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Philb 09-12-2008 02:17 PM

Low Voltage/Transformer Question

Wondering if someone can help or offer an opinion.

I'm using a Magnitude M200S transformer for a residential application (my kitchen) running 6 WAC HR-86 Under Cabinet Button Lights. Each light is spaced about 2 feet apart from one another. The transformer is 110/120v input, 12v 200watt out. The lights are 12v/20 watt each.

The 1st light in the run is about 15 wire feet from the transformer. The last light is about 30 wire feet from the transformer. Although the lights are within 2 feet proximity to one another, two of them have about 15 wire feet between them as I had to run a loop around some cabinets. The lights are wired in a series. The wires are all hidden behind the sheet rock.

I used 12 gauge copper stranded wire from the transformer to the lights. The supply wire (a/c side) to the transformer is 12/2 bx.

I just got done making final connections and when switched on the lights are very dim. Each is less bright than a birthday candle, as a comparison.

I would imagine I have one of two problems as to why the lights are dim.
- Too much resistance due to wire length

- Too little volts because I wired in series

I'm 99% certain it is the "series" wire configuration that is the cause.

I reviewed this with the retail outlet that sold me all the parts, and they feel it is resistance when the wire steps down from the 12 gauge stranded supply line to the 18 gauge leads hanging off the lamps. They recommend I remove the 18 gauge leads from the lamps and just go 12 gauge direct to the lamps, and the problem will be corrected.

This just does not sound right to me.

If the issue is due to the series wire configuration, I think I have two options:
1 - Home run each light individually to the transformer. Now that all cabinets and back splash is installed, this is very difficult.
2 - Wire three 24 volt 40 watt (minimum) transformers in a series to create 72 volts at the line, and that should enable the lights to operate at the correct luminosity. I am not certain, however, if this is even possible, or safe.

Does anyone have any experience with this or pointers on next steps?

Thank you,

micromind 09-12-2008 05:30 PM

With a 12 volt transformer, and 12 volt lights, the lights must be connected in parallel, not series.

In a parallel connection, voltage stays the same (12 volts in this case), and current adds.

In a series connection, current stays the same, and voltage adds.

Simply re-connect each light in parallel, and you'll have the full 12 volts going to each one.

The current on each light will be 1.67 amps, and 6 of them will total 10.2 amps.


Philb 09-12-2008 06:46 PM

Thank You - One More Question
1 Attachment(s)
The complexity is running the additional wiring to create the parallel configuration. The walls are all sealed up, cabinets hung, back splash in place.

I can get two leads from the transformer to one light. I can do this a second time, getting two leads from the transformer, to a single light. So running parallel to two lights is possible.

The problem area is a cluster of 4 lights, which I can only get two leads to from the transformer. Couldn't I run these two leads to the area where these four lights are, and then run each light to these two lead wires? In a sense, instead of home running each of these four lights separately, I running one set of wires from the transformer to this area, and then parallel to each of these four lights. Not sure if I am explaining this correctly, so I included a (very rudimentary) sketch.


220/221 09-12-2008 07:16 PM


instead of home running each of these four lights separately, I running one set of wires from the transformer to this area, and then parallel to each of these four lights.

Series...... heh heh :jester:

If your cabinets don't go all the way to the ceiling, you can often run on top and sneak down between them

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