Alternating Station Circuit

[Greg Elmassian]

Yeah, but the current through a varistor generates heat, which matches the definition of thermistor, and of course Wikipedia is a poor source.

I have a number of electrical and electronic engineers working for me, some with PHD's, you always specify the temperature coefficient, or there are just certain other descriptions, everyone understands the temp coefficient and use of a MOV for example....

In any case without specifying PTC or NTC you are asking for confusion. There is also a small typo on the variable resistor, "device that can adjust it's resistance".... I surely hope not! When potentiometers start adjusting themselves, we are in trouble!


Greg

 

[JimmyB]

Yeah, but the current through a varistor generates heat, which matches the definition of thermistor, and of course Wikipedia is a poor source.

I have a number of electrical and electronic engineers working for me, some with PHD's, you always specify the temperature coefficient, or there are just certain other descriptions, everyone understands the temp coefficient and use of a MOV for example....

In any case without specifying PTC or NTC you are asking for confusion. There is also a small typo on the variable resistor, "device that can adjust it's resistance".... I surely hope not! When potentiometers start adjusting themselves, we are in trouble!


Greg

Greg it would seem you are never wrong, just everybody else

 

[Greg Elmassian]

No, it's just in my area of expertiese, our current designed board is 12 layers and 4,000 components. I am well versed in "parts description frustration".

The salient part, the Negative Temperature Coefficient, vs. Positive Temperature Coefficient makes a HUGE world of difference in using these components. Get the wrong one and your circuit works in reverse.

Your inrush limiter (in a keepalive situation) becomes a current blocker, for example

Merely copying stuff from Wikipedia is dangerous, as virtually anyone can post to Wikipedia.

You do not see me advising in scratch building, 16mm scale, weathering, live steam port timing do you?

Finally this is not a case of being wrong, just insufficient information to be successful.

Greg

 

[fairflixt]

Yeah, but the current through a varistor generates heat, which matches the definition of thermistor, and of course Wikipedia is a poor source.

I have a number of electrical and electronic engineers working for me, some with PHD's, you always specify the temperature coefficient, or there are just certain other descriptions, everyone understands the temp coefficient and use of a MOV for example....

In any case without specifying PTC or NTC you are asking for confusion. There is also a small typo on the variable resistor, "device that can adjust it's resistance".... I surely hope not! When potentiometers start adjusting themselves, we are in trouble!


Greg

So I get that NTC and PTC apply to a thermistor but I'm still struggling to see how a varistor and a thermistor are the same thing and how NTC and PTC apply to a varistor. Perhaps you can help by educating me. As I understand it, the varistor is for over-voltage protection where the thermistor is either for over-current protection (NTC) or temperature sensing (PTC). Are they using the same principle of physical operation or something that makes them the same?

When I look up the components on digi-key, there are separate listings for varistors and NTC and PTC thermistors. Specifications for each are different, so this leads me to conclude that they are different components and someone must be selecting, e.g. varistors, for a specific purpose. Also no NTC/PTC differentiation for available varistors there.

And to be cheeky - if Wikipedia is such a bad source, you, quite literally, have the ability to rectify that!

 

[Greg Elmassian]

I've stated that the definition is simple, although most people recognize varistor as you describe it.

I've tried to correct something in Wikipedia a few times, not very successful.... it really irritates me how difficult it can be in some instances to correct something that was put in place by someone much less qualified that the person trying to correct it. It seems to depend on who you have "judging" the change.

I do use their reference lists though...

Greg

 

[Paul M]

I've stated that the definition is simple, although most people recognize varistor as you describe it.

I've tried to correct something in Wikipedia a few times, not very successful.... it really irritates me how difficult it can be in some instances to correct something that was put in place by someone much less qualified that the person trying to correct it. It seems to depend on who you have "judging" the change.

I do use their reference lists though...

Greg

I've never understood Wikipedia, what's the point of having an encyclopedia the any Tom, Dick or Harry can alter on a whim?

 

[dunnyrail]

I've never understood Wikipedia, what's the point of having an encyclopedia the any Tom, Dick or Harry can alter on a whim?

In theory I believe that Wiki is moderated to stop false information, also there is a membership element that only allows those members to update or so I believe. But that of course could be Wiki speaking.

 

[fairflixt]

I've stated that the definition is simple, although most people recognize varistor as you describe it.

I've tried to correct something in Wikipedia a few times, not very successful.... it really irritates me how difficult it can be in some instances to correct something that was put in place by someone much less qualified that the person trying to correct it. It seems to depend on who you have "judging" the change.

I do use their reference lists though...

Greg

You stated that current through a varistor generates heat. But if it does not conduct when below the voltage threshold, which would be consistent with how varistors are described, then there is no current and hence no heat. Is my understanding correct here?

I imagine that once the voltage threshold has been surpassed, then the current flow increases temperature of the component and that could facilitate more flow (as per a PTC thermistor) but it seems that would be secondary to the function of not conducting until a certain voltage is met. If that is part of the function of the component then NTC would be counter to the purpose of maximizing current flow until voltage is below the threshold.

 

[JimmyB]

You stated that current through a varistor generates heat. But if it does not conduct when below the voltage threshold, which would be consistent with how varistors are described, then there is no current and hence no heat. Is my understanding correct here?

I imagine that once the voltage threshold has been surpassed, then the current flow increases temperature of the component and that could facilitate more flow (as per a PTC thermistor) but it seems that would be secondary to the function of not conducting until a certain voltage is met. If that is part of the function of the component then NTC would be counter to the purpose of maximizing current flow until voltage is below the threshold.

You are relatively new here, you need to appreciate that Greg is very rarely wrong, even when he is

 

[Greg Elmassian]

look at the graph at the beginning

https://www.electronics-tutorials.ws/resistor/varistor.html