lankyphil Posted February 28, 2011 Share Posted February 28, 2011 Hi all, I'm trying to install some lamps on the platform of my layout, and they're lit with 1.5V grain of rice bulbs. Now I'm running a DCC system, but I have my old Hornby controller (R965) supplying 16VAC for Accessory decoders. I was planning on using the (now ex) track supply, which is up to 12VDC for lights in buildings etc. How do I keep the voltage low for the grain of rice bulbs? (Most other buildings are lit with 12V grain of wheat bulbs) As far as I understand, putting a resistor in would only lower the Amps in the supply, and I can't make head or tail of Voltage regulators... Cheers Phil Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted February 28, 2011 RMweb Gold Share Posted February 28, 2011 If you wire 8 x 1.5 volt lamps in series you can run them off of a 12v supply. Safer to put 10 lamps in the chain though, the slight under voltage will increase the lamp life significantly. Andi Link to post Share on other sites More sharing options...
shortliner Posted February 28, 2011 Share Posted February 28, 2011 There is a very simple circuit for an LM317T (needs a heatsink) and a couple of resistors which will let you set whatever output voltage you want. Google will bring it up - and a calculator where you put in the output required and it tells you what resistors you need. The device will shut itself down if overloaded http://www.electroni...articles/LM317/ a 220 ohm for R1 and a 47ohm for R2 will give you 1.52 volts at output for 12-16v input Link to post Share on other sites More sharing options...
lankyphil Posted February 28, 2011 Author Share Posted February 28, 2011 If you wire 8 x 1.5 volt lamps in series you can run them off of a 12v supply. Safer to put 10 lamps in the chain though, the slight under voltage will increase the lamp life significantly. Andi Oh.... Hmmmm...... Yeah... I knew that.... That's really basic stuff that I knew... And forgot Cheers! That LM317T circuit looks useful and intriguing though Link to post Share on other sites More sharing options...
Guest baldrick25 Posted February 28, 2011 Share Posted February 28, 2011 Have a look at the back of all the drawers for an old mobile phone charger or calculator power unit etc that's no longer used with preferably a much lower output voltage to start with , like 3V, 4V, or 5V. Push that sort of thing into use would be more preferable than using an LM317 circuit to drop 12Volts to 1.5V or thereabouts. It will work , don't get me wrong , but you are wasting a lot of power in the regulator . Lets say you have 10 bulbs in parallel , at typically 20mA per bulb, that's 200mA consumption. The voltage drop across the regulator is 12V-1.5V , ie 10.5V ( or more as thge supply is not very well regulated to start with. So the power the regulator has to dissapate is 10.5V x 200mA ( or 0.2A) or 2.1Wattts - that is gonna get hot!! Stick the same regulator circuit , on a much lower input and it will still work and be much cooler. Link to post Share on other sites More sharing options...
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