Can 2 varistors with same Vrms of 480V be interchangeable?

Thread Starter

Younes Thabet

Joined Jan 9, 2019
71
Hello,

I have a power supply which have V480LA10P varistor connected at input between line and neutral but I want to replace it with the V480LA40AP from same family. Looking at datasheet they seem to have almost similar characteristics except for "Peak Current 8 x 20µs" and "Energy 10 x 1000µs" !

varistor.png

Can I still replace the V480LA10P with V480LA40AP? if yes, would there be any electrical risk?

Thanks,
 

Hymie

Joined Mar 30, 2018
1,081
Yes, but the rms continuous working voltage (at 420V) seems quite high for normal mains use. A 240Vac sinewave will have a peak voltage of around 340V, whereas these devices will not limit any peak voltage below 675V and possibly as high as 825V, limiting the effectiveness in reducing mains voltage spikes.

Normally a varistor with a 300V rms continuous working voltage (connected line to neutral) would be a better choice for use on a 240Vac mains system.
 

Thread Starter

Younes Thabet

Joined Jan 9, 2019
71
Yes, but the rms continuous working voltage (at 420V) seems quite high for normal mains use. A 240Vac sinewave will have a peak voltage of around 340V, whereas these devices will not limit any peak voltage below 675V and possibly as high as 825V, limiting the effectiveness in reducing mains voltage spikes.

Normally a varistor with a 300V rms continuous working voltage (connected line to neutral) would be a better choice for use on a 240Vac mains system.
Sorry for bumping this thread back so late!! just want to confirm something!
If my varistor has a 480V RMS continuous voltage and a clamping voltage of about 750V (between 675 and 825V) meaning it will not suppress any voltage spikes that is between 480-750V or even those between 330 peak voltage of mains and 480V!? and does a voltage of less than 480 damage my board!!?
Do i really need to replace my 480V varistor with a 300-ish one!?

Thank you very much in advance!
 

DickCappels

Joined Aug 21, 2008
8,710
...and does a voltage of less than 480 damage my board!!?

We don't know. That's why there are companies and consultants that charge a lot of money to help with the board design and then test prototypes to see what happens under various fault conditions.

It will suppress spikes below the clamping voltage but now as well as at or above the clamping voltage. I have seen it written that in most cases the power supply bulk capacitors and their associated rectifiers clamp most transients to protect the MOV. MOV's on the other hand don't have the equivalent series inductance and resistance of those large capacitors, so then we are now considering which part of the spike goes through which components. I use MOV's because I have seen what a nearby lightning strike can do to a power supply.
 

Thread Starter

Younes Thabet

Joined Jan 9, 2019
71
...and does a voltage of less than 480 damage my board!!?

We don't know. That's why there are companies and consultants that charge a lot of money to help with the board design and then test prototypes to see what happens under various fault conditions.

It will suppress spikes below the clamping voltage but now as well as at or above the clamping voltage. I have seen it written that in most cases the power supply bulk capacitors and their associated rectifiers clamp most transients to protect the MOV. MOV's on the other hand don't have the equivalent series inductance and resistance of those large capacitors, so then we are now considering which part of the spike goes through which components. I use MOV's because I have seen what a nearby lightning strike can do to a power supply.
Thank you very much for your reply,

The board has a universal power supply so it should work fine in 85VAC-265VAC.
The bulk capacitor is rated for 450V.
The bridge rectifier (MiniDIP package) has a maximum recurrent peak reverse voltage of 600V and a maximum RMS voltage of 420V.

Does these ratings above mean that bulk capacitor and the bridge rectifier will clamp those transients ( 480-750V and 330-480V)!!?
 
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