Low voltage runs

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Old 09-28-16, 07:23 AM
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Low voltage runs

Hi,

I had a 200w transformer that was powering 17 10w deck lights - worked great. I recently added 4 20w landscape lights that illuminate a sidewalk. So I upgraded to a multi-tap 300w transformer to handle the new load. I connected both old and new runs tap into a single run into the transformer. I started out with one wire in the COM tap and the other into the 12V. The original deck lights were fine but the end of the landscape lights (probably 50 feet from the transformer) we very dim, not useful at all. So I bumped it up to the 14V tap, better but still weak on the final light.

I can bump it to 15V but had a question. Would it be better to have 2 runs into the transformer - separating the deck and landscape lighting? In that case I'd have COM/12V wired to the deck (light before) and the COM/!2/13/14V (whatever looks best) for the landscape. Is this a better approach for my application or should I keep the lines spliced and jump up to 15V? From what I understand, the higher the voltage, the shorter the life of the lights so my thinking is separating them might prolong life of the deck lights.

Thanks!
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Old 09-28-16, 09:31 AM
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I would separate them, and at 50' it an increase in wire size maybe needed.
 
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Old 09-28-16, 11:16 AM
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Thanks - that makes sense. I don't relish digging up the cable to do that but will do!
 
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Old 10-02-16, 06:19 AM
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Do not bump up the voltage. You will burn out the lights closest to the transformer.

You are running into voltage drop problems. The thinner the wires the greater the voltage drop. The more amperes the lights draw the greater the voltage drop.

Since there are lights spaced all along the line, the voltage drop in each segment varies. Some math is needed to figure it out but the math can be reduced at the risk of more overkill on the wires (cost, thickness) by pretending the entre load is at the far end.
 
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Old 10-02-16, 07:34 AM
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You may also find it useful to have the run from the transformer connect into the middle of the sidewalk run rather than at one end. Doing that will better balance the voltage drops along the sidewalk string. Check the voltage at the lamp closest to the transformer connection; you can safely use a higher tap on the transformer to compensate for voltage drop as long as the voltage at the closest lamp doesn't get much higher than 12 volts. If those steps don't get you adequate results than heavier gauge wire would be next step.
 
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