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Voltage drop at high rpm

Discussion in 'Technical and Troubleshooting Torque' started by 9psi, Oct 13, 2010.

  1. After reading this site for a few months I bought a spada for my L's. It had a starting problem when I went to test ride it but the seller said it was plugs and he got it fixed. Tried it out and it was all good.

    After riding it for a week and a half, the battery got low yesterday and I had to roll start it yesterday.

    After riding for an hour I stopped at home and after 10-20 mins went out to restart it (to put it away) and it turned over slow and wouldn't start. I roll started it again and let it idle.

    I put a multimeter on the battery and it had 12.8V but when I gave it a rev it dropped to 12.4V. When I turned the headlight off and let it idle it went to 13.4V

    I figure it is probably the rectifier/regulator diodes are cactus and any high current draw is dropping voltage.

    Any other ideas and how to test to confirm the problem?
    I've read spada regulators are $$$ and unreliable and others are better and bolt up....any info would be appreciated.
  2. actually I think it is working fine given that description.

    I'd be looking elsewhere for the problem. Disconnected the battery and leave it overnight. testing voltage before and after.

    do the same with the battery connected.
  3. Will check battery tonight. Ride (pushbike) to work day today.
  4. Battery was 12.21V before doing anything. Bike started first go and voltage increased to 12.8V. once I turned choke off the voltage went up to 13.4V. I turned the lights on and the voltage dipped 12.9V and I could see the lights dim when I revved it.

    I let it idle with lights off for a while and the volts came up to 13.79V. Then the the volts stayed over 13.2V no matter what. But the voltage still dips when I rev the bike.

    Bike started first thing. This morning.
  5. could be the reg starting to go, but it doesn't seem that bad. I wouldn't think it would fail like that.

    12.2v seems like a pretty solid drop overnight (I assume it was 12.8V when you turn it off).

    So if the battery was disconnected I'd say you battery is on the way out. If it was still connected it could be that or you have an electrical leak.
  6. #6 9psi, Oct 19, 2010
    Last edited by a moderator: Apr 17, 2014
    I thought it all came good but then the bike dies (on the road like it is running out of juice) unless it gets some idle time. So I've had to modify my riding style to lots of coasting.

    So I've done some more investigation

    Bike stopped left for 2hrs battery at 12.4V starts easy (hooray battery not dead)

    idling, lights off, 13.4V

    revving to 2500rpm, lights off, 13.9V

    revving to 5000rpm lights off, 13.4V :(

    lights on idling 12.8V

    lights on 2500rpm 13.2V

    lights on 5000rpm 12.4V (now running off battery)

    I can see the headlight get brighter with a few revs and then die so the measurements make sense, and you can see the tail light get brighter and dimmer too switching the lights.

    Diodes measure 4.9V and Open (rectifier seems to be okay)
    OV drop battery to chassis with lights on (i.e. good earth)

    I'm figuring the alternator is the cause. hopefully just brushes are worn or springs broken....is this a hard job? I've done car brushes & springs, I'm hoping the slip rings aren't trashed :(

    Should I disconnect the 3 wire connector and measure AC circuit voltage to ground?

    Battery is good after a week off (not that anyone is replying - but hey it might help someone in the future)

    Measured open circuit AC voltage out of the alternator/generator with connector disconnected - 39V which means its a permanant magnet AC generator rather than a powered stator winding.

    Next trick is to measure the AC V into the regulator. If I have volts in but no volts out I'll know it is the regulator.
  7. Good plan, measuring the diode drop does not necessarily tell you that the regulator function is Ok just that the rectifier is intact but I have known them to break down under operating voltage. Honda's do have a poor reputation for Regulators so it is more than likely that. The float charge of a battery is 14.4 volts so to charge it you should be getting that across the battery when reving.

    More rare but possible is that one phase of the alternator has failed. A multimeter because it is calibrated around standard waveforms may not see this. I assume that the 39V you speak of you got on each winding ??? if so then it is ok.
  8. Measured across all phases with AC Mulitmeter - OC at idle is 16V (all good) but plugged in (measuring through the back of the 3 pin connector) I get only 7V AC!

    Meanwhile the battery is at 13.9V and charging.

    But then I read that the generators all make a fixed amount of current (although impossible because OC you have no current!) but if the regulators work by shunting current which would explain why the RMS AC V is low

    I'll order rectifier tonight after I check the part because wemoto has a different one to regulatorrectifier.com

    The honda owners manual has 5pin connector but the picture on regulatorrectifier has flying leads with 3 and 2 pin connectors

    I hope the stator isn't stuffed - making me nervous now I better check again that the winding resistances are all the same (I guess if one is blown then one measurement is going to be double the resistance of the other two measurements).

    I wish I had a schematic of the guts of the regulator!
  9. Regulator is SH693-11...after poking around the site I've bought a replacement from regulatorrectifier.com. Conventional wisdom seems to be the Honda OEM part is crap. Heres hoping I'm not flushing $150 (what is with that freight cost!)

    Will have to get some thermal compound as well
  10. Yes not all regulator structures but I am pretty sure the Spada had a permanent magnet alternator so the regulator is a "shunt" regulator. So to regulate the voltage it shorts the output of the regulator with a periodic short. When you remove the regulator the output of the alternator will rise to its full voltage. When you put the regulator back the voltage will drop on the AC input side and the rectified/regulated 12V DC side.

    Hope the new regulator solves the problem. Good Luck.

    New regulator arrived from regulatorrectifier.com.

    Voltage now behaves like you would expect and maxs at 14.00V. High beams just mean it need 2500rpm.

    general comments about the new regulator compared to the unit installed (factory CR250 unit)

    the new one is bigger and heavier (+ve)
    the new one is painted black instead of anodized (-ve)
    the new one is potted from underneath instead of having an aluminium interface so no point in using thermal compound(-ve)

    I hope they are bigger meatier shunt SCRs, The sales guy was very helpful.

    It is nice to have bright headlights!
  12. Glad you are up and going. :)
  13. 9psi, you probably weren't getting many replies because you seem to know more about it than most of us!
  14. Thanks, but I knew nothing about stators and shunt regulators before this problem. My technical background is in electronics, and hobby was cars. But I haven't done any real technical work for years.

    At least this way if anyone else has the same problem they can track the same symptoms and then know just to go buy a new regulator.

    More importantly I'm so glad I bought a 90 degree V-Twin the sound is so good on the bike (no idea what it sounds like for everyone else)
  15. +1
    I've been in love with V twins ever since my GF bought a brand new Guzzi LeMans lll 25 years ago!
  16. Hi,
    Interesting thread. My Spada died on me this morning. It felt like I had run out of fuel but there was plenty and when I came to restart the engine would not turn over so I assumed a flat battery. Of course it died at a busy intersection and I had to push it across lanes of traffic to get to the hard shoulder,. :(
    I scored a lift home (thank you Geoff?) and went back mid morning with the trailer (third time in two weeks!!) Any way got it home and charged the battery and started it. The voltage across the terminals was about 12.4 and dropped when I revved the engine. The manual says 14.4 to 15.3 at 3000rpm so I figure it is not charging. I disconnected the alternator and I get about 39V AC + when I rev the engine from one of the yellow cables and an erratic figures (but climbing ) from the other two , but that might be just a bad connection with the meter. The manual says nothing about the voltage but says measure the resistance between the yellow wires, it should be between 0.1 and 1 ohm but I could not get get a reading, beginning to wonder if my multi meter is sensitive enough. I took the regulator off and it's not the original but according to google off a kawasaki! The manual says test the resistance between the yellow inputs and red output, and it should be between 500 ohm and 10 K ohm but that's for the Honda part, however I do have diode tester on my meter and as the rectifier is a bunch of diodes I thought I'd try. My meter says the diodes are fine, but that tells me nothing really.

    I'm tempted to buy a new (and correct?) reg and put it in and see what happens. I'm a bit worried about the alternator, I would have expected to to see similar voltage on each wire.

    Have to wait until after Easter now until I can get to this.

    Have a good Easter.

  17. Yes, you should see similar AC voltage between each of the three wires from the alternator, 1-2 2-3 3-1 Wildly different voltages can indicate shorted turns in the alternator.

    Resistance measurement should also be similar between windings but as you surmised you may need a multimeter with enough oomph to overcome the inductance of the windings.

  18. easy test is if your lights go brighter intitially when you rev and then go dim with increasing revs. Then you know your stator is good just you regulator is cactus

    cjvfr is right the voltages should increase with revs and be similar across all the inputs

    diodes crap themselves at high current, its a pretty basic and brute force design (car ones reduce the stator current to reduce the rotor current, but with perm magnets the faster it revs the more output it makes, and that has to go somewhere)
    • Winner Winner x 1
  19. Hi,
    I took the alternator cover off with the intention of examining the stator and a lot of engine oil ran out. I figure the explosion (see blown head gasket post ) that blew the rocker cover gasket off has damaged the crank case oil seal. Oil sloshing about would explain the erratic AC voltage readings I got. I'll have to rig up a tool to lock the fly wheel so I can undo the retaining bolt. Now I'm wondering what other unseen damage there is :( .

  20. hmmmm. Don't get too far ahead of yourself. Some bike alternator run in oil. Check your arrangement first.