varistor

[333rocky333]

we have a peice of equipment with one across L and N of the supply and it has shorted.
however it has various numbers and symbols , that I dont understand.

One number on it , looks like P275L40, seems to match the two types sold at RS.

however the other markings, barely readable, dont match and dont know where else to get one that does.

Question is are they all compatible as the spec on the two RS ones seems mostly the same and the bits that are different, Clamping voltage and Varistor voltage, does it matter, my instinct tells me the higher spec one, would be suitable
thanks

These are the two RS TYPES

 

[JohnW2]

You obviously want a similar maximum working voltage to the existing one (275V, which seems appropriate to go across a 230V supply). Assuming they are intended for 'surge suppression', I wouldn't have expected to see much variation in varistor voltage or clamping voltage for a particular working voltage ...

The data I'm looking at indicates that the P2750L40 has a varistor voltage of 389-473V (at 1mA test current) and a maximum clamping voltage of 710V. All other 275V varistors in the same range have those same specs (so, I would guess, similar transient-suppressing performance), the only difference being the peak transient current, which varies from 1,200A to 6,500A. The P275L40 is at the top of that range, with a peak transient current of 6,500A, so would presumably the 'safest' bet. What is the spec of the RS ones you've found??

Kind Regards, John

 

[333rocky333]

They are two RS types in the pics and the link seems to have gone
What do they mean by clamping voltage, Varistor voltage and transient current

Littelfuse LA Series Metal Oxide Varistor 900pF 100A, Clamping 710V, Varistor 473V
Littelfuse LA Series Metal Oxide Varistor 900pF 100A, Clamping 680V, Varistor 389 → 453V

543-5142
Quick View

760-6942

 

[JohnW2]

They are two RS types in the pics and the link seems to have gone

Does this help (click here) ??

What do they mean by clamping voltage, Varistor voltage and transient current

As I undertsnad it .... the maximum 'clamping voltage' is the maximum value to which the varistor will limit the voltage across it when a current pulse ('surge') of standardised rise time/duration etc. is passed through the varistor. The 'varistor voltage' is the voltage that will appear across the varistor if 1 mA is passed through it. The maximum transient current is, I think, the maximum magnitude of current pulse (again of specified rise-time/duration) that the device will tolerate/survive. When subjected to surges, MOVs progressively deteriorate in performance.

Kind Regards, John

 

[endecotp]

the other markings, barely readable, dont match

They could simply be manufacturing date codes or similar.

 

[bernardgreen]

The application of varistors is explained here

www.littelfuse.com/data/en/Application_Notes/Littelfuse_app-note_an9767.pdf

 

[Gerrydelasel]

As indicated on the datasheet the other numbers are the week and year code. Both the RS parts would be suitable replacements -there's bugger all difference between them. Transient suppressors are not precision-critical parts.

 

[333rocky333]

Thanks lads.
I take it that it can be connected either way round.
The existing one had a wire soldered to one leg, is that ok for me to do, or could the heat damage it, its not essential its soldered

 

[endecotp]

Yes, either way around, they are symetrical.
Soldering specs for most components these days say "up to 10 seconds at 230C", or somesuch; you'll be fine unless you're trying to solder with a blowlamp or something crazy. If it's taking a while and getting hot, stop, let it cool down for a minute, and try again.