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XS400 1980 not charging battery

Discussion in 'The Garage' started by K3ith, Jun 9, 2020.

  1. K3ith

    K3ith XS400 Member

    Hello

    Just finished rebuiling my 1980 XS400. I have problem, alternator is not charging battery.
    It's my first bike and I bought it last september. Started rebuiling it straight away, because I didn't have my license yet. The bike ran just fine when I drove few kilometers before the rebuild. But I thing it was too little to make sure alternator was working.
    Maybe someone can tell me what tests I can do to make sure if alternator is ok or not.

    Also the original separate rectifier and regulator is replaced for rectifier/regulator together in one thing.
    Tested it like showed in this video:
    One number that was showed and supposed to be 0.300-0.500 was 0.535 on mine. Can this be the problem?

    Im didn't have any experience with bikes before this and I'm pretty glad I got everything else working by myself :D Now would be perfect to get it charging.
     
  2. Specdog

    Specdog XS400 Addict

    Here is how to test your stator (alternator). Pull apart the three pin connector for the stator somewhere near the battery. The wires are the same colour. Set your multi meter to AC volts 200 range ( not DC). Test the pins that are attached to the stator. You're testing AC volts so it doesn't matter which + or - you use. Start the engine then insert your meter probes to #1 pin and #2 pin. Write down the result, likely 25 VAC. Test pin #1 and #3, then #2 and #3. Compare the AC volt results. Next rev the engine to 5000 RPM and do the test over again. A good result would be around 85 VAC. Do this test quickly when the engine is running. It will not harm your engine, however be aware that running the engine without the stator hooked up will cause the stator to overheat over a longer period of time. Reconnect your pin connector.
     
  3. K3ith

    K3ith XS400 Member

    Tried it and everything showed 0. The wires are pretty rough also, fixed parts that i can see, but i think they may be broken inside the wire tubing, its stone hard from oil. I'll open it up and replace the wires, hope this will help.
     
  4. K3ith

    K3ith XS400 Member

    Completely rewired the stator and still nothing :/.
     
  5. K3ith

    K3ith XS400 Member

    I mesured the continuity between 3 wires coming from stator and it showed 0.7 ohms. I read that normal is up to 0.5. Is it possible to fix the stator or is it dead? Pretty hard to find new in Europe.

    Edit:
    I looked manual for 1980 XS400 and it showed 0.7ohms is ok. Am I right?
     
    Last edited: Jun 16, 2020
  6. BBS360

    BBS360 XS400 Guru Top Contributor

    Yes. .72 +/- 10%
    Your stator is fixed!
     
  7. K3ith

    K3ith XS400 Member

    But still no power from alternator. :D
    Ill test the field coil and check wiring today, just in case i've missed something.
     
  8. K3ith

    K3ith XS400 Member

    How do i check field coil ohms? There's green and black wires coming from it. I read somewhere If field coil is working than it should hold razor blade. I connected the field coil straight to battery and it didnt happen.
     
  9. K3ith

    K3ith XS400 Member

    Im really confused . Some wiring diagrams show that the wires coming from field coil needs to be connected to regulator. Green to green and black to brown, so like both need to be on positive. But some diagrams show that black needs to go to ground.
     
  10. markmakeitso

    markmakeitso XS400 Enthusiast

    Looking at my schematic the brown wire to the field coil (which changes to black) is fused power, the green from the coil to the regulator would be "low". The regulator has 3 wires: the same brown high side as supplies the field coil (and a bunch of other functions), the green from the coil, and a black ground. If you have a combined regulator/rectifier it may only have a single black wire ground rather than one each for both the regulator and rectifier functions.

    To check the field coil resistance just measure ohms across the stator side of the connector from green to black. Engine off, ignition and key off. While you're in there also make sure that green and black have very high resistance to ground, indicating no short to ground inside the windings or wire lead inside the cover. There might be a spec, otherwise I'd guess over 50k Ohms is probably okay.

    When measuring a pretty low resistance like the field coil winding it also pays to compensate for internal resistances. My nicer Fluke has a zero button that you can use with just the probe tips pressed together. That measurement will be the new "zero ohms" reading, and everything after that will be automatically compensated. On all my other meters (mostly $15-30 Amazon and Craftsmen models, nothing fancy) you can do the same check, but just have to remember to subtract the probe tip reading yourself. Not a huge deal for many measurements, but for ignition and field coils not compensating can put you into or out of spec incorrectly.
     
  11. K3ith

    K3ith XS400 Member

    When measuring ohms between black and green wires coming from field coil it show "1" which means open line i think. And when measuring resistance to ground it shows "1" also.
     
  12. markmakeitso

    markmakeitso XS400 Enthusiast

    Ahhhh, boo. Not a good sign. I'd perhaps try with another multimeter to be sure, and maybe take readings while twisting and flopping the lead around to see if there's possibly just a bad wire. It's a decent job to replace, and some extra hassle if you try to repair it instead.
     
  13. K3ith

    K3ith XS400 Member

    I checked both wires and both of them were broken from the connection that's between engine cover. Fixed them and it shows 4 ohms between green and black, but still wasnt working. So i measured to ground and green wires shows 6ohms and brown 2ohms. Is it really bad and not fixable If the field coil is grounded?
     
  14. markmakeitso

    markmakeitso XS400 Enthusiast

    EDIT: 4 ohms is correct. Did you try the internal resistance compensation trick from above? Also make sure you're using appropriate resistance ranges on the meter. Lots of them you have to have a good idea what the max reading could be. For instance the one I was using yesterday has 200, 2k, 20k and 1 Mohm ranges I believe.

    If the field coil is grounded inside the case it's pretty bad news. From my diagram it goes battery positive->main fuse->main switch-> (field coil input, regulator input, and back fuse box to everything else on the bike). Best case is it burns up the main fuse as you flick the switch on in the driveway before leaving. We should all be so lucky. Your 6 and 2 ohm readings to ground are likely just a single short to ground on the brown side, with the 4 ohm field coil resistance added on for the green side reading.
    I'd doublecheck your readings again, and then pull apart. It's possible that it that might just be a chafed or corroded wire inside the cover. Cross fingers.
     
    Last edited: Jun 22, 2020
  15. K3ith

    K3ith XS400 Member

    Yea, i used the resistance compensation trick. Manual shows that field coil resistance should be 4.04 +-10% ohms or is it something else?
    I'll look the wires again tomorrow.
     
  16. markmakeitso

    markmakeitso XS400 Enthusiast

    Yep, you're right. Just looked it up in the manual out in the garage. I was maaaaaybe thinking of the stator branch resistance, but learned my lesson about not checking. Edited my response above.
    I'd check the field coil supply voltage, maybe key on and also running. Have you done the AC volts checks also? Perhaps drill down to your problem from both the upstream and downstream sides.
     
  17. K3ith

    K3ith XS400 Member

    Yes, i did AC voltage check, everything 0. How much voltage field coil needs? I think my battery was pretty dead, even below 12 volts i think.
     
  18. markmakeitso

    markmakeitso XS400 Enthusiast

    First things first then is to get it charged up before continuing to test, otherwise you can chase your tail quite a bit. A trickle charger on the battery whenever you're not taking readings can help a bit, or even a second battery in parallel to the one in the bike.

    Within reason higher voltage at the field coil input makes it easier for the regulator to produce even more electricity. I usually measure both the field coil input voltage compared to battery negative, and also the drop from battery positive to the field coil input. Ideally the input is just a couple tenths of a volt lower than battery voltage itself, but a drop of one or two full volts is both quite common and also might work okayish.

    If you haven't tried the direct battery power to the field coil test since you repaired the field wires you could try that again. You might have several issues going on that you're figuring out individually.
     
  19. K3ith

    K3ith XS400 Member

    I think my battery is done. When fully charged its giving out 12.4 volts. When ignition is turned on its giving 12 volts and only 11.4 to field coil. Does it need more?

    Today checked field coil ground resistance readings again and now its not showing that it gets any ground. Shows "1" on multimeter. Havent touched anything, so im not hoping its fixed yet.

    I also tried the direct power to field coil and razor blade test. But it still didnt hold the razor blade

    I'll try to find new battery and then continue with testing.
     
    Last edited: Jun 25, 2020

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