Hello!
Years ago I built an infinity mirror with a shadowbox and LED strips. It's great! I hang it on the wall or ceiling, depending on my space. I just moved into a new apartment and want to replace a ceiling light with my mirror. I removed the light and wired a short extension cable into the electrical wires of the two-wire ceiling port. Unfortunately, when I plug in my fixture and turn it on, the infinity mirror flashes on then turns off repeatedly. It seems like it is drawing too much current and shutting off, then it tries again in a loop. I see the small light on the power supply flash on and off as well. It is an old building, but surely this thing doesn't draw THAT much power! The previous light fixture was also LED. Some important details and debug that I've done:

• Power measurement of my fixture: 750 mA at 12V = 9 W
• Power measurement of previous light fixture: 230 mA at 55 V = 12.65 W
  • Note that I could not measure the voltage, 55 V is the minimum that the power brick label says.
  • So the old light fixture draws MORE power, yet has no problem!
• Sometimes the previous light fixture would strobe before fully turning on.
• My infinity mirror works in other wall outlets in the apartment. Thus, the power supply and LED system are working.
• I have redone the ceiling wiring many times. They are securely connected. I plugged in the old light into my fixture and it works fine.
• No other devices on the circuit are on when I test my infinity mirror.
• If I set the lights to very dim on my mirror, it stays on. Then, I gradually increase the brightness. At peak brightness, the LEDs go back to fluctuating on/off. I thought perhaps there was an initial in-rush of current at power up, so I thought starting at dim and gradually increasing would work.
• A hair dryer also barely turns on when I plug into this ceiling port (makes sense, that's a lot of power)
• The 20A circuit breaker does not trip.

I have not spoken to my superintendent/landlord yet about this. Could something be wrong with this circuit in my apartment or is this normal? What is going on??? I'm not an electrician, but as an electrical engineer I'm stumped!

Thanks!!

 

Welcome to AAC.

Flashing LED lamps are usually caused by a faulty capacitor in the power supply. Do you have a supply you can swap out for testing?

I would have suggested a faulty LED except you said the supply power indicator also flashes, and you said “LED strips” which would almost certainly not all be wired in a series. Sometimes the die wire in one of the chips becomes detached an when the wire is heated it loses contact, then cools and reconnects—over and over.

I would bet on a cap, though.

 

Welcome to AAC!

A hair dryer also barely turns on when I plug into this ceiling port (makes sense, that's a lot of power)

It's difficult to believe that your light fixture would be drawing enough current to cause a voltage drop significant enough to affect it.

I suspect a resistive (i.e. loose) connection in the circuit somewhere upstream of your light fixture. Measure the voltage in the receptacle while the dryer is running. Being an electrical engineer, you know that these are lethal voltages so do it carefully.

Once you verify a significant voltage drop, you should inform your landlord before it starts a fire.

 

Flashing LED lamps are usually caused by a faulty capacitor in the power supply.

I thought the power supply might be faulty too, but it works fine in any other outlet in the apartment.

Measure the voltage in the receptacle while the dryer is running.

What do you mean by receptacle? I'm not sure I want to try measuring voltages that high on my own with my DMM. I might need to recruit a professional at some point.

In wiring this fixture I noticed that power is kind of daisy chained from light to light. In other words, multiple wires were connected at this ceiling port, cascading power to lights down the chain. Though this one is quite secure, perhaps there is a loose wire in the chain upstream from this light. It's still odd that the old light fixture works, but mine doesn't. Unless it just happens to draw little enough that a loose wire isn't an issue. I'll check it out!

Thank you both for the quick reply and welcome message!

 

What do you mean by receptacle?

The power receptacle that you plugged the dryer in to; also called a power outlet or just outlet.

In wiring this fixture I noticed that power is kind of daisy chained from light to light.

This is common for much electrical wiring. Only appliances get home runs.

Though this one is quite secure, perhaps there is a loose wire in the chain upstream from this light. I'll check it out!

Something upstream could be loose. Running something like a dryer can cause a resistive connection upstream to get hot enough to cause a fire.

The fact that your fixture ran at low power, but fails with high power, works in another outlet and a hair dryer won't work means it's not likely your fixture.

 

Gotcha. So it's definitely not normal then, right? I wanted to confirm my suspicions before bringing it up to my landlord. It seems clear that something in my wiring needs to be fixed. Now I'm paranoid that there could be dangerous wiring in the rest of my place!

 

Now I'm paranoid that there could be dangerous wiring in the rest of my place!

Unfortunately, this happens too often. If you operate a high power appliance on a circuit, the wires, and associated connections, are subject to repeated heating and cooling cycles. Over time, connections can become loose and the problem accelerates with use.

This can also happen with shoddy workmanship, running circuits longer than code allows, using undersized wire, switching 15A breakers to 20A because something is causing the breaker to trip, etc.

You're lucky you noticed the problem.

I had a similar situation in an outlet. It sparked when I plugged something in so I opened the box to see what was going on and the receptacle fell apart while I was checking the connections.