Snubber Cap Value?

[YANIR GVIRTz]

My Kenwood KR 8050 makes a loud 'pop' sound when shutting the unit down. The on/off switch includes this capacitor marked 103P.




Would this Cap be a good replacement?

 

[gadget73]

103 is 0.01uf. 10,000 picofarads.


The 0.1 would probably work fine though.

 

[YANIR GVIRTz]

The 0.1 would probably work fine though.

Thank you @gadget73 for the super-quick reply!
How about the 275VAC - am I good there (for US 115V)?

 

[gadget73]

yes, rating just means it can handle up to 275vac so you have plenty of margin.

 

[egellings]

Any cap placed across the AC line needs to have the appropriate UL (and possibly others) approvals for that use, even if the listed WVDC rating on the cap is more than adequate.

 

[YANIR GVIRTz]

Any cap placed across the AC line needs to have the appropriate UL

Thank you for this remark @egellings - this is from Panasonic:

 

[YANIR GVIRTz]

Works like a charm!
'Pop' is gone.
Thank you!

 

[tarior]

X and Y capacitors aren't snubbers.
Snubbers have a capacitor and a resistor in series.

 

[egellings]

Yup. They are jus capacitors with special qualifications.

 

[gadget73]

can also just mount the resistor externally and make your own RC snubber for less money. Doesn't look quite as clean. Plenty of mfg used just a cap though, no resistor in the mix anywhere. I've had them fail shorted too, but all that happens is that it never turns off. Not a catastrophe.

 

[egellings]

A resistor is needed in series with the snubber capacitor as a dissipative element to absorb and then dissipate a transient.

 

[jlb2]

That is correct, a capacitor is not exactly a snubber network, and is deemed less effective as a spark / pop suppressor. However it is considered sufficient by most hifi manufacturers, and you will fing a mere capacitor in many schematics. If the manufacturer did not see the point of spending more on a snubber, you may consider that the original capacitor is good enough. For the ins and outs of spark suppression there are at least two technical documents available on the internet: https://www.illinoiscapacitor.com/pdf/Papers/spark_suppression.pdf and especially https://led.cdiweb.com/datasheets/okaya/noisesurgecatalog2014.pdf (pages 50-59).

As for the case that we are discussing, it is true that a capacitor of 10 times the required value (like the one we have here) will suppress the sparks, but one should keep in mind that a capacitor in an AC circuit draws current (that is basic EE knowledge) and the higher the capacity, the larger the power drained when the device is off (yes, you read well: a power device draws power even when it is off if it has a spark suppression capacitor across its power switch). In some cases, it can even even let enough current flow to keep the equipment on even when the switch is open - I've seen it personally. In other words, it can easily be a nuisance. I would replace that 100nF cap with a X2 capacitor of the correct 10nF value when possible.

 

[tarior]

I have seen an awful lot of failed switches that had an X (if even that) cap across them instead of a correct snubber.

 

[gadget73]

In this case the cap won't really drain anything, it will just pass some small amount of current through it to the load. Z of 0.1uf at 60hz is basically 26.5k, so 120v / 26500 = 4.5 milliamps of current leakage. Original 0.01 would have beeb 265k, so 0.45 ma of leak current.

 

[jlb2]

In this case the cap won't really drain anything, it will just pass some small amount of current through it to the load. Z of 0.1uf at 60hz is basically 26.5k, so 120v / 26500 = 4.5 milliamps of current leakage. Original 0.01 would have beeb 265k, so 0.45 ma of leak current.

I have the same figure, but there is more to it than you think. 4.5 mA on 120 V is a reactive power of 0.5VAr ("VAr" is the name of the reactive watt). Assuming you don't turn on the device at all, this means it draws 4.5 kVArh each year while not doing anything for you. Granted, this is not a big part of your yearly electricity bill, but if you consider that the cost of a kVArh is the same as a kWh (now that we have meters that measure both active and reactive powers), that small capacitor will cost you much more than its price in electricity for no particular reason, so you might want to pick the correct value in the first place. Many years ago a consumer association calculated that over its lifetime a domestic appliance (they took the example of a VCR) drew more energy when it was off than when you used it - not just because of the switch caps, of course, but they did have their share. And as I said, I've even seen a case (a turntable, if I remember well) where this very mistake caused the appliance to stay on while the switch was off - a strange experience.

 

[jlb2]

I have seen an awful lot of failed switches that had an X (if even that) cap across them instead of a correct snubber.

I have never seen that, yet I've gone through a lot of old clunkers. I don't know what kind of machines you were working on, but I assume they were not the same as those that I work on. I've seen very high end machines (Schlumberger comes to mind) that don't even have an X capacitor and are still perfect after 50 years. It all depends on the specifics of the design, so if the schematic says you need an X capacitor, you may not need to try and improve it - especially given the difficulty to determine the right snubber and source it on the retail market. Besides, Kenwood engineers were not necessarily idiots, you know.

 

[tarior]

Kenwood, Pioneer, Concept, etc.