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Thread: Lights buring out 47 HD EL

  1. #1
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    Default Lights buring out 47 HD EL

    I wrestled whether to post this in the Knucklehead forum or the Electrical forum. Decided to try here first.

    Bike is a bone stock '47 HD EL with a 32E standard generator. Bike was recently brought back to life after being under a tarp for 50 years. Generator was rebuilt. Cut-out is original. Battery is one of Tedd's new replica batteries in 6V. Bike was completely rewired due to shredded original wires. I have put a little over 1000 miles on the bike since the riding season started this spring.

    I burned out the low beam about a month ago. It was the original bulb. My friend with an old bike shop had a box of the correct bulbs and I bought them all. I replace the bulb with one of those. It's the 21/32 CP bulb. I forget the code right now.

    So, earlier this week I checked my lights and tail light was burned out. Stop was fine. I replaced it with a new bulb and while out riding, my low beam died again. Switched to high and all was well. I'm not well versed on 3 brush generators, but did my homework and understand how they work. Actually pretty much understand how the system works, or at least think I have figured it out. I'm not stranger to electrical systems and worked on sophisticated control systems when I was working. But I'm not an electrical engineer. This is how I understand these systems to work.

    The cut-out relay simply disconnects the battery from the generator when the engine is off. It also is the switch for the charging indicator light on the dash.
    There is no voltage regulation for the system. The only adjustment is for current output via the position of the 3rd brush. 4 amps is the standard setting and this setting is for lights off. Intent is to run the ignition and charge the battery without over charging it.

    With the lights on, a second lighting coil is turned on which adds I believe 3 amps to the system to power the head, tail and speedo lights. Again, left over current to the battery should be enough to charge, but not overcharge.

    Voltage regulation is via the load on the system. So the battery acts like an "absorber" of voltage for lack of a better term. The generator puts out whatever voltage comes out at a given rpm and the battery just levels it out to a nominal 6 volts. The cut-out turns on and puts the battery into the charging circuit at around 6.3 or so volts. But I assume the voltage continues to rise with RPM from the generator since there is no regulator.

    So, is my problem old bulbs that just cannot survive given their age or is the system frying them for me? I don't think it is road vibes for the simple reason that the roads were a lot worse in 1947 and I can't see anyone that rode any distance on a bike doing so with all his pockets full of light bulbs.

    I need to test the output of my generator. But even if it were higher than 4 amps, I would not expect excess current to affect a bulb. The bulb will only see the current it needs to work. The battery is what will suffer with excess current. This is why I'm struggling with what is killing these bulbs.

    The taillight bulb is new production and only a few days old. It was okay this morning when I checked. It may just be that I'm running old bulbs and it is that simple.

    Any thoughts from those of you with more experience with these old unregulated 6 volts systems?

    I have an inquiry into Splitdorf for their regulator that is disguised as a DR cut-out relay. I did that mod on my '39 Indian Four using Gene Harper's regulator and it was the best thing I could have done for that bike. I now run a VRSLA battery in a replica box with zero issues/worries. Since I ride all my bikes, I would love to do the same mod on the EL.


    Thanks,
    Rob
    Rob Sigond
    AMCA # 1811

  2. #2

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    Read your book again.The voltage is adjustable in the cutout relay.Voltage should be 6.3-6.8 volts depending on RPM.Test your voltage when running & revvving

  3. #3
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    Quote Originally Posted by duffeycycles View Post
    Read your book again.The voltage is adjustable in the cutout relay.Voltage should be 6.3-6.8 volts depending on RPM.Test your voltage when running & revvving
    Pretty sure that the 6.3v - 6.8v spec is for the min voltage for the Cutout relay to pick up, closing the generator to battery bridge and opening up the indicator light circuit. That is simply a relay pick-up setting. It does not control the voltage of the generator output. Once the relay picks up, it stays closed as long at the generator is running. Therefore, it has no way of controlling the output of the generator. If it did control generator output, there would be a drop-out setting as well, somewhere above 6.8 volts and the relay would open and close rapidly, which is pretty much how the other relay in a mechanical voltage regulator works.

    Rob
    Rob Sigond
    AMCA # 1811

  4. #4

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    Have you tried adjusting the output of your 3rd brush? How bright were the bulbs before they blew?

  5. #5
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    I think 4 amps is a shade high on the generator output. The VL uses the same model 32E and aims for 1-2 amps charging on the ammeter with the lights on or off. Dial down the generator output a tad, check the ground connections, try again and let us know the results. Contemporary Harley spares literature emphasises their bulbs are specially robust for motorcycle use, and this may not have been just advertising puff.

  6. #6
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    I'll answer my own question here since it might help the next guy. Gene's write-up on the 3rd brush generator, which I did not notice until today, and an email conversation with Dave Benassi has cleared things up for me.

    First, my mistake on the charging rate in the manual. It does say 4 amps, but this is max rate with lights on. Gray hair is my running excuse these days.

    I'm going to share what I've learned. The 3rd brush controls the field strength by controlling the current provided to the field coils on the generator. The voltage out of a generator is controlled by the speed at which the coils cut the magnetic flux AND the speed at which they do that. So, adjusting the 3rd brush will have an effect on voltage as well as current.

    So, needless to say, I need to test the output of my generator and more than likely, make an adjustment to the 3rd brush. Gene's article also leads me to believe that if you blow one bulb, chances are, others are now at risk. This is because the output is intended to be adjusted for a fixed load which is the same number of lights and the battery. If you lose part of the load, via a blown bulb, more power is put into the existing lights if the battery is fully up and this could blow others. In my case, what may have happened was my very old headlight bulb blew and that caused the taillight to blow. I did not notice the taillight and installed a new headlight bulb. It blew because the taillight was out. Now that I have a new headlight and taillight bulb, the system is happy again and I may not have another failure. This is just an educated guess on my part.

    This is also explains something I never quite understood. My bike as accessory spot lights. The factory wiring turns off the headlight when the spots are one. That made no sense to me. But now it does. If the spots were run with the headlight, the battery would probably have to provide some of the power to the system and would drain slowly as you rode with all of those lights on.

    I'm a little more knowledgeable now... I think. Thanks for all the inputs on this. I'm probably going to install one of Dave's regulators in place of my cut-out relay. This will make the generator system more of a modern system and issues like lights blowing out should go away. The battery will probably be a lot happier, too.

    regards,
    Rob
    Rob Sigond
    AMCA # 1811

  7. #7
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    I ran a current check on the bike by putting an ammeter in series with the +6v lead between the gen and the battery. I got as high as 6 amps. Manual says 4 amps, with or without light on. I failed to check the voltage at the battery during this test. I adjusted the third brush to get about about 3.75 amps at cruising RPM. I then did a check across the battery and saw a max of about 6.75 volts. Going to leave it there and see what happens

    Before I did the testing, first thing I did was check the electrolyte in the battery and the plates were just starting to poke out. Filled it up to the max line. Battery voltage at rest was 6.43v.
    Rob Sigond
    AMCA # 1811

  8. #8
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    A lot has transpired and I thought I'd close the loop on this thread in case somebody goes down a similar path some day. I put voltmeter on the bike and went for a ride. Saw voltage as high as 10vdc. Not good. So, I put the bike on the lift and played with the third brush just watching voltage. The full range of the brush had very little effect on the voltage. With an increase in revs, the voltage followed.

    Conversations with Dave Benassi and Paul Benassi helped me understand better what was probably going on. Paul rebuilds these generators and has rebuilt hundreds of them. He has rebuilt some with aftermarket field coils that exhibited the same high voltage issue mine did. We believe that the repop coils put out more power than the stock HD coils and this is the root cause. So, I decided to do the 3-brush to 2-brush mod called out in Bulletin 418 and install his brother Dave's solid state regulator.

    Rewiring the generator was pretty easy. When I got it apart, I confirmed that the field coils in my generator were new, replacement coils. So, with the generator rewired and the 3rd brush removed, I modified the wires to what the 2-brush generator and Dave's regulator required. It's pretty easy. You cut the black wire (indicator light) at the generator and put a terminal on each end. The light end goes to the relay terminal and the regulator end goes to the old switch terminal. The green wire between the relay and relay terminal on the generator remains. The green wire from the switch terminal to terminal #2 on the ignition switch is eliminated and the red wire remains the same.

    Dave's regulator replaces the cut-out relay and mounts in its place. It accepts the original cut-out relay cover and the terminal layout on the regulator is identical. If it were not for the fresh, new zinc plated finish, you would never know it was not the original cut-out relay.

    With everything wired up, I fired up the bike and with a DVM across the battery measured 6.43v with the engine off and 6.8v +/- a few tenths with the engine running. The voltage held at 6.8v regardless of the rpm.

    Dave told me that the regulator controls both voltage and current out of the generator based upon the load demanded by the system. It does that by regulating the excitation current going to the field coils. So, the generator is only putting out the power it needs too, which helps it run cool. Being a sealed unit with no air fans, this is an important consideration.

    My lights are nice and bright and I swear the bike runs better. I think it leaks less oil, too.

    Dave and Paul both have run these regulators on their panheads for the last 5 years with zero problems. The other advantage is this regulator allows you to run VRSLA batteries, also known as AGM or simply sealed batteries. So, no more acid leaks. The beauty of those batteries is they last forever without needing a charge. I run one in my Indian Four with one of Gene Harper's regulators and I thought my charger was bad because it always says "CHARGED" when I put it on the battery. Dave uses two 12AH Duracell sealed batteries in parallel for 24AH and it fits in the oil tank battery box. He tapes them together.

    I have not posted any pictures because there is really nothing to see. Bike looks just like it did before the mod, short of the wires being moved on the generator terminals and the base of the cut-out relay looking better.

    regards,
    Rob
    Rob Sigond
    AMCA # 1811

  9. #9
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    Great info here, especially about the AM field coils. Thanks for the follow ups as you progressed.
    Bob Rice #6738
    He that conquereth his own soul is greater than he who taketh a city.

  10. #10
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    Thanks. Another thing I learned from Paul Benassi and should have mentioned is that some of the repop coils are wound backwards, which means you have to reverse all the connections when doing the 3 to 2-brush mod. The test for this is motoring the generator. It should turn CCW looking at the gear (driven) end. If it rotates CW, you have reverse wound coils.

    Paul recommends using the original HD coils if at all possible. If insulation is frayed, repair the wires and insulate with shrink tubing. He said the HD coils hold up much better in the long run than AF coils. I hope he is wrong about that last point. But I doubt he is.
    Rob Sigond
    AMCA # 1811

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