RoyS Posted February 27, 2008 Share Posted February 27, 2008 Hi All. I have recently been overhauling some old luminares including some very old Patt 23’s.Inside one of the 23’s was the old balloon type lamp (Philips 559C G3 500W) as these old lamps are a touch on the warm side they were replaced with a new halogen lamp. Now the real question:The old lamp is still working and I would like to make an illuminated ornament for (perhaps) domestic use. I therefore only want the filament to glow. Can anyone think of a simple way of achieving this that avoids using a dimmer? I was thinking along the line of a resistor network or perhaps a transformer. (..and the first one to suggest finding another 9 lamps and conneting them all in series will get a prize... :) ) Thanks and best regards to all.. RS Link to comment Share on other sites More sharing options...
Ike Posted February 27, 2008 Share Posted February 27, 2008 Transformer seems like the way forward. As a guess I'd say you'd be looking at around the 20-25V mark but I'd wait for a few more replies before you actually buy anything just to make sure I'm not talking rubbish! :) Link to comment Share on other sites More sharing options...
DaveP Posted February 27, 2008 Share Posted February 27, 2008 Its all very well.... But ! How glow is glow ... In order to work out what transformer output or to calculate the current for a resistive volt dropper your going to have to use a dimmer to find your correct level of glow and measure the voltage at the lamp. It may in fact be cheaper to replace the lamp holder and use a 15w lamp ... but will that be to bright a glow ? Link to comment Share on other sites More sharing options...
KevinE Posted February 27, 2008 Share Posted February 27, 2008 You can use a motor-run capacitor or power-factor capacitor in series with the mains lead. Unfortunately you'll need to choose the capacitance by trial and error unless you're some kind of maths whizz. Link to comment Share on other sites More sharing options...
Jivemaster Posted February 27, 2008 Share Posted February 27, 2008 First thought is a transformer, what do you have to try? Possibly a 2 x 12v at 100w see what it glows like. Do you have a 12v lighting transformer to hand to play with? There is going to be a substantial power requirement. 240v 500w is 2.08 amps corresponds to 115 ohms BUT this is HOT the resistance will be much lower cold. Really the best place to start is what you have at the moment, 12, 12-0-12, 55v transformer or whatever you have in the scrap bin. Yes you lamp will draw real power, and make real heat. Link to comment Share on other sites More sharing options...
Jack Posted February 27, 2008 Share Posted February 27, 2008 A transformer or a pot. The pot would be a cheaper and quicker solution. Link to comment Share on other sites More sharing options...
pritch Posted February 27, 2008 Share Posted February 27, 2008 Can you get your hands on a variac? Try that first off, that'll give you an idea of what voltage you want. You can then either stick with the variac for permanent use, or figure out what sort of transformer you need. There's a few on ebay. Link to comment Share on other sites More sharing options...
Suzette Posted February 27, 2008 Share Posted February 27, 2008 "Find another 9 lamps and connect them all in series...." Shall I PM you my address to send my prize????? Link to comment Share on other sites More sharing options...
dbuckley Posted February 27, 2008 Share Posted February 27, 2008 A capacitor is by far the best solution. The only question is finding what value. In this old post I posted a chart of the behaviour of a 500w linear halogen. You need to do something similar, and find out at what voltage you like the look of the lamp. Lets guess it's 30V. You also need to know the current flowing through the lamp, which was 0.7A So, the lamp resistance is (Ohms Law) R=E/I, so R=30/0.7, so R = about 43 ohms. Nex step is to make a potential divider, so assume for the moment a resistor in series with the lamp, what value would it need to be so that there is 30V across the lamp when the mains is 240V? So get the ratio of the voltages, and the resistances are the same. the lamp voltage is in this example 30V, and the dropped voltage is (240 - 30) = 210V. So the ratio is 210 / 30 = 7. Thus the dropper resistance needs to be 7 * 43 = 301 ohms. Now we don't really want to use a resistor, as it'll get hot and waste energy, W=E^2/R, so we would generate 191W of heat. So we'll use a capacitor, which will do the same thing but without the heat. So what value capacitor do we need that at 50Hz has an impedance of 301R. We calculate it using this simple formula: http://www.cvs1.uklinux.net/calculators/gifs/cap_imp_equa.gif Or just go to this handy electronics calculator site, select the menu item for Capacitor Impedance, and fill in the frequency (50, select a multiplier of 1) and the impedance (301 select multiplier of 1), and press calculate now and the capacitance required is 10.5750 µF. Go to somewhere like here and purchase said cap, lie back and enjoy. Link to comment Share on other sites More sharing options...
paulears Posted February 27, 2008 Share Posted February 27, 2008 It may in fact be cheaper to replace the lamp holder and use a 15w lamp ... but will that be to bright a glow ?The idea isn't to use it as a light source, it's that the old lamps were huge and I quite agree, a bit of a nice 'feature'. Link to comment Share on other sites More sharing options...
Ike Posted February 27, 2008 Share Posted February 27, 2008 Not really much to add to Davids post but I would be tempted to fit a surge limiting resistor in series with the lamp to prevent it blowing at switch on. Do motor run capacitors have a built it discharge resistor? If not you might want to fit one as well to prevent someone getting a nip if they unplug it and touch the pins. A transformer or a pot. The pot would be a cheaper and quicker solution.I'd love to know your cheap source of few hundred watt pots. :) Link to comment Share on other sites More sharing options...
Jivemaster Posted February 27, 2008 Share Posted February 27, 2008 I like the capacitor route but if the lamp were removed the centre contact would be at 240V which wouldnt be nice domestically. If you use the transformer route rou could chose the earthing configuration -or just ignore it! as the open cct volts should be less that 48. Link to comment Share on other sites More sharing options...
paulears Posted February 27, 2008 Share Posted February 27, 2008 Um. the table light here has a couple of prongs sticking up when the bulb's removed, isn't this the same? Link to comment Share on other sites More sharing options...
IRW Posted February 27, 2008 Share Posted February 27, 2008 How about a standard wall-mounted dimmer light switch? An easy and cheap solution if it can be incorporated into the design! Link to comment Share on other sites More sharing options...
DaveP Posted February 27, 2008 Share Posted February 27, 2008 An easy and cheap solution Until some one turns up the brightness... I don't think the 500w versions are 'cheap' :) Link to comment Share on other sites More sharing options...
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