Dynamo Lighting - fit and forget?

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andrew_s
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Re: Dynamo Lighting - fit and forget?

Post by andrew_s »

Greystoke wrote:Are LED lights really fit and forget? My 2 off 3w halogen dynamo lights worked fine this morning but my led head torch packed in.

Nothing is proof against failure, but dynamo LED lights are closer to fit & forget than halogen (not that they were all that bad). Most problems are wiring problems, which will be common to both.

The only failure I've had since I got my first Edelux in 2008 is a mudguard rear that I bashed the lens/reflector off (still had the bare LED though), and the only other thing I've done was the squeeze the spade connectors a little tighter. Most work required is installation niggles, or replacement by newer better models.
Before that, I'd had a Solidlight that failed such that it turned off at 10-12 mph, and wouldn't come on until I'd come to a complete stop, and a rear light with a duff standlight circuit.

With halogen lights there are the occasional bulb blowouts (or 5 £5-6 p.a. cost of preventive bulb replacement), and the ability to open up the light to replace the bulb is itself is a potential cause of failure (eg a broken catch allowing the front of the lamp to fall off).
MikeF
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Re: Dynamo Lighting - fit and forget?

Post by MikeF »

Brucey wrote:I have heard of folk carrying a dark-coloured plastic bag around with them to cover up the standlight.... FWIW I think that fully discharging a supercapacitor is considered to be 'bad for it'; my understanding is that (like most forms of electrolytic capacitor), they need to be 're-formed' when they are charged from fully flat, and each time this procedure is carried out there is a chance that the capacitor may suffer damage or even fail.

So of the two options

a) installing a shorting device or
b) installing a switch that isolates the capacitor

I fundamentally favour the latter approach, unless the former can be made to leave the capacitor with some (rather than none) in the way of charge in it (eg by using diodes in the discharge circuit, and of course series resistance to limit the peak current). Adding a shorting device is probably easier, in that it can be set in parallel with the capacitor, and requires no breaking of tracks on the circuit board.

cheers
The shorting device should be OK if it incorporated a resistor so that there isn't a "dead" short. Maybe incorporate a series diode as well so the capacitor isn't completely discharged.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
MikeF
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Re: Dynamo Lighting - fit and forget?

Post by MikeF »

Gattonero wrote:By the way, at the rear I've a B&M Secula which seems really good except one thing: the capacitor is inside and you can't switch it off :?
They do give a very good light, but are not that large. On one bike I have two: one each side of the bike wired in parallel. They seem to draw more current (at least when on a DC supply) than some other rear lights.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
edocaster
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Re: Dynamo Lighting - fit and forget?

Post by edocaster »

Here are a few images from my old Axa Pico 30. As outlined previously, it started to cut-out at speed. I'm loathe to chuck it just yet - maybe the teardown will help someone.

I was surprised that the whole thing came apart from unscrewing just one screw. There were no seals and no real waterproofing whatsoever. Nevertheless, there's no corrosion or water damage (I used mudguards). You can see the rear casing at the top, and the (acrylic) lens to the left.
IMG_20181201_182650s.jpg


The lens could perhaps be used in a modded torch, but the Pico's LED is indeed pico, smaller than most modern power LEDs.

Not much going on at the back of the circuit board. One 1F 5.5V coin capacitor. There was enough space to fit three times as many.
IMG_20181201_182743s.jpg


Here's the front of the circuit board. I can't see any smoothing capacitors. Just the rectifier ('S125'), one large resistors, two small resistors, what looks like a transistor ('tw1 29'), and an unidentified two-terminal chip with markings scrubbed off (a diode?).
IMG_20181201_182847s.jpg


...and a shot with the traces a little more visible.
IMG_20181201_184335s.jpg


I think sketching out a circuit is beyond me. I'll try this at Candlepowerforums too, but hopefully this helps someone with the appropriate knowledge.
Greystoke
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Re: Dynamo Lighting - fit and forget?

Post by Greystoke »

Are the Axa Pico lights any good? Everyone seems to think so.
What's the beam like?
robc02
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Re: Dynamo Lighting - fit and forget?

Post by robc02 »

robc02
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Re: Dynamo Lighting - fit and forget?

Post by robc02 »



It looks like a fairly simple circuit, probably just a bridge and linear regulator circuit.
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mjr
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Re: Dynamo Lighting - fit and forget?

Post by mjr »

Greystoke wrote:Are the Axa Pico lights any good? Everyone seems to think so.
What's the beam like?

They're OK. We've had three in the shed: one snapped in two in a crash (they're mostly plastic) and one has a slightly dicky wiring connector, but it and the newer one keep working and only seem to need a wipe over every so often. As mentioned elsewhere, no signs of corrosion despite having little obvious waterproofing (I've only used them above mudguards, though.)

They're 30 lux, which is almost the minimum I want for cycling along unlit country roads at touring speed. Even so, I slow a bit for sharp corners because of how the beam fades to the sides.

I've not found a good way of photographing the beam shape while moving (mine's a dynamo light so only a weaker standlight when stopped). I think I'd describe the beam as a broad inverted U shape with a rapidly-fading brighter narrow V in the centre, so there's a brighter zone directly where your front wheel is pointed and more overspill directly ahead than some other road-shape beams like Crivit, which is useful for illuminating reflective signs, without being dazzling. It's also a lot more evenly distributed than my very old British Standard light's beam shape, which always felt like someone had drawn the light patterns onto the road with sweeping curves.

In short, it works - it won't be troubling the expensive lights from B+M or similar, but I think I paid £13 for it 5 years ago, so it's been excellent value.

Edit: the current Pico 15 is 15 lux. The Blueline 30 may have replaced the old Pico. €15 at bike-discount just now. Axa are annoying with their product range sometimes!
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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edocaster
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Re: Dynamo Lighting - fit and forget?

Post by edocaster »

mjr wrote:Edit: the current Pico 15 is 15 lux. The Blueline 30 may have replaced the old Pico. €15 at bike-discount just now. Axa are annoying with their product range sometimes!


Honestly, for them to release a 15 lux version they would have to purposefully gimp the 30 lux version. These lights have to run at 6v, and it's actually more hassle trying to force the light to take less current. I hate it when manufacturers go out of their way to reduce functionality.

For the Pico 30, I would say that I really like the beam pattern. It's not as sharply defined as the B&M Cyo, but has a nicer 'patch' in front of the bike. But, really, it could do with being about twice as powerful. Looking at the tiny LED, it's SMT and mounted on a board with no heatsinking. There's no way it is built for 2.4-3.0W, so I would say Axa went with minimum thermal design and kept everything else for lights further up the range.
Brucey
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Re: Dynamo Lighting - fit and forget?

Post by Brucey »

FWIW I have had a 3W rated headlight LED fail by simply getting a bit too hot for a bit too long; the wafer was held (inside the package, to make electrical and thermal contact to an alumina plate behind) by a plastic overmoulding, and over time the overmoulding just relaxed its grip. This allowed an intermitted contact to occur at the back of the wafer and the effect was that the headlight became intermittent.

cheers
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The utility cyclist
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Re: Dynamo Lighting - fit and forget?

Post by The utility cyclist »

mjr wrote:
Brucey wrote:I have heard of folk carrying a dark-coloured plastic bag around with them to cover up the standlight....

Me! I don't like to show a red light on a railway platform.

I would think it would be against the railway by-laws to have a red light on a platform in any case so you do right.
edocaster
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Re: Dynamo Lighting - fit and forget?

Post by edocaster »

I finally had a chance to sketch a circuit diagram for the Pico 30. It might have a few errors and non-standard symbols, unfortunately:

IMG_20181227_205608s.jpg


The above was achieved by looking at the traces and a bit of prodding around with a multimeter.

I was surprised the transistor was on the AC side of the circuit. I imagine it will reach some kind of equilibrium if the voltage is too high. But the method of operation eludes me. Time to learn more about transistors!
jb
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Re: Dynamo Lighting - fit and forget?

Post by jb »

Wouldn't the transistor put it into a dead short when switched on?
Cheers
J Bro
Brucey
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Re: Dynamo Lighting - fit and forget?

Post by Brucey »

that is how 'crowbar' circuits work I think. Hub dynamos are current-limited anyway, so this means of limiting the voltage is actually quite a neat arrangement. Also, isn't shimano's voltage regulator gizmo similarly configured?

cheers
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jb
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Re: Dynamo Lighting - fit and forget?

Post by jb »

Ah, I was confused as there is nothing in a hub generator apart from the windings - but if I understand correctly, it's the winding configuration that limits the output current?
Cheers
J Bro
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