Bridge rectifier overheating

Discussion in 'General Electronics Chat' started by Gabriell, Jan 16, 2016.

  1. Gabriell

    Thread Starter Member

    Jan 16, 2016
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    Hi guys
    Im working on a project but im running into some issues. Please keep in mind i dont know much about circuits and power supplies.

    Im using a MOT ( rewired secondary coil, primary is original) that puts out 32v and im using a bridge rectifier that is rated 1000v 50A but it keeps overheating even when im drawing only 4A. Any idea what can i do? And also my primary coil get pretty hot after a while.
    Suggestions???
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    What is connected to the + and - terminals of the bridge? Can you post a schematic? And a photo of your setup (one overview and some closeups.
     
  3. Gabriell

    Thread Starter Member

    Jan 16, 2016
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    Thank you for your reply.
    Sorry but i cant do a schematic its a bit over my head. But i can explain what is connected to.

    Im using it to power 2*100w LED. The positive side of the rectifier is connected to 2 capacitors 50v 2200uf in series and the its connects to the positive side of the led. The negative lead is connected straight to the negative side of the led. The leds are wired in parallel with 2 resistors between the negative leads ( 5w 1.5ohm each ).
    I cant put up any pictures today as i pulled the whole thing apart. Could do it tomorrow if it helps!

    Any suggestions are welcome to improve the power supply.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You are connecting 2 LEDs at 100 W each (200 watts total) to a transformer of 32 v. That means you will need about 6 amps to make your 200 watts. I don't know the Vf of the LEDs, I assume they are 36v diode arrays.

    How hot is "hot"?
     
  5. Gabriell

    Thread Starter Member

    Jan 16, 2016
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    Yes you are correct. The forward voltage of the LED is 32-36v and 3-3.5amps.I try to under power it so it doesn't burn out hence the 4 - 4.5 amps.

    The rectifier gets hot to the point where i cant touch it anymore without burning my self. I mean it gets really hot in about 3-5 min.

    Here is a picture of the led im using.

    I also tried higher voltage ( 120v and 4*100w led ) but my secondary coil can't take it, it starts to smoke in less then a min...
    100w led.JPG .
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    If you cant draw it, then take pictures of it and post it.
     
  7. Gabriell

    Thread Starter Member

    Jan 16, 2016
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    IMG_1649.JPG IMG_1650.JPG IMG_1651.JPG IMG_1652.JPG IMG_1653.JPG IMG_1654.JPG IMG_1655.JPG

    So here are the pictures.
    The MOT transformer is connected to 240v, secondary coil gives 32v. That is connected to the bridge rectifier. Positive lead goes through the capacitor and then connects to the led. Negative lead goes through the capacitor then to the leds negative. Both leds in parallel with 2 resistors ( also in parallel on the negative lead ). Disregard the middle leds as they are not connected to the system at the moment.

    Im working on this water cooled led system but i cant figure out the power supply. I always have over heating issues in the rectifier and in the primary coil.
     
  8. Dodgydave

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    Jun 22, 2012
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  9. profbuxton

    Member

    Feb 21, 2014
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    Look to me like you two resistors in parallel in series with one led and the other led is straight across the supply.
    Which means the left hand LED is practically shorting the 32V.
    You prob need a resistor in each LED positive lead (or negative).
    Also are you sure the resistors are correct value required? What is required volts on LED?
    Assuming negligible LED volt drop 8ohm resistor is needed to limit current to 4 amps(per LED).
    Why capacitors in series???. Have you done any measurement of volts and current.
    I am not surprised that everything is getting hot since as mentioned it appears that the left hand LED is across with no limiting resistor the supply and may be shorting the supply.
     
  10. Gabriell

    Thread Starter Member

    Jan 16, 2016
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    Yes you are right i only put resistors between the two leds. Im not using the right resistors i know, thats something i need to figure out. I noticed they get hot as well.
    I didnt know i need a resistor between the power supply and the first led as well.
    8-ohm Non-inductive Resistor 20 Watt would work?
    I will change the capacitors and i will put them in parallel.
    The voltage needed for the leds is 32v each with 3amps. ( i prefer a bit lower so the leds dont get hot, around 2.5amps )
    The highest current i was able to achieve was about 4.5amps if i remember correctly. I will have to remeasure it again tomorrow.
    Thank you profbuxton i will do your recommended adjustments and see what happens!


     
  11. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    That style of rectifier needs to be mounted on a heat sink.
     
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  12. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    I get different values for the resistor.

    Before we address that, you need to correct the location of the capacitors. They should be connected across the +- contacts of the rectifiers.

    This will give you 45.5VDC. 32VDC X 1,414 to get peak voltage. 45.5VDC - 32VDC leaves 13.5VDC across the resistor. R=V/I, or 13.5VDC/4A= 3.3Ω. Wattage is 13.5VDV x 3.3Ω=44.7W (use 75W or better)

    A resistor is needed in each leg of the parallel LEDs. Without them, your current draw will run away and hence heat up your components. Not surprising.
     
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  13. Gabriell

    Thread Starter Member

    Jan 16, 2016
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    Thank you for your detailed message. This is exactly what i was hoping for.
    I couldn't find 3.3Ω 44.7w resistors in jaycar but i bought a few different ones anyway just to give it a try. But again overheating issues.


    I bought a few of each and tried to wire them in different ways to all the leds and dc power supply but either overheats or does not give enough amps to the leds.
    IMG_2298.JPG
    After searching the net for resistors this is the only one i found that is close enough to what you recommended:

    http://www.ebay.com.au/itm/3-3-ohm-...153996?hash=item4640ef95cc:g:zVAAAOSwuTxV8cH8

    Would this work? Does it allow enough current flow and forward voltage to pass through without overheating?
     
  14. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Yes, as long as the wattage is higher its better, .
     
  15. profbuxton

    Member

    Feb 21, 2014
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    Ok, so your LEDS are rated at 32v DC and 3 amp?
     
  16. Gabriell

    Thread Starter Member

    Jan 16, 2016
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    yes thats correct
     
  17. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    I thought you had said they were 4A. That changes my calculations.

    13.5VDC/3A=4.5Ω
    13.5VDCx3A=40.5W

    Use a 4.7Ω or 5.1 Ω 100W or higher resistor.

    Can you draw a schematic on a piece of paper, snap a pic and upload it?
     
    Last edited: Jan 17, 2016
  18. Gabriell

    Thread Starter Member

    Jan 16, 2016
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    Sorry i think we are getting a bit confused here.
    So the led is rated 32v 3amps each
    Since is use 2 ( and i want to under power them for longer life ) i need 4 amps ( 4.5max ) for both.
    As i pointed out earlier im sure how to draw up a schematic in a proper way. But i can put up pictures of the setup.

    IMG_2302 - Copy.JPG
    Transformer supplies 32v ac to bridge rectifier
    IMG_2303 - Copy.JPG
    Rectifier is connected to 2 50v 2200uf capacitors ( wired in parallel ) and the negative lead in connected to a 50w 6ohm resistor ( its the best i have right now ) and then it connects to the negative terminal of the led.
    IMG_2304.JPG
    Both leds are wired in parallel with a 50w 6ohm resistor between them on the negative lead.
    ( first resistor gets really hot and the current drops to 1.8amps at the moment )
    Please note that im not using the 2 middle leds in this circuit.
     
  19. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Can you read a schematic? I've developed this one for you.
    Hot LEDs.PNG

    If you can read it, it will help in further testing.
     
  20. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The show resistor can also be mounted on the heatsink.
    Mounted it can dissipate the rated wattage.
    Unmounted it will be much less.

    Bertus
     
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