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IndustryArena Forum > CNC Electronics > Gecko Drives > Did I shortcut the gecko drives?
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  1. #1
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    May 2006
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    Did I shortcut the gecko drives?

    I removed the paint inside the box and had cooling paste on all fet transistors, but when i had mounted it back and tried to apply current, there was no light in the led and the fuse was blown out. Does that mean that the backplate of these fets are connected with the electronic inside the transistors and may have shortcut the system?

  2. #2
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    Re: Did I shortcut the gecko drives?

    There are two package types for power transistors. One type is fully enclosed in plactic:



    The other type has exposed metal plate for better heat conductivity:



    That metal plate is electrically connected to the center lead of the transistor. It (usually) needs to be insulated from the heatsink.

    Did the transistors originally have any insulator (a ceramic plate or a gasket) under them?

  3. #3
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    Re: Did I shortcut the gecko drives?

    No they were insulated by the paint at the inside of the box and I removed the paint in order to get a better termal conductivity.

  4. #4
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    Re: Did I shortcut the gecko drives?

    I cannot imagine the paint serving as the only insulator, not even in a Chinese drive. Do you have any photos? Sounds like you need to disassemble the box again anyway, so take some pictures while you are there.

  5. #5
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    Re: Did I shortcut the gecko drives?

    Here and here are some pictures.

  6. #6
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    Re: Did I shortcut the gecko drives?

    Ok, the G540 case that the FETs are mounted to are hard anodized. Hard anodising is an insulator and is essential for the drives to operate correctly.
    If you have removed the anodizing, the drive won’t work.
    Contact Geckodrive and speak to them about getting the drive repaired.
    Cheers

    Peter


    Sent from my iPhone using Tapatalk Pro
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com/store

  7. #7
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    Re: Did I shortcut the gecko drives?

    OK. The Chinese engineers did indeed use the paint/oxide as the isolation. Which is ridiculous, but I guess it has somehow worked.

    Since you have removed the paint, you now have to get a thermal pad. Fortunately, they are not expensive these days:



    https://www.ebay.com/itm/Blue-100mmx...0AAOSw3w9c2iXK

    And, of course, you have to replace the blown fuse and test all 8 transistors. (The 9th device is probably a voltage regulator, not a transistor.)

  8. #8
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    Re: Did I shortcut the gecko drives?

    I think the only damage that happened was that the 10 a fuse blow out. I´ve now replaced it with a new fuse and mounted the drivers one at a time and now the green led lights with all drivers mounted, so I believe it will work also when I put in stepper motor cables. Are there different termal effect on these pads or will it just be the same for all of them. Is silicone a good termal conductor?

  9. #9
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    Re: Did I shortcut the gecko drives?

    Is the hard anodizing a better termal conductor than termal pads? How can I fix it? I´ve heard that the temperature inside can reach 200 degr. C so I believe I need somthing else than normal paint.

  10. #10
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    Re: Did I shortcut the gecko drives?

    Silicone may not be the best heat conductor, but it works quite well, costs peanuts and is easy to use. In terms of heat transfer, a slightly better solution in your situation might be a piece of mica sheet with a thin layer of thermal paste on both sides.

  11. #11
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    Re: Did I shortcut the gecko drives?

    Quote Originally Posted by jaru-eri View Post
    Is the hard anodizing a better termal conductor than termal pads?
    It probably is, because it's much thinner. If I may ask, what inspired you to mess with the cooling? Were the transistors overheating?

  12. #12
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    Re: Did I shortcut the gecko drives?

    Quote Originally Posted by CitizenOfDreams View Post
    It probably is, because it's much thinner. If I may ask, what inspired you to mess with the cooling? Were the transistors overheating?
    I thought I would get a better termal conduction with termal paste than the layer, but didn´t know it would shortcut anything.

  13. #13
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    Re: Did I shortcut the gecko drives?

    Quote Originally Posted by CitizenOfDreams View Post
    Silicone may not be the best heat conductor, but it works quite well, costs peanuts and is easy to use. In terms of heat transfer, a slightly better solution in your situation might be a piece of mica sheet with a thin layer of thermal paste on both sides.
    Is mica sheet an electric insulator and a good termal conductor? And what about the termal paste if some of it squeeze beyond the sides of the sheet, can that transfere current? I use Arctic Cooling MX-2 paste.

  14. #14
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    Re: Did I shortcut the gecko drives?

    Quote Originally Posted by jaru-eri View Post
    Is mica sheet an electric insulator and a good termal conductor?
    It is. Mica has been used for many decades for those exact purposes. It is still a valid solution even though more convenient (not necessarily better) materials exist today.

    And what about the termal paste if some of it squeeze beyond the sides of the sheet, can that transfere current? I use Arctic Cooling MX-2 paste.
    Most thermal pastes, including MX-2, do not conduct electricity. It is perfectly fine if a small amount squeezes out and gets on the circuit board. Just dont get crazy with it, the paste layer needs to be as thin as possible.

    I personally prefer regular cheap white silicone based thermal paste because it is much easier to spread than the fancy "gaming" stuff. Performance wise, the difference between different pastes is negligible for most situations.

  15. #15
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    Re: Did I shortcut the gecko drives?

    Quote Originally Posted by jaru-eri View Post
    I thought I would get a better termal conduction with termal paste than the layer, but didn´t know it would shortcut anything.
    Well, you found out the hard way. You should have applied the paste without removing the paint, that would have improved the thermal contact.

  16. #16
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    Re: Did I shortcut the gecko drives?

    Are there different types of mica. When i search on the web there are many places that cescribe mica as a termal insulator. https://www.google.com/search?client...mal+properties Thermal conductivity perpendicular to cleavage plane W/(m•K) 0.7

  17. #17
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    Re: Did I shortcut the gecko drives?

    0.7W/m/K may not seem much, but it is perfectly adequate considering the thickness of a mica sheet. They make 0.1mm and even 0.05mm mica sheets. 0.05mm mica would have the same thermal performance as 2mm alumina.

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