Join Date: Jan 2007
Location: Cheyenne, WY
Bikes: 1975 Peugeot UO8 (many, many upgrades ;-)
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Building my own standlight...
I've got a Shimano Dynohub powering a B&M Lumotec headlight and a B&M DToplight. Last year I had the same setup powered with a homemade 6V NiMH battery pack (6 "D" cells). Like most others I love the Shimano hub, but having all of the lights go out at a stoplight stinks. I'd like to use a smaller battery pack from all-battery.com as a fallover standlight, so when I'm slowing to a stop the relay kicks off and the battery powers the headlight. When I take off again and get over 5 or so mph, the relay closes and I'm back on the hub power.
To that end, I've gathered the parts I think I'll need: full wave rectifier (Radio Shack 276-1152 Silicon Bridge Rectifier) to convert the 6+ volts AC off the Shimano to 6+ volts DC, NTE962 voltage regulator to clamp the excess voltage to 6 volts, SPDT relay (NTE R48-5D5-6L), a good switch, and 3 mono speaker jacks (gen in, batt in and out).
I Am Not An Electrical Engineer ;-), but my understanding of how relays work (and tested with some bare wire from the battery pack) is that when 6 volts is passed across the coil pins of the relay, the switch closes. In my case I'll want to wire the Shimano (rectified and voltage regulated) 6V+ to one of the switch pins, and the 6V+ from the battery pack to the other. The common pole in the middle of my relay is connected to the positive terminal of my out jack. I think I can put all of the negatives together on the same circuit.
My question then is is how I can wire the Shimano across the coil? Do I just tack a small wire from the 6Vout pin of the regulator to one side, and the GND from the regulator to the other? That would mean two wires off the Vout pin--one to the coil and one to the NC side of the switch.
The relay I have is low resistance off the coil (340 ohms) but I don't want to lose all of my power just running the relay.
If this works like I hope, I'll do a writeup with schematic and photos.