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The fan diode on my 2006 650 V2 failed and I simply bypassed it. How important is this diode? Do I need to replace it?
 

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The diode on my T cat failed the first trip I took it on, I took the
Diode out and ran a jumper wire where the diode was, essentially
wiring the ground side of the fan directly to ground. 4000 miles
later it is still wired like that with no problems.

As far as the fan generating electricity, I doubt it. The
diode was put in the system to slow the fan speed down and
hopefully make the fan last longer according to one of the
Arctic Cat people that I talked to back in 2008.
 

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The diode is essentially a one way valve as I understand it allowing current to only flow in one direction.
 

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Correct, and yes a fan turning on its own will produce a DC voltage (it acts like a generator) The diode blocks this voltage from going back into the wiring. Reason is the voltage would be "noisy" and could screw up the electronics. It is also true that a diode also provides a small voltage drop, usually 0.7 volts. That is the reason for having it in the fan circuit.

Mike



The diode is essentially a one way valve as I understand it allowing current to only flow in one direction.
 

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A DC motor driven fan will produce a DC voltage when power is removed and is driven by wind passing through it. This voltage is reversed biased or has a reversed polarity from the voltage that it takes to normally run it. Meaning the positive wire become negative and negative become positive. The un-powered rotating fan by wind will not generate full reversed voltage and not a whole lot of amperage though. Apparently Quadman15's observations show or prove no real problems or damage results. At least in his observations since he has experienced no problems. If a wind driven fan did not produce a voltage then the DC generator never would of been invented and never placed into service. There is a voltage drop when current runs through a diode, that is the nature of diodes only. It has nothing to do with slowing down the speed of the fan even though that is the result of powering a fan through a diode. If a fan operating at a lower speed was desired, they would just build a fan with less windings in the armature and save on copper wiring costs too instead of adding to the cost by including a diode.

There maybe is one scenario where damage to the sensitive electronics could be damaged though. This is if while you are riding at speed and for some reason the 30 amp fuse opens or you shut the key off to perform a plug chop or maybe even accidentally hitting the kill switch. An open 30 amp fuse or the key off removes power to the ATV that would normally be from the battery and or the stator. All wiring downstream of the switch or fuse would see a reverse polarity voltage generated from the wind rotating fan. The transistors and integrated circuits in the ECU and the LCD may get a dose of this reverse polarity voltage. Enough to fry them? I don't know. Perhaps? Perhaps not?

It's a common practice to include a blocking diode in any DC driven motor just because it could prevent possible negative results when coasting down after power is removed. Especially in circuits that include digital components, like the ECU and the LCD display do. Personally I'd use the diode myself and not take a chance.
 
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I have had several occasions where I've shut the key off on my 99 500 and the quad continued to run for several seconds afterward. It seems this happens when the key is shut with the fan running. The only thing I could attribute this to is the fan diode being shorted and allowing the fan to generate enough electricity to keep the ignition on until the fan winds down. Been meaning to test to see if the diode is in fact shorted, this thread has gotten me a bit motivated and I plan on doing this over the weekend.
 

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I wish Arctic Cat would sell the Diode as a part. It is only included
as part of the $500+ wiring harness for my machine. My Diode
fell into 2 pieces when I removed it from the harness as the
Solder between the wire connector and the diode failed/broke.
I soldered it back together and it checked out O.K. so as with several things AC made the quality was suspect.

Wouldn't it make more sense to put a Zener diode in the Positive
wire to the fan to stop possible feed back from a rotating fan under remote circumstances, the Zener would only allow
voltage from the battery to the fan, not from the fan to the
battery or other components.
 

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I wish Arctic Cat would sell the Diode as a part. It is only included
as part of the $500+ wiring harness for my machine. My Diode
fell into 2 pieces when I removed it from the harness as the
Solder between the wire connector and the diode failed/broke.
I soldered it back together and it checked out O.K. so as with several things AC made the quality was suspect.

Wouldn't it make more sense to put a Zener diode in the Positive
wire to the fan to stop possible feed back from a rotating fan under remote circumstances, the Zener would only allow
voltage from the battery to the fan, not from the fan to the
battery or other components.
The fan draws about 7-10 amps of maximum amperage +/- a amp or two. 15-20 amp blocking diodes or even larger (larger just for a margin of safety to prevent burnout and larger than or equal to the fuse rating) are readily available on Ebay or even Radio shack for a dollar or two. If arctic cat sold them they probably would be very expensive.

A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an a regular diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage" or "Zener voltage" or "Avalanche point". What this means is of you have a 12 volt Zener it will behave the same as a regular diode up to 12 VDC. At above 12VDC it behaves like a piece of wire or a fuse and allow two way current to pass until the voltage was equal to or less than 12VDC where it would work like a regular diode again. No benefit as a blocking diode and since Zeners are more costly I doubt if they would use zeners if even there was some benefit.

If I sound like a electronics engineer its because I was a digital electronics technician in a former life. <grin> Yup I was a Geek. I've forgotten most of it though <grin>
 

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I have had several occasions where I've shut the key off on my 99 500 and the quad continued to run for several seconds afterward. It seems this happens when the key is shut with the fan running. The only thing I could attribute this to is the fan diode being shorted and allowing the fan to generate enough electricity to keep the ignition on until the fan winds down. Been meaning to test to see if the diode is in fact shorted, this thread has gotten me a bit motivated and I plan on doing this over the weekend.
Umm not sure if the CDI will still operate with a reversed voltage. Maybe? Most likely caused by red-hot carbon buildup in the cylinder. Also caused by a spark plug that may be too hot in heat range and is red hot and maybe even jetting too rich or two lean. The glowing carbon deposits can act like a spark plug and ignite the a/f fuel mixture once the cylinder pressure reaches near the auto-ignition pressure/temperature point. Auto-ignition is the basis of how diesel engine operate and commonly called Dieseling when it take place in a gasoline engine.
 

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From a theoretical engineering analogy, How fast would a quad
have to go, heading into a 30 MPH wind to induce reverse
fan speed sufficient to produce in excess of the 12 volt
avalanche point of a 12 volt Zener Diode.
 

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46.7665 miles per hour:)
 

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Umm not sure if the CDI will still operate with a reversed voltage. Maybe? Most likely caused by red-hot carbon buildup in the cylinder. Also caused by a spark plug that may be too hot in heat range and is red hot and maybe even jetting too rich or two lean. The glowing carbon deposits can act like a spark plug and ignite the a/f fuel mixture once the cylinder pressure reaches near the auto-ignition pressure/temperature point. Auto-ignition is the basis of how diesel engine operate and commonly called Dieseling when it take place in a gasoline engine.
I would have suspected "dieseling" as well but it literally runs perfectly, just like when the key is on. Maybe there's just a relay that's hanging up when I shut the key? I'd have to go dig into the manual and have a look at the schematics.

John
 

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Discussion Starter #15
Update + new issue

Thanks for all the feedback with regards to the diode, but I now have a new (hopefully unrelated) problem.

After taking a ride of 50+ miles I shut off my ATV but when I went to unload it I got no power when I turned my key on. No display, no brake lights, etc... I still have power since my auxiliary plug still works and the battery tested fine. No blown fuses or loose connections, and the ground wire is securely attached. I'm thinking it may be a faulty ignition\key switch.


Could the missing diode have burned out my CDI or other electronics?

Any thoughts?
 

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My diode is bypassed and I have had no problems for the past 2 years. I think it's something in the switch.
 
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