Multiple switches

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Alwayslearningelec

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Can a remote 120v to 12v xfrmr have multiple switches( switch different sets of 12v lights or do you need separate xfrmrs for each switch?
 
Alwayslearningelec said:
Can a remote 120v to 12v xfrmr have multiple switches( switch different sets of 12v lights or do you need separate xfrmrs for each switch?
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there is nothing that says you can't put the switches on the 12V side of the xfmr. Just have to be aware of the voltage drop requirements of the system.
 
Strathead said:
there is nothing that says you can't put the switches on the 12V side of the xfmr. Just have to be aware of the voltage drop requirements of the system.
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So you can have power directly to the transformer then 12v wiring from lights and xfrmr to switch?
 
Strathead said:
Just have to be aware of the voltage drop requirements of the system.
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Just emphasizing this point. To deliver the same power at 12V you need 10x the current. So your switches have to handle 10x the current, you get 10x the voltage drop (on the same wires), and the baseline for voltage drop is 1/10 the original value. So your % voltage drop is 100x what you'd get on the 120V system. On the plus side, everything is at 12V, with corresponding easy safety requirements.

So as a design preference, you might find it easier to use separate 120V switches to drive separate 120V:12V transformers. But for some applications it makes sense and is perfectly kosher to have a single transformer driving separate 12V switches. I'm thinking different 12V lights all in a single location, because if they are separated by any significant distance you will slam into the voltage drop problems.
 
Out of curiosity, with typical 120:12 lighting transformers:

• Would switching the line side of the transformers significantly affect lifespan (vs. switching the load side)?
• Would there be any significant energy savings switching the transformers off for lighting control?

I just thought these might be added considerations.
 
winnie said:
Just emphasizing this point. To deliver the same power at 12V you need 10x the current. So your switches have to handle 10x the current, you get 10x the voltage drop (on the same wires), and the baseline for voltage drop is 1/10 the original value. So your % voltage drop is 100x what you'd get on the 120V system. On the plus side, everything is at 12V, with corresponding easy safety requirements.

So as a design preference, you might find it easier to use separate 120V switches to drive separate 120V:12V transformers. But for some applications it makes sense and is perfectly kosher to have a single transformer driving separate 12V switches. I'm thinking different 12V lights all in a single location, because if they are separated by any significant distance you will slam into the voltage drop problems.
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I went to work for a company many years ago, and the first call they sent me out on, was to troubleshoot why some low volt lobby lights were burning out the transformer. This was back before led, and the lights were strips of xenon bulbs, around 100’, around 200 watts of lights.They were trying to run them off a 50 watt transformer. “But it was low voltage, they can’t draw that much” LOL!
 
Electromatic said:
• Would switching the line side of the transformers significantly affect lifespan (vs. switching the load side)?
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Yes. Your switches will last longer switching one tenth the current.

Electromatic said:
• Would there be any significant energy savings switching the transformers off for lighting control?
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Yes. You won't waste money on idle current and heat production.
 
I was thinking more the lifespan of the transformers and/or the lights themselves. It seems like the repeated inrush, etc. wouldn't be good, but it probably is relatively minor in smaller equipment.
 
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