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Last Post 27 Apr 2004 09:41 AM by  seamus88
Alternator/Battery Kill Switch
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mister2dood
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08 Apr 2001 05:47 PM
    I have an ITA MR2. I'm trying to hook up my kill switch and I think I got the alternator part wrong. Which wire is the switch supposed to interrupt? The large white 8 gauge wire, or one of the 3 small wires?

    Thanks
    Aaron
    Lemke
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    10 Apr 2001 03:40 PM
    If you are using the correct type of kill switch, in addition to the two large terminals, there also four smaller terminals used to "kill" the alternator.

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    Lemke Design+Fabrication
    ITA-MR2
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    12 Apr 2001 07:09 PM
    Unless you plan to cut off the master switch with the car running, the cheaper 2 terminal seitch works just fine, and costs about half as much. that'swhat I've got on mine.

    Norm
    Lemke
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    13 Apr 2001 08:15 AM
    Isn't that the purpose of a kill switch, to stop the car when it is running...

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    Lemke Design+Fabrication
    DataTech
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    13 Apr 2001 09:30 AM
    [QUOTE]Originally posted by Lemke:
    [b]Isn't that the purpose of a kill switch, to stop the car when it is running...
    [/b]


    Oh... the two pole version will stop the car from running...... when the computer/ignition system burns up because the alternator spikes. Don't ask how I know.

    -dave
    ITA-MR2
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    14 Apr 2001 05:02 PM
    [QUOTE]Originally posted by Lemke:
    [b]Isn't that the purpose of a kill switch, to stop the car when it is running...

    [/b]



    Not necessarily. It's to remove power from all the electrical systems and lessen the probablity of an electrical fire. In virtually, all instances, the engine is already not running when the switch is activated. (If is is, you're probably not going to use it in that car again, anyway - unless some smarty shuts it down for you while you're on the grid.)

    The 4 pole ones insert a resistor across the field winding to keep it from spiking. And, yes, you do stand about a 1 in 4 chance of zapping the alternator if the switch is flipped with the engine running. FWIW, if you're not still running the ignition off the stock switch, you probably don't have the right stuff in the circuit, anyway.

    Bad diodes?? You mean my alternator would quit draining so much power? Like on my GT car?? And, yes - I really do know the answer.
    JHH
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    14 Apr 2001 06:52 PM
    Just to satisfy my curiosity, is there a good schematic in one of the prep books on the absolute best way to wire a kill switch? I'd like to make sure mine is set up correctly AND understand why...

    ITA MR2, now, about that 16 valve starter motor you were using....
    Anubis
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    14 Apr 2001 07:58 PM
    I am glad to see so much thought being given to this critical safety item. Just make sure it shuts off ALL electriconic equipment, many a time the kill switch shuts the engine but somethin like the fuel pump keeps pumpin not good. Place it in a conveniant spot both for you and us flaggers, mark it WELL and we'll all be happy. Pray to God ya never have to use it though.

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    Lance Snyder
    Atlanta Region F&C
    http://mars.de2000.net/
    stevei35
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    15 Apr 2001 05:45 PM
    Does anybody know which of the 3 wires coming from the alternator is wired to the
    resistor to ground? One goes to the computer,
    one goes back to the fuse box and one to the dash light indicator. Now, Which one gets
    grounded to stop the alternator output???
    Anybody wire these themselves???
    A little help....needed.
    Steve
    Lemke
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    16 Apr 2001 02:10 PM
    [QUOTE]Originally posted by ITA-MR2:
    [B]
    Not necessarily. It's to remove power...

    My reply really wasn't a question, the kill switch is required to "stop" the car when it is running. Period. If someone's car continues to run after the kill switch has been turned, there is still electrical current (whats making the spark plugs spark?)that represents a potentially dangerous situation.




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    Lemke Design+Fabrication
    SA McChesney
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    17 Apr 2001 07:19 PM
    The Big wire, or "D+", from the alternator is routed back to one of the NORMALLY CLOSED terminals on the kill switch , and the other NORMALLY CLOSED terminal (makes contact with kill switch OFF) is wired to ground THROUGH A RESISTOR. The D+ wire is also jumpered to the open side of the main huge terminals for the battery kill. (Otherwise the alternator won't work.)

    A lot of the kill switches come with this resistor. Don't just ground your alternator output.

    The NORMALLY OPEN terminals (little ones, makes contact with the kill switch ON) can be used for ignition, fuel pump, computer, etc. However, computers are sensitive to voltage spikes - be careful. I use them to interrupt the + wire on the coil. Car won't run without that, you can be sure.

    The full text of a good installation article from our Regional Tech Inspector can be found at the link below:
    [url="http://users.tellurian.net/hughes/articles/master.html wrote:
    http://users.tellurian.net/hughes/articles/master.html

    HOW TO WIRE A MASTER SWITCH

    [/URL]

    Hope that helps. Email me if you have questions. The worst part is isolating the alternator, and punching a hole big enough in your firewall to pass the battery cables (if you want the kill switch inside).

    -steve


    [QUOTE]Originally posted by stevei35:
    [b]Does anybody know which of the 3 wires coming from the alternator is wired to the
    resistor to ground? One goes to the computer,
    one goes back to the fuse box and one to the dash light indicator. Now, Which one gets grounded to stop the alternator output??? Anybody wire these themselves??? A little help....needed.
    Steve [/b]


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    Steve McChesney [url="http://www.ssdiv.com wrote:
    http://www.ssdiv.com[/URL]


    [This message has been edited by SA McChesney (edited April 17, 2001).]
    RSTPerformance
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    17 Apr 2001 10:00 PM
    On our Audis we have had lots of trouble with our Kill switch. I think we have run into every problem listed here!!!. Tell me if we have it done correctly now??? we have a 4 connector switch. WE ran 2 cables from the batery to 2 different connectors on the kill switch then off 1 connector oppisite the + input from battery we ran the charge wire from the altinator, This charges the battery when the car is running and the swith is on. Then from the last connector oppostie the other positive input we ran the starter and a wire that runs to the fuse panel that powers ALL electrical components. This seems to be working because it shuts the car down at all times and NO power goes to anything. WE previosly had the altinator and other things all connected together which ment that the car would stay running and after it was shut off it would still drain the battery??? this new way I set it up seems to work but I just did it today so we'll see if the battery is dead tomorrow. Do you guys think this is correct??? another thing on the altinator there is two connections. one normally has a red wire which goes back to charge battery and the other is a blue wire. WE took the blue wire and jumped it across the two because another person told us to do this. All I know is that if the wire is not jumped the altinator will not charge the battery however if it is jumped then it will charge the battery??? any thoughts??
    SA McChesney
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    18 Apr 2001 10:40 PM
    An alternator is different from a generator in that it produces AC current, like what's in your house, rather than DC current, like what your car battery needs.

    It also differs from a permanent magnet DC generator, in that it has no magnets. Instead, a field coil surrounds the armature, and works like a large electromagnet. By controlling the current in the field (the small wire on the alternator) you control how much current the alternator produces -- so you don't overcharge the battery.

    At the output of the alternator are several large diodes. These devices only pass current one way, so they "filter" the alternating current (AC) and convert it to a direct current (DC) (D+, or the big alternator wire) to charge the battery.

    A couple of caveats. First, because the field is a big electro magnet, and because the alternator produces way more current than it needs to run, once the field is charged it will stay charged until the current to the field is interrupted - as in turning the ignition off. As long as the engine has gasoline, and the field is charged, you can disconnect the battery and throw it away - the engine will keep on running electrically from the power of the alternator.

    Well, it's easy enough to take the D+ (big, usually red, usually part of the battery positive terminal) and put the NORMALLY OPEN part of the kill switch terminals in this wire. This interrupts the D+ alternator output, and doesn't allow it to charge the battery, run the fuel pump, or even keep the alternator field charged. The BAD news is that the diodes don't like a sudden voltage spike associated with a field collapse.

    What happens is that the coil of wire electromagnet field stores a lot of energy. If you interrupt the field suddenly, e.g. throwing the kill switch, all that energy has to go somewhere in a hurry. And it goes right into the diodes, which are now unfortunately also disconnected from the battery. The energy destroys the diodes, ruins the alternator, and perhaps even destroys some electronic voltage regulators.

    SO . . . what you have to do, when you throw the kill switch and open up the D+ (big wire) connection to the battery, is to immediately short the D+ to ground through a ballast resistor. This allows all the stored engery in the alternator to be quickly discharged, causing no harm to diodes or other components. You can do this by using the NORMALLY CLOSED contacts of the kill switch, so it makes like a gate or a railroad switch. The D+ wire from the alternator is on one side of both the normally open and normally closed switches. When the switch is ON, or RUN, the normally open contacts are closed, and the other normally open contact is wired back to the battery, completing the charging circuit. Everything is as normal and cool.

    Then, when you throw the kill switch to the OFF position, these contacts open, and the alternator can't power the vehicle anymore. At the exact same time, the gate is thrown on the normally closed side, and this circuit is complete. The other terminal of the normally closed side is wired to a big resistor, like an ignition ballast resistor, which is then connected to a good ground.

    So it's like a valve, and it directs the D+ alternator output either to the battery as normal when the kill switch is ON, or to a resistor ground drain when the switch is turned off.

    It's a lot harder to explain than it is to wire. Take a look at the above link. Bill Hughes is our Regional Tech inspector, and he does a pretty good job of explaining it. The setup works well for most every car with an alternator.

    As far as the Audi, it sounds to me like your field is always energised, and you'll always be charging. You'll overcharge your battery, especially on the track. The small (blue) wire on the alternator should always lead back to the voltage regulator or the fusebox/ignition switch. No need to do anything special with this wire. It's the big D+ wire that needs to be wired to the switch.

    Hope that helps. I should make a drawing if this gets too out of hand.

    -steve

    -steve


    [QUOTE]Originally posted by RSTPerformance:
    [b]On our Audis we have had lots of trouble with our Kill switch. ... blue wire and jumped it across the two because another person told us to do this. All I know is that if the wire is not jumped the altinator will not charge ... [/b]




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    Steve McChesney
    http://www.ssdiv.com
    mister2dood
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    19 Apr 2001 02:24 PM
    Thanks for all the replies...but I'm still confused. My kill switch has 4 poles - 2 large ones, 2 small ones. With the switch "ON", the large poles are connected (no resistance) and the small poles are connected (no resistance). Right now I have the battery ground going through the large poles, so with the switch "OFF" the battery is not grounded, no juice flows. I mistakenly hooked the small poles up to the 8 gauge wire coming from the alternator...those wires now get warm when the car is on and my car's battery drains as it sits with the switch in the "ON" position with the car turned off. There are 3 smaller wires (12 or 14 ga) going to the alternator, so I assumed one of those is supposed to go to the small poles on my switch. So,

    It sounds like I need a 6 pole switch to do Steve McChesney's method, which sounds reasonable.

    However, if I have the right switch (2 big, 2 small), what are the small poles for? ITA-MR2, does your kill switch cut all electrical? Any other MR2 drivers with a wired switch?

    I'm going to get my car tech inspected this Saturday - I'll ask around there, too.

    [This message has been edited by mister2dood (edited April 19, 2001).]
    SA McChesney
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    19 Apr 2001 03:59 PM
    The two-pole (4 terminal) switch is for cars without alternators. It sounds like you're shorting your alternator output to ground, which isn't good. You need a 3-pole (6 terminal) switch. It had the BIG terminals for the battery, the Norm Open small terminals for ignition/coil/computer/fuelpump/etc, and the Norm Closed small terminals for the alternator grounding resistor circuit.

    So that's a 3-pole (which means it's three seperate switches operated by the same lever) with 2 BIG NO terminals, 2 small NO terminals, and 2 small NC terminals.

    Here's a diagram showing how to wire it . . . pic worth 1024 words and all that.

    (Note that I stole.... er, "borrowed" it off a British website, so when they say earth they mean ground. Heh.
    [url="http://www.ssdiv.com/killsw.gif wrote:
    http://www.ssdiv.com/killsw.gif[/URL]

    Note that the (#2) terminals are the Norm Open and the (#1) are the Norm Closed. And also when I say "NORMALLY" that refers to the switch in the OFF or OPEN position.

    Good luck!

    -steve


    [QUOTE]Originally posted by mister2dood:
    [b]My kill switch has 4 poles - 2 large ones, 2 small ones . . . It sounds like I need a 6 pole switch to do Steve McChesney's method, which sounds reasonable.

    However, if I have the right switch (2 big, 2 small), what are the small poles for? ITA-MR2, does your kill switch cut all electrical? Any other MR2 drivers with a wired switch?[/b]


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    Steve McChesney [url="http://www.ssdiv.com wrote:
    http://www.ssdiv.com[/URL]


    [This message has been edited by SA McChesney (edited April 19, 2001).]
    usguys
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    19 Apr 2001 06:14 PM
    The kill switch should shut off the car and kill the ground for the battery.
    The ground should be wired though the large connectors on the switch.
    The smaller poles on the switch should cut the power to the alternator so that the car will stop running.
    There are two ways to do this easily.
    The first way is to wire the main power line to the fuse box thru the smaller posts on the kill switch. This is usually a direct line from the positive post of the battery to the fuse box. When you turn the switch to the off position the ground is cut and the positive is also cut. This shuts the whole car down. Without the positive power line being cut the alternator will continue to provide power to the ignition.
    The other way is to wire the main power at the ignition switch thought the kill switch. This will have the same effect as turning off the key.
    No matter which you use, be sure to use large enough wires for the circuit. Bigger is better so you reduce resistance.
    SA McChesney
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    25 Apr 2004 08:56 PM
    Just an update...


    keywords master switch kill switch master kill switch


    [url="http://www.ssdiv.com/master.html"]Master Kill Switch Wiring for Cars with Alternators[/URL]

    I hope that helps somebody . . . I still get hits from this topic years later! :eek:

    -steve
    seamus88
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    27 Apr 2004 09:41 AM
    All you need is a single pole switch. Not any of the fancy ones that you see out there. The way to connect it so it does not toast the altenator is to connect the charging wire from the alt. to the same side of the switch as the batt. It realy is that simple! When the switch is turned off the alt.still sees the batt. until the engine stops spinning but the switch being open stops the alt. from keeping the engine running.
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