All,
I've been putting into some research into alternatives for the lighting / charging systems for my Dad's PE400 and my DT175A.
I bought a cheap Chinese regulator/rectifier off ebay and wasn't having much luck so I poked around on the net till I found an elegant solution.
The above schematic is taken from this website
http://www.reuk.co.uk/LM317-High-Current-Voltage-Regulator.htmModifications i've made to this circuit are:
- Include a bridge rectifier between the lighting/charging coil and the input of the circuit to get DC.
- The PNP Darlington transistor (shown as Q1 in the schematic) I used is a BD650 which is good for 8A of current. It's possible to use a different transistor if you require more current/wattage.
For 6VDC output use:
- Resistor R1 = 120 Ohms
- Resistor R2 = 470 Ohms
For 12VDC output use:
- Resistor R1 = 120 Ohms
- Resistor R2 = 1 KOhms - 1.2 KOhms
A 1 KOhm resistor is calculated to give 11.67 VDC, 1.2 KOhms will give you 13.75 VDC
For additional functionality/precision R2 could be replaced with a variable resistor or trimpot to provide more light or get more precise voltages, similar to a product that Trail Tech produce.
I've used resistors rated for 1 Watt to provide a bit of safety margin.
Remember also to get caps with adequate voltage ratings.
I mounted the circuit on some stripboard from Jaycar.
All components are readily available from Jaycar and can be had for < $15.
Note, that it's highly recommended to provide adequate heat sinks for the LM317T and the Transistor. I'll also be looking to pot these using an appropriate resin in the near future.
In order for the circuit to work correctly the supply voltage must exceed the desired output voltage by a 1.5 - 2V or so. So, if you're looking to change your 6V system to 12V ensure that your lighting/charging coil at idle produces around 14VDC after it's gone through the bridge rectifier.
