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Old 13th June 2003, 08:23 PM   #1
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Default Question for the electrically gifted...

I'm interested in operating a 36volt 400 watt bulb off of a 120vac household current source. Is a transformer necessary, or can the voltage reduction be made by a wire-wound rheostat (or pot?)? Is there a better way? In the end, I need about 11-12 amps of 36 volt power to the bulb. Any help or guidance would be appreciated. Thanks, Smoke Eater
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Old 13th June 2003, 08:26 PM   #2
SY is offline SY  United States
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If you don't mind wasting an enormous amount of power and generating kilowatts of heat, a resistor will work. A transformer might be a bit more sensible.
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Old 13th June 2003, 08:30 PM   #3
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Thanks, SY, I just seem to have trouble finding a transformer that takes 120vac and outputs 36 with at least 11 amps. Either I'm not searching for it correctly or they don't make many. Is an 11 amp output asking a lot of a transformer? Or should I be looking for some other "factor" that would help me properly size it?
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Old 13th June 2003, 08:38 PM   #4
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I don't think there should be much of a problem to find such
a transformer. A 400VA should do the job. Just as a sample
I cheked Plitron and they have a 400VA toroid with 35V
secondary. I suppose that would be close enough for your
purposes.
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Old 13th June 2003, 09:15 PM   #5
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Thanks Christer, I'll start searching by "400va" and see if I can turn up any that have 35-36 volt secondary. I'm just looking for an inexpensive way to upgrade from a 24volt 275watt halogen bulb to a 36volt 400w bulb.

Question for SY (and anyone else), Is the heat generated by the resistance of the rheostat greater than what would be generated by a transformer? I guess what I'm asking is, are transformers more capable of dealing with the heat, or do they not create as much heat as a rheostat? (I always thought that a transformer worked similar to a rheostat, just using more windings and not adjustable ) Thanks for you help, Smoke Eater
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Old 13th June 2003, 09:24 PM   #6
SY is offline SY  United States
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Enormously greater heat from the resistor. At 11-12 amps, you'll be radiating a kilowatt from that poor little thing. A transformer will only have a few percent loss, adding up to a few watts.
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Old 13th June 2003, 09:41 PM   #7
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Thanks for all your help, I found the Plitron site and located the transformer that Christer had mentioned. Sounds like just what I need. (Also stumbled across a "wind your own transformers" website...egads!) Thanks again to both of you, Take Care, Smoke Eater
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Old 13th June 2003, 09:53 PM   #8
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I won't hurt to look around a bit for other brands. I have no
idea if Plitron are cheap or expensive, I just checked their
site since I know many of you in the US buy their stuff.
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