Safety capacitor value

Thread Starter

tarapoochy

Joined Aug 2, 2017
11
Sorry to ask what is probably a very simple question for most of you guys, but I have tried to work out the value of 2 yellow safety capacitors on a plug in light remote switch and I cannot believe the values I am getting.

Here is a photo of the two in question:
Remote switch capacitors.jpg

According to everywhere I have looked (and others here) a .033K value would be 0.000033uF and the one labled .1K would be 0.0001uF, but if that is the case then they are very small values and no-one seems to make anything like as small as that! I must be missing something. I have 2 of these switches and both seem faulty, but my meter rates the ones labled 0.033K as a .001uF and 0.02uF. Clearly one or both is faulty, and I guess that measuring them "in situ" might be giving false readings because of the other components, but I am getting very confused as to what I should get to replace them. The other ones (labled .1K of which there are 2 on each board, so 4 in all) measure 0.1, 0.01, 0.07 and 0.002uF, again all measured in situ.

Any suggestions?
 

MrChips

Joined Oct 2, 2009
24,415
Improper wording. There are no safety capacitors.

.033K is 0.033μF or 33nF
.1K is 0.1μF or 100nF

It is very unlikely that those are bad.
 

Thread Starter

tarapoochy

Joined Aug 2, 2017
11
Improper wording. There are no safety capacitors.

.033K is 0.033μF or 33nF
.1K is 0.1μF or 100nF

It is very unlikely that those are bad.
Hi Mr Chips,

Thanks for the advice.

I have come to the same conclusion - having taken apart a similar working unit (but slightly different design) it had a capacitor labled .22K and it measures .22uF on my meter. I think the "K" must refer to tolerance or something rather than thousands of pico or nanofarads.

I think the ones in mine are bad as only one of the 0.1K labled ones actually reads 0.1uF, all the rest are way down. I have changed quite a few similar ones to these on other switches when they start getting unreliable and a new capacitor has fixed every single one (and the old ones that I have taken out have all dropped to a very low capacitance - usually 0.001uF or less) so for the price of a few on eBay I might as well give it a go and see if it fixes them
 

ebp

Joined Feb 8, 2018
2,332
Such capacitors are very widely known as "safety capacitors" which is rather a misnomer. "Safety" refers to failure modes - they are designed to fail in a way that greatly reduces the probability of fire (the "X" types) or electrical shock (the "Y" types).

The K in the markings denotes the tolerance (limits of variation of actual capacitance), in this case ±10%.
 

MrChips

Joined Oct 2, 2009
24,415
You should explain that to Mouser and the people who make them.:) The one on the left in the picture shows it to be a X2 cap, can't see the other one.
https://www.mouser.com/new/wurth-electronics/wurth-X2capacitors/

And our website - https://www.allaboutcircuits.com/technical-articles/safety-capacitor-class-x-and-class-y-capacitors/
You're right. I shouldn't have stuck my foot in.

I suppose manufacturers can label their products anyhow they wish.
Now I'm off to find me some safety winter tires.
 

Thread Starter

tarapoochy

Joined Aug 2, 2017
11
You should explain that to Mouser and the people who make them.:) The one on the left in the picture shows it to be a X2 cap, can't see the other one.
https://www.mouser.com/new/wurth-electronics/wurth-X2capacitors/

And our website - https://www.allaboutcircuits.com/technical-articles/safety-capacitor-class-x-and-class-y-capacitors/
To be fair, I'm a total amateur, but when I search "X2 capacitor" most web sites call them Safety Capacitors, even the manufacturers. I've no idea why, but that's good enough for me!
 

ebp

Joined Feb 8, 2018
2,332
Because of the surrounding circuitry, it can be nearly impossible to measure capacitance in-circuit for such cap. The 0.1 µF is probably straight across the AC line, so there would be little to interfere with the measurement, other than a high-value resistor which is usually in place to discharge the cap within a specified time to prevent electrical shock from contact the power plug. The other cap is likely "in board" of rectifiers and other components and the capacitance meter is likely to be confused.
 

shortbus

Joined Sep 30, 2009
8,871
I have come to the same conclusion - having taken apart a similar working unit (but slightly different design) it had a capacitor labled .22K and it measures .22uF on my meter. I think the "K" must refer to tolerance or something rather than thousands of pico or nanofarads.
The easiest way of finding out this kind of thing, the meaning of "K", is to go to the manufacturers website and look at the data for that series of component. Most if not all of them have explanations of their product values.
 

ebp

Joined Feb 8, 2018
2,332
It is possible that one of those capacitors is used in a transformerless power supply for the board. They are quite common for such products.
 
Top