Author Topic: Rear dynamo light compatibility  (Read 581 times)

Rear dynamo light compatibility
« on: October 21, 2019, 05:39:29 pm »
I've searched and searched and searched, but for the life of me I can't work out what rear lights are compatible with my B&M Lumotec IQ2 Luxos U.

Can anyone explain?

I'm not very impressed with the build quality of B&M lights so far, so I'm hoping for something a bit sturdier on the back (SON perhaps?).

Re: Rear dynamo light compatibility
« Reply #1 on: October 21, 2019, 06:31:54 pm »
any nominally 0.6W, 6V dynamo light will work.  The (simple) reason you won't find much discussion/description about this is that pretty much all rear dynamo lights are made to (sort of) meet this specification.

There is a much more complicated reason instead/as well (which varies a bit with the situation, and becomes important if you run the rear light only from the generator), but you probably won't be interested in that.

cheers

fuaran

  • rothair gasta
Re: Rear dynamo light compatibility
« Reply #2 on: October 21, 2019, 07:01:35 pm »
Yes, any of the B&M and SON dynamo lights should work together.
So long as you have a wire with the right sort of connections. Can crimp spade connectors on, if you want to plug it into a B&M front light.

Think some of the Supernova lights are a bit non-standard. ie the standlight for the rear uses power from the front. Would probably still work with a B&M front light, but without a standlight.

Re: Rear dynamo light compatibility
« Reply #3 on: October 21, 2019, 08:31:06 pm »
I see – thanks!  What confused me was the lack of information about the voltages accepted by rear lights, and the voltage produced by the B&M Lumotec.  I couldn't even figure out if the Lumotec produced an AC or a DC output from the rear light terminals – such is the dearth of information ???

Anyhow, that's good news – I will treat myself to a SON rear light :)

As for B&M, I'm especially unimpressed by the gaping holes in the bottom of my recently purchased B&M Secula light, through which I'm apparently supposed to attach unfinished wires to bare metal terminals? :-\ The frame attachement is so flimsy that I wouldn't trust it still to be on the bike at the end of an audax.  The Lumotec has worked well so far – I'm just hoping it doesn't die from exposure as well, like some others have reported...

Re: Rear dynamo light compatibility
« Reply #4 on: October 21, 2019, 08:40:42 pm »
There is a much more complicated reason instead/as well (which varies a bit with the situation, and becomes important if you run the rear light only from the generator), but you probably won't be interested in that.

cheers

Actually, I am interested ;D Would you mind elaborating?

Re: Rear dynamo light compatibility
« Reply #5 on: October 21, 2019, 08:45:18 pm »
Front dynamo lights just pass through the same AC waveform they’re getting from the dynamo. There’s no spec for it because it’s all standard.

*Except* the Luxos U passes through half rectified AC, which for some rear lights only works if the wires are connected in the same direction. But it’s easy enough to swap them over.

Re: Rear dynamo light compatibility
« Reply #6 on: October 21, 2019, 08:54:32 pm »
Front dynamo lights just pass through the same AC waveform they’re getting from the dynamo. There’s no spec for it because it’s all standard.

*Except* the Luxos U passes through half rectified AC, which for some rear lights only works if the wires are connected in the same direction. But it’s easy enough to swap them over.

My electronics is pretty rusty – does this mean that the power available to the rear light is lower than for plain AC? Presumably it would be rectified again somehow in the light's electronics?

fuaran

  • rothair gasta
Re: Rear dynamo light compatibility
« Reply #7 on: October 21, 2019, 08:58:28 pm »
As for B&M, I'm especially unimpressed by the gaping holes in the bottom of my recently purchased B&M Secula light, through which I'm apparently supposed to attach unfinished wires to bare metal terminals? :-\ The frame attachement is so flimsy that I wouldn't trust it still to be on the bike at the end of an audax.  The Lumotec has worked well so far – I'm just hoping it doesn't die from exposure as well, like some others have reported...
Doesn't it have a pair of male spade connectors? So crimp a pair of 2.8mm female spade connectors onto the end of the wire, then plug it in. Should be fairly secure, if you crimp it properly.

Or it seems the Secula includes a pair of plastic connectors, so c can use those to hold the wire, instead of spades.
https://www.youtube.com/watch?v=HLf1dDsSyLo

quixoticgeek

  • Mostly Harmless
Re: Rear dynamo light compatibility
« Reply #8 on: October 21, 2019, 09:17:31 pm »
I'm not very impressed with the build quality of B&M lights so far, so I'm hoping for something a bit sturdier on the back (SON perhaps?).

I have 2 B&M rear lights, one dynamo, one battery, I think it's the secula. One on each seat stay. Despite occasionally being knocked into the spokes, having been to Hell and back, across Pavé, gravel, offroad, Belgium, -6°C, and 43° heat. They have survived great. Absolutely no complaints about build quality.

I have them paired with an Edelux II at the front.

J
--
Beer, bikes, and backpacking
http://b.42q.eu/

Kim

  • Timelord
Re: Rear dynamo light compatibility
« Reply #9 on: October 21, 2019, 09:43:22 pm »
Front dynamo lights just pass through the same AC waveform they’re getting from the dynamo. There’s no spec for it because it’s all standard.

*Except* the Luxos U passes through half rectified AC, which for some rear lights only works if the wires are connected in the same direction. But it’s easy enough to swap them over.

My electronics is pretty rusty – does this mean that the power available to the rear light is lower than for plain AC? Presumably it would be rectified again somehow in the light's electronics?

Yes, but it's not an issue in practice, because the rear light only draws a small fraction of the power available anyway.
Careful, Kim. Your sarcasm's showing...

vorsprung

  • Opposites Attract
    • Audaxing
Re: Rear dynamo light compatibility
« Reply #10 on: October 21, 2019, 09:47:25 pm »
Front dynamo lights just pass through the same AC waveform they’re getting from the dynamo. There’s no spec for it because it’s all standard.

*Except* the Luxos U passes through half rectified AC, which for some rear lights only works if the wires are connected in the same direction. But it’s easy enough to swap them over.

My electronics is pretty rusty – does this mean that the power available to the rear light is lower than for plain AC? Presumably, it would be rectified again somehow in the light's electronics?

Yes

If you google "What is half wave rectification?" you can see that it is just a much more spikey waveform than that produced by a bridge rectifier

The rear light will have large capacitors in it though and should be able to convert it to DC

I ran a Luxos U with a B&M Seculite Plus on PBP if that's any help

I have never had any problems with any B&M front and rear lights in any combination.  I would guess if you have a 1.5W generator hub that might be more likely to cause an issue.  I only have the 3W ones

Sorry, I should have said "more lightly", missed pun opportunity
Audaxing Blog follow @vorsprungbike on

Re: Rear dynamo light compatibility
« Reply #11 on: October 21, 2019, 11:02:42 pm »
There is a much more complicated reason instead/as well (which varies a bit with the situation, and becomes important if you run the rear light only from the generator), but you probably won't be interested in that.

cheers

Actually, I am interested ;D Would you mind elaborating?

Most front lights pass on AC to the rear light, and the rear light sorts its own standlight etc out (if it does something different it will normally make it clear in the instructions).  However it matters if the front light is there or not.

Generators of the hub dynamo variety produce a (no-load) voltage which is roughly proportional to the speed of rotation (some have been measured over 100V AC).  However they have very much finite internal resistance and there are other tricks which are played internally which mean that (to a first approximation)  the generator won't produce more than a certain amount of current, and that the speed at which that current is produced varies with the load that is driven by the generator.

The usual spec to which generators are made is the Stvzo (German) spec.  This spec (IIRC) calls for generators to be able to drive into a (purely resistive) 12 ohm load and that a nominal 3W (no more and no less within defined parameters) is produced over a wide range of road speeds.  Another requirement is that more than a certain percentage of 3W is produced  at some low speed, (something like 80% @ 12kph springs to mind, but do look it up if you are interested).  This spec has been in existence for many decades and (along with rules that said battery lights were verboten) essentially meant that for a long time all German bicycle lights were the same; a 3W generator system. Most other countries in Europe to some extent harmonised their regs with the German standard which (amongst other things) meant the original Sturmey Archer dynohub went out of production sometime around 1980.

  You can tell if a generator(or other lighting component) meets Stvzo regs because it will be marked with a number " ~K***" .  in recent years they have relented; some battery lights are now legal in Germany and so are nominally 1.5W generators.


Anyway if you connect a 12ohm load to a typical 3W hub dynamo it will perform to (or close to)  Stvzo standards.  Thing is, modern LED lights are not like 12 ohm loads; they quite often don't conduct at all until a certain threshold voltage is reached and when they do there is a relationship between voltage and current that varies with speed in a different way. The upshot of all this is that

1) you normally get a greater fraction of the nominal light output at low speeds and
2) if the LED in the headlight isn't able to use all the current produced by the generator, there will be some kind of voltage regulation built into the headlight.
3) As long as the headlight is working normally you shouldn't get much more than 6V AC down the wires that go to the rear light.
4) Provided you are happy that you are going to be riding fairly swiftly, you can wire two nominally 6V headlights in series and they will illuminate (giving about twice the usual power), just at higher speed than normal. [If you use this scheme it is important that you wire the rear light in parallel with one light, not both.]

So in essence by loading up the generator the front light exerts a strong influence on the voltage that is passed to the rear light. Without that load, the  voltage would be way higher.

So read the weasel words in the rear light instructions carefully; there are three main variations

1) rear lights that make no mention of voltage regulation; if the front light fails these lights will usually blow up instantly
2) rear lights that have voltage regulation that is suitable for temporary use.  These will survive a short period of 'rear light only' running but not more than that (not reliably anyway)
3) rear lights that are designed to operate in isolation, i.e. without a front light at all.

So depending on what you want to do a light of the second or third sort is probably  the better choice.  If not then a loose wire or something might cause the rear light to blow up, which would be a PITA.

The third sort will cope with voltages that can be about ten times higher than normal; many recent B&M designs are of this type, but not all.

hth

cheers



FifeingEejit

  • Not Small
Re: Rear dynamo light compatibility
« Reply #12 on: October 21, 2019, 11:50:35 pm »
I see – thanks!  What confused me was the lack of information about the voltages accepted by rear lights, and the voltage produced by the B&M Lumotec.  I couldn't even figure out if the Lumotec produced an AC or a DC output from the rear light terminals – such is the dearth of information ???

Anyhow, that's good news – I will treat myself to a SON rear light :)

As for B&M, I'm especially unimpressed by the gaping holes in the bottom of my recently purchased B&M Secula light, through which I'm apparently supposed to attach unfinished wires to bare metal terminals? :-\ The frame attachement is so flimsy that I wouldn't trust it still to be on the bike at the end of an audax.  The Lumotec has worked well so far – I'm just hoping it doesn't die from exposure as well, like some others have reported...
I drowned a Secula... I mounted it upside down to solve a mounting issue I had.
The rain got in the holes round the connectors that day.
The road flooded at Ettrick Bridge between the first and last finishers riding it (around 3 hrs), it rained incessantly.
Other than the rubbish switch on early model battery versions I haven't had any other problems with the Secula I have...
Except for the mounting demanding perfectly circular seat stays which one of my bikes doesn't have, but I sorted that by putting it on the seat post and using a top light that is mounted to my bagman when I'm using that.



Sent from my BKL-L09 using Tapatalk


Re: Rear dynamo light compatibility
« Reply #13 on: October 22, 2019, 08:33:09 am »
I'm not very impressed with the build quality of B&M lights so far, so I'm hoping for something a bit sturdier on the back (SON perhaps?).

I have 2 B&M rear lights, one dynamo, one battery, I think it's the secula. One on each seat stay. Despite occasionally being knocked into the spokes, having been to Hell and back, across Pavé, gravel, offroad, Belgium, -6°C, and 43° heat. They have survived great. Absolutely no complaints about build quality.

I have them paired with an Edelux II at the front.

J

Maybe I'm being too harsh on it!  The Secula is currently flapping around on the seatstay – I've pulled the cable tie as tight as I can and shimmed it out with a section of inner tube, but it still doesn't feel very secure.  The bolt that secures the light on its axis of rotation, well... doesn't.  It holds itself up, but I'm not confident that it would remain pointing in the same direction after a bit of rough and tumble.

Do you have any specific tips about mounting it, or am I just not having enough faith in the light?

I'm also annoyed that it's not waterproofed – surely that's not difficult to do? A bit of glue would do the job. As it is, they've left the light's internals completely exposed through the holes in the bottom.  The rubber lugs supplied might help a bit, but it's still a lousy solution.

Cudzoziemiec

  • Dormant but requires tea
Re: Rear dynamo light compatibility
« Reply #14 on: October 22, 2019, 08:54:05 am »
As for B&M, I'm especially unimpressed by the gaping holes in the bottom of my recently purchased B&M Secula light, through which I'm apparently supposed to attach unfinished wires to bare metal terminals? :-\ The frame attachement is so flimsy that I wouldn't trust it still to be on the bike at the end of an audax.  The Lumotec has worked well so far – I'm just hoping it doesn't die from exposure as well, like some others have reported...
Doesn't it have a pair of male spade connectors? So crimp a pair of 2.8mm female spade connectors onto the end of the wire, then plug it in. Should be fairly secure, if you crimp it properly.

Or it seems the Secula includes a pair of plastic connectors, so c can use those to hold the wire, instead of spades.
https://www.youtube.com/watch?v=HLf1dDsSyLo
I've got a Secula and as Fuaran says, it should have a pair of spade connectors on the underside. If they're missing then there might be gaping holes, and that's wrong! As to which connector is which, in practice it doesn't make any difference, although B&M instructions tell you to connect them a certain way round.
At some point in the ride, you might find yourself in Osaka with Spanish speakers where you had expected Edinburgh talking Greek. This does not mean you are lost, or even off route.

Re: Rear dynamo light compatibility
« Reply #15 on: October 22, 2019, 09:39:47 am »
The Secula is designed for seatpost mounting and even in that role it’s not particularly convincing. So the narrower the bar you mount in on the worse it is. I drilled a couple of small holes in mine (on a rack stay) and cable tied it to an adjacent mudguard stay to keep it pointing the right way.

Re: Rear dynamo light compatibility
« Reply #16 on: October 22, 2019, 10:38:53 am »
I have a dynamo light that is P-clipped to the seatstay and it is always getting knocked. That the clamp is not tight enough to prevent movement probably saves it from damage. As it happens it can't swing too far inwards because it hits the brake cable (cantis at the rear). If this gets bad enough it interferes with the brake.

With lights (with plastic housings) you have to either mount them so they can take a knock and move out of the way, or not knock them. If you mount them rigidly and they are knocked, they break.  I have seen countless broken lights that were knocked; the  brackets are commonly about x10 stronger and stiffer than the housing that they are attached to.

cheers

Kim

  • Timelord
Re: Rear dynamo light compatibility
« Reply #17 on: October 22, 2019, 12:41:26 pm »
I'm also annoyed that it's not waterproofed – surely that's not difficult to do? A bit of glue would do the job. As it is, they've left the light's internals completely exposed through the holes in the bottom.  The rubber lugs supplied might help a bit, but it's still a lousy solution.

In general, it's easier to prevent water damage by providing a route for the water to escape through than it is to seal things well enough that water doesn't get in in the first place (it's easy to make things adequately splashproof, but keeping moisture from finding its way in and condensing over a wide range of temperature and humidity is Hard[1]).  If you've got an enclosure with wires going into it, imperfect waterproofing will generally cause it to fill up with water.


[1] Except in the case where the device generates a reasonable amount of heat, and is never switched off.
Careful, Kim. Your sarcasm's showing...

FifeingEejit

  • Not Small
Re: Rear dynamo light compatibility
« Reply #18 on: October 22, 2019, 12:49:57 pm »
My supposedly waterproof edelux2 I vested moisture The same day as I drowned the Secula, it took all summer in  the sun porch for it to finally dry out, considering it was this time last year I drowned it...

The B&M Ixon-Is i have have both ingested moisture but also dried out without any assistance. And my other Seculas despite signs of water penetration at the power lug holes are both working nicely. It's the crud the water carries of the road that's built up.

Sent from my BKL-L09 using Tapatalk


Re: Rear dynamo light compatibility
« Reply #19 on: October 22, 2019, 01:50:31 pm »

I've got a Secula and as Fuaran says, it should have a pair of spade connectors on the underside.

Mine hasn't ever suffered from water ingress. I wonder if the muduard flap has anything
to do with surface water not getting splashed upwards the light?

Re: Rear dynamo light compatibility
« Reply #20 on: October 22, 2019, 01:52:36 pm »
I'm also annoyed that it's not waterproofed – surely that's not difficult to do? A bit of glue would do the job. As it is, they've left the light's internals completely exposed through the holes in the bottom.  The rubber lugs supplied might help a bit, but it's still a lousy solution.

But it is a lot cheaper than either:-

a, Properly sealing the case OR
b, sealing the electrics in resin.

You could always use some silicone sealant on the wire terminals, But it would be vulnerable to changes in barometric pressure.

Re: Rear dynamo light compatibility
« Reply #21 on: October 22, 2019, 08:01:41 pm »
There’s generally a thin layer of resin over the circuit board (“conformal coating”) that stops moisture corroding the tracks away or affecting the electronics too much.

With lights (with plastic housings) you have to either mount them so they can take a knock and move out of the way, or not knock them. If you mount them rigidly and they are knocked, they break.  I have seen countless broken lights that were knocked; the  brackets are commonly about x10 stronger and stiffer than the housing that they are attached to.

The mudguard-mounted rear light on my Motobecane has a separate metal guard around* it that you’ll bash before you hit the light. It also has a cracked rear mudguard, so you can’t win.

(* the housing is missing in this picture because I was in the middle of figuring out how to wedge an LED in there)