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Headlight dim at rev

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Hey guys, general question, is it common for a stock crf450x incandescent bulb headlight setup to dim when the bike is reved or held at a higher RPM then idle? Or is it indicative of a failing stator or R/R or dirty connectors?

Before I go digging into the wiring harness looking for things I wanted to know if it's sucky OEM design or some other issue.

 

I heave read in other posts where someone had a similar issue and it was a bad hi/low switch. I will be taking the switch out of the loop over the weekend to see if it has any effect. I will also test with a incandescent bulb and the new LED bulb. In theory the LED shouldn't  dim at all since it's only pulling 20 watts on low and 30 on hi and the stator is rated for 35w. 

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Not sure about the dimming, but the front bulb is wired on AC, not DC, so you can't hookup a LED there.  The taillight however is wired on the DC side.

 

And stock stator output is 70 watts (45 watts AC and 25 watts DC for battery charging and taillight).

 

Jim.

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I don't know the answer to that.  I would strongly suspect it should not, but I don't know for sure.  Outside of a bad ground, I'm not sure what would cause that.   If a stator problem, I would think it would be a matter of heat; once the motor would warm up, then it just won't work at any rpm.  That's usually how stators act or they just outright quit from a short or an open.

 

As far as the LED, you can't simply hook one up to the existing headlight circuit.  You need to add a rectifier to convert the AC to DC.   The existing rectifier only supports 25 watts and that's just enough to charge the battery and tail light.  If you disconnected both of those, then you could use a LED on that circuit as a test, but then your getting regulated voltage as well, so that's really not a true test of the head light circuit either.

 

Jim.

Edited by Jim Dettman

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I have the stock headlight setup on my X still and I can't say I have ever noticed it dim with higher rpm. I don't normally ride during the time a headlight would be needed though so I usually just have it turned off unless I'm on a public road (plated bike).

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I have the stock headlight setup on my X still and I can't say I have ever noticed it dim with higher rpm. I don't normally ride during the time a headlight would be needed though so I usually just have it turned off unless I'm on a public road (plated bike).

 

If you think of it could you fire the bike up one of these nights and see.

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If you think of it could you fire the bike up one of these nights and see.

Yeah I'll see about firing it up tonight or tomorrow night and double check it for you.

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Got home too late last night to fire it up. Didn't want to wake the neighbors on either side of me. Should be able to tonight though.

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The stock light does not dim when the bike is revved up.

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Ok, fired it up this evening to double check it. At idle(just under 1600 rpm) I have a ever so slight pulsing of the light. It's faint and barely noticeable.  Any throttle input above idle smoothes out the slight pulse and is a constant beam. No dimming and no pulsing.  :thumbsup:

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Thanks!

 

I dug into the bike a little tonight, cleaned all the connectors with deoxit, cleaned the ground wire to the motor under the carb.  Nothing looked bad, ground looked fine too. I still am getting a dim on rev. I even by passed the hi/lo switch to see if that was causing issues. Are there any other grounds I am missing on the bike that need to be cleaned? Any other ideas?

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There is another ground behind the left side number plate to the sub frame. Also I think there may be another under the left side fairing on the frame above the petcock.

Edited by spaceboy

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Dimming when revved is usaully the regulator failing.

Normally, but on these bike, AFAIK, the headlight is wired directly to one o fthe stator windings. The other stator winding goes to the RR and drives everything DC. The headlight is AC. Kinda baffling, unless someone messed with the factory wiring.

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The voltage regulator is also regulating the AC to the headlight, so a failed regulator will exhibit this issue. Very common when AC regulators circuits fail for the light to dim when revved . The r/r regulator on this bike is also an AC regulator, same set up used on the CRF250X, WR250/450 and KLX450.

Edited by RickyStator

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There is another ground behind the left side number plate to the sub frame. Also I think there may be another under the left side fairing on the frame above the petcock.

About the non dimming, are you running a lithium battery by chance or a lead acid?

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What's the capacity of your lithium battery? Is it a name brand off the shelf buy or a home made pack? Do you have a 12v lead acid battery you could hook up just for testing purposes to see if that solves your dimming issue? If the battery pack you have has a weak cell in it its possible it could be contributing to your issue.

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The voltage regulator is also regulating the AC to the headlight, so a failed regulator will exhibit this issue. Very common when AC regulators circuits fail for the light to dim when revved . The r/r regulator on this bike is also an AC regulator, same set up used on the CRF250X, WR250/450 and KLX450.

Thanks Ricky. I had no idea it was also an AC regulator.

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