Dynamos and hills - battery backup?

[mercalia]

hmm how tech hasnt move on? in the old days some hub dyno bikes had a battery on the seat tube? I assume it was rechargeable? I remember seeing those longish tubes attached there?

[edocaster]

3mph is below walking pace, and not much light is needed to spot potholes then - you could probably get by with a non-searingly bright headtorch (which is a good thing to have anyway - even if you don't feel like carrying an extra light). If you only need it for the first 600m, one battery (you could go down to a single AA/AAA if you wanted a lightweight headtorch) would last you that journey hundreds of times. This is the simplest solution.

A charged standlight would actually be enough light, but the problem is most dynamo lights focus their lights forward.

But even then, a charged standlight is better than uncharged. You can encourage it to charge by spinning it by hand before, or riding a couple of minutes in a car park. Also, if your light allows the standlight to be switched off rather than just discharging over time, you *should* actually have a standlight right from the start, assuming it wasn't discharged at the end of the previous ride.

A light with a battery backup or high discharge rate capacitor backup wouldn't actually be extremely complicated, but most makers avoid this so they can stick with coin-type supercapacitors, which aren't really designed for high discharge rates, but can withstand repeated charge and discharge cycles better than the average NiMH cell. A light with *non-rechargeable* battery backup would be even simpler, but there's little demand for that.

[beardy]

I dont see how the standlight can be an answer.

If the capacitor contributes to the lighting output at very slow speeds then even if it was fully charged by riding around a carpark at the beginning it will have been used up by the time 600' have been climbed and the streetlights end.
If the capacitor doesnt contribute to the lighting output when moving, even at very slow speeds which appears to be the case with mine, then it will not make the lights any brighter then either.

The capacitor certainly doesnt knock out enough light to make cars dip their headlights, the standlight is much dimmer than that inorder to stay on longer and a static cyclist not needing to see very far.

[stanron]

I recently rigged up an old SA dynohub with a couple of wheatstone bridges from old power supplies and linked them up with four recharchable batteries to screw in led bulbs in old dynamo lights. Unfortunately the batteries only work on the rear light but otherwise the system works OK. If I used only one bridge and linked the batteries up after that I imagine it would work fine. An alternative would be to use something like the old Cateye three led battery front light I used to use. If you used it just on the uphill section the batteries would last a long time. That light puts out a good beam.

[pete75]

AT 3 mph you'd be at least as quick getting off and walking.
I've 3 different dynamo lights on 3 different bikes - will check them tonight and see if one does give decent light at low speeds from the off.

[stewartpratt]

Two pages of replies and no-one's yet asked what light it is?

…What light is it?

[[XAP]Bob]

Two pages of replies and no-one's yet asked what light it is?

…What light is it?

The first reply asked that - and the OP hasn't been back

[Audax67]

I have a CatEye HL-EL530 mounted alongside my dynamo light, mainly because the rules of some Audaxes require a backup lamp. It not only serves as backup, but can be swivelled left & right to pinpoint verges etc, or detached to use off-bike. The light is brilliant and concentrated in the centre, with a dimmer wide spread that is quite helpful even with the dynamo light on. I have it mounted on a Topeak T-piece hung from the stem: it peeks out under my HB bag.

The HL-EL530 is symmetrical, unlike later Topeak lights, so you can let it hang from the T-piece. You'll find them on Amazon/eBay if not in the shops. Make sure you get the latest version: early models have a raised ring in the lens, and are not half as bright.

[stewartpratt]

The first reply asked that

Well, not quite; it asked a question that would narrow it down to about 99% of lights on the market

[[XAP]Bob]

The first reply asked that

Well, not quite; it asked a question that would narrow it down to about 99% of lights on the market

It was going in that direction though - My response would have been a model...

[cotswolds]

Wow, what a lot of responses, I wasn't expecting so many, thanks everybody. In answer to various points raised:

The light came free with with the wheelset from Rose Versand. It's very basic, labelled 'Town & Country halogen' FWIW. I know there are many better dynamo lights, and I expect to buy one if I stick with dynamo lighting. Trouble is, my impression is that a more expensive light won't solve my key problem with dynamo front lights, which makes me reluctant to spend the money.

The flicker isn't a problem to me as such, my problem is having a bright enough light to get cars to dip their headlights. Oversimplifying a lot, dim(flickery) is enough for me to see where I'm going at 3mph as long as there are no cars; bright is needed to get all cars to dip; medium might be enough to get most cars to dip, and throw enough light on the road for me to keep going when I've lost my night vision because of car that didn't dip. But it sounds as if no dynamo light is going to manage medium at 3 miles an hour.

Standlights: I'm not sure how much variation there is in standlight implementations, but my assumption is that either they only come on when stationary, which is no use to me, or they come on to supplement the dynamo when power is low, in which case, even if I find a way of charging it up before I start the hill, it will have discharged in the long (10 minutes) unproblematic street-lit section before I get to the properly dark bit. (A minor frustration with the issue is that I've usually descended the hill a few hours earlier and had surplus power which I have to get rid of by wearing out my rims - it would be nice to capture some of that to light my journey back up rather than generating it myself, but the technological solution seems overkill.)

Bottle dynamos: it had never occurred to me that they should have better low speed performance than a hub dynamo. I have one on the tandem for charging gadgets when on tour, but it would seem somewhat ridiculous to attach it to my solo bike when I have a hub dynamo wheel.

Battery lights: I have several battery lights, at least two of which solve the problem, I'm just trying to find a way of avoiding using them. Much of my riding is utility in nature, and the closer I can get to unlock and go, the better. I reckon any (battery) light bright enough to force motorists to dip is probably going to look attractive to thieves and so has to be removed from the bike when parked, which isn't a big deal but is a minor hassle. And I think pretty much every battery light I've ever owned has at some point managed to turn itself on in a pocket or pannier, which is another hassle I wouldn't miss.

USB charging a battery light: hadn't thought of that one, and one of my battery lights does have a recharging socket (not usb, looks like a small jack plug and not designed to be used in the wet). This approach will still mean I have an expensive battery light on show which will have to be removed when parked, so not quite what I'm looking for, but I'll look into it further.

Headtorches: I have two of those, a 1W which gets most cars to dip, and a Cree T6 which wins the lighting war but sprays light everywhere, so I have to aim it at my front wheel once they have dipped. But I'll probably go back to using one of those, as it's useful to have for punctures/repairs, and I can't accidentally leave it visible on the bars when parked.

Thanks for all your thoughts, I've learned quite a bit, not least that there isn't really an ideal solution to my problem (which I was hoping there would be). In the medium term I think I'll explore battery backup for the dynamo light with manual switching, which I think will provide a good enough solution.

[[XAP]Bob]

OK - I'd suggest that an LED front light is worth a shot.

I have a Lyt - which is inexpensive, but does a pretty good job. The standlight keeps it at full brightness when it can - and it doesn't take much speed to get to the stage where it does that for several minutes.

Halogen lights are much simpler electronically, but they don't cope well with low power input. LED based lights OTOH are much better at it.

[stewartpratt]

Oh, a free, basic halogen light… As Bob says, try an LED one. I've used four types of B&M LED light and have never run out of light even at walking pace (though they do flicker below ~6mph), and all of them make a 2.4W halogen bulb look like a candle. The Cyo Premium at £44 is about as good a light as you'll get; you can spend a lot less and almost certainly still solve your problem.

http://www.rosebikes.co.uk/products/bik ... eadlights/

[Audax67]

+1 on B&M lights. Even my 6-year-old IQ/Fly outshines any dynamo-compatible halogen. Caveat: if you use a wireless bike computer that just picks up electromagnetic pulses without ANT+encoding or similar, many LED lights will screw it up. That's why I'm still using an old light.

[mercalia]

some of your trouble is the free Halogen light. Maybe try a cheap led one like the Axa Pico30. gives 30 lux - prob more than twice what you get from the halogen & better at low speeds. You will prob still get flicker but will be much brighter. I got my pico30 from Rose - is a basic one with no standlight cost about £13 - here they cost I think more like £20 but cheaper than the BM ones. I am really impressed by the Axa light. You can get ones with standlights. Is also very small. When I first saw the size I thought how can it be any good. But it is. Is all I need for going at 12 mph in complete dark roads.