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  1. #1
    Engineer-in-Training
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    Feb 2015
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    SSR keeps melting.

    I have upgraded the relay on my printer to a SSR following the guide posted here. For some reason I have gone through 3 relays. They keep melting on the 12v load side.

  2. #2
    Technologist
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    Jun 2014
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    Do you have the SSR mounted to a heat sink or other metal surface to conduct away the excess heat?

  3. #3
    Engineer-in-Training
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    Feb 2015
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    Yes I do. It is melting the terminals were power being supplied by my power supply.

  4. #4
    Technologist
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    Jun 2014
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    If it's melting on the power supply side, that's the supply side, not the load side as stated in your first post. Important distinction!

    Are you using crimp type connectors on those wires, or are the wires wrapped around the terminal screws or under the terminal clamp plates?

    A photo of the damaged device would be helpful.

  5. #5
    Technologist
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    Oct 2014
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    A photo and the specs/model number of the relay that you are using would be very helpful in figuring this out.

  6. #6
    Engineer-in-Training
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    Feb 2015
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    Quote Originally Posted by fred_dot_u View Post
    If it's melting on the power supply side, that's the supply side, not the load side as stated in your first post. Important distinction!

    Are you using crimp type connectors on those wires, or are the wires wrapped around the terminal screws or under the terminal clamp plates?

    A photo of the damaged device would be helpful.

    I am using 12 gauge wire and just using bare wires into the screw terminals. it is melting on the side the power supply is attached to, not the side my control board is attached to. I have used the Omron and a different SSR with no long term luck.
    IMG_6139.jpgIMG_6138.jpgIMG_6141.jpgIMG_6142.jpg

  7. #7
    Staff Engineer printbus's Avatar
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    Add printbus on Thingiverse
    I couldn't tell from the photos - what seems to get the hottest (i.e., where is the worst damage)? Is it where the wire wraps around the screw or where the terminal attaches to the circuit board inside the relay?

    Damage from heat means there's a high resistance at that spot for the current being carried. Some general thoughts (which may or may not apply to your case, and some of which have brought on counter-arguments in past threads) -

    * Make sure the wire gauge is adequate for the current.
    * Make sure no strands are nicked or cut off when stripping the wire. Missing or damaged strands won't carry their share of the current.
    * Make sure there is NO wire insulation under the screw terminal - wire strands only. Tightening the terminal on the insulation can leave the wire strands somewhat loose.
    * Make sure all strands are under the wire capture part of the terminal. Strands not captured can't carry their share of the current.
    * Always retighten screw terminals periodically.
    * Solder creeps with pressure. Don't tin stranded wire being used with a screw terminal.
    * Don't let wires flex at fixed terminals with use. Doing so can eventually lead to metal fatigue at the terminal, leading to higher resistance. Doing so also puts a bit of push-pull action on the terminal; over thousands of movements this can then lead to the solder connection degrading with time. Strain relief the wire somehow away from the terminal so the flex occurs somewhere other than at the fixed terminal.
    * In an application where wires flex constantly with use, consider using high-strand silicone insulated wire like that often used in RC hobby stuff
    * Where I worked, the assembly techs were not allowed to attach stranded wires directly to screw terminals. Stranded wire always had to terminate with a lug, crimp pin, or whatever that could then be properly grabbed by the screw terminal.

    IMO, the majority of issues people have had with the OEM MakerFarm heat bed relays were caused by wires flexing at the relay every time the heat bed moved.

  8. #8
    Super Moderator Roxy's Avatar
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    Those Fortec SSR's you get on eBay are usually counterfeit. They work... But not at the current they are rated at. You need to go with a much higher current rating than what you are really doing if you use 'Fortec' SSR's.

  9. #9
    I second the last posters comments about reliability. You are absorbing 12V and up to the power supplies max amperage into the device. I have a Fotek DC-DC with a 30A rating that has been running for 2 years since I burned up the originally supplied relay. Suggest Amazon rather than E-Bay - more accountability from the supplier if you do see a failure.

  10. #10
    Student
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    Jul 2018
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    Canada
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    Use a current measurement device (ampmeter) to see how much current is travelling through the Solid State Relay. That will help you determine the relay size needed.

    And, if you don't want to burn your house down, I strongly suggest to use a circuit breaker to protect your wiring and relay. See your local electrical code.

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