Low voltage transformer

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  #1  
Old 01-11-13, 09:10 AM
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Low voltage transformer

I'm replacing a low cost, electronic 120v to 12v dimmable power supply that is driving 6 halogen lamps in my basement. This power supply radiates all kinds of noise in the radio services, and I'm going to replace it with a old fashioned iron transformer. I have a .15kvA Cutler-Hammer buck/boost transformer that is rated for indoor use, and comes in a NEMA3R case. It is a isolation type transformer that is OK for use in a low voltage output configuration.
So, my question. Is it necessary to ground one side of the 12v winding? I seem to recall reading where LV transformer need to have one terminal of the secondary bonded to earth, but can't now find that requirement. Any help here?
 
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Old 01-11-13, 05:57 PM
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Is 150 watts enough for your 6 halogen lamps?

A buck/boost transformer raises, or lowers, the voltage a certain amount listed on the nameplate. I do not think this is the right transformer for your application. You need a transformer with a 120 primary and a 12v secondary.
 
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Old 01-12-13, 08:09 AM
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I think I'm good to go. Its a "isolation transformer" so it does have 12V secondary, actually two 12v secondaries and two 120V primaries to give this guy lots of flexibility. Like you say, they are normally used for buck/boost, but can wire to deliver straight LV as well. Turns out i'm driving little "car brake light" bulbs, 6 of 'em, rated at just over an amp each. Had to buy a $40 Luton dimmer, special model to drive a magnetic load, something about not having any DC output content from the dimmer to overheat a transformer. All is well. No radio noise, and nice smooth control of brightness.

Never really noticed this before, but there are at least 3 classes of dimmers. The most common, less $ to drive incandescent loads, a model that needs a neutral to drive electronic AC to LV AC loads, and a third type to drive magnetic loads.
 
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Old 01-12-13, 09:57 AM
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It has to do with the switching device......triac.....scr.....mosfet.
 
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Old 01-12-13, 11:43 AM
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Yes, with all the new lamps that are out there now you have to watch when you buy a dimmer to make sure they are designed to handle the load. Otherwise they will either not perform as desired or will fail early.
 
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