Halogen lights to LED using existing PCB

Discussion in 'General Electronics Chat' started by jaeger, Jan 10, 2014.

  1. jaeger

    Thread Starter New Member

    Jan 10, 2014
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    I am replacing the halogen lights on a hood stove to LEDs. The light switch and blower controls are tied into a PCB. A transformer exists for the lights (<12V ac output). The blower controls do not run if I disconnect the light transformer input to the PCB. The LEDs require 12V dc. I have a transformer for this but do not want to run a separate switch for the lights (for aesthetic and cleanliness because I have to drill into the stainless steel hood). Is it possible to use existing light switch for the oven hood? Thank you.

    (ps) limited elect background - not an electrician
     
    Last edited: Jan 10, 2014
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    maybe... without knowing the exact schematic we can't be sure.
     
  3. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Mcgyvr is right, a schematic will help... Which order do these items operate in... all at once, or separate light / blower... some compromise may be in order...
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    and don't forget.. LED's require current limiting..
     
  5. jaeger

    Thread Starter New Member

    Jan 10, 2014
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    I'm trying to get a schematic from the manufacturer - existing one cannot be read anymore due to cleaning. The lights and blower have separate controllers/buttons.
     
  6. jaeger

    Thread Starter New Member

    Jan 10, 2014
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    If I have to use a transformer for the leds and bypass the existing pcb, is it possible to use the existing on/off buttons? I can take a picture of it if I can attach it. The on/off button is connected to a small board along with the oven controls. From here the flat cable goes to the PCB.
     
  7. mcgyvr

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    see post #2.. It still applies..
     
  8. jaeger

    Thread Starter New Member

    Jan 10, 2014
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    Hi,
    Sorry it took awhile - attached is the schematic from the manufacturer.
     
  9. mcgyvr

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    Oct 15, 2009
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    So do the LED's have built in resistors or other form of current limiting?

    assuming they do..
    At the very least I would rectify the AC to DC with a bridge rectifier at the output of C8.
    One wire to ~ and the other wire to the other ~ terminal.
    Then I would measure the output voltage across the + and - terminal of the rectifier.
    Assuming its 12V then you can attach your LED's to those terminals.
    I'd expect the output voltage to be greater than 12V though.. If so you still could be fine but the LED's will possibly be overdriven which would lead to premature failure.
     
  10. jaeger

    Thread Starter New Member

    Jan 10, 2014
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    Right now, I have a separate LED transformer to the lights - just wondering if I can use the existing on/off buttons on the controls without drilling/installing another switch. Thank you.
     
  11. crutschow

    Expert

    Mar 14, 2008
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    It depends upon the type of on/off button it is. Can you show detail of the front and back of that switch?
     
  12. mcgyvr

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    One could "assume" its just a regular on/off switch and its only job is to disconnect one of the legs from the transformer to the C8 connector (basically a switch inline with one of the wires from C7 to C8).. But you would need to trace the wires from the switch into that circuit board that has all the connectors on it that the old lights plugged into and ensure its not switching something else too or connected to something else.

    So we need a complete schematic of that connector board that the lights/switches plug into.. Then you need to include the wiring of exactly how the switches come and go from that board.. See how complex a question can be when you try to rely on an internet forum to rewire something you don't have the knowledge to do on your own.

    Frankly its probably just easier to do what I said and add a small bridge rectifier vs having to add another transformer. But this is exactly why you should know what you are doing before playing with electricity vs spoon-feeding an internet forum hoping they guess correctly.

    I'd guess you reason for this is to same some "money".. But I'd guess that the ROI on this change you are doing is something like 50 years when you include time spent,etc...if at all..
    Sticking another transformer in there will include more losses that could possibly wipe out any savings from LED's.. So when all is said and done there is a chance that this is actually costing you money vs saving anything.

    After I said all that I would say "Just put the halogens back in"

    Man..I'm crabby today :)
     
    Last edited: Jan 13, 2014
  13. Brownout

    Well-Known Member

    Jan 10, 2012
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    If the total load of the LED's and transformer is less or equal to the load of the original halogen light, you should be fine. If the load is greater, then you might need to replace the existing switch with one rated for more current.
     
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