Thursday, August 29, 2013

LED Lighting: Circuit Board and LED's

The previous "LED Lighting" post covered preparing the original Sturmey Archer lamp housings and making "heat sinks" for the LED's.  This post will describe the circuit board and LED's.  The circuit board only contains two components, a Bridge Rectifier, and a Capacitor.  I ordered both components and the circuit board from Digi-Key.

The Bridge Rectifier converts the alternating current (AC) supplied by the Dynohub to direct current (DC) which is required to power the LED's.  The Bridge Rectifier has 4 leads.  The two center leads marked "AC" are used to receive the the AC input from the Dynohub.  The two outer leads, "+" and "-" are used to output the converted DC current to the Capacitor.

Bridge Rectifier 40 Volt, 2 amp, Digi-Key # 641-1213-1-ND
The Capacitor will receive and store the converted DC current from the Bridge Rectifier.  This will help smooth the current going to the LED's to reduce flickering caused by the 20 poles within the Dynohub which act like on/off switches.  The Capacitor has two leads "+" and "-', the negative lead is marked on the outside to the can with a Gold stripe and negative sign "-".  This lead will be connected to negative DC output from the Bridge Rectifier.  The other lead will be connected to the "+" output from the Rectifier.  Capacitors are rated by micro-farads, this is a 10,000uf capacitor, the high number the more storage capacity and a smoother current to the LED's; however, as the numbers increase so does physical size of the capacitor. This is the same size capacitor I used for the 1949 Comrade LED conversion, but it had a bigger lamp housing. Using a 10,000uf capacitor for the smaller 1953 Sports housing is really pushing the space available inside the housing.

Capacitor, 10 volt, 10,000uf, Digi-Key # P10241-ND 
Circuit board comes in many shapes and configurations.  This particular board is from Digi-Key, it's a extra piece from the Comrade conversion.  The original board was 3" x 3.5" and has a "common bus" configuration.  This means any component leads that are connected to a common row on the board will be connected electrically.  As an example, to connect the "+" Bridge Rectifier output to the "+" Capacitor input the leads must be positioned on the board in the same row.  The board has two sides, the leads are inserted on the plain side, and are solder into place on the printed side.

Circuit Board (plain side), Digi-Key V2018-ND
Circuit Board (printed side), component leads are solder on this side.  Any leads solder in the same lettered row will be connected electrically.

This is the circuit board and mounted components.

This is the board after adding the leads for the input from the Dynohub (Blue) and output to the LEDs (Red (+) and Black (-).  I also trimmed the board to better fit within the housing and added Velcro to hold the board in place within the housing.

This is the board positioned within the housing.

Next I mounted the LEDs onto the heat sinks.  I'm using the same type of LED as the Comrade conversion, they are Luxeon Rebels (neutral white) pre-mounted on a 10mm base.  They produce 230 lm @ 700mA.  It is much easier soldering the leads to the LED if they are mounted on a base which contains a separate soldering pad for each input.  I'm also using 10mm adhesive pads to mount the LED and base to the heat sink.  I centered the LED and then marked the holes to drill for the leads that will be connected to the circuit board.

Front heat sink, LED, and adhesive pads 

Mounted LED and solder  leads

Front LED and heat sink mounted in original reflector.

And the same for the rear LED.

Rear heat sink and mounted LED

Heat sink and LED mounted in original rear bulb housing.
I wanted a quick test to make sure the circuit board and LEDs were working up to this point.  Using some alligator leads I connected the front and back lights to the Dynohub and gave the front wheel an easy spin. Let there be light!

The next step will be mounting the light housings and running wire from the Dynohub to the circuit board mounted in the front light housing, then running wires from the circuit board to the rear light housing.

Please share your comments and experiences.

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