# LT Spice Simulation help needed

#### mishra87

Joined Jan 17, 2016
621
Hi Guys,

Please find attached simulation file attached.

V1 = 254Vrms

D1 =D2 = FM4007 ( I am not able to find same part number so tried with equivalent)
D3=D4 = 47V Zener ( I am not able to find same part number so tried with 51V Zener equivalent)

I want switch on and off AC (V1) for 20s ON and 10S off for testing. And this is to be controlled by switch and i am not able to design model for the same.
While performing this test R1 is getting open.(https://www.mouser.in/datasheet/2/447/Yageo LR_FMP_2013-594466.pdf)

So i want to simulation what spikes at R1 during turn on and off.

Could anybody help me on the same issue ?

Regards,

#### Attachments

• 2.4 KB Views: 3

#### ericgibbs

Joined Jan 29, 2010
9,370
hi,
This is using a Switch Model, what are you trying to do.?
E

#### Attachments

• 2.5 KB Views: 1

#### crutschow

Joined Mar 14, 2008
24,125
V1 = 254Vrms
You show 180V peak (127Vrms)
You have I1 as a current source, not an inductive load.

What is the inductance of the load?

That's a strange circuit.
What is its purpose?

Last edited:

#### mishra87

Joined Jan 17, 2016
621
hi,
This is using a Switch Model, what are you trying to do.?
E
View attachment 197327

I ran the simulation and i do not see any AC signal at node Vs when switch is closed. there has to voltage at node VS.
One more thing switch is ON for 20s and off for 10sec and when switch is on for 20s.

Then only i can see the waveform across R1 during the turn turn.

Thanks again

#### mishra87

Joined Jan 17, 2016
621
You show 180V peak (127Vrms)
You have I1 as a current source, not an inductive load.

What is the inductance of the load?

That's a strange circuit.
What is its purpose?
Yes you are correct the RMS voltage is 254VAC.
I do have inductance value of motor. But is motor running with AC and used in vacuum cleaner.
Application of this circuit is to run the motor at 4A and measure the current of it and based on the current run another motor with potential free contact. That circuit is not included here. 51V zener here is used to energize the relay.

Now problem with this circuit is when we ON -20s and 10s - 4A motor after endurance of 100 cycle R1 sees high impedance and become open circuit.

To simulate this problem , i wanted to simulation and see the voltage across R1 and find root cause of failure.

Hope this explanation will clear perception.

Thanks.

#### ericgibbs

Joined Jan 29, 2010
9,370
hi,
So R1 is failing.??
Why do you have a 4 Amp current source.??
E

Have you see the power in R1.??

#### Attachments

• 32.2 KB Views: 2

#### mishra87

Joined Jan 17, 2016
621
hi,
So R1 is failing.??
Why do you have a 4 Amp current source.??
E

Have you see the power in R1.??

View attachment 197342
Hi ,

Yes R1 is failing,

I explained the end application in my post #5.
You can used any inductive rated VRMS, 4A for this simulation.

Regards,

#### mishra87

Joined Jan 17, 2016
621
hi,
So R1 is failing.??
Why do you have a 4 Amp current source.??
E

Have you see the power in R1.??

View attachment 197342
Hi,

I think you forgot to attached simulation file.

Yes i wanted to see voltage , current and power at R1 during turn and off of the motor.
Because i have used 2W resistance as attached datasheet in post #1 as theoretical value of power dissipation is around 63mW so there is no reason of failure.

Thanks again,

#### ericgibbs

Joined Jan 29, 2010
9,370
hi,
The asc sim file is in post #6.
E

#### mishra87

Joined Jan 17, 2016
621

#### mishra87

Joined Jan 17, 2016
621
Hi.

Post #6 has only .gif file not .asm file if you you can check again ?

Thanks

#### ericgibbs

Joined Jan 29, 2010
9,370
OK,
Will try again.
E

#### Attachments

• 2.5 KB Views: 3

#### mishra87

Joined Jan 17, 2016
621
OK,
Will try again.
E
now i got file.

voltage at node vs in incorrect even if i removed 4A load.
It should be 360vp-p

Correct me if i am wrong ?

#### Attachments

• 87 KB Views: 4

#### ericgibbs

Joined Jan 29, 2010
9,370
hi,
Look at this, modified Vt in the switch parameters

#### Attachments

• 2.3 KB Views: 2
• 32.7 KB Views: 2

#### mishra87

Joined Jan 17, 2016
621
hi,
Look at this, modified Vt in the switch parameters
Could anybody suggest type of resistor to be used in this application which can withstand peak pulse power.

High voltage spike seen during turn off the inductive load.

There is two way to do this :

1. High quality resistor to be used.

Regards,
Shiv Mishra

#### ericgibbs

Joined Jan 29, 2010
9,370
1. High quality resistor to be used.
hi,
For an inductive spike of that magnitude, I would use a snubber or MOV, it should protect R1 and any other electronics in the project.
E

#### mishra87

Joined Jan 17, 2016
621
hi,
For an inductive spike of that magnitude, I would use a snubber or MOV, it should protect R1 and any other electronics in the project.
E
[/QUOTE