Boost dynamo lights w/ DIY combo?

[TheFoo]

Hi all,

At the moment I ride with an Ay-Up battery headlight (2x3W) along with a home-made tail light (2x3W red Luxeon).

However I am putting together a new fast commuter / brevet bike which will be fitted with stock dynamo kit : the SON hub, Schmidt Edelux and B&M DToplight. This will allow me to jump on and ride through the night without the hassle of charging anything.

But, what I would like to do is boost the dynamo lights as follows:

- run one 3W red LED full time off the hub to reinforce the B&M taillight
- mount the Ay-Ups as a 'full beam' for descents/sign reading, again off the dynamo (but with a handlebar switch).

From what I understand about the SON hub, it will provide 6V/3W at a brisk walk and can put out 12V/6W at 12mph. My commute averages 18-20mph so in theory, when I'm not waiting at red lights the hub could provide 18V/9W (please correct me if I've got the wrong end of the stick!)

So, I am not so worried about meeting the overall requirements of the lighting system. However, I would really appreciate some help figuring out how to wire these elements together for best results at low speed (or pointing out any wrong assumptions I have made!)

Here are my thoughts so far:

I could just daisy-chain the Edelux, Ay-Ups (shorted by a switch) and the red power LED in serial.

If I'm correct, the Edelux is a 6V light system, while the Ay-Ups contains two 3W LEDs (2x 3.5V ) plus around 3V for the tail light. This makes a total load of 9V with the Ay-Ups switched out, and 15V with them switched in (so within my performance envelope).

However, when there is less juice available, I would like to maintain full power to the Edelux / DToplight, and cut what is drawn by the 3W tail light first (that way I have full-power lighting at all speeds, and the standlight won't be drawn down trying to boost the light while I'm still moving).

This sort of thing is where I start to come unstuck. I can solder things in serial or parallel, but that is the limit of my DIY mastery! :(

Is it straightforward to bias the circuit towards fulfilling the Edelux' demands first? Does anyone have any tips or pointers?

Thanks in advance!

PS. you can see a Youtube clip of my DIY taillight at http://www.youtube.com/watch?v=SzhNwT6RZCk

 

[unterhausen]

turns out it's not all that easy. You're asking for a switching scheme. This would have two independent drive circuits in a system that currently doesn't use a drive system.

 

[TheFoo]

Thanks unterhausen - I'm pretty sure that an extra manual switch would be a better option for me.

As an alternative, then, is there an easy way to reduce the power of the red LED permanently? I just looked at 1W LEDs for an alternative, but of course the voltage is the same - so it will still draw 3V/0.5A.

Could I wire the 3W LED in parallel somehow to reduce the voltage it sees - i.e. to consume 250mA at 1.5V instead (I really am a beginner at this stuff)?

Maybe I should just HTFU and pedal over 12mph always (or manually switch out the tail light when I'm riding up a steep hill)...

 

[Steve K]

Thanks unterhausen - I'm pretty sure that an extra manual switch would be a better option for me.

As an alternative, then, is there an easy way to reduce the power of the red LED permanently? I just looked at 1W LEDs for an alternative, but of course the voltage is the same - so it will still draw 3V/0.5A.

Could I wire the 3W LED in parallel somehow to reduce the voltage it sees - i.e. to consume 250mA at 1.5V instead (I really am a beginner at this stuff)?

Maybe I should just HTFU and pedal over 12mph always (or manually switch out the tail light when I'm riding up a steep hill)...

The Edelux may be the wild card in this equation. I generally like the idea of wiring lights in series to get more light, but I'm not sure what the Edelux's voltage-current relationship is.

My personal preference is to use a headlight built with two groups of two 3W leds. At low speeds, just two 3W leds are powered at 0.5A. At higher speeds, the second group of two 3W leds are added in series, for a total of 4 leds. Pretty simple, really. To be honest, for my commute, I'm pretty happy with just the two 3W leds.

I also use a series taillight, but use 5mm leds wired in parallel in order to benefit from their lower Vf. It's still quite bright, pretty cheap, and not very big. I also chose to only run half of the AC power cycle through the red taillight leds. The other half is conducted through a schottky diode. I do this because my commute includes a 14% grade, and I need to produce light at 3.5mph.

regards,
Steve K.

 

[TheFoo]

Actually, I just realised a pretty big flaw in my plan.

All off-the-shelf dynamo lights run on AC, while DIY lights use DC via a rectifier.

Unless I'm missing something, there's no way to run the Edelux in series with my own LEDs (can't combine AC and DC!) and if I put them in parallel, I'd only get 250mA. :(

Game over?

 

[jMud]

I have wired up an edelux with two extra LEDs in series. The edelux must have its own rectifier, which you won't have access to, so you'll have to add another one of your own. Just disconnect one of the leads from the SON and insert the new circuit there.

I believe the edelux has some circuitry that bumps up the current to 1A. I don't know if it affects the other LEDs or not. The addition of extra diodes just makes the whole set-up less efficient. I had a switch to short the whole DIY portion except for high speed decents, where the extra power for the LEDs and the wasted power for the diodes is abundant anyway.

Does anybody have a link to some free software for drawing up cicuits? - I'd be happy to sketch this out.

 

[unterhausen]

I think they are rectifying just like you are. I believe people run two commercial lights together all the time, and both have internal rectification.

As far as circuit software, you can get a non-commercial license for Eagle at cadsoft.

 

[TheFoo]

Thanks guys. I was out-thinking myself back there... assuming that the Edelux would be connected after my DIY rectifier and so getting DC when it expects AC! :oops:

If I understand correctly, what I need to do is build one of Pilom's rectified circuits for my tail light and (switched) Ay-Ups *only*... I can test this on the hub with the Edelux removed.

Then the Edelux and this DIY circuit are put in series, so both the rectifier and the Edelux are seeing AC?

Thanks!

 

[Humph]

At higher speeds, the second group of two 3W leds are added in series, for a total of 4 leds.

Steve, are you running the LEDs straight off the dynamo or through some smoothing caps. If so, how have you gone with the additional cap capacity requirements when you switch on the extra 2 LEDs.
Cheers

 

[markus_i]

The Edelux has an internal current doubler (roughly), which means that it'l look (_very_ roughly) like two series LEDs with a rectifier (and a few extras). As far as I know, you can also run the Edelux from DC, but need to take care of the polarity. Easier and safer option would be to wire all in series (although I doubt the need for the 3W rear LED, but it's your bike), with dedicated rectifiers for each light (group) and no other electronics (especially no drivers in the Ay-Ups). Then throw in a short circuit switch over each rectifier/light you want to shut off independently.

Or design a circuit that does the switching automatically, depending on the SON AC frequency, possibly using (freakishly expensive :-( ) optomos switches for the short circuiting and a PIC for the control. That's an idea that has been bounced around my head for a few years now, but somehow I just don't seem to get around to do it.

Bye
Markus

 

[Steve K]

Steve, are you running the LEDs straight off the dynamo or through some smoothing caps. If so, how have you gone with the additional cap capacity requirements when you switch on the extra 2 LEDs.
Cheers

I don't bother with extra circuitry. All I have is a bridge rectifier. The two leds are used at speeds as low as 3.5mph (my commute includes a 14% grade, and my recumbent is heavy), and I can still see where I'm going.

I know that Martin's circuits have their fans, but I never saw that the improvements justified the extra complexity nor the use of so many large capacitors. Heck, I'm not sure that I can even justify the use of four series leds, but they are installed, so I might as well use them. <grin>.

Steve K.

 

[TheFoo]

The Edelux has an internal current doubler (roughly), which means that it'l look (_very_ roughly) like two series LEDs with a rectifier (and a few extras). As far as I know, you can also run the Edelux from DC, but need to take care of the polarity. Easier and safer option would be to wire all in series (although I doubt the need for the 3W rear LED, but it's your bike), with dedicated rectifiers for each light (group) and no other electronics (especially no drivers in the Ay-Ups). Then throw in a short circuit switch over each rectifier/light you want to shut off independently.

Thanks markus!

As far as the rear LED goes, I have enjoyed far fewer close passes at night since I started running a rear power LED. I think because when motorists see a cyclist they know how close they can squeeze past, but a bright solid light looks too much like a bigger obstacle (much of my commute is unlit country roads so there are no streetlights to give me away).

When an LED costs just a few pounds, it's hard not to :)