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Author Topic: Blowing Running Light and Voltage Drop. Rectifier?  (Read 1281 times)

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Honda3

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Blowing Running Light and Voltage Drop. Rectifier?
« on: June 14, 2019, 02:55:55 PM »
On my 1977 I noticed the running light part of the brake bulb keeps blowing.

Today I got out my multimeter. As the bike idled it stood at 13.3 v. When I rev it, it gets up to 14.5.

HOWEVER I noticed that when its idling, it will DROP down to 6v then go right back up to 13.3, then hold for a while, and drop to 4v - 7v and come right back up.

Im thinking the rectifier is dying?
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Offline TwoTired

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Re: Blowing Running Light and Voltage Drop. Rectifier?
« Reply #1 on: June 14, 2019, 04:56:16 PM »
Stock bike or modified?

Battery fully charged?

Unlikely the rectifier.  Or you wouldn't ever get 14.5 volts.
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Honda3

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Re: Blowing Running Light and Voltage Drop. Rectifier?
« Reply #2 on: June 14, 2019, 05:01:24 PM »
Quote from: TwoTired on June 14, 2019, 04:56:16 PM
Stock bike or modified?

Battery fully charged?

Unlikely the rectifier.  Or you wouldn't ever get 14.5 volts.

Stock bike.

Battery is fully charged. Its a Lithium ion battery, not stock and I made no changes to accommodate it. Just put it in and let her rip. Maybe its too powerful for the rectifier and is over charging.

The reason I think its the rectifier is because they start to go bad slowly. It can still read 14.5 but be "going" bad.
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Offline Scott S

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Re: Blowing Running Light and Voltage Drop. Rectifier?
« Reply #3 on: June 14, 2019, 05:46:36 PM »
What bike?
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'71 CB500 K0
'17 Triumph Street Scrambler
'81 Yamaha XS650

Honda3

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Re: Blowing Running Light and Voltage Drop. Rectifier?
« Reply #4 on: June 14, 2019, 06:10:45 PM »
Quote from: Scott S on June 14, 2019, 05:46:36 PM
What bike?

I have five bikes, this isnt a Honda though but it is a 77. Im guessing since electrics are the same across brands, any general answers may apply.
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Offline Scott S

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Re: Blowing Running Light and Voltage Drop. Rectifier?
« Reply #5 on: June 14, 2019, 06:24:20 PM »
  They're not all the same. There are different types of regulators, rectifiers, etc.
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'71 CB500 K0
'17 Triumph Street Scrambler
'81 Yamaha XS650

Honda3

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Re: Blowing Running Light and Voltage Drop. Rectifier?
« Reply #6 on: June 14, 2019, 06:38:50 PM »
Quote from: Scott S on June 14, 2019, 06:24:20 PM
  They're not all the same. There are different types of regulators, rectifiers, etc.

1977 Kawasaki KZ750B twin with 9k original miles. Pristine condition
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Offline TwoTired

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Re: Blowing Running Light and Voltage Drop. Rectifier?
« Reply #7 on: June 14, 2019, 08:01:43 PM »
Quote from: Honda3 on June 14, 2019, 06:38:50 PM
Quote from: Scott S on June 14, 2019, 06:24:20 PM
  They're not all the same. There are different types of regulators, rectifiers, etc.

1977 Kawasaki KZ750B twin with 9k original miles. Pristine condition

As stated, they are not all the same.   I don't know how the Kawa's functions.  So, I can't help you.

If you are certain that rectifiers go bad gradually, go ahead and replace it.  Not in my experience.  But, perhaps you have knowledge I don't.

Anyway your post should be in "other bikes".  Perhaps there, someone more familiar with you bike can be of more help.

I hope you meant lithium iron battery LiFePO4, rather than lithium ion.  The latter behaves badly when not charged correctly.

Cheers,
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline bryanj

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Re: Blowing Running Light and Voltage Drop. Rectifier?
« Reply #8 on: June 15, 2019, 02:34:33 AM »
More likely regulator than rectifier but i think its a combined unit anyway
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Honda3

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Re: Blowing Running Light and Voltage Drop. Rectifier?
« Reply #9 on: June 15, 2019, 04:51:53 PM »
I disconnected the stator and regulator and let the bike run off battery. Well, I really just unplugged the stator from the rectifier....and there was still that drop. I think its a ground somewhere and not the stator or regulator
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