Stators demystified

Discussion in 'Thumpers' started by Luke, Dec 17, 2006.

  1. Luke

    Luke GPoET&P

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    The cap smooths the output voltage from the regulator. The regulator limits the peak voltage by clamping the stator to nearly 0 volts after the output voltage exceeeds 14V or so. It resets at the beginning of each AC cycle. If there is no smoothing device (cap or battery) the lights just get a series of short (less than 1milliSecond) pulses of 14V. The higher the RPM, the shorter the pulses.

    It's likely there's nothing damaged at all besides your old dead cap. I'd get a new one, 6uF won't do much of anything. It probably won't hurt anything to try it, though.
  2. Luke

    Luke GPoET&P

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    Ah, the stalled project. I may have some of those sitting around. :lol3
  3. Dolly Sod

    Dolly Sod I want to do right, but not right now

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    Is this what the capacitor does on the 640 ADV as well?
  4. Tremelune

    Tremelune Adventurer

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    It's what they all do...You can get one from an electronics store for a couple of bucks. My guess is that any cap 15+V and above, with 4000+ uF will do the trick.
  5. gravityisnotmyfriend

    gravityisnotmyfriend Long timer

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    Well, that's really great news. I'll try the old Cap, but I suspect it'll need to be replaced. The KTM version is about $60. Curiously, a 25V 10000 uF Cap out of an online store is only about $3. That's an amazing mark up! I'll try my old one - maybe tonight. Then, I'll see if the local radio shack has one. If not, I'll get one on order.

    Thanks for the response. If this works, you've really made my day!
  6. Dolly Sod

    Dolly Sod I want to do right, but not right now

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    I guess I don't understand why a bike with a full sized 12 volt battery, 3 phase charging system, and a typical VRR would need with the capacitor? The batterie's job is to absorb the spikes from the VRR, no?

    It seems to me like it's something there to allow you to run the bike without a battery and not fry the VRR.

    ?
  7. Luke

    Luke GPoET&P

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    Yes. On the bikes with a battery I think it's redundant. However, since the CDI on the newer LC4s draws its power from the +12v supply that redundancy is very nice to have. If the battery dies then the cap allows the ignition to still function.

    Running without the cap or battery won't damage the RR, but the RR will hold the voltage too low for any of the electronics to work.




    Just to clarify: in case anyone is confused, the capacitor we are talking about is not the C in a CDI (Capacitor Discharge Ignition). It's the same type of part, just not the same one.
  8. gravityisnotmyfriend

    gravityisnotmyfriend Long timer

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    I've got the original owner's handbook. I can post a scan of the electrical diagram up if you'd like to see it.

    I did find this '97 version online:
    [​IMG]
    It's very close, except in the RR area, mine only has 4 wires going to the RR. The yellow and blue come in from the alternator and the brown and red/white go to the capacitor. There is no extra green one going to the cap.
  9. Luke

    Luke GPoET&P

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    If adding the cap doesn't fix the problem, then yes that'd be helpful. The '97 diagram looks a bit different to the one I read, it has a different regulator and has a battery.
  10. gravityisnotmyfriend

    gravityisnotmyfriend Long timer

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    Well, adding the old cap didn't fix the problem. But, as it seems to have stopped capacitating, I'm not surprised.

    So, studying the schematic, it seems like the battery is hooked up in parallel to the capacitor with the exception of a diode that keep the battery from draining into the capacitor. What if a guy were to remove that diode and remove the capacitor?

    That would eliminate the redundancy - but since the bike doesn't need the battery, I don't see it as a big deal. Would the battery take the place of the capacitor and allow the stator to power the lights. The battery would be the filter instead of the capacitor.

    Here's my thoughts, and maybe this would be better in a "Bike wiring schematics" demystified thread.

    The battery is there to power the parking lights. The diode is there to keep the battery from discharging - so if you've had the bike shut off for a long time, you can still turn on the parking lights.

    I guess the part I don't understand is why there's a capacitor in addition to the battery. Why not eliminate the cap all together?

    I'm thinking I'll just stop by radio shack tonight and see what they have for capacitors. And if they have nothing appropriate, I'll ride without a headlight this weekend and order one.

    But, I'm really tempted to run a jumper from the positive side of the cap to the positive battery post and see what happens.
  11. Luke

    Luke GPoET&P

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  12. gravityisnotmyfriend

    gravityisnotmyfriend Long timer

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    The only thing that a Radio shack capacitor has going for it is that I may be able to pick one up tonight after work. If they don't have something big enough, I'll go ahead and order one with the screw on terminals.

    I do like the idea of soldering wires and taping/ziptying them to the case. I'll have to do something to make the can big enough to fit in the rubber holder for the old cap anyway.

    It sounds like a good night to have a beer and work on the bike. I hope Radio Shack has something in stock.
  13. gravityisnotmyfriend

    gravityisnotmyfriend Long timer

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    The local radio shack failed to deliver. The biggest cap they have is a 4700 uF 15V. I'll just get one on order. Looks like I'm riding in the dark tomorrow I'll disconnect the RR just to be safe.
  14. gravityisnotmyfriend

    gravityisnotmyfriend Long timer

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    Just wanted to wrap this up. The bad capacitor was indeed the source of my problems. I ordered a 10,000uf 35V unit from Digi-key.com at less than 1/10th the price of the KTM unit. I finally got around to wiring it up last night. Headlight is working great! I did a quick test drive in the dark last night and was able to bring her to work this morning!

    Thanks for all the advice, Luke!
  15. jm-2008

    jm-2008 Been here awhile

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    Luke
    Recently returned to this site and must commend you on out standing work and unwavering support for the inmates here
    Certainly have managed to remove some of the mystery associated with stators
    Recent events have caused me to reconsider a higher output system for my XR650R however I'm interested on your thoughts re loading on reg/regulars
    Australian models are supplied with rec/regulators to run indicators etc
    System also appears to have an AC reg for lights (memory check here)
    Considering one of the 2 x 100W stators on offer however my question is if one of the 100W supplies is run as per the OEM Setup with little additional load is the rec/reg likely to survive ie do the rec/reg's sink the extra unused current or only generate heat equivalent to power requirements of the circuit (accessories, GPS, HID lights)
    Also notice people run a variety of battery types NiCad, SLA etc how do they get around charging requirements for the various chemistries?
    Any info would be useful
    Regards
    JM-2008
  16. Tremelune

    Tremelune Adventurer

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  17. winch

    winch Adventurer

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    I would like to run a full DC system on my XR650R. I want to run a 55/60 W headlight, LED taillight, signals, horn, etc.

    What's the best way to rewire my stator? Would running 300 turns over 10 poles with 16 awg wire work for this? Or should I do something different? Right now the tech talk is sorta going over my head.
  18. Luke

    Luke GPoET&P

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    Modern (post 1980-90) regulator/rectifiers generate about the same amount of heat when they pass current to the load as they do when they sink the current. So as long as the stator winding puts out less power than the regulator rating you should be fine regardless of load.

    My impression is that regulators work well for lead chemistry batteries. That's what they are designed for. They happen to work ok for LiFePO4 batteries. They don't work very well with ni-cad, but the battery lasts long enough to pass inspection for a dualsport conversion which is enough for most people.
  19. Luke

    Luke GPoET&P

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    That would work, but will actually generate more power than you need.

    I'd suggest 18ga wire, with 400 turns. That'll get you about 130 watts. Compared to 300 turns it'll generate less power at speed and more power at idle which will keep the stress down on the battery and regulator. 18ga is plenty thick enough for that power and much easier to wind.
  20. scot511

    scot511 n00b

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    This is a great thread and has given me confidence that I can resolve my problem. I have a 1972 Suzuki TS400 (the trail bike version of the infamous motocrosser) which I have converted into a street tracker. It has the typical suzuki charging system from back then - a stator made up of two large charging coils in series with a center tap between them. The center tap was routed through the headlight on/off switch to provide different charging rates with the light on or off. Each coil and the center tap then went to a six-diode rectifier, the output of which supplied the battery and the bus. Originally there was no regulator - I suppose it used the natural capacitance of the battery as the regulator. I figured that I could just use the two coils in series (omit the center tap) to supply a generic R/R as I have done on many bikes over the years. At idle with no load I get about 12.7v out of the regulator but the 25/35w headlight on low beam drags this back down to about 10.5v, and it does not take long for everything to go dim. It's not charging at all. I assumed that the R/R would be an improvement over the stock system but now I'm not so sure. Maybe this system is just so marginal that the regulator itself loads the output too much. Or maybe the alternator will simply work best the way it was designed to work. Did I "improve" this prehistoric system a little too much? Could I rewire the coils for more output? Any advice or suggestions?