Richard Cranium

While riding home the other night it dawned on me that one aspect of using bike lights that can be annoying is having to remove or change batteries for recharging.

I know about some of the nicer generator setups that use capacitors as a power source for short run times.

What I would like to know is if anyone has either rigged their own self-controlled generator system that could be set to only run when a brake is applied or manually switched to "on all the time." The idea being to run off battery power most of the time but run the generator and charge batteries during breaking or downhill/downwind cycling.

Does anyone know if this is on any manufacturers radar? It ought to be feasible and attractive for anyone but all out racing cyclists.

ItsJustMe

I really doubt anyone's using capacitors to hold power. A capacitor the size of a baseball would still only run a moderately bright LED for 10 or 15 seconds, and would be pretty expensive. You'd want to use batteries to hold charge.

If you wanted to use them for braking, you wouldn't want to use a conventional generator, which A) only put out 6 watts or so, and B) don't really brake very much. You'd want to get about a 100 watt generator, maybe even more than that. Honestly I think what you'd want is an ebike hub motor. Those can act as fairly powerful generators.

Thing is, with a 6 watt generator, even if you're going downhill for a long time, it's what, maybe a minute? 6 watts for a minute is a miniscule amount of power.

I think that even on ebikes, where a lot of this equipment is already there, most manufacturers don't feel it's worth it. Even on the really high end digital controllers, I don't think anyone's doing regenerative braking. There just isn't enough energy to recapture to make it worth the bother.

Richard Cranium

Yeah - I can understand how so little time is invested in braking - yet my point is that the system would utilize "both" energy sources and give a rider a chance to manually "put up with" charging the system when he chooses. Or if necessary - go ahead and plug in the battery at the end of a ride.

I think the technology exists - whether it is marketable or can be made attractive - I don't know.

I do know, that if you ran current hub generators every time you "coasted" downhill you could keep a battery charged. And leave these generators off during hill climbing or most of the flat part of a route. (OK maybe not in the desert)

2_i 

Supercap in IQ Cyo can power the front lamp for minutes and can, otherwise, hold charge for days without it leaking out. This type of system, LEDs + supercaps, both front and rear, begins to be adequate for most riders. Myself, I ride with a hybrid system of my own design, based on rechargeable batteries, in fact 3rd incarnation already. The power is always there and no maintenance of any sort is required.

Richard Cranium

Did you build with an AC generator and rectifier? Are there pre-configured ICs/PCBs that can maintain say 8.5V so as to charge Li Ion cells - even though the current may be low at slow speeds?

You can charge a big battery in 3 hours at 1.5A -but I'm thinking a generator could never deliver that kind of current at low RPMs -maybe more like 30-40mA...... I wonder what the silly hand crank radios deliver, maybe 10-20mA@3.5V?

2_i 

I use a hub dynamo and currently Eneloops for the batteries. Within an usual application and under the requirement of high efficiency, you are basically on your own in terms of electronic design. An IC is just a compact realization of a circuit that has common applications.

A bicycle dynamo maxes out at 0.55-0.6 A. In my case, I may draw 0.3 A with pretty empty batteries. Most often I might be drawing 0.1A or less. The essence is to fill batteries when there is excess power and use that reserve power when there is a deficiency.

znomit

I usually run a 3W light off a hub dyno. The hub efficiency is around 50% and theres a couple of watts lost to mechanical drag(don't know what the drag on a normal hub is) so say 7W.

Now downhills and tailwinds are maybe going to come up 1/4 of you ride time(probably a lot less). So you want to generate enough power to give you 3W for the other 3/4 of the ride, plus your 3W for your light.
Add in battery charging efficiency of ~50%.
3W + 3W*3/0.50 = 21W (I think the hubs can output a maximum of around 12W)
Hub generating efficiency is 50%... so you are losing over 40W for 1/4 of your ride.

Compare this with 7W for the entire ride without the battery charging.

I've used supercaps for "standlights" in the past with good results. They are very small and provide a "be seen" light for 5 minutes, enough for traffic stops.
I currently run a non standlight dual led light and a cateye uno beside it for redundancy(it gets a battery recharge every month or so).

Now what would be nice is the opposite of what you want, a dyno light that charges a battery/cap to provide a little higher power for the short times when you want a burst of extra light. 30s at intersections(they seem to all be strewn with gravel here) and downhill moments when you get over 50k.

2_i 

Power balance has changed for me with an LED. To the best of my knowledge, I run my front LED lamp at a fairly substandard power 1 - 1.5W and still have plenty of illumination, far more than with a halogen at 2.4 - 3W. With halogen, during a rough winter and slow riding, I might need to replenish my rechargeable batteries externally, once a month or so. With LED, this is the thing of the past.

Metzinger

My LBS has this on a hands on display on the counter:

Induction charging and capacitor storage. The 120 model claims 120 seconds of illumination after stopping. Review here.

Richard Cranium

I don't know of any way for a single light to have real "dynamic" output - so either you run a light at efficiency or you purposely under power it.

ItsJustMe

I guess it depends on your definition of "moderately bright". I'd call 200 to 400 lumens moderately bright. Those look more like 50 lumen lights.

Richard Cranium

OK look at this little "baby gen" - according to text in article it delivers 6V@.330mA - now go figure and put one on each wheel and VOILA - you have 6V@ over 600mA - now that's enough power to charge a couple 26650 Li Ion cells in a couple of hours - and a single 26650 can supply a 200 lumen light head several hours.

This whole thing is completely doable - I'm guessing there just isn't enough "geek" utility bike market to warrant a "start up" venture. For one thing, first you have compete with the "general" bike-light market, and then select the slim piece of that market that cares whether or not they have to change batteries or charge batteries often. I'm guessing that' s just not enough market share to warrant some one putting the piece together, branding and advertising it.

But a starting place would be to take what you can get from one of these existing hub setups and expand it's possibilities. For instance, have it perform double duty by charging a battery for a tail light during the day, down hill, and then have all of its out put go to the head light when needed - after dark.....

PaulRivers

A "dynamo" hub generates power. I know other people have mentioned it already, but that's the term to look for.

I don't know of any system that does what you're saying - turns on on downhills and off on uphills.

In the last year they have come out with chargers that you hook up to the dynamo hub and then it charges something else - often a cell phone or gps via a usb connection. There's a couple available now I believe - I know there's one available through the Peter White site.

I *have* heard of electronic-assist bikes recharging the battery when you brake. I've even heard of systems that are designed to also power a light. Obviously that would be fairly expensive, though.

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However, I'm not sure any of these solutions are the best for what you're thinking about. You wrote "While riding home the other night it dawned on me that one aspect of using bike lights that can be annoying is having to remove or change batteries for recharging."

A dynamo hub and light removes need a battery from the equation entirely. I bought a front wheel with a Shimano dynamo hub for $150, and my light cost another $120 or so. Not "cheap", but not to far from being on par with any system that comes with a lith-ion battery. With the battery you'll have to replace it eventually as well (I think they're usually only rated at like 500 charge/discharge cycles), so that will add cost down the road. With LED's, a dynamo light and hub last a really really long time. With LED's, dynamo lights finally put out a respectable amount of light (scroll down to the ones at the bottom) -
https://www.peterwhitecycles.com/headlights.asp

Actually - here's a picture -


I have a dynamo hub and light on my winter bike. However, to be fair I wanted the "ride like it's daylight without a helmet light experience" on my road bike, and while I haven't quite found it yet I do have battery, lith-ion lights on my road bike.

But I never remove the batteries from my bike to charge them. Both the Dinotte lights and the Light and Motion lights I've tried/bought have a charger that just has a cord that plugs directly into the battery. I keep my bikes inside, and just unplug the battery from the light and plug it into the charger without ever removing the battery from my bike.

znomit

Well, I designed one to run brighter as speed increases. Thats fairly dynamic. You can see how small the standlight circuit is.
https://www.candlepowerforums.com/vb/...5&postcount=68

Those reelights aren't bright at all. More like 10lm.

ps underpowered is efficient. LEDs peak efficiency is at around 50mA

Richard Cranium

Nice job, and I was just getting around to to searching the net for ready made regulators and other lighting components.

I saw how you can buy emitters already mounted on a board with a regulator. This is another subject, but I wonder what I need to "drop in" to old cat-eye opti-cubes that already would provide a 4xAA battery case and switch.

Have you ever experimented with modding cheap flashlights with some decent newer emitters from Cree etc...?

BarracksSi

I still don't understand the question.

What are you trying to do that isn't already on the market?

Road Fan

Richard,

Ignoring cost and whether anything similar exists for bikes, it is possible to design a circuit that directs hub dyno output from the lights to an AC/DC converter (a term that includes many types of rectifier) and then to a battery or even a brace of USB devices for on the road recharging. There's IMO as an electronics engineer nothing in physics that prevents such a thing, and complex power management functions exist today in vehicles ranging from motorcycles and cars to aircraft and spacecraft (my old field). Depending on the DC voltages needed the circuit can be simple or quite complex.

To control it so it detects braking, coasting, climbing/descending, or when dyno output capacity is greater than the lighting requirement can get very complicated. It could actually results in a bike with an electrical system comparable to a simple car. I think that the actual circuit could just come down to a small number of surface-mount ICs in a high-production manufacturing scenario, but as a "bikie" product it won't be cheap.

In electronics price is dictated by volume. Amazingly complex products can have consumer costs in the 10s of dollars if the production volumes are high enough. However, electronics engineers say we can make one of anything - the question is, are you willing to pay what that costs?

If you can solve a part of what first you asked for, with modded flashlights or on-line circuits, do that. I think the full monty you started out with is a pretty complicated system. A worthwhile benefit to cyclists, but a big project.