HT Bicycle Engine Generator Characteristics

I have read all the threads that I could find regarding the HT engine generator and the possibilities of using the White Wire to power a self contained lighting system. There still seems to be a lot of confusion regarding output voltage and available power. I have done a lot of experimenting and would like to share my findings with the community. The configuration I am using is a fullwave bridge rectifier connected between the WW tap and the grounded end of the coil. I unsoldered the grounded end from the laminate and made a binding post using a 1/2 watt resistor epoxied into the hole in the core adjacent to soldered attach point. I clipped the lead off one side and left 1/8" on the exposed end of the resistor to wrap and solder the fine copper wire of the coil. The '-' pin of the bridge is grounded to the engine case and "+" pin is the output. A schematic of the test circuit is shown in the attached jpg. I used several resistors to load the output and measured the load voltage over 3 engine speeds. The lowest was a putt-putt idle, then a faster idle, and finally rev'd to the equivalent of about 15 mph. The chart on the left shows load voltage on the x axis and load current in amps on the y axis for the 3 engine speeds. The chart on the right is the power out curves for the 3 speeds. The x axis is load resistance and the y axis is the load power in watts. What may be surprising to some is the usable voltage is in the 20V range and around 4 watts can be extracted at reduced voltage. The tradeoff is you have to reduce the load at idle or the CDI will be starved and the engine will die. This is my first post and I am not sure if the the jpg file is attached.

Re: HT Generator Characteristics

Thanks for your quick response Scotchmo. I have seen a lot of discussions on charging cicuits and SLA batteries. I have not seen much in the way of measured data and that's why I wanted to share this. BTW I have a LED based system on my bike that I will share. I chose to not use a battery because I wanted a system that turns on when I start the engine and turns off when I kill it.

Re: HT Generator Characteristics

I have attached the schematic for my lighting system. I admit that it is a lot more complicated than what everyone else is doing but it works really well and requires zero maintenance. The thumbnail file size limitation makes it real grainy and I appologize for that. If anyone is interested in a high res version of the schematic maybe someone can tell me how to include it in a posting. The key to this approach is to use a buck regulator to efficiently convert the relatively high output from the generator down to about 3.5V for the head light LED. I modified the feedback circuit to make it a constant current source for the head light. There is also an astable multivibrator to blink the lights during day light rides and a low voltage shut down to lighten the load on the generator when the engine is at idle. I connected the LED's for the tail light and side lights all in series fed by a curent source. The system draws about 3 watts when the lights are constant on (not blinking). The low voltage circuit limits the supply voltage to 17 volts minimum. When the engine is at idle, the generator outputs only about 1 watt without degrading the CDI. The low voltage circuit limits the consumption to 1 watt by causing the lights to flicker at the rpm rate of the engine. A little throttle and the flicker gives way to solid light. The engine speed at 10 mph and above produces 20-24 volts DC at the input. I added a snubber (27V zener + 33 ohm resistor) to clip glitches produced by the ignition circuit which caused the voltage on the big electolytic cap to creep up to 40V when the lights were turned off. This exceeded the voltage rating of the cap and was at the max for the LM 2575 regulator. Oh, and the other thing I added to the generator compartment is a low voltage controlled engine kill circuit.

I have added a higher resolution schematic of my light system.

Re: HT Generator Characteristics

Scotchmo - Thanks for the continued interest. Here are the test circuit and charts with labeled axis. I think the resolution is adequate for viewing.

Re: HT Generator Characteristics

Scotchmo - I ran an experiment today using a single diode as you suggested. The results are attached. I forgot to write down the part number but I used a Radio Shack 3A 400PIV diode. I tried to determine if loading the negative or positive half cycle would affect the CDI but with my engine, shorting either the positive or the negative half cycle to ground through the diode killed the engine. This happened at low as well as at very high idle engine speeds. I am not sure what this means since the common belief is the CDI uses only the positive half cycle. At any rate I attached the results in a jpg file.