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Old 11-08-2009, 09:46 AM   #1
 
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Blinking low voltage light


I just finished installing a low voltage monorail. Well actually two rails, each with a 300 watt electronic transformer. Before having everything closed up by sheetrock I figured I would test it out. I attached one of the monorails to one of the fixtures and added one 12v 50 watt fixture and lamp. I turned on the switch and the light lit. Luckily I left it on for a while. After a few minutes the light started to blink. The longer I left it on the faster it blinked till it got to the point where it was on for a couple seconds and off for one second or so.

I changed the bulb to rule that out. Same result. I then attached that monorail to the second fixture which is powered by the second transformer. Same result.

In both cases the transformers didn't appear to be even warm so I'm guessing the problem is not an overheating issue. While in the basement where the transfomers are I did hear the transformer buzz on and off, I'm guessing in unison with the flashing light.

Any ideas what could be the problem? My initial thinking is that my wiring should be fine as I assume that if there was a problem with it it would result in either the light not lighting or a dim light. For about 95% of the length of wire from the transformer to the fixture (total length probably 14') I'm using 6# stranded wire. I do step up/step down the gauge to 10# at the transformer and light fixture.

Thanks,
Nick
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Old 11-08-2009, 10:26 AM   #2
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Whenever you assume something is NOT the problem, that is what it is!

Wiring can heat up as it is used. Heat causes things to expand and move. When things move, this can cause a loose connection to disconnect.

So suspect/test/check everything.
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Old 11-08-2009, 11:10 AM   #3
 
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What would be the best way to do this test/check? Sounds like a ohm meter checking the continuity of the circuit on the DC side would be one possible test, though that starts in the basement and goes to the ceiling on the first floor. Not sure of an easy way to check that.

Thanks,
Nick
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Old 11-08-2009, 11:48 AM   #4
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I don't know what components are involved...

But lately, things are not manufactured as they should be. I find that wires may be loose. Crimp connections may not be crimped tight enough. Then things may just be designed poorly.

There may be a wire going to the track or whatever and one of the connections is not on good enough.

Just inspect everything the best you can. Test with a volt meter if you can safely do that.

Or isolate it to a faulty part and return that part to the store if you can't fix it.
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Old 11-08-2009, 01:00 PM   #5
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Quote:
Originally Posted by nickdu View Post
each with a 300 watt electronic transformer.
The longer I left it on the faster it blinked till it got to the point where it was on for a couple seconds and off for one second or so.

I changed the bulb to rule that out. Same result. I then attached that monorail to the second fixture which is powered by the second transformer. Same result.
Some kind of thermal overload is cycling on and off. Since it's mostly on, the temperature is almost cool enough for the light to be on continuously.
or
both 'formers are defective and both have failed in the same way.

I have the impression that, unlike a working magnetic 'former, a working elec. 'former with no load will show zero volts, so troubleshooting can be a bear.
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Old 11-08-2009, 01:25 PM   #6
 
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Here are the components:

transformer: http://www.lbllighting.com/Products....QBWzpzHXyYaMN6

rail: http://www.lbllighting.com/images/pr...sheets/315.pdf

power canopy: http://www.lbllighting.com/Products....g4EdwXGGpYC+kX

head: http://www.lbllighting.com/Products....XkfM0I5lrA+fA3

Attached are pictures of some of the wiring.

Thanks,
Nick
Attached Thumbnails
Blinking low voltage light-img_2534.jpg   Blinking low voltage light-img_2535.jpg  
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Old 11-08-2009, 04:00 PM   #7
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See if there is a minimum load spec. for your 'former, or load it with 300w (25A) instead of 50w (4A).

The max voltage drop spec. along the wires seems to be 2% (0.24v at 12v).

Make sure your wirenuts on the 12v side are installed correctly, and tight. At this current it can make a difference.
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Old 11-08-2009, 06:48 PM   #8
 
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What's the correct installation of a wire nut? I just twist the wires together and then screw on the wire nut. It's a bit more difficult with the large gauge wires. They don't wind together tightly like 12 or 14 gauge. They're along side each other and I assume the wire nut connects them snug enough plus the wire inside the nut will provide conduction between the two, right?

Thanks,
Nick
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Old 11-08-2009, 07:07 PM   #9
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Quote:
Originally Posted by nickdu View Post
What's the correct installation of a wire nut? I just twist the wires together and then screw on the wire nut. It's a bit more difficult with the large gauge wires. They don't wind together tightly like 12 or 14 gauge. They're along side each other and I assume the wire nut connects them snug enough plus the wire inside the nut will provide conduction between the two, right?

Thanks,
Nick
I can tell you that a bad wirenut installation leaves one or more wires untwisted when you remove the nut and
with a 10A load there is a voltage drop across the nut of >0.5v.
Your system specs allow no more than a 1/4 volt wiring drop @ 25A.

I've never worked with heavier than #12.

With these kind of specs you may want to bolt the splices.
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Old 11-08-2009, 08:09 PM   #10
 
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I guess there is this bolt product I can pick up from the hardware store? What's it called? How do I insulate the result? Electrical tape?

thanks,
nick
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Old 11-08-2009, 08:32 PM   #11
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Quote:
Originally Posted by nickdu View Post
I guess there is this bolt product I can pick up from the hardware store? What's it called? How do I insulate the result? Electrical tape?

thanks,
nick
The electricians can better answer this.
I guess I'd go with insulated butt splices or small split bolts and UL-rated heat shrink tubing to insulate.

How does the manuf. recommend you make these low impedance splices? Maybe the wires are heavy so that the splices are allowed to have some non-zero contact impedance.

What a hassle.

You could also check your existing wiring from one end to the other with a lantern battery or car battery and the heaviest 12v load you can find.
For a 12v, 50w, 4.2A load you should see no more than a 0.24(4.2/25) = 40 mV difference from source to load, if my math is correct.

If the light also blinks with the battery, you need an Exorcist.

Last edited by Yoyizit; 11-08-2009 at 08:40 PM.
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Old 11-09-2009, 09:09 PM   #12
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I'd agree that with the voltage drop specs provided a bad splice could be the problem. Electronic transformers can be a bit finicky. I didn't see whether or not you had a dimmer on the circuit. If so, you need an electronic low voltage dimmer with a neutral at the switch. I'm not sure that the problem you describe would be directly related but it is important that you have the right dimmer. Try adding more load to the rail and see if it stays the same or worsens. As it has been said, there may be a low end "cut off" that may be causing the problem.
I have to say this because I saw the canopy near a j-box. I'm assuming that you'll provide access to that splice.
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