RC snubber circuit design and calculations for inductive loads 

The resistor calculation is incorrect. Makes no sense to set R = Vm/Im. R should be calculated by setting the desired time constant RC, which will be dependent on the switching frequency. Al alternative is to set R by it's desired maximum power rating, which is also dependent of the time constant RC.

Thank you. A very useful and excellent video. I used to know this but have long forgotten it. Erich a 76 year old teacher

Excellent. Very good explained. But when using high frecuencies switching, calculating snubber circuit I think it would be more complex.

Very good explanation. Thank you teacher. But, how I calculate r c when connecting a battery directly in a motor with a big current like 40A?

I may have to revise what I am going to say but I do not agree with his mathematical analysis presented in this video as the capacitor will never see the 50 volts voltage suggested across it. Here is the engineering reason for my conclusion. 1. When the switch is on, the energy calculation in the inductor was correct. The heat energy stored in the 10-ohm resistor cannot be returned, so that is correct in using only the inductive/magnetic stored energy. When the switch is on, the load to the battery consists of the resistor 10 ohms, the transient impedance of the inductor, and the zero output impedance of the battery acting as a VOLTAGE SOURCE which is basically zero ohms and the small resistor in the MOSFET. 2. When the switch is opened all the above changes, as with the inductor being present the battery and 10-ohm resistor and inductor will become a CURRENT SOURCE, with the current stated flowing, and this needs to keep instantaneously flowing at any voltage really!! So when the switch is open the current must be retained into the RC snubber which behaves as follows. Since the action is very fast, the capacitor or any value will be a dead short circuit and so the 50-volt voltage at the snubber acting as a load to the current generator, note "current generator", will be the current (1.2 amps) flowing through the resistor (41.7) ohms. This flow of current in the resistor will use some of the electromagnetic energy in the inductor with the additional energy being used to heat the 10-ohm resistor in the circuit, and hence one cannot use the full energy stored n the inductor to finish up charging the capacitor, as it does not, most of the energy goes in heating the resistor 41.7 ohm in the snubber, and the resistor 10 ohm in series with the inductor. 3. As was said before, any value of capacitor for a very fast voltage change across it will act as a DEAD SHORT CIRCUIT so the initial zero voltage of the capacitor will rise from 0 volts to 12 volts of the battery and the final value of the energy stored in the capacitor is due to the battery voltage only,. which is 12 volts. It is an interesting integral function that goes on in that capacitor as the current is slowly decaying in value. 4. 288 micro-Farads are just too high for an RC snubber where the MOSFET is periodically switched as the high energy in the capacitor will have to be dissipated by the Mosfet when it comes on, and it would not like it at all with all that energy in that large value capacitor. The approximations of theory and simulations are one thing, while the practical circuit is another. A suggestion as to the amount of energy the snubber and other existing resistance is required to dissipate is the amount of energy stored in the snubber capacitor. It is recommended that you choose a capacitance value that causes the resistor to dissipate one half the wattage rating of the resistor. Note that though the load /battery feeding the snubber is a current source with its own imperfect high output impedance also containing the 10-ohm resistor. Due to reasons not mentioned in this video, the snubber capacitor would be more likely to be around 1000 PICOFARADS and not MICROFARADS. It scares me to even think about that high value.

Great video. Thank you. What does the power dissipated in the snubber resistor look like as a function of switching frequency? The 1.2A is the current charging the capacitor, but not the current through the snubber circuit when the switch turns back on and the capacitor discharges through the switch, forming the loop Rsn, Csn, and Rsw (sn= snubber, sw = switch). So, Rsn sees both charging current and the discharge current. What is the best way to compute the power dissipation of this snubber resistor?

very very useful .thanks my master

Thanks, now i am ready to over protect my circuits :)

Thank you very much for an easy explanation of a complicated subject. I appreciate the flow of explanation was fantastic. I was just curious if the calculations remain the same with 230V AC signal? Could you refer some site on this subject. Further, if Snubber is in parallel to the load, will it be better option.

I've been looking for this for quite a while. Thank you!

39 OHM.............100nF

Thanks. I tried playing around with a snubber circuit, but it seems my 50MHz scope is not fast enough to see the transient voltage spike. My effort was kinda pointless anyways. I don't know how to effectively calculate a universal motor's inductance. My circuit just uses the default 100nF/100R values and with my scope, I guess ignorance is bliss because it works. Thanks for the upload. -Jake

Super useful video. I was just learning about how to design a snubber circuit for a TRIAC in an AC application. The catch there is that you also have to keep in mind the reactive power that will be flowing through the snubber when the switch is not closed.

When you are calculating the energy stored in the coil, as you assuming that it is oscillating at the coil’s resonant frequency? Because a coil’s voltage and capacitance varies depending on the frequency of the LC circuit and it only achieves it’s maximum energy storage value when it is oscillating in resonance.

Nice video. I have a question though, the energy stored in induction is 0.36J, then we use this same amount of energy to workout the capacity of the capacitor. Because of the existence of bottom R(the one 41.7 ohms), some of the energy is consumed by resistive loss. So I assume there is a step of the calculation proving the energy consumed on R41.7, for some reason, has to equals to the enemy provided by battery AFTER switch is turned off. Would it be possible to elaborate a bit on this? Thanks a lot

it's well simplified example and calculations were very easy to understand, thank you

did anyone else come from school LMAO

I'm using an electromagnet that is rated at 12 volts at 0.5 amps. Checking with the Oscilloscope the half inch ball bearing hits the aluminum foil every 0.8 seconds and arcs that are visible. I purchased both a electrolytic capacitor kit and 1 watt resister kit. Hopefully the wattage on the resisters is more then enough. I take it on your resister and capacitor values you pick the next highest value out of the kit?

A very nice example, for AC voltage would the same formula still apply?. I have a small coil with hydraulic motor that measures 4106 mH/10VA according to the plate and 240V /60 Hz. supply. the maximum amperage we could permit is 1 amp

Sir what about switching frequency(ex. 16kHz) incase of inverter Please let me know

When you close the switch at about timestamp 11:51 why doesn't the simulator show the exponentional delay (due to the L/R delay) during the fall of the voltage?? THANKS MUCH!!

In practice, I found it difficult to get reliable values for the inductance L for solenoids. The iron losses are highly dependent on frequency, which is not well definable for this switching circuit. If there is a better way, please let me know

Dear, i need 1000vdc x 20a its possible use snubber in contactors AC ?

I like that you included calculation. One question, for example i need to install snubber in my circuit which controls motor via relay (because micro controller restarts from the motor spike). i don't know the inductance of motor. Should i use LCR meter to measure the inductance of motor? Is that a correct way? If not then can you calculate the Energy from the spike using oscilloscope? Thanks.

Sir. Pl confirm RC value for 24VDC,2AMP solenoid load Inductance is 46.70mH for 1Khz

Thank you

Does anyone see when the switch is open, the current induced from the inductor is flowing into capacitor, then via 2 resistors in series; and the induced voltage is in series with the battery ? Also some energy is dissipated via the 2 resistors. After suffucient time that the current via the inductor becomes zero, the voltage across the capacitor equals battery voltage. Now if the switch is closed, there will initially more than 1.2A current flowing thru the switch due to discharge from the cap, and gradually goes down to 1.2A.

hi...pls clear me if i'm wrong. why you considered 50v in the calculation of Capacitance finding. as the circuit is operating with 12v supply. Also, you have calculated the circuit current by taking 12v voltage. I think if took 50v instead of 12v calculation will be wrong. as we taking calculating value wtih 12v in all formulas.

I have a snowblower that was designed by an idiot. It has momentary switches to rotate the discharge direction and angle. You can only actuate the switch a few dozen times before so much carbon builds up on the contacts that it stops working. I'm thinking this would be the fix, but have no idea what size cap and resistor to use. Not sure it matters too much as anything would prob help.

Thisis great, but I don't get why you use 50V for both the capacitor and resistor calcs. That would make 100V across the switch. They should both see a fraction of the voltage across the switch (and i can see that changes over time as the cap is first charged up then discharged by the resistor).

great explanation sir THANKYOU SIR

Thanks very much for this awesome video, could you please explain snubber circuit in switching power supply.

Nice approach and very simplified but it has some physics error which is the energy was being stored in the inductor will not be fully delivered to capacitor and will be less because both resistors will consume it while transfering to steady state after resonance period , am I wrong ?! ...

Lol.WhyNotPutCapacitorAcrossInductor?

Silly noob Q, why doesnt current pass through the snubber when the switch is open at 3 minute mark . why is the snubber active only when the switch is closed

then when am I to use the formular C= 1/freq x Vsquared, coz you didn't mention the switching frequency?

Hello, i need a snubber for my circuit but do not have the specific ressistors and cappacitors on hand, what if i were to use a much higher value? would it still funcion?

I very much wish to understand what the voltage will do if we take out the resistor and just use the capacitor to dampen the switch?

I assume the voltage rating of the snubber cap is at least 50v ?? great VIDEO!!

Is there some impedance matching going on in this example? Great video

It's an estimation method to find out the values and make understanding about snubbing circuit. Plz add a real time experimental experiences

this vs a flyback diode?

Thanks good work.

great vidio, thank you Please tell me about the simulator software etc.. It looks useful.

Is this method appropriate to calculate the snubber for AC? Specifically a 230V AC contactor coil. Currently i use 100R (3W) and 100nF (440V X1 class) and it mostly solved the problem of EMI (IRQ false triggering and MCU resets) but i still occcasionally get false triggering of the IRQ line. The AC contactor coil (230V AC) is controlled by a smaller 10A relay which has freewheeling schottky diode on it coil (5V DC). The snubber is installed in parallel to the contactor coil.

288uF, that is very big capacitor, I never seen such big snubber, are you sure?

Great video but what should be the max voltage for snubber cap ? 50v or 5kv ? and also the power of snubber resistor 1/3w or a 1watt resistor ?

I don't get it... if switch is closed or open the circuit is still complete ? am I missing something ?

This is snubber simplied. Thanks for the video. I did deduce something from your explanation, the RC network can also be calculated from the inductance voltage formula thus: VL = L I/(RC), by substituting those calculated values and the inductance value into above formula the predetermined spike voltage arrived at. Thank again

Y la potencia de la resistencia snubber, como la calcula?.

Great video. As you doubtless know, a flyback diode across the coil will clamp transients to around .6 volts. I suppose a snubber network is used in situations where a diode can't be used, like in an ac circuit.

Hello my friend. This is a very usefull explanation. I wonder... how this calculus change when there is frecuency? Greetings from colombia!

Thanks for a most useful and excellent Video, No idea what the inductance of the motor I want to use is ? However I guess I will figure it out, one (constructive) criticism, ditch the potato mic, hard to pick up some words. Maybe its the encoding settings?

thanks for the great video. I still see RC packages on EMRs and mercury relays. Sometimes I see a flyback diode instead on the EMR coil. Any advantage to RC snubber vs flyback diode? Any reason to use both? Thanks!

Why do you have choosen the whole inductance for the calculation ? As far as I know you choose the leakage inductance because this is the part that you can´t use (magnetic loss into air) and it comes back as the spike to the circuit. Of course I don´t know If we are talking about a transformer or air coil here ? If it is the second you are right just wanted to clearify things. :)

Thank you very much for this very informative video. I have a question. Right after opening the switch all voltage will drop across a resistor since a capacitor will be shorted and then all the voltage will be transferred across a capacitor during transient and then no current will flow through a snubber circuit. But then how does a capacitor discharge ? As per the simulation, we can see a voltage spike of 50 V acorss the switch and so across the capacitor, but after that moment voltage dropped down to 12 volt, so how did capacitor get discharged from 50 V to 12 V ? Through a resistor? If yes, then what should be the direction of current flow ?

Hi could you help with a problem ...how to calculate a rc snubber for a bidirectional dc motor operating at14v that is damaging the switches controlling it ( power window circiut) thank you

Very Nice, I would like to take this to next step. Can we snub the inductor instead of the switch or both at the same time. If we added a diode in parallel with the inductor; How can we explain this type of snubber across the inductor with RCD? This is problem I am having on a project now.

I have been waiting for days n months for this detailed knowledge, searched hell loft of videos, asked many ppl but no where I found the solution... Thx sir....m subscribed, liked n shared u r channel...... How do I contact you... Could you help me with your email.... Plz

SORRY, I meant timestamp 1:43

Very nice explanation. I am designing a contact point triggered ignition, i replaced the hv contact with an nchannel mosfet 3205, triggered by p channel mosfet and the regular kettering contact point, i am having a problem i kept on burning the 3205 mosfet i already placed a diode between drain and source on 3205 but when installed it burns. Can you create a video of this using mosfet? Thanks a lot.

Thank you sir.

very useful information...Thanks lot...few doubts.... 1.if we are not using current limit resistance means what will be I?Can we take motors Coil reistance and Rds on as Resistance.....2.What will be voltage rating of snubber capacitor (C volt=V*2) 3.Power rating of snubber resistor

Regarding the RC snubber network, is it mainly to discourage charge from building up on the negative plate of the capacitor? As well as bleed any charge that might build up during normal operation?

thank you so much 💛😍

How we take 50v as maximum

Sir, I am using a 3 phase contactor to switch a 25kvar capacitor at 440V(33A at 440V), can u suggest the right values of capacitor and resistance that can be used as a snubber to supress arc

Hello, can you please explain to me why there's a need to place a resistor in series with the capacitor? Can't I already get by with only a capacitor? Thank you.

great video , thanks for sharing the valuable knowledge.

Thanks a lot, very nice and simple explanation.

How should we calculate resistir power? Considering that peek power will be very high and impractical to use that value for selecting a resistor.

Hi, what in case it's a switching circuit where there is a time limitation where the capacitor needs to be charged and discharged in some predefined time set as per the frequency of switching.....

Sir. Excelent work. It’s gonna be so usefull for school. Thank You very much. My best regards from Mexico 🇲🇽

Usefull ty so much!

Shouldn't 50V be divided among capacitor and resistor being in series?

Here you know the length of coil that is 500mH what if I want to design it for my water pump in that situation i do not know the lengh of its winding and i am unable to get any data related to it then how should I do this calculations.

Sir , rc sunbber curcite is paller of igbt how to calculated the resistance, capacitor value pl. Send video

Very well explained! Thanks

You can share key software circuit wizard 3?

Why 50 v

Thanks 🇧🇷

Does the current thru the circuit not depend on the total impedence of the circuit? Why do you use only the resistor value?

A very well explained snubber video, probs the best on YT! I love well explained videos! Everything can be simplified and well taught. I'm curious about one thing however. If our coil had quite a few turns (say primary of a transformer), it would have its own resistance. Let’s say our coil measured 10 Ohms for example. Wouldn't this greatly affect the calculations due to the current restriction of the coil itself?

Excellent explained ! Thank you !

Thankyou for uploading this. Really appreciate the work. I was wondering, which software is being used for demonstration?

Hi (from Egypt). That's very informative. However, I have a solenoid (240 VAC, 6 watt, resistance across its contacts is 3.68 kohm) that I plan to control with a solid state relay. The solenoid has no data sheet available (I don't know the inductance nor the current). Is there a way to calculate an approximate values of R and C?

Thanks sir , peace upon to you and your family ,

hi , how do you calculate the power dissipation of the resistor , watts

Will a snubber circuit recharge battery if it was switching a DC motor on and off? Making the whole system more efficient?also increase battery run time?

in AC?

Bravo

Thank you very much for the video. Few Questions though 1. The power rating of the 10 Ohm resistor should be 1.2*1.2*10 = 14.4 Watt ? 2. If I am using the Inductive load of a Transformer, How do I calculate the saturation current of the transformer.? 3. I want to maximize the output voltage of a pulse transformer, How do i achieve that through circuit design? Thanks in Advance

Does this have a time constant tau within which it will remove the spike voltage??

Excellent explanation. A question: Is this method also valid for AC? Thank you so much.

how to make this snubber with resistor and capacitor in parallel ?

Excellent, thanks alot for the video !

Very informative .. I was in search of this and I do have a doubt that is , Why we need to keep the snubber circuit current equal to the current through he main solenoid circuit?

How do we calculate for AC mains voltage

Which V rating should the cap have?

How to calculate required watt of the resistor?