question.
[Re: StealthWedge67]
#1599673
03/28/14 08:44 PM
03/28/14 08:44 PM
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Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,421
Balt. Md
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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
Last edited by 383man; 03/28/14 09:00 PM.
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Re: Power Cut Off switch Question.
[Re: 383man]
#1599674
03/28/14 10:07 PM
03/28/14 10:07 PM
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Joined: Nov 2003
Posts: 10,384 Upstate NY
Bigcube
I Live Here
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I Live Here
Joined: Nov 2003
Posts: 10,384
Upstate NY
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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.
Jim
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