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Thread: SSR or Mosfet

  1. 01-05-2016, 11:50 AM #1
    nitrografix
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    SSR or Mosfet

    I have a Geeetech Prusa i3 x and was wondering if and how anyone else has ran their heatbed off of an external 12 or 24v power supply. From what I been reading, I think whatever you use you have to use a diode for backfeed but I was wondering which one would be more reliable and work the best. Thanks guys
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  2. 01-05-2016, 02:14 PM #2
    BLKKROW
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    Quote Originally Posted by nitrografix View Post
    I have a Geeetech Prusa i3 x and was wondering if and how anyone else has ran their heatbed off of an external 12 or 24v power supply. From what I been reading, I think whatever you use you have to use a diode for backfeed but I was wondering which one would be more reliable and work the best. Thanks guys
    I have a SSR for my heatbed. It has worked flawlessly for a few months now. It is connected through my Rumba board and shares the power supply with everything else.
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  3. 01-05-2016, 07:15 PM #3
    Roxy
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    Quote Originally Posted by nitrografix View Post
    I think whatever you use you have to use a diode for backfeed
    Typically, the mechanical relays with an electromagnet need a reverse biased diode across the relays coil. That is because when the current is switched off to the relay's coil, you get a big inductive kick that can fry the circuitry driving the coil. That is the only time a diode is required as far as I know. And a you wouldn't need that with a solid state relay because there is no coil. Maybe the Solid State Relays need a diode for another reason?
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  4. 01-06-2016, 03:18 AM #4
    Mjolinor
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    Quote Originally Posted by Roxy View Post
    Typically, the mechanical relays with an electromagnet need a reverse biased diode across the relays coil. That is because when the current is switched off to the relay's coil, you get a big inductive kick that can fry the circuitry driving the coil. That is the only time a diode is required as far as I know. And a you wouldn't need that with a solid state relay because there is no coil. Maybe the Solid State Relays need a diode for another reason?
    Probably true that you do not need a protection diode but just stick them in anyway. They do no harm and cost pennies so if you don't know if it needs a protection diode or not it makes sense to just use one.

    Transistors often have them built in anyway.
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