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Author Topic: Voltage drop at Key Switch  (Read 546 times)

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Offline scottly

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Re: Voltage drop at Key Switch
« Reply #25 on: August 08, 2018, 08:07:41 pm »
Just checked, 12.20 at the battery; 11.63 at the black ignition wire at the regulator; 1.5 at the white wire.
 I rechecked the continuity at the terminals of the regulator and again I am getting continuity between all three and the frame of the regulator. 
So now I'm thinking the regulator needs to be changed, after all it is only 40 years old.
1.5V on the white wire??  Connect the white field wire to the battery plus terminal with a jumper, and start the bike and check the voltage. Remove the jumper after the test.
BTW, it's normal to have continuity between all three regulator terminals with the stock reg.
Don't fix it if it ain't broke!
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Offline TwoTired

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Re: Voltage drop at Key Switch
« Reply #26 on: August 08, 2018, 09:18:29 pm »
Just checked, 12.20 at the battery; 11.63 at the black ignition wire at the regulator; 1.5 at the white wire.
 I rechecked the continuity at the terminals of the regulator and again I am getting continuity between all three and the frame of the regulator. 
So now I'm thinking the regulator needs to be changed, after all it is only 40 years old.
At what RPM?  At idle speed, the White wire should read same as black wire.  Actually, anytime the black wire terminal reads under 13V-ish.

The Vreg has a 10 ohm resistor inside. You can get continuity through that.  It's normal.

It does sound like the internal contacts need cleaning.  Lack of thorough test details make us unsure.  And the .6V drop from battery to black doesn't exactly help.  Was this test done with the lights on?  The Vdrop will be worse when it is.

Cheers,
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

Thinking:  It's like reading with your own mind

Offline Staypuff 68

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Re: Voltage drop at Key Switch
« Reply #27 on: August 10, 2018, 10:34:12 am »
The voltage at the battery was 12.63 to begin with, key off. 
With the jumper wire to the white field wire  the volts at the battery was 12.23. 
Key on 11.90 at the battery and on the white wire.
Engine running the volts stayed the same.


Thats is when I saw the smoke and smelled burning plastic and the regulator was VERY hot to the touch.  So it looks like I will have to get a new one.

The headlight is LED, I have checked the voltage with and without it connected and there was no change to the voltage. The RPM is a best guess for now until I can get a tachometer hooked up, the bike doesn't have one.

Offline scottly

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Re: Voltage drop at Key Switch
« Reply #28 on: August 10, 2018, 09:42:25 pm »

Thats is when I saw the smoke and smelled burning plastic and the regulator was VERY hot to the touch.
What?? Where did the smoke come from?? Where was the regulator VERY hot to the touch? If it was the resistor on the back of the reg, it's normal for it to get hot, but not so hot plastic burns or smokes.
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Voltage drop at Key Switch
« Reply #29 on: August 11, 2018, 09:05:40 am »
I've smoked a rectifier before but never a regulator.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Staypuff 68

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Re: Voltage drop at Key Switch
« Reply #30 on: August 11, 2018, 01:22:16 pm »
The regulator was very hot to the touch, the smoke and smell came from the coil on the back of the regulator.

Offline TwoTired

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Re: Voltage drop at Key Switch
« Reply #31 on: August 11, 2018, 02:02:07 pm »
That wire wound resistor is something like a 30 watt dissipator, or more.  And, in normal operation dissipates 15 W max.

Have you measured the field coil resistance?  S/B about 5 ohms (550)  0r 6.8 ohms if 750.  If that white wire has lower resistance than that, it would explain the overheat,  (or if the white branch is shorted to ground).

I think you have have wiring issues.

Cheers,
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

Thinking:  It's like reading with your own mind

 

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