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Charging using granny cable with smart plug

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21K views 37 replies 14 participants last post by  benwillcox  
#1 · (Edited)
Still getting mixed answers regarding charging with a granny cable. I've been doing it at 10A for over 3 weeks with no issues - no trips, no heat from the plug or control box.

More to the point, I'm considering using an energy monitoring smart plug from TP-Link to keep track of kWh usage. Has anyone used this with a portable 3-pin charger? Is this adding additional risk? The smart plug is 13A rated, to me it's effectively like using an extension cord?

Mainly for my current landlord's records as they pay the bills. I'm currently manually doing this based on SOC. It's really not a big deal but just something I thought would be interesting to see anyway (energy losses etc.)
 
#3 ·
Hmm why does the manual for this plug say maximum W is 1500 bu
125818
t
max output on the plug itself says 13A? 240x13=3.1kW.

Still trying to wrap my head around all this
 
#27 ·
Hmm why does the manual for this plug say maximum W is 1500 but
max output on the plug itself says 13A? 240x13=3.1kW.
Yes a bit strange that it contradicts itself. I use a simpler device like this: https://www.ebay.co.uk/itm/LCD-Powe...Electricity/223752370665?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649 which has no switching capability but simply displays the cost and usage etc on the built in screen. Been using this for a few weeks with no issues, nothing gets warm at all.

Ben
 
#4 ·
Its a modern way of doing things. The max value in this case, and most, is determined by the rating of the components, they can handle that current, in the short term. Long term is a different beast, thermal considerations move to the fore, and you end up with a lower value. We see the same game played with everything now, including DC car chargers/batteries!
 
#6 ·
I just had my house meters upgraded to smart meters , When charging my 24KW leaf it takes 10 hours on the granny charger , The meter shows a £0.40p per hour charge cost , So £4.00 for a charge , I get 71 miles 3 journeys to and from work for that , In my previous diesel I would get 60 mpg at £5.94 , am I happy . Oh yes and my Leaf does not have a rented battery pack
 
#7 ·
Heaters are a very inductive load which can cause spikes on the relay contacts. As the car has a soft start via electronics instead of a physical switch, I'd expect it to be fine. Just check after a few hours. Unplug everything and see if any pins are getting hot (slightly warm is ok, nothing more).

Regarding using the granny charger, as long as you're not using extension leads and are plugging it into a decent, modern socket on a main ring main then it's fine to run at 10A as much as you want.
 
#8 ·
Thanks Richard. This is exactly the kind of nuanced response I was looking for!

The flat is only a few years old, it's a new build so I suspect the socket is modern. How can I verify it's on a main ring main? I have access to the fuse box.
 
#10 ·
Oh wow brilliant. Which granny charger/manufacturer is that? Switch longevity?

So did you just leave it on continuously and let the car manage power draw or switch it physically when needed?

Thanks a lot!
 
#25 ·
My question is whether the switch longevity issue you mentioned is still a problem if the car isn't drawing any current when you toggle ON/OFF from the smart plug app e.g. when it's stopped charging however it does.
 
#28 ·
Thank you dave, you've been super helpful.

Yes a bit strange that it contradicts itself. I use a simpler device like this: https://www.ebay.co.uk/itm/LCD-Power-Consumption-Meter-Energy-Monitor-Calculator-Usage-Plug-In-Electricity/223752370665?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649 which has no switching capability but simply displays the cost and usage etc on the built in screen. Been using this for a few weeks with no issues, nothing gets warm at all.

Ben
Thanks for the suggestion.

As an update, I've been using the smart plug for nearly 4 hours with no issues so far.

I know that the circuit the charger is on is 32A capacity. Unless, I run the radiator (5A), kettle (13A) and microwave (5A) at the same time, I should be fine.

I do have a RCCD in the fuse box but how I do know which devices it is protecting? There's an arrow pointing towards the right where there are about 5 circuit breakers. Is it all of them? Does the RCCD have a max capacity?

Other thing I've heard being mentioned is an independent earth. Does this mean that normally everything on a single circuit/ring is connected to a single earthing point and it's worth having a independent one for high current loads?

Final consideration is this idea of 'ring faults' that @poddick mentioned. Essentially at this stage I'm just gathering information to be better informed and understand the material risk involved.
 
#35 · (Edited)
Whether or not the load is inductive, isn't a smartplug more likely to use a triac rather than a relay to switch the power? 40 amp triacs are cheaper and a lot smaller, plus they will prevent any need to worry about arcing. Where they may give a problem is causing distortion of the sine wave due to switching at each half-cycle of the mains. Also the smart plug will only switch the live line whilst the neutral will remain connected, although I doubt that would be a problem.
 
#38 ·
Whether or not the load is inductive, isn't a smartplug more likely to use a triac rather than a relay to switch the power?
The problem with triac based switches (and dimmers) is that often there is a small leakage current which means they don’t play nicely with very low current devices such as LED and CCFL lighting. It causes these devices to flicker or even just light up when ‘off’. All the smartplugs I’ve seen use a relay, presumably to avoid any complication about what type of load they might be switching.