EEVblog 1481 - Dodgy Dangerous Heater REPAIR

[EEVblog]

A heater that doesn't heat up should be an easy and quick repair, right? RIGHT?
This Arlec space heater also has a rather dodgy and dangerous construction!

[madires]

This is a classic fault in capacitive droppers. And since I'm the family's repair shop I keep a good stock of class X and Y caps.

[Scherms]

D'arlec >>> EXTERMINATE - EXTERMINATE! 

[wraper]

In this application using a usual 630V (DC) film cap is fine. Actually in most of the cases non safety rated capacitors are used for such droppers. Most likely X2 capacitor was used with no safety requirements in mind. Probably it was even a cheaper and more common part since produced in larger numbers. Not that many 220n 630V usual caps are needed these days but X class will be in most of the mains powered equipment. Even if this cap went short, 47R resistor would blow and open the circuit.

[Kleinstein]

A failing cap in a capacitive dropper supply is very common. It is not just cheap Chinease ones, but also the top brands. I may be less of an issue in the US or other 110 V countries.  If the capacitor is not class X the series resistor should be a fusible one. As 220 nF is quite common for X class caps it absolutely makes sense to use one there. It still makes sense to have a resistor that fails gracefully.

[Monkeh]

At this point I just go straight to checking the dropper cap - rarely do I find any need to go further. Space heaters, dehumidifiers, smart plugs, heating thermostats.. dropper cap. Over and over.

I suspect repeated application of transients is the cause. I tend to fit higher voltage rated parts when possible.

[EEVblog]

Even if this cap went short, 47R resistor would blow and open the circuit.

Might even be a fusible resistor.

[EEVblog]

A failing cap in a capacitive dropper supply is very common. It is not just cheap Chinease ones, but also the top brands. I may be less of an issue in the US or other 110 V countries.  If the capacitor is not class X the series resistor should be a fusible one. As 220 nF is quite common for X class caps it absolutely makes sense to use one there. It still makes sense to have a resistor that fails gracefully.

Surges on the mains are very rare for me, so rarely see this kind of fault. This heater did come from the blue mountains west of Sydney though which is famous for power surges.

[Per Hansson]

Using X2 class for capacitive dropper supplies is not recommended in the datasheet of several reputable capacitor brands.
They have special designs rated to be used for that, but they cost more of course, they also have not been on the market for a very long time.
Here is a direct quote from the Kemet F862 datasheet, a capacitor approved for dropper supply usage:
"Typical applications include connection in series with the mains, capacitive power supplies and energy meters, with special emphasis in automotive applications for severe ambient conditions."

I made a post on the Badcaps forum about it, linked here: Capacitive dropper supplies not lasting

[thm_w]

So question is which is going to last longer then, 250V X2 cap or 630V DC film cap?

On digikey its about 84C for a 220nF X2 and $1 for 630V polyester. Seems worth the 16c premium if it means the device won't die again.

Using X2 class for capacitive dropper supplies is not recommended in the datasheet of several reputable capacitor brands.
They have special designs rated to be used for that, but they cost more of course, they also have not been on the market for a very long time.
Here is a direct quote from the Kemet F862 datasheet, a capacitor approved for dropper supply usage:
"Typical applications include connection in series with the mains, capacitive power supplies and energy meters, with special emphasis in automotive applications for severe ambient conditions."

I made a post on the Badcaps forum about it, linked here: https://www.badcaps.net/forum/showthread.php?t=80208

fixed link

[wraper]

On digikey its about 84C for a 220nF X2 and $1 for 630V polyester. Seems worth the 16c premium if it means the device won't die again.

I don't think one is more reliable than other. All depends on quality of implementation. In cases when X2 caps have DC rating, usually it is somewhere around 600V. Often capacitive droppers use film capacitors with 400V DC rating, and IME it's very unreliable.

[insine]

Why there are holes drilled near some pads?

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