Is a Capacitor in Parallel With a MOTOR Really Necessary?

Added: 2026-06-01

[00:00:01]Hello everyone. This is Professor Nelson from electronics. In this video, we're going to learn how important it is to use non-polarized capacitors like these.

[00:00:11]You can use ceramic or polyester capacitors to protect your integrated circuits or any electronic board.

[00:00:20]And not only that, but you'll also learn how to protect your boards in the power stages.

[00:00:26]For example, here I have a power circuit board. It uses alternating current and is composed of two triacs.

[00:00:36]And here I have another power board for direct current, which uses a MOSFET transistor.

[00:00:44]These power boards must be protected against voltage spikes generated by alternating current or direct current motors.

[00:00:55]Or from voltage spikes from solenoid valves like this 220 V one or from any other inductor.

[00:01:04]Therefore, in this video, we'll talk about how capacitors protect other electronic components from the voltage spikes they deliver.

[00:01:14]So, without further ado, let's watch the video.

[00:01:19]Okay, but first let's look at some theory.

[00:01:23]Now, to understand how capacitors protect integrated circuits from voltage spikes delivered by motors or other inductors, we need to talk about one of the most important characteristics of capacitors.

[00:01:39]And I'm talking about capacitive reactance.

[00:01:43]Capacitive reactance is a property of capacitors that indicates they act like resistors.

[00:01:51]Like this one here.

[00:01:53]This happens when alternating current is applied to them, whether from a transformer or a wall outlet, or from the electrical signals or noise delivered by motors or inductors.

[00:02:04]In other words, in the presence of this noise, capacitors act as resistors.

[00:02:11]They can allow more or less current to pass, depending on the capacitor's capacitance and the frequency of the signal.

[00:02:21]Therefore, capacitive reactance is the resistance that capacitors offer to this electrical noise. And this would be the formula, which is equal to 1 / 2 * π * the frequency and multiplied by the capacitor's capacitance.

[00:02:41]The frequency is in hertz and the capacitance is in farads. Right now, I have several capacitors of different capacitances.

[00:02:50]Therefore, we observe what the reactance or resistance they offer would be when we connect them to the electrical grid, which operates at 50 hertz.

[00:03:01]That is, if the frequency is equal to 50 hertz.

[00:03:08]And if we have a capacitor of 8.2 nanofarads, the capacitive reactance in this situation would be 388 kiloohms.

[00:03:28]This 8.2 nanofarad capacitor would offer 388 kiloohms of resistance if I apply alternating current voltages of 50 hertz.

[00:03:42]However, we must not forget that the electrical noise produced by motors and inductors operates at megahertz frequencies.

[00:03:51]In this case, let's assume we are working at 5 MHz.

[00:04:03]If the noise frequency were 5 MHz and the capacitance remained the same, the capacitive reactance at that frequency would be 3.8 ohms.

[00:04:17]That is, the higher the frequency, the lower the resistance.

[00:04:22]Therefore, the lower the resistance, the more current there will be. That is, the electrical noise will be significantly reduced.

[00:04:35]Now, let's see what the capacitive reactance would be for the other capacitors. I have a 47-nF capacitor.

[00:04:45]And if we have a 47-nF capacitor and maintain 50 Hz, the capacitive reactance in this situation would be 67.7 kiloohms.

[00:05:01]But if we use it at 5 MHz, in that case, the resistance it will offer is only 0.67 ohms.

[00:05:12]Notice that the value is quite small at 5 MHz.

[00:05:16]That is, the electrical noise of this motor will be almost completely attenuated.

[00:05:24]However, I have other capacitances.

[00:05:28]For example, I have a 100-nF capacitor, double the previous one.

[00:05:34]The capacitive reactance, therefore, would have to be half in this case.

[00:05:40]And we have 31 kiloohms at 50 Hz.

[00:05:46]And at 5 MHz, we'll have 0.31 ohms.

[00:05:53]Notice that the value is almost 0 ohms.

[00:05:57]And even better, I have a 2.2 microfarad capacitor.

[00:06:05]This high capacity capacitor will offer less resistance if we use it at high frequencies.

[00:06:14]However, if we use it at 50 Hz, it will offer a reactance of 1.44 kiloohms.

[00:06:27]At 50 Hz, it offers this resistance.

[00:06:31]But at 5 MHz, it offers a very small resistance.

[00:06:40]Notice that it offers 0.014 ohms.

[00:06:44]This is a very low resistance.

[00:06:47]Therefore, this capacitor would create a short circuit at the terminals of this motor for high frequency signals.

[00:06:54]Therefore, the electrical noise would be completely attenuated.

[00:06:59]However, the other capacitors can also be used without problems. For example, the 100 nanofarad capacitor offers 0.31 ohms. The 47 nanofarad capacitor also offers a very similar value. Therefore, we can choose different capacitor values to filter or eliminate noise.

[00:07:20]However, this needs to be looked at practically. So, let's move on to the practical part.

[00:07:26]But first, a big hello to all my subscribers, to those who comment and share the videos, and especially to the channel members. A big hello to all the channel members. Guys, thank you so much for your support. Seriously, thank you so much.

[00:07:43]And if you're not yet a channel member, you can become one in the members section. Without further ado, let's continue with the video.

[00:07:51]Very well. Now we move on to the practical part.

[00:07:56]And in this way, we can confirm that our capacitors work as resistors.

[00:08:02]Depending on the frequency of the alternating current signal and the capacitance of the capacitors.

[00:08:09]We're going to use the multimeter to measure the current that will pass through the capacitors.

[00:08:16]And in this way, we will confirm the resistance they offer when an alternating current voltage is applied to them.

[00:08:25]For this, the first thing we need to know is the transformer voltage.

[00:08:37]And in this situation, we have 15 volts.

[00:08:42]Therefore, if we use a capacitor of 2.2 microfarads, we will have a resistance of 1.44 kiloohms.

[00:08:52]Therefore, the current that will pass through the capacitor will be 10.4 milliamperes.

[00:09:09]We switch to alternating current.

[00:09:14]We measure the current, and we have 9.6 milliamps.

[00:09:19]Now, to confirm that the greater the capacitance, the greater the current that passes through the capacitors, because they supposedly offer less resistance, we're going to place another capacitor in parallel with the first one.

[00:09:34]Therefore, we should measure twice the current.

[00:09:41]And we have twice the current.

[00:09:45]Therefore, a capacitor does work like a resistor depending on the signal frequency.

[00:09:54]The higher the frequency, the lower the resistance.

[00:09:59]Now that we know how capacitors work, let's move on to eliminating the electrical noise caused by motors and other inductors.

[00:10:09]Very well. Now we'll see how capacitors can eliminate or attenuate the noise generated by motors or inductors.

[00:10:19]However, the first thing we're going to do is look at the frequency of the noise generated by this motor.

[00:10:53]And we can see that the frequency is 16.6 MHz.

[00:10:58]That is, this motor generates electrical noise at a frequency greater than 5 MHz.

[00:11:05]Therefore, the resistance that the capacitors will offer to that signal will be much lower, so that noise should be attenuated considerably.

[00:11:15]Let's see that by placing the capacitors and testing which one works best.

[00:11:28]First, without a capacitor.

[00:11:42]>> Now we're going to place the 8.2 nanofarad capacitor.

[00:11:47]Which should give us 3.8 ohms at 5 megahertz.

[00:11:59]>> [screaming] >> And there's no noise.

[00:12:04]We can see that it is just attenuated.

[00:12:09]Let's try again.

[00:12:13]There's the noise.

[00:12:17]It is just softened. However, there is still some noise.

[00:12:25]There we can observe it better.

[00:12:28]We have noise of approximately 5 volts.

[00:12:35]Now let's try the 47 nanofarad capacitor.

[00:12:48]And there's no noise.

[00:13:06]There's the noise, but now we only have 2 volts of noise.

[00:13:12]It's much lower. It's just been attenuated much more.

[00:13:19]Now let's try the 100 nanofarad capacitor.

[00:13:32]>> And there's no noise. It's just been attenuated much more.

[00:13:42]You can see that the noise has just been attenuated considerably. It's less than 1 V.

[00:13:48]Therefore, by using a capacitor, the noise is attenuated.

[00:13:53]And the higher its capacitance, the better. However, it's important to note that in most cases, capacitors of approximately 47 to 200 nF are used.

[00:14:04]Since the resistance they offer is quite small, it's close to 0 ohms, especially at very high frequencies.

[00:14:16]Keep in mind that capacitors are normally placed in parallel with the DC motor connections.

[00:14:23]The capacitor will help filter electrical noise or reverse voltage or peak voltage, helping the diode in the process of eliminating almost all the noise generated by the motor.

[00:14:36]This applies if we use direct current.

[00:14:38]However, it can also be found in alternating current.

[00:14:42]But in this case, a capacitor is usually used along with a resistor.

[00:14:48]And this combination is called a snubber filter.

[00:14:54]Something similar to this.

[00:14:58]This combination here is used in alternating current.

[00:15:03]And its function is the same as what we're seeing.

[00:15:06]The purpose of capacitors is to eliminate or attenuate that noise or voltage spike, preventing damage to components. In this case, it will protect our triac. And it also prevents damage to our integrated circuits.

[00:15:23]Well, guys, as you've seen, capacitors are very useful and necessary.

[00:15:29]And that concludes the video. And if you like the video, don't forget that a like helps the channel a lot. See you in the next video. Bye-bye.