Our home has a Malibu 300 watt transformer for landscape lights. The lights are on during the day. I have checked the photo sensor and have replaced it but the lights keep coming on regardless of what I set the transformer to except for "off". There is a delay of about 15 seconds. Malibu is out of business. Am trying to see if there is a fix to this or if I need to buy a new transformer.

  • Does the photocell have a built-in relay, or does it control an external relay? – ThreePhaseEel May 15 '17 at 18:00
  • @Texasish How did you check your photo sensor ? – Ken May 15 '17 at 18:19
  • The photo sensor plugs into the unit. After making sure that it was in the sunlight and also shinging a flashlight into it, I tried putting the setting on the transformer to each different option. In all cases, no matter the setting, the lights went on after about a 15 second delay. It was my understanding that this was what should happen in the "test" setting. I then went and bought another unit and tested the new photo sensor from that unit and the same thing occurred. – Texasish May 15 '17 at 19:08
  • There is a reset button that I do not think is working properly and do not know if this is related or not. When you push it, there is no resistance of any kind and no sense that you are resetting anything. Again, not sure if this is how it should be or not. When we bought the house, all was fine and the lights came on at dusk nightly and off after 4 hours. Only recently we have not seen the lights on at night which seems like it is coming on in the daytime and shutting off after 4 hours. – Texasish May 15 '17 at 19:10

Old photocells do age. Sort of by convention, they are often designed to fail "on". For instance most street lights and discharge loghts use $15 replaceable hockey puck photocells, designed to fail "on" so city staff can distinguish a failed sensor from a failed bulb, and go up in the boom lift with the right part. The manufacturer will happily sell you a special model designed to fail "off", if you really want that.

New photocells have a different "problem". They have a microcomputer and a clock, and are able to observe light levels over 24 hours and "learn" what night and day look like. This makes them resistant to shadowy locations or slow accumulation of dirt. However they also need 24-48 hours to get acclimated, and if you cut power to them, they may forget and have to learn all over again.

That last bit is important because some people like to put their photocell lights on a switch or mechanical timer too... their modern sensor will never perform right for them.

The transformer is probably solid, the sensor not so much. You also have to watch voltages, you need a different sensor on the 120/230V versus the 12/24V side. You may be better off bypassing the sensor on the transformer, then using a modern photo sensor upstream to switch the entire system on and off.

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Typically the sensor 'sees' light and triggers a transistor that turns on a relay. In your case that transistor can be an ic op amp that has a gain setting (how bright it has to be to turn on). Then you have a delay circuit. Obviously it is seeing everything DARK. Meaning the Photo cell is dirty, the cover over the cell is dark, the cell does not connect to your amplifier, your adjustment for brightness is not correct or that potentiometer is broken.

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  • Or the other electronics are bad. I would probably install a new photocell on the primary side of the transformer. I like the tork 2021 for 120v, it can handle 1800 watts, intermatic makes a similar product but lately they have been failing (on) really fast so I quit ordering after 5+ failures. – Ed Beal May 15 '17 at 18:53
  • Thank you. The photocell appears clear and I bought another one to plug in and try and had the same problem so it would appear that it has to do with internal issues. Not sure how long this has been going on as no one home during the day and frankly when we are on weekends am not paying attention to landscape lights being on. – Texasish May 15 '17 at 19:05
  • @Texasish if you replaced the unit and it is similar to the Tork Ed spoke of - then you have a wiring issue or an additional relay is in the circuit and broken , the transformer is always hot meaning the primary side has voltage all the time - that means there is either a stuck relay in between the photocell and the transformer or the photocell is not wired properly to the transformer / relay. – Ken May 15 '17 at 19:10
  • Since this was working previously, is this something I can open the unit and unstick what is stuck? COuld something like a piece of bark cause a physical blockage and this is what needs to be jarred lose? – Texasish May 15 '17 at 19:11

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