I often recommend Mosfets over trying to use an SSR in some janky way.

3D Printing
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I often recommend Mosfets over trying to use an SSR in some janky way. Here’s what you’ll need to look out for!
http://www.youtube.com/watch?v=ND8uJWlOgIQ

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Thanks! Few days ago I was thinking about replacing my relay modules with something more reliable and cheap, seems like this is it.

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@Thomas_Sanladerer , thank you so much for this video. For once I actually have some questions: Can you put FETs in parallel in order to effectively lower the RDS(on) ohm rating and get more power out of it? Heaters are typically 40w; car headlights are about 65w. I’m thinking of making a car headlight module for my car :stuck_out_tongue:

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@ThantiK I saw a video in the electronics community for wiring up transistors in parallel, so I would not be surprised if you could. Of course, I am not expert for MOSFETs, but I don’t see why it would be any different. Of course I will defer to whatever @Thomas_Sanladerer says. lol

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Ssr is not an specific device. A single mosfet can be an ssr. Ssr is just the use that you give to the component.
Your terminology is wrong.

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@Mario_Chirinos_Colun , an SSR is typically an opto-isolated triac.

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No . A ssr can be or not opto isolated and the switching can be done by a triac, transistor a mosfet or other device.

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@Mario_Chirinos_Colun https://en.wikipedia.org/wiki/Solid-state_relay – “The control signal must be coupled to the controlled circuit in a way which provides galvanic isolation between the two circuits.” – So in general, yeah - they’re isolated. You’re right about them being built with MOSFETs, etc – but they way they’re built is generally an isolated input with a much lower control voltage to control a larger input, which is isolated.

So yes - his terminology is correct.

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http://www.omega.com/temperature/z/pdf/z124-127.pdf

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@ThantiK yes, you can use multiple identical Mosfets in parallel to lower the DC losses. Unlike bipolar transistors, the current will balance out over the individual Mosfets, even if they are not thermally coupled, for example by sharing the same heatsink.

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@Thomas_Sanladerer - thanks so much for this… I have a huge stock of IRLB3034 MOSFETS (195A, switch at 4.5v but high internal resistance), which when put in parallel should work, and the new printer’s coming this week so, Imma gonna give this a shot and see what happens, it’s basically the same circuit I wire almost every day too.

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I like SSR for heavy duty stuff… Like my digital kiln that uses some pretty heavy amperage and 220 voltage. Just my 2¢

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Hmm, tried the IRL3034’s in parallel with a 15k resistor (what I have in currently) and have just realised, that you’re recommending using P channel MOSFETs. whereas the IRL3034 is a N channel. I was wondering why it was constantly heating. I my basic-ish understanding of MOSFETS, going by my knowledge of the circuit I use, which uses an N channel to switch on the negative side, I used a P channel I need to switch it on the positive side. So, by my thinking I should be correct that it should work with the IRL3034 if I switched the polarities? IE ground to gate, positive to source, positive of the heater to to drain? Going to give it a shot tomorrow, but please stop me if you think something will go tits up.

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I would think SSRs best for switching AC loads and MOSFETS for DC loads. I have seen those tits go up when the transistor goes topless!