Best practices using a smart plug with a high wattage appliance - or not at all?

[davie25]

Hello

Happy New Year I hope you all had a great Christmas / Holidays.

A friend recommended your community as somewhere that would be able to put this to rest, so:

I am based in the UK and have a couple of TP-Link Kasa HS100 smart plugs: https://www.kasasmart.com/us/products/smart-plugs/kasa-smart-wifi-plug-hs100

Note: I must have an earlier hw revision, as the spec in the link above says 15A, whereas my plugs clearly state on the front of the housing that they are a maximum of 13A (I've had mine for ~8 years ish).

I want to give the plugs to a friend who wants to use them for an iron and portable heater. With the end goal being: If left house and plugs on, then turn off. A simple safety implementation.

My initial thoughts on this were that it may not actually be a very good safety implementation due to the high wattage of an iron and heater, but having done a bit of googling, it seems perhaps it could be safe enough. Most the disasters I can find seem to be people using un-fused cheaper imported units from China and running them well beyond their rating. For example, I note that a couple of the plugs of Amazon state 10A, but I bet they're way below that and un-fused.

Assuming that the UK market TP-Link plugs are up to spec, I calculate:

1. Iron = 2400W (2400W/240V) = 10A
2. Heater 3000W (3000W/240V) = 12.5A

What are the opinions of the folk here? Is this acceptable or a house fire waiting to happen?

The iron is well within tolerance, but the heater would come close and this is the one that I am not sure about. My gut says that even though it's within tolerance, to not run it so close to the limit.

Perhaps the purchase of one of the newer plugs with 15A rating or a device such as the Shelly 1 (which does seem to be discontinued but can find on eBay) or there are other Shelly units rated at 16A also, such as https://shellystore.co.uk/product/shelly-1-gen3/ and https://shellystore.co.uk/product/shelly-plus-1/ which would give much more leeway. Shelly have an excellent track record, so no doubt their units are up to spec.

What are the thoughts of those here?

Thanks

[brucehoult]

I've been using these to control a 2400W oil column heater for many years (since ~2012) with no problems, using a 433 MHz transmitter on an Arduino to control them.

https://www.jaycar.co.nz/remote-controlled-3-outlet-mains-controller/p/MS6147

I do find that they have a limited number of switching cycles under load and my Arduino application was turning them on or off potentially every 30 seconds (when 1200W was the desired average heating), and maybe two winters of that made them unhappy and needing replacement. I'm pretty sure I've only had failures in the OFF position, and no magic smoke, but at least in my application the consequences of leaving the heater on would just be wasted electricity -- and the heater itself has safety cutout etc.

The heater has about a 10 or 15 minute time constant from thermal mass, so probably a 5 minute PWM frequency would be fine in practice, and make the switches live 5x longer.

If only switching them a couple of times a day they should last forever, even with the maximum rated load.

[Solder_Junkie]

The newer model is the Tapo P110, currently £8.99 at Amazon. That model shows power consumption too. Resistive loads, such as irons and heaters are not going to be a problem to switch… a bigger issue is that someone who leaves appliances turned on is equally likely to forget to add a remote switch.

They are good for switching on an electric blanket too…

SJ

[brucehoult]

15A = 1.8 kW is correct for 120V RMS AC, is it not?

[BeBuLamar]

Please do not take the Import from China as a factor. TPLink is a Chinese company and very likely their products are all imported from China. I would be surprised if you can find such a plug not made in China.

[davie25]

Thank you for the replies.

a bigger issue is that someone who leaves appliances turned on is equally likely to forget to add a remote switch.

Ahh now this is where I come in! I love home automation and one of the reasons I am giving my friend these plugs is because I have just setup a Home Assistant instance for him.

So it is trivial to setup automations like After 1 hour > plug off, or When leaving house > plug off.

I do find that they have a limited number of switching cycles under load and my Arduino application was turning them on or off potentially every 30 seconds (when 1200W was the desired average heating), and maybe two winters of that made them unhappy and needing replacement. I'm pretty sure I've only had failures in the OFF position, and no magic smoke, but at least in my application the consequences of leaving the heater on would just be wasted electricity -- and the heater itself has safety cutout etc.

The heater has about a 10 or 15 minute time constant from thermal mass, so probably a 5 minute PWM frequency would be fine in practice, and make the switches live 5x longer.

If only switching them a couple of times a day they should last forever, even with the maximum rated load.

So this is a concern of mine, how long they will last and what if the relay starts malfunctioning while he is out. I guess the obvious answer here is to go for a higher spec for the heater like the Tapo's Solder Junkie mentioned.

15A = 1.8 kW is correct for 120V RMS AC, is it not?

We are in the UK - so 240V?

Please do not take the Import from China as a factor. TPLink is a Chinese company and very likely their products are all imported from China. I would be surprised if you can find such a plug not made in China.

Apologies - what I meant was half the dodgy stuff on Amazon (which has obviously come from AliExpress) vs a product that is made to EU standards. I'm totally aware it's all made in China, but there's China to China's standards and China to EU/UK standards sold via official channels?

I can find my plug listed on the UL page here: https://www.tp-link.com/uk/ul-listed/product-list/

[Siwastaja]

The risk is mostly with self-importing random stuff from Ebay/Aliexpress/etc. If you buy a name brand imported into EU or UK region by a legitimate importer (who also puts them to the market in brick&mortar stores), the stuff is tested compliant as required by law. Of course legal violations happen (and sometimes leads to recalls), but the risk isn't particularly big.

I'm pretty certain you are safe by buying the TP-LINK plug and using it up to the rated 13A, and you don't really need to add safety margins to that.

[brucehoult]

15A = 1.8 kW is correct for 120V RMS AC, is it not?

We are in the UK - so 240V?

That was in reference to a message (now deleted) which referred to the specs of the Tapo P110 on amazon.com in the USA.

[davie25]

That was in reference to a message (now deleted) which referred to the specs of the Tapo P110 on amazon.com in the USA.

Ah ok!


Well thanks to everyone who has taken time to advise with this. I think we'll go ahead with using the plugs then.

Many thanks 

[antenna]

I use one of those 15A remote control outlets to drive the coil on a heavy contactor so I can run a 1HP water pump with it.  Maybe that is a solution that will work for you, adding a contactor.

[davie25]

I use one of those 15A remote control outlets to drive the coil on a heavy contactor so I can run a 1HP water pump with it.  Maybe that is a solution that will work for you, adding a contactor.

I will look into this - thank you