Stuffing electronics into steerer tube and other questions

[rickson]

As soon as all the parts come in, I'll starting working on a dynamo system using circuit 8 in Pilom. Two SSC-P4s with 15 deg and 5x20 lenses and one Luxeon III red-orange with 5x20 for the rear. All will be wired in series.

As a continuation on the dynamo circuit with capacitors, I've got a few more questions as this is my first project. I am thinking about housing the electronics in the steerer tube. Do I need to drill any holes anywhere to have the wires routed properly?

I have one of those large soldering guns 140 watt. Will that suffice, or do I need a smaller one?

For that killer capacitor, is that the one in parallel with the LEDs? How about the tuning capacitors? Should I do away with capacitors altogether to be on the safe side?

What is the easiest housing to use with some consideration for aesthetics, considering a lack of metal working tools?

What gauge wire for DC would your run back to the tail light?

Thanks.

 

[Martin]

Hi Rickson,
on a suspension fork, the wires can in most cases run out the bottom of the steerer tube.
With a rigid fork, it's a different story; you might want to put the electronics in the headlight assembly or a small box, then. If you decide to go this way, you might find circuit 10 useful. It's a bit smaller.

Assuming you LEDs are on star PCBs, your solder gun should be fine (though I myself would pick a more appropriate tool for this job). For soldering, place the stars on a metal surface. Solder swiftly: If you are not done in 4 seconds, let them cool down and start over again. Protect the domes of the LEDs with a valve cap, to avoid hot tin and flux doing damage to them.

Correct, C1 is the killer cap. Being the author of Pilom, I believe that this won't kill if properly attached to the LEDs. I mean, if the wheels of your bike or the flyback capacitor inside your telly are not properly attached, you also run into trouble and this is why certain things in life just have to be properly attached...
I recommend you put C1 into the headlamp housing, this way it won't ever disconnect when an outside cable breaks. If it doesn't fit, you may split it into several smaller capacitors that connect in parallel.
You can leave out ALL capacitors, but will lose the doubler function so that you end up with circuit 1 and I don't think this is what you want. Just leaving out C1 I cannot recommend, as the remaining capacitors in conjunction with the switch produce surge currents and C1 is there to absorb these.

For the housing, I can recommend the sugar caster. You need some basic tools like vice, hacksaw, file, hand drill, taps, scissors, but no lathe. The result is very durable and the appearance is not all bad.
Since you will only put 2 LEDs, you might well be able to fit all electronics and the switch inside.

The wire gauge for the tail light is defined by the mechanical strength that you desire. With today's runtime of battery tail lights however, I'm tempted not to run a cable and use batteries, instead.

Good luck with your first project.

 

[rickson]

Thanks. No suspension fork here.

I guess if I am going to go for a tail light that the wire must be permanently connected to the front housing. Otherwise, a disconnect would risk a capacitor surge. Is that correct? I would like a strong rear tail light that could be visible for day riding.

Regarding soldering, the metal plate is for heat dissipation right? I guess that a granite slab surface would work as well.

The sugar caster idea looks nice in that it will hold the electronics as well. Was it difficult to cut the round aluminum heat sink?

 

[Martin]

Using two front LEDs, you will want to go for circuit 4 (circuit 3 will exceed the max reverse voltage limit of the red LED).
With this, there's no risk to any component should the tail light disconnect, short to ground or short to itself.
Neither is there such a risk in circuit 3, but as said, you want two front LEDs.

Yes, for heat dissipation to cool it down quickly after you finish soldering. Fine if your granite is flat on top.

Cutting the aluminium disc is no big deal with a vice, a hack saw, a file. It doesn't have to be beautiful around the edges, as it's inside the can. In 20 minutes, you are done. The most difficult part is cutting the can (if its stainless steel). But it doesn't have to be beautiful either, the edge that you cut hides inside.

 

[znomit]

Steerer tube is a nice place to store bits. You have to navigate your way around the star nut (or remove it) and get the wires in and out. You can probably run the wires in the top but it looks a little naff. At least all the ideas I had were.
I didn't put the circuitry in there on my road bike, there wasn't room above the tire for the wires. MTB was fine. Everything fitted nicely in a small plastic box that hides under the stem(now aero bars).
Capping the steerer tube with the appropriate switch is nice too.
Martins sugar caster is very elegant. If you can't find an appropriate caster it doesn't get much easier than this from ktronik. Dynamo housings are much simpler because you don't need to fit a driver or control switch in, and you don't need finning to cool when stationary.

 

[rickson]

Using two front LEDs, you will want to go for circuit 4 (circuit 3 will exceed the max reverse voltage limit of the red LED).
With this, there's no risk to any component should the tail light disconnect, short to ground or short to itself.
Neither is there such a risk in circuit 3, but as said, you want two front LEDs.

Following up on circuit 4, given that the Luxeon II red-orange has a voltage of 2.95, what is an appropriate resistance for the resistor in series? Also, it says that the tail light will be damaged if the front light is inadvertently disconnected. I guess this is better than all the leds being destroyed. Will this setup give me enough rear brightness somewhat close to a dinotte tail light? Wouldn't putting the tail light in series with the other LEDs be brighter? There are no enforced lighting laws here in California, so the brighter the better.

 

[rickson]

Steerer tube is a nice place to store bits. You have to navigate your way around the star nut (or remove it) and get the wires in and out. You can probably run the wires in the top but it looks a little naff. At least all the ideas I had were.
I didn't put the circuitry in there on my road bike, there wasn't room above the tire for the wires. MTB was fine. Everything fitted nicely in a small plastic box that hides under the stem(now aero bars).
Capping the steerer tube with the appropriate switch is nice too.
Martins sugar caster is very elegant. If you can't find an appropriate caster it doesn't get much easier than this from ktronik. Dynamo housings are much simpler because you don't need to fit a driver or control switch in, and you don't need finning to cool when stationary.

That switch looks like it was made for the bike. Very nice. Regarding ktronik's housing, the post doesn't describe what they actually are? Do they come like that and from where?

 

[Martin]

Following up on circuit 4, given that the Luxeon II red-orange has a voltage of 2.95, what is an appropriate resistance for the resistor in series? Also, it says that the tail light will be damaged if the front light is inadvertently disconnected. I guess this is better than all the leds being destroyed. Will this setup give me enough rear brightness somewhat close to a dinotte tail light? Wouldn't putting the tail light in series with the other LEDs be brighter? There are no enforced lighting laws here in California, so the brighter the better.

You are right, it wouldn't be very bright with a reasonable power loss in the resistor. It's definitely more efficient to put the red LED in series with the white ones (circuit 9):

To minimize the damage caused by a disconnect, you could connect C1 across the headlight LEDs only (in your case LED2 and LED3 as LED4..6 don't exist) and put it into the headlight enclosure. A disconnect/reconnect of the LED string will then only damage the tail light LED due to the energy stored in C4, C5. The same goes for short-circuit of the headlight. Short-circuit of the tail light won't do any damage.
If your tail light has sufficient space for a larger capacitor, connect one across LED1 and depending on its capacity, it might fully protect LED1.
An alternative approach to protection of the LEDs: Starting from circuit 9 above, add the overvoltage crowbar from circuit 12 (D5, T1, R17). In case of a disconnect, it will discharge C1 quickly and hence avoid damage upon reconnect. However, this won't help if some LEDs of the string get shorted out.

 

[rickson]

Understood. LED1 in parallel with capacitor but in series with the rest of LEDs which are in parallel with C1. 4700 uF for LED1 as well?

 

[Martin]

Understood. LED1 in parallel with capacitor but in series with the rest of LEDs which are in parallel with C1. 4700 uF for LED1 as well?

Well, if you can fit 4700uF in, this is great. It has to be IN the tail light enclosure, as not to give chance to a disconnect. Given the forward voltage of red LEDs (<2V), you can take a capacitor of the lowest voltage rating available. This saves space.

You might be tempted to use a GoldCap (large storage capacitor) but its impedance is too high to provide protection against this sort of surge.
You can however add a GoldCap in parallel to a regular electrolytic if you want a little bit of a stand light / safe-stop feature (though it will dim rather quickly without more complex electronics).

By the way, here's two more sugar shaker solutions:
Quad Cree XR-E and Triple Luxeon Rebel

 

[rickson]

Those magnetic spice tins look promising and only 2 inches tall. They come in a pack of 3 for only $4. They're only 2 inches tall. Does that mean no cutting?

Thanks for the links.

 

[Martin]

Those magnetic spice tins look promising and only 2 inches tall. They come in a pack of 3 for only $4. They're only 2 inches tall. Does that mean no cutting?

Thanks for the links.

I got one here, 5cm tall. It may not be the perfect size, but if it's a bit taller than needed, it's not a problem. If you still want to cut them, be aware there's a bulge 15mm from the end. So you either cut away at least 15mm or leave it.
Coming back to the sugar casters, these are stainless steel and a lot harder to cut. Well, 20 minutes with a Dremel and 5 cutting discs is not a big deal either.

The aluminium disc for the light engine you may simplify like this:
At a hardware store, check out the large washers. You may not get aluminium, might be brass (extra weight). Either you tolerate the hole in the center or you go through a pack of 1000 to find the one where the hole has been forgotten. You probably get this one for free..

If you intend to build more lights like this, you can also go to a hardware store that stocks 50mm massive aluminium rods and ask them to cut 10 slices, 5mm each. They have the right machine, it takes no time.

 

[rickson]

I've got 9 of those cans on order. Whatever I don't use will be for spices.

I might just stack two washers to raise the leds. The optics are 20 mm, so no problem fitting two in a can. Thanks for your information.