both ends lit with white wire

Discussion in 'General Questions' started by emdude, Mar 22, 2009.

  1. emdude

    emdude Member

    OK, here's some experiences I've had with the white wire on my motorized huffy that I've been trying "light up". I need to point out that I'm more interested in being seen at night than I am in seeing much based on any lighting I install. Mainly to keep the generally friendly local cops friendly should I want to ride at night. I've done a lot of searching on the forum for information and this did help. least to me:

    The magneto system in these engines puts out a high voltage (blue wire) and a low voltage (white wire) AC signal. Relative to GROUND, the black wire.

    This signal is not remotely sinusoidal, and this stands to reason if one carefully examines the mechanical arrangement.

    The ignition system is a CDI unit of sorts (possibly much, much more in a later post) that uses ONE HALF ONLY of the AC signal to power and trigger the CDI unit.

    Any additional load on the white low voltage wire will decrease the overall output of the magneto generating system.

    Any additional load on the low voltage side of the generating system must be kept below a given value so as not to reduce the output to the CDI unit below a value at which sufficient spark can be generated, especially at low RPM's.

    Since the CDI uses only the aforementioned ONE HALF of the high voltage output, a load on the UNUSED half of the low voltage side of the magneto generator will have less effect on reducing power to the USED half of the high voltage output used to run the CDI.

    The above was a mouth full, based on reading some measurements taken and reported by other forum users in which the waveform was observed using an oscilloscope. One person reported a significant difference in peak amplitude of the positive and negative output of the low voltage magneto generator with no or only insignificant load on said. The lower output on one of the output cycles indicates the load presented at THAT cycle by the CDI unit.

    The output of the white wire is said to be in phase with that of the blue wire, i.e the both put out a positive and signal at the same. This would indicate that based on all of the above the negative half of the white wires output could be used more heavily without affecting power to the CDI unit.

    I question the consistency of the above and think this may not always hold true. Since the wires use is intended just as an AC output, its phase could be considered to be irrelevant and may in fact vary from unit to unit based on the mood of the assembler.

    The REAL rms output of the low voltage section is not easily assessable without the use of an oscilloscope, appropriate loads and some significant math. Standard multimeters will NOT yield accurate results as these do not really give true rms readings despite advertised claims. This is why true rms meters use thermocouples for these measurements are generally at least moderately expensive.

    Rational experimentation can yield usable results, read on if you not bored or turned off yet.

    OK, after all that, here's what I did:

    I got one of the combination kits with the sweet little red bullet taillight and the standard chrome headlight and the generator I didn't intend to ever use but took just in case all else fails. The headlight in mine has 2 bulbs in it, one was a small bulb in the top of the light, the other a standard 12 V bulb in the center. Lights are switched on in various combination's with the headlight switch on top of the headlight. Curiously the smaller ones in the headlight and the taillight were marked as 6 Volt units. Although an explanation is likely, I didn't care because 6 Volt units were a much better starting point anyways.

    I decided to not even bother with the main bulb in the headlight for now. If I could successfully get the smaller bulb in the headlight and the taillight to run I would be OK. Again it was matter of being seen more than seeing.

    I initially ran just the rear light off the white wire. No problem at all. Plenty bright, in fact far more than needed for a taillight. Of course if the low voltage generator does deliver 6 Volts at 3 Watts the above is entirely understandable. And it should run a a single 6 Volt 3 Watt head light only just fine, as some seem to have found.

    It was even quite noticeable in plain daylight I then connected the smaller headlight bulb, in other words twice the load. No dice. As soon as the headlight was turned on the engine stalled. If the engine was at a reasonable RPM it would momentarily stall until the headlight came on and then would run but not idle in a stable manner.

    This of course was quite explainable. When the light bulb is "OFF" and hence cold the resistance of the filament is much lower than when it's "ON" and hot. Current draw is initially much higher than when the bulb is warmed up.

    We've all seen this in action. You got to turn on a light in your house somewhere and bam, as soon as you hit the switch the bulb burns out. This because the cold and worn bulb will draw significantly more current at "start up" and burn out. The same bulb on a slow start up circuit would go many more hours.

    OK, so one bulb was OK and in the case of the rear light brighter than needed. But two identical bulbs were marginal. Power to the rear light could be reduced and was achieved by simply using only one half of the low voltage output cycle. A 1N4007 rectifier diode was placed in series with the (cut) wire. This of course left only half the voltage to run the light. The direction was chosen empirically by trying both and choosing the "brighter" direction, assuming this was the half of the output that was out of phase with that of the high voltage output needed by the CDI. Voltage drop in the diode in association with the rectification significantly reduced the light output from the taillight. It now was OK but could use improvement.

    The headlight was now connected and the engine was able to power BOTH quite well. It would still stall at a low idle occasionally and I did have to reduce the spark plug gap to stock. I run a VERY large spark plug gap on my engine with huge benefit.

    The headlight with the bulb used was quite anemic. The taillight OK but the whole system did work. The only option was to attempt to maximize on the amount of power the low voltage magneto could deliver. It was not doing much with the 6 Volt 3 Watt bulbs installed since it could not deliver enough power as it was.

    A trip to the hardware store and the purchase of numerous bulbs for experimentation resulted in a setup that works pretty nice. I ended up using 3.7 V bulbs rated at 0.3 Amperes, that's 1.11 Watts, in both the taillight and the headlight. The taillight is now plenty bright and headlight works just fine. The engine does NOT stall when the headlight is turned on and idles just fine. I think I could even return the plug gap to "wide" but cannot find out until the heavy winds here have died down and are no longer blowing crud from the spawning trees up that causes my severe allergies.

    The lights, more so the taillight of course, do flicker quite a bit at idle. But it will sure get me noticed.

    Now, before we all worry too much about the bulb choices I made let me end this post by saying the following:

    The low voltage section of the magneto generator may be specified at 6V @ 3 Watts. And maybe it will run a single 6 V 3W bulb just fine. I have not tried this beyond what I described above. In the end I wanted to light up BOTH ends of my bike. I was too lazy to take exhaustive measurements of my engines low voltage output and so based what I did on the experience of others and simply experimented until I came up with a "format" of load that best matches the "format" of output from my generator considering this to be not really known. Keep in mind that with bulbs like this it's mostly a matter the RMS power delivered to said that will dictate if the whole thing works. And it may have worked just as well had I found 6 Volt 1 Watt bulbs or even a 6 Volt 1/2 Watt bulb and left out the rectifier for the rear. But in the end the goal was achieved.

    Maybe the above will help some others on this forum a bit in getting both ends of their bikes lit up.
    Last edited by a moderator: Dec 15, 2015

  2. duivendyk

    duivendyk Guest

    Please consult the following threads for possibly useful background info, "white wire a success story",started by BSA. and "solid HT white wire data",started by etacovda .We are engaged in designing a 12V WW charge system for 12 V batteries for this type of application.