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Heated Bed - Fake Fotek Solid State Relays (SSR)

Discussion in 'Mods and Upgrades' started by Ziggy, Dec 16, 2014.

  1. Ziggy

    Ziggy Moderator
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    When I was looking for a Solid State Relay (SSR) to control the heated bed I bought one of these on eBay
    index.php.jpg

    Solid State Relay SSR-40 DD DC-DC 40A 3-32VDC Input 5-60VDC Output

    Looked perfect. Fotek is a reputable brand and the SSR has a 60 volt, 40 Amps DC rating which should handle the 10 Amps for the Robo heated bed no problem.


    But when I connected it up and turned the heated bed on, you would not believe how hot the Fotek SSR was when I turned it off about 30 seconds later. Even the plastic case melted as you can see in the pic!!! So it must have reached a temperature of around 200C or more.

    IMG_0495.JPG

    There is no way a 40 Amp SSR should get that hot when all it is handling is about 10 Amps.

    Then I found this

    http://canada.ul.com/safetyalerts/u...nterfeit-ul-recognition-mark-release-13pn-52/

    It turns out many of the so called "Fotek" solid state relays sold on eBay are fakes and will not carry the load. Obviously the FET inside the SSR has way too high an "on" resistance to handle 40 Amps. But it's not possible to see the components as the SSR case has been filled with some gunk.


    IMG_0497.JPG

    I am just posting this in the hope that others won't get caught out by the fake SSRs. And many of the SSRs sold on eBay under this "Fotek" brand are high voltage AC types. Obviously there is a safety issue if these are also fakes.
     
    #1 Ziggy, Dec 16, 2014
    Last edited by a moderator: Dec 17, 2014
    2 people like this.
  2. Mike Kelly

    Mike Kelly Volunteer

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    Ouch! I wonder if the ones sold on amazon have the same risk.
     
  3. Ziggy

    Ziggy Moderator
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    Just looking at the SSR photo on Amazon

    411URtdqYBL.jpg

    and the warning information at the canada.ul.com site, the Amazon SSR is not UL authorized.
     
  4. Mike Kelly

    Mike Kelly Volunteer

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    What's funny is the one I got the voltages didn't even match the description. It's been running fine for almost 8 months now, but I'm using a heatsink on it.
     
  5. Ziggy

    Ziggy Moderator
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    Mike, Maybe you have a genuine one? Maybe some of the fakes are better than others?

    Have you compared yours with the photos on the canada.ul.com site?
     
    #5 Ziggy, Dec 16, 2014
    Last edited by a moderator: Dec 16, 2014
  6. John Durr

    John Durr Member

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    Hello
    has anyone found a good spot to buy a good one I would like to add it to my printer?
    thanks
     
  7. Stephen Capistron

    Stephen Capistron Active Member

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    Omega.com

    McMaster

    Neither of which are the cheapest, but your odds of getting a fake are almost zero.
     
  8. Mike Kelly

    Mike Kelly Volunteer

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    AutomationDirect sells probably the cheapest.

    I got my 40A fotek from amazon.
     
  9. CAMBO3D

    CAMBO3D New Member

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    SSRs require a heatsink to use the max rated amps.. if not.. your looking at a meltdown as you describe. A 40amp ssr is worthless without a proper heatsink. Without a heatsink.. your looking at 5 amps max.. when you buy an ssr. Always read the datasheet.. understand how it works and dont based it off the advertised claim. That 40 amps is probably max with a heatsink and active cooling...
     
  10. John Durr

    John Durr Member

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    How would you use a heat sink / thermal grease with these units. I looked on line but saw no pictures. Can you please show me how?
     
  11. John Durr

    John Durr Member

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  12. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Should work fine.
     
  13. Ziggy

    Ziggy Moderator
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    This is a a regular electromechanical relay. The Omron brand relays are good quality but a regular relay will be physically operating in bang-bang mode very frequently during a print. A solid state relay is a better option, but it appears decent quality SSRs are difficult to find on eBay.
     
  14. David Sparrow

    David Sparrow Member

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    Can someone tell me why to use a SSR over a MOSFET?
     
  15. Mike Kelly

    Mike Kelly Volunteer

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    Less voltage drop so you get more power. You can also run higher voltages more easily with a SSR.
     
  16. David Sparrow

    David Sparrow Member

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    Thanks. Just FYI items designed for AC usually can't carry as much Amperage when used for DC (since AC is technically pulsed) so I'm not surprised there are heat problems. Definitely use the heatsink. :) Thanks for the claification, I'll add this to my things to do.
     
  17. David Sparrow

    David Sparrow Member

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    Are you using the output on the MOSFET to turn on the SSR? In this way using the same system but taking the load off the RAMPS board?
     
  18. Mike Kelly

    Mike Kelly Volunteer

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    Yes that's the common method.
     
  19. David Sparrow

    David Sparrow Member

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  20. David Sparrow

    David Sparrow Member

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    After you have moved the bed load off the mosfet does the ramps board still need to be cooled? I'm asking because the fan would probably be put to better use cooling the SSR heatsink?
     

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