Ac Solenoid snubber ciruit help

[capacitor1]

hi everyone

I have a soleinoid 220VAC ,10A MAX ,L=0.55H , R=11 ohm

I control this solenoid with a relay 16A ( contacts current ).

can anyone help me to design this snubber circuit? Is it a RC snubber or should I add a diode?

I saw 2 types :

the series type like this :

the Parallel type like this:

thanx

 

[capacitor1]

no answers!!!

 

[chuckey]

No diodes its AC. Think about the max energy stored in the coil. When the switch is opened, this energy then oscillates around the the tuned circuit, coil, cap and resistance. So you can work out the frequency from L & C and its Q from the Rs. So if you adjust the Q to be 1, the the voltage across the tuned circuit will not go beyond that of the applied mains voltage, though at a very different frequency.
Frank

 

[capacitor1]

hi chuckey
thanx for your help

I found on the internet 2 rules about RC snubber :

**broken link removed**

for E=220VAC,I=7A

C=5uF but R=2.5ohm

but when I calculated the power rated of resistor : 220^2/2.5=88Watts

can you give me an analysis about that

 

[FvM]

The said "rules" seem to miss a substantiation. The quadratic relation isn't plausible at first sight.

Regarding your circuit, I wonder how you get 7A for a 0.55H/11ohm solenoid?

Presuming the 2.5 ohm/5µ snubber would be reasonable, the 88 Watt number is irrelevant though, be aware of about 0.35 A continuous current through the snubber resistor and provide sufficient pulse power rating for the inrush current. A regular 1W resistor should work.

Generally snubbers should be fitted to the L and R of an inductive load.

 

[capacitor1]

Hi Eng FvM

why sure that the quadratic relation isn't plausible ,and why you wondered how I got 7A for a 0.55H/11ohm solenoid?

how did you calculate the power rated to the resistor ?(1W)

please help me to understand

thanx

 

[FvM]

I calculated 0.35 A for the snubber resistor, power disspation considerably below 1W. But i added some margin for inrush current.

how did you calculate 7 A?

 

[capacitor1]

hi again

The information about 7A inrush current is provided from the datasheet of solenoid .
and I want to remember you that it's 220VAC coil.

I knew that the 1W is calculated by RI^2 rule , but how did you find the current for resistor , isn't equal to inrush current??

thanx for you help Eng Fvm

 

[chuckey]

Xl = 2 X PI X 50 X .5 ~ 150 Ohms, so the circuit impedance (Z) ~ 150 , therefore I ac ~ 230/150 ~ 1.5 A (not 7). So C = I^2/10 MF = .3 MF So the current flowing through the snubber resistor will be limited by the impedance of the C. Xc =1/ 2 X PI X 50 X .3 X 10 ^-6 = 10^6/ 100 ~ 10 ^4. So the current will be 230/10 mA = 23 mA. R ~ 230/18 = 13 ohms. So the power in the resistor = .023 ^2 X 13 ~ 13/1600 ~ 8 mW.
Hope you can follow the maths and the approximations
Frank

 

[capacitor1]

Hi

thanx very much for your detailed answer Eng Chuckey , I understood every calculation you did.

but in the datasheet of the solenoid , I read that the normal current is that you calculate (1.5A), but the inrush current ( the current when the solenoid pull the Load (6 Kg per example)) is 7A.

what do that mean ??impedance change !! ? I don't know

please help me to know.

thanx

 

[FvM]

but in the datasheet of the solenoid , I read that the normal current is that you calculate (1.5A), but the inrush current ( the current when the solenoid pull the Load (6 Kg per example)) is 7A.

what do that mean ??impedance change !! ? I don't know

It means that the inductance of unengaged solenoid is lower than 0.55H, e.g. 0.1 H. That's the typical behaviour of most solenoids and contactor coils. Usually it doesn't affect snubber calculation because the contact won't be opened during inrush current.

 

[capacitor1]

Eng FvM

sorry but the definition of inrush current is
Inrush current, input surge current or switch-on surge refers to the maximum, instantaneous input current drawn by an electrical device when first turned on

but if you meant by inrush current , the current generated by the coil after power off, ok , i can understand that the current generated by coil after power off isn't equal 7A , it's lower than this number , 1.5A??

ah ok is this current determined by the load of coil ( Resistor and capacitor)

sorry for the many question i'm beginner in this domain

Mr FvM and Mr Chunckey , I'm very grateful

 

[FvM]

sorry but the definition of inrush current is
Inrush current, input surge current or switch-on surge refers to the maximum, instantaneous input current drawn by an electrical device when first turned on

Yes. "Unengaged" in my post is another word for the state before the solenoid is turned on. Where do you see a contradiction?

 

[capacitor1]

Hi again Eng FvM

ok , sorry it was a wrong question

I'm so thankful