Topic: 1974 CB550 Shorted field coil

[ggriffith]

Bike: 1974 CB550
Issue: Charging System Not Working

Question: With the field coil disconnected from harness. I am performing a resistance check and getting 5.6ohms. Which is, from what I can find, still within spec. Now the weird part is when I perform a continuity test on both white and green wires coming from disconnected field coil, it shows grounded. Engine off, and key off. I know green is universal ground for the bike, but should I also be getting ground on the white wire leading to field coil?

Had a fried/melted rec/reg combo a few weeks ago. Even with a new reg/rec combo charging system has been spotty since then. Has my field coil shorted? Even with ohms with in spec? Stator Ohms with in spec as well.

[strynboen]

there must not be any ground konneltion on vhite and green...they must be total isolated from all..so id you can get any ohms from metal to the vires..there is a total short to ground...

put one probe on the klean metal..and the other on the vhite vire...and you get???hopeful nothing

[ggriffith]

Okay with a probe on the white wire from the field coil to clean metal I am getting 5.5 ohms. The internal resistance of my meter is .5ohms. So basically I have a short to ground on the white wire?

[strynboen]

and the green too..those vires is inn and aut terminals on the magenet coil inside...so both are now groundet..uou just have some coil vire in betveen to give some restistens..

normaly you can not blow those..as they normaly have 12 volt in use..so hard to kill..even reversed polarity dont kill those ..its just a spool of kobber vire..

[ggriffith]

Yeah green wire has .3ohms resistance.  All three yellow stator wires are with in spec, and show no short to ground. Only feild coil is showing abnormal resistances. So basically trace wire to find a short, and if none is found then the field coil itself has shorted?

[TwoTired]

Okay with a probe on the white wire from the field coil to clean metal I am getting 5.5 ohms. The internal resistance of my meter is .5ohms. So basically I have a short to ground on the white wire?

Using an ohmmeter, the white a green wires should present nearly 5 ohms to the applied power and make an electromagnetic field with a strength proportional to the voltage applied.

Your ohmmeter is applying a very small voltage to be sensitively read and interpreted as ohms across its probes.  A "short" or shorted winding, would have an indication of something less than 5 ohms.  If you can't obtain a resistance reading less than 5 ohms, then the field coil should do its job in operation.

It is possible that the winding has an intermittant grounding of one or more wire coils, brought on by heat expansion or vibration.

Cheers,

[ggriffith]

Yeah it's possible I'm about to start taking it apart. I'm getting correct ohm readings across white and green but if I just ohm white to engine block I'm getting 5 ohms. It should be zero correct? If the windings came apart wouldn't I be getting out spec readings on the stator side?

[TwoTired]

Yeah it's possible I'm about to start taking it apart. I'm getting correct ohm readings across white and green but if I just ohm white to block I'm getting 5 ohms. It should be zero correct?

No, the green wire connects to the block though the coil mounting means, a common electrical path.
I sugestest you look for problems elsewhere.

What problem are you trying to solve?


Cheers,

[strynboen]

you can try to konnekt it to a battery,,and thek for amp...if it goes mad and blov a 25 a fuse you have a problem...if it can be magenetic..and the power use is under 5 amps..it probly is fine...but strange vith that short to ground/metal..can it be a messuring fail..or is the coil melted through the isolation..so the coil is groundet....(but still have 5 ohm in the viring)
ythink it vill blow thew fuse on the bike..id there is groundet coils....so thek that aut ...renember to take all vires off the bike ,, taking the tests...so nothing on the bike make any thangings on the results..

[ggriffith]

Yeah it's possible I'm about to start taking it apart. I'm getting correct ohm readings across white and green but if I just ohm white to block I'm getting 5 ohms. It should be zero correct?

No, the green wire connects to the block though the coil mounting means, a common electrical path.
I sugestest you look for problems elsewhere.

What problem are you trying to solve?

Not charging at all, with a recently fried rec/reg combo.
Cheers,

[strynboen]

the green is only konnekted to ground..vhen it are mounted in the viring harenes

..if you isolate it from the viring and take the messurings..there is no kontakt..from vhite/green to ground...

[ggriffith]

Correct but if I am getting contact to ground then it's shorted.

[strynboen]

vhy is there a green vire? if it already are groundet at the coil.

..then the vhite one  can do the job..as i renember ,vhen i soldered the new vires in the coil..both vas isolated..and seperated from metal frame

..but i can be vrong..anyone else have a shot,on this one

[ggriffith]

Okay so the white wire  and the green wire disconnected coming from the field coil. Should I show any continuity to ground on the white wire?

The issue is no charging at any RPMs. I  had a fried rec/reg combo about a month ago. Which I have replaced with a new unit. Bike is still  not charging. That's' which I am thinking field coil failure. Stator yellow wires ohm out correctly and show no continuity to ground. What else would cause a fried rec/reg unit?

[TwoTired]

Terms:
Continuity means electron flow is possible.
5 ohms is still continuity.  Your field coil should read 5 ohms between its coil wires and only one of those wires should read zero ohms to engine/ frame (green).

If you supply 12v to a field coil, it has no choice but to make a magnetic field. Law of physics.
If the energized field core metal spins (the rotor), the magnetic field with alternate pos to neg, etc.
This alternating field excites the stator windings and produces an AC votltage in those windings.  Then the rectifier converts that AC voltage to DC voltage which can be used by the bike's systems and battery.

I don't know the conditions under which your vreg "fried".  But, a measured 5 ohm field coil should not be a cause for a properly designed and functional regulator.  However, if the battery was ever connected in reverse polarity, even momentarily, that would be sufficient to cause any number of failures in a combo reg/ rectifier unit, and the interconnected wires as the battery dumps all its power into those items.  The system is not fused, unless you consider the weakest component in the operating circuit to open as a "fuseable link".

Cheers,

[ggriffith]

Checked power going to field coil through standalone white wire connection at vreg. 11.6V on white. Voltage at yellow wires is 6.9 volts. Battery voltage key off 13v. Battery voltage at 4K rpm 13.2.
Battery voltage at black standalone wire key on engine off 11.8.

 I think I found the issue the black wire coming from harness to regulator, if I move it around in certain detections it drops to 0V with key on. That is the wire that supplies vreg with power am I correct?


EDIT: Okay I "fixed" the charging issue. The switched power for the vreg standalone black wire connection was bad and not making proper contact. I repaired the connection and now I'm getting 13.3 at 4K RPMs at the battery. One last issue is the battery is at 12.9 volts with key on engine off. When I connect the meter between black standalone wire from the regulator it's only showing 11.8. Is it normal to see a 1V drop between the battery and black supply wire, or should it see closer to battery voltage?

[TwoTired]

EDIT: Okay I "fixed" the charging issue. The switched power for the vreg standalone black wire connection was bad and not making proper contact. I repaired the connection and now I'm getting 13.3 at 4K RPMs at the battery. One last issue is the battery is at 12.9 volts with key on engine off. When I connect the meter between black standalone wire from the regulator it's only showing 11.8. Is it normal to see a 1V drop between the battery and black supply wire, or should it see closer to battery voltage?

Ideally, the Vreg terminal should "see" the same voltage as the battery.  The vreg makes its decision based on what it is told about battery charge status.  Lying to it allows incorrect decisions, and can lead to overcharging the battery because it thinks the battery is 1 volt lower in charge state than it really is.
It normally is still ok if there are small inaccuracies.  Personally I accept no more than a 0.5V difference between the Vreg "sense" Black connection and the battery actual voltage at its terminals.
Voltage loss in black wire distribution is commonly caused by poor connections at terminals, switch contact degradation, and fuse block issues.  All can add in line resistance to the circuit which both drops voltage and consumes power dissipating it as heat rather than having it used to maintain battery or operate desired components.

Cheers,

[ggriffith]

EDIT: Okay I "fixed" the charging issue. The switched power for the vreg standalone black wire connection was bad and not making proper contact. I repaired the connection and now I'm getting 13.3 at 4K RPMs at the battery. One last issue is the battery is at 12.9 volts with key on engine off. When I connect the meter between black standalone wire from the regulator it's only showing 11.8. Is it normal to see a 1V drop between the battery and black supply wire, or should it see closer to battery voltage?

Ideally, the Vreg terminal should "see" the same voltage as the battery.  The vreg makes its decision based on what it is told about battery charge status.  Lying to it allows incorrect decisions, and can lead to overcharging the battery because it thinks the battery is 1 volt lower in charge state than it really is.
It normally is still ok if there are small inaccuracies.  Personally I accept no more than a 0.5V difference between the Vreg "sense" Black connection and the battery actual voltage at its terminals.
Voltage loss in black wire distribution is commonly caused by poor connections at terminals, switch contact degradation, and fuse block issues.  All can add in line resistance to the circuit which both drops voltage and consumes power dissipating it as heat rather than having it used to maintain battery or operate desired components.

Cheers,

Yeah I tested power at red terminal on the ignition switch 13.0V going in with key in off position. Once flipped to on position red terminal voltage drops to 12.3V and 12.3V is also showing on black terminal side. Why such a drop between 13V to 12.3V?

[TwoTired]

Sounds like your internal switch contacts need maintenance.  Could be worn or have carbon buildup on the mating contacts.   It's been awhile since I rebuilt one of the 74 style switches.  I may recall a rebuild post a while back.  But, I don't remember if the early style was also addressed.

IIRC bending the tabs allows the unit to be disassembled.  But, there be springy bits inside that seek dark crevasses to escape to.  Sometimes it's too late and things need more than restoration.  It might test your manual dexterity prowess.

I used to know where my spare was.  (to take some pictures)  But, I haven't seen it since my move to AZ.  It's here, somewhere,  But, my stash hasn't been reorganized yet.  I need to bring the rest of my shelving on my next and last move trip.

Cheers,

[ggriffith]

Thanks for the help! I noticed if I switched the kill switch on and off I gain half a volt back. I measured between black signal wire to vreg and pos battery post I am getting 1.1V. Do you think cleaning up connections and cleaning ingition switch contacts will get this under .6? Or is there any other major connections I need to check for voltage drop?

[TwoTired]

The way it works is that the more current that passes through a resistance the more voltage drop there will be through that resistance. And, the more heating will take place, which is bad for the contact/connection.

I can't say what other resistances are in your circuit distribution.  But, the connectors and contacts were not coated with noble metals by Honda.  Further, they were not protected by the elements.  Surface oxidation was therefore guaranteed.  And that oxidation is resistive.  It's not uncommon to take apart and clean EVERY connection and connector on ta 40+ year old  bike and then coat the contacts with dielectric grease to delay further degradation.  While you are at it make sure every connection is mechanically tight. 

Yes, it takes time and effort.  But, thereafter you have a reliable and efficient electrical system, probably for the rest of your ownership.  As a bonus, your headlight will be far brighter when it gets full battery voltage to it.

Cheers,