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Old 08-29-2006, 07:40 AM
Beenaway2long's Avatar
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Race car emergency shut off

In a NHRA/IHRA drag car, we are required to install a switch to kill all power.

Would it be better to open the ground or hot lead?

I would think that by opening the ground, it would not be affected by the alternator and immediately kill the car.

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Old 08-29-2006, 10:46 AM
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Quote:
Originally Posted by Beenaway2long
In a NHRA/IHRA drag car, we are required to install a switch to kill all power.

Would it be better to open the ground or hot lead?

I would think that by opening the ground, it would not be affected by the alternator and immediately kill the car.
It's been a few years, but I think they require the hot to be wired to the cutoff switch. Their thinking was it must kill the fuel supply. Now this was before alternators became a hot item on race cars.
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Old 08-29-2006, 03:23 PM
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NHRA accepts this arrangement:
Attached Files
File Type: pdf moroso switch.pdf (122.8 KB, 383 views)
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Old 08-29-2006, 04:12 PM
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Doc here,

You want to Cut the power side AND be sure the Alternator output is Isolated (on the right side of the Cutof) as well in "OFF".

By interrupting ground, the Alternator , unless totally Isolated off the Steel parts of the engine, will continue a Ground, as the Body of the Alternator is at ground potential, as well as the ground lug..An easy way to think of it is, A ground circuit exists anywhere metal exsists..(in a perfect world..) If grounded and properly Bonded, the Body, frame, Fenders, Engine , Transmission, are all at the same ground potential..so just removing the charge circuit from ground, will not open the circuit..(except to the Battery..not the Alternator)

On the other hand, By removing the Charging circuit from battery , BUT not the power Buss support wire to the Car..(wrong side of the contact.) Will allow power to remain on the Car EVEN though the battery is disconnected..The alternator will still put 14.4 volts into the Ignition system (or support switched buss) anytime it's turning.

So you need to Isolate it from the Ignition (Switched Buss) AND the battery, Most disconnects provide this isolation.

Doc
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Old 08-30-2006, 12:59 AM
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Many racers run the alternator wire to the battery. This complies with NHRA rules, but the alternator wire is always hot as long as the battery is connected. So if the charging wire shorts out somewhere along its length, the cutoff switch won't stop the short circuit. The engine does always stop however. Other problem with this is the limited charging current with the long run of 10 gauge wire to the trunk mounted battery.

If you run your ignition wire through the switch small terminals it will still kill the engine every time. This would be the MSD small red wire going to the box. This wire takes very little current (hence the problem with feedback from the alternator warning light keeping the engine going until you install the resistor), and the long run doesn't bother the unit at all. The Flaming River PUSH OFF unit I installed also had a small resistor to save the alternator diodes for the split second the battery is disconnected (large terminals) from the wiring while the charging current is still flowing. This isn't a worry if the alternator wire runs directly to the battery, but is a concern with either the Moroso wiring or the Flaming River wiring.
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Old 08-30-2006, 06:36 AM
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I have the Flaming River unit, but don't remember anything other than the two large terminals.

So, should I run a 10ga.(or 8?) wire from the alternator to the battery + terminal? I was going to use a stock sized one wire alternator until the budget allowed a smaller one.

(I'll run the disconnect on the positive side instead of neg, like I planned)

Man, I thought I remembered every time I pulled the negative off the battery, my old cars would die, but pulling the positive would allow it to keep running (Alternator feedback). But then again, that was 25 years ago...
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Old 08-30-2006, 01:58 PM
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Doc here,

Just to clarify,

If you wire PAST the Master Disconnect switch with anything related to the Vehicle...You WILL NOT pass Tech Inspection.

The Flaming River is a Beefy Constructed Bus BAR switch , Configured as a Single throw, Double row, Single Pole (Two Single Pole Isolated contacts.One mechanical throw device)

It provides a terminal for a 2 AWG or better cable to the Battery..This should be considered as the Common point Center~Wiper to the switch..(The movable contact.)

It then Provides a Terminal for a 2 AWG cable To go to the Starter Solenoid Battery Terminal Bolt..(Where the Battery Cable is located now) If the Vehicle NOW Has another wire (s) located here (as well as fuse links..) Leave them there..just swap the cables.

Then The switch Provides a Terminal for a 10 gauge wire to be the main output lead for the Alternator..and it's fuse link.

There is another small terminal that is jumpered to the Battery Terminal , although the schematic Does not show it..One assumes it is a jumper for the Movable wiper portion of the switch Buss Bar to Battery power in the "ON" Side of the switch.

When the switch is put in the "OFF" position, The Mechanical Cam~Lock (or other Linkage Arrangement ) Moves the Big Brass Bars internal to the switch from making contact from the output terminals, to "Open" or no connection..

This opens EVERYTHING to the Battery, Alternator and Solenoid (where the Vehicle Buss Support system is currently connected) and No power will be found PAST the point of the Master Disconnect switch.

When the switch is placed in the "ON" position, The mechanical linkage (or Cam locks) Close the double Brass BUSS bars internal the switch, providing Connection Through it to the battery and the Alternator/Solenoid Terminals.

As far as the Charging wire for the system..Just because an alternator Say's 100 amp..Does not mean that is what it runs at all the time (or ever..)..You need to find the total draw , worst case scenario, for the Vehicle, (everything running) .. Then measure the Distance from the battery to the Device termination point, Look up on an AWG Chart and gauge your wire accordingly. Then Fuse link it slightly less than the wire capability. That will serve you well.

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Old 09-01-2006, 07:13 AM
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Doc, I'll double check the switch tonight. I would have sworn that there was just the (2) 3/8" lugs for the primary. Thanks for the info!!!
Its appreciated!


Jeff
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Old 09-01-2006, 10:29 AM
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Moroso has a nice NHRA accpetable switch. Has the two main lugs for the battery cable and two smaller ones to run the alternator wire through and then to the battery. So when the switch is off, it opens the main power and power to and from the alternator.
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Old 09-05-2006, 06:14 AM
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Doc,
The Flaming River "Big" (250 amp) only has the 2 big lugs. There are 2 more screws, but the hold the bake-olite to the metal casing.

I know Jegs offers some sort of relay, but no clue how it wires in.

Would I just run an 8 ga. wire back to the battery then? (assuming I use a one-wire alternator)
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Old 09-05-2006, 05:14 PM
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Doc here,

What will you be switching? the alternator or Battery..? 8 is good for the alternator..

Won't work for battery support..

A solenoid like a Ford type is the answer for total switching, except you need use a marine or industrial application type solenoid, that is rated 100% duty cycle, a Ford type is not..and will get HOT..

Wiring is simple should you decide to go with it..battery cable to E~Stop switched side, The switched side to the solenoid coil, ("s" terminal) The other unused bolt terminal to the alternator..this way, when you shut the E~stop down the solenoid coil drops out and the alternator goes dead also (no run on..)

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Old 09-05-2006, 06:05 PM
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I believe that you will still have run on with your solenoid because the alternator will continue to energize the "s" terminal and the vehicle will continue to run. The "s" terminal will still be getting juice from the alternator on the engine side of the switch. Or I didn't interpret your wiring correctly.

I played around with several relays and a half different wiring schemes and the *$#/@ engine would always keep running. That is when I admitted defeat and ordered the Push/Pull Flaming River switch with the extra contacts. If you use the standard 2-pole kill switch, the alternator charging wire will have to be on the battery side of the kill switch. If you use one of the multi-contact switches you can either wire the extra terminals to kill the ignition directly or interrupt either the voltage sensing wire, or the actual higher amperage charging wire (if the secondary contacts in the switch are rated for it). Were you meaning to come off the secondary switch for the solenoid?

One other ray of hope. On our other vehicle, the Firebird with the trunk mounted battery and one-wire alternator, the simple kill switch stops the engine cold when it is at idle. I believe it's because the one-wire alternator is not charging at idle since these require more RPM. This gets us by tech. I have a suspicion that if the engine was revved when the switch was turn off that the engine would then keep on running since it would be charging at the higher RPM.

Like I said, there seems like there should be a solution without having to spend the extra money on the smart switch, but we never found it.

Last edited by lust4speed; 09-05-2006 at 06:13 PM.
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Old 09-05-2006, 07:37 PM
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Quote:
Originally Posted by lust4speed
I believe that you will still have run on with your solenoid because the alternator will continue to energize the "s" terminal and the vehicle will continue to run. The "s" terminal will still be getting juice from the alternator on the engine side of the switch. Or I didn't interpret your wiring correctly.
Doc here,

You didn't interpret the wiring correctly..

Try this First attempt to see if it will not get run on:
  • The Big bolt from Either Side goes to the alternator output ONLY...
  • The "S" or solenoid COIL terminal Jumpers to the OTHER big terminal..
  • The Big terminal then goes to the Power "ON" side of the E~Stop...

In this configuration, the Solenoid Can ONLY fire once the power From the E~Stop is "ON" , as well as provide power from the alternator THROUGH a normally open contact held closed..

When you shut the E~Stop "OFF" It kills power to Solenoid Coil..and the contact that is NOT on the alternator side..The solenoid Coil opens, the contacts open , and the circuit is open and isolated to the alternator.

This, However, does give the possibility of the alternator some back feed through the energized solenoid on some setups..



IF it should backfeed or suffer "Hang Time" and hold the Solenoid high..(run on) you can alternatively wire the solenoid :
  • "S" is isolated to the "ON" side of the E~Stop ONLY,
  • power to the battery from either big solenoid contact terminal,
  • alternator output to the other big solenoid contact terminal..

All 3 will then be isolated from power and each other until E~Stop is "ON". It Can not backfeed at all..

The trick is , to get a 100% duty cycle solenoid to avoid heat / burnout..

Doc
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Old 09-06-2006, 06:19 AM
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Doc-
I know this is simple stuff for you, but I am so confused right now. I think some of the terminology is throwing me.

The E-Switch I have has 2 terminals. Load and Battery (Terms I understand ).

If I were to use #8 wire to the Battery side of the switch (Or just the battery for that matter) with the "one wire" alternator, I would assume it would shut down as no power can jump the switch. (No run on). The #8 wire should be big enough to get from the alternator to the battery without too much loss, wouldn't it? I think they use a #10 for a 4' run, don't they??

I sure do appreciate the help guys. I hate the thought of dragging a battery charger out after each round.
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Old 09-06-2006, 07:49 AM
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One more reason

These are all good answers.
One good reason for cutting the hot side is if you run braded or metal fuel line, cutting the ground would make this the primary ground if you have a fuel pup bolted to the frame.

I've never seen a fuel line heat up but I have seen a nitrous line burn in two. Lucky the bottle was empty.
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