Topic: Field Coil Problem

[mkarcz]

Hey,

I have a '75 CB 550K with a field coil that is testing at about .5 ohms with the meter set to Rx10.  I think it is supposed to be at about 4.9 Ohms so I ordered a replacement off ebay.  The replacement is also testing at .5 ohms also.  I am really happy now.  To top this off I can't even get the screws out of the cover for the stator.  They are screws.  They are old and on there tight.  When I turn them I can feel the metal bend.  I need help on these fronts, please.  I just want to ride.

mark

[bryanj]

If you have two coils reading the same its your meter thats wrong and in 30 years i have NEVER seen a field coil go down electrically---Wiped off in an accident yes---As to removing the screws its an impact screwdriver job

[mkarcz]

I would love to agree with you, but it looks like both stators are working properly.  I therefore don't think that is the problem.  The battery is brand new and fully charged.  But when I run a current check on the battery and run it through the RPM's it the voltage reading doesn't go up.
Maybe the regulator is shot... but how do I isolate/ determine if that as the problem?
mark

[TwoTired]

The stock regulator simply puts a 10 ohm resistor in series between battery and field coil when the battery voltage reaches 14.5 volts.

For test purposes, you can bypass the regulator by jumpering 12V onto the white wire of the field coil. The alternator will then put out all it can fro any given RPM.  Rev the engine and monitor the rectifier output.
Make a chart of voltage vs RPM and report back.

I agree with Bryanj.  I suspect your meter or your test technique is wrong.
What reading do you get when you touch the tips of your probes together?
The one I'm using here reads .3 to .5 ohms depending on how good the contact is between the probe tips.
Whatever you read on yours is a measurement error that must be subtracted from any future resistance readings you wish to measure.
Next, remove the black and white wires from your regulator.
What is your resistance reading between the regulator black and white spade terminals?
It should be quite close to 0 ohms. (subtract your measurement error)
Next remove the cover off the regulator.
Again measure the black and white terminals while pushing down on the contact arm so neither contact is touching.  I measure 10 ohms while no contact and 7.7 ohms when the lower contact is made.
Report your findings.

[mkarcz]

Quick update: I checked a friend's 550 with my ohm meter and got all the same #'s for the stator/ field coil, yet his battery gets charged.  Rectifier is good on my bike, by the way.

But, I am not an electrical person at all so...

For test purposes, you can bypass the regulator by jumpering 12V onto the white wire of the field coil. The alternator will then put out all it can fro any given RPM.  Rev the engine and monitor the rectifier output.
Make a chart of voltage vs RPM and report back.

...doesn't make too much sense to me.  How do I jump 12V onto the white wire.  I am imagining that this is taking the wire from the field coil (white) and connecting it to the wire that goes from the rectifier to the battery (color?).  is there then a wire that goes from the battery to the rectifier that tells the rectifier when it should come on and off?  Sorry, electricity is new to me.

I think I understand the second part:

Whatever you read on yours is a measurement error that must be subtracted from any future resistance readings you wish to measure.
Next, remove the black and white wires from your regulator.
What is your resistance reading between the regulator black and white spade terminals?
It should be quite close to 0 ohms. (subtract your measurement error)
Next remove the cover off the regulator.
Again measure the black and white terminals while pushing down on the contact arm so neither contact is touching.  I measure 10 ohms while no contact and 7.7 ohms when the lower contact is made.

But it is currently too dark to check this stuff.  Hopefully I can first thing in the morning.

thanks
mark

[Dennis]

a field coil that is testing at about .5 ohms with the meter set to Rx10.  I think it is supposed to be at about 4.9 Ohms

Meter set to X10. Hmmm........ I think .5 X 10 = 5 ohm,  close enough to 4.9?

TwoTired says

I agree with Bryanj.  I suspect your meter or your test technique is wrong.

Looks like the test technique. Why not use RX1?

mkarcz,
If you are not familiar with meter useage, you might want to scan through the book that came with the meter.

Not trying to be mean or derogatory here, but it is difficult to use a tool if you don't understand how it works

[TwoTired]

...doesn't make too much sense to me.  How do I jump 12V onto the white wire.  I am imagining that this is taking the wire from the field coil (white) and connecting it to the wire that goes from the rectifier to the battery (color?).  is there then a wire that goes from the battery to the rectifier that tells the rectifier when it should come on and off?  Sorry, electricity is new to me.

Assuming you can locate the regulator, ther are three wire attached to it.
Green = ground or battery minus
Black = 12v when ignition switch turned to ON. (check it with your voltmeter)
White = field coil

 Connect the black to the white (jumper wire) and the alternator will put out its maximum power relative to engine RPM.
This is a temporary test.  When the charging system works properly, it will put out too much power and cook the battery over the long term.  But, it can withstand an over charge for short durations.

I can't get much clearer.  If you are still baffled, take it to a professional.  Otherwise, post the test numbers and we can take you to the next step.  You might also describe your test instrument; name and model number.

[mkarcz]

sorry, I have been really busy this last week and haven't had time till now to work on the bike.

I put a jumper from the black to the white wires, while they were still connected to the regulator.  I didn't get any change in the battery voltage.  So I shut off the bike and adjusted the connection to make sure they were solid.  Tried to start her and the main fuse was blown.  Changed it, and now I can't get any power at all.  The new fuse looks good still.  So where could my new problem most likely be?.. One possibility.  When I noticed it wasn't starting again I started checking all the connections,  I came across a green wire with a female end that was attached to anything.  every connection in the area had a mate, including the one to the regulator.  The inside of this connector looks like it was sitting disconnected for a while, dust and even cobwebby, with no sign it just slid out of somewhere.  Help.

As far as my test equipment is concerned. 

GB Instruments
GMT 18A
It is an Analog

The multimeter has a zeroing out thing on the side.  So I set it to Rx10, which is what my manual says, and put the ends together. When it stops moving dial it to zero.  When I put it to the Green and white wires it goes to .49.  my book says 4.9.  If I set it to Rx1 it goes to zero.

To be clear that I am using the right to wires they go into the plug like this
Yellow           --------                White
Yellow           --------                Green/red-line
Yellow           Green                Blue/red-line

When I put it to any two yellows I get .2/.3 in that area.

Thank you all a bunch though.  I am learning tons.

I am going to try and track down the problem, starting with a newer new 15a fuse.

mark

[TwoTired]

I put a jumper from the black to the white wires, while they were still connected to the regulator. 

For the test, disconnect from the regulator and use jumper instead.  This bypasses the regulator completely.

I didn't get any change in the battery voltage.  So I shut off the bike and adjusted the connection to make sure they were solid.  Tried to start her and the main fuse was blown. 

The green wire is a ground, sure you didn't jumper black to green accidentally?  That'll cook off the fuse!

Changed it, and now I can't get any power at all.  The new fuse looks good still.  So where could my new problem most likely be?..

Set your meter to read voltage and make sure both sides of the fuse have battery potential.

One possibility.  When I noticed it wasn't starting again I started checking all the connections,  I came across a green wire with a female end that was attached to anything.  every connection in the area had a mate, including the one to the regulator.  The inside of this connector looks like it was sitting disconnected for a while, dust and even cobwebby, with no sign it just slid out of somewhere.  Help.

Solid Green wires are system returns and should all connect back to battery minus eventually.  The wire you found is probably next to the signal flasher unit.  It doesn't have to be connected, and can be ignored.

The multimeter has a zeroing out thing on the side.  So I set it to Rx10, which is what my manual says, and put the ends together. When it stops moving dial it to zero.  When I put it to the Green and white wires it goes to .49.  my book says 4.9.  If I set it to Rx1 it goes to zero.

Are you aware that you may have to re-zero your meter whenever you change resistance ranges? .49 on the Rx10 scale IS 4.9 ohms. (Multiply the meter reading times 10)

When I put it to any two yellows I get .2/.3 in that area.

This is good if you were on the Rx1 ohms range and properly zeroed.

[mkarcz]

Hey,
So I am figuring out some of these electrical things.  YES I have been testing with my meter poorly.  the thing goes from x1K to x10 and I for unknown reasons was looking at 1k and 10.  So .5 is 10ohms!  The alternator is working great and I have an extra.

The new fuse was bad the newer fuses are all working nicely.

The regulator.  In trying to get at the regulator and get the plugs on it I pulled the fuse box and the starter box off to reach it.  I blew another fuse and blew another fuse, reattached the fusebox and didn't blow fuse.

With the black and white wires jumpered and the regulator completely out of the picture it was showing up to 14v with the light off and would drop to about 13 with the light on.

Pulled the regulator completely off.  Have a slight problem.  Because my ohm meter only goes down to x10 these readings are super inacurate.  But, it zeroed out with it at the upper and looked like 10 for touching either and 7.7 for just touching the bottom.

What is next masters???

mark

[TwoTired]

I had a lot of difficulty parsing your last post.

I looked up your meter on the net. Your lowest resistance scale is X10 that means what ever number the needle points to on the scale, you have to mentally multiply times 10.

13 and 14 volt means your alternator is capable of charging your battery.  If you can't get similar voltages with the regulator in circuit, then your regulator is suspect.

The resistances you've measured for the regulator look reasonable except you left out the measurement for reistance when the upper contact is made.  The at-rest contact position should give you near 0 ohms.  If not, get another regulator.

If all the resistances do check out, then reinstall the reg with the cover off  the contacts should remain up until the voltage reads about 14.5 volts across the black and green wires at the regulator.  Probably have to rev the engine to see any movement, and it may oscillate faster than you can see, or the meter movement can respond too.

Anyway, if you can get a 13-14v reading on the battery with your meter, button up the bike and go ride.
Cheers,

[mkarcz]

Thanks, looks like bike is working now.  I put the regulator back in the system and the bike seems to be working now.  So thanks a bunch for the help, I just learned how the charging system works, and hopefully it will stay working.
mark