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Malibu Landscape Lighting Parasitic Draw

dave9

Mar 5, 2017
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I'm tasked with repairing a Malibu Landscape Lighting set that is exhibiting parasitic draw.

It's a 12VAC setup, old (20+ years?) unregulated linear transformer design with optical sensor, multi-position switch for hours runtime, and a relay to switch power on and off. Originally had ~10W incandescent bulbs.

After swapping (AC tolerant) 1.5W LED bulbs in, it is now lighting the LEDs very dimly after the intended power on period has ended, and they stay on dimly until next power on cycle. They do get up to full brightness when they are supposed to be powered. It occurs to me that this parasitic draw may have been present previously, but had gone unnoticed because not enough current to make the original incandescent bulbs glow.

Does anyone know of a schematic for this or similar non-SMPS based outdoor lighting?

Any ideas on what could be causing the parasitic draw? I have not had a chance to tear it apart yet, but wondering if it might be something like carbon fouling in the relay. Given it is outdoors I suppose it could even be bug parts or spider webs causing a resistive path, but doubt it is water as it has had plenty of chances to dry out after rain and isn't very exposed to it.

I suppose after being outdoors for so long it could even be traces coming off the PCB to cause a short but I'd think that soon enough, that would have stopped normal power-on operation while it has done this for months now.
 

bushtech

Sep 13, 2016
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I am sitting with the same situation with a fanlight that I've changed to led. With incandescents it worked perfectly via the remote but with leds the glow remains. I will be forced to install a wall switch upstream to totally switch it on and off. Bummer
 

Martaine2005

May 12, 2015
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Seems to be a lot of complaints about LEDs staying on dimly when switched off.
On both AC and DC, there is stray current or capacitance which seem to be the culprits.
On DC a load resistor helps. On AC, the definitive solution is to switch both phases. A DPDT relay for example for these garden lights.
It would be nice to know exactly what’s going on though.

Martin
 

Harald Kapp

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Nov 17, 2011
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Check the relay contacts. Sometimes you can find capacitors or Varistors across the contacts as a protective measure (protect the contacts from an electric arc). The leakage through such a component may be enough for an LED to be dimly lit.
 

73's de Edd

Aug 21, 2015
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HEY ! You'se Guys . . . . .

Can you install DVM metering . . .so as to be in its AC ammetering(milli) series as an inline installation . . . . . going to one LED lamp being lifted from its transformer wire and thereby, seeing just how much ? ? AC current that LED is pulling when in " its supposedly " OFF condition . . . . yet,was still dimly glowing ?
Considering, when using conventional halogen lamps , a lamp may be pulling 10 watts in using ~ 830 ma amps or a whole yard cluster may be taking 100 + watts from the transformercontrol unit.
Considering that some select 50 watt spots might not have also been used on tall trees.
BTW isn't that Maliboo-boo (RIP Malibu) transformer / control unit having AC Line power initially coming into a Photocell controller and then out of it into an ADJUSTABLE knob set / tab set / or digital set timer that then has its isolated transformer secondary winding fused to feed its 12V AC to all of the lamps ?

AND you apparently don't have the timer program set early enough in its coming on, or late enough in its turning off, or you wouldn't even notice the dim LED lighting condition.
In that way it is over commanding the photocell. Then only the different daylight length times need to be correcteded for seasonally.


INITIAL FACT FINDING EVALUATION . . . . .

Try a 47 ohm resistor directly across the LED lamp terminals, to then see if the dim light is then being quenched in a testing in a dark outside condition for the evaluatiion.

THE LED LAMP . . . . .

We can already visualize a one way diode or semiconductor being involved in the lamps internal design.
Since you are using an AC supply source and UNLESS they are specifying that if a DC supply is being used instead of AC that DC positive be aplied to a SPECIFIC terminal on the lamp; try a series inserted diode, of 1N4007 current capability, from one transformer supply wire to its LED lamp terminal, then do the dark test.
Then you reverse that same diodes polarity and dark test again.
If you have not been met with " dark" success yet, reinstall that AC transformer wire to its companion LED lamp and then do the same procedure with the other transformer wire and its connection into the LED lamp.

The reason for the thoroughness / inclusiveness of all possibilities . . . is for the unknowing if their manner of AC / DC compatibility is being accompished by use of a single series diode inside of the unit or if they used a FWB to auto-steer the AC -DC voltage to the LED from the AC supply.


Thaaaaaaaaassit . . . . .

73's de Edd . . . . .


upload_2021-3-4_3-43-36.png

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dave9

Mar 5, 2017
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I'm going to have to open it up... probably due to be cleaned out anyway. I've been waiting for the snow to melt then mud to subside before disturbing the lighting set. Seems that if you move any of the cables much, they may need redone at the nearest lights due to the now non-air-tight, insulation displacement piercing connection design. A few I've soldered to be rid of that marginal connection but not all.

The photocell turns it on, at which point the ambient light is low enough that you can already notice the LEDs glowing. No need to have them running all night, even with LED instead of incan bulbs. Shaving off another 60% power consumption by not having them on till dawn is preferred, and that they are glowing at all, suggests that it may be due for some refurbishment.

I thought about a basic FWR/cap to make DC, but with such a light load, it overdrives the bulbs, some of which are not regulated, just series resistor built in. Obviously there are ways to fix that but since the set works acceptably in the on state, for now I'm just focusing on the fault in the off state.
 
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dave9

Mar 5, 2017
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Had a chance to tear into it today. First, it's Twilight brand, not sure why I thought Malibu, except that I'm sure Malibu made something similar back in the day and was a very popular brand in the US for a while.

There is a 0.22uF film cap across the relay but it is not leaking. Removed it, no change, swapped in a new one anyway since it was out, still no difference.

Measured around 1MOhm resistance between the switched contacts in-circuit, with a load on it was giving the bulbs around 7VAC which is apparently enough to just barely light them.

Desoldered the relay to measure out of circuit, measured open circuit, resistance gone. Measured circuit pads where relay was, measured no resistance. Puzzled, I soldered the relay back in and the fault is gone, lights now stay off when they're supposed to.

I had already cleaned the entire unit of flux residue, wasp nest debris, cobwebs, etc and the fault was still present afterwards, so all I can figure is that the heat of desoldering the relay, broke open the conductive fault path in it. Unfortunately it's sealed so I don't have a reasonable chance to clean it out, ordered a new one instead. Might do a destructive autopsy later.

Old part was TE/Tyco OEG SRUDH-SS-112D1, now out of production. Found a substitute Omron G5LE-14-CF DC12 for a dollar and change at Arrow Electronics. Started looking on Digikey, only to find that their parametric search wasn't showing the choice of relay dimensions, so wasted some time there before finding a workable part #, only to find it out of stock on Digikey but now knowing a viable part #, could find it elsewhere.
 
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dave9

Mar 5, 2017
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Replacement relay came in the mail today, soldered it in and reinstalled it outside powering the lights, seems to work fine again.

I cut open the old relay with a rotary tool but did not observe any carbon or other material that would have caused a short. It looked clean inside, besides a few particles of the plastic casing I'd just cut open. I may tear it apart further to get a look at the contacts, but even if I find something, it doesn't really give me any useful info to use in the future as all I really needed to know was that it was passing power when supposed to be in the open circuit state.

I had to laugh at the amount of packaging to send me a ~$1 relay... outer box big enough to put a small pair of shoes in, inner packing paper above and below, anti-static metallized bag, roughly 18 cubic inch anti-static coated box inside, with anti-static tape around the perimeter, anti-static soft foam in the lid, anti-static dense foam in the bottom. The inner box alone would have been more protective by itself than the packaging for the majority of things I receive in the mail, and all that packaging might have cost them near as much if not more than the relay did.
 
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