Topic: 'flat part' on starter... oops, maybe it's the charging system!

[TwoTired]

Any Shmutz on the slip rings is going to add resistance to the field coil circuit loop.  This is why a suggested earlier to move the crankshaft to see what effect it had, (maybe dislodge some crud).  The brushes rub on the slip rings while running, and sort of clean as the engine runs.

If Kitsune's bike had measured 13.9 ohms I would be looking elsewhere for a problem.   I think she reported over 100.  And this resistance will not allow a big enough electromagnetic field to form inside the alternator.  No, or small electromagnetic field means no or small power output from the alternator.

Still if you wish to test rather than take the alternator apart, then do the battery voltage vs. engine RPM test described earlier.  That will tell us if the battery is charging or not.  I suspect not.

Another clue is that she reported under an 8 Amp draw with the key switch on.  I would have expected about 10.  So, the draw is low.  Which seems good, until you consider a working field coil would add 1.8 amps to that draw.  Bringing it pretty close to the expected 10 Amps.
A 100 ohm alternator field circuit would only draw 0.126 amps, a 7 ohm field circuit draws 1.8 amps.

Cheers,

[martino1972]

oke,i took off the alternator cover for you....
if your carefull,you can safe the gasket...and there is no oil there..

here you can see the inside of the cover,it has the coils in there and the 2 brushes for your black and white wires..



now i took my ohm meter and went directly on the rotor,where the 2 brushes run on..
and there it measured this..



4.6 ohm...

[Frankenkit]

Martino, did you disconnect the battery before doing that, or doesn't it matter?  I was going to post a ton of pics (still will) b/c I was a little alarmed at the reddish 'varnish' stuff on the rotor, but it seems like you have it, too (?)

What are these rings I should clean, and anything else I should examine there?  Might replace the gasket just b/c I have one and the old one is pretty worn looking, what do you think?

[martino1972]

i measured it on the cb650 with the higher reading off the black and white wires,theres no battery in it,but that shouldnt matter..
on the front side of the rotor,you can see the 2 shiny "rings"where the brushing in the cover slide against..
if you look at my last picture you can see i have the 2 leads from the multimeter straith on those 2 rings..
i would start by measuring those,i came up with 4.6 ohm,this will tell you if your rotor is oke..
i asume you could clean the rotor with scotts brite or a fine sanding paper,you dont have to clean the entire rotor,just where the rings are is good...
if the rotor rings measure out oke,i would clean the rings,and the brushes...

what i also did was put one lead from the multimeter on a brush and the other lead on the connector plug at the r/r....the top brush will be the black wire,the bottom brush the white..
it measured out 0.2 ohm on both the black and white,telling me the wires are oke..
then i shorted out the brushes(by laying a bolt from brush to brush,connecting the 2,and then measured at the connector between black and white,i came up with 0.1 ohm again..
so that tells me,that it was dirty rings and brushes..

[scunny]

just tested my two. one reads 4.6ohms across the slip rings and the other is an open circuit(bugger)

[martino1972]

your 2??? like in 2 bikes??  if you read open circuit from ring to ring,then your rotor is shut..

[martino1972]

well,i went ahead and cleaned the front of my rotor,took less then a minuted,but it shows clearly what rings we are talking about..>>



pretty,huh.??   

[Frankenkit]

Did the same thing... read 4.6 ohms ring-to-ring at first, then 4.4 after cleaning.  Read brush-to-plug and black was 0.4 ohms and the white hovered around 0.7. 

[martino1972]

good news...
clean off the brushes and slap her back together,with that pretty new gasket...
thats what im doing right now(except for the new gasket,)as soon as she is back together ill measure black to white wire again,should read around 6 ohms then..

[martino1972]

got it back together,and looky what it reads..



hope you have the same results...

[TwoTired]

It makes sense that the field coil would be 4.6 ohms.

The 550 Coil is 4.9 ohms.
The 750 coil is 6.8 ohms.

The last person I helped with a 650 told his new one measured 6.8 ohms.  I haven't personally measured any 650 field coil.

Sure is nice to have someone with the same bike do the same things you need to do in parallel.

Hopefully, when you put it back together the white/black will read something reasonable.
Checking the wire continuity before reassembly would be prudent.  Wiggle the wires around a bit while doing this, too. and and intermittent wire will go bad  sooner or later.  Best to find it now.

Do clean up the slip rings surface and verify that the brushes have a wire attachment in good condition.  Since they've moved since your first test, best to make sure intermittents aren't in there.

Cheers,

[Frankenkit]

How would I check wire attachment to the brushes, just unscrew the black sort of panel that seems to hold them in, and look at whatever holds them?  Had a silver deposit on the tops of my brushes, a touch with a fine sand paper (just real light) and it removed it, but the brush material seems awful soft...

[martino1972]

It makes sense that the field coil would be 4.6 ohms.

The 550 Coil is 4.9 ohms.
The 750 coil is 6.8 ohms.

The last person I helped with a 650 told his new one measured 6.8 ohms.  I haven't personally measured any 650 field coil.

Sure is nice to have someone with the same bike do the same things you need to do in parallel.

Hopefully, when you put it back together the white/black will read something reasonable.
Checking the wire continuity before reassembly would be prudent.  Wiggle the wires around a bit while doing this, too. and and intermittent wire will go bad  sooner or later.  Best to find it now.

Do clean up the slip rings surface and verify that the brushes have a wire attachment in good condition.  Since they've moved since your first test, best to make sure intermittents aren't in there.

Cheers,

yes,having a person with the same bike,doing a parrallel fix is awesome,lot of joy in exchanging info and pic's,knowing the other person is doing the same thing,many miles away..

can't wait for her next problem,love to do this again..

and thanks twotired for pointing out 50 ohms was too high,you got me to do something usefull today..

and thanks kitsune for sharing pic's and info and keeping us updated so fast..

[martino1972]

did the wiggle test and the readings stay solid at my end,perfect..
hope you get the same results kitsune

[TwoTired]

The brushes are soft. 

I can't be certain of the brush attachment method.  At least not enough to guide you through it.

Use the ohmmeter from the black wire to the brush face and move  things about to simulate vibration effects.  The wire resistance reading should remain steady, as physical motion does not change resistance.  Do the same thing for the white wire to brush face.  If all seems stable, then put it back together and verify resistance at the white and black connections, as Martino did.

If you get similar resistance as Martino, then plug it all together, start the bike and monitor your battery voltage with RPM changes. 

Fingers crossed!

[Frankenkit]

can't wait for her next problem,love to do this again..

hush! That's as bad as saying it's a slow day or something! How dare you!    just wanted to hang out in here until I saw a couple more entries, then run out, clean, wiggle test, and reconnect...

[martino1972]

you just go and wiggle...

[Frankenkit]

Wiggled and everything tested out ok, hooked everything up and got a reading of 4.9.   Right On!

[martino1972]

awesome....\
now did you measure battery charge with engine running..

[Frankenkit]

Wasn't sure I could without poofing the meter.  It tops out at 20A

[martino1972]

oh,go parrallel over the terminals with voltage....

[Frankenkit]

You're going to have to explain that, Martino.  Until last week, I had never picked up a multimeter... so I'm really a novice.

[TwoTired]

If you measure the battery voltage, you can infer the charge currents while running.  This is recommended for newbies.

The other technique (requiring some skill) for measuring charge currents is to insert the ammeter, then short the probes together while using the starter motor.  Then remove the shorting bar (that was capable of 200 amps) to enable the meter and read the engine running charge currents. 
Or, push start the bike.

The trick is to never lose continuity between the cable and the bat terminal while running the engine.  Hand holding probes are not reliable.

Cheers,

[Frankenkit]

I have gator clips for the probes, just not sure what you mean by going parallel over the terminals...

[Hush]

Hey it wasn't me you can't prove a thing!!