Low voltage LEDs fluctuate from full to half to off and repeat

Question

I purchased and installed 100' of 16/2 wire and eight lamps (LED Lawn Light 12W 2800K AC/ DC 12V) and Malibu’s 200 Watt Low Voltage Transformer. 96 watts of lamps, I was told, would be perfect for a 200 watt transformer.

I carefully installed the system checking each item as I completed it. The transformer was placed 18 inches from the outdoor ground fault plug with the nearby light sensor. The first light was installed 22' from the transformer with connectors to each of the wires from the lamp. Each time I connected another lamp, I would double check that each connection was successful by turning on the transformer. I then buried the wire 2 1/2 to 3" beneath the mulch after safely taping each connector. The last lamp was attached 18" from the end of the cable.

Testing each connection showed a prefect system installation. However, when the sun set and the system came on automatically, lights began to blink, not in unison, but alternately at random. Each light had full brightness for about 45 seconds, then go to half for about 20 seconds and then turn off for about a minute before it would turn on again with full force to repeat the pattern.

As time has continued, I find the connectors of the cable and the lamps disconnect (lousy connectors, I think, but Amazon reviewers say they are best) and at this time only one lamp is lite. Even with the one lamp it jumps back and forth from full to half every two minutes or so but unlike before, it does not turn off. I now have a full system that is unusable.

Can you help in any way with advise or whatever? Thank you very much.

Answer 1

I see several problems.

Provenance

A quick google of the terms you gave lead me to a quality power supply, but straight to eBay/Amazon for the lights proper. The Amazon items were "cheap Cheese junk" that lacked even a UL listing to assure product quality.

The cheapie lights also came with "pierce the wire" type connectors that jab a spike into the wires. These fail very quickly. These appear to be unique to the halls of China; I don't see any "spike" connectors from any reputable vendors.

Voltage drop

I checked a voltage drop calculator for what happens to 12V at 8 amps over 22 feet of #16 wire. It says you get 1.41 volts of drop. Leaving 10.59 volts at lamp 1.

Now assuming it's 8' from lamp 1 to lamp 2, that wire needs to carry 7 amps. Plugging that in, it's telling me 0.45 volts; totalling 1.86V so far. So at lamp 2, voltage is 10.14V. Continuing to assume 8' between lamps...

Wire from lamp 2-3 carries 6A, dropping 0.39V. Lamp 3 sees 9.75V.
Wire from lamp 3-4 carries 5A, dropping 0.32V. Lamp 4 sees 9.43V.
Wire from lamp 4-5 carries 4A, dropping 0.26V. Lamp 5 sees 9.17V.
Wire from lamp 5-6 carries 3A, dropping 0.19V. Lamp 6 sees 8.98V.
Wire from lamp 6-7 carries 2A, dropping 0.13V. Lamp 7 sees 8.85V.
Wire from lamp 7-8 carries 1A, dropping 0.06V. Lamp 8 sees 8.79V.

A bump in wire size to something like #12 would probably make a big difference here. Alternately, going with smaller lights would work. A top rate kit made by Volt includes #14 wire for 5W lamps.