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Charging system (maybe)

Discussion in 'Technical and Troubleshooting Torque' started by RussellDP, Oct 14, 2015.

  1. Hi all you guru's out there.

    I have an '04 Hyosung GT250, and I am suspecting that I may have an issue with the charging system.

    For a start - a list of things I have noticed.

    When starting the bike, I do not get enough power to start it if I happen to have the indicators or headlight switched on.

    When it is started ( which has been easy enough once all the electrical load is off ) and is in neutral, if I turn on the headlights and/or indicators, I get a noticeable decrease in the intensity of the lights on the dash ( especially the neutral light ) which also changes intensity in time with the flashing indicators.

    I checked across the battery terminals, with the engine off it was approx. 12.8 volts, while running it lifted to about 13.5 v ( but seemed to take a while to get there )

    From my past ( ex diesel mechanic ) I know I should be getting around 14.5 volts at idle, so I guess I need to be looking at the stator ( as I understand it the stator will output whatever voltage it can ) as opposed to the rectifier which will limit the voltage so as not to cause damage to the system. EG if the stator is outputting ( for example ) 20 volts the rectifier will condition that down to a useable voltage, BUT if the stator is not outputting enough volts, then the rectifier has nothing to do with the issue.

    Is that logic correct?
  2. Sounds good to me. I take it you've cleaned and tightened battery terminals and all the connections?
  3. I don't think there is a problem with your charging system. Depending on the battery status I would not expect things to be much different at idle. With a few revs the voltage should reach up around the 14 volt mark and should not go above about 14.5 through out the rev range. Before I started delving into things too much I would have the battery tested. Should cost nothing and I think it sounds more like a weak battery than the charging system.
  4. Pod is right. It wouldn't hit 14+ volts at idle. Needs more revs.
  5. Ah, sorry, should have been a little more clear.

    At revs...eg approx. 5000 rpm, it wont read over about 13.2. I tried to take the revs up consistently to see if that made a difference, but as I said before, it seems like it will eventually climb to about 13.5 but that takes about 10 minutes
  6. I would still have the battery checked by a professional. They can load test it and it is cheaper and more convenient to eliminate that first. The accuracy and type of meter you use to measure the voltage can have a bearing on the readings.
    • Agree Agree x 1
  7. How old is the battery?
    I had similar problems with my bike. First of all the bike didn't want to start. But when it did after charging the battery the headlights and lights on my digital speedo were dimming intermittently on idle and more often when i pull the throttle. At one point the speedo started playing up while i was riding and everything just disappeared; so i couldn't see how fast I was travelling etc.
    The problem was the battery. Replaced the battery with a brand new SSB AGM one and haven't had any problems ever since.
  8. No expert but my understanding was that if it started more than once and gave a charge greater than 0, that was pretty much good for a Hyo.

    Agree though that you shouldn't expect 14.5V at idle and I wouldn't expect much more than 13.5 running.
  9. As others have said at cruise revs you should get 14.5V at idle you won't get that high.

    There is a fundamental difference between car/truck charging systems and bike charging systems. In larger vehicles with higher power requirements the regulator controls the voltage by changing the field current in the rotating part of the alternator.

    In bikes the alternator has no field winding in the rotor instead it has fixed permanent magnets. The stator provides maximum voltage it can depending on its rev speed. The Regulator/Rectifier shorts that voltage out periodically to average the voltage out. This is known as a Shunt regulator.

    So low output can be a failure of the regulator/rectifier or the stator. Start with the stator, disconnect it from the regulator/rectifier and measure AC voltage from 1-2 2-3 3- 1 wires while reving the engine, they should 30volts or more.

    I suspect your battery though, measure the DC voltage of the battery after it has sat for a night.
    • Informative Informative x 1
  10. How did you go with this issue RussellDPRussellDP ?
  11. Hyosungs have been around since '04??? Who'd a thunk it????
  12. Ive tested the stator. At idle about 5v per coil. Lifts to about 6 v at 4000 rpm. Forgot to check if stator had continuity to ground, so gonna do that and change brake fluid this weekend
  13. I know, right? This little bike is still strong
  14. I'm thinking changing the brake fluid is unlikely to affect the charging rate.
  15. If that is the open circuit AC voltage (i.e. regulator disconnected) then it is far to low. 30 - 50 volt AC is what you should be expecting. Which points to stator windings. test resistance of windings with stator disconnected and engine off. 1-2, 2-3, 3-1
  16. Haha....true enough. I'm not sure when it was last changed though so I reckon its a good thing to do.
  17. Gotcha. Sunday is pull apart the bike day. Thanks for the input
  18. Ok, so disconnected the stator with engine off and have continuity between all three phases. Looks like time for a replacement
  19. And open circuit AC voltage when running? I.E. Disconnected from the regulator. It could still be the regulator or is the Reg/Rec what you have decided to replace?
  20. Ahhh, see i didnt got that far. I thought a grounded stator diagnosis meant just replace that. Back to the multimeter