-1
\$\begingroup\$

Hello,

I have a circuit in which a voltage source is connected to some sort of RC Load. To protect this circuit , there is an Metal Oxide Varistor (MYN15-681K). The Pics of circuit and datasheet specification of MOV are attached here.

My system rated rms supply is 240 volts and i have to test my circuit for system voltage up to 280 volts rms.

I want to find these hings as they are confusing terms:

1- What does it mean that MOV has Varistor rms voltage of 680 V, When this voltage appears across varistor, or what happens to mov when system voltage goes to 680 rms. (i read that this voltage is such at this current through mov will be 1mA, is it correct?)

2- Varistor voltage (AC) of 420 volts, (this voltage is maximum allowable means if system voltage up to 420 volts appears across mov, then it won't damage mov, is it correct understanding??)

3- Maximum clamping voltage of 1120 volts with current 50A. Is this the voltage appears across mov when current through mov is 50A?? or when 1120 is applied across mov, current through mov will be 50A, if this is the case then what would be the voltage across mov??

4- Here energy rating is 190 J for 10/1000us pulse (what pulse?? is it the voltage of the system or current through mov?? what its magnitude??). Energy rating of 136 J,for 2ms (what is this duration? if it is duration of what??) And is the energy rating for once?? or it can stand this much energy no matter how many times the specified signals are applied??

5- Peak Current: these are the currents that mov can withstand without damage, according to manufacturer technical info. after this pulse is passed through mov, it should be replaced. Is it correct?? as before claping voltage was 1120 when 50A passes through mov, then for these peak currents. what wold the apllied voltage??or the voltage appear across the mov??

6- What will happen if i give surge of 5000 V for 1.2/50us timing along with main 240rms voltage. What will be the V/I values be of mov under these conditions??

7- Given device specification, is there a way (a formula or equation) to calculate mov voltage and current depending upon the system voltage/current??

I know its much lengthy question, but i have been trying really hard to know the answer to these question because no forum or site is helping (google doesn't give much info). and about the info present, only definitions of mov specification which are also different on different sites..so please help me out on this.

Thanks a lot in advance..!

MOV Specifications Circuit Containing MOV

\$\endgroup\$
1
  • \$\begingroup\$ Can you narrow your question down a bit? Think in terms of a "ghost" range between 420 to 1120 V where you can't tell if it's clamping or not, so the manufacturer will characterise the MOV below and above those values and you need to design your circuit accordingly. Most of your questions can be answered by the datasheet and/or application note for the device. \$\endgroup\$
    – winny
    Aug 20, 2018 at 7:28

1 Answer 1

Reset to default
2
\$\begingroup\$

Using the data sheets of a more reputable supplier (Littelfuse for instance): -

enter image description here

  1. What does it mean that MOV has Varistor rms voltage of 680 V

It doesn't have an RMS voltage rating of 680 V - it starts to clamp at a voltage between 612 volts and 748 volts taking a current of 1 mA. I think the 1 mA specification is missing from your datasheet hence why I chose a similar device that had that spec.

  1. Varistor voltage (AC) of 420 volts

This would be the RMS AC voltage (sinewave) that is allowable so the device does not exceed the power requirements (0.6 watts in your device).

  1. Maximum clamping voltage of 1120 volts with current 50A

Typically, if 1120 volts is applied for a very short duration a current of 50 amps would flow (don't try this at home!).

  1. energy rating is 190 J for 10/1000us pulse

Energy is volts x amps divided by time so, for instance, the 1120 volts, 50 amp scenario would imply a continuous power of 6000 watts and this means 6000 joules per second so, if the peak energy limit is 190 joules then the 1120 volts must not be applied for longer than 31.6 ms.

For questions 5, 6 and 7 I urge you to take on-board my answer and do some more research (if necessary) with different manufacturers.

\$\endgroup\$
5
  • \$\begingroup\$ '''Typically, if 1120 volts is applied for a very short duration a current of 50 amps would flow (don't try this at home!).''' The Ipp is the maximum permissible peak pulse current (for a 10/1000us or 8/20 double exponent strike) not what it will limit it to. The limit is based upon the source impedance of the strike. If the source impedance or strike potential is higher then a different TVS would be needed \$\endgroup\$
    – user16222
    Aug 19, 2018 at 11:45
  • \$\begingroup\$ Thanks @Andy_aka, now its a bit clear, so i have to use datasheet of some reputable manufacturer like you have said. Mine is locally made which doesn't even include graphs like V/I characteristics etc. \$\endgroup\$
    – BetaEngineer
    Aug 19, 2018 at 11:59
  • \$\begingroup\$ "Typically, if 1120 volts is applied for a very short duration a current of 50 amps would flow (don't try this at home!).". So if 1120 is applied , and 50 amps flows through mov, then at voltage will it clamp the applied 1120, will it clamp the voltage level at 612-748 v range, or it will result 1120 as well?? and if applied voltage is more than 1120, what will be the resultant voltage at mov (lets ignore current and energy for now, and assuming the applied voltage which is >> 1120, is for very short duration)?? \$\endgroup\$
    – BetaEngineer
    Aug 19, 2018 at 12:02
  • 1
    \$\begingroup\$ This is source impedance dependant. say you have a strike potential of 2kV... the MOV will clamp this (power permitting) to a level and that level is dependent on the current it needs to shunt. IF it clamps at 612-748 then there is at least 1mA flowing. The higher the shunted current, the higher the Vclamp UNTIL 1120V @ 50A is reached. IF this is further exceeded (source impedance still low...) then you have exceeded Ipp and PeakPulse power and it is dead. you need a different device in such situations \$\endgroup\$
    – user16222
    Aug 19, 2018 at 13:03
  • 2
    \$\begingroup\$ BASICALLY... you need to do the calculations, you cannot just randomly pick a Transient suppression device and expect it to work. if you are in an environment where indirect strike is a reality then you should also have source impedance data to help you size the protection circuit. Take the DO160... Waveform5 has a Voc=1600, Isc=1600 => source impedance = 1R... If I needed to protect a cct that can experience that I couldn't use this MOV as I would still need to shunt 480A (but I wouldn't use MOV's ... deterioration over time) \$\endgroup\$
    – user16222
    Aug 19, 2018 at 13:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.