Related headlamp issues

I've got a rig set up for testing what a Schmidt hub will drive. I've got the hub in a truing stand, driven by variable-speed drillmotor via a flat vacuum-cleaner belt. It's a kluge, but it works. I monitor the output with an oscilloscope, and have a magnet attached to the hub which drives a standard cyclocomputer so I can determine the equivalent road speed for the testing.

The output from the hub goes to a small packaged bridge rectifier, and I've got a 1000 uF 25WV electrolytic capacitor hung across the DC output to help "smooth in the gaps" in the AC waveform from the hub. 4700 uF would be better but I didn't have one on hand. Without a load the hub will put out LOTS of voltage, I've got data which shows about 180V p-p at speeds in the 20 MPH range. So the next addition to the DC output circuit is either a shunt regulator set at about 18V (see coming comments about a 4-cell Li-ion battery pack) or an 18V Zener diode if I can find one which will handle 5W or so. In the meantime I keep the simulated speed down and always have the load connected. And I think it's prudent with this solid-state electronics hardware to make a point of always connecting / disconnecting the hub when stopped, so there isn't the possibility of really high voltages getting to the diodes etc.

A few days ago I ran a test with the two Luxeon-I BISY conversion lamps I recently completed, driven in series by the hub / rectifier circuit via a TaskLED nFLEX constant-current regulator. This regulator with lights at max brightness setting draws about 350 mA and I've forgotten what DC input voltage was required, about 9V minimum I seem to recall to keep the lights from dimming. More voltage doesn't concern the regulator, it adjusts for it. Will handle up to about 24 V I think, can check the spec sheet but it's not nearby.

So then I took a series stack of 4 Li-Ion 18650 cells, connected a diode in series so the battery couldn't attempt to drive the hub when the DC output was below that from the battery pack, and connected this rig in parallel with the regulator. At 9V it didn't make any difference because it wasn't charging, needed to see about 16 V from the hub to charge. But by the time I got the (simulated) speed up to the 12-15 MPH range the hub was keeping the lamps at full output and charging the battery pack too. Not a real fast charge with the lights on, since the hub puts out 500-600 mA maximum and I'm already using 350 for the lamps. But it would do the job. My intent is to power the lights from the battery and use the hub to recharge the battery when I'm going fast enough or it's daylight and the lights are off. At this point it appears this arrangement will work.

Return to Converting a BISY headlamp to LED