Topic: Field and stator coil resistance test

[amitr0]

Bike : '76 cb550k

I am tearing resistance for field and stator coils.

I am seeing :

Field resistance : 4.1 ohms
Stator resistance : .70 ohms

Does this mean that i need to replace both cois?

Ref from the book attached.

[TwoTired]

No. They are both operable.  Though the field coil report is a bit low.  Even if you have a digital meter, it doesn’t mean the display is absolute.  Have you checked the meter lead resistance?  What does display show when you touch the two leads together?  Meter and test setup error must be accounted for in measurement readings.  Especially with instruments being used at the margins of their capability.

Much of electrical testing is knowing proper technique for the measurements you make?  Didn’t I already post the methodical charging system check out?

[amitr0]

Much of electrical testing is knowing proper technique for the measurements you make?  Didn’t I already post the methodical charging system check out?

If i missed that post, please help me by sharing the link

[Deltarider]

Amitr0, the field and stator are rarely the cause and some will say: never, unless there's damage like caused by an accident or a drop. What you could do, is inspect the wiring is not chafed, where it exits the left crankcase cover. I have not studied all the replies in the other thread yet, so forgive miss something, but here's a question:
Is there anything not OEM on your bike, that could draw excessive current whilst riding, like an electronic ignition or grip heaters? I find it hard to believe that will be the cause, but...
If it was my bike, I would temporarily connect an ammeter between the NEG battery terminal and the thick NEG cable, to monitor what is going on whilst riding, but my meter has clamps and can handle 15A. Be aware that in that situation you can NOT operate the electric starter!!!
I'd choose the NEG route over the POS route, because I hate a dangling POS cable that, when not well isolated, will accidentely contact the NEG frame.

[TwoTired]

Charging system methodical verification checks, CB750, CB550, CB500, CB400, and CB350.

Begin with problem verification and characterization with recorded data.
A -- Fully charge a known good battery.  Let it rest for 2 hours, off the charger, and measure the battery voltage.  (Target is 12.6-12.8V.)
B -- Start the bike and measure the battery voltage at idle, 2000, 3000, 4000, and 5000 rpm.
C -- Repeat the measurements of B with lighting off.

The above tests identify charging system success, failure, or degree of "faulty".  The success voltages are listed in the Shop manual.

D -- Assuming the above indicates faulty, do check the RECTIFIER diodes with a diode tester or ohmmeter capable of testing diodes and uses more than .7 volts to make the test(s).
Of the twelve test made in D, six must read low ohms and six must read very high ohms.

E- assuming no faults were found in D,  Measure the white and green wires disconnected from the REGULATOR.  CB750s should 6.8 ohms - ish,  CB550s/350s/ and 400s should read 4.9 ohms- ish.

F- If there are no bullet holes or road rash/divots on the alternator case, the stator is probably good.  But, you can check for yellow to yellow continuity (.35 ohms) among all the wires, and that no yellow wire has continuity to the engine case.

G- Assuming no faults found in D, E, and F, measure the disconnected terminals of the REGULATOR.  The black and white terminals should measure zero ohms (subtract meter error if there is any).  Higher than Zero ohms, indicates internal contact contamination needing cleaning and attention per shop manual.

H - Assuming D, E, F, and G have not found faults. We can verify all the of the charging system minus the regulator is functioning correctly, by using a temporary jumper to connect the disconnected white wire (normally attached to the REGULATOR) and connecting the White directly to the the battery POS terminal.  Repeat the B and C tests.  However, if at any time the battery voltage rises above 15V, stop the test.  Such an indication would prove the charging system capable of maintaining a known good battery.  If this test never achieves 15V, then there is a wire/connector issue in either the ground path leading back to the battery NEG terminal, a wiring/ connector issue withe the rectifier RED path to the battery POS terminal, or you made a mistake in D through G.

I - (not used, can be confused with L)

J -  The only parts that remain to prove or expose are the REGULATOR (in active mode) and the electrical path between the battery POS terminal and the black wire that connects to the REGULATOR.

K - Lying to and starving the regulator
The regulator can only do its job correctly if it gets a proper voltage report of true battery voltage status.  The Vreg monitors the Black wire for this status.  Measuring the voltage lost between the Battery terminals and the Vreg connections identifies problems that are not really the charging system's fault.
Two connection paths must be checked, the Battery POS terminal to the Black wire connection at the VReg, and the Battery NEG terminal to the Green wire connection to the Vreg.  A volt meter can measure these losses directly by placing a probe between the two identified points, Black path and then the green path.  The numbers are summed and the error seen by the Vreg quantified.  Anything over .5V loss is cause for concern and anything over 1V is a certain issue to be corrected.  Each connector, terminal, fuse clip, or switch in the pathway can cause voltage reporting loss.

The regulator also passes the received voltage on to to the Alternator field coil to create a magnetic field within the alternator,  The voltage level determines the strength of the magnetic field and the maximum output capability of the alternator.  Therefore, starving  the Vreg of true battery voltage leads to reduced max output capability of the alternator.

L - regulator operation/verification.
  The Vreg sends voltage to the alternator field in response to measured voltage which is battery state of charge.  Any voltage at the battery of less than 13.5V sends full black wire voltage to the alternator's white wire.  The alternator output will vary with RPM, even if "told" to produce max power by the Vreg.  If the alternator has enough RPM to overcome system load, any excess power is routed to the battery which will raise the battery voltage (slowly if depleted and rapidly if nearly full).   When the battery reaches 14.5V, the regulator reduces the voltage to the alternator, reducing output strength and preventing battery overcharge.  If the battery exceeds 14.7V, the regulator clamps the alternator field coil power to zero (0V), effective shutting off the alternator.

Because, there is electrical load from the system, an alternator that is not producing power allows the battery to deplete and the voltage falls.  The Vreg responds by turning the alternator back on in accordance with battery state/ charge level.

The Vreg state changes can be monitored/verified by observing the battery voltage state, and the White wire to the alternator field.  (Two meters are handy for this.)  The "trip" voltages can be adjusted with the adjust screw, while changing engine RPM and electrical load that the bike presents to the battery/charging system to "make" the battery reach the voltage levels need for the set trip points.  IE. with load reduced (lighting off) and the engine above 2500 RPM, a charged battery will attain 14.5 V.  Anything above that and the adjust screw needs to be backed out to keep the battery safe from harm.
The shop manual outlines bench set up mechanical adjustments that should be performed on unknown or tampered units.  These should be resolved before final trip point adjust tuning.

Note that while the system is working, the Vreg can change states rapidly before your very eyes., changing 5 times or more while you blink.  Therefore, you may have to mentally average values measured on the White wire if your selected meter doesn't do that for you.

[amitr0]

Amitr0, the field and stator are rarely the cause and some will say: never, unless there's damage like caused by an accident or a drop. What you could do, is inspect the wiring is not chafed, where it exits the left crankcase cover. I have not studied all the replies in the other thread yet, so forgive miss something, but here's a question:
Is there anything not OEM on your bike, that could draw excessive current whilst riding, like an electronic ignition or grip heaters? I find it hard to believe that will be the cause, but...
If it was my bike, I would temporarily connect an ammeter between the NEG battery terminal and the thick NEG cable, to monitor what is going on whilst riding, but my meter has clamps and can handle 15A. Be aware that in that situation you can NOT operate the electric starter!!!
I'd choose the NEG route over the POS route, because I hate a dangling POS cable that, when not well isolated, will accidentely contact the NEG frame.

To the best of my knowledge, the only non-stock electrical thing on the bike is the points. It has dyna EI points. Everything else, is bone stock.

I will try to see if I can get such an ammeter connected while riding, it will take a few days atleast to get the gear and then proceed with the experiment.

[bryanj]

The Dyna takes more power than points and the bike will not charge till a higher rpm

[amitr0]

The Dyna takes more power than points and the bike will not charge till a higher rpm

General question, i see folks updating to not just dyna ignition but dyna or magna coils as well.

How do they manage to keep their bikes running?

[Deltarider]

As said before, the effects of extra consumption by an EI are usually exaggerated in this forum. The stock ignition in its distributorless and wasted spark configuration, is more than adequate, provided the sparkplugs and plugcaps are healthy. Personally I find a transistorized ignition like mine or Hondamans, a good option, but that's about it. If I was forced to choose a full EI, I'd probably favor the Tytronics over others, as that particular brand was smart enough to limit duty cycle to 50%. But then... you'd have to have confidence in their precision in machining the rotor. I believe it was in the German forum, a member once discovered a deviation of 1,5-2^o between the 1+4 and 2+3 cam. I consider that a bit much. I forgot which brand that was.
As far as coils, I'd stick to coils that have a primary resistance of 4-5 Ω.

[TwoTired]

General question, i see folks updating to not just dyna ignition but dyna or magna coils as well.

How do they manage to keep their bikes running?

The 750 has a stronger alternator than the 550 or 400, and that is where Dyna is usually installed.  The 750 has pretty much the same ignition system as the 550.  So, it was inevitable that non-engineers would “see what happens” and install it there, too.  With a battery at full power, lo and behold the bike starts and runs!  So declare victory.

But the Dyna is actually poorly designed, as while it could mimic the stock point behavior it doesn’t.   The stock points and its cam charge the each coil during 190 degrees of crank rotation. The Dyna charges during 270 degrees of rotation. Well beyond the point of coil total saturation.  And that just wastes energy of the bike’s electrical system.  And the 550’s nominal 150 watt charging system doesn’t have a lot to spare.

With stock lighting on, the stock bike draws about 10 amps (130watts), leaving 20 watts about 1.5 to 2 amps available for battery charge…when the alternator is spinning well above idle.  At idle, the alternator only makes about 1/3 of rated, or about 50 watts.  With the key switch on the battery is in depletion mode every time the engine idles.  Only restoring battery strength when the engine is revved.  Adding electrical drain over stock depletes the battery faster at idle, and prolongs the recovery time of battery restoration when revved, as more is diverted to the added device consumption rather than to the battery.

So, will the bike still run with a Dyna?  Yes.  But, depending on how it is ridden, will eventually not, when the battery depletes to levels where spark can no longer be generated.  A separate lighting switch will allow that energy to be available to restore battery much more quickly in daylight operation. (Which is illegal in some parts of the world where legislation conflicts.)

Dyna doesn’t recommend their device and 3 ohm coils for the 550 or 400.  And power drain is the reason why.  City driving makes the bike unreliable, unless your trips are short and externally recharge the battery while the bike is parked.  Now, if you can keep the engine revved over 3000 all the time, you might be able to declare “no problems”.

Engineers have to write specifications for their designs.  In fact, because of production and part variables, not all one million of a particular design type will perform identical.  The testing specs in the book are minimum acceptable values to make the machine perform to minimum requirements.  This means that some systems will actually perform better than spec, when all the production variables stack in a beneficial way.  What this means is that the while the alternator is specified at 150 watts,  most will make a bit more than that by some percentage.  If, through testing, part of the system causes less output, that component is changed to make it behave at or above minimum requirements. What this means is that some samples of systems and bikes will tolerate extra electrical loads without noticeable repercussions.

You reported your field coil measurement at 4.1 ohms, while 4.8 ohms is median spec.  If that is indeed accurate, it is possible that it can not make as strong a magnetic field for operation of the alternator to full strength specification and be some percentage lower than factory rated.  This would make it weaker and less able to tolerate the added power drain of the Dyna, to keep the battery near its full charge state.  It will still depend greatly on how the bike is operated, and RPM raised over the idle state.

Another thing to check is what voltage is actually being delivered to the alternator field.  Ideally full battery or system voltage will make the alternator be all it can be at whatever RPM it is spinning.  Less voltage in=less power out.  And parts of a volt do matter.

Cheers,