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  #21  
Old 3 Days Ago
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There's a diode in gen wire could be problem with light.http://xlforum.net/forums/showpost.p...09&postcount=1
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  #22  
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not all machines have the diode.
in the scenario described in the link, the diode prevents the generator output from by-passing the regulator and prevent the generator from burning out the bulb.
on machines with out the diode, when key is on, power is sent to the bulb to the genny and its ground brush, as soon as the genny output exceeds battery voltage, the ground through the genny is lost.
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The diode was added when electronic ignition was added (I believe).

At any rate it prevents the bulb from glowing if the generator output exceeds the voltage applied to the other side of the bulb.

I believe the diode was installed to prevent the flow of power back through the light circuit and possibly keep the motor running with the key off. (although it would take a perfect storm to cause that)
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I thought the diode was added to cut down on gen light complaints/customer returns from the light flickering.
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Quote:
Originally Posted by doodah man View Post
I thought the diode was added to cut down on gen light complaints/customer returns from the light flickering.
That is why I posted
"At any rate it prevents the bulb from glowing if the generator output exceeds the voltage applied to the other side of the bulb."

I don't see customer complaints as a valid reason for a production change due to the bean counters.
Lawyers however can easily affect production changes. Look at why there are two throttle cables on 81+ models
That is my reasoning for the second statement.
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there are some misconceptions here.
first is how power flows through the diode
hd used the diode in a couple of scenarios
when used in the gen circuit, power came from the ign switch to the light and then into the diode (called rectifier in some books) negative or cathode side. the power would flow out the anode side to the armature of the genny and ground out through the negative brush, there was also a jumper that lead to the regulator "D+" terminal. when the engine was running and genny output was higher than the battery , the ground was lost through the genny since output power was now flowing to the regulator and out to the system. of note is that on the older machines with no battery, the circuit worked the same. since the diode blocks reverse current, power could not go back to the ign sw and if it did, full current (10amps) would blow the bulb.
look at another circuit
in later years, hd used the diode to separate left/right control circuits and was only on a year or so model. what is strange is that before and after that year, the diode was not present.

it is feasible as mr. rick said, shorted diode would feed back voltage to the ign sw and cause engine not to shut down with a battery system.
they added a capacitor to reduce flickering at low speeds. on the non battery systems, there was a sizeable amount of ac ripple which the capacitor sent to ground, the battery makes an excellent capacitor, hence filter capacitor not needed.

Last edited by bustert; 2 Days Ago at 16:24..
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For simplification and as it applies to the topic here.

The diode blocks current from traveling backwards from the gen through the gen light to the ignition circuit.
The diode also lowers the voltage passed by .7 volts, so the bulb does not illuminate as readily.
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