Standlight circuits (Will this circuit work?)

[jdp298]

I'm not sure why there are zeners in parallel with the LEDs.

Because that's what the datasheet says on page 13. So it's not like I can get rid of them.

The LDO isn't doing anything that R2 can't do. I'd get rid of the LDO

Would agree completely, but the prototypes of the ones on the current bikes never lasted. It was only when I added the LDOs that I got decent run-time. However in this case you're probably right and I'm not (as usual):sigh:

I'm not sure why the current is being limited to 370mA

I've cocked up there. Datasheet says 6v for 400ma = 2.4W. That's as much power as I want, since there's at least 0.5W going to go into the Lucas 525 motorbike light housing at the rear and it's a 3W hub. Having a conceptual struggle here with Ohm's law. Give us a hand????

 

[Steve K]

that's a rather unique LED. Strictly for motorcycle apps? It does seem to need a specific optic or reflector design to get a good beam.
The built-in zeners do explain how it achieved a 8kV ESD rating.

The LED is rated for 1.5A, so that's not a reason to limit current to 400mA.
Adding a series resistor will increase the voltage that the dynamo produces.

Using data taken by Nick Ray for the SON28, and just assuming that the speed is 15mph, to limit current to 400mA, the total resistance needs to be 30 ohms, and the dynamo will output 12.4Vrms. The dynamo will be producing close to 5 watts, which means that you'll be burning up about half of that power in the resistor.

If you just let the dynamo source current into the dynamo, then it only has to produce 3 watts or so, and will produce less drag while creating a small amount of extra light. The bigger factor might be that you won't have to burn up 2.5 watts of extra power in the light and have a larger heatsink to get rid of the heat.

Fortunately, it's not too hard to play around with resistors and see which you like better.

Some of these calculations can be tricky because the dynamo isn't a simple voltage source and it's not a simple current source. It can be modeled as a variable voltage source in series with an inductance and resistance, where the voltage source varies linearly with the speed. Without spending a fair bit of time taking "lab" data, you end up making educated guesses about what will come out of the dynamo.

edit: taillight?? I just noticed that part. That can affect things a lot too. It needs to be part of the calculations; specifically, the design for the taillight needs to be considered in order to provide the correct power to it while sending the right amount of power to the headlight.
Life was simpler back in the incandescent days.
<end of edit>

 

[jdp298]

It is a pretty unique LED, but appears to be the latest and greatest in Busch & Muller front lights, hence I'm pretty interested in it.

The 2 tail-lights use my (not) patented LDO solution with their own bridge rectifiers. This way if anything stops or rattles out of place, I only lose 1 light, not everything. On the potholed road of London, it took 8 months of repairs to lock down something that didn't shake loose or break wires somewhere in the process. 3 bridge rectifiers on different lights was a price worth paying several times over when reduced to a single tail light 6 miles from home.

 

[Steve K]

so your taillights are current-limited? If so, then it shouldn't matter if the headlight allows the dynamo voltage to increase.
Plus.. since it sounds like the taillights are connected in parallel with the headlight, they will draw current that will cause the dynamo voltage to decrease.
My guess is that you won't need a current limiting resistor in the headlight, but a quick experiment should show whether it is needed or not.

 

[jdp298]

Thanks Steve. Whether I use a resistor or not kind of depends on whether the rear lights suffer from having all the power taken by the front. When I ran a commercial halogen front in parallel with a home-built LED one, it was very noticeable how much more light I got when the halogen was switched off.

Should I use the twin transistor current limiter at the front?

 

[Steve K]

You don't happen to have the schematic for your taillights, do you?

If your taillights are designed to draw 100mA (that is the standard, isn't it?), then there will be 400mA (or somewhat less) left over that will go to the headlight. No need for further current limiting.

Putting current limit circuits in each of the lights could be problematic. If, for instance, the taillights are limited to 100mA and the headlight is limited to 300mA, the total draw will be 400mA and the dynamo voltage will rise to the point where the output current is 400mA. This will most likely be a point where more total power is produced, meaning that more power is wasted in the current limit circuits. It works, but is rather wasteful (and engineers get extremely OCD when it comes to efficiency).

I'm still thinking back a post or two to the part where a light failed because it didn't have the LDO. Assuming that the LEDs are rated for more than 500mA, I can't see how anything would fail. ... .. unless the series resistor was a small part that couldn't handle the power? i.e. it turned into a small black lump of coal? I've seen a resistor do this when asked to handle about 5 times the power it was rated for, and it did turn black, but still worked. I was stunned. It seems unlikely to happen for the resistor between the supercap and lower LED.

 

[jdp298]

Yes to the schematic, but it's almost easier to describe (that's also the front light version). Bridge rectifier, zener clamp, 5.5v supercap, LDO, resistor, LED(s). The Lucas 525 now has 11 x 8mm red LEDs which got me to 0.5W, and there's a copy with single LED in the mudguard light. The single die in the pic was replaced pretty soon after as not nearly good enough to fill the lens.

And when you ask about the zener value, the supercaps from Maplins do say it's ok. 5 years and 8k5 miles later they still are.

Oddly I don't mind spending a bit of wasted power to get the rear lights on full early, and not affected by the front drawing all the power. That's the choice this engineer is comfortable with.

So when you say an LDO failed, clearly I wasn't making sense. All the lights have an ultra-low LDO, or multiple in parallel to get the current capacity. What would break would be a wire, usually in the housing, or something soldered onto the vero-board. Non-suspended bike on high pressure tires on shoddy roads. I ended up with a lot of blu-tac and tape holding things in place to stop it shaking itself to bits, but every time I thought I'd cracked it, a week later it'd go somewhere else. So it was a routine of stuffing in packing peanuts, they'd flatten and 3 days later one of the fronts would stop. I also cracked 3 calliper light mounts in the process.

 

[Steve K]

hey, I just noticed that your signature mentions a Cruzbike... how do you like it? I've got a couple of 'bents myself... both Bacchettas.

okay, back to the electroncs!

The schematic for the taillights would be okay as long as the headlight is happy getting no more than 6.5V or so. However, your schematic for the headlight shows that you need roughly 6.6V just for the LEDs, and need some more voltage for the schottky diode and the series resistor.

Practically, you only need to limit the voltage at one place. Everything connected in parallel will then be limited too. My inclination would be to use the headlight LEDs to act as the voltage limiter, since they are already connected to heatsinks and can absorb all of the dynamo's current. In this scenario, I would then just pick out a series resistor value at the taillight(s) to limit its current.

changing subjects to the LDO again... if the LDO didn't fix anything, then why not replace it with the resistor that is already in the circuit?

Wire failure is a big concern. I think my pictures show that I use plasti-dip inside my lights to provide water immunity (to a degree) as well as to keep the wires from moving and vibrating. Outside of the lights, I keep the wires tied to the bike's structure at regular intervals. This is a result of my experience working on aircraft, which required that all wire bundles be secured at regular frequent intervals.

by the way, have you ever played with circuit simulation? This would be an excellent tool for trying out different ideas for this light.

 

[jdp298]

Just got the frameset, building up components now. Shimano 3N30 built up now at the back, and Sturmey Archer 8-sp at the front on order. Pedals arrived today for the 33T chainset. Not yet ready to ride.

The front schematic is merely a proposition, so content to change whatever. Proviso that the rear light design will almost certainly endure and have to coexist with whatever we come up with for the front.

The point of the LDO is to let me charge a supercap to 5.5V on one side of it, while its output is 3v which I use the resistor for. It's the simplest way I've found to maximise the use of the energy available in the supercaps.

 

[Steve K]

my only issue with the front light design is putting a zener diode in parallel with the supercap. Instead of drawing less current when the supercap is charged, it will continue to draw current through the zener. That's not a good thing.

The approach of the simple standlight circuit is to use the two LEDs to clamp the voltage, and then use a suitable diode to drop enough voltage to limit the supercap charging to a safe voltage. This lets (almost) all of the dynamo current go to the LEDs once the supercap is charged.

 

[jdp298]

Happy; so ditch R1, the LDO, the zener and replace SD1 with a normal diode to get the voltage down to something that won't hurt the supercaps?

 

[Steve K]

for the sake of argument, I threw together a simulation with a headlight and taillight. Both the headlight and taillight have a bridge rectifier and 2F supercap. The taillight has a resistor to limit the current, and the headlight gets the remainder of the current. The headlight LEDs and series schottky clamp the dynamo voltage.

The simulation shows roughly 100mA for the taillight, and the rest goes to the headlight. The simulation is having trouble converging, though. It was working fine with just the headlight though. If any LT Spice experts are reading this, I'd appreciate some suggestions.

The screenshot of the simulation is here:
https://www.flickr.com/photos/kurtsj00/25395618601

and a quick & small version of it....

 

[jdp298]

Steve, that's some excellent work you've done out of the goodness of your own heart. Would it make a difference to insert the zeners inherent in the front LED? Them being there was the only reason I inserted the Shottky.

 

[Steve K]

well, I've been using LT Spice for other dynamo light circuits and for developing a better model for the SON dynamo. I'm still working on figuring out why it seems to hang up at some key points of the simulation too..

The zeners won't/shouldn't affect anything, so that's why I left them out of the simulation.

If I ever get the simulation to work, it will show what happens after the dynamo stops. It was working okay before I added the taillight <scratches head>. I've got a book on LT Spice that I hope will shed a little light on the issue. This is certainly one advantage of working with actual hardware; things don't just stop because the math gets harder.

 

[jdp298]

Sorry old chap, not a simulation expert. I've spent limited time with MATLAB and didn't enjoy that a great deal either.

 

[Steve K]

simulations are a great tool, but.... sometimes they have troubles handling some situations.

I haven't done a lot in LT Spice, but used to do some simulations of switching power supplies and such. A closed-loop system can be hard for the software to figure out how to get things going when everything depends on everything else. The usual method was to give it a hint as to the initial values and tell it to not worry about precision. I've got to figure out how to do these things in LT Spice, I suspect.

My goal is to figure out how to simulate varying the speed of a dynamo, which means varying the frequency and the voltage. I need to spend some time reviewing LT Spice to see what special functions it has.

 

[pbrena]

Re: Will this circuit work?

hi Syc,

...note that I use a switch to disable the standlight when the bike is parked. It's not desireable to fully discharge the nicad.

Steve K.

Hello Steve & All,

I would like to retake Alex's circuit based in Caps in post #73.

Although i have no objection using Batteries, I personally have a terrible memory so I will surely forget using the switch. I also find single nicad AA cells with tabs to solder relatively big (or are there a suitable option similarly sized as Caps?)

So, first I paste a corrected version including the shutdown circuit from your post 76:

Link


Tested combinations:

a) R1 - 150 ; R2 - 100 ; Supercap: Taiyo 2.3V 4.7F
b) R1 - 180 ; R2 - 200 ; Supercap: Maxwell 2.7V 10F

Please point out any mistake, as I m a total newbie.

Now my questions:

1) I would love to extract all juice posible, but I'm currently not sure if the shutdown circuit is working, how do I check?.

I can see no difference (sometimes I even think the standlight is shorter), I've also tried to omit the diode and connect instead a jumper from the + in the bridge rectifier, but it seems to shutdown the light while standing, any idea why?

2) I remember an old Busch&Muller Oval that used a PowerLed while cycling and a smaller led (not useful to light the road but good enough as a "be seen") for standlight i remember that it was quite durable. I have the feeling that it would be easy to adapt this idea and modify this circuit and make the standing light use a different, smaller led for the standing function that only would be on while standing (exactly when the main led would be off) and so make it last much longer, so:

* would this change make the stand light last longer?
* what components would be suitable? I remember having read about super bright thru the hole leds somewhere in this forum.
* what changes should I make to the circuit?

thx, pbrena

 

[pbrena]

Re: Will this circuit work?

Disregard! ... in error

 

[Steve K]

Re: Will this circuit work?

Hello Steve & All,

I would like to retake Alex's circuit based in Caps in post #73.

Although i have no objection using Batteries, I personally have a terrible memory so I will surely forget using the switch. I also find single nicad AA cells with tabs to solder relatively big (or are there a suitable option similarly sized as Caps?)

So, first I paste a corrected version including the shutdown circuit from your post 76:

Tested combinations:

a) R1 - 150 ; R2 - 100 ; Supercap: Taiyo 2.3V 4.7F
b) R1 - 180 ; R2 - 200 ; Supercap: Maxwell 2.7V 10F

Please point out any mistake, as I m a total newbie.

looks like the right values for the capacitor voltage ratings.. so far, so good.

Now my questions:

1) I would love to extract all juice posible, but I'm currently not sure if the shutdown circuit is working, how do I check?.

Regarding how to check to see if the shutdown circuit is working... the obvious answer is to short the pin to ground and see if the boost convert stops running.
However, in the 9 years since that thread took place, I've had a chance to build a somewhat similar circuit. I've learned that the LED will still conduct current through the boost converter's inductor if the supercap is charged to 2.5V or so. It's just a dim glow, but it surprised me.
I also realized that the voltage across the lower LED will charge the supercap to the LED's forward voltage (usually around 3V). To prevent this, I added a schottky diode in series with the boost converter's output.

I have a suspicion that your question might be more like "why doesn't the boost converter run? Is the Shutdown function activated?". In that case, which is pretty common, since nothing ever works when you first build it, is to go back to the basics. Is there at least 1V at the Vcc pin? Is everything really connected to what you think it is connected to? This is the time to get out the meter and check everything... check resistance from end to end of things that should be connected. Check the voltage at each pin of everything and write it down on the schematic. Does it all make sense?

I can see no difference (sometimes I even think the standlight is shorter), I've also tried to omit the diode and connect instead a jumper from the + in the bridge rectifier, but it seems to shutdown the light while standing, any idea why?

which diode are you referring to? Is it the upper LED in Alex Wetmore's circuit in post #73? Looking at the schematic now, I suspect that if the upper LED was removed, then the input to the LM317 will be limited to 3V, since that is the voltage across the lower LED. Roughly 2V is dropped across the LM317 (more or less), which would only leave a volt or so to charge the supercap. Of course, the voltage across the LED will also cause current to flow backwards through the inductor (if the converter is shutdown), so that would allow the cap to charge up.

2) I remember an old Busch&Muller Oval that used a PowerLed while cycling and a smaller led (not useful to light the road but good enough as a "be seen") for standlight i remember that it was quite durable. I have the feeling that it would be easy to adapt this idea and modify this circuit and make the standing light use a different, smaller led for the standing function that only would be on while standing (exactly when the main led would be off) and so make it last much longer, so:

* would this change make the stand light last longer?
* what components would be suitable? I remember having read about super bright thru the hole leds somewhere in this forum.
* what changes should I make to the circuit?

thx, pbrena

Using 5mm LEDs for the standlight is fine too. That's what I did for my first standlights (back when the headlight was incandescent!). I also do it for the taillight. In my designs, I was using red LEDs in the back, and yellow LEDs in the front (I don't think white LEDs were common yet). To use white LEDs, you'd probably just use two in series, instead of the 4 LEDs that I used.
Here's the schematic....

and this is what it looked like when it was built up.. not pretty, but it worked for many years (and probably still does)

 

[pbrena]

Re: Will this circuit work?

Thanks a lot for your comprehensive reply and sharing your circuits, i will surely give it a try to the first one although it might take a while to get all he parts.

meanwhile...

...which diode are you referring to? ...

This is the circuit i built

I was referring to the one equivalent to the D1 in your first circuit, i just tried to connect R4/C2 to the + side of the rectifying diodes, i guess maybe some flow from the supercap can go to the shutdown without it.

Is there at least 1V at the Vcc pin? Is everything really connected to what you think it is connected to? This is the time to get out the meter and check everything... check resistance from end to end of things that should be connected.

I will work on this, thank a lot for the pointers.

I suspect that if the upper LED was removed, then the input to the LM317 will be limited to 3V, since that is the voltage across the lower LED. Roughly 2V is dropped across the LM317 (more or less), which would only leave a volt or so to charge the supercap. Of course, the voltage across the LED will also cause current to flow backwards through the inductor (if the converter is shutdown), so that would allow the cap to charge up.

yes i will only use one led Cree Led... i will make some test including more or maybe a couple of 5mm