Has anyone tried this? If so, have you tried anything other than Martin's ubiquitous circuits?

I've got myself a single mini XPG on my commuter bike with a simple rectifier and nothing else which is great for 100% road and town miles and an MCE on the MTB which has a smoothing capacitor and low speed boost. They're so good I wonder what I've been doing with batteries all this time.

Next step is standlight, I was wondering if anyone had implemented one, if so, roughly what components have you used and how much time can I expect to get? I was planning a single 5.5V 1.5F super capacitor, discharging through at 50ohm resistor, which should give me a half decent level of brightness. Is it as simple as:

E = 1/2 x C x V^2

for the energy storage, and then trying to get the V of the capacitor as close to its rated value as possible, i.e charge the capacitor over two LEDs, using a pair of diodes to both drop the voltage from the approx 6.4V (measured) to 5.0V, assuming dropping 0.7V over each diode, these diodes can then be serve the double function to make sure I don;t discharge through the two LEDs but through the resistor over a single LED. If that makes sense.

So, I can expect the LED, using V=IR, where the LED Vf = 3.2V and R = 50ohms, to run at 0.064A, which, at 3.2V is 0.2W. I can expect the capacitor to store 1/2 x C x V^2, where C=1.5, V=3.2, 7.68W or energy, giving me 7.6/0.2 = 40 seconds of light before the thing starts to dim?

Please correct me if I'm wrong, which I fully expect to be somewhere!

From memory, to double this time I can run two capacitors in parallel to double the capacitance, but maintain the same voltage rating? Similarly halving the resistor value should double the brightness (but halve the burn time)

Cheers for your help/comments/advice

Rob

The thing will start to dim from the moment you stop, due to falling drive voltage (and hence current). Whether that's noticable or not is a different matter. I've no time to check your maths but yes parallel caps double capacitance and halving the resistor will double the current (not necessarily brightness) and shorten burn time.

A friend of mine is running a led home brew light, front hub dynamo, with a disc.
The guy that built it moved to NZ last year.
I have not a clue how it's done but it's very bright and been using it for the last 2 years.

Interesting. I've not gotten round to wiring up my nexus dynohub for 4 years and been meaning to do it,

What light & hub are you using? (googled "mini XPG" to no avail)

IIRC theere is stuff on the candlepower forums about this. too complex for me

why do we bother with batteries?

whats the weight of a hub dynamo (and its extra drag) and the weight of a 1.5f capacitor (I'm guessing arround 800-1000g for the capacitor).

2xAA batteries give enough light and btn time for most rides, when I need more light/time I just add more batteries, I could go for weeks with enough batteries to fill a 1.5f capacitor!

Capacitors ae designed to charge/discharge very quickly, 1.5f capacitors are typicaly found in portable PA equipment where the 12v batteries can't supply the peak current required by big bass bins. Youd have a lighter setup building a charger and battery into the space you had the capacitor.

A capacitor is like holding a brick at arms length, it starts to drop fairly quickly as you get tired, putting it on the shelf is like putting thr energy in a battery/cell, takes a little more time and effort but will stay there for years (untill the shelf falls down).

It's about not having to take your lights on and off all the time for me.

As TJ mentions, CPF would be a good place to pick up with like-minded folk. Theres quite a few there applying dynamo stuff to bikes, using the Martins circuit, as you mention.

Might be Ok for commuting, but I'm not convinced (yet) its for me when I'm cycling off-road.

What light and hub are you using? (googled "mini XPG" to no avail)

If I've read that coreectly, I'm pretty amazed at that. This forum has been awash with talk of the Cree XP-G LED for most of this winter.

🙂

L.

"The thing will start to dim from the moment you stop, due to falling drive voltage"

NO! – the capacitor will drive the LED at full brightness for the time I've calculated. I know as I've made a little tset circuit with different value componentsd

thisisnotaspoon – NO! Dyno hub wieghs 600g, the MCE light I've made weighs 42g, that's the normal light with the supercaps on the scales. Assuming 200g for a front hub that's 442g heavier than no light at all. Now go and weigh your barrety light, with battery. And how much burn time do you get for 580lumens? I get, erm… all night!

I also never have to chareg my lights, don't need to worry about the batteries screwing up in cold weather. Plus I do a good few endurance races so not having to swap batteries on and off all the time is a huge boon. I did the SDD last year and this set up would have offered me way more light for significantly less weight than my battery setuop, running at a mid power setting with a second set of batteries.

What is missing now is a 20mm thru axle dynamo
For commuting I've used a IQ FLY for 2 years and it is fantastic

If I've read that coreectly, I'm pretty amazed at that. This forum has been awash with talk of the Cree XP-G LED for most of this winter.

I don't read every thread, and the correct search is helpful, thanks.

I CBA with making lights up myself, unless I can get a kit with housing etc that's reliable – does this exist?

I have dynamo lights on my road bike. I got bought a B&M IQ Fly, and it is good enough (very good), so I've never bothered building a front. The rear light is a red 1W cree, that I picked up for about £3 (I think I got it off Dealextreme, can't remember), a white plastic cone to roughly point it out, a 20p rectifier from maplin and a bit of old aluminium seatpost. Shockingly bright for a rear light, very solidly built out of metal, sticks on top of my mudguard, and just goes on when the front light is on.

whats the weight of a hub dynamo (and its extra drag) and the weight of a 1.5f capacitor (I'm guessing arround 800-1000g for the capacitor).

Weight difference on the hub was about 200g. The front light unit is the lightest light I've ever had – weighs about 50g. So basically it is a 250g weight penalty compared to not having lights on. I imagine very few lights have <200g batteries except the really tiny ones (exposure joystick etc.)

It is a great advantage on a road bike just having the lights with you all the time too – they even magically turn on, so if you go into a dark tunnel, lights on, it gets very rainy and turns pitch black, on they pop. You never have those situations where you stay out later than expected and haven't charged your lights, they just always work. Before I fitted them, I had so many sketchy moments coming home on just flashy lights, getting caught out by having to do stuff late at work or impromptu trips to the pub or the cinema in summer on days when I usually wouldn't need lights. I had one pretty sketchy moment in New Zealand, when a ride across the top of some mountains took longer than it should, and I ended up descending 300m and 4km of very tight curves on a fancy LED light that had a very very low battery, and having to do it in a hurry so that at least I had some light to get down (it was complete pitch dark, especially under the trees). I never have those moments with the dynamo, it is great.

I've also done a fair few rides in the past where long runtimes were needed (like 6-8 hours or more), so have a house full of expensive batteries, and on all the lights I've had, at some point I've run out of battery at an inconvenient point, or had to do long sections of rides in the dark because I knew I only had 8 hours of run time. The time I did London-Brighton all in the dark, I did a whole load of it by moonlight, which was pretty sketchy.

In terms of drag – my light system uses a total of about 6W, maybe a bit under. I have the latest shimano dh-3n80 dynamo hub (this is worth getting – very efficient, supposedly way less drag than the older ones). If I go into a tunnel and the light turns on, I can't feel in my legs when it turns on. It obviously does use a little bit of energy when the light is on, but it is not enough that you can tell when you're riding. It is nothing like those old dynamo things that buzzed on the tyre.

2xAA batteries give enough light and btn time for most rides, when I need more light/time I just add more batteries, I could go for weeks with enough batteries to fill a 1.5f capacitor!

If you're using a light that runs off 2AA batteries and goes for more than about an hour, it isn't very bright – it will be way less bright than the modern commercial dynamo road front lights, and significantly less bright than a home-brew one with multiple LEDs (or those crazy german 3 LED dynamo lights). What you should compare a homebrewed dynamo light to are the lower end of the offroad lights – things like the hope and exposure 2 LED lights – which typically weigh about 4-500g, and have only 3 hour or so run times.

Joe

Oh yeah, for anyone not bothered to build em up themselves (but with plenty of spare cash), here it is, the monster light:

"Not compliant with German traffic laws (far too much power)."
http://www.supernova-lights.com/shop/show_product.php?products_id=151

The person they get their recommendation from on the site is an ex-olympic xc mtb person, who apparently has won a bunch of other stuff, so I guess they work okay off road.

are these fancy dymanos and things available under cycle2work scheme?

Cynic-al. I Agree that the search on here can be a little hit-n-miss.
The Troutlight comes in kit form I believe.
😉

There may be little difference in weight, by your calculation, but how much drag does one get from a hub dynamo ?. Also, hubs, as with the rest of the wheel are unspended weight and contribute to wheel weight with the obvious consequences for braking, turning(direction), etc.

I'm always interested to see what others are upto though.

Of course, I'm guessing you'd still use a battery powered light for the helmet.
Furthermore. Battery lights go onto any number of bikes with little more modification than the addition of a bar clamp.

Got any pics of your set-up ?.

🙂

L.

Luminous – whether 400g of weight is mounted on the frame, or in the centre of the wheel (essentially bolted to the fork), compared to the weight of a rider and bike is utterly irrelevant. It's also worth noting that hub weight will have zero effect on steering as it's not "rotating weight" like a rim or tyre so will not affect steering/handling in any way what so ever. In fact, it could be argued that adding the weight of a battery higher up, like on a stem or top tube will have a greater negative effect of lifting the CofG compared to it being low down on the fork (but again, the 400g is such a small amount of the total weight that the real world effect is zero). I'm not sure how, if at all, this shows through as "obvious" consequences for braking???

The drag is simple, it's the power draw from the light, which is a paltry 7W. Thsi wasn't enough to slow Bart Bretjens down when he and his team won the 24hrs or the Nurburgring using dynamo lights.

Any more questions? 😛

What people are missing here is that, using XPG LEDs, I can run a whopping 700lumens all night, when battery lights will be switching to lower light outputs to eek out battery life, or carrying round extra battery packs that add significant extra weight to the light setup, and have to be swapped on and off the bike. What's more I can use the bike to get to and from work the day of a ride, and again the next day, without worrying about removing the battery to charge it inbetween.

Photos, yes, but not at my desk at work….

I like the idea of a guy building a set of lights and a dynamo – and then running away to NZ just in case they went off with a really big bang.

Rob.

In Automotive, they reduce unsuspended mass in order to contribute to improvements in ride and handling. But, on a bike, it will be much less pronouced so far as for some to disregard it.
I thought a Dynamo hub did rotate…
F1 reduces unsuspended weight as much as possible and to much expense.
Adding batt and light to a bike may move the CoG 1mm, 2mm ?, not counting mud, water bottle, etc…

You may have ambitions of glory in a 24Hr race, but that isn't a reality for me now.

Anyway, the weight debate probably isn't that significant for most. Its just a techincal point.

And if people are missing anything…

As I wrote earlier, I'm always interested to see what others are doing, and unlike some, I try to keep an open mind/approach to stuff like this. I looked at Dynamo last year, and I too feel the attraction to some of the points you make on the plus side for dynamo. But I'm sure you can see that there are also some drawbacks too and I'm asking what they might be. I'm assuming that you require a custom built wheel ?.

I can't say for others here, but I don't think I'm missing anything. As above, I can appreciate the plus-side to such a set-up, but there are issues that I can't help but wonder about.

How long does your current set-up run for at full power, when you are stopped ?. I assume that you can maintain ~700 lumens at lower speeds ?.

🙂

L.

As coffeeking said, the illumination level *will* drop, but it may not be initially perceptable to you.

Also your energy-based calc isn't helpful – eg as the cap discharges it's voltage will drop to the point that you won't have any significant conduction (=light) from the LED. LEDs aren't *exactly* a constant voltage device – and you'd normally think of driving them at a particular current – but they do have limited operating range (dunno offhand, but it might be 3-3.6V according to the current through it)

But assuming you're not exceeding the diode specs/applying the wrong polarity, there's nothing particularly wrong with what you're doing from the sound of it..

There may be little difference in weight, by your calculation, but how much drag does one get from a hub dynamo ?. Also, hubs, as with the rest of the wheel are unspended weight and contribute to wheel weight with the obvious consequences for braking, turning(direction), etc.

It is surprisingly low the amount of drag that a modern dynamo adds. Not enough to be able to tell in your legs.

The hub is rotating weight, but because it is pretty much in the centre of the wheel, the moment of inertia relating to the rotation is very low (because rotational inertia is proportional to the square of the distance from the centre).

How long does your current set-up run for at full power, when you are stopped ?. I assume that you can maintain ~700 lumens at lower speeds ?.

Not answering for Rob's setup, but the normal ones come on at very very low speeds (if you walk with them, 1-2 mph they start up), and get to full brightness at 3mph or so, I'd expect a larger setup to require maybe 5mph for full brightness, but only testing can tell (and you still get a decent amount of light at low speeds).

You do have to build a wheel, which adds to the expense (my wheel cost a hundred quid or so). But it is oh so worth it.

On my bike, basically in terms of handling and noticeable bike weight or drag, there is no difference to having no lights. You just always have a light with you, that never runs out, with no penalty. And with the latest LEDs they are bright enough that you can potentially make a usable MTB dynamo. How awesome is that?

Joe

hang on a minute a 1.5f capacitor is the size of a litre water bottle? Are you sure you have your units right?

It's slightly harder to wheelie with a dynamo hub, and it does increase the unsprung mass so the fork can't react quite as quickly, but it's not really noticable. The big flanges make for a stiff hub though. Yes you need a custom wheel. I've got mine with a XM719 rim & XTR rotor, so it's not too heavy.

You can spare 6-7W easily 🙂 And when it's off I think it only drags by another 1W. As LED efficiency improves I think the possibilities will juts grow & grow.

Interestingly the IQ FLY won't work at all off DC.

What I want for the summer is a little battery to charge that could then charge your phone, gps, camera etc. … like this
http://www.copycatsolar.com/index_files/Page7674.htm

just the ting for a self-sufficent MTBer 🙂

Joe.

Good post.

I wasn't so much high-lighting the rotational mass issue as you point out, its very close to the wheel centre. But it is never a bad thing to reduce your unsuspended weight if you can.
😉

It is surprisingly low the amount of drag that a modern dynamo adds. Not enough to be able to tell in your legs.
Liking the sound of that. Assuming that these hubs are quite durable and will maintain efficient, inpreceptable drag over a winters riding ?.

You do have to build a wheel, which adds to the expense (my wheel cost a hundred quid or so). But it is oh so worth it.
Another good point, but has to be added to the sums of price/cost of a dynamo set-up to a battery and light arrangement.

On my bike, basically in terms of handling and noticeable bike weight or drag, there is no difference to having no lights. You just always have a light with you, that never runs out, with no penalty. And with the latest LEDs they are bright enough that you can potentially make a usable MTB dynamo. How awesome is that?

I agree, this side of it is very attractive. As has been pointed out. Being able to jump onto my hack bike, stay out as long as I like and know I've still got lights to get me home, is a plus-point.

There probably is some mileage in this for certain types of bike use, but I still like my battery light on full power for a few hours, and being able to sling it onto any of my 3 bikes in an instant.

Cheers.

😀

L.

If you're super-anal then weight, drag etc may be a factor, in the real world it's just nice never to have to worriy about flat batteries or getting your lights nicked.

Anyway, the weight debate probably isn't that significant for most. Its just a techincal point.

L.

EDIT: Yeah, any dynamo system might still need to include some "difficult to nick" features.

I happen to have an eco-light set, where the front light detaches from the bike, but powers both front and rear light.

I park the bike up, the rear light and wiring is still there when I return.
🙂

sounds perfect for one of the first lights I hacked out of a lump of ali

it could be even smaller now with the xp leds and the electronics in the hollow stem

Rob nip over to mtbr forums and make contact with Znomit and Ktronik They have done loads with dyno hubs and super caps

dang that's neat

trout – that looks like the Canondale Headsight system of a few years ago.

"You may have ambitions of glory in a 24Hr race, but that isn't a reality for me now."

Erm, I won SITS solo last year. Oh, and I did the SDD in <20hrs, about an hour faster than Rob Lee. That's ambition more than harboured 😉

While I agree unsuspended mass is important, and why we no-one runs URT full suspension designs anymore, I thing we can agree that the extra weight of a dyno hub, over a normal hub, really is not significant on the front of a MTB. I work in the automtive industry too, F1 teams also spend ages calculating damping factors and tuning spring weights, which I'm sure non of us do on our forks. Also, as the weight is in the centre of the wheel, as stated above this is not a real difference to rotating weight as the radius it acts at is almost zero, and half the weight does not rotate in the centre of the hub anyhow.

Yes, it dos need a "custom" wheel, but most lots of people have "custom" wheels here. The dynamo hubs cost around £60-£80 from Shimano, compared to say £55 for a Hope ProII front hub, and you can always lace the dynamo into your existing rim. So the costs are not that great, even to switch rather than when looking at building a new wheel with or without a dynamo.

I didn't mean to come across aggressively/over defensively, I just got a bit frustrated when posting looking for advice, having got what I considered a nice bright light working for a zero weight penalty, that people who hadn't even tried a dynamo light with power LEDs, let alone tried making one, or perhaps hadn't even set eyes on such a thing, were guessing at supposed negatives, without anyone guessing at supposed positives!

I posted about my DIY/homebrew battery powered LEDs back in 2003 (the monster thread that got shut as it slowed the site down, that actually got trout started off) and got a similar set of negative reactions from people that had never tried or even set eyes on the technology.

It happens that I commute off road for >1hr every morning, 30mins home and ride at least one evening with friends so always have at least one light on charge at all times, and find myself flicking between high and med on my MaXx-D constantly (great light BTW) to get good light and eek out battery life, where as the dynamo is about half way between the two power levels, is brighter as these DX lights everyone is riding at the moment, and is there, all the time, all week every week.

To answer another question, the super capacitor weighs less than 1g (not 1kg) and is 20mm in diameter and 5mm thick, not the size of a water bottle. It's a 5,5V memory back up capacitor normally, I'm using two of them and, and the stanndlight power I'm running, it lasts about 2mins 30seconds and will then dim rapidly unless I start moving again. But I have a joystick on my head too.

So, has anyone on here actually tried making one yet?

Rather than start new thread this seems a good place to ask. Is it possible to damage a xp-g light using a hub dynamo? Is the over voltage protection in the hub or the light?

You will need some kind of over voltage protection for the supercap else it will overcharge then overvolt then fail, you could probably do this with a chunky zener diode and a dump resistor . . . you should also be using a constant current drive for the LED . . . in your example it will probably be about 95+% efficient rather than the extremely inefficient (I guess 50% or so) resistor solution . . . it will also maintain constant LED output over a much larger range of supercap voltage (as it charges and discharges) . . . the net of this is that you stand some chance of getting reasonable stand light burn time rather than just wasting half of the charge heating up your series resistor . . .

$0.02

Fd

You should also be using a constant current drive for the LED

Really? I understood that the nature of the dynamo circuit itself limits the current?

Certainly seems to be the case on my dynamo rear light – it gets to full brightness at about 3-4mph, and I've taken the bike up to >40mph loads of times, and ridden it in the dark for hundreds of hours, and it certainly doesn't have any protection circuit.

Rob: Any chance you could post up the circuit / parts you're using and pictures of your current light with the supercapacitor standlight. I've seen martin's circuit things, but they seem a bit complicated and it is hard to know exactly which one to use and how to put it together.

Joe

If the dynamo has an inbuilt rectifier and current/voltage limit then that's great . . . but I've seen dynamos that simply output unregulated AC – that is what a dynamo produces in it's raw and original form . . . regardless . . . using a resistor to control current through the LED is hugely wasteful . . . with the XP-G LED voltage of about 3 volts and your supercap voltage of 5V you are wasting 40% ish of the energy stored in the supercap in the series resistor . . . it simply isn't sensible design . . .

Your dynamo may not work like another dynamo, but one thing is for sure, you require a regulator somewhere be that in the dynamo or the lamp or the supercap charging circuit . . .

Fd

Your dynamo may not work like another dynamo, but one thing is for sure, you require a regulator somewhere be that in the dynamo or the lamp or the supercap charging circuit . . .

Have you actually built dynamo circuits – because as far as I know, this is completely wrong, unless the supercap changes things a lot from a normal dynamo circuit.

I understood that it was in the nature of the construction of hub dynamos that they were self regulating to about 500ma. Certainly appears to be true for Shimano ones in my experience, and I know people have done similar things with the schmidt dynohubs, so I imagine it is true there. I don't think they have any regulation circuitry, I think it is something to do with the actual characteristics of the dynamo circuit. It certainly appears that you get an AC current out, which can go as high as you want voltage wise, but never goes about about 550ma current.

http://pilom.com/BicycleElectronics/DynamoCircuits.htm
says something about this.

What they don't have (for sure) is any voltage regulation – which is why we can run loads of LEDs in series off a dynamo (and why shimano make a separate voltage regulator for use with standard bulbs rather than LEDs, where too high a voltage makes them go bang).

Joe

hub wieghs 600g, the MCE light I've made weighs 42g, that's the normal light with the supercaps on the scales. Assuming 200g for a front hub that's 442g heavier than no light at all. Now go and weigh your barrety light, with battery. And how much burn time do you get for 580lumens? I get, erm… all night!

Well 400g of LiIon (the extra weight of your "battery") gives 66Whr. AT 6.5W (about what you're running the MCE at) that will give you 10 hours of light – not too shabby, and certainly plenty enough for a summer 24 hour race – with the bonus that you can carry a 200g battery on the rare occasions when you're only going for a 5 hour night ride 😉

dynamo wiring
circuit 1 with a xpg triple board makes a fantastic little light no need for capacitors as its plenty bright enough from about 5mph.

If you want to learn, first you need to learn to listen . . . but that's not happening . . . I feel I should give you one last safety tip, when you connect your supercap to your AC output dynamo . . . wear some safety goggles eh 😉

Fd

I found this in another place which seems pertinent:-

Alex W. said…

just for the record, as facts on dynamo hubs are rare here: the Novatec hub does indeed have roughly the same drag (measured in watts needed to turn the axle at a certain speed) as many other dynamos hub out there: about 6W at 20kmh and 8W at 30kmh. only the SON 20R is noticeably better (roughly 4W and 6W, respectively).

The big difference is when you cycle with the lights off: because the Novatec hub has its excess voltage inhibitor IN the hub and has to 'swallow' all that energy no longer being sent to the lights, you are using more power with the lights off: a whopping 9W at 30kmh. (ideally the resistance of bearings and seals in such a hub would be ca. .5W; The SON 20R is 1W).

for more info see Aktiv Radfahren, issue 1-2/09. there's a PDF summary of all this (in german . . .) but the charts are there too.

If you want to learn, first you need to learn to listen . . . but that's not happening . . . I feel I should give you one last safety tip, when you connect your supercap to your AC output dynamo . . . wear some safety goggles eh

Is it only because of the supercap that you're recommending regulation circuits etc.?

Presumably you're agreed that without a capacitor, you can just run the LEDs straight off the rectified AC current?

Joe

(who has no knowledge about supercapacitors and only enough knowledge of dynamos to know that they are current limited without a regulator, but no idea why)

Is it only because of the supercap that you're recommending regulation circuits etc.?

Presumably you're agreed that without a capacitor, you can just run the LEDs straight off the rectified AC current?

Anyone on here now who knows the answer to this?