LED light is blinking in sync with a Parmak fence charger

I replaced a dead barnyard light with a new LED light (a Defiant unit from Home Depot) that is bolted to the outside of large metal barn. I also have a old Parmak FM-1 electric fence charger connected to a separate circuit breaker. After the light has been turned off, I can see the LEDs in the light blink softly, in sync with the 'click' from the Parmak. Somehow, there is voltage from the Parmak leaking through either the circuit panel or the metal barn, energizing the LEDs.

The Parmak is in a wooden box mounted on the side of the barn. There is a single ground rod for the Parmak, which is located about an inch away from the metal barn. If I disconnect the Parmak, wait 20 seconds, and reconnect the Parmak, the LEDs no longer blink. My guess is that some capacitors in the LED light had enough time to discharge so the leaking voltage is no longer strong enough to energize the LEDs. The LED light is connected via 12/2 with a bare copper ground wire. It is possible that the bare copper wire is touching the light's metal mounting frame, which is bolted to the metal barn. It is also possible that the internal electronics of the LED light are directly grounded to the mounting frame.

I am thinking that the Parmak's ground rod is too close to the metal barn, effectively making the entire metal barn part of the ground circuit for the Parmak. The metal barn then conducts the voltage into the LED light.

Does this theory make sense? Aside from actually putting in a new ground rod some distance (20-30 ft?) away from the metal barn, any suggestions for other diagnostic testing that would help identify the cause of the voltage leakage? Thanks!

I would think that a ground rod that close to the metal barn should also have a physical connection to the barn metal.

Possibly RFI, (radio frequency interference), early radio transmitters were called spark gap. An electrical discharge of high voltage was made across a spark gap and used to create Morse Code. Early ham operators some times used Model T Ford coils as part of their transmitters. Early radio receivers used tuneable circuits and crystal detectors, which have been replaced by diodes now. An LED is a light emitting diode. I hope I wrote this as I understand it and so it makes sense. It will take someone more knowledgeable than me to design a filter for your application to stop this interference or you can live with it. I've been told if you hold a florescent bulb near an electric fence it will glow but I have never tried that. Leroy

I also believe that idea. I also believe the bare ground in the supply to the LED should be connected to the frame of the fixture, and the breaker box ground buss. If it continues to do the blinking, a Faraday cage (tin box) around the charger might squelch the RFI. Jim

My day job is a firmware engineer and I'm currently working with RFID hardware from ThingMagic and also involved in RF/SARS testing of cell modems. I'm not an electrical engineer but I'm doubtful that RF signals can energize the LEDs either directly or via the metal barn. The ground here in Oregon is rather wet and acts as a conductor. The metal barn is certainly in contact with the ground. I'll go with conductivity from the ground rod through the damp soil into the metal of the barn. Also, I have multiple other LED lights in the barn and they are behaving normally.

Just jumper that ground rod to the barn metal and I think your problem will go away.

The LED's themselves operate of off DC and are no doubt fed by a switching power supply, likely containing diodes, a transformer, and capacitors.

All sorts of interesting stuff could be going on there! Voltage spike from the fencer could be getting into the SPS unit and getting rectified and charging the filter caps in the power supply to enough voltage to partially light the LED's, IMHO.

We have led string lights on an outside tree
for Christmas. 3 are plugged end to end and 1
is plugged separately. On the same duplex
circuit is a set of electronic bells. The
other night I saw just the single string
blinking in cadence with the bells. The next
night the single string failed to light. Next
day found plug fuse blown, when replaced the
fuse there was arcing coming from the female receptacle of the string and the fuse blew. Close examination revealed moisture in the electronics of the led and burnt up. Perhaps your led fixture electronics have moisture in them.

Eddy currents in neutral of a multi-wire branch circuit. No current should be passing into a ground rod. If it is you have more problems than can be fixed by computer.

If the bare ground wire is grounded on both ends, it is at least grounded. If an LED is near voltage, or can have Stray Magnetic
fields around it, it will blink faintly. Put a choke filter on the power supply of the charger (or an isolation transformer) and
the issue will disappear. Having faith that the earth will carry a ground from sheet metal is not best practices. Jim

Where is the hot wire coming off the fencer?

I had an experience where I laid a box of flourecent tube parallel to and about 2 feet away from the wire leading from the fencer out to the pasture. First time I walked in the barn in the dark it was a bit
suprising to see that box flashing!

Also they make indicators to show you your fence is working, that are a LED that clips to the fence wire. No ground involved, and the LED flashes as the fencer runs. I would vote for there being enough RF
energy from the fencer to power the LEDs.

I think that I've found the issue. I was cleaning the charger's ground rod and discovered that buried in the ground was a second ground clamp. The original installer (from 20+ years ago) had connected the ground from the charger to the ground rod for the main electrical panel in the barn. Ugh.

The original installer (at least two owners ago) violated the requirements that I've seen in every electric fence installation guide that I can find, which is to keep the charger's ground rod at least 50' from any other grounding system. No need to assume a ground rod to ground to sheet metal to LED light connection when I've got a direct connection.

I'll be able to get the new ground rod and install it in a few days. I'll report back then with the results.

Thanks for all your help and ideas!

Thanks for the reply. Dead and or crippled is not worth cute. Giving the info about Carbon Tet has been my task when it comes before a body of people that could have one on hand. Jim

I think you are on a possible fix. The more that is described the more it sounds as if the whole shed is aluve. LEDS are very sensitive and require very little power. Get a load of this video. Takes a little time but ispretty neat.
tubes in a field

Electric fences are famous for all sorts of interference and I've seen on this site references to LEDs interfering with garage door openes etc so theres two villians. In New Zealand where electric fences are used very extensively, grounding is considered critical. It usually involves a ground wire connected to several rods about two mteres long, in damp ground if possible

Is there an open neutral and the neutral current is now flowing through the ground system?

Success!

I connected the ground wire from the Parmak to a new ground rod that is 30' from the original electric panel ground rod. No more LED blinking!

I'm fairly certain that somewhere on the backside of the 3 mile long electric fence, there is a bush or blackberry cane that is touching the electric fence. This would complete the fence circuit, sending current through the ground rod. When the charger's ground was directly connected to the main panel's ground rod, the charger's current showed up as the blinking LEDs. Remove the direct ground connection and it all works as expected.

Thanks to all of you for your time and suggestions!