GM High Tech Performance
Click here to find out more!

Master Disconnect switch for rear mount battery

GM High-Tech Performance
Item Posts    Sort Order

Master Disconnect switch for rear mount battery

srh4life89 srh4life89
New User | Posts: 3 | Joined: 12/13
Posted: 12/16/13
08:51 AM

I have a 92 camaro with a lsx 418 and f1 procharger unit and having to relocate battery from engine bay to rear trunk area, and I have also a high output alternator. Looking to find wiring diagram to wire in master disconnect switch and shut down everything for the track regulations for nhra. Anyone have any info where i could look also its a 2 wire for alternator like 4th gen camaro wiring.  

wayne712222 wayne712222
New User | Posts: 33 | Joined: 10/13
Posted: 12/16/13
07:57 PM

a few years ago.. i wrote these people an email about high amp solenoids and master cut off switches.. look what they have come up with  and there are several versions

75903 DPST Master Disconnect Switch

Two positions: Off-On. For 6-36V DC systems.
dpst: Will disconnect the battery and the alternator or generator field circuit.
Electrical ratings: Large studs: 1000A intermittent. 15 seconds On, 5 minutes Off. 125A continuous (unless noted). Small studs: 20A continuous.
Chrome-plated diecast lever.
Plated steel case.
Brass contacts.
Brass mounting stem 3/4" -16 thread 23/32" (18.3mm) long.
Fits panels through 3/16" (4.8mm) thick.
Two 3/8" -24 and two 10-32 studs.

here is a look at the brass case version..

M 290 05

these should be available thru your normal performance parts suppliers.

or .. stop at a big rig electrical rebuilder, heavy duty alternator/starter shop..

i have been worried about how to cut off the alternator output without blowing the diodes out of the alternator..  but i rarely work on full drag race cars anymore..

mostly street cars..

you are probably going to need to talk to a performance alternator rebuilder and give them the exact model of your alternator..

what happens is the spinning rotor is sometimes grounded at one brush.. sometimes it has positive and the other brush is controlled..

the voltage regulator on the controlled brush.. actually sends positive and negative pulse to the rotor winding..

on a grounded brush type of rotor.. to create a magnetic field it gives a little positive pulse.. this creates a magnetic field that breaks the stator windings and creates current.. but there is some magnetic field reflected back to the rotor.. this tries to create more voltage in the rotor.. so to dampen the raising voltage in the rotor.. the voltage regulator connects to ground for a split second. this reduces the magnetic field to reduce the current output..

but .. when you chop off the power to the alternator  will it shut down fast enough.  or.. will the residual magnetism continue to put out current and because there is NO load to push the current into.. the current builds up and becomes voltage.. its really easily for alternators to put out over 100 volts in a split second when the output is disconnected from the battery..

since the diodes are usually rated at 25 to 35 amps at 100 PIV.. and heavy duty versions are rated at 50 amps at 200 PIV..

PIV is the rating on the diode.. to pass voltage below or up to that level without shorting out..  once you get to that may either blow out the diode or short it out..

sorry to have raised more questions than i answered..

post more alternator info.(parts number). i will look around my tons of info..  its amazing what i have collected.

the original camaro alternator is a CS130 model.  At 105 amps.  

wayne712222 wayne712222
New User | Posts: 33 | Joined: 10/13
Posted: 12/17/13
10:31 PM

oh.. and they also have a DPST that has 4 3/8 studs.. for 2 circuits.. same ratings as above..  

srh4life89 srh4life89
New User | Posts: 3 | Joined: 12/13
Posted: 02/22/14
09:24 AM

My alternator is a Nations alternator for a corvette xp series 245 amp . But my main thing is getting everything wired in properly for tech inspection.  

srh4life89 srh4life89
New User | Posts: 3 | Joined: 12/13
Posted: 02/22/14
09:25 AM

My alternator is a Nations alternator for a corvette xp series 245 amp . But my main thing is getting everything wired in properly for tech inspection.  

wayne712222 wayne712222
New User | Posts: 33 | Joined: 10/13
Posted: 02/23/14
03:36 AM

wow.. that's a lot of amperage for an alternator..  you might want to go to a 4 gauge alternator to starter cable section.. but you will need to figure out some kind of fuse or fusible link. talk to the alternator provider.
there is a phone number at NHRA web site for individual tech inspections or tech questions. I don't know how this works with them.  probably cheeper than fuel but it depends on where you are located.

i spent some time this evening and tossed this together..  i still messed it up slightly.. and with that much alternator.. you will NOT want a 15 pound mini battery..

why do i say.. a braided ground strap between the back of the engine block and the body.. because the negative current coming out of the alternator is higher than from the battery so it needs to get into the body in the shortest direction..

you will also want to if you have an MSD or other brand remote box ignition .. ground the large black wires with that.. to the Engine block where the ground strap is attached or on the body where the ground strap is attached..  why.. where does the high voltage spark go after it jumps the spark plug gaps into the cylinder head..  into the heads.  but it must get back to the ignition module.. so if the big black wire is grounded to the engine block from the MSD BOX.. you will have the shortest path for the high voltage spark to make its complete circuit..  saving it a path that might end up back at the battery in the trunk and blowing out electronics along the way...

Disconnectswitchwiriringwayne Zpsc5377a58

you may also want one of these..

24505 Cole Hersee Zps60ad6353 or one of the push rod disconnect kits..

this diagram i cobbled together should disconnect the starter and alternator circuit and also the rest of the car and the ignition circuits individually..

so you will need a LONG section of 2 gauge cranking battery cable.. and  you will probably want a 4 gauge positive cable to supply the car from the switch terminal.  you might get by with a 6 or 8 gauge.. but it sounds like you might have serious other electronics to operate also..

Pushrodbatterydisconnect Zpsf609fe5a

since you sound like this is a serious build..  there is one more thing i might mention.. i don't know how NHRA will handle this.. but. if i was creating  this... i would have the switch mounted with the shaft vertical. an easily unbolted mounting plate.. so you could get to the back of the switch easily without needing to unmount it from the bracket..

pick up a pair of these 4 inch ABS closet flanges from the hardware or plumbing store.  and a short section of pipe to connect them.  you now have a flanged insulated mounting bracket to mount your disconnect in at any height..    cut U shaped slots in the sides and thru the flange so you can lay the cables in when you mount the bracket and switch.  this allows you to remove the switch and wiring easily.. and nothing rolling around inside the trunk can get at the switch posts..


this is just an idea..  i looked at other installations.. terminals exposed to the inner fender..  only an inch or so of clearance..  not for me.. forward thinking makes it work better..

lastly..  depending.. a morse cable to shut off the switch lever.. installed all the way to the front .. so you can shut off the entire car from the drivers seat..  one could also use something like a door lock solenoid or even a door popper wired to the ignition switch power side..  yes.. it would loose power as soon as the switch is shut off..  but thats the idea..  again just thoughts..

nhra also says in PRINT...

Mandatory when battery is relocated, or as outlined in Class Requirements.

An electrical power cutoff switch (one only) must be installed on the rearmost part of each vehicle and be easily accessible from outside the car body. This cutoff switch must be connected to the positive side of the electrical system and must stop all electrical functions including magneto ignition. The off position must be clearly indicated with the word “OFF.” If switch is “push/pull” type, “push” must be the action for shutting off the electrical system, “pull” to turn it on. Any rods or cables used to activate the switch must be minimum 1/8-inch diameter. Plastic or keyed switches prohibited. Switches and/or controls must be located behind rear wheels on rear-engine dragsters  

wayne712222 wayne712222
New User | Posts: 33 | Joined: 10/13
Posted: 02/23/14
04:28 AM

an additional thought..

pickup 8 of these if you can get them individually

Dorman - Autograde Copper Washer-1/16 Inch x 3/8 Inch x 3/4 Inch
Part No. 725-003

3 8 Copperwasher Zpsb5b48e37

these will reinforce the studs grip on the battery cable ring terminals when you install them above and below the ring terminals to reduce the vibration from burnouts from fatiguing the ring terminals or loosening the nuts..

will you need to trim them slightly??? don't know.. i actually have some of these in my junk drawer and i use them on the starter solenoid connections..  and yes.. i have to open the inside to use them on 10MM metric studs.. not an easy thing .  

tuffnuff tuffnuff
Moderator | Posts: 4 | Joined: 12/10
Posted: 02/23/14
01:18 PM

Great posts Wayne

When The Flag Drops.,.


The Bull ***t Stops.,.

P. Engineer, Engine Builder