Capacitors Explained - The basics how capacitors work working principle — Transcript

Full transcript

1. 0:05Hey, there, guys.
2. 0:06Paul here from TheEngineeringMindset.com.
3. 0:08In this video, we're going to be looking at capacitors
4. 0:10to learn how they work, where we use them,
5. 0:12and why they are important.
6. 0:14Remember, electricity is dangerous and can be fatal.
7. 0:17You should be qualified and competent
8. 0:19to carry out any electrical work.
9. 0:21Do not touch the terminals of a capacitor,
10. 0:23as it can cause an electric shock.
11. 0:25So, what is a capacitor?
12. 0:27A capacitor stores electric charge.
13. 0:30It's a little bit like a battery,
14. 0:31except it stores energy in a different way.
15. 0:34It can't store as much energy as a battery,
16. 0:36although it can charge and release its energy much faster.
17. 0:40This is very useful, and that's why you will find capacitors
18. 0:43used in almost every circuit board.
19. 0:45So, how does the capacitor work?
20. 0:47I want you to first think of a water pipe
21. 0:49with water flowing through it.
22. 0:51The water will continue to flow until we shut the valve,
23. 0:54then no water can flow, however, if after the valve,
24. 0:58we first let the water flow into a tank,
25. 1:00then the tank will store some of the water
26. 1:02but we will continue to get water flowing out of the pipe.
27. 1:05Now when we close the valve,
28. 1:07water will stop pouring into the tank
29. 1:09but we still get the steady supply
30. 1:10of water out until the tank empties.
31. 1:13Once the tank is filled again,
32. 1:14we can open and close the valve as many times as we like.
33. 1:18As long as we do not completely empty the tank,
34. 1:20we will get an uninterrupted supply of water out
35. 1:22of the end of the pipe.
36. 1:24So, we can use a water tank to store water
37. 1:26and smooth out interruptions to the supply.
38. 1:29In electrical circuits, the capacitor acts as the water tank
39. 1:32and stores energy.
40. 1:34It can release this to smooth out interruptions
41. 1:36to the supply.
42. 1:37If we turned a simple circuit on and off very fast
43. 1:40without a capacitor, then the light will flash,
44. 1:43but if we connect a capacitor into the circuit,
45. 1:46then the light will remain on during the interruptions,
46. 1:48at least for a short duration,
47. 1:50because the capacitor is now discharging
48. 1:52and powering the circuit.
49. 1:54Inside a basic capacitor,
50. 1:56we have two conductive metal plates,
51. 1:58which are typically made from aluminium or aluminum,
52. 2:01and these will be separated
53. 2:02by a dielectric insulating materials such as ceramic.
54. 2:05Dielectric means the material will polarize
55. 2:07when in contact with an electric field,
56. 2:09and we'll see what that means shortly.
57. 2:11One side of the capacitor is connected
58. 2:13to the positive side of the circuit,
59. 2:15and the other side is connected to the negative.
60. 2:18On the side of the capacitor,
61. 2:19you will see a stripe and a symbol.
62. 2:21This will indicate which side is the negative.
63. 2:24If we were to connect a capacitor to a battery,
64. 2:26the voltage will push the electrons
65. 2:28from the negative terminal over to the capacitor.
66. 2:31The electrons will build up on one plate of the capacitor,
67. 2:34while the other plate, in turn, releases some electrons.
68. 2:38The electrons can't pass through the capacitor
69. 2:40because of the insulating material.
70. 2:42Eventually, the capacitor is the same voltage as the battery
71. 2:45and no more electrons will flow.
72. 2:47There is now a buildup of electrons on one side.
73. 2:50This means we have stored energy
74. 2:52and we can release this when needed.
75. 2:54Because there are more electrons on one side compared
76. 2:56to the other, and electrons are negatively charged,
77. 2:59this means we have one side which is negative
78. 3:01and one side which is positive,
79. 3:03so there is a difference in potential,
80. 3:05or a voltage difference, between the two,
81. 3:07and we can measure this with a multimeter.
82. 3:10Voltage is like pressure.
83. 3:11When we measure pressure, we're measuring the difference
84. 3:14or potential difference between two points.
85. 3:17If you imagine a pressurized water pipe,
86. 3:19we can see the pressure using a pressure gauge.
87. 3:22The pressure gauge is comparing two different points, also:
88. 3:25the pressure inside the pipe compared
89. 3:27to the atmospheric pressure outside the pipe.
90. 3:30When the tank is empty, the gauge reads zero
91. 3:32because the pressure inside the tank is now equal
92. 3:35to the pressure outside the tank,
93. 3:37so the gauge has nothing to compare against;
94. 3:39both are the same pressure.
95. 3:41The same with voltage, we're comparing the difference
96. 3:44between two points.
97. 3:46If we measure across a 1.5 volt battery,
98. 3:49then we read a difference of 1.5 volts between each end,
99. 3:53but if we measure the same end, then we read zero
100. 3:56because there's no difference and it's going to be the same.
101. 3:59Coming back to the capacitor, we measure across
102. 4:01and read a voltage difference between the two
103. 4:03because of the buildup of electrons.
104. 4:05We still get this reading
105. 4:07even when we disconnect the battery.
106. 4:09If you remember, with magnets,
107. 4:11opposites attract and pull towards each other.
108. 4:13The same occurs with the build-up
109. 4:15of negatively charged electrons.
110. 4:17They are attracted to the positively charged particles
111. 4:20of their atoms on the opposite plate.
112. 4:22They can never reach each other
113. 4:24because of the insulating material.
114. 4:26This pull between the two sides is an electric field,
115. 4:29which holds electrons in place until another path is made.
116. 4:33If we then place a small lamp into the circuit,
117. 4:35a path now exists for the electrons to flow
118. 4:37and reach the opposite side.
119. 4:39So, the electrons will flow through the lamp, powering it,
120. 4:42and the electrons will reach the other side
121. 4:44of the capacitor.
122. 4:45This will only last a short duration, though,
123. 4:47until the buildup of electrons equalizes on each side.
124. 4:51Then the voltage is zero.
125. 4:52So, there is no pushing force and no electrons will flow.
126. 4:55Once we connect the battery again,
127. 4:57the capacitor will begin to charge.
128. 4:59This allows us to interrupt the power supply
129. 5:01and the capacitor that will provide power
130. 5:03during these interruptions.
131. 5:05So, where do we use capacitors?
132. 5:07They look a little bit different but they're easy to spot.
133. 5:10In circuit boards, they tend to look something like this,
134. 5:13and we see them represented in engineering drawings
135. 5:16with symbols like these.
136. 5:17We can also get larger capacitors,
137. 5:19which are used, for example, on induction motors,
138. 5:21ceiling fans, and air conditioning units.
139. 5:24We can get even larger ones,
140. 5:25which are used to correct poor power factor
141. 5:27in large buildings.
142. 5:28On the side of the capacitor, we will find two values.
143. 5:31These are the capacitance and the voltage.
144. 5:34We measure capacitance of the capacitor in the unit
145. 5:37of Farads, which we show with a capital F,
146. 5:39although we will usually measure a capacitor in microfarads.
147. 5:43With microfarads, we just have a symbol before this,
148. 5:45which looks something like a letter U with a tail.
149. 5:48The other value is our voltage,
150. 5:49which we measure in volts, with a capital V.
151. 5:52On the capacitor, the voltage value is the maximum voltage
152. 5:55which the capacitor can handle.
153. 5:57We've covered voltage in detail in a separate video.
154. 5:59Do check that out, link's down below.
155. 6:02As I said, the capacitor is rated
156. 6:03to handle a certain voltage.
157. 6:05If we were to exceed this, then the capacitor will explode.
158. 6:09Let's have a look at that in slow motion.
159. 6:13Eh, pretty cool.
160. 6:15So, why do we use capacitors?
161. 6:17One of the most common applications of capacitors
162. 6:19in large buildings is for power factor correction.
163. 6:23When too many inductive loads are placed into a circuit,
164. 6:26the current and the voltage waveforms will fall out of sync
165. 6:29with each other and the current will lag behind the voltage.
166. 6:32We then use capacitor banks to counteract this
167. 6:35and bring the two back into alignment.
168. 6:37We've covered power factor before in great detail.
169. 6:39Do check that out, link's down below.
170. 6:41Another very common application is to smooth out peaks
171. 6:44when converting AC to DC power.
172. 6:47When we use a full bridge rectifier,
173. 6:49the AC sine wave is flipped
174. 6:51to make the negative cycle flow in a positive direction.
175. 6:55This will trick the circuit into thinking
176. 6:56it's getting direct current, but one of the problems
177. 6:59with this method is the gaps in between the peaks.
178. 7:03But as we saw earlier, we can use a capacitor
179. 7:05to release energy into the circuit
180. 7:07during these interruptions,
181. 7:08and that will smooth the power supply out
182. 7:10to look more like a DC supply.
183. 7:13We can measure the capacitance
184. 7:14and the stored voltage using a multimeter.
185. 7:17Not all multimeters have the capacitance function,
186. 7:20but I'll leave a link down below
187. 7:21for the model which I personally use.
188. 7:24You should be very careful with capacitors.
189. 7:26As we now know, they store energy
190. 7:27and can hold high voltage values for a long time,
191. 7:30even when disconnected from a circuit.
192. 7:33To check the voltage, we switch to DC voltage on our meter,
193. 7:36and then we connect the red wire
194. 7:37to the positive side of the capacitor
195. 7:39and the black wire to the negative side.
196. 7:42If we get a reading of several volts or more,
197. 7:43then we should discharge that
198. 7:45by safely connecting the terminals to a resistor
199. 7:48and continue to read the voltage.
200. 7:50We want to make sure that it's reduced down
201. 7:52into the millivolts range before handling it,
202. 7:54or else we might get a shock.
203. 7:56To measure the capacitance, we simply switch the meter
204. 7:59to the capacitor function.
205. 8:01We connect the red wire to the positive side
206. 8:02and the black wire to the negative side.
207. 8:05After a short delay, the meter will give us a reading.
208. 8:07We will probably get a reading close to the stated value
209. 8:09but not exact.
210. 8:11For example, this one is rated at 1,000 microfarads,
211. 8:14but when we read it, we get a measurement of around 946.
212. 8:18This one is rated at 33 microfarads,
213. 8:20but we measure it, we get around 36.
214. 8:23Okay, guys, that's it for this video,
215. 8:25but to continue your learning,
216. 8:26then check out one of the videos on-screen now
217. 8:28and I'll catch you there for the next lesson.
218. 8:30Don't forget to follow us on Facebook, Twitter, Instagram,
219. 8:33and of course, TheEngineeringMindset.com.