 Hi, I'm MPI. Hi, I'm MPI. I'm brought to you by DigiKey and Adafruit this week. It is in Seattle. Lady Aida, what is the MPI of the week this week? I'm glad you asked. This week is in Seattle. We've not covered them before, but them and Cryden, I think Cryden is their sub-brand, make solid-state relays, and that's what we're going to talk about there. Series 1 Hockey Puck SSRs. They have a bunch of, this is a generic image, the one we've got actually triggers off of DC at a lower voltage, but DigiKey carries a lot of relays. I kind of went to the relay section, they have like 30,000 different options, and relays look usually something like this. Cryden, since I don't have non-solid-state relays, they only make those, but this is a mechanical relay, and this image from the DigiKey site shows on the right you have an electro, sorry, on the left you have an electromagnet, and when current goes through that copperish coil, it turns into a magnet, which then pulls the two flanges on the right together and make the contact bridge. They join together, thus connecting the circuit. People have been using electromagnetic relays for a very, very long time, and they're inexpensive, and again, there's hundreds of thousands of them available, different sizes, configurations, currents, et cetera, they can switch AC or DC, all's good, but there's one, there's actually two kind of big deal problems with mechanical relays. One is that, and this is the one that happens the most, is they have to be replaced after a while because the contact are only rated for a certain amount of planks, connections and disconnections. After a while, especially if you're switching high currents and high voltages, you'll get arcing on the contacts, and the contacts, even if they're gold plated, will eventually start corroding, and you see this is an image from Wikipedia on the right, on the middle left, that's what a clean contact set looks like on the middle right, that's what corroded contacts look like, and so a lot of relays are designed to be plugged in, to unplug them basically, and replace them when they've reached their life limit, so often you are like, oh, the local stop lights stop working, it's because the relays inside broke and they just have to be replaced. The other thing with mechanical relays is they're slow, like the electromagnetic has to turn on, and then the magnet has to pull that flange of metal over from left to the right, and so they're not fast, you can't, for example, use them to like PWM to dim lights, or dim, you know, high power heaters or whatever, you can only use them to turn on and off, which is, you know, again, fine, but sometimes you want more control, and that's where an SSR comes in, so there are, there's many families from the, in sizes from Criedon, Sinsata, we're going to just talk about series one, but they have a couple different variations, some of them can do AC, some of them do DC, some of them do have back-to-back SCRs, and some of them have thyristors, and, you know, they have documentation showing all the differences between why I might want one or the other, and these are often used in, you know, robotics, automotive, automation, where you're switching huge amounts of current, for example, you know, we had our oven serviced only about a month ago, so you had to open up the oven, and you can see on the bottom there, those blue things, if we zoom in, those are the controllers for the heating elements, which are, you know, like up to 100 amps total across all of the different heating zones, so these are like, you know, easily 20, 40 amps at 200 plus volts, you can see the, you know, honky-puck style relay down there, each blue one wired up to each set of heaters, multiple heaters for top and bottom, so not surprising that these SSRs, you want something that's reliable, that can switch a huge amount of current, and won't fail on you, especially you don't want an oven to fail, and the contact sticks, and then it like stays on, that's no good. This latest family from Crydom has a couple, you know, nice, nice these added, basically improving thermal performances and making, you know, cables, the internal connections thicker, so inside this hockey-puck design is a circuit board that has, you know, an opto-isolator and circuitry that will switch on and off the AC current output, so, you know, the inside of it is not that complicated, so you want something, you basically want to make sure that you have one that's easy to heat sink, has good accessories, fits well, is designed safely. Some things I like is that, you know, on the top left they have anti-rotation barriers on the terminal blocks, and on the back they have a really nice flat area for the heat sink to connect, we'll talk about. So, if you look for the, this family of SSRs at Digikey, there's about 3,000 options. Again, I'm only going to talk about, like, one in particular, but all of them have very similar setups, you know, you want to make sure that it's rated for your voltage input and output, and particularly some of them only do AC, some of them can do DC as well. You'll see here, like, the wiring diagram that shows the inside of it, and then you can have the load on either side, but they are opto-isolated, which is kind of nice, and a lot of them you can drive from little as 3 volts DC. You tend to be able to drive them from DC or AC, but the output, sometimes you can only drive AC depending on what's inside. For example, this one, the one I picked, can do up to 280 volts AC, up to 90 amps, and can be controlled from 3 to 32 volts. There's two output types. There's the zero cross and instantaneous. It is easier on everybody if you only switch current on or off on the zero crossing, or at least, you know, switch off on the zero crossing, switch on the zero crossing, because then you don't have as much in-wash current. However, there are some times where you might want to turn on or off in the middle of the cycle, and so some are kind of set up to do one or the other. It's not the one of the configurations that's often set up. All these have the same kind of chassis mount, and they have different current ratings. You're going to pay more for bigger current ratings, so they start at 10 amps, they go up to 125 amps, but each one of them has basically the same forward voltage, and that's the thing you have to watch out for when using SSRs. One thing that's nice about relays is besides just being inexpensive and plentiful is they don't need heat sinking, because the contact resistance is nearly negligible. There's no circuitry inside, so you don't have a forward voltage drop. You don't want to drop across it. Whereas these, if you see kind of on the top area, middle, they save maximum on-state voltage drop at rated current 1.15. So that's 1.15 ohms, which means that as you are at volts, which means as your current goes up, 10 amps, now your peak dissipation is 11.5 watts up to 100 amps. Now you're talking about 115 watts that you might have to dissipate, and these come up to 90 amps. So yeah, we're talking about 100 watt dissipation, and the circuitry inside definitely, definitely cannot handle dissipating that much current through the past transistors on the output. So what you definitely need to do is have heat sinking for them, and that's a very common issue with SSRs is you're like, how come I can't control the current that I think I can is because you're not dissipating the current off of it, you're not dissipating the power off of the body of the SSR. So Crydom has some documentation showing here's how you do the calculation. You basically treat it like it's a transistor, but it's just very mechanically large. Maybe I'll show it on the overhead real fast, because I happen to have this. So this is the, really, I just got the, you know, it's only I think 25, 25 amps maximum, the 1225, low voltage input high, up only up to 100. Yeah, so the 12 here is 120 volts AC and 25 amps. This is kind of the least expensive, most common for basic American or Japanese power. And then on the back, you see you've used these to bolt onto here, and this is your nice flat heat sink surface. So don't forget to also pick up a heat sink, and they come in different sizes for the different amount of degrees per watt. You'll need to dissipate, do the math, right? You don't, you can get away with, looks like the HS172 if you're only dissipating 10 watts, but if you're doing, you know, 100 watts, maybe I'll have to check out that HS2201DR, the gigantic thing in the middle there. They're going to be more expensive the bigger they are. So, and of course, they'll take up more mechanical space. I have so far not seen any actively cooled SSRs. I think that they're not done because it's just another thing that could possibly go wrong with your setup. Okay, next up, they also have covers. Yes, I actually got one, this is quite nice. Cheap SSRs don't come with covers. Some of these, you know, the SSRs actually come with them already attached in, but I really like it. It's a nice clear safety cover. Protect you from the SSR, it's high voltage, and protect the SSR from you. You don't want your oily fingers getting all over the contacts and possibly loosening them. That's no good. So, this is the one I picked, you know, but there's a gigantic family of them, but this is the 25 watt, sorry, 25 amp, 120 volt AC version. What I particularly liked about it is you could control it from as little as three volts DC. We have a video that they post showing how to test it, which is a common thing I've seen from people that are like, I don't understand, there's no, I'm doing, you know, I'm doing a contact measurement using an ometer on the output when I switch it and I'm not getting a beep. Why not? Because it's solid state, it's not mechanical. So, let's check out the video. Yeah, longest video for this segment, but we think it's worth it. Really good. So, watch it. Welcome to this edition of Crydom Tech Lab. One of the most common questions we receive through Crydom Tech support is, how does one perform a simple operational on-off test on a solid state relay? We will demonstrate such a test here today. Unlike electromechanical relays that can be given a basic test with a continuity checker or ometer, solid state relays, SSRs, require a minimum amount of load current to switch. Testing with a meter does not present enough of a load on the SSR to allow it to turn on. And there is no mechanical contact closure within to show continuity on the meter. Additionally, since an SSR is by definition a relay with no moving parts, there is no audible click to provide confirmation that the input is actuating the output. All of that being said, the basic setup and operational bench testing of an SSR is quite simple. Note that line voltage will be present during this test on various terminals, so be careful. For this demonstration, we'll be testing a Crydom D 2450. This is a DC input 240 volt 50 amp AC output SSR. Since this particular relay output is usable on AC line voltages from 24 to 280 volts AC and requires only a minimum load current of 40 milliamps using a standard 25 watt lamp and a 120 volt source is perfectly adequate. The wiring is quite simple. Here are the connections. One side of the 120 volt AC line goes to one of the SSR output terminals. It doesn't matter which either number one or number two. The other side of the solid state relay goes to one side of the load and the other side of the load comes back to the other remaining AC line connection. For testing purposes, there is no particular attention needed for hot or neutral connections. A solid state relay will switch either leg. The last item needed is the input power signal with a three to 32 volt DC input SSR such as the Crydom D 2450. A single good nine volt battery is a convenient input source. Just be sure to observe the polarity. The plus of the nine volt battery needs to go to the plus terminal number three of the relay input. If the SSR to be tested is an AC input type rather than a DC input as this is, the input signal would of course need to be the appropriate voltage. The first test step is to simply apply the line voltage while observing the lamp with the D 2450 being a normally open relay. The lamp should remain off when power is first applied. If the lamp is on at this step, then the output of the SSR is shorted and therefore bad. If the lamp is off, the next step is to see if the output will switch on when the input is applied. By touching the nine volt battery terminals to the input terminals of the relay, the lamp should come on if the SSR is good. Removing and applying the battery should correspondingly flash the lamp on and off. As seen here, this solid state relay passes the basic operational tests. There are many more detailed tests that are performed on SSRs at the factory during production, but a simple bench test performed as shown provides a quick indication of SSR operation. We hope this has been helpful. Thanks for watching this edition of Crydom Tech Lab.