Broken photo sensor on outdoor lamp, can replace?

Discussion in 'General Electronics Chat' started by kshahn, Feb 10, 2005.

  1. kshahn

    kshahn Thread Starter New Member

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    Feb 10, 2005
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    I have an outdoor wall-mounted lamp with a photo sensor, to turn it on when it gets dark. Lamp looks like those on this page (though mine wasn't that expensive)

    http://www.lamf.com/goshop/category.php?cat_id=10

    Anyway, the sensor on one of the lamps broke, and the lamp remains always on. The sensor itself is the size of a pencil eraser, has a brass-like housing with ridges on the side.

    Should I try finding and replacing the sensor or should I replace the whole lamp. I'd have to replace both if I can't find an exact replacement.

    Thanks.

    Ki Suk
  2. Firestorm

    Firestorm Senior Member

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    Jan 24, 2005
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    yes, i think u can replace the sensor...it shouldnt be that hard depending on the sensor and how it is placed...hopefully u will get a second opinion on this just to make sure... good luck

    -fire
  3. mozikluv

    mozikluv AAC Fanatic!

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    hi,

    you can replace with the exact replacement which you won't have the problem of recalibrating the sensitivity. but if you replace that by substitution, you just have to recalibrate the sensitivity by trial and error.

    but are you sure it is the sensor that is defective? :blink:
  4. kshahn

    kshahn Thread Starter New Member

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    Well, I'm just going by the fact that it's always on. The other lamp will turn off in the morning. I tried shining a light directly into the sensor but it would not turn the lamp off.

    If anyone knows a mail-order place where i can buy a replacement sensor that would be great.

    Ki Suk
  5. Maxx

    Maxx Active Member

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    Oct 30, 2004
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    Do you have two physicly seperate light fittings or is it one light fitting that has two lamps?

    The reason i ask is because it might not be the photo sensor that is faulty!

    It sounds like it is the triac in the control circuit that is at fault, usually when they blow, they blow in a short circuit condition which results in the lamp staying on all the time.

    If it is a single light fitting with two lamps in the one unit i am still not convinced that the fault is the photo sensor, because both lamps would use one common sensor, the same would usually be true for the triac but i guess some manufactures might use one triac per bulb, although that would seem more costly to me.

    If the sensor on the lamp is just a common LDR (light dependant resistor) you can test this easily using a multi meter set to the resistance range (ohms).

    Be sure to SWITCH OFF the mains supply to the whole light fitting before attempting this or better still disconnect and remove the lamp fitting first and test the sensor indoors so you are not up a ladder at the time and there is deffinately no power applied that you could get an electric shock from.

    With your multi meter you should get a varying amount of resistance reading as you change the light level on the sensor. Usually, waving your hand over the sensor should be enough to see the changes.

    If it appears that the sensor works fine then the next thing to suspect is deffinately the triac.

    To be honest though, i would be inclined to just replace the whole light fitting, unless they are very expensive as you will probably end up spending more time and money fault finding than it is worth. But if you want to do it yourself for the challenge and lurning curve then good on ya!

    Goodluck
  6. kshahn

    kshahn Thread Starter New Member

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    Thanks for your reply. Sorry to be unclear about the configuration. There is one bulb per "lamp" (as in the whole thing, the fitting), so one sensor controls one bulb. There are two fittings, one on either side of the garage door. I was saying that one was broken and the other one wasn't.

    Thanks for supplying the term "light dependent resistor" as I might try looking for one of those.

    I also thought that I ought to just replace the whole thing. They were not that expensive (maybe that's the reason the fitting went bad after 2 years?), though I may have to replace the working one as well if I can't find a close replacement.

    Thanks again for your help.

    Ki Suk
  7. Maxx

    Maxx Active Member

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    Oct 30, 2004
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    Your welcome, there are other light sensitive devices too such as a photo transistor but it would be more common to expect it to be an LDR, and all the ones i have seen have been an LDR.

    I'm still convinced it is not the sensor that is the problem and more likely to be the triac on the circuit board. Usually triacs are rectangular, black devices, often with a metal tab attatched. They have 3 wires leading into them from the circuit board and should have some numbers and letters printed on them.

    The triac would be fairly easy to change with a soldering iron and ideally a solder sucker.

    If you do go into this in any detail, you will need that number printed on the device so you can obtain a replacement, they are quite cheap from most electronic component suppliers, but you need one with the correct ratings. Usually something like 4 amps at 400 volt, which is about the minimum spec for a mains operated device.

    If you take the light down at some point to look at it see if yuo can spot this triac inside and see what the numbers say on it.

    Either of these parts can be tested using a simple multi meter, especially a triac that has been blown short circuit!

    Also you could look for parts inside that appear damaged, like that have gone black or may have cracks appearing in them. Another thing to look out for could be water damage.

    goodluck anyhow, but it probably would be easier just to change the whole light fitting!
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