TP-Link Kasa KP105 - rapidly power cycling when plugged in

[spleenharvester]

One of my KP105 smart plugs failed today. It started very rapidly power cycling (you could hear the relay clicking on and off and the LED was going green/orange repeatedly).

I was going to just bin it but I opened it up out of curiosity. Found a swollen cap in the corner (bottom right of image). AiSHi brand, 470uF 10V 105*C. Not sure what purpose it serves exactly so can't comment on whether it is appropriately specced. Other members of this forum have reported similar findings with off-brand smart plugs but this is the first time I have seen evidence of this happening with a brand like TP-Link. This seems to be a common failure mode looking at their forums so I bet there are a lot of these out there.



Anyway I don't plan on repairing it as I smashed the casing with a hammer to remove it. But if you want to try and repair it in a manner that does not involve a hammer, there are 7 clips you need to overcome - one at the bottom, two on the sides and two at the top. You will have a really hard time getting it open but with the right tools it might be possible to do non-destructively.

[spleenharvester]

Just smashed a fully working one open, this time a Tapo P100 (I trust none of them now so a worthy sacrifice) - it has an identical PCB (2084500437) and an identical spec capacitor in that position but it is ChengX brand this time. It isn't vented but these plugs have not had the same amount of use so I am not certain this issue is fixed.

I can't see any date or batch codes on them that clearly indicate which might belong to a faulty batch

[CapLeaker]

Usually what makes them not work are bad capacitors, cracked solder joints and bad flash, doesn’t matter what brand. These things are so cheap, mass produced, manufacturing cost cutting, expect cheap. But cheap works too, if you know how to fix it.

[Agent24]

Bad capacitor can't hold up the voltage supply to the circuit, when the relay pulls in and draws current, the voltage sags, and the CPU resets...

[spleenharvester]

Does anyone know of a smart plug that doesn't have this problem? It seems like it has been reported to occur with every Kasa/Tapo plug. Not really sure what to do about these other than go back to the old analog timers. I only have 1 alive now

[CapLeaker]

Does anyone know of a smart plug that doesn't have this problem? It seems like it has been reported to occur with every Kasa/Tapo plug. Not really sure what to do about these other than go back to the old analog timers. I only have 1 alive now

I’ve got some Shelly smart plugs. So far I had one device with cracked solder joints that lives in a light switch. Quite tight in there too. Some Shelly devices can run on low voltage DC. Got my air exchanger hooked up to a Shelly running on 12v DC. Then I run 2 smart Shelly smart plugs on the Shelly button to turn stuff on and off.

[stj]

i run a rocker-switch.
it's 100% reliable

[CapLeaker]

i run a rocker-switch.
it's 100% reliable

Broke those too before.

[spleenharvester]

I tried out some Meross plugs but couldn't get the app to work, it kept telling me to connect to WiFi even though it was already connected. So I've caved and bought some more Tapos and will just fix them when they break. But I just checked my last working P100 out of curiosity and there isn't a junk high ESR AiSHi cap like in the OP, instead there's a low ESR cap so maybe they've resolved the problem?

[CapLeaker]

Cap suppliers change. If there is a cent to save, the cheaper one goes in. Profit has to be made after all.

[spleenharvester]

FWIW I received the brand new Tapos today and they also have the new low ESR caps instead of the junk AiSHi normal-ESR ones on the failed units, time will tell if they're more reliable