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.