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Battery disconnect

Discussion in 'The Hokey Ass Message Board' started by Hotrodmyk, Mar 27, 2013.

  1. A short while back I read a thread about where to install a battery disconnect. It seems to me there was discussion about the ground side or the "hot" side. I can't seem to find it. I would like to hear both sides again.

    I'm talking about a disconnect like the one pictured.

    Thanks.
     

    Attached Files:

  2. Normal Norman
    Joined: Aug 9, 2006
    Posts: 510

    Normal Norman
    Member
    from Goshen IN.

    I believe the NHRA requires the pos. side to be the one disconnected by the switch. I wired mine that way FWIW. Normal Norman
     
  3. CutawayAl
    Joined: Aug 3, 2009
    Posts: 2,144

    CutawayAl
    Member
    from MI

    Switching the positive battery cable allows the alternator/generator to continue supplying power to the car. The fix for that is to either put the charge wire on the battery side of the switch, or get a switch that has a separate set of contacts for the alternator/generator charge(+) wire.

    Some of those switches have a current rating that is less than the starter draws. Although you can usually get by with it, if you don't have the switch yet, best sure to get one that's rated for what it's being asked to do.
     
  4. denis4x4
    Joined: Apr 23, 2005
    Posts: 3,555

    denis4x4
    ALLIANCE MEMBER
    from Colorado

    I prefer the negative side for the battery switch for my boats and banger powered hot rods.
     

  5. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    I run them on the positive side because in the event of a short you want to be able to kill the current flow. All the cars and boats I have ever wired are done that way.


    Don
     
  6. 39 Ford
    Joined: Jan 22, 2006
    Posts: 1,558

    39 Ford
    Member

    Both ways will accomplish the job.
     
  7. Willy301
    Joined: Nov 16, 2007
    Posts: 1,426

    Willy301
    Member

    Ok, first, the reasoning behind switching the positive lead:
    If you get a short, and you "disconnect" the ground, you have not fixed anything. The short becomes the ground.

    Second, these switches are usually rated 300 amps, with a very high intermittent load rating to cover for starter usage. That only plays into it as long as you don't have to crank excessively. You do need to connect the charge wire to the car side of the cutoff switch, or as pointed out above, it will keep running.
     
  8. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    And always shut the motor off before shutting the battery disconnect switch off. Otherwise, you can damage the alternator.

    Don
     
  9. BootleggerMatt
    Joined: Aug 17, 2011
    Posts: 258

    BootleggerMatt
    Member

    I am disapointed that so many do not know how a battery works.
     
  10. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    Are you going to leave it at that or enlighten us ?

    Don
     
  11. Hamtown Al
    Joined: Jan 17, 2007
    Posts: 2,393

    Hamtown Al
    ALLIANCE MEMBER
    1. Virginia HAMB(ers)

    Don, the guy is a bootlegger... he already made off with the answer!!
     
  12. BootleggerMatt
    Joined: Aug 17, 2011
    Posts: 258

    BootleggerMatt
    Member

    I will take the socratic approach and rather than explain how it works, I will ask a question to the select few that demonstrated inaccuracies in their idea of how one works.

    If you disconnect the ground, and there is a short in the cars electrical system, why do you think the short will become the ground? Were is the current flowing when the negative cable is disconneted? Is it going into the actual ground (dirt)?

    Sorry if I sounded like a dick, or still do... I'm bored and washing clothes for Viva Las Vegas tomorrow.
     
  13. The37Kid
    Joined: Apr 30, 2004
    Posts: 27,353

    The37Kid
    Member

    A simple YES or NO, will this Pollak switch work on my Roadster project, or did I piss away money on my first electrical part? Bob
     

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  14. raengines
    Joined: Nov 6, 2010
    Posts: 227

    raengines
    Member
    from pa.

    you can come up with a case to make both ways look best, but in the end it don't make enough difference to matter. either one does the job.

    switch is fine 37
     
  15. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    Yes, it will work.

    Don
     
  16. fiftyv8
    Joined: Mar 11, 2007
    Posts: 5,120

    fiftyv8
    Member
    from CO & WA

    Those battery isolation switches are great insurance for your hot rod, consider a fire extinguisher as well.

    I isolate the earth side as per an earlier explanation.
    I am sure either side works better than nothing.

    I use the RED removable key type so I can take the key with me when locked up.

    I know it is only a soft anti theft effort but again better than nothing.
     
  17. garvinzoom
    Joined: Sep 21, 2007
    Posts: 1,169

    garvinzoom
    Member

    My thoughts exactly.
     
  18. LAROKE
    Joined: Sep 5, 2007
    Posts: 1,732

    LAROKE
    Member

    I have wired it on the ground side in both my trucks. I had it wired on the positive side at first and have a pile of alternators with burned out diodes to prove it.

    I admit to being "lost at sea" regarding electrical issues. I also note that most procedures regarding the battery instruct you to remove the ground terminal first and connect it last. Why is that.
     
  19. The37Kid
    Joined: Apr 30, 2004
    Posts: 27,353

    The37Kid
    Member

    ONE more YES or NO answer what wire/cable does the disconnect switch attach to + or - and IS THERE a differance with 6 and 12 Volt systems? BONUS question, why does REBEL WIRE offer LEFT and RIGHT hand drive wiring kits? Bob
     
    Last edited: Mar 28, 2013
  20. Carter
    Joined: Mar 18, 2006
    Posts: 1,406

    Carter
    Member

    There have been opinions offered in this thread for both positive and negative side installation, 6V or 12V shouldn't matter, and the bonus, I'd guess it's because the harness is engineered for position of steering column and switches and possibly fuse box.

    Sent from my DROID device using the TJJ mobile app
     
  21. Little Wing
    Joined: Nov 25, 2005
    Posts: 7,501

    Little Wing
    Member
    from Northeast

    Our old Charger had that on the back ( Drag car ) , though if a short or anything was going on think by the time you got to the back of the car, damage done
     
  22. G-son
    Joined: Dec 19, 2012
    Posts: 666

    G-son
    Member
    from Sweden

    Use a metal wrench to loosen the terminal. If you:

    A: Start at the positive, and touch any grounded metal part around the battery with the other end of the wrench you have made a short curcuit. Most of the car is grounded, so this is VERY likely to happen.

    B: Start with the negative: No danger if you touch any other grounded metal with the tool, since both the negative terminal and the rest of the car both are negative (or at least, not positive). The only thing that will make a short is if you manage to reach the positive terminal with the tool as you unscrew the negative terminal.

    Once one terminal is disconnected a short can only happen by touching that terminal with something connected to the other.


    Putting the breaker on the positive or negative lead does not matter very much, but it has some significance. If the circuit is broken, the circuit is broken - nothing can happen there anymore. You still have a live wire from the battery to the breaker ofcourse, so it should be as near the battery as possible, securely mounted and well insulated. Breaking the negative does have one advantage - if the breaker connections is shorted to the body or other grounded parts, nothing dangerous will happen since they are already supposed to be negative. If the positive goes through the breaker, and it touches ground in an accident or something like that... BBQ-time!
     
  23. You disconnect the ground first and reconnect it last because if your spanner slips while you are tightening the battery terminal and you touch the body, you can't get a short circuit, thereby welding (or worse) your spanner to the frame.
    It also gets REAL hot quick too.
     
  24. BootleggerMatt
    Joined: Aug 17, 2011
    Posts: 258

    BootleggerMatt
    Member

    Great explaination, very well thought out.
     
  25. Hnstray
    Joined: Aug 23, 2009
    Posts: 11,584

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL


    Yo, Socrates.......

    I see your point about the incomplete circuit when the ground post is effectively disconnected. I actually DO understand how all this works,...Hell, I taught it 40 years ago and within the last week posted (accurately) on a thread on a related issue.

    I have deleted the erroneous post. My excuse, if I need one (and I do :(), is failure on my part to think it through to it's logical conclusion as I apparently have (had) a bias to interrupt the positive side. My brain short circuited..........:)


    Ray


    Edit: just read G-Son's explanation and THAT also was humbling because it is EXACTLY what I have been doing for many, many years when changing a battery for the very reasons he mentions. I have to ask myself WTF was I thinking when I weighed in on this subject. Dang!!
     
    Last edited: Mar 28, 2013
  26. the answer is..........................................42
     
  27. Fenders
    Joined: Sep 8, 2007
    Posts: 3,922

    Fenders
    Member


    And that's the reason I install my battery disconnect in the negative (ground) lead.
     
  28. tommy
    Joined: Mar 3, 2001
    Posts: 14,758

    tommy
    Member Emeritus

    I wire mine in the positive cable so that it DISCONNECTS the battery from the car. The main wire from the alternator to the battery can be shorted out and since the battery is the source of the power it is no longer connected to the car there is no problem. If it was in the negative side, any short on the positive side can still burn the car down because the source of the power (the battery) is not isolated. That's my theory and I'm sticking to it.
     
  29. Carter
    Joined: Mar 18, 2006
    Posts: 1,406

    Carter
    Member

    I'll be installing mine on the positive side, which will be the ground side of my system.

    Sent from my DROID device using the TJJ mobile app
     
  30. G-son
    Joined: Dec 19, 2012
    Posts: 666

    G-son
    Member
    from Sweden

    Please give us a step-by-step explaination of what way the current goes from the batteries positive terminal to the batteries negative terminal, when a switch on the negative wire has disconnected the negative terminal from the rest of the car.

    No completed circuit? Then, no current. :cool:
     

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