Safe, or pushing it? (charge rate from 3 pin plug)

[richlove]

This is probably not MG4 specific, so feel free to move if not appropriate. [Edit: Moved to General Chat.]

I have this new charger (10m extension) that I've been using as I don't have a proper home install (and can't), it plugs in to the 3 pin mains. It has an amp limit setting which I've been using set to 10 amps, which has been giving me 2.5kw from the charger, 2kw seen by the car.

I was interested to see what would happen if I switched it to the 13 amp setting. It seems now I'm getting 3kw at the charger, 2.7kw at the car, drawing 12 amps:

This would get me 5% per hour (vs 4% per hour @ 10 amps), it doesn't sound much, though would be quite helpful during the 00:30-->04:30 Octopus Go cheaper window.

Question is, am I fairly safe to be running this or beginning to push things uncomfortably? I'm tempted to run it a couple of hours and monitor the temperature displayed (it usually goes to about 30 degrees).

 

[Coulomb]

This would get me 5% per hour (vs 4% per hour @ 10 amps), it doesn't sound much, though would be quite helpful during the 00:30-->04:30 Octopus Go cheaper window.

Usually, the rule of thumb is that you should only draw 80% of the rated current from a circuit long term continuously. You should check that the extension cord has adequate copper, the conductors should be at least 1.5mm². You can see the temperature of the EVSE ("charger" box) plug on the display (very handy), but of course it can't see the temperature of the extension cord's plug. Use a non contact thermometer to monitor that.

The problem is that plugs, especially domestic plugs, tend to degrade over time, so the plugs get gradually hotter, and humans forget to check regularly. So my suggestion is to leave it on 10A all the time. You might want to play with 13A during the night when it's usually cool even in summer, but I predict you'll get sick of changing all the time. If you don't drive much and can often get by with only charging during the lowest tariff, that might be ok.

In Australia, we can get industrial style plugs and outlets with a screw in shroud; these are much better quality and are splash proof. I happily run mine at 100% of rated current. I assume that you can get similar gear in the UK and elsewhere. Perhaps consider a dedicated outlet, at least where the extension cord plugs in, if that's allowed. And of course a plastic cover gizmo for the EVSE's plug, making that end somewhat weather resistant.

This is the plug on my adjustable, portable EVSE, plugged into an actual industrial outlet at a shopping centre (it's designated for EV charging). I have a similar outlet at home (photo not handy at present).

This is what I mean with the plastic cover gizmo, available from my local hardware store. They usually have a sort of ¾ grommet to better seal the ends:

 

[richlove]

Thanks very much, appreciate the detailed response. There's no outside 'join' the extension has the type 2 ending straight into the car (this is the unit).

I ran it for a couple of hours just now, the internal temperature of the unit went up to 35 degrees this time and both the back of the plug and the surrounding area of the plug socket felt noticeably hotter, so I'm not feeling comfortable with it. I will revert to using the 10 amp setting.

The unit does seem to have various protection systems in place, though I'm not sure any are enough to prevent overheating and possible fire at the plug/socket.

 

[Matt x power]

I have a similar granny cable but I set it to 10 amps for safety as you are drawing a lot of amps over a long period of time

 

[Coulomb]

There's no outside 'join' the extension has the type 2 ending straight into the car (this is the unit).

Oh, I see, the EVSE has a 10 m lead and that's long enough for your situation. I would not call that an "extension cord". That "brick" with the display is your EVSE.

The unit does seem to have various protection systems in place, though I'm not sure any are enough to prevent overheating and possible fire at the plug/socket.

Well, it seems to be aware of the temperature at the plug. Perhaps do some experiments and measurements. With no actual extension cord, and if it really has the ability to measure the plug's temperature, I'd be more confident about running it at 13 A.

 

[mst33594]

I’ve just had to replace my 10m granny as running it at 13a fried the plug. With the reduced battery range in winter I upped the rate to 13 from 10 as I am on Octopus Go so only get four cheap hours. The plug had melted due to the fuse overheating. Socket was scorched and cracked with the heat.
I think this was due to trying to catch up on range after a long journey so I charged for four hours during the day then into the cheap night period.
I’ve had a lucky escape as the plug was in the garage which contains my motorbike and Z4M.
New build house modern electrics.etc. Looks
Like I pushed it too far and got lucky. Have a new 10m granny new socket and I’m keeping my rate down to 10a now.

 

[Coulomb]

I’ve just had to replace my 10m granny as running it at 13a fried the plug.

Interesting, thanks for the report.

Did your EVSE (granny) have a temperature display, and if so did it seem to sense the plug temperature or just the internal electronics?

 

[richlove]

I’ve just had to replace my 10m granny as running it at 13a fried the plug. With the reduced battery range in winter I upped the rate to 13 from 10 as I am on Octopus Go so only get four cheap hours. The plug had melted due to the fuse overheating. Socket was scorched and cracked with the heat.
I think this was due to trying to catch up on range after a long journey so I charged for four hours during the day then into the cheap night period.
I’ve had a lucky escape as the plug was in the garage which contains my motorbike and Z4M.
New build house modern electrics.etc. Looks
Like I pushed it too far and got lucky. Have a new 10m granny new socket and I’m keeping my rate down to 10a now.

Thanks for reporting this, helpful information and glad to hear things didn't turn out worse. That's the exact situation here, trying to eke out a little more charge during that window, especially during winter. That's certainly helped me not be tempted to push it with 13 amps.

I did notice on the product description for my EVSE it says:

"A temperature controlled 3 pin plug adds an extra layer of protection, preventing overheating at the power source"

I'm not sure if that would provide adequate protection against things going wrong at 13 amps, though I feel it's best not to try given the report above.

 

[Rolfe]

It's so variable. The plug on my granny lead never even gets warm, even if I charge for 24 hours and more. Last week I unplugged it to take it on a long journey, and the pins were shiny and new-looking, just as when I first took it out of the box. The 13A socket is metal-jacketed and mounted on a bare breeze-block wall in my garage, but it's just what came with the house.

I've never done anything to limit the power and the car charges at about 1.87 Kw. I don't know if this will go on forever or if karma will catch up with me.

 

[richlove]

Interesting, I wonder what current it's delivering for 1.87 kW. Mine's drawing 9 amps to provide 2.5kW at source, 2kW at the car, so perhaps yours is a tad less than 9 amps. Not sure why that would be from a 13 amp socket if it's a standard granny cable

 

[Jomarkh]

I’ve just had to replace my 10m granny as running it at 13a fried the plug. With the reduced battery range in winter I upped the rate to 13 from 10 as I am on Octopus Go so only get four cheap hours. The plug had melted due to the fuse overheating. Socket was scorched and cracked with the heat.
I think this was due to trying to catch up on range after a long journey so I charged for four hours during the day then into the cheap night period.
I’ve had a lucky escape as the plug was in the garage which contains my motorbike and Z4M.
New build house modern electrics.etc. Looks
Like I pushed it too far and got lucky. Have a new 10m granny new socket and I’m keeping my rate down to 10a now.

Have you got any pictures of the damaged caused by running continuously at 13A?

 

[Gomev]

Interesting, I wonder what current it's delivering for 1.87 kW. Mine's drawing 9 amps to provide 2.5kW at source, 2kW at the car, so perhaps yours is a tad less than 9 amps. Not sure why that would be from a 13 amp socket if it's a standard granny cable

Simple arithmetic. Watts = Volts x Amps

Yours delivering 2500 watts at 9 amps = 277.7 volts. I would check your supply that sounds a bit odd.

1870 watts at a nominal 230 volts = 8.1 amps. Of course there is a tolerance around 230 volts between 216 and 253 which at extremes would be 8.7 amps and 7.4 amps respectively.

 

[tsedge]

Most sockets are only rated for 10A maximum continuous use in the UK. Even 10A is too much if anything else is running on the same circuit. And that assumes perfect wiring.

Attempting to run beyond this at 13A for extended periods is a huge risk for little benefit.

By far the best option is a dedicated outlet with its own circuit breaker and minimal connections. I appreciate this isn't always an option but it is senseless to take risks.

Often the failure isn't the first time or first ten times you use it, it is a few dozen or hundred times later when the cumulative damage of the thermal stress progressively increases resistance, raises temperatures and results in something burning out. If you are unlucky, it then causes a fire.

 

[richlove]

Simple arithmetic. Watts = Volts x Amps

Yours delivering 2500 watts at 9 amps = 277.7 volts. I would check your supply that sounds a bit odd.

1870 watts at a nominal 230 volts = 8.1 amps. Of course there is a tolerance around 230 volts between 216 and 253 which at extremes would be 8.7 amps and 7.4 amps respectively.

Thanks for that, the display on the EVSE shows 250ish volts most of the time, it's set at 10amp max, so i guess that kind of makes sense, as it also shows 2.5kW at the EVSE, with 2kW being delivered to the car

 

[Gadget Geek]

I fitted one of these.

Masterplug IP66 13A 1-Gang Weatherproof Outdoor Unswitched Active Plug Socket With RCBO - Screwfix

Order online at Screwfix.com. 13A charging socket for electric vehicles. Robust housing is IP66 waterproof rated and has a see-through cover to protect in the most ardous condition. Seals plug when in use. Socket is protected by a safety DP RCD and is suitable for periods of prolonged charging...

www.screwfix.com

 

[mst33594]

Have you got any pictures of the damaged caused by running continuously at 13A?

I’ll take some photos and post. Scary as the plug had melted around the fuse. Just away atm

 

[Ruislip Resident]

I fitted one of these.

Masterplug IP66 13A 1-Gang Weatherproof Outdoor Unswitched Active Plug Socket With RCBO - Screwfix

Order online at Screwfix.com. 13A charging socket for electric vehicles. Robust housing is IP66 waterproof rated and has a see-through cover to protect in the most ardous condition. Seals plug when in use. Socket is protected by a safety DP RCD and is suitable for periods of prolonged charging...

www.screwfix.com

I don't use one of those (as I have a hypervolt 2) but the property I stayed in over Christmas let me plug a granny charger into one very similar to that. I ran it over Christmas Eve evening to Christmas Day morning and again over Chritmas Day evening to Boxing Day morning. That was sufficient to charge it up from 20 % to 100% ( LRTC). Worked fine with no heating damage to the charger cable plug.

 

[Deleted member 7316]

I would guarantee that if you removed all of your plug top fuses a significant number would have tarnished end caps and the copper fuse clips will not be bright metal either.

A true zero ohm connection is not that easy to achieve and at these currents resistance = heat. The plastic of the plug body will not let the heat dissapate easily either. What you can't see is the quality of the contacting surfaces inside the socket and obviously the switch poles themselves, any of which could contribute to heat generated.

This issue has been subjects of discussion on a number of sites for electrical engineers with differing continuous currents quoted, sometimes as low as 8A. Hypothetically it could be argued that any rating is going to be compromised by age so should a socket being used in this manner be replaced after 10, 5 or even 3 years. Then what do you do about the plug itself, a life limit on the granny charger itself as they are supposed to have thermal sensing inbuilt might be required.

 

[Grriff]

It has always seemed to me that the weak points of the circuit are the clips which hold the fuse. If these fail to hold the fuse tightly then a poor contact will cause heating. My advice would be to check that that the fuse is held tightly, and the wires are securely held in the pins.

 

[gazza487]

I honestly thought all the “approved” type granny chargers ran at 10A max UK as 13A continuous wasn’t allowed. That said Argos were selling a selectable ring branded one that would go to 13A but they have since discontinued it. There were some 16A ones with 3pin plugs on knocking around on aliexpress, I think it’s ignorance on makers parts - not knowing the foibles of our ring mains so they swap the plug, which would be fine on a non fused radial as per other countries.

Before getting a wall box and a day or 2 before my car I purchased the mater plug 10m granny charger from screw fix with a discount code from work for about £170 to completely avoid extensions (the route was through bathroom window so ANY possibility of water near connections was avoided). Even with all new sockets on the lightly loaded ring and the master plug lead it still worried me to be honest sucking the electrons at night when I was sleeping. I personally wouldn’t crank it up