Thanks for all the replies - very informative.
- I had an incident a couple of weeks ago that instantly converted me into an advocate of permanent daytime lights: It was a bright sunny day, I was going around a round-about that I use everyday. This one car was approaching the round-about at a spot where I'm used to seeing cars stopping and waiting for me to pass as I have right of way, however this one car didn't stop, it just kept on going, and I was completely at the mercy of whatever would happen next. All I could do was say 'F**k...'. Then it suddenly screeched to a halt. As I rolled past, I looked into the face of the driver, and staring back at me was the face of a shocked old man. I couldn't be angry - he just couldn't see me. And it was at that moment that I fully appreciated that a lot of people on the road just can't see as well as I can... so from now on its lights all the time for me.
Furthermore, this Oxydrive ebike that the lights are for is for my mum, so I'll be damned if shes going out on to the roads without the full works, especially in London.
- I'll definitely be trying to implement the methods suggested above of wiring the lights directly to the battery or controller.
- However, I'm just wondering, with this method, if the battery runs out during a ride, then the lights also go out... For this circumstance, would there be some way of making the motor act as a generator/dynamo hub to power the lights? Would this require a different kind of controller? Do customisable controllers exist?
Thanks!
While D8vh, is technically correct in that a dynamo , being driven by a motor is inherently less efficient than any direct electrical connection, I think he is missing the point. A dynamo is very much a set and forget product. With LED bulbs, they wont blow or wear out . Moreover were the battery to fail they will still produce light. Lights get stolen with ease from bikes and it is no consolation on a dark night that they are cheap. There are plenty of people out there who would take them just for devilment.
Many of the urban or city type bikes bikes made by the major companies will come with a front wheel hub dynamo and an already wired in set of lights front and rear. They are not super bright , but are good enough for city and suburban commuting. There is no value in stealing these as they are built into the bike.
The power loss into one of these dynamos is probably 5 to 6 watts, and that is negligible in the context of the 100 watts a person is generating.
Lets just recap on the ways of lighting a bike.
Modern White Light LEDs require a voltage of 3.5 to 5 volts across the diode junction to work RED Leds need 1.6 Volts but those used in White Lights need the 3.3V , as the mechanism for creating light is different. . If higher voltages are used then either a number of diodes are being run in series connection , or a voltage dropping circuit is being used.
A single Lithium Ion cell at 3.7 to 4.2 V or as was previously used 3 standard alkaline cells at 1.6V each is a good match to the voltage requirement. A current of 1Amp will produce a very bright level, and be consuming about 4W of power. . The type of lamp that D8Vh is proposing is of these types. Halfords have reasonable alternatives at about the 15 pound level
It would seem obvious that the big battery in the ebike motor should be able to supply that voltage, but the problem is that it is at 36 vollts . Therefore a major amount of voltage reduction is required. Unless one is prepared to live with major inefficiencies and use a series resistance or current regulator, The best way is to use a dc to dc stepdown convertor as these can be 80 to 90% efficient . . Some motor controllers can provide this type of auxiliary output for both the lighting and for auxiliary purposes eg phone charging. . As another Kiwi has indicated, The DC to DC convertor can be packaged internally within the lamp casing
There are two types of bike dynamo. The old fashioned bottle dynamo which is driven by the tyre wall in a friction drive... as per your initial picture. They have the advantage of being cheap and easily to retrofit. Their disadvantages are that they are horribly inefficient , friction drives are just not good, and they wear the tyre, and they also slip when the tyre is wet.
The hub dynamo is a much more robust product, it may well be just as old as the bottle type.. strumley archer were making them many decades ago. , has no friction losses . The most recent versions have a supercapacitor built in so that the lights remain on for a few minutes even after the bike is stopped. .. A useful feature when stopped at traffic lights. The 1950s Rudge Bikes , used to have a small lead acid battery, storing the SA dynamo power for exactly the same reason.
The notion of using the main motor as a generator is not worth pursuing
