Choosing a MOV for my application.

[maniac84]

Hi guys, I've been wondering how to choose a MOV for my application. I've done a search in this forum and found this thread:
https://www.edaboard.com/threads/26841/

If I want to protect my device which uses 12V DC, what is the 'Maximum Continous voltage' of a MOV I should choose? Is it anything higher than 12V?

 

[D.A.(Tony)Stewart]

depends what sort of transient you expect and the device it is protecting. MOV's have limited lifespan for transients. Perhaps you want TVS protection. What is the app?

 

[maniac84]

I'm protecting a 12V DC motor. So, which do you recommend?

 

[D.A.(Tony)Stewart]

from what a blown 12 V regulator? Car operation @ 14.4V? regulate it better Certainly not EMI?
Polyfuse it for over current or use an SCR crowbar OVP protection with a fuse.

 

[maniac84]

from what a blown 12 V regulator? Car operation @ 14.4V? regulate it better Certainly not EMI?
Polyfuse it for over current or use an SCR crowbar OVP protection with a fuse.

My 12V input is from an dc adapter. It is an indoor device, not a car device.
Just want to know if I were to use MOV, what is the 'Maximum Continous voltage' of a MOV I should choose? Is it anything higher than 12V?

 

[D.A.(Tony)Stewart]

If your design is regulated, the motor should not need protection, but it is normal to add OVP and perhaps OCP and OTP. OVP is crowbar SCR and polyfuse. If you need motor stall protection too, you need polyfuse.

 

[maniac84]

If your design is regulated, the motor should not need protection, but it is normal to add OVP and perhaps OCP and OTP. OVP is crowbar SCR and polyfuse. If you need motor stall protection too, you need polyfuse.

Can I add a MOV into it? MOV also can do over voltage protection right?

 

[D.A.(Tony)Stewart]

MOV will burn out on DC over protection, for motor and PS failure you need Over current protection with POlyfuse.

 

[maniac84]

MOV will burn out on DC over protection, for motor and PS failure you need Over current protection with POlyfuse.

OK.
Just asking out of curiosity, other application which needs a MOV, is it that the 'Maximum Continous voltage' of a MOV means the voltage of the input voltage. Like if the input voltage is 12V, then is it that I should use a MOV with Maximum Continous voltage of 12V?

 

[D.A.(Tony)Stewart]

I would use an MOV for AC line surge protection which happens rarely, never for steady state DC over voltage or OVP and never to protect a motor.
Then maximum continuous voltage will be safe to use and not heat up the device.

Pls ensure you understand MOV characteristics. HERE
and read all the SEE ALSO

 

[maniac84]

You mean only use a fuse to protect a motor?
Then MOV is use to protect what?

 

[D.A.(Tony)Stewart]

PolyFuse > Motor for DC operation in windshield wipers protect motor on stalled motor. Same for Power Windows.
MOV> to protect electronics from power surge.. ie from 1kV spikes use say 500V protection for 240Ac line.. works on both polarities
TVS> has small nS clamp time > so use to protect line signals on cables from ESD eg. 5.5V clamp on 5V signals.
Gas tube, SCR crowbar,, many many other OVP methods depending on surge, signal and reason

 

[maniac84]

Ok.
Actually I'm designing a dc motor controller. Will the motor cause interference to the circuit when it is power on?

 

[D.A.(Tony)Stewart]

Your question originally was "protect my device which uses 12Vdc" then that was found to be a motor THat means "ingress".. but interference from motor we call "egress"
Read Page 14

 

[maniac84]

Your question originally was "protect my device which uses 12Vdc" then that was found to be a motor THat means "ingress".. but interference from motor we call "egress"
Read Page 14

Yes. I think this is what I meant. Sorry for letting you guys misunderstood my question.
So, I think if protecting my circuit against motor EMI then I can use MOV right?

---------- Post added at 10:53 ---------- Previous post was at 10:46 ----------

From the slide you post SunnySkyGuy, it uses an X2Y Attenuators. So, should I use this device to have maximum protection?

 

[D.A.(Tony)Stewart]

very bad assumption.
1) what is sensitive Define !
2) what is threat level ( IEC standard? ) radiated? conducted, what source just motor? how big, how close? how much noise.
3) how can it be protected? conducted filter? radiated shield?

Now dont ask any more questions until you read my links .. No more answers

 

[maniac84]

I'm not sure about all those. I just want a general opinion. I just want to know how do you guys generally protect the circuit against the DC motor EMI. Or I should say how do you guys generally do dc motor EMI filtering?

 

[D.A.(Tony)Stewart]

Generally I would use a common mode ferrite choke and cap across motor.

 

[maniac84]

Generally I would use a common mode ferrite choke and cap across motor.

But my DC motor is just 12Vdc and I think the current is low too. So, is it ok using a choke?