My community has low voltage (12 volt) lighting that illuminates our entrance signs. It’s 4 – 20 watt halogen bulbs connected to a 300w transformer. There’s a problem that has made them go dim. The setup is relatively simple; a transformer and two pairs of lights wired in parrallel. Initially I thought it was the transformer. When I measure voltage at the output with the lights on, I’m only getting about 5 volts. I figured it was the transformer, but when I disconnect the lights (no load) I get 12 volts. Given that, I assumed a short or leak to ground in the wiring. So, I connected the whole setup to a car battery. All the lights lit at full brightness when connected to the battery. I then brought the transformer and 4 bulbs home; wired them all up and all for light lit at full brightness. Did they light when on the battery because the battery can provide a ton of power and can overcome the short or leak?
So, they light on the in-ground wiring using a car battery; exonerating the wiring and fixtures.
They light on the transformer when the in-ground wiring is out of the picture, exonerating the transformer.
What’s left? What am I missing?
Replies
wire size will cause major voltage drop if too small, I cannnot tell u a size w/ knowing the distance, however a loop set up w/ a return balances the load so the last light is as bright as the first, also do not exceed 80% of x former max rating if you want to do it right.
lots of places on line will gice suggestions based on distance, also x former should be as close as possible to lights and make sure any switch is on the line voltage side of it, not the low voltage side
I should add, this setup once worked properly when initially installed, probably 2 years ago and has worke fine until a few weeks ago. Wire is #10; maximum run is about 60'
You either have a short in the wiring/fixture causing higher current draw that what the transformer can supply. A charged car battery can supply several hundred amps (see the cranking amps specs) while the transformer only about 25. A clamp on amp meter can verify the current when connected to the transformer (most won't measure the DC current when on a battery). It should be more more than 7 amps. But I don't think that is the case here high enough current draws to drop the transformer out that much would likely burn out the short. Specially when hooked up the the battery.
"or leak to ground in the wiring"
The low voltage side is not grounded.
More likely the problem is/was a bad connection. Most likely on the secondary side of the transformer.
But it could be on the primary.
Has the transformer be re-installed? Was the primary voltage (120) checked?
It is also possible that there is temperature or moisture problem with the transformer. Is it real transformer (iron core - heavy) or an "electronic transformer".
William the Geezer, the sequel to Billy the Kid - Shoe
It's a "real" transormer with iron core. I didn't check input voltage since I saw 12v on the output with no load. I'll check that and report back.
PS... I didn't have them on the battery for long; maybe a couple of seconds.
I will agree with Bill on this one. What type of conductors wire on the load side, of the transformer? How are the fixtures connected to these conductors? At sixty feet of 10AWG with 80W demand, voltage drop is not a factor. 80W demand is like less than 1 amp. Are those lights the only device on that circuit?
Don't forget that they worked with the car battery. So there aren't any poor series connections after the battery/transformer.With the possibable except of one right near the transformer, which there normally would not be one, and move the wires from the transformer to the battery affected it..
William the Geezer, the sequel to Billy the Kid - Shoe
Could be as simple as a loose wire-nut.
Happy New Year!
The connections on the transformer are screws with compression plates. I've remade those connections but I don't think they were ever the problem. I'm reasonably convinced that there's a bad connection-they're buried and I don't know where they are. I just can't figure out why they worked when I used the car battery.........
I would suspect the transformer.
It's possible that you're seeing some sort of cross-connection between the conductors out by the lamps, but it's unlikely that you would get one that would still leave the lamps burning dimly.
Whereas if the transformer just isn't supplying enough current, you would see exactly what you are seeing.
My recommendation is that you put an ohmmeter on the wires that go out to the lamps. Then using V= IR you can easily figure out whether the current draw is reasonable or not for the lamps that you have.
I first suspected the transformer as well. But, using a bunch of alligator clips, I connected the same four bulbs directly to the transformer. And they light at full brightness.......
The connections can be really flaky, changing from bad to good or back just because you handle them a little.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
LV wiring is a PITA sometimes because of the high current and the unreliability of the various "easy" connection schemes used. Odds are high that it's a bad connection somewhere, but hard to say where.