Comments on: Lighting control circuit, this time for sure http://dr2chase.wordpress.com/2009/02/22/lighting-control-circuit-this-time-for-sure/ Just another WordPress.com weblog Thu, 09 Apr 2009 16:16:34 +0000 http://wordpress.com/ hourly 1 By: dr2chase http://dr2chase.wordpress.com/2009/02/22/lighting-control-circuit-this-time-for-sure/#comment-20 dr2chase Fri, 06 Mar 2009 13:24:06 +0000 http://dr2chase.wordpress.com/?p=293#comment-20 The board is already on order, so you might as well wait until I see if it really works. There's nothing in the board that I have not already built in some form or another over the years, so I have pretty high confidence, especially given the simulation, but it's also compact, so soldering it might be an issue. The board cost is $2.50/square inch + $10 + S&H, so the savings/board are around $5 going from 1-2. The most expensive part, after the hub ($$$) and the board, is the BuckPuck ($20?). The board is also designed around the power characteristics of a specific hub (Shimano 3d71); I know this would be "wrong" for a SON, though it would probably work fine with a sidewall dynamo. I have a shunt already, built for a BuckToot (25V limit, not 32) that gets the job done, but it could be loads better, which is what the newer one is supposed to do. Shunt version 1 (shunt v0 got cooked) dumps excess power into a 3-LED "Endor Star", which, in this weather, goes into a spectacularly annoying thermal oscillation. LED forward voltages fall with temperature, which means that until the shunt reaches a higher threshold (in 25-degree weather), it does not conduct, but once it begins to conduct, the junction heats, and so it can continue to conduct as the stored voltage falls below its initial value, until it falls so low that the shunt turns off. So, flash-flash-flash, except it is more like FLAAAAASH-flash-flash-FLAAAASH-FLASH---flash. Really random looking, usually really bright. This shunt is current-limited at 350mA (so it maxes out at 10W), and the nature of the oscillation guarantees that the LED is going on full, at least briefly, so these are 240-lumen flashes. I could not stand to look at it, and ended up aiming it straight down at the pavement. The newer design, in the-o-ry, won't do this -- I forgot to simulate this bit at first, but it turns out that the current through it is pretty much invariant with respect to the voltage drop above the shunt transistor (within reason, of course). In practice, this means that the oscillation should be much more rapid, hopefully fast enough that we won't see it. I could also modify the heat sink, to put a larger conductive mass between the fins and the LED, so that the thermal swings will be smaller, which should also increase the flash frequency. And of course, I'm already thinking about a second-second system :-). The board is already on order, so you might as well wait until I see if it really works. There’s nothing in the board that I have not already built in some form or another over the years, so I have pretty high confidence, especially given the simulation, but it’s also compact, so soldering it might be an issue.

The board cost is $2.50/square inch + $10 + S&H, so the savings/board are around $5 going from 1-2. The most expensive part, after the hub ($$$) and the board, is the BuckPuck ($20?). The board is also designed around the power characteristics of a specific hub (Shimano 3d71); I know this would be “wrong” for a SON, though it would probably work fine with a sidewall dynamo.

I have a shunt already, built for a BuckToot (25V limit, not 32) that gets the job done, but it could be loads better, which is what the newer one is supposed to do. Shunt version 1 (shunt v0 got cooked) dumps excess power into a 3-LED “Endor Star”, which, in this weather, goes into a spectacularly annoying thermal oscillation. LED forward voltages fall with temperature, which means that until the shunt reaches a higher threshold (in 25-degree weather), it does not conduct, but once it begins to conduct, the junction heats, and so it can continue to conduct as the stored voltage falls below its initial value, until it falls so low that the shunt turns off. So, flash-flash-flash, except it is more like FLAAAAASH-flash-flash-FLAAAASH-FLASH—flash. Really random looking, usually really bright. This shunt is current-limited at 350mA (so it maxes out at 10W), and the nature of the oscillation guarantees that the LED is going on full, at least briefly, so these are 240-lumen flashes. I could not stand to look at it, and ended up aiming it straight down at the pavement.

The newer design, in the-o-ry, won’t do this — I forgot to simulate this bit at first, but it turns out that the current through it is pretty much invariant with respect to the voltage drop above the shunt transistor (within reason, of course). In practice, this means that the oscillation should be much more rapid, hopefully fast enough that we won’t see it. I could also modify the heat sink, to put a larger conductive mass between the fins and the LED, so that the thermal swings will be smaller, which should also increase the flash frequency.

And of course, I’m already thinking about a second-second system :-) .

]]> By: joelparks http://dr2chase.wordpress.com/2009/02/22/lighting-control-circuit-this-time-for-sure/#comment-19 joelparks Fri, 06 Mar 2009 04:45:49 +0000 http://dr2chase.wordpress.com/?p=293#comment-19 Hi David, If there's any savings to be had by buying in quantity > 1, I'd be interested in a board and bag-o-parts to help defer your costs. I'm not qualified to follow your design but I can run a soldering iron. By the way I believe I've seen you several times on m'sex tpk in Burl, and at least twice of those I've been on my big dummy. Though I admit to not having been riding to work much yet this year... I don't actually have the dyno-hub yet either, Joel Hi David,
If there’s any savings to be had by buying in quantity > 1, I’d be interested in a board and bag-o-parts to help defer your costs. I’m not qualified to follow your design but I can run a soldering iron. By the way I believe I’ve seen you several times on m’sex tpk in Burl, and at least twice of those I’ve been on my big dummy. Though I admit to not having been riding to work much yet this year…
I don’t actually have the dyno-hub yet either,
Joel

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