1
00:00:00,000 --> 00:00:03,401
What do you do when you need to control an
electrical device?

2
00:00:03,401 --> 00:00:05,819
Most of the time we use simple switches.

3
00:00:05,819 --> 00:00:09,632
Any device, be it a light bulb, desk fan, or toaster oven

4
00:00:09,632 --> 00:00:13,607
needs to be part of a complete breakfast— 
sorry, circuit in order for it to work,

5
00:00:13,607 --> 00:00:17,061
so if we put a break somewhere in the circuit…

6
00:00:17,061 --> 00:00:20,842
then it’s no longer complete and power cannot flow through it.

7
00:00:20,842 --> 00:00:23,049
And that’s all that most switches do:

8
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,

9
00:00:28,204 --> 00:00:31,602
and when the plastic toggle is moved to the “off” position,

10
00:00:31,602 --> 00:00:35,341
they’re pulled apart so power cannot flow through the switch anymore.

11
00:00:35,654 --> 00:00:39,176
Ideally that happens with a snap-action to minimize arcing,

12
00:00:39,176 --> 00:00:41,281
and that’s why most switches make a clicking noise,

13
00:00:41,281 --> 00:00:43,584
but that’s a topic for another video that I’ve already made.

14
00:00:43,584 --> 00:00:46,977
But what if you want to control something… big?

15
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.

16
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.

17
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?

18
00:01:05,628 --> 00:01:08,834
Looks like you’re gonna need a contactor.

19
00:01:08,834 --> 00:01:12,690
Contactors are the unsung heroes of industrial equipment control.

20
00:01:12,690 --> 00:01:15,133
They’ve come up a few times on this channel,

21
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.

22
00:01:21,441 --> 00:01:23,012
Time to fix that!

23
00:01:23,012 --> 00:01:26,975
Contactors aren’t something you typically find inside the home...

24
00:01:26,975 --> 00:01:31,300
except for that one just outside — don't worry, we’ll get there.

25
00:01:31,300 --> 00:01:33,924
A contactor does what it sounds like it does:

26
00:01:33,924 --> 00:01:36,942
it decides whether there’s contactor not.

27
00:01:37,725 --> 00:01:38,765
I’m sorry.

28
00:01:38,765 --> 00:01:43,778
This is a typical two-pole contactor for controlling single-phase loads.

29
00:01:43,778 --> 00:01:46,292
Notice that there are six electrical connections:

30
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.

31
00:01:52,239 --> 00:01:55,084
If I pry this cover off the face of the contactor,

32
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,

33
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.

34
00:02:08,022 --> 00:02:11,358
Right now, there’s a gap between the top and bottom terminals,

35
00:02:11,358 --> 00:02:15,781
so this contactor is open and power cannot flow through it.

36
00:02:15,781 --> 00:02:18,744
That floating middle section can move, though.

37
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.

38
00:02:25,551 --> 00:02:29,101
When in this position, power can flow through the contactor.

39
00:02:29,336 --> 00:02:33,336
Normally, though, it’s not a finger that pushes the contacts together -

40
00:02:33,336 --> 00:02:36,800
that role is usually handled by an electromagnet.

41
00:02:36,800 --> 00:02:39,629
And that’s what the terminals on the sides are for.

42
00:02:39,629 --> 00:02:42,116
Send the appropriate voltage to those terminals,

43
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.

44
00:02:48,933 --> 00:02:49,608
[CLACK]

45
00:02:49,608 --> 00:02:53,641
A contactor in this state is often said to be “pulled in,”

46
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.

47
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.

48
00:03:06,670 --> 00:03:07,170
[THUNK]

49
00:03:07,170 --> 00:03:10,651
That’s done with not one, but three springs.

50
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.

51
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,

52
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.

53
00:03:31,370 --> 00:03:37,745
Once released, they provide an inertial kick
by quickly flinging the arches away at high speed,

54
00:03:37,745 --> 00:03:41,097
and once they’re extended enough to catch the copper links,

55
00:03:41,097 --> 00:03:45,810
well they get yanked away and off the contacts just as quickly.

56
00:03:45,810 --> 00:03:47,488
Now, some of you might be thinking,

57
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:

58
00:03:52,625 --> 00:03:53,943
yeah, pretty much.

59
00:03:53,943 --> 00:03:55,939
But there are some differences.

60
00:03:55,939 --> 00:04:01,720
For a start, most relays offer both normally open and normally closed contacts,

61
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.

62
00:04:09,112 --> 00:04:12,866
Often incorporating multiple sets of each contact type,

63
00:04:12,866 --> 00:04:18,292
relays can perform fairly complex switching tasks when combined with other circuitry.

64
00:04:18,292 --> 00:04:22,253
But a contactor is generally just a big power switch.

65
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,

66
00:04:28,397 --> 00:04:33,598
but contactors can and do - that’s why it’s so bulky.

67
00:04:33,598 --> 00:04:38,050
The large gap maintained between the contact points when the contactor is open

68
00:04:38,050 --> 00:04:43,891
allows it to handle a maximum of 600 volts AC -
much more than a typical relay.

69
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

70
00:04:49,800 --> 00:04:52,854
(or 40 amps if it’s not a resistive load).

71
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,

72
00:04:59,872 --> 00:05:04,948
like the kind you encounter when switching on
large inductive loads such as motors.

73
00:05:04,948 --> 00:05:10,515
That’s what the LRA figure is for - that stands for locked rotor amps.

74
00:05:10,515 --> 00:05:15,059
Induction motors, by far the most common
motor type that this fella will control,

75
00:05:15,059 --> 00:05:20,889
pull very large amounts of current if the rotor cannot move - or is locked.

76
00:05:20,889 --> 00:05:22,853
(the rotor is the spinny bit)

77
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 -

78
00:05:28,319 --> 00:05:32,568
which is often several times what it pulls when at operating speed.

79
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

80
00:05:38,471 --> 00:05:40,604
(that’s rated load amps)

81
00:05:40,604 --> 00:05:44,495
but its locked rotor amp draw is 67.8.

82
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.

83
00:05:51,169 --> 00:05:56,876
Since this can handle a motor that might draw
a whopping 240 amps at startup,

84
00:05:56,876 --> 00:06:00,214
it sure seems like a decent fit for controlling an air conditioner.

85
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

86
00:06:05,134 --> 00:06:07,034
what should we find but…

87
00:06:07,034 --> 00:06:08,838
a contactor!

88
00:06:08,838 --> 00:06:11,149
And some other stuff, but don’t worry about all that.

89
00:06:11,149 --> 00:06:15,876
This contactor is some kinda budget model
that only breaks one leg of the circuit.

90
00:06:15,876 --> 00:06:17,921
It’s built just like the one we’ve been looking at,

91
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.

92
00:06:23,019 --> 00:06:25,825
I can only imagine this is very slightly cheaper.

93
00:06:25,825 --> 00:06:27,545
Now, here’s the important bit:

94
00:06:27,545 --> 00:06:31,885
the contactor, or more specifically the gap between its contacts,

95
00:06:31,885 --> 00:06:37,107
is literally the only thing keeping this air conditioner from running right now.

96
00:06:37,107 --> 00:06:40,342
Unless you bother to shut off the breaker to it in the winter time,

97
00:06:40,342 --> 00:06:46,650
the wires on the input side of the contactor
are live at 240V all the time.

98
00:06:46,650 --> 00:06:50,907
And, since this has this weird bargain-basement single-pole contactor,

99
00:06:50,907 --> 00:06:56,065
that means every electrical connection in this device
always has 120V potential on it.

100
00:06:56,065 --> 00:06:57,387
Neat!

101
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

102
00:07:03,382 --> 00:07:06,750
[BRRGSHSSWMMMMAHHHHHHHH]

103
00:07:06,750 --> 00:07:08,279
it starts right up.

104
00:07:08,879 --> 00:07:10,347
Weird, right?

105
00:07:10,347 --> 00:07:15,941
That contactor really is the only control mechanism in this air conditioner.

106
00:07:15,941 --> 00:07:19,358
Yeah, this is about as basic an air conditioner as you can get,

107
00:07:19,358 --> 00:07:23,249
so mediocre it can’t be legally installed in the Southwest!

108
00:07:23,249 --> 00:07:26,548
But there’s plenty of these machines out there.

109
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.

110
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.

111
00:07:41,313 --> 00:07:46,249
[CLACK and then the air conditioner starting]

112
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.

113
00:07:51,779 --> 00:07:53,612
What would that be?

114
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?

115
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.

116
00:08:06,200 --> 00:08:11,752
See, although the air conditioner is effectively a standalone device
with its own power supply,

117
00:08:11,752 --> 00:08:15,955
it needs to cooperate with the rest of the HVAC system it’s a part of.

118
00:08:15,955 --> 00:08:18,468
In this case, that’s a gas-fired furnace,

119
00:08:18,468 --> 00:08:24,943
and the control board that operates the furnace
just so happens to run on 24V AC.

120
00:08:24,943 --> 00:08:29,335
That is in fact the de-facto control voltage in the HVAC world.

121
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?

122
00:08:35,400 --> 00:08:37,996
Well, only sort of.

123
00:08:37,996 --> 00:08:42,553
One of the main reasons HVAC systems operate at this low control voltage

124
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.

125
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:

126
00:08:57,079 --> 00:08:59,247
one to signal a heating request,

127
00:08:59,247 --> 00:09:01,032
another for the blower fan,

128
00:09:01,032 --> 00:09:02,929
and the third for cooling.

129
00:09:02,929 --> 00:09:06,678
The furnace will respond accordingly to whatever signal it gets back.

130
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,

131
00:09:13,451 --> 00:09:17,529
from there it goes right to the contactor outside.

132
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.

133
00:09:24,441 --> 00:09:29,269
If I take the leads of a multimeter set to current
(so basically a jumper wire)

134
00:09:29,269 --> 00:09:31,253
and do this…

135
00:09:31,253 --> 00:09:33,358
here’s what’s happening outside.

136
00:09:33,358 --> 00:09:37,320
[rapid and loud clicking and clacking]

137
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.

138
00:09:43,082 --> 00:09:45,714
Once it makes it back to the furnace’s control board,

139
00:09:45,714 --> 00:09:48,442
it becomes spliced with a second wire.

140
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.

141
00:09:56,699 --> 00:10:00,159
Once there, it’s wired to the contactor’s coil.

142
00:10:00,159 --> 00:10:05,433
All a thermostat does when it calls for cooling
is connect these two wires together

143
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.

144
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.

145
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.

146
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

147
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.

148
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.

149
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,

150
00:10:47,930 --> 00:10:50,889
and power on G will turn on the blower fan.

151
00:10:50,889 --> 00:10:55,106
So in older setups, as far as the furnace or air handler knew

152
00:10:55,106 --> 00:10:57,520
it was just supposed to be running the fan.

153
00:10:57,520 --> 00:10:59,589
It had no idea why.

154
00:10:59,589 --> 00:11:03,240
So by now, I’m sure you get the point of having that contactor.

155
00:11:03,527 --> 00:11:06,955
It allows us to switch on the big and power-hungry air conditioner

156
00:11:06,955 --> 00:11:10,914
with a low-voltage signal wire controlled by a thermostat.

157
00:11:10,914 --> 00:11:15,080
But there are actually more benefits to this
approach than it may seem.

158
00:11:15,080 --> 00:11:19,178
If you look closely at the thermostat wiring
once it enters the air conditioner,

159
00:11:19,178 --> 00:11:23,380
you’ll notice that it’s not directly connected to the contactor.

160
00:11:23,380 --> 00:11:29,040
It actually heads inside to a pressure switch
attached to the refrigerant lines.

161
00:11:29,040 --> 00:11:31,086
That switch is normally closed,

162
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.

163
00:11:38,180 --> 00:11:42,801
That will of course shut off the air conditioner,
protecting its compressor from damage.

164
00:11:42,801 --> 00:11:47,472
More sophisticated systems might have multiple
safety switches all arranged in series

165
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.

166
00:11:54,992 --> 00:11:58,655
Without the help of a contactor, every one of those safety devices

167
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,

168
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

169
00:12:11,929 --> 00:12:15,831
to stop by and run through every safety device.

170
00:12:15,831 --> 00:12:19,384
Anyway, before we get too far lost in HVAC trivia,

171
00:12:19,384 --> 00:12:23,556
I do want to go back to that current-handling ability of the contactor.

172
00:12:23,556 --> 00:12:26,237
Remember the locked rotor amps thing?

173
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.

174
00:12:31,410 --> 00:12:32,786
[unit switches on]

175
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!

176
00:12:40,370 --> 00:12:44,916
Thanks to the fast action of the contacts, though, hardly any arcing occurs.

177
00:12:45,855 --> 00:12:51,310
Hardly any isn’t “none,” though, and already we can see pitting on the contacts.

178
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.

179
00:12:57,434 --> 00:12:59,800
It could be much worse, though.

180
00:12:59,800 --> 00:13:04,697
If I use my high-tech insulated poking device, 
I can create some gnarly arcing -

181
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.

182
00:13:12,839 --> 00:13:15,672
You can hear it humming but it's not turning.

183
00:13:16,428 --> 00:13:23,226
[abnormal buzzing and humming when contactor is pushed in]

184
00:13:23,226 --> 00:13:28,046
This is why modern thermostats might delay
the startup of your air conditioner.

185
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.

186
00:13:33,639 --> 00:13:37,535
And if left powered on in this locked state
for any length of time,

187
00:13:37,535 --> 00:13:43,540
that can damage the compressor as its motor windings
 will get very hot very quickly.

188
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,

189
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

190
00:13:54,791 --> 00:13:57,135
that’s annoying if nothing else so

191
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.

192
00:14:04,728 --> 00:14:07,418
But I said we wouldn’t get lost in HVAC trivia.

193
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.

194
00:14:13,320 --> 00:14:18,680
For a start, 24V is by no means the only option for the coil voltage.

195
00:14:18,680 --> 00:14:22,274
In fact, through the Magic of Buying Two of Them,

196
00:14:22,274 --> 00:14:25,843
I have a 120V contactor right here.

197
00:14:25,843 --> 00:14:32,018
This is nearly identical to the first one,
but the coil runs on ordinary AC power.

198
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.

199
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.

200
00:14:46,740 --> 00:14:49,180
I’m still not letting you look inside of there, though.

201
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,

202
00:14:54,190 --> 00:14:57,547
and allows them to send power to large three-phase motors,

203
00:14:57,547 --> 00:15:01,370
like for instance exhaust fans in a commercial kitchen.

204
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

205
00:15:08,407 --> 00:15:11,928
to ensure that those fans run whenever the kitchen is occupied.

206
00:15:11,928 --> 00:15:16,607
And inside really big HVAC systems with three-phase compressors,

207
00:15:16,607 --> 00:15:20,802
you’ll find them there, too, though usually with 24V coils.

208
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.

209
00:15:27,860 --> 00:15:33,149
And for really big motors, there’s a subset of contactors
known as motor starters.

210
00:15:33,149 --> 00:15:37,589
Those might be as simple as a conventional contactor
which can monitor current flow

211
00:15:37,589 --> 00:15:41,467
and will shut down the motor if it exceeds a certain threshold.

212
00:15:41,467 --> 00:15:49,365
But it might also involve multiple contactors that can dynamically rewire a motor between two configurations.

213
00:15:49,365 --> 00:15:54,000
Really gigantic three-phase motors pull so
much current from a stop

214
00:15:54,000 --> 00:15:59,483
that it’s effectively impossible to start them
by simply applying power as normal.

215
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

216
00:16:06,440 --> 00:16:10,427
which limits its starting current at the expense of reducing torque.

217
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,

218
00:16:14,866 --> 00:16:18,268
the motor’s windings are switched to a delta configuration,

219
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.

220
00:16:25,534 --> 00:16:27,860
But why stop at just three poles?

221
00:16:27,860 --> 00:16:32,399
One of my favorite contactors is the answer to a question I’ve long had:

222
00:16:32,399 --> 00:16:37,430
how do big buildings turn on so many lights at the same time?

223
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,

224
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,

225
00:16:50,950 --> 00:16:54,352
are automatically coming on together at dusk.

226
00:16:54,352 --> 00:16:56,249
How’s that happening?

227
00:16:56,249 --> 00:16:59,560
Well, with one of these gnarly contactors.

228
00:16:59,560 --> 00:17:03,377
You can have perhaps a dozen circuits all controlled by this thing,

229
00:17:03,377 --> 00:17:05,544
they don’t even need to be the same voltage,

230
00:17:05,544 --> 00:17:09,796
and it can be hooked up to either a mechanical timer or a photocell.

231
00:17:09,796 --> 00:17:13,982
One of these might even control the lights in a large store or warehouse,

232
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.

233
00:17:19,864 --> 00:17:23,674
And that really gets to the heart of what contactors do.

234
00:17:23,674 --> 00:17:28,969
Like relays, they are electrically-operated
switches that we can do pretty much anything with.

235
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.

236
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.

237
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.

238
00:17:48,400 --> 00:17:52,320
The role of the contactor is arguably changing, though.

239
00:17:52,320 --> 00:17:55,948
While this one is doing a fine job of controlling my air conditioner,

240
00:17:55,948 --> 00:17:59,730
the on-or-off nature of it is quite limiting.

241
00:17:59,730 --> 00:18:02,934
The compressor is just a simple AC induction motor,

242
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,

243
00:18:09,995 --> 00:18:15,630
so the motor will only ever run at the two speeds of high or off.

244
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.

245
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.

246
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,

247
00:18:33,546 --> 00:18:38,468
creating our own flavor of AC voltage with fancy electronicals.

248
00:18:38,468 --> 00:18:41,998
Some might view this as a needless layer of complexity,

249
00:18:41,998 --> 00:18:46,375
but when we can spin the compressor (and fans) and any arbitrary speed,

250
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.

251
00:18:53,570 --> 00:18:56,141
Yeah it’s not strictly necessary,

252
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.

253
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.

254
00:19:09,421 --> 00:19:14,767
And with such a small load the air conditioner was only drawing about 7 amps.

255
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.

256
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.

257
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.

258
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,

259
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.

260
00:19:47,731 --> 00:19:50,865
That would reduce pumping and frictional losses in the compressor,

261
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.

262
00:19:56,059 --> 00:19:57,868
Over the lifetime of the air conditioner,

263
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.

264
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.

265
00:20:12,390 --> 00:20:17,320
Of course, the downside is that the VFD boards
required for variable-speed compressoring

266
00:20:17,320 --> 00:20:20,680
are a lot more expensive than contactors.

267
00:20:20,680 --> 00:20:23,548
These things cost about $15 bucks retail,

268
00:20:23,548 --> 00:20:27,016
and a replacement inverter board is, uh,

269
00:20:27,016 --> 00:20:28,720
more than that.

270
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,

271
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.

272
00:20:40,960 --> 00:20:43,540
But I do get the concern.

273
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.

274
00:20:51,000 --> 00:20:55,497
Rather than rely on an electromagnet and physical
movement of copper links,

275
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.

276
00:21:02,020 --> 00:21:06,854
They are at least in theory more robust than
an electromechanical device,

277
00:21:06,854 --> 00:21:11,490
but they are a lot more expensive and aren’t suitable
for every application.

278
00:21:11,490 --> 00:21:15,690
It is effectively the same device,
just with different technology inside of it,

279
00:21:15,690 --> 00:21:17,630
but it is interesting to note.

280
00:21:17,630 --> 00:21:24,111
However, just because we might be using contactors less as a means of control

281
00:21:24,111 --> 00:21:26,520
doesn’t mean we’re giving them up altogether.

282
00:21:26,520 --> 00:21:32,919
Increasingly, we see them getting used as
isolation devices that are mainly used for safety.

283
00:21:32,919 --> 00:21:36,515
As I talked about in my video on electric
vehicle supply equipment,

284
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.

285
00:21:43,940 --> 00:21:48,136
That contactor is really the only active component
in one of these chargers,

286
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.

287
00:21:54,234 --> 00:21:59,970
But this contactor shouldn’t ever operate
under load except in an emergency.

288
00:21:59,970 --> 00:22:02,930
It will close before the car starts drawing power,

289
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,

290
00:22:10,226 --> 00:22:14,100
so the load will instantly drop off before the contactor opens.

291
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

292
00:22:19,300 --> 00:22:22,334
(or on the rare occasion it detects a fault).

293
00:22:22,334 --> 00:22:28,706
And actually, an electric car’s battery pack 
has some very important contactors inside of it.

294
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.

295
00:22:35,025 --> 00:22:37,006
That’s important not only for safety

296
00:22:37,006 --> 00:22:41,765
but also keeps the high voltage battery from discharging
when the car’s powered off

297
00:22:41,765 --> 00:22:44,972
(at least assuming the manufacturer has figured that part out)

298
00:22:44,972 --> 00:22:46,644
*cough*
Rivian

299
00:22:46,644 --> 00:22:52,046
So, the battery’s power output is run through some big, beefy DC contactors

300
00:22:52,046 --> 00:22:56,846
that can physically disconnect the battery cells from the pack’s power terminals.

301
00:22:56,846 --> 00:23:01,157
And those contactors are controlled by the car’s low-voltage system.

302
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.

303
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,

304
00:23:12,700 --> 00:23:17,660
and that battery is what closes in the contactors
inside the traction battery

305
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.

306
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.

307
00:23:28,775 --> 00:23:32,320
[ka-chunk, followed by a buzz, some whirrs, etc]

308
00:23:32,320 --> 00:23:34,921
There are usually even more contactors, though,

309
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.

310
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,

311
00:23:45,746 --> 00:23:50,383
because having 400 (or even 800V) DC on these exposed pins

312
00:23:50,383 --> 00:23:54,020
is not a fun way to learn what a DC arc flash is.

313
00:23:54,020 --> 00:23:57,733
And depending on other components, there may be even more.

314
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,

315
00:24:04,795 --> 00:24:07,354
the charger’s contactor clacks to life,

316
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.

317
00:24:13,907 --> 00:24:14,407
[snap]

318
00:24:14,825 --> 00:24:16,522
[clicketyclack Ka-Chunk]

319
00:24:16,522 --> 00:24:17,809
[whirr]

320
00:24:17,809 --> 00:24:18,456
[thunk]

321
00:24:18,456 --> 00:24:19,207
[CLACK]

322
00:24:20,094 --> 00:24:24,035
And it’s not over until the disembodied lady sings.

323
00:24:24,035 --> 00:24:25,957
[seemingly from nowhere]
"Charging Started"

324
00:24:25,957 --> 00:24:28,489
Anyway, I’ve been going on for long enough.

325
00:24:28,489 --> 00:24:32,805
Who knew I could stretch a video
on contactors past the 20 minute mark?

326
00:24:33,743 --> 00:24:35,761
Oh, who am I kidding, we all knew this would happen.

327
00:24:35,761 --> 00:24:39,252
I’m really not cut out for this whole one minute video stuff.

328
00:24:40,139 --> 00:24:42,336
I am wearing shorts, though.

329
00:24:42,336 --> 00:24:43,594
Anyway, thanks for watching.

330
00:24:44,481 --> 00:24:47,046
♫ flowingly smooth jazz ♫

331
00:24:50,462 --> 00:24:53,772
But what if you want to control something… big?

332
00:24:53,772 --> 00:24:55,594
Lll *cough* oops

333
00:24:55,594 --> 00:24:58,925
Or even switch power from one path to another.

334
00:24:58,925 --> 00:25:02,304
Often incorporating multiple sets of each compact tight…

335
00:25:03,738 --> 00:25:05,609
[the line was “contact type”]
Type!

336
00:25:05,609 --> 00:25:07,249
That’s why it’s so bulky.

337
00:25:08,579 --> 00:25:09,614
Bulky.

338
00:25:09,614 --> 00:25:11,648
I hope that sounded OK. I’m not recording that again.

339
00:25:11,648 --> 00:25:13,187
The large gap.

340
00:25:13,187 --> 00:25:15,321
The large gap ma… huh guboy

341
00:25:16,573 --> 00:25:18,642
It could be…

342
00:25:18,642 --> 00:25:21,706
land somewhere and stop flying.

343
00:25:21,706 --> 00:25:23,239
[there was a bug in the room]

344
00:25:23,239 --> 00:25:25,141
Good golly willikers gee.

345
00:25:25,141 --> 00:25:28,403
... it can safely run at its full power...

346
00:25:29,889 --> 00:25:31,102
Wrong!

347
00:25:31,102 --> 00:25:32,622
That’s not how the sentence worked.

348
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.

349
00:25:37,114 --> 00:25:39,805
Is that mostly an American thing? I can very much see that being the case.

350
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,

351
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.

352
00:25:48,910 --> 00:25:49,581
And that's how my brain works!