Another question on LED bike lighting systems

[eHomer]

Thanks for the kind offer MTB1956, but I'm still mulling over all the ideas given on here.


Yes, I quite understand the basic inefficiency of using battery electricity to move a bike and then generating more electricity from that movement to power the lights, but I mentioned in my original question that this was for my human powered bikes.

On my "almost" UK road legal bike, (see, I'm learning ! ), there's a very nice LED rear lamp incorporated into each rack battery pack, and quite a powerfull front LED lamp, so that's what rather spoilt me when I use my non-electric bikes.

Thanks again for all the ideas, much appreciated.

I do actually have a rather nice Sachs hub dynamo in a spare 700c front wheel, and the idea of a hybrid DIY led system with battery backup is appealing, but the comments about how practical self contained LED lights are now with their much longer battery life makes the simplicity of that even more attractive.

..and I could even just buy one good quality set and shift it quickly to whichever bike or Trike I'm using.

I was looking at the Cree T6 that d8veh mentioned and they look pretty good for the front.

 

[rog_london]

I was thinking along those lines when I asked the original question (honest )

I thought a really good dynamo hub, originally designed for incandescent bulbs would be a really efficient set up with LEDs, requiring about a tenth of the power generation.

I can appreciate that the up market systems designed for the German regs would be quite sophisticated in that respect, but was surprised that the bulk producers hadn't by now produced the same systems at much lower prices.

Ah, well, the Germans are nothing if not thorough - I understand that lights on a bicycle are compulsory. Generally the 'dynamo' - quite right it's not a dynamo it's an alternator - is the same unmodified unit designed for 6 volt filament lamps - I believe something like 3.6 watts is the rated output, with about half a watt for the tail light and the rest for the front.

You need to appreciate the difficulties of driving LEDs efficiently. They generally only need a couple of volts but they're very much 'constant current' devices, and without the right 'ballast' they would burn out rapidly. The best way to achieve the necessary current limiting without compromising efficiency is to use a switch-mode electronic regulator. Add in the cost of high-output LEDs and other development costs such as specialized reflectors to get a sensible beam pattern and you can see where the money goes.

They're not so much 'up market' as properly made for the German market.

We don't buy bikes with lighting sets - we're much too mean and the perceived wisdom is that it's unnecessary weight and complication if you only ride in the daytime. That's apart from those cyclists who would never have lights at any time of day!

I didn't mention it before, but Busch and Muller do make a lighting set which is designed to run off an e-bike battery. From memory I seem to recall they're rated for any supply between 24V and 48V. They're used on S-class pedelecs which are NOT bicycles - so the rule of needing a dynamo doesn't apply. You can probably get them here but don't expect much change out of £100 for a set.

I know many members would rather put their own sets together - some have done so with considerable success - but not everyone has the time or interest to want to tinker - and even at £100 it's only two hours' work if you're paying yourself. Never forget what your time is worth!

Rog.

 

[Jeremy]

One of my ebikes has permanently on lights, wired to the main power feed. They are home made, just a couple of big reflectors (red for the rear, white for the front) drilled and fitted with lots of 5mm LEDs. The front light isn't good enough for riding in totally dark lanes, but is more than good enough to be seen well on normal roads, mainly because of its large size.

Because I made these up with lots of series wired LEDs, I could get away with just using a small linear constant current source to regulate the LED current. There's no change in brightness from the battery being fully charged to being almost flat, plus the whole lot draws less than 40mA from the battery, not enough to worry about. Overall, this is probably more efficient than using a switched mode converter, rather bizarrely.

If anyone else want to try it, then the front light is 10 off 5mm bright white LEDs, set into an 80mm diameter round white reflector, the rear light is 14 off 5mm red LEDs (not the super bright ones, as they are just ludicrously bright I found). I've been running the front LEDs at 25mA and the rear ones at 10mA. The rear ones are a bit too bright even at that current, but the front ones could be a bit brighter and I may boost them up to 30mA.

A clip on narrow beam very bright battery powered LED headlight is all that's needed if I ever need to ride any distance at night.