3D printing guides: Going big with Solid State Relays!


Hi everyone, Tom here, and, sometimes, normal
just doesn’t cut it anymore. Like for my pet project, the CerbrisReborn Printer, which
has a pretty massive heated bed with an outer diameter of 350 millimeters. And since i hate
waiting, i decided that it needed an equally massive heated bed. So in my case, i ordered
a 650W silicone heater, but now that i think about it, i should have gone with a full kilowatt.
Still, it heats up the bed to 120°C within about five minutes. Which is ok.
Now, with insane loads like these it is going to practically impossible to run them off
of a 12 or 24V power supply – not only is the power supply going to be ridiculously
large and expensive, but you’ll also have to deal with the kinds of current a bed with
this kind of power would draw – about 55A on 12V, so you’d have to use super-massive
wiring as well. Which is a real pain to do right.
So to deal with this, we’re going to need AC straight from the plug – of course, using
a heater made specifically for your mains voltage of choice – don’t connect a regular
12V heater to the mains. And another word of warning here, mains voltage is always painful
and sometimes deadly. So please, be very very careful when you start working with 120 or
230V AC, make sure you take care of every possible way you could touch high voltage,
and don’t be ashamed to get assistance from someone who at the very least knows how to
properly use protected earth. So what a solid state relay can do, just like
a regular relay, is to take a low-voltage and low-power control signal and use that
to switch a high-power or high-voltage load. The input is 100% insulated from the output,
so you don’t have to worry about the mains voltage frying your electronics. Hooking up
a solid state relay is pretty easy, actually. Connect the output side in series with your
load, so connect one lead of the load or heated bed or whatever you want to drive / directly
to one side of your power source, your mains input preferably the neutral phase, and connect
the # other lead to one of the output terminals of the relay. Which terminal on the SSR you
use doesn’t matter, since you’re dealing with AC voltage here. As long as you connect
it to the # output side of the SSR, that is. Connect the other terminal of the SSR to the
remaining side of your input power, this time preferably the live phase, and you’re good
to go. Then, to actually switch / things, connect the input side of the SSR to the power
output of your control board. This time around, polarity does matter, so connect the positive
side of your output to the positive side of the SSR input. If you’re in doubt which
side on your control board is positive or negative, check out whatever documentation
about your board is available # online / or use a multimeter to measure the output when
that output is turned on. Then, if you just hooked up a heater, connect that heater’s
thermistor just like you would with a regular, low-voltage heater and you should be good
to go. These SSRs don’t require much or any cooling
if you’re using them for what they’re intended.
And you might ask, well, what exactly are they intended for, then? So, the most crucial
thing about most of them is, through the way these work internally, they can only switch
AC voltages properly. If you try to use them for 12 or 24V DC, like what your typical power
bricks output, you are running them outside of their specifications. And what will happen
is that either the SSR gets hot, melts down, always leaves your load powered up, summons
magical unicorns or other stuff like that. There are special solid state relays that
are specifically made to also switch DC, but they can be hard to find and are more expensive
than regular, AC-only relays. So really, if all you want to do is to control DC, you’re
probably better off just using a properly sized-Mosfet – once I get around to making
a video about using them properly I’ll have it linked right here.
The other thing you should know about solid state relays is that they can’t actually turn
off all the way – so when their output should be off, they’ll always have a slight leakage
of a few milliamps. Which isn’t a huge deal with heaters, but it might cause some trouble
if you’re trying to switch electronic loads with them. There is always going to be a small
current that might make, say, a power supply, behave erratically.
And lastly, if your firmware lets you configure the PWM frequency of the output you’re using
to control the SSR, use the lowest frequency possible. With an SSR, this will actually
make the heating cycle # more accurate, even if it says something else in the comments
to that setting. If you keep these things in mind, even the
very cheapest 5 dollar Fotek SSRs will run cool and reliably, even when you’re switching
insane heaters, like this one. If you now feel like buying an SSR and want
to support my channel at the same time, feel free to use the ebay links in the video description,
those give me a small kickback when you buy 3D printer parts or anything else.
Rate this video with a thumbs up or down, depending on whether or not you want me to
make videos like this one, subscribe if you’re already totally convinced that you want to
see everything i upload, and as always, thanks for watching, i’ll see you in the next one.

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