82 xj750j Charging System Problems

First I want to thank everyone who regularly contributes to this site. I have used it countless times and it has always been helpful.

I have an '82 xj750 Maxim (Model ID: 15R) that I am working on. The PO started to chop it so it came with the wiring harness cut up. I put on LED head and tail lights and basically rewired the entire bike.
My problem is that the charging system is not charging. I believe I must have something wired wrong, let me tell you what I have done.

I Replaced the stator and rotor (used in good condition), put in new brushes and polished the copper rings on the rotor until they are shiny. Using the fault diagram here http://www.electrosport.com/media/pdf/fault-finding-diagram.pdf, I ran a jumper wire from battery + to brown wire and battery - to green wire, I then started the bike and tested the AC voltage output of the generator at the 3 white wires. I am getting a gradual increase of VAC as the RPMs increase with over 50VAC at @5K RPM on each white wire. I also did continuity tests and they are good - my conclusion is the generator is good.

I replaced the Regulator/Rectifier (RR) with a brand new part. I have done continuity tests of the capacitors according to the chart in the manual (and chart posted by Rooster53 here http://xjbikes.com/forums/threads/vacuum-leak-on-xj-550-maxim.116946/page-3). I am a little confused because my readings are opposite of the chart, but they are consistent, so it may just be me - let me explain. The chart says d(Red wire) with red meter probe attached and a(white wire(s)) with black meter probe attached should be continuity, but I get an open, however if I reverse the probes (red probe to d and black probe to a) I get continuity. Same behavior on all three white wires (and it turns out to be the same behavior on my old RR so it is probably still good also).

Let me try to paint a picture of the wiring. The RR has an 8 pin (male) connecter with 1 empty slot
- Fused wire from battery + to red wire of RR.
- RR black wire is connected to harness ground which is grounded to engine and then to battery Neg
- Brown wire to brown from generator and also wired to key switch power on.
- Green wire to green from generator
- 3 white wires to stator, I ditched the pigtail plug so these wires go directly into the 8 pin (female) plug that connects to the RR plug

I am using a brand new fully charged battery, I have thoroughly cleaned the battery terminals and the 8 pin RR connectors.

I have thoroughly reviewed http://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/ and http://www.jetav8r.com/Vision/IgnitionFAQ.html, both of which have been incredibly helpful.

No matter what I do I still only get 12Vdc across the battery when running at over 3k RPM (I know there is no or little output at idle and it must be rev'd to over 2k RPM to see an output).

My big question is the brown wire to the generator. Based on the wiring diagram(s) I have looked at (and there have been a few) the brown wire gets power from the key switch and goes both to the RR and the generator. Is this correct? Do any of you wizards out there have any other thoughts or questions. Fire away!

Again thanks for the great forum and to all those who contribute.

 

when testing voltage regulator you use the diode setting on your meter and should only get a reading in one direction

 

Understood, and I am getting a reading in only one direction. It's just that the direction is the opposite of what I expected based on the chart. Must just be that I was interpreting the chart incorrectly. Either way I believe the RR is good based on the fact that I get the same reading from all 3 white wires (continuity in one direction and open in the other).

It feels to me like it is down to wiring, which I did myself, but I cannot figure out where I went wrong. My next step is to double check the ground to ensure that I have a good solid ground to the RR, if that doesn't fix it then I don't know where to look next.

 

read about testing your charging system in this thread. http://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/

start by ohming out the charging system.
excerpts for above thread
If your charging voltages are too low, suspect the alternator brushes first, then perform the alternator stator and rotor checks as described in the Alternator Section.

If your charging voltages are too high, suspect your Regulator - Rectifier unit first, and perhaps dirty or corroded electrical terminals. The procedure for checking these is too detailed to describe here, and you should consult your service manual for additional details.

Checking Alternator Stators:

Measure the resistance across each pair (white1 to white2, white1 to white3, and white2 to white3) of the three white wires (white1, white2, and white3) at the connector; the specifications should be:

0.50 ohms +/- 10% for all XJ550 models.

0.46 ohms +/- 10% for all XJ650, all XJ700, all XJ750, and XJ900RK models.

Checking Alternator Rotors:

Measure the resistance across the two lead wires (usually brown and green) at the connector; the specifications should be:.

4.5 ohms +/- 10% for all XJ550 models.

4.0 ohms +/- 10% for all XJ650, all XJ700, all XJ750, XJ900RK, and XJ1100 models.

Note that worn, dirty, or damaged alternator brushes can affect these readings, as can "dirty" copper commutator rings on the rotor face (where the brushes contact the rotor):

 

The "pocket testers" that Yamaha used have the polarity reversed when checking continuity. It was quite a common thing on the older analog DVM"s so yes as long as you read open in one direction and the diode in the other direction the Rect portion of the Rect/Reg should be OK.

Yes that is correct. The brown wire to the Rect/Reg is the voltage sense. The brown wire that goes to the generator goes to the brushes and is used as power for excitation of the AC Generator field coil (rotor).

So doing this test should confirm that the AC Generator is functioning. The only difference when everything is connected is the Regulator portion of the Rect/ Reg will control the low side of the field coil (green wire), and consequently regulate the output voltage. If you look at the chart in the FSM the green wire referred to as V2 is specified to be less than 1.8V (note it should also say not zero) when the key switch is turned on. With V2 at 1.8V, and the other side of the field coil (brown wire) connected to 12V, this results in maximum output of the AC Generator. As the engine speed increases, less excitation is needed in the field coil so consequently V2 should rise as stated in the FSM.

Note some of the FSM's reverse V1 and V2, the one below is correct.

 

Thanks everyone for your replies and help. I finally got this figured out and it is now charging.

As I noted in my original post I tested my old RR and it tested virtually the same as the new RR. Well as you know with troubleshooting, sometimes you have to backtrack and put the old stuff back in to verify results. So I plugged the original RR back in to the system and wha-la, fired the bike up and it started charging. The "new" RR is not exactly the same as the original, but it was advertised as an OEM replacement. Unfortunately I cannot find the records of where I ordered it from (if I come across them I will post later).

My guess (and this is only a guess) is that the new RR is more sensitive and all things combined with the old system it just isn't detecting things correctly. Anyway it is now running and I have had it on two different 10+ mile trips. Still have a couple more things to tune, but she's a runner and up for sale if anyone is interested (southern California).

Happy Trails