Posted by John T on February 04, 2008 at 14:36:57 from (24.227.192.14):
In Reply to: Wrong Diode I guess posted by TWheat on February 04, 2008 at 12:36:09:
TW, just about any diode rated more then a few amps (I like at least 5) with a PIV of 50 to 100 or even over volts will work fine TO PREVENT RUN ON WHEN THE IGNITION IS OFF VIA ALTERNATOR BACKFEED..........
NOTE That diode or a resistor (which I recommend n use) is NOT to prevent battery discharge like it sounds like you may be thinking butttttttttt it can make the engine stop when you switch off the ignition since if its not there the coil can get a back voltage feed from the alternator n keep running even with ignition OFF.......
NOTE to work as a backfeed preventer it must be wired negative end towards alternator.
NOTE Theres NOTHING wrong whatsoever with using a diode to prevent run on, Ive done it n seen em used for years NEVER any problem, there is like a 0.6 voltage drop across them
However being conservative n believing an ounce of prevention is better then a pound of cure n also thinking its better to be safe then sorry n based on some GM literature Ive read plus a GM engineers advice, I use n highly recommend a 10 ohm or more safety current limiting resistor be used in lieu of or in addition to (no problem with BOTH) a diode n in cases Ive observed with the resistor the diode isnt even required !!!!!!!!!!
When an idiot light is used instead of a diode or a resistor its resistrance is likely wayyyyyyyyyyy more then 10 ohms anyway (even more safety current limiting then a 10 ohm resistor) yet THE ALTERNATOR STILL WORKS FINE WITH NO DIODE AT ALLL since the idiot light or the current limiting safety resistor I use absorbs enough energy so run on doesnt occur when the ignition is OFF
BOTTOM LINE
THERES NOTHING WRONG WITH A DIODE ONLY
BUTTTTT AN IDIOT LIGHT OR A SERIES RESISTOR CAN ADD SOME CURRENT LIMITING AS A SAFETY FACTOR WHICH CANT HURT NOTHING PROVIDED ITS NOT SO MUCH RESISTNCE SHE CANT EXCITE AT ALL LOL
THERES ALSO NOTHING WRONG WITH USE OF A RESISTOR OR AN IDIOT LIGHT
Its your tractor and YOUR CHOICE and either a diode alone or the added safety of some degree of current limiting provided by a resistor ar an idiot light WILL EITHER OR EVEN BOTH WORK FINE.......
Hope this helps yall understand the whole alternator excitation n resistor n diode thing a bit better. I believe Bob has some great alternator internal wiring diagrams which may help even more
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