Sturmey Archer X-FDD technical

I have got the hub brake on the custom wheel working now.  I had to wait a couple of days for the special Sturmey Archer brake cable.  Now I have one, I think I should be able to replace it with a standard brake cable without too much heartache when the time comes.  The brake is about as good as the Tektro V-brake which came with the bike, but it will still be just as good in the pouring rain.  Hub brakes behave a little differently from the rim and disc brakes I have used, the best way I can describe it is that instead of a constant braking force being applied at the wheel when you apply a given force at the lever, the braking force seems to grow over a period of a few seconds when a constant force is applied at the lever.  The result is a nice quick stop but to the uninitiated the brakes feel odd.  I do quite like the fact that I won’t have to do any maintenance on the brake for a very long time.

CIMG2088

The other feature of the hub I have been playing with is the integral dynamo.  I am quite happy with my existing battery LED lights and I am not currently planning to replace them with dynamo lights.  The hub outputs 6 V of AC which is great for filament lamps but sucks for LEDs and lots of other devices.  I purchased a bridge rectifier from Maplin for 27p to convert the 6V AC into 8 and a bit V DC.  I connected the output from this to both a fixed positive voltage regulator (£1.02) to produce 5V DC, and a battery pack (89p) containing 4 rechargeable Ni-Cad AA batteries.  This allows the Ni-Cad batteries to charge when no other load is attached, and they work in series with the dynohub to power a device when connected.

CIMG2087

The whole lot is inside a clip-sealing tupperware box, and the 5V DC and ground wires are connected to a pair of USB ports:

CIMG2085

The end result is able to charge devices which are able to charge from USB:

CIMG2083

I’m planning to mount the tupperware box on the now unused rim-brake bosses tomorrow.

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7 thoughts on “Sturmey Archer X-FDD technical

  1. Shimano do a centerlock version of this hub for disc brakes if that is any use to you. I remember hearing that Sanyo make the internals on both and that they are pretty much identical in electrical characteristics. I think I might add one to the Yuba one day, it could be great on yours.

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  3. I hadn’t seen that you had done this until now.

    If I may offer some advice, as someone who has worked with electronics for many years, I’m afraid that if your circuit is as simple as you describe then there are several things wrong with it.

    Firstly, the voltage from the dynamo will rise well above 6 V if there is no load. You must protect the regulator chip from this. One adequately rated zener diode connected across the DC output of the bridge rectifier is the easiest way to do this. I would suggest clamping the voltage to below the rated maximum input voltage of your regulator chip, or perhaps below the rated voltage of the capacitor that comes before the regulator.

    However, you don’t mention any capacitors at all. They are required to make the voltage regulation stable, both before and after the regulator. If you look up the data sheet for the chip that you are using you will find out what the manufacturer recommends.

    You appear to be using the batteries as the capacitors on the side of the circuit after the regulator. There is a problem with this too. When you stop pedalling (or indeed without the input capacitor, several times per rotation of your wheel) current will flow backwards through your circuit, discharging the batteries through the IC. This is really not good at all. Regulators are not designed as devices for discharging batteries.

    For that reason, you must have a diode between the output of the IC and the battery to prevent reverse discharge. However, this will drop the voltage from the regulator by about 0.6 V, so instead of your fixed 5 V regulator chip, you need to use something like an LM317 adjustable regulator chip to produce 5.6 V.

    Now I’ve described more or less the same circuit as I have built several of and which have been working very nicely for some time.

    • Thanks for the tips David. Sadly, due to the budgetary constraints of being a student until recently, the components used in this have long since been repurposed for other projects. Eventually I’ll probably build a version two and I’ll take your feedback into account when I do.

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