Author Topic: No Charge! ( I believe a bad Field Coil )  (Read 435 times)

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Offline redcon

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No Charge! ( I believe a bad Field Coil )
« on: July 23, 2017, 07:22:24 PM »
Hello!

Been a while, I hope everyone is doing well!

Like many other threads, I'm having issues with my charging system. I've looked through the first two pages of threads to find an answer, but every issue seems to be specific to that bike. So Here's another thread.

I have a new battery all charged up and ready to go.

Go for a rip around town, dies after about 15-20 minutes of riding. All lights out, can not start again. I can then let it sit for a 10-15 minute break and the battery will come back to life enough for me to get home swearing as I go. Charge the battery up over night, tested good and repeat with same results ( This happened twice at the same spot, luckily close to home, down hill... )

I haven't tested the bike after it dies, and I'd rather not go out again and chance being stranded, as I do not have access to easy rescue...I got lucky twice, don't want to tempt the third.

Fully charged and tested battery.
It's testing at around 12.5v with key off.
Turn the key on, 11.9v
At idle, 11.9v
At 3k rpm, 11.9v

My understanding is that with the bike at idle or revved up, the battery should be reading at around 13-14v due to the charge being sent through the system. Eh?

I looked around and saw the field coil / feeler gauge test. So I grab my feelers, select the thinnest one and test by holding next to a small magnet so I know the feeler will work with the bike. Position feeler and turn key on. Nothing...Tried a couple times too with different positions, and still no slappy feeler. Watched the video too just to make sure I was holding in the proper place...

That had me confused as I was under the impression that you can not start the bike if the field coil is bad.

So here I beg assistance from the wonderful XS500 Forum gurus!

What gives?!?

 :o
« Last Edit: July 23, 2017, 07:26:16 PM by redcon »

Offline guylr

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Re: No Charge! ( I believe a bad Field Coil )
« Reply #1 on: July 24, 2017, 03:33:29 PM »
The XS500 uses a battery-coil ignition system that is dependent on the battery to power the coils and other electrical systems on the bike. The generator is just there to charge the battery like the alternator on your car. The fact that you get no magnetism on the field coil test shows that the input side of your charging system is dead and that means you are running at or near total loss on the battery. Once it gets weak, no spark. So, troubleshoot the battery power supply to the field coil and find out where the problem is.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline redcon

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Re: No Charge! ( I believe a bad Field Coil )
« Reply #2 on: July 24, 2017, 11:35:57 PM »
Nice, thank you for the lead!

Now to figure out how to test. Electric Diagram here I come...If only I knew what I was doing!

Offline dankeller

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Re: No Charge! ( I believe a bad Field Coil )
« Reply #3 on: July 26, 2017, 09:47:54 PM »
Hi redcon. Your 11.9v at battery terminals, at 3000 rpm, with a fully charged battery is not good.  You should get a reading of 13.5 to 14.5 volts.  If you're failing the field coil magnet test, it could be a faulty voltage regulator or field coil.  The field coil looks fairly robust, so I would start testing the regulator. The regulator controls current to the field coil to turn it into a magnet, which is needed for the stator to make electricity. You can bypass the regulator by connecting the brown wire from the field coil to battery negative (I think!), which would turn on the field coil magnet fully. So if this bypass gives you charge, it would indicate a bad regulator (and a good field coil). Note that if your battery is dead or weak, there will not be enough current to power the field coil and make charge.

The problem can also be a faulty rectifier, and there is a test for that that can be done with a volt meter (you can find a how to on google).  And of course the fault could be the stator coil as the insulation can degrade and give you a short to ground, or the wires can break in the coil causing discontinuity.

Search charging issues on this forum.  There is a lot of good information on trouble shooting poor charging.

But maybe start by checking that your wire connections between these components are clean and make good contact.

Let us know how you make out.

Dan
« Last Edit: July 26, 2017, 09:53:53 PM by dankeller »

Offline guylr

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Re: No Charge! ( I believe a bad Field Coil )
« Reply #4 on: July 27, 2017, 02:09:30 AM »
You've already done the feeler gauge test so jump to the check of the brown and green wires for the field coil below. DO NOT GROUND THE BROWN WIRE. You will release a cloud of smoke if you do. You can ground the green wire to bypass the regulator and make the system go to full charge. Look for pinched or broken wires to the generator.

See this old post in the electrical section. I've copied it below.

http://www.xs500forum.com/index.php?topic=469.msg2236#msg2236


OK, the charging system on the TX/XS is and excited field three phase type and not a flywheel magneto magnet type. The three white wires are from the stator assembly and output AC current to the rectifier which turns it into DC current to light the lights and charge the battery. The current output is varied by the voltage regulator increasing and decreasing the strength of the magnetic field from the field coil in the side cover. The steel rotor on the crank end is there to break up the field in such a way as to induce the current flow from the stator. It's a variation on the type used in the XS650 but with the big advantage of not having a spinning rotor coil with brushes.


So how to check it in less than 5 minutes with a feeler gauge and volt-ohm multimeter?
 
1. Take a very thin feeler gauge like 0.005" or so and hold it next to the generator cover about 1/2" away. Then turn the main switch on. If the field coil is working the feeler gauge will slap against the side cover due to the magnetic field. If it doesn't then check the brown and green wires that connect to the field coil. The brown supplies battery current to the field coil when the key is on and the green wire is the ground side to the regulator. (So check for 11.5VDC or more on the brown wire with the key on.) The regulator varies the resistance on the green wire to control the strength of the field.

2. If the field coil made a good magnet then move on to the stator and check the unloaded white wire to white wire output with the multi-pin connector unplugged. No need to rev it up , just check it at idle and you should see 16-18 AC volts. Do the three possible connections A-B, A-C and B-C. They should be close to the same. Now plug the connector back together and check them again in a loaded check from the back side of the connector. The rectifier places a load on the stator as the current passes through the diode pairs. This time the voltage should drop evenly on the three possible connection to about 10.5 to 13 AC volts. If they are all the same your stator is fine. If you get a very low reading on one or more of the white to white loaded connections then you likely have a shorted diode in the rectifier. If you see a high reading as in the unloaded check then you may have an open diode in the rectifier. 
3. It's also possible the stator white wires are shorted to ground somewhere so use the ohmmeter to check each one for a circuit to ground by touching one leg of the tester to the engines cases. You should see no circuit (infinity) on the meter.The most common fault in stator wires is a pinched or damaged wire from the case cover up to the connector.

As always check and clean your connections on everything before you condemn a component and start with a fully charged battery.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline redcon

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Re: No Charge! ( I believe a bad Field Coil )
« Reply #5 on: October 10, 2017, 04:24:50 PM »
OK! Finally got around to checking my coil. ( I'm veerrryyy sloooowww....)

Checked resistance of the green-brown wires to the field coil and got no reading. According to page 188 #3 of the shop manual, "When the resistance is 0 or infinite, the coil is shorted or broken, and no power is generated."

Seems like my issue right there...

So I guess, my questions at this point, before I tear in:

Is there anything else I need to check before I go ahead and spend the cash for a NOS coil?

Should I be replacing the stator at the same time?

And will the coil from earlier models work with my 78 E model?

Thanks so much for the help!!

Offline guylr

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Re: No Charge! ( I believe a bad Field Coil )
« Reply #6 on: October 11, 2017, 09:34:47 PM »
Before you give up on the old field coil, did you pull the cover and check the lead wires all along their length?  A cut wire outside the coil is not uncommon when people change their sprockets.

The older coils will fit your E model.

Guy
 
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline redcon

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Re: No Charge! ( I believe a bad Field Coil )
« Reply #7 on: October 18, 2017, 08:21:30 PM »
Welp, I'm glad you advised to look at things a little deeper.

I found one the white wires going to the generator had been shredded by the drive chain....I solder/sleeved the break with some new wire and retested. Now it is at least reading the correct ohms for that connector. Still not getting the field coil to magnetize though.

There's one other thing I want to check before I tear the cover off. I actually bought a regulator/rectifier unit from Ricks Motor Sports a while back. Long story short, I've been in contact with them today about the connectors to the regulator possibly being pinned out incorrectly. I read that some places might be going off of the xs400 diagrams, so I've got a line in to them just to double check and be positive that unit is not the issue.

Thanks for your help Guy, I'll let you know what Ricks has to say.