Attn: Krusty Critter:Re Charging 81Cb650

Krusty,
Thanks for all the good info on the charging system.
I checked everything the best I could with an ohm meter and all seems
to be in order. I have the second bike, so I ended up swaping the
known good voltage recifier/regulator and re-starting the 81, and once
again there should be 14.5 volts at anything above 2000rpm, but there
is only 11 to 11.5 volts going in even at 5000 rpm.
So it is looking like the alternator is the problem. Here is the ohm
findings from the connector, no wires have continity to ground.
The 3 yellow wires have full continuity to each other and according to
the book should be between .041 to .051 ohms. There is no resistance
on the 3 yellows, but they are all the same, so there does not seem to
be an open winding. Would this be a brush problem considering that
some of the juice is going to the battery?
I have not removed the alternator yet, as do not have a fly wheel
puller, but will have to get one soon. Wondering if you have any ideas
or further tests that can narrow the stator / brush problem?
Tim.C

 

There is an electrical phenomenon called "clamping". If a generator
isn't producing a whole lot more power than the dead (or discharged)
battery it's connected to is putting out, the voltage will the
*clamped* to the same level as the dead battery. I don't remember if
you said you had a reasonably new battery or not, but there is that
clamping possibility with a discharged battery...

That's why manuals always tell you to check the alternator output with
a fully charged battery...

ground. The 3 yellow wires have full continuity to each other and >
according to the book should be between .041 to .051 ohms.

Maybe you have an internally shorted stator, or maybe it's your tester?

Are you using a digital VOM, or an analog volt VOM with a needle? My
Harbor Freight digital VOM has a 0.2 ohm scale. It cost me $7.00.
A digital VOM will show constantly changing readings due to the fact
that resistance of the test probes against the part you're trying to
measure constantly varies because your hands are shaking a little. At
least it will read low enough to differentiate between zero ohms and
hundredths of an ohm...

But the analog Micronta VOM I bought from Radio Shack many years ago
has an exponential scale reading from infinity down to zero. It has a
zeroing potentiometer to eliminate the small resistance of the meter
leads and compensate for low voltage on the AA battery that powers the
meter...

It's hard to tell what exact reading you have with an analog meter when
you're trying to read 100th's of an ohm and the zero to 1 ohm division
on the Rx1 scale is less than 1/8th of an inch wide...

I wouldn't be able to read .041 to 051 ohms on an analog VOM...

going to the battery?

Have you pulled the brushes out and measured them against the
specifications in a repair manual? Output from an alternator or
performance from an electric motor is very dependant upon resistance
across the brushes and slip ring or brushes and commutator, and, as the
brushes wear down the resistance across that connection rises, and some
DC motors will actually run faster because there's less spring pressure
on the brushes. That works until the brushes are too worn out to make
good contact, and then the motor won't run. And brushes on an
alternator will have too much resistance when they're worn out, you
won't get the excitation current you need to charge the battery...

While the engine is running, do you have DC voltage on one of the
brushes? The regulator rectifier of an excited field alternator is
going to apply some level of DC voltage to the brushes...

You might try disconnecting the power lead to the brushes and applying
DC voltage directly to the slip rings while the engine is running to
externally excite the field. But I wouldn't do what the other guy did
on his CB-750F. he applied full battery voltage to the
brushes. That might burn out the rotor windings from too much heat...

I would use a flashlight battery to see if voltage increased when I
hooked it across the brushes...

Since I don't have a Honda shop manual, I can only tell you
generalities about how charging systems work, and relate to my own
experience and information from the manuals I do have...

I own two bikes with excited field alternators...

I looked at the schematic for the regulator circuit on my GSXR-750.
It shows that there is a diode of unknown resistance in series with a
power transistor of unknown resistance. The transistor is switched on
and off by an integrated circuit that counts the voltage output of the
alternator and converts that digital information into an analog signal
to tell the power transistor to switch on and off. But Suzuki never
bothers to tell me what the output voltage of that transistor is.

My Yamaha manual doesn't even go that far, it tells me to do the open
circuit voltage test, and if I get high voltage, replace the regulator,
but if I get low voltage, check the wiring, the brushes and the
resistances of the stator and rotor...

 

The battery is not new but was fully charged, it dropped to 10volts
when hitting the starter button, probably not the best battery, but
with the headlights on the voltage remains around 11 volts, will try a
new battery, but I should still have the charging force of 14.5 even
on a weak battery but your clamping force sure explains a possiblility
Thanks.
I am using the radio shack needle micronta. I understand that I will
not get a fully accurate reading, but if I zero it to where the needle
all the way up to 1k, my understanding is that if the resistance
should read.5 the needle should be around half way and other test
have worked that way but I am a real novice, I should get a digital
ohm meter. Is there one that can also be an amp meter and also have
the capability of having a switchable to postive ground?? I could sure
use that!
I have not been able to pull the unit apart as I do not have a fly
wheel puller. That is something that will be next on the agenda. I am
just trying to get closer to where i feel it absolutley necessary to
remove it. (trying to get up the strength and courage to do that)
I also just had the oil cover off and had a difficult time installing
it will pull the oil pump cover again and check to make sure I did not
pinch the wires. Then I will pull the cover off the alternator, and
see what that look like.
Thanks for the expanation about the brushes! I have no idea about how
these things work and I think really these brushes and unit needs
further inspection, will have to remove I guess.
You talked about testing further when the bike is running, excuse my
ignorance, but how do I know which are the brush wires, for testing
the DC voltage? There is the top connector that comes from the stator,
and it has 5 wires, 3 that are yellow, 1-Black and 1 white. I would
like to do that test, set the volt meter to the 15v scale and connect
the poitve lead to where and the ground to the black wire?
Thanks again, I really appreciate your help, I wish that I had your
electrical knowledge! Will look for a new digital tester after you
make a reccomendation as to a brand or type that will work for these
sorts of things.
Tim C.

 

You ought to check for continuity through the rotor.

Remove the positive lead to the brushes and check for continuity
between the positive brush and ground. I don't know the exact
resistance you should see but it should be non-zero and not
infinity.

If you see infinity when testing from the positive brush, then make
the same test between the two slip rings. If you see aome reasonable
resistance value between the slip rings and not between the brushes
then look for brush problems (worn brushes, bad springs, bad solder,
etc).

If you see a complete open (infinity) between the slip rings
then most likely your your rotor has a break in the wiring.

If you see zero resistance, then you most likely have a short
either from the brushes or more likely in the rotor. You can
isolate the brushes by slipping pieces of paper between the
slip ring and brushes. This lets you figure out which may have
the problem.

If the brushes and rotor check out OK, then it may be a problem
with the regulator.

Pulling a stator and rotor is pretty easy with good directions
and the right tools. You probably need a rotor puller designed
for your bike plus some ordinary wrenches and maybe a couple
of dental picks to fiddle with the brushes. Remember to take
the spring load off the brushes before trying to remove anything
so as to avoid damaging the brushes. To keep the engine from
turning over, put the bike in top gear and apply the rear brake.

Go slow and be prepared to back off and rethink the problem if
you're applying so much force that you're close to doing damage.

 

You ought to check for continuity through the rotor.

Remove the positive lead to the brushes and check for continuity
between the positive brush and ground. I don't know the exact
resistance you should see but it should be non-zero and not
infinity.

If you see infinity when testing from the positive brush, then make
the same test between the two slip rings. If you see aome reasonable
resistance value between the slip rings and not between the brushes
then look for brush problems (worn brushes, bad springs, bad solder,
etc).

If you see a complete open (infinity) between the slip rings
then most likely your your rotor has a break in the wiring.

If you see zero resistance, then you most likely have a short
either from the brushes or more likely in the rotor. You can
isolate the brushes by slipping pieces of paper between the
slip ring and brushes. This lets you figure out which may have
the problem.

If the brushes and rotor check out OK, the problem may be in
the regulator.

Pulling a stator and rotor is pretty easy with good directions
and the right tools. You probably need a rotor puller designed
for your bike plus some ordinary wrenches and maybe a couple
of dental picks to fiddle with the brushes. Remember to take
the spring load off the brushes before trying to remove anything
so as to avoid damaging the brushes. To keep the engine from
turning over, put the bike in top gear and apply the rear brake.

Go slow and be prepared to back off and rethink the problem if
you're applying so much force that you're close to doing damage.

 

Here's the best troubleshooting guide I've seen:

http://www.electrexusa.com/electrex_fault_finding.html

bob prohaska

 

Tim C wrote:

the needle all the way up to 1k, my understanding is that if the >
resistance should read.5 the needle should be around half way and >
other test have worked that way

Interesting thought. Where the needle goes to on the scale is dependant
upon the total resistance in series with the 1.5 volt battery and the
meter coil. The voltage is assumed to be fairly constsnt at 1.5 volts,
but a battery will discharge over time so there is a variable resistor
you can use to compensate for a weaker battery. And, you may be using
different sets of test leads, so by turning the zero adjustment wheel
you can nullify the resistance of the leads and only read the
resistance of the item you're testing...

On the R x 1 scale, 1000 ohms is far over to the left. When you switch
to the R x 10 scale, the amount of resistance in series with the meter
movement is only 10% of the resistance when you're in the R x 1 scale
so the needle is at the 100 ohm mark when you're actually measuring
1000 ohms...

But the meter needle doesn't move 10 times as far across the face of
the meter. The ohms scale is an exponential scale...

When you go to the R x 100 scale, there is 1/100th of the total amount
of resistance in series with the movement as there was on the R x 1
scale. 1000 ohms is now indicated at the 10 ohm mark. But the needle
*still* hasn't traversed the whole dial of the meter, it's only moved
2/3rds of the way across the full arc...

And so on with the R x 1000 scale, where 1000 ohms is indicated by 1 on
the meter scale. There is 1/1000th as much resistance in series with
the meter coil as there was on the R x 1 scale and the needle has moved
almost all the way across the scale...

But you want to read very small resistances which would normal be read
on a milliohmmeter. We used a an expensive Shallcross milliohmmeter on
aircraft and spacecraft to check the tiny resistance from one of the
metal parts of the aerospace vehicle to all the adjacent parts, because
we were using the structure of the vehicle as a return path for most of
the electrical circuits. That cuts the number of wires needed for a
circuit in half, saving a lot of weight...

But, suppose all you had was a Radio Shack analog VOM and you wanted to
read resistances below 1.0 ohms. If you had a precision 1.0 ohm
resistor and you attached your test leads to it and zeroed your meter
out to where 25 ohms on the R x 1 scale was at the mid range, then 25
ohms would actually be about 1.0 ohms...

But 12.5 ohms on the R x 1 scale wouldn't be 0.5 ohms because of the
exponential scale on the meter face that I mentioned above...

The biggest diffculty would be in figuring out what the meter reading
really meant...

The digital voltmeter is a lot simpler, but it can't be zeroed, it
always reads the resistance of the meter leads, so you have to touch
the leads together before testing the item you want to measure, then
you know what to subtract from the test reading on the object of
interest...

sure use that!

You'll have to check some online catalogs to find a digital VOM that
will measure more than a few milliamps, and you'll have a very hard
time finding one thta measures more than 10 amps. If you want to
reverse the polarity on your meter, you can just switch the test leads
in theit sockets...

am just trying to get closer to where i feel it

courage to do that)

Don't pull the rotor off until you have absolutely made certain it's
defective. It has to be removed very carefully, with the correct puller
and, on reinstallation the bolts attaching it to the crankshaft has to
be properly torqued, or it might come loose on you at high RPM and
wreck the alternator...

my ignorance, but how do I know which are the brush wires,

from the stator, and it has 5 wires, 3 that are yellow,

meter to the 15v scale and connect the poitve lead to where

Check the circuit diagram in your manual for the color codes that have
been used on the wiring, but I would expect the black wire to be ground
and the white wire to have somewhere around 12 volts on it (same as
battery voltage) whenever the ignition switch is on and the the
connector is disconnected from the stator (engine off, not running)...

as to a brand or type that will work for these sorts of things.

If you go to a place like Harbor Freight, looking for bargains, you
will wind up taking what you can get, and you will be happy that you
saved the money. If you have some specific application in mind that
requires reading very high amperage or very low ohms, you'll wind up
paying more for the meter. But, again, I recommend checking some online
catalogs for a better VOM...