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RE: Batt. cutoff switch

Subject: RE: Batt. cutoff switch
From: Chuck Rothfuss <>
Date: Wed, 09 Feb 2000 21:34:55 -0500

  This is a hot topic on both the shop-talk and land-speed lists tonite.  I
know what you mean about disconnecting the positive lead without also
shutting off the alternators field lead.  I "saw the light" as I melted
every light bulb in the car down to their ceramic base and fried an electric
fuel pump when my alternator lost it's reference source.  The solution is to
disconnect both the positive wire (neg ground system) and the field wire to
the alternator with the cut-off switch.  No field current = no magnetic
field in the rotor and zero current production.  

Chuck "Do you smell something burning?" Rothfuss
East Coast Timing Association #9
Pole Cat Hollow, NC

At 02:33 PM 2/9/2000 -0800, you wrote:
>Breaking the circuit (on either side) between a running alternator and the
>battery is NOT a good idea.  The alternator is fully capable of generating
>enough voltage to fry it's diodes (and possibly even you) when it's load is
>suddenly disconnected.
>IMO the big advantage of putting the cutoff on the chassis side is that then
>you can short either battery terminal to the battery (one at a time) without
>damage.  If the cutoff is on the hot side, then shorting the hot battery
>terminal to the chassis will produce *sparks*.
>> -----Original Message-----
>> From:
>> []On Behalf Of Mark J. Bradakis
>> Sent: Wednesday, February 09, 2000 11:39 AM
>> To:
>> Cc:
>> Subject: Re: Batt. cutoff switch
>> If you put the cutoff switch on the non-chassis side, the
>> alternator or
>> generator can still be turning enough to keep the ignition system
>> energized, so the motor may keep running.  If the cutoff switch has
>> connections for also breaking the alternator or generator
>> circuit, then
>> it can go on that side.
>> mjb.

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