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Very Hot Topic (More than 25 Replies) I Hate Charging Problems! (Read 498 times)
Justin B.
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I Hate Charging Problems!
09/21/18 at 14:47:30
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Have had the '81 R100RT mothballed for a while due to a charging issue.  Multiple "spare" bikes makes it not that big of a deal and I kept putting off troubleshooting but decided it was time to figure it out today.

The symptome was no rise in voltage when revved and the charge light stayed on all the time.  I put a jumper between the DF and D leads going to the regulator and voltage remained flat.  Great, just what I wanted to do, tear into the front of an Airhead with full fairing... Angry

I pulled out the diode board and all diodes checked good so ohmed out the rotor and found it had about 56 ohms resistance!  A bit more than it should but I had never had one go bad that didn't just open up and cause charge light to go out.  I had also checked this last since I had put in a new one (EME replacement)  about 15 years ago and probably only have 20k miles on it.  Oh well, ordered another one from EME along with a new brush hopder/brush assembly so hopefully in a few days it'll be back on the road.

Has anybody else had a rotor go bad that didn't either read a dead short or open?
  

Justin B.

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georgesgiralt
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Re: I Hate Charging Problems!
Reply #1 - 09/21/18 at 14:54:05
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Hello Justin,
You bike has been mothballed for a long time. So corrosion has taken it's toll.
I would try to clean the brush area with smooth sandpaper and check that the brushes are making good contact.
Also, check that the 3 stator winding give around the same voltage (alternate current here) by checking the wires two at a time.
You should get high voltage if the system is running fine : maybe 25 to 30 V~
Of course, if the rotor is dead you won't get any voltage at the stator...
Hope this helps.
  
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Re: I Hate Charging Problems!
Reply #2 - 09/21/18 at 18:21:10
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When I had the charging problems right after I bought my bike all of the simple testing I could do came out fine.

I told a guy at the local shop that the rotor tested OK and he told me that they could sometimes do that sitting still but could have a break in a connection/wire that could open up once it got to spinning and heating up.

He wasn't trying to sell me a new one so I don't think he was BS'ing me.
  

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Re: I Hate Charging Problems!
Reply #3 - 09/21/18 at 18:35:17
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Swap rotors with the junkyard dawg LS . Smiley
  

'81 R65
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Re: I Hate Charging Problems!
Reply #4 - 09/21/18 at 21:21:20
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I suspect there is nothing wrong with the rotor
If the rotor was open  the light would not come unless it is
shorted in the winding or shorted to ground

Did you check the rotor for shorts to ground
If you ohm from either slip ring to the claws you should get infinite With the brushes NOT touching the slip rings

The brush that has the BROWN wire connected to it is Grounded
Make sure the Brush with the Black wire connected to it is NOT grounded

More than likely you have not checked all of the diodes in the diode board or have not done it    correctly
Did you check the 3 smaller diodes that feed power to  the rotor
Their are a total of eleven diodes in the diode board did you get them all

If you are sure the diode board is good then make sure the large red wire that feeds the charging voltage to the battery cable on the starter is good    
  

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Re: I Hate Charging Problems!
Reply #5 - 09/21/18 at 21:33:22
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BPT wrote on 09/21/18 at 18:21:10:
When I had the charging problems right after I bought my bike all of the simple testing I could do came out fine.

I told a guy at the local shop that the rotor tested OK and he told me that they could sometimes do that sitting still but could have a break in a connection/wire that could open up once it got to spinning and heating up.

He wasn't trying to sell me a new one so I don't think he was BS'ing me.


If this was the case the GEN light would go out as soon as it opened up
  

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Re: I Hate Charging Problems!
Reply #6 - 09/21/18 at 21:49:37
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georgesgiralt wrote on 09/21/18 at 14:54:05:
Hello Justin,
You bike has been mothballed for a long time. So corrosion has taken it's toll.
I would try to clean the brush area with smooth sandpaper and check that the brushes are making good contact.
Also, check that the 3 stator winding give around the same voltage (alternate current here) by checking the wires two at a time.
You should get high voltage if the system is running fine : maybe 25 to 30 V~
Of course, if the rotor is dead you won't get any voltage at the stator...
Hope this helps.


Check the stator for shorts to ground also
Opens are rare
  

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Justin B.
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Re: I Hate Charging Problems!
Reply #7 - 09/21/18 at 23:25:00
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All diodes (including small ones) were checked and the rotor is not shorted or open but has around 56 ohms instead of the ~2.6 it is supposed to have.  The bike has been sitting BECAUSE of the charging issue, it's not something that developed while sidelined.

My only head-scratcher is that I've never personally had a rotor winding fail with this reading before.
  

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Justin B.
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Re: I Hate Charging Problems!
Reply #8 - 09/21/18 at 23:26:09
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Bob, the 'Dawg has went to live with somebody else!
  

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Justin B.
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Re: I Hate Charging Problems!
Reply #9 - 09/22/18 at 15:05:08
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Pulled rotor and now reads 36 ohms!  I think the solder joint from the windings to outer slip ring is flaky as I can probe the wire just behind the joint and get right at 3 ohms.  I will resolder and if it checks out keep as a spare since the new one is on it's way.
  

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Re: I Hate Charging Problems!
Reply #10 - 09/22/18 at 18:13:26
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Dry joint is what i would have said and that is what you have found. Make sure it is cleaned up well before re-soldering
  
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Justin B.
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Re: I Hate Charging Problems!
Reply #11 - 09/22/18 at 18:35:58
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Yeah, just kinda laying there with solder on top of it.  I cleaned everything up really good, soldered, and have the proper resistance between slip rings now.  I guess I should have investigated this before ordering a new one but EME has them on sale sale so I now will have an emergency spare.
  

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Re: I Hate Charging Problems!
Reply #12 - 09/22/18 at 23:23:05
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Justin B. wrote on 09/21/18 at 14:47:30:
I pulled out the diode board and all diodes checked good


I have hard personal experience of a diode board that tests just fine with a meter, but fails as soon as a real world load is placed on it. Near drove me mad finding this out.

If all else fails, borrow a diode board and swap it in and see what happens.
  

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Re: I Hate Charging Problems!
Reply #13 - 09/22/18 at 23:27:09
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yes, it's nice having a spare parts bike for trouble shooting !!
  

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'82 R65 LS  
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
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I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!
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Justin B.
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Re: I Hate Charging Problems!
Reply #14 - 09/23/18 at 05:40:40
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Tony, I'm 100% positive about the rotor failure and it is now repaired.  However, the new rotor will be here tomorrow so it will go into the bike and the repaired one into "stock," so to speak.

Bob - no way I'm going to tear wife.gov's bike apart to donate a diagnostic part!
  

Justin B.

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Re: I Hate Charging Problems!
Reply #15 - 09/23/18 at 17:35:02
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I like to use my old APO No2 meter to check diodes as it uses 15 volts in the resistance measuring cct.
  
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Re: I Hate Charging Problems!
Reply #16 - 09/23/18 at 19:14:50
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Justin B. wrote on 09/23/18 at 05:40:40:
Tony, I'm 100% positive about the rotor failure and it is now repaired. 


Was it the old broken wire from slip rings to rotor widings? In australlia our indigenous Ford/GM/Chrysler vehicles were nearly all afflicted with Bosch alternators (once they gave up generators and actually started fitting alternators). I have soldered up those wires and attemtped to re-secure them with various glues, varnishes and magic potions more times than I care to remember. Most recently to repair the alternator in SWIO's VW Kombi.

Personally I'd use the one your repaired - it is goign to be good for at least another 30 years.
  

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Tony Smith
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Re: I Hate Charging Problems!
Reply #17 - 09/23/18 at 19:16:24
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skippyc wrote on 09/23/18 at 17:35:02:
I like to use my old APO No2 meter to check diodes as it uses 15 volts in the resistance measuring cct.


The next time I have to test a diode board I intend to use a 12v supply and test lamps.


Here's a funny thing. I think I may have gone over a little too far to the dark side in my use of Facebook. I spent at least a minute after reading your post trying to find the "like" button

  

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Justin B.
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Re: I Hate Charging Problems!
Reply #18 - 09/23/18 at 21:44:09
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Tony - the failure mode was that the wire just made it to the edge of the groove in the slip-ring and I think was just being held against it by solder flux or potting compound.  I was able to dig out enough compound from underneath the wire to pull it a mm or so which allowed it to terminate in the groove.  I then soldered it into the groove.  I will be using JB-Weld to fill in and secure.

I think I'm going to use the new rotor as it has a bit lower resistance windings.  Seems I read that the rotors with lower resistance will start generating at a lower RPM albeit with a small sacrifice of total output.
  

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Re: I Hate Charging Problems!
Reply #19 - 09/24/18 at 02:35:34
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Hello
Those diodes are crimped. Twice (at least).
The first crimping is in the box, as the wire soldered to the chip is crimped to one of the terminals, and then the box of the diode to the diode board.
Sometimes, the crimping to the diode board "fails" by vibrations or corrosion and when the diode is requested to flow the maximal current, there is not enough pressure to convey it. But there is enough pressure to convey the micro to milli amps the ohmmeter provide. This is why one should test for dead diodes with an ohmmeter and then in situ with the "full mighty power" of the alternator... This is the problem when dealing with 30 years + components...
« Last Edit: 09/24/18 at 15:01:41 by georgesgiralt »  
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Justin B.
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Re: I Hate Charging Problems!
Reply #20 - 09/24/18 at 12:12:18
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George, I agree.   Snowbum has a diagram on his site for a simple diode tester utilising a 12VAC transformer and a bulb that can be used to probe around on the diode board.  If I had not found the rotor fault that would have been my next step.
  

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Justin B.
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Re: I Hate Charging Problems!
Reply #21 - 09/24/18 at 19:39:49
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Care package got here from EME this morning so I put in the new rotor and I now have CHARGING!!!
  

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Justin B.
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Re: I Hate Charging Problems!
Reply #22 - 09/25/18 at 22:48:15
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Drained the gas tank of the year old varnish that was in there , filled with fresh gas and went for a ride!  Grin Life is good... Cool

I guess storing with carbs empty helped as the idle jets were not clogged but need to re-synch carbies...
  

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Re: I Hate Charging Problems!
Reply #23 - 09/27/18 at 21:51:37
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I am still trying to figure out why your GEN light would illuminate with a bad rotor
  

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Re: I Hate Charging Problems!
Reply #24 - 09/27/18 at 22:28:23
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Would the resistor that can be added  to prevent the charging system from failure if the bulb fails, have any bearing on this ??
  

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'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
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Justin B.
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Re: I Hate Charging Problems!
Reply #25 - 09/28/18 at 16:15:15
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I have not done the "resistor" mod, so no.  I'm guessing the light was coming on because there was not a complete "open" in the rotor, just increased resistance which allowed the light to come on but not enough flow to energize the rotor.

The reason I started the thread was to see if anybody else ever had a rotor that failed with anything other than as open condition.
  

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Re: I Hate Charging Problems!
Reply #26 - 09/28/18 at 21:19:04
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Anything is possible when you’re talking about electricity  Shocked
I have seen things that make absolutely no sense
  

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Justin B.
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Re: I Hate Charging Problems!
Reply #27 - 09/29/18 at 11:18:32
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I know, was an electronic tech for years and have ran into a number of "head-scratchers."
  

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