Tech Electrical Question for the Bedroom.

Submitted: Saturday, Aug 09, 2003 at 03:29
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I have changed the 20w halogen bulbs over the bed to 10w halogen but the bulb is not a spot beam like the original so gets in your eyes still. Can anyone tell me if a 240v light switch with dimmer will work with 12v or is there not enough voltage / too much resistance for them to work across the dimmer pot contacts with 12v ? Maybe the dimmer wont handle the 2 amp draw ? Would be great to leave the 20w spots in and just dim them down when needed .... would that hurt a halogen bulb ? I had an electrician install dimmers when the girls were infants and was thinking of using one of that type. Measures about 85mm x 35mm with a switch and dimmer. With all the 12v lights outside in gardens now has anyone seen a dimmer switch for low voltage ? Anthony
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Reply By: Deleted User - Saturday, Aug 09, 2003 at 03:31

Saturday, Aug 09, 2003 at 03:31
Anthony, I hope you find the following illuminating.


The 240v dimmers are exactly that. They work by modifying the 'quantity' of the AC waveform by electronicly stipping out some of the AC(alternating current) waves. The lamp 'sees' this as a change in current and hence a change in quantity of light. Make sure you get a 'zero crossing' dimmer as they give off negible RFI (radio frequency interference). Older dimmers do not. These worked by stopping each part of the wave at a point somewhere along its' curve which modified the effective curent.The rapid transition from a high potential to zero this resulted in RFI being emitted. Also when purchasing 12V flouros make sure to get the low RFI type.

For 12VDC it is possibe to contruct a variable voltage device which would dim the lamp but I've never heard of a commercial one.

Halogen lamps are 'element' types like all the others and will work at any voltage within its' rating.


Ernie


AnswerID: 559368

Reply By: Deleted User - Saturday, Aug 09, 2003 at 03:32

Saturday, Aug 09, 2003 at 03:32
Thanks Ernie, I did find it illuminating .... and I like it when my ideas go bang in a flash of light. [smile] Ok ! I'll turn 90 degrees and go down another road. What about using an interior light dimmer from a car ? Could mount that in bedside cupboards ..... wire it in ...voila ???? Anthony
AnswerID: 559369

Reply By: Deleted User - Saturday, Aug 09, 2003 at 03:33

Saturday, Aug 09, 2003 at 03:33
Anthony, interesting but I'll have to pass on that one. Any auto sparkies out there lurking?????????


Ernie


AnswerID: 559370

Reply By: Noosa Fox - Saturday, Aug 09, 2003 at 03:34

Saturday, Aug 09, 2003 at 03:34
Anthony, When I was buying the spot light that I put on the outside of van, the salesman at the specalist lighting shop asked me if I wanted spot of spread beams. If you go to another supplier you might find that the amount of light that you wish to obtain may be available with the correct globe. Brian.
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Reply By: Deleted User - Saturday, Aug 09, 2003 at 03:35

Saturday, Aug 09, 2003 at 03:35
Brian, The bulb in question is an Osram Decostar 51S/44860SP 12V/20w 10 deg spot,50mm dia. I asked at the 12v shop at Strathpine and they replied that this bulb is the lowest wattage in the 50mm dia that "they" have seen. I'll try a bigger specialist lighting shop over the weekend. I'm going to connect it to my little Sierra interior light socket tomorrow and see if it dims. If it does I'm off to the wreckers for two dash dimmers .... Anthony
AnswerID: 559372

Reply By: Noosa Fox - Saturday, Aug 09, 2003 at 03:36

Saturday, Aug 09, 2003 at 03:36
The lighting shop I went to was the normal household lighting type shop, and they stock lots of 12volt globes now that there are so many installed in houses as down lights etc. Brian
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Reply By: Deleted User - Saturday, Aug 09, 2003 at 03:37

Saturday, Aug 09, 2003 at 03:37
Anthony
Halogen globes with inbuilt reflectors (called diochroics) are available in angles from 12 to 36 degrees - but not sure if obtainable at 10 watts - they are for 20 watts.

Twelve volt dimmers are available but costly. Try Quirk's Victory Light in Sydney. Their techo women are very knowledgable re anything low voltage.

It's actually a good idea to dim halogens slightly as they are designed to work at 11.8 volts. Can dim via 240-volt dimmers but in my experience is RFI noisy.
Collyn Rivers
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