But has it definitively been found to be a MOV, OR a thermistor?

Thanks for your reply. How would i be able to find out exactly what it is?

 

Well a MOV even a 9v version will measure an open circuit on a normal VOM.
Whereas a thermal PTC/NTC will show a measurable resistance.
But it is knowing the actual value/part no. that is important.
Max.

 

Ok i am pretty sure it is an EPCOS C985-120-1336 thermistor, although the numbers are hard to make out, it could be C885. Here is a photo i took of it

 

MOV as in in Metal oxide varistor? What do you mean there are not many about at less than 12v? You mean not many manufactured? I know very little about electronics or their workings.

Also is it correct what Analogkid said about this device only being of use for about ten times and then it will be unreliable?

MOVs take a hit every time they clamp a surge event - how big a hit they take depends on how big the surges they're hit by.

AFAIK; Sidacs are the new modern thing that's trendy - but I think they clamp to a low voltage when they breakover, if that's the case; they'll blow the fuse every time there's a surge.

MOVs could prevent the sidac from breaking over for as long as they last - when they stop doing that its time to replace the MOV.

Maybe someone who spends more time at that end of equipment can clarify the details.

 

Thanks Ian.

Does anyone else have any input on the above?

 

If it is still good, you could remove it and find out by a series of empirical tests what the nature of the device is.
Max.

 

A copy of my quick'n'dirty zener tester might clear things up.

The gadget I built was made with 2 identical mains reservoir electrolytics strapped to a bridge rectifier with the tap between the series pair of electrolytics connected to one AC arm of the bridge to make a voltage doubler. For current limiting; I included a series pair of 2W 68k resistors in series with the live wire in.

This tester violates various safety regs, so I never offered the project to any hobby magazines, and some care is required using it!

Of course, after making a test with it, you need to dump the charge on the electrolytics somehow - if you just fit a shorting switch, it'll blow the contacts away first time you close the switch! - put an inrush limiting NTC thermistor in series with the shorting switch.