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Author Topic: diagnosing the voltage regulator 81 cb650  (Read 1423 times)

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Offline oddballmotorsports

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diagnosing the voltage regulator 81 cb650
« on: October 30, 2017, 07:57:00 PM »
so I think I have a bad voltage regulator.  here's how I arrived at this conclusion..  ok so we have coming from the regulator 8 wires.  3 are the stator, 2 are the field coil, 1 is battery charge, and keyed ignition and a ground.  I see 12v from battery charge to chassis ground,  regulator ground,  and I see 12v off the black wire coming from the ignition switch when its on.  I have no opens / shorts on the field or stater windings,  I have ziltch coming from the field coil output,  so to me that says the regulator isn't turning on the field coil. and is now a paperweight..  Did I forget to do anything?  or check?  just want to make sure before I plunk down some $$$ for a new regulator.. 
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Offline scunny

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Re: diagnosing the voltage regulator 81 cb650
« Reply #1 on: October 30, 2017, 09:10:53 PM »
what's the ohms between the slip rings on your rotor, should be about 4.5 from memory. This is "normally" the weak link in the charging system of the 650.
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past-cb100,ts250,cb500,cb500,gs1000,gs650g.phillips traveller
present-CB 650 retro
            VTR1000F3
           XL250S riverbed rocket
           TS250[sold]
           TS185[sold]
           XL125S[sold]
           MT50 (white)
           MT50 (red)[sold]
           KN250/XS400 project
           XR/XL250 bitsa under construction
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Offline TwoTired

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Re: diagnosing the voltage regulator 81 cb650
« Reply #2 on: October 31, 2017, 12:17:28 AM »
The regulator drives the rotor with voltage.  If there is no voltage, either the regulator stopped sending or the rotor is demanding too much current and holding the voltage down.

Scunny is correct about checking the rotor resistance.  If too low it demands more current.  if the rotor is shorted, it can overlaod the regulator and damage it's output.  If so, there is risk to a brand new regulator being destroyed by a faulty rotor.

Best check the rotor resistance.  I think 4.5 ohms is just about the lower limit, which would be nearly a 3 A draw from the Vreg.  I think it is normally closer the 6.5 ohms, which would be a 2 A draw.  The lower the ohms, the more current draw.  Enough current draw and the drivers will fail in the regulator.

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

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Offline oddballmotorsports

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Re: diagnosing the voltage regulator 81 cb650
« Reply #3 on: October 31, 2017, 05:30:35 AM »
well I'm glad I asked,  cruised on over to the manuals section started to read,  IIRC my ohm readings were much higher,   which wouldn't cause the reg to fail I don't think,  but its worth noting.  I'm going to recheck everything today...
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Offline TwoTired

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Re: diagnosing the voltage regulator 81 cb650
« Reply #4 on: October 31, 2017, 10:59:25 AM »
Quote from: oddballmotorsports on October 31, 2017, 05:30:35 AM
well I'm glad I asked,  cruised on over to the manuals section started to read,  IIRC my ohm readings were much higher,   which wouldn't cause the reg to fail I don't think,  but its worth noting.  I'm going to recheck everything today...

Just something to note.  If the slip ring brushes are not making solid contact, the resistance can be high intermittently, and low while spinning.

Since you didn't say how high your rotor resistance was, note that too high, might not be enough to properly activate the output transistor in the regulator.

I don't believe you want a rotor resistance reading through those brushes more than 7 ohms.

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 oddballmotorsports

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Re: diagnosing the voltage regulator 81 cb650
« Reply #5 on: November 01, 2017, 05:57:53 PM »
its my volt meter..  somethings wrong with it,  just ohms. with the two leads of the meter held together it reads 73 ohms and then drops to 43ish,  hoping it just needs a battery...
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Offline oddballmotorsports

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Re: diagnosing the voltage regulator 81 cb650
« Reply #6 on: April 01, 2018, 10:01:49 PM »
ok I finally got to measuring out the coil, 1.2 at the rings..  time for a new rotor?  and what makes them fail like that? cross short in the coil?
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Offline TwoTired

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Re: diagnosing the voltage regulator 81 cb650
« Reply #7 on: April 01, 2018, 10:51:48 PM »
Heat a centrifugal force damages the wire insulation the winding wraps then short to each other.  This lowers the resistance and reduces the magnetic field strength.  The later reduces the alternator output.  And the lower resistance draws more power from the bike's system.  Double whammy.

 Replace or get it rewound.

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 oddballmotorsports

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Re: diagnosing the voltage regulator 81 cb650
« Reply #8 on: April 02, 2018, 11:30:59 AM »
thanks again guys..  the regulator was super hot while testing other things,  hopefully a(nother) new regulator isn't in my future as well...
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Offline oddballmotorsports

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Re: diagnosing the voltage regulator 81 cb650
« Reply #9 on: April 02, 2018, 01:46:46 PM »
forgot to ask,  what size are the threads on the inside of the rotor?
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Offline scunny

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Re: diagnosing the voltage regulator 81 cb650
« Reply #10 on: April 02, 2018, 10:48:35 PM »
either the rear axle or rear engine mount are the same thread, can't remember which, it was 10 or so years ago I did mine. screw in tight, give her a wee wack on the end and rotor should come free.
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past-cb100,ts250,cb500,cb500,gs1000,gs650g.phillips traveller
present-CB 650 retro
            VTR1000F3
           XL250S riverbed rocket
           TS250[sold]
           TS185[sold]
           XL125S[sold]
           MT50 (white)
           MT50 (red)[sold]
           KN250/XS400 project
           XR/XL250 bitsa under construction
           SL100[sold]
           XL250R
           pedal(pub bike) leaks oil
my gallery http://gallery.sohc4.net/members/personal/scunny

Offline oddballmotorsports

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Re: diagnosing the voltage regulator 81 cb650
« Reply #11 on: April 03, 2018, 06:47:45 AM »
well..  that would figure,  neither the cb axle nor the rear motor mount are what was originally found on the cb...
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Offline oddballmotorsports

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Re: diagnosing the voltage regulator 81 cb650
« Reply #12 on: April 06, 2018, 10:39:32 AM »
well after searching and digging, M18-1.5 which isn't a common hardware store bolt,  it is however an automotive drain plug bolt, their made soft to save the oil pan, but should work I'll test and report :)
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