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Farmall & IHC Tractors Discussion Forum
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diode question

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keith smith

10-31-2007 19:07:36




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first of all i would like to thank all those who
were kind enough to help me with my charging problem.....

question i installed a diode going to #1 terminal,engine
no longer runs after shutting down...but the diode get real hot with switch on engine off...
ok with engine running.


diode 3 amp 200piv radio shack 276 1143

thanks




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John T

10-31-2007 21:12:49




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 Re: diode question in reply to keith smith, 10-31-2007 19:07:36  
Keith, Instead of a diode I use a 10 ohm current limiting protection resistor in that excitation circuit and when guys use idiot lights in the same location they are even more resistance then that. The resistor alone should prevent run on from alternator feed back but if not, only then would I add a diode. If the ignition is off there shouldnt be any voltage source getting to that diode if your excitation circuit is wired corectly and when on there will only be current flow until such time the alternator is self exciting so it shouldnt get hot IF THE ALTERNATOR IS OKAY AND SHES WIRED CORRECT UNLESS YOU LEAVE THE IGNITION ON????

John T

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keith smith

11-01-2007 15:12:14




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 Re: diode question in reply to John T, 10-31-2007 21:12:49  
wow calm down boys...i noticed the diode was getting hot after installing it then double
checking for currant!!!!
thanks again keith



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Bob

10-31-2007 22:17:33




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 Re: diode question in reply to John T, 10-31-2007 21:12:49  
In MANY industrial and ag applications of these alternators, a diode was used, from the factory.

There's absolutely NOTHING wrong with using a diode.



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John T

11-01-2007 07:26:14




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 Re: diode question in reply to Bob, 10-31-2007 22:17:33  
I agree 100% Bob, Excellent point THERES NOTHING WRONG WITH THE DIODE. I dont recall ever saying there was, they work just fine to prevent run on. I just prefer the current limiting possible (even if never needed, Im a Conservative lol an ounce of prevention n cheap resistor is worth more then a pound of cure n expensive alternator repair) protection of a little resistance in that circuit plus a resistor (depending on its qulaity) may be less prone to failure, may be chaeper, and usually stops run on to the point the diode isnt even needed.

Heck, Ive seen em work for years With No Diode, With a Diode, With a Resistor, With Nothing and no problem, I just like the safety a resistor might offer even if its a slim one, better safe then sorry is my motto.

NO PROBLEM WITH A DIODE I AGREE

AND LIKEWISE, THERES NO PROBLEM WITH HAVING SOME CURRENT LIMITING RESISTANCE IN THAT EXCITATION CIRCUIT EITHER

Take care Bob, fun discussion, hope we dont bore the non sparkies lol

John T

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Bob

10-31-2007 19:42:22




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 Re: diode question in reply to keith smith, 10-31-2007 19:07:36  
WHY are you leaving the ignition switch "ON" without the engine running???

It serves NO purpose, and will burn the points, and overneat the ignition coil, IF the engine has stopped with the breaker points closed.

That being said, when the engine is RUNNING, the diode is reverse-biased, and carries no current.

The alternator's internal diode trio rectifies a portion of the stator's output to power the rotating field winding, through the voltage regulator. As the battery voltage comes up, field current drops, and field current drops.

When the engine is stopped, battery voltage has dropped enough to cause the regulator to ramp up the field current to "max", 3 to 5 Amps, which is now "sourced" through the diode, from the ignition circuit. That's why your diode is heating up. NOW SHUT THE DARNED KEY "OFF" BEFORE YOU BURN THE POINTS!

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