Right, first up, here’s a page on that there Internet. It’s a nice page because it means an idiot like me can avoid having to understand too much, and simply go to the leccy shop with a nice readymade list of transdinglers and thruppits to weld together at my leisure:

http://www.pilom.com/BicycleElectronics/DynamoCircuits.htm

For the moment, let’s refer to the first and simplest circuit, enigmatically named “Circuit 1”. This circuit is essentially the bit that sits between a dynohub and an LED to make one of them light up, hopefully the latter. Happy days.

Now, my first question is: Can I simply yank the diode out of that diagram and replace it with a single-LED head unit taken from any of the myriad lights (Magicshine etc) that are available? (ie are those head units free from other interesting stuff that will mean having to change the rectifier bridge?)

Second question, if the answer to the first is yes: does it then follow that the other modifications in that page are unaffected? (mainly interested in the smoothing and tuning capacitors in circuits 2 and 6)

Third question: how is all of this affected if I were to use a multi-LED head unit? (given that the hub is a constant-current source whereas the head units are designed for use with cells, ie constant voltage, I assume they would wire the diodes in parallel and if I wanted multiple LEDs I’d need to build my own circuit with the diodes in series)

If the answer to the first question was no, anyone got any pointers to info on how complex it would be to do any necessary modifications or build my own head unit from readily available parts?

Essentially I want to use this as a switched main beam in conjunction with a proper dip beam (which I already have), so the requirements are ~600lm of light in a symmetrical beam and no standlight – a combination for which there is (AFAIK) no out-of-the-box dynamo-ready unit (possibly the KTronic K-Lite, but that’s the only possibility I’ve found).

do a search for troutie’s 700 lumen light on here, someone made a dynamo version, might help.

http://robdeanhove.blogspot.com/

has some details plus there was a thread that rob posted to on here last week.

bobblehat made a dymo light on this tread

http://singletrackworld.com/forum/topic/diy-700-lumen-batteries-inside-light/page/31

Yeah, I’ve seen the Deanamo and the Exposure light and the Supernova E3, but they’ve all got standlights. That means they’re no good for what I want: when I flip the switch to dip beam I need the light to go out immediately. Also (and this is true of the K-Lite as well), they’re all going to be quite expensive 🙂

Bookmarks that page for future tinkering……..

1. Yes you can. Assuming you’re using a hub dynamo, they’re usually current limited (to about 500mA) so you’re unlikely to damage the LED.

2. Yes to smoothing but tuning may depend on the forward voltage of your LED which will probably be different to the ones in the circuit.

3. You can only get about 6v out of a dynamo under load so two decent LED is about all you’ll be able to drive.

Here’s my build:-
http://www.candlepowerforums.com/vb/showthread.php?310903-My-first-light-dynamo-powered

Note: this advice is worth what you paid for it.

Thanks Nick. Question 1 above is the key one. You’ve used “raw” LEDs, I notice – but you’re sure that a nice self-contained head unit will behave equivalently?

I’d like to avoid having to construct a head unit as I currently don’t have the tools/workspace to do it. For now hopefully I can limit the effort to a little plastic box with some jack sockets and some gubbins inside.

You’re also using two LEDs – is using just one equally feasible using Circuit 2/6 without blowing it up at high speed?

Q1 If by “yank the diode out” you mean use a single LED DealExtreme type head unit in place of the “LED 1 headlight” then yes, that is exactly what is intended. (after removing all electronics from head unit.)

Q2 The other mods should work just fine also

Q3 Adding LEDs should be done in series – circuit 7 is optimised for this – I guess it may work on the other ciruits but will not be optimal

Q3a All LED lights should be current controlled there is a constant current circuit in the DX headlight.This circuit must of course be removed.

I think you could do what you want but getting the dynamo hub to power two separate head units one of each beam type. Only one unit runs at a time and the power is fed to the head unit with a toggle switch, flick it one side to power one and the other way to swap lights.
However there will be a momentary period where no LED is powered and this may create a big spike of power on re-connection to the new head unit, this may be huge problem or insignificant – I dont know

“(after removing all electronics from head unit.) … there is a constant current circuit in the DX headlight.This circuit must of course be removed.“

Aha! So the answer to Q1 is no. Shame on you, Nick 🙂

Guess I need to see if I can find out how complex that gutting process is…?

Interesting point on the spike. Hmm.

Ah yes, didn’t read the question properly. You will need to remove any electronics and connect the LED(s) directly.

I suspect the spike issue is a real one.

Hm. I’m now leaning back towards fitting a dynamo-specific head unit. I think the only way of broadly achieving what I want would be to use another Cyo, but one without the standlight, and just angle it upwards. Not really an ideal beam (or lumen output) for this purpose, though.

Maybe I need to investigate the K-Lite. Bit spendy, though.

I’ve built that first circuit (for my rear light), and to be honest, if you don’t want a standlight, I wouldn’t bother building anything more complex. It is a bit flickery below about 3 mph, but you won’t need a high beam going that slowly anyway surely? It works fine in conjunction with the iq fly front light that I have.

Personally, if I could find / had a housing for 2 or 4 leds, I’d be tempted to try just taking the dynamo AC, and wiring it up across two (or maybe four) identical LEDs, with one being wired in each direction. I can’t see why that wouldn’t work – essentially you’d be rectifying the current, but each diode in the rectifier would be an LED. The LEDs have a low breakdown voltage of about 5v, but because the current flowing through the circuit is limited to 500ma, the voltage across the LED in the opposite direction will always be less than 5v, so it shouldn’t matter. Oh and obviously you’ll only get 500ma per pair of LEDs light output maximum. And they’ll flicker at low speeds. Basically it’s a disgusting hack relying on the current limited nature of the dynamo, but then so is my rear light, and that works fabulously well.

Oh and the magicshine etc. lights won’t work without clever circuitry as the LEDs used in them require 2amps, and the max a hub dynamo will put out is 500ma. I think that’s why high powered dynamo lamps tend to use 3 or 4 LEDs in series rather than one bright one.

You can only get about 6v out of a dynamo under load so two decent LED is about all you’ll be able to drive.

Not true. If all you could get was 6V, then it would work awfully with 2 LEDs in series – high power LEDs tend to be barely switched on at 3V. The voltage you can get out of one does depend on how fast you’re going, but with sufficient speed you can certainly run 4 LEDs in series at 500mA. The clever bit then is switching LEDs in and out of the circuit depending on how fast you’re going. Read down that page and you’ll see he makes that comment and has some circuits which either do that, or something even cleverer.

Oh and the magicshine etc. lights won’t work without clever circuitry as the LEDs used in them require 2amps, and the max a hub dynamo will put out is 500ma.

That is indeed the case for the single LED ones – the multi LED ones though will work fairly decently with 500mA through each LED.

Yeah, I’ve seen the Deanamo and the Exposure light and the Supernova E3, but they’ve all got standlights. That means they’re no good for what I want: when I flip the switch to dip beam I need the light to go out immediately

I have it on good authority (I made the Deanamo and have held the Exposure light) that both the Deanamo and the Exposure Dynamo (which was available to be seen at the recent London Bike Show) have switches that, when you flick them, turn off the standlight…..

Rob – my wife posted on your blog about an insight into your set up. Very interested in getting more info on your SP dynamo hub (as they seem quite rare at the moment) and Tout Terrian Plug set up.

Cheers

I don’t know about making lights but I’d love to hear about the Tout Terrain/Supernova Plug if you’ve used one Rob?

My random hijack…where could I get 4 leds for Joemarshall’s “design”.

The simplicity appeals greatly.

“I have it on good authority (I made the Deanamo and have held the Exposure light) that both the Deanamo and the Exposure Dynamo (which was available to be seen at the recent London Bike Show) have switches that, when you flick them, turn off the standlight….. “

Handy. Is that just the standlight, or the whole light? For what I have in mind I think it’d need to be the former, otherwise I wouldn’t be able to use a remote switch, in fact I assume I wouldn’t even be able to wire the thing in series at all.

I’d vaguely considered using an E-Werk or a Plug to power a DX-type head, but that just seemed a lot of money for an obscure solution 🙂

Information on the SP Hub:

http://www.facebook.com/pages/Intelligent-Design-Cycles/312101062142744?sk=wall

http://www.sp-dynamo.com/index.html

6-Bolt Disc and non-disk versions of the SP dynamo hub range are available from their ebay store HERE

CLICKY LINK

There’s a couple of words, pics and specs on my blog HERE

A pic of the full bike, and just how teeny the hub is, can be seen HERE

I’m a big fan of the SP hubs that are the lightest out there, as efficient as anything else available, and have extremely low drag when unloaded (not true of all older hubs available).

I’ve not tried the tout-terrain or plug devices, but I should imagine they’d work superbly with an SP hub as a lighweight touring set-up to charge a GPS, phone etc., there is no reason why it wouldn’t work and these devices have been designed to work with exactly the output the SP hub gives.

Hope that helps.

And now you can read a little bit about my dynamo light, the deanamo, on Fresh Goods Friday from this week!

CLICKY LINK

Cheers for the info Rob

You’re welcome Rik, I’m looking forward to seeing the finished bike and complete set up 🙂

No probs