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30A LED dimmer will not work for controlling electric throw?

Discussion in 'Power Electronics' started by jon5500, Dec 2, 2020.

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  1. jon5500

    jon5500

    45
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    Oct 31, 2020
    The question concerns whether or not a LED dimmer, rated for 30A and 12-24VDC, can be used to control the heating of an electric throw?

    The reason for the question: I have a 12VDC heated throw that I wanted to try controlling temperature since the voltage was fixed with no way to adjust. I bought a 30A 12-24 VDC LED dimmer thinking I could control the throw since the maximum VDC is 11.5 and no more than 4.5 A current, but within a short time, and to my great surprise, the dimmer became so hot I could hardly touch it and began smoking. I would have thought "LED" dimmers would be like other 12V dimmers and with the "30A" rating, there'd be no issues but I was wrong..

    Two questions:

    1) Why did the dimmer burn out?
    2) If a "LED" heavy duty dimmer can't do the job, what type of dimmer could at 12VDC?

    Thank you.
     
    Last edited by a moderator: Dec 5, 2020
  2. bertus

    bertus Moderator

    1,336
    525
    Nov 8, 2019
    Hello,

    Where did you buy the dimmer?
    When on alibaba, ebay or aliexpress, they values can well be overrated in the advertisement.
    I found the page:
    https://www.calrad.com/92-342-hg
    What are you using as 12 Volts supply?

    Does the blanket not have its own temperature regulation?

    Bertus
     
  3. jon5500

    jon5500

    45
    1
    Oct 31, 2020
    It was a dimmer I bought from Amazon, Chinese origin. Overrated perhaps, but that much overrated?? Inside the dimmer were
    two HY1707 Mosfets, an LM358, a 78L05, a 555 timer, and support parts. I would have thought it would have easily handled the task, which is why I was inquiring whether or not LED dimmers were for LED only.
    Yes, 12 VDC for the blanket. Normally plugged into the car cigarette lighter, I used a spare 12VDC @ 7 amp switching supply. No, the blanket was fixed so I had hoped to insert the dimmer inline.
     
  4. bertus

    bertus Moderator

    1,336
    525
    Nov 8, 2019
    Hello,

    When the mosfet was driven from the 5 Volts, it can well be that it is not fully driven and still in the linear region.
    When in the linear region, the dissipation will be high and the mosfet will heat-up.

    Bertus
     
  5. Audioguru

    Audioguru

    3,042
    678
    Sep 24, 2016
    When you buy cheap junk from over there then you get cheap junk.
    Maybe the rated 30A is missing a decimal point to make it 3.0A.
     
    Martaine2005 likes this.
  6. jon5500

    jon5500

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    Oct 31, 2020
    5V from where? I was driving the dimmer with the 12V switching supply.
     
  7. jon5500

    jon5500

    45
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    Oct 31, 2020
    Normally, and after my experience, I would agree, but the mosfet has a very high current rating. Even with no heatsink on them (dual mosfet circuit), it still shouldn't have burned at the low amperage. I'm just wondering if I should be using a different type of dimmer in this application, or even a motor speed controller of some type?
     
  8. Audioguru

    Audioguru

    3,042
    678
    Sep 24, 2016
    You said there is a 78L05 voltage regulator in it. The Mosfets barely turn on with a 4V gate voltage and need 10V to fully turn on.
     
  9. Martaine2005

    Martaine2005

    3,104
    851
    May 12, 2015
    I agree with your last statement.
    Is the 'throw' resistive?
     
  10. jon5500

    jon5500

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    Oct 31, 2020
    Agree with, that I should be using a different type of dimmer? Yes, the throw is resistive, appears to use heating wire within.
     
  11. Audioguru

    Audioguru

    3,042
    678
    Sep 24, 2016
    We do not know if that Chinese circuit is linear then it would produce a lot of heat. A modern dimmer circuit uses Pulse Width Modulation to stay cool.
     
  12. jon5500

    jon5500

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    Oct 31, 2020
    According to the info, it does use PWM.
     
  13. Bluejets

    Bluejets

    4,424
    938
    Oct 5, 2014
    Is the power supply suitable......Did you try it on a 12v battery for example..?
     
  14. jon5500

    jon5500

    45
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    Oct 31, 2020
    So far, just the 12V switching supply I have available. Would a 12V battery make a difference?
     
  15. Bluejets

    Bluejets

    4,424
    938
    Oct 5, 2014
    Not normally but the spec does refer to not using ac and just thought maybe your supply might have some ac content and we don't know what you supplied it with.
    Just grasping at straws here as apparently it worked originally so that just leaves something you may have done.

    92-342-HG | 12VDC / 24VDC Hi-Capacity In-Line Single Color L.E.D. Lighting Dimmer (30 AMP). Will not work with RGB L.E.D. tape lighting or 120V L.E.D. lighting. Provides the ability to carry large current loads for adjustable dimming of multiple L.E.D. lighting strips from Calrad, part numbers 92-401-WW (5M Warm White L.E.D. Strip Lighting), 92-401-WH (5M Cool White L.E.D. Strip Lighting) products. (will NOT work with 12\24 VAC transformers).
     
  16. jon5500

    jon5500

    45
    1
    Oct 31, 2020
    Thanks for all the suggestions here. Since the dimmer is now hard to trust after what happened, and since I want to run additional tests, what sort of a set up would be recommended since I don't want to stink up the room with the smoke smell again? I was thinking a couple of fast blow fuses and a smoke detector placed nearby for starters, but welcome other suggestions. Just to note that problems didn't start until after the system had been in operation for quite some time. Thanks.
     
  17. bertus

    bertus Moderator

    1,336
    525
    Nov 8, 2019
    Hello,

    Can you trace the 78L05?
    Does the 78L05 feed the 555 and 358?
    What is driving the MOSFETs?
    Is it from the 358?

    Bertus
     
  18. jon5500

    jon5500

    45
    1
    Oct 31, 2020
    I have an unused one here. Perhaps I will try and draw a schematic from the board, but it won't be for a few days. Just to note that I'm not very good at such a task so there might be errors. In a pinch, I could share circuit board images more quickly.
     
  19. bertus

    bertus Moderator

    1,336
    525
    Nov 8, 2019
    Hello,

    Make some sharp pictures from the component side and the PCB traces side.
    The pictures must be shrinked to about 300 kB to be able to post them.

    Bertus
     
  20. jon5500

    jon5500

    45
    1
    Oct 31, 2020
    dimmercomponentside.jpg dimmertracesside.jpg
     
    davenn likes this.
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