WEBVTT Kind: captions Language: en 00:00:00.000 --> 00:00:03.401 What do you do when you need to control an electrical device? 00:00:03.401 --> 00:00:05.819 Most of the time we use simple switches. 00:00:05.819 --> 00:00:09.632 Any device, be it a light bulb, desk fan, or toaster oven 00:00:09.632 --> 00:00:13.607 needs to be part of a complete breakfast— sorry, circuit in order for it to work, 00:00:13.607 --> 00:00:17.061 so if we put a break somewhere in the circuit… 00:00:17.061 --> 00:00:20.842 then it’s no longer complete and power cannot flow through it. 00:00:20.842 --> 00:00:23.049 And that’s all that most switches do: 00:00:23.049 --> 00:00:28.204 a light switch like this is really just two weird little bits of wire that come together in the middle, 00:00:28.204 --> 00:00:31.602 and when the plastic toggle is moved to the “off” position, 00:00:31.602 --> 00:00:35.341 they’re pulled apart so power cannot flow through the switch anymore. 00:00:35.654 --> 00:00:39.176 Ideally that happens with a snap-action to minimize arcing, 00:00:39.176 --> 00:00:41.281 and that’s why most switches make a clicking noise, 00:00:41.281 --> 00:00:43.584 but that’s a topic for another video that I’ve already made. 00:00:43.584 --> 00:00:46.977 But what if you want to control something… big? 00:00:46.977 --> 00:00:54.092 A light switch can only break 15, maybe 20 amps of current, and there’s a lot of stuff that needs more than that. 00:00:54.092 --> 00:01:00.481 Plus, sometimes you have to control something that runs at a higher voltage, or possibly even uses more phases. 00:01:00.481 --> 00:01:05.628 And what if you want to automate whatever it is you’re powering with some kind of control system? 00:01:05.628 --> 00:01:08.834 Looks like you’re gonna need a contactor. 00:01:08.834 --> 00:01:12.690 Contactors are the unsung heroes of industrial equipment control. 00:01:12.690 --> 00:01:15.133 They’ve come up a few times on this channel, 00:01:15.133 --> 00:01:21.441 but I’ve never really explained what they are and why they’re so useful in so many applications. 00:01:21.441 --> 00:01:23.012 Time to fix that! 00:01:23.012 --> 00:01:26.975 Contactors aren’t something you typically find inside the home... 00:01:26.975 --> 00:01:31.300 except for that one just outside — don't worry, we’ll get there. 00:01:31.300 --> 00:01:33.924 A contactor does what it sounds like it does: 00:01:33.924 --> 00:01:36.942 it decides whether there’s contactor not. 00:01:37.725 --> 00:01:38.765 I’m sorry. 00:01:38.765 --> 00:01:43.778 This is a typical two-pole contactor for controlling single-phase loads. 00:01:43.778 --> 00:01:46.292 Notice that there are six electrical connections: 00:01:46.292 --> 00:01:52.239 we have two up top, two down below, and another smaller pair on the sides of it. 00:01:52.239 --> 00:01:55.084 If I pry this cover off the face of the contactor, 00:01:55.084 --> 00:02:02.036 at first glance what we find appears to be two large copper links straight from the top connections to the bottom connections, 00:02:02.036 --> 00:02:08.022 but looking from an angle reveals that the center section of copper is actually floating above the rest. 00:02:08.022 --> 00:02:11.358 Right now, there’s a gap between the top and bottom terminals, 00:02:11.358 --> 00:02:15.781 so this contactor is open and power cannot flow through it. 00:02:15.781 --> 00:02:18.744 That floating middle section can move, though. 00:02:18.744 --> 00:02:25.290 If I push down on one of these little rectangles, the center links come into contact with the top and bottom links. 00:02:25.551 --> 00:02:29.101 When in this position, power can flow through the contactor. 00:02:29.336 --> 00:02:33.336 Normally, though, it’s not a finger that pushes the contacts together - 00:02:33.336 --> 00:02:36.800 that role is usually handled by an electromagnet. 00:02:36.800 --> 00:02:39.629 And that’s what the terminals on the sides are for. 00:02:39.629 --> 00:02:42.116 Send the appropriate voltage to those terminals, 00:02:42.116 --> 00:02:48.933 and the electromagnet inside pulls down on the center section by way of these arches, which bridges the gap like so. 00:02:48.933 --> 00:02:49.608 [CLACK] 00:02:49.608 --> 00:02:53.641 A contactor in this state is often said to be “pulled in,” 00:02:53.641 --> 00:03:01.409 and when the cover is installed the recess created by the moving contacts provides a visual indicator of the contactor’s current state. 00:03:01.409 --> 00:03:06.670 When power is removed from the electromagnet, of course, we need the contacts to open back up. 00:03:06.670 --> 00:03:07.170 [THUNK] 00:03:07.170 --> 00:03:10.651 That’s done with not one, but three springs. 00:03:10.651 --> 00:03:18.519 The first is sandwiched between the two cores of the electromagnet and keeps them physically separated unless the magnet has power. 00:03:18.519 --> 00:03:24.583 That spring is pretty weak, though, so to ensure the separation of the electrical contacts happens very quickly, 00:03:24.583 --> 00:03:31.370 these additional springs between the arches and the center links become compressed when the contactor is pulled in. 00:03:31.370 --> 00:03:37.745 Once released, they provide an inertial kick by quickly flinging the arches away at high speed, 00:03:37.745 --> 00:03:41.097 and once they’re extended enough to catch the copper links, 00:03:41.097 --> 00:03:45.810 well they get yanked away and off the contacts just as quickly. 00:03:45.810 --> 00:03:47.488 Now, some of you might be thinking, 00:03:47.488 --> 00:03:52.625 “Wait a minute. So this thing is just an overgrown relay?” and to you’d I say: 00:03:52.625 --> 00:03:53.943 yeah, pretty much. 00:03:53.943 --> 00:03:55.939 But there are some differences. 00:03:55.939 --> 00:04:01.720 For a start, most relays offer both normally open and normally closed contacts, 00:04:01.720 --> 00:04:09.112 meaning they might actually disconnect something from power when energized, or even switch power from one path to another. 00:04:09.112 --> 00:04:12.866 Often incorporating multiple sets of each contact type, 00:04:12.866 --> 00:04:18.292 relays can perform fairly complex switching tasks when combined with other circuitry. 00:04:18.292 --> 00:04:22.253 But a contactor is generally just a big power switch. 00:04:22.253 --> 00:04:28.397 And that’s the other difference: relays usually aren’t designed to carry much current or handle high voltages, 00:04:28.397 --> 00:04:33.598 but contactors can and do - that’s why it’s so bulky. 00:04:33.598 --> 00:04:38.050 The large gap maintained between the contact points when the contactor is open 00:04:38.050 --> 00:04:43.891 allows it to handle a maximum of 600 volts AC - much more than a typical relay. 00:04:43.891 --> 00:04:49.800 On top of that, the thick copper links inside allow this contactor to carry up to 50 amps continuously 00:04:49.800 --> 00:04:52.854 (or 40 amps if it’s not a resistive load). 00:04:52.854 --> 00:04:59.872 And on top of that, its contact points are designed to withstand arcing caused by much higher temporary current spikes, 00:04:59.872 --> 00:05:04.948 like the kind you encounter when switching on large inductive loads such as motors. 00:05:04.948 --> 00:05:10.515 That’s what the LRA figure is for - that stands for locked rotor amps. 00:05:10.515 --> 00:05:15.059 Induction motors, by far the most common motor type that this fella will control, 00:05:15.059 --> 00:05:20.889 pull very large amounts of current if the rotor cannot move - or is locked. 00:05:20.889 --> 00:05:22.853 (the rotor is the spinny bit) 00:05:22.853 --> 00:05:28.319 And whenever a motor is started from a stop, for a brief moment it will pull locked rotor amps - 00:05:28.319 --> 00:05:32.568 which is often several times what it pulls when at operating speed. 00:05:32.568 --> 00:05:38.471 As an example, the compressor in this air conditioner normally draws 12.8 amps at its rated load 00:05:38.471 --> 00:05:40.604 (that’s rated load amps) 00:05:40.604 --> 00:05:44.495 but its locked rotor amp draw is 67.8. 00:05:44.495 --> 00:05:51.169 That really high initial current draw is the reason your lights dim for just a moment when your air conditioner switches on. 00:05:51.169 --> 00:05:56.876 Since this can handle a motor that might draw a whopping 240 amps at startup, 00:05:56.876 --> 00:06:00.214 it sure seems like a decent fit for controlling an air conditioner. 00:06:00.214 --> 00:06:05.134 And wouldn’t ya know it, if we take a peek inside the electrical cabinet of this air conditioner 00:06:05.134 --> 00:06:07.034 what should we find but… 00:06:07.034 --> 00:06:08.838 a contactor! 00:06:08.838 --> 00:06:11.149 And some other stuff, but don’t worry about all that. 00:06:11.149 --> 00:06:15.876 This contactor is some kinda budget model that only breaks one leg of the circuit. 00:06:15.876 --> 00:06:17.921 It’s built just like the one we’ve been looking at, 00:06:17.921 --> 00:06:23.019 but the right half of it has turned into a simple link permanently connecting the top and bottom. 00:06:23.019 --> 00:06:25.825 I can only imagine this is very slightly cheaper. 00:06:25.825 --> 00:06:27.545 Now, here’s the important bit: 00:06:27.545 --> 00:06:31.885 the contactor, or more specifically the gap between its contacts, 00:06:31.885 --> 00:06:37.107 is literally the only thing keeping this air conditioner from running right now. 00:06:37.107 --> 00:06:40.342 Unless you bother to shut off the breaker to it in the winter time, 00:06:40.342 --> 00:06:46.650 the wires on the input side of the contactor are live at 240V all the time. 00:06:46.650 --> 00:06:50.907 And, since this has this weird bargain-basement single-pole contactor, 00:06:50.907 --> 00:06:56.065 that means every electrical connection in this device always has 120V potential on it. 00:06:56.065 --> 00:06:57.387 Neat! 00:06:57.387 --> 00:07:03.382 Anyway, if I take a high-tech insulated poking device and press in on the contactor’s pressy bit 00:07:03.382 --> 00:07:06.750 [BRRGSHSSWMMMMAHHHHHHHH] 00:07:06.750 --> 00:07:08.279 it starts right up. 00:07:08.879 --> 00:07:10.347 Weird, right? 00:07:10.347 --> 00:07:15.941 That contactor really is the only control mechanism in this air conditioner. 00:07:15.941 --> 00:07:19.358 Yeah, this is about as basic an air conditioner as you can get, 00:07:19.358 --> 00:07:23.249 so mediocre it can’t be legally installed in the Southwest! 00:07:23.249 --> 00:07:26.548 But there’s plenty of these machines out there. 00:07:26.548 --> 00:07:33.327 Really, it’s just two motors: a big one in the compressor, and a smaller one for the condenser fan. 00:07:33.327 --> 00:07:41.313 They both run directly from AC power, and the unit can only ever be on or off, so a simple contactor is all we need. 00:07:41.313 --> 00:07:46.249 [CLACK and then the air conditioner starting] 00:07:46.249 --> 00:07:51.779 But of course, something needs to turn that contactor on in order to turn the air conditioner on. 00:07:51.779 --> 00:07:53.612 What would that be? 00:07:53.612 --> 00:08:00.865 Well, did you catch that the contactor we've been looking at has a coil meant to run at 24V AC? 00:08:00.865 --> 00:08:06.200 That might seem like a weird choice, but that is in fact a very common coil voltage. 00:08:06.200 --> 00:08:11.752 See, although the air conditioner is effectively a standalone device with its own power supply, 00:08:11.752 --> 00:08:15.955 it needs to cooperate with the rest of the HVAC system it’s a part of. 00:08:15.955 --> 00:08:18.468 In this case, that’s a gas-fired furnace, 00:08:18.468 --> 00:08:24.943 and the control board that operates the furnace just so happens to run on 24V AC. 00:08:24.943 --> 00:08:29.335 That is in fact the de-facto control voltage in the HVAC world. 00:08:29.335 --> 00:08:35.400 So, then, the furnace supplies power to the contactor when it wants the air conditioner to run, right? 00:08:35.400 --> 00:08:37.996 Well, only sort of. 00:08:37.996 --> 00:08:42.553 One of the main reasons HVAC systems operate at this low control voltage 00:08:42.553 --> 00:08:48.891 is that we can safely send it through inexpensive thermostat wire that snakes around wherever it needs to go. 00:08:48.891 --> 00:08:57.079 With a basic four-wire system, the furnace sends its 24V out to a thermostat which can then return it on one of the other three wires: 00:08:57.079 --> 00:08:59.247 one to signal a heating request, 00:08:59.247 --> 00:09:01.032 another for the blower fan, 00:09:01.032 --> 00:09:02.929 and the third for cooling. 00:09:02.929 --> 00:09:06.678 The furnace will respond accordingly to whatever signal it gets back. 00:09:06.678 --> 00:09:13.451 But when the thermostat sends a cooling call, although it does send 24V back to the furnace on the yellow wire, 00:09:13.451 --> 00:09:17.529 from there it goes right to the contactor outside. 00:09:17.529 --> 00:09:24.441 Take a look, I’ve shut the power off to the air conditioner because what I’m about to do is very not good for it. 00:09:24.441 --> 00:09:29.269 If I take the leads of a multimeter set to current (so basically a jumper wire) 00:09:29.269 --> 00:09:31.253 and do this… 00:09:31.253 --> 00:09:33.358 here’s what’s happening outside. 00:09:33.358 --> 00:09:37.320 [rapid and loud clicking and clacking] 00:09:37.320 --> 00:09:43.082 What I’m doing here is taking the 24V from the red wire and sending it back on the yellow wire. 00:09:43.082 --> 00:09:45.714 Once it makes it back to the furnace’s control board, 00:09:45.714 --> 00:09:48.442 it becomes spliced with a second wire. 00:09:48.442 --> 00:09:56.699 This one is part of an entirely different run of thermostat wire that follows the refrigerant lineset of the air conditioner all the way outside. 00:09:56.699 --> 00:10:00.159 Once there, it’s wired to the contactor’s coil. 00:10:00.159 --> 00:10:05.433 All a thermostat does when it calls for cooling is connect these two wires together 00:10:05.433 --> 00:10:12.139 which sends power to this contactor which in turn sends power to the compressor and condenser fan motor. 00:10:12.139 --> 00:10:19.100 So it is in fact the thermostat which is in direct control of whether the air conditioner runs or not. 00:10:19.100 --> 00:10:24.964 Of course, the furnace is supplying the 24V AC, so without it the contactor wouldn’t do anything. 00:10:24.964 --> 00:10:30.785 And this more modern furnace does pay attention to whether there’s power coming back on the Y terminal 00:10:30.785 --> 00:10:36.529 so it can run the blower motor at a different speed between fan-only and cooling calls. 00:10:36.529 --> 00:10:41.638 But a lot of older systems had no idea whether the air conditioner was running or not. 00:10:41.638 --> 00:10:47.930 Thermostats generally send power on both the Y terminal and the G terminal when calling for cooling, 00:10:47.930 --> 00:10:50.889 and power on G will turn on the blower fan. 00:10:50.889 --> 00:10:55.106 So in older setups, as far as the furnace or air handler knew 00:10:55.106 --> 00:10:57.520 it was just supposed to be running the fan. 00:10:57.520 --> 00:10:59.589 It had no idea why. 00:10:59.589 --> 00:11:03.240 So by now, I’m sure you get the point of having that contactor. 00:11:03.527 --> 00:11:06.955 It allows us to switch on the big and power-hungry air conditioner 00:11:06.955 --> 00:11:10.914 with a low-voltage signal wire controlled by a thermostat. 00:11:10.914 --> 00:11:15.080 But there are actually more benefits to this approach than it may seem. 00:11:15.080 --> 00:11:19.178 If you look closely at the thermostat wiring once it enters the air conditioner, 00:11:19.178 --> 00:11:23.380 you’ll notice that it’s not directly connected to the contactor. 00:11:23.380 --> 00:11:29.040 It actually heads inside to a pressure switch attached to the refrigerant lines. 00:11:29.040 --> 00:11:31.086 That switch is normally closed, 00:11:31.086 --> 00:11:38.180 but if the refrigerant pressure should get too high it will open and break the circuit powering the contactor. 00:11:38.180 --> 00:11:42.801 That will of course shut off the air conditioner, protecting its compressor from damage. 00:11:42.801 --> 00:11:47.472 More sophisticated systems might have multiple safety switches all arranged in series 00:11:47.472 --> 00:11:54.992 so that if any one of them opens, the contactor will, too, and thus power is removed from the compressors or whatever else. 00:11:54.992 --> 00:11:58.655 Without the help of a contactor, every one of those safety devices 00:11:58.655 --> 00:12:06.090 would have to break the full operating current of the motors - which is not only difficult for a switch to do, 00:12:06.090 --> 00:12:11.929 but would also require a maze of heavy-gauge wiring capable of handling the full load of the machine 00:12:11.929 --> 00:12:15.831 to stop by and run through every safety device. 00:12:15.831 --> 00:12:19.384 Anyway, before we get too far lost in HVAC trivia, 00:12:19.384 --> 00:12:23.556 I do want to go back to that current-handling ability of the contactor. 00:12:23.556 --> 00:12:26.237 Remember the locked rotor amps thing? 00:12:26.237 --> 00:12:31.410 Well, I’ve got a fancy multimeter that can tell us the current spike that the contactor has to deal with. 00:12:31.410 --> 00:12:32.786 [unit switches on] 00:12:32.786 --> 00:12:40.370 That’s not quite as high as the LRA on the data plate, but 55.1 amps is still quite a spike! 00:12:40.370 --> 00:12:44.916 Thanks to the fast action of the contacts, though, hardly any arcing occurs. 00:12:45.855 --> 00:12:51.310 Hardly any isn’t “none,” though, and already we can see pitting on the contacts. 00:12:51.310 --> 00:12:57.161 These don’t last forever, and the need to replace a contactor here and there is certainly not out of the question. 00:12:57.434 --> 00:12:59.800 It could be much worse, though. 00:12:59.800 --> 00:13:04.697 If I use my high-tech insulated poking device, I can create some gnarly arcing - 00:13:04.697 --> 00:13:12.839 especially because right now the compressor’s rotor is in fact locked as it can’t overcome the high pressure in the system right now. 00:13:12.839 --> 00:13:15.672 You can hear it humming but it's not turning. 00:13:16.428 --> 00:13:23.226 [abnormal buzzing and humming when contactor is pushed in] 00:13:23.226 --> 00:13:28.046 This is why modern thermostats might delay the startup of your air conditioner. 00:13:28.046 --> 00:13:33.639 The compressor needs some time for the refrigerant pressures to equalize or it may not be able to start. 00:13:33.639 --> 00:13:37.535 And if left powered on in this locked state for any length of time, 00:13:37.535 --> 00:13:43.540 that can damage the compressor as its motor windings will get very hot very quickly. 00:13:43.540 --> 00:13:49.460 The compressor usually has its own overload protection, so it’s generally not too much of a concern, 00:13:49.460 --> 00:13:54.791 and the circuit breaker protecting this circuit would probably trip before that even comes into play but 00:13:54.791 --> 00:13:57.135 that’s annoying if nothing else so 00:13:57.135 --> 00:14:04.206 pretty much any electronic thermostat will enforce a delay period between the last shutdown and the next startup. 00:14:04.728 --> 00:14:07.418 But I said we wouldn’t get lost in HVAC trivia. 00:14:07.418 --> 00:14:13.320 Of course, there are many other things one can do with a contactor besides just turn on an air conditioner. 00:14:13.320 --> 00:14:18.680 For a start, 24V is by no means the only option for the coil voltage. 00:14:18.680 --> 00:14:22.274 In fact, through the Magic of Buying Two of Them, 00:14:22.274 --> 00:14:25.843 I have a 120V contactor right here. 00:14:25.843 --> 00:14:32.018 This is nearly identical to the first one, but the coil runs on ordinary AC power. 00:14:32.018 --> 00:14:40.250 This could be useful to, say, turn on some high-voltage overhead lighting in a gymnasium or warehouse with an ordinary light switch. 00:14:40.250 --> 00:14:46.010 Or perhaps create some sort of mystery box for controlling whether a water heater has power or not. 00:14:46.740 --> 00:14:49.180 I’m still not letting you look inside of there, though. 00:14:49.180 --> 00:14:54.190 There are plenty of contactors that have three poles rather than just the two you see here, 00:14:54.190 --> 00:14:57.547 and allows them to send power to large three-phase motors, 00:14:57.547 --> 00:15:01.370 like for instance exhaust fans in a commercial kitchen. 00:15:01.370 --> 00:15:08.407 With a 120V control coil, you could wire that contactor (or multiple contactors) up with the room lights 00:15:08.407 --> 00:15:11.928 to ensure that those fans run whenever the kitchen is occupied. 00:15:11.928 --> 00:15:16.607 And inside really big HVAC systems with three-phase compressors, 00:15:16.607 --> 00:15:20.802 you’ll find them there, too, though usually with 24V coils. 00:15:20.802 --> 00:15:27.860 Really, any time you need to control a big electrical device, a contactor is probably doing the gruntwork. 00:15:27.860 --> 00:15:33.149 And for really big motors, there’s a subset of contactors known as motor starters. 00:15:33.149 --> 00:15:37.589 Those might be as simple as a conventional contactor which can monitor current flow 00:15:37.589 --> 00:15:41.467 and will shut down the motor if it exceeds a certain threshold. 00:15:41.467 --> 00:15:49.365 But it might also involve multiple contactors that can dynamically rewire a motor between two configurations. 00:15:49.365 --> 00:15:54.000 Really gigantic three-phase motors pull so much current from a stop 00:15:54.000 --> 00:15:59.483 that it’s effectively impossible to start them by simply applying power as normal. 00:15:59.483 --> 00:16:06.440 So instead, the motor is temporarily run with its windings wired in a star- or Y-configuration 00:16:06.440 --> 00:16:10.427 which limits its starting current at the expense of reducing torque. 00:16:10.427 --> 00:16:14.866 Once it’s up to a predetermined speed and it can safely run at its full power, 00:16:14.866 --> 00:16:18.268 the motor’s windings are switched to a delta configuration, 00:16:18.268 --> 00:16:25.534 and that’s all done with some contactors and timers which form a star-delta (or Y-delta) motor starter. 00:16:25.534 --> 00:16:27.860 But why stop at just three poles? 00:16:27.860 --> 00:16:32.399 One of my favorite contactors is the answer to a question I’ve long had: 00:16:32.399 --> 00:16:37.430 how do big buildings turn on so many lights at the same time? 00:16:37.430 --> 00:16:44.169 Think of, like, a hotel with a parking lot, exterior wall sconces, signage, bollard lights in pathways, 00:16:44.169 --> 00:16:50.950 and somehow all of those lights, even though they’re all over the building and can’t possibly be on the same circuits, 00:16:50.950 --> 00:16:54.352 are automatically coming on together at dusk. 00:16:54.352 --> 00:16:56.249 How’s that happening? 00:16:56.249 --> 00:16:59.560 Well, with one of these gnarly contactors. 00:16:59.560 --> 00:17:03.377 You can have perhaps a dozen circuits all controlled by this thing, 00:17:03.377 --> 00:17:05.544 they don’t even need to be the same voltage, 00:17:05.544 --> 00:17:09.796 and it can be hooked up to either a mechanical timer or a photocell. 00:17:09.796 --> 00:17:13.982 One of these might even control the lights in a large store or warehouse, 00:17:13.982 --> 00:17:19.864 allowing you to switch on dozens of kilowatts of lighting with just a single ordinary light switch. 00:17:19.864 --> 00:17:23.674 And that really gets to the heart of what contactors do. 00:17:23.674 --> 00:17:28.969 Like relays, they are electrically-operated switches that we can do pretty much anything with. 00:17:28.969 --> 00:17:35.278 But they’re just more focused on raw power-handling ability than they are speed or complexity. 00:17:35.278 --> 00:17:40.913 And while I’ve talked about a few types that are out there, trust me there are plenty more. 00:17:40.913 --> 00:17:48.400 Take a look at speed control for locomotive DC traction motors if you want to see some wild contactor configurations. 00:17:48.400 --> 00:17:52.320 The role of the contactor is arguably changing, though. 00:17:52.320 --> 00:17:55.948 While this one is doing a fine job of controlling my air conditioner, 00:17:55.948 --> 00:17:59.730 the on-or-off nature of it is quite limiting. 00:17:59.730 --> 00:18:02.934 The compressor is just a simple AC induction motor, 00:18:02.934 --> 00:18:09.995 and with a contactor the only thing we can feed to it is raw 240V AC power at 60 Hz, 00:18:09.995 --> 00:18:15.630 so the motor will only ever run at the two speeds of high or off. 00:18:15.630 --> 00:18:22.935 But we are starting to see variable frequency drives proliferate into more and more air conditioning, heat pump, and refrigeration systems. 00:18:22.935 --> 00:18:28.370 They’ve been common on mini-splits for many years now, often marketed as an “inverter” compressor. 00:18:28.370 --> 00:18:33.546 And these systems allow us to spin the motors at virtually any speed we want by, in essence, 00:18:33.546 --> 00:18:38.468 creating our own flavor of AC voltage with fancy electronicals. 00:18:38.468 --> 00:18:41.998 Some might view this as a needless layer of complexity, 00:18:41.998 --> 00:18:46.375 but when we can spin the compressor (and fans) and any arbitrary speed, 00:18:46.375 --> 00:18:52.710 we can optimize the device’s operating efficiency for any given load which can save a lot of energy. 00:18:53.570 --> 00:18:56.141 Yeah it’s not strictly necessary, 00:18:56.141 --> 00:19:03.400 but the operating characteristics of a refrigeration system change depending on the temperatures both inside and out. 00:19:03.400 --> 00:19:09.421 In this footage, it was only mildly warm outside and inside the temperature was actually kinda chilly. 00:19:09.421 --> 00:19:14.767 And with such a small load the air conditioner was only drawing about 7 amps. 00:19:14.767 --> 00:19:21.361 Keep in mind that its rated load, when including the fan, should be somewhere north of 13 amps. 00:19:21.361 --> 00:19:27.929 The compressor just isn’t working that hard because the refrigerant pressures it’s fighting against are quite low. 00:19:27.929 --> 00:19:35.541 But because the compressor can only operate at full speed, it’s always trying to pump the same volume of refrigerant. 00:19:35.541 --> 00:19:40.811 Yes, it’s using less power than it would if it were really hot out since the pressures are lower, 00:19:40.811 --> 00:19:47.731 but it could be using even less to deliver the same amount of cooling if it could simply slow itself down. 00:19:47.731 --> 00:19:50.865 That would reduce pumping and frictional losses in the compressor, 00:19:50.865 --> 00:19:56.059 and we could even slow down the condenser fan because we don’t need as much heat transfer. 00:19:56.059 --> 00:19:57.868 Over the lifetime of the air conditioner, 00:19:57.868 --> 00:20:04.860 there’s a lot of energy being left on the table if you can’t dynamically adjust for load conditions. 00:20:04.860 --> 00:20:12.390 And that’s why this thing is only rated at 14 SEER while my cheap mini-split attains 19 SEER. 00:20:12.390 --> 00:20:17.320 Of course, the downside is that the VFD boards required for variable-speed compressoring 00:20:17.320 --> 00:20:20.680 are a lot more expensive than contactors. 00:20:20.680 --> 00:20:23.548 These things cost about $15 bucks retail, 00:20:23.548 --> 00:20:27.016 and a replacement inverter board is, uh, 00:20:27.016 --> 00:20:28.720 more than that. 00:20:28.720 --> 00:20:35.046 It’s not impossible to design a very robust inverter board that should last the life of an air conditioner or heat pump, 00:20:35.046 --> 00:20:40.960 and I’m happy to report that my cheap mini split is still pumping just fine after four winters now. 00:20:40.960 --> 00:20:43.540 But I do get the concern. 00:20:43.540 --> 00:20:51.000 In a similar vein, electromechanical contactors like these are starting to become displaced by solid-state contactors. 00:20:51.000 --> 00:20:55.497 Rather than rely on an electromagnet and physical movement of copper links, 00:20:55.497 --> 00:21:02.020 those devices use electronic components like transistors or triacs to turn the flow of power on and off. 00:21:02.020 --> 00:21:06.854 They are at least in theory more robust than an electromechanical device, 00:21:06.854 --> 00:21:11.490 but they are a lot more expensive and aren’t suitable for every application. 00:21:11.490 --> 00:21:15.690 It is effectively the same device, just with different technology inside of it, 00:21:15.690 --> 00:21:17.630 but it is interesting to note. 00:21:17.630 --> 00:21:24.111 However, just because we might be using contactors less as a means of control 00:21:24.111 --> 00:21:26.520 doesn’t mean we’re giving them up altogether. 00:21:26.520 --> 00:21:32.919 Increasingly, we see them getting used as isolation devices that are mainly used for safety. 00:21:32.919 --> 00:21:36.515 As I talked about in my video on electric vehicle supply equipment, 00:21:36.515 --> 00:21:43.940 your standard AC car charger has a contactor inside of it to control whether the charge cord has voltage on it or not. 00:21:43.940 --> 00:21:48.136 That contactor is really the only active component in one of these chargers, 00:21:48.136 --> 00:21:53.388 and the incoming power wires get connected straight through to the charge cable when it’s pulled in. 00:21:54.234 --> 00:21:59.970 But this contactor shouldn’t ever operate under load except in an emergency. 00:21:59.970 --> 00:22:02.930 It will close before the car starts drawing power, 00:22:02.930 --> 00:22:10.226 and a switch in the charger handle will signal to the car to immediately stop pulling current when you reach to unplug it, 00:22:10.226 --> 00:22:14.100 so the load will instantly drop off before the contactor opens. 00:22:14.491 --> 00:22:18.857 It’s really only there to kill power to the cord when it’s not plugged into a car 00:22:19.300 --> 00:22:22.334 (or on the rare occasion it detects a fault). 00:22:22.334 --> 00:22:28.706 And actually, an electric car’s battery pack has some very important contactors inside of it. 00:22:28.706 --> 00:22:35.025 When it’s not turned on, we want to be able to isolate the high-voltage battery from the rest of the car. 00:22:35.025 --> 00:22:37.006 That’s important not only for safety 00:22:37.006 --> 00:22:41.765 but also keeps the high voltage battery from discharging when the car’s powered off 00:22:41.765 --> 00:22:44.972 (at least assuming the manufacturer has figured that part out) 00:22:44.972 --> 00:22:46.644 *cough* Rivian 00:22:46.644 --> 00:22:52.046 So, the battery’s power output is run through some big, beefy DC contactors 00:22:52.046 --> 00:22:56.846 that can physically disconnect the battery cells from the pack’s power terminals. 00:22:56.846 --> 00:23:01.157 And those contactors are controlled by the car’s low-voltage system. 00:23:01.157 --> 00:23:07.169 Electric and hybrid cars have a low-voltage system that’s basically no different from an ordinary car. 00:23:07.169 --> 00:23:12.700 In fact plenty of EVs have a plain ol’ 12 volt lead acid battery in there somewhere, 00:23:12.700 --> 00:23:17.660 and that battery is what closes in the contactors inside the traction battery 00:23:17.660 --> 00:23:23.890 so it can send out its spicy voltage to all the spicy stuff and the car can fully power on. 00:23:23.890 --> 00:23:28.775 If you listen closely as I power on my car, you can hear those contactors clicking to life. 00:23:28.775 --> 00:23:32.320 [ka-chunk, followed by a buzz, some whirrs, etc] 00:23:32.320 --> 00:23:34.921 There are usually even more contactors, though, 00:23:34.921 --> 00:23:39.945 such as the pair that connects the battery pack to the DC pins of the charge port. 00:23:39.945 --> 00:23:45.746 You only want that to happen when the car knows for sure that it’s plugged into a DC fast charger, 00:23:45.746 --> 00:23:50.383 because having 400 (or even 800V) DC on these exposed pins 00:23:50.383 --> 00:23:54.020 is not a fun way to learn what a DC arc flash is. 00:23:54.020 --> 00:23:57.733 And depending on other components, there may be even more. 00:23:57.733 --> 00:24:04.795 When I plug my car in to charge, there’s a short symphony of clicking that occurs as the car locks the charge handle to the charge port, 00:24:04.795 --> 00:24:07.354 the charger’s contactor clacks to life, 00:24:07.354 --> 00:24:13.047 and the contactors inside the battery pack click to allow the onboard charger to juice up the pack's cells. 00:24:13.907 --> 00:24:14.407 [snap] 00:24:14.825 --> 00:24:16.522 [clicketyclack Ka-Chunk] 00:24:16.522 --> 00:24:17.809 [whirr] 00:24:17.809 --> 00:24:18.456 [thunk] 00:24:18.456 --> 00:24:19.207 [CLACK] 00:24:20.094 --> 00:24:24.035 And it’s not over until the disembodied lady sings. 00:24:24.035 --> 00:24:25.957 [seemingly from nowhere] "Charging Started" 00:24:25.957 --> 00:24:28.489 Anyway, I’ve been going on for long enough. 00:24:28.489 --> 00:24:32.805 Who knew I could stretch a video on contactors past the 20 minute mark? 00:24:33.743 --> 00:24:35.761 Oh, who am I kidding, we all knew this would happen. 00:24:35.761 --> 00:24:39.252 I’m really not cut out for this whole one minute video stuff. 00:24:40.139 --> 00:24:42.336 I am wearing shorts, though. 00:24:42.336 --> 00:24:43.594 Anyway, thanks for watching. 00:24:44.481 --> 00:24:47.046 ♫ flowingly smooth jazz ♫ 00:24:50.462 --> 00:24:53.772 But what if you want to control something… big? 00:24:53.772 --> 00:24:55.594 Lll *cough* oops 00:24:55.594 --> 00:24:58.925 Or even switch power from one path to another. 00:24:58.925 --> 00:25:02.304 Often incorporating multiple sets of each compact tight… 00:25:03.738 --> 00:25:05.609 [the line was “contact type”] Type! 00:25:05.609 --> 00:25:07.249 That’s why it’s so bulky. 00:25:08.579 --> 00:25:09.614 Bulky. 00:25:09.614 --> 00:25:11.648 I hope that sounded OK. I’m not recording that again. 00:25:11.648 --> 00:25:13.187 The large gap. 00:25:13.187 --> 00:25:15.321 The large gap ma… huh guboy 00:25:16.573 --> 00:25:18.642 It could be… 00:25:18.642 --> 00:25:21.706 land somewhere and stop flying. 00:25:21.706 --> 00:25:23.239 [there was a bug in the room] 00:25:23.239 --> 00:25:25.141 Good golly willikers gee. 00:25:25.141 --> 00:25:28.403 ... it can safely run at its full power... 00:25:29.889 --> 00:25:31.102 Wrong! 00:25:31.102 --> 00:25:32.622 That’s not how the sentence worked. 00:25:33.874 --> 00:25:37.114 So I'm wondering how many people will have gotten the "part of a complete breakfast" gag at the beginning. 00:25:37.114 --> 00:25:39.805 Is that mostly an American thing? I can very much see that being the case. 00:25:39.805 --> 00:25:44.699 In case you don't know, breakfast cereal commercials usually say that at the end with imagery of a bowl of your Lucky Charms or whatever beside a glass of orange juice, 00:25:44.699 --> 00:25:48.910 maybe some bacon and eggs, basically acknowledging that the cereal really shouldn't be the only thing you eat for breakfast. 00:25:48.910 --> 00:25:49.581 And that's how my brain works!