Granny Charger

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Daveion
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Post by Daveion »

A question for anyone with more electrical knowledge than I have. I am using the Granny Charger a lot until I can proceed with a 7kw home charger. I have to wait another 6-8 weeks at present.
The charge periods are daily around 5-6 hours and the plug feels warmish. Measures 32C with my IR Thermometer on and around plug. Allthough that doesnt seem that hot it was higher than I expected on a 10C day.
Its a good quality MK IP65 outlet SWA supplied.
Charge speed varies between 7mph and 10mph.
Any advice gladly appreciated.
Dave
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simonrg
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Post by simonrg »

Daveion wrote: Fri Apr 02, 2021 11:50 am A question for anyone with more electrical knowledge than I have. I am using the Granny Charger a lot until I can proceed with a 7kw home charger. I have to wait another 6-8 weeks at present.
The charge periods are daily around 5-6 hours and the plug feels warmish. Measures 32C with my IR Thermometer on and around plug. Although that doesn't seem that hot it was higher than I expected on a 10C day.
Its a good quality MK IP65 outlet SWA supplied.
Charge speed varies between 7mph and 10mph.
Any advice gladly appreciated.
Dave
I approach electrical systems from my knowledge of physics, so please check with somebody with practical electrical knowledge - but basically check all the connections.

If the plug itself is getting hot and not the socket or the cable, then there must be resistance in the plug hence generating heat. All wires carrying electricity will have some resistance so will generate some heat, but 32C could be a bit hot, however if the charger has been on for some time then as the plug is fairly well thermally insulated so the local temperature near the source of heat would rise slowly. My thoughts are that the most likely causes for the resistance are going to be poor contacts, so either inside the plug (unlikely as presumably supplied with the charger - if so faulty and should be returned as defective) or between plug pins and the socket. Is the socket outside and has corrosion occurred to the socket connectors?

I haven't noticed the plug on my granny charger getting hot, but I don't often touch it immediately after charging.

I have decided not to get a wall charger. While nowadays we don't use many 10A electrical appliances continually, a couple of decades everybody had 3 bar electrical fires where each bar was 1kW, so 12.7amps total. This forum discussion here covers the issues involved https://www.electriciansforums.net/thre ... et.111739/. My conclusion is that I don't need a wall charger as my granny charger is plugged into the garage 40amp circuit breaker with normally nothing else drawing power, the wiring has been checked recently and I rarely need to replenish more than 100miles travel in a day. I also have a heat pump in the ID.3 so in winter I believe the granny charger will supply sufficient power to pre-heat the battery, effectively supplying the 6kW of heat needed from 2kW of electricity.

I did originally try to get a Zappi installed as I have solar, but with quotes of around £1200 via OLEV electricians, based on internet or telephone surveys I wasn't impressed. My house is fitted with Lightwave RF sockets, so I can synchronise my charging with solar generation, only turning on the charging when excess solar would otherwise be exported through controlling the granny charger's socket.
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Daveion
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Post by Daveion »

Thanks Simon. The granny is the VW accessory which the dealer included in my deal. Its really well made and sealed IP65 or better. All connections you can access are fine so any heat that is arising is the transfer of current and the cross section of the conduction at any point. I am going to keep an eye on it but 32C is not yet going to melt anything.
With the mileage I generally cover I could probably manage with a granny but have needed to do a lot more miles with Grandchildren childcare recently and the house has plenty of spare electrical capacity. I have had a number of quotes for a home charger but have not been happy about any of them. The delay I have is a Bulb trial I became involved with and how that pans out.
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HeidiFlowerpt Driver
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Post by HeidiFlowerpt Driver »

The cartridge fuse inside a standard UK 13A plug is a fairly crude device, simply a filament of wire, of appropriate gauge so that if you pass too much current through it, it will melt and break the circuit. I've often wondered, I assume that if you pass current close to its rated value through the fuse for a long period, the fuse is going to get hot but not hot enough to melt. Maybe you could experiment, immediately after a charge session, expose the fuse and feel it to see if it's the source of the warmth. Take care not to burn yourself!

It's also important that the wall socket you're plugging the charger into is in good condition (the pins of the plug make good electrical contact with the receptacles in the socket). If the wires that feed the socket, most likely a 'ring' circuit, are getting warm, you have a major safety issue and you should not use your charger until you've had it checked by an electrician.

Granny chargers generally take 10A, and the plug will likely have a 13A fuse in it. A 'proper' wallbox will take 30A and charge your car three times as fast.

I have a Zappi chargepoint, and paid over £1000 after the OLEV grant. Ouch.
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Daveion
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Post by Daveion »

HeidiFlowerpt Driver wrote: Sat Apr 03, 2021 11:38 am The cartridge fuse inside a standard UK 13A plug is a fairly crude device, simply a filament of wire, of appropriate gauge so that if you pass too much current through it, it will melt and break the circuit. I've often wondered, I assume that if you pass current close to its rated value through the fuse for a long period, the fuse is going to get hot but not hot enough to melt. Maybe you could experiment, immediately after a charge session, expose the fuse and feel it to see if it's the source of the warmth. Take care not to burn yourself!

It's also important that the wall socket you're plugging the charger into is in good condition (the pins of the plug make good electrical contact with the receptacles in the socket). If the wires that feed the socket, most likely a 'ring' circuit, are getting warm, you have a major safety issue and you should not use your charger until you've had it checked by an electrician.

Granny chargers generally take 10A, and the plug will likely have a 13A fuse in it. A 'proper' wallbox will take 30A and charge your car three times as fast.

I have a Zappi chargepoint, and paid over £1000 after the OLEV grant. Ouch.
Thanks for this. The granny is new from VW and wall socket also new MK IP65. Fed as a radial from a separate 32amp mcb in SWA. I will do as you say though and check the fuse and pin temperature on the VW granny next time I charge.
If the external temperature of a heavy duty rubber type plug is 32C then internally something is much hotter! How hot is ok is the question.
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simonrg
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Post by simonrg »

Daveion wrote: Sun Apr 04, 2021 9:02 am .....If the external temperature of a heavy duty rubber type plug is 32C then internally something is much hotter!....
Internally something does not have to be much hotter that 32C, to have an external temperature of 32C.

Over time the whole plug will get to nearly the same temperature as heat from the inside will be conducted to the outside through the plug. Once at the surface of the plug the heat will only be convected slowly away by the air which has a low thermal capacity and so the temperature will equilibriate towards the internal temperature.

The granny charger is designed to charge an electric vehicle at 10A, so if the plug is getting unreasonably hot, then it is either damaged or is not fit for purpose due to poor design.
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HeidiFlowerpt Driver
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Post by HeidiFlowerpt Driver »

Daveion wrote: Sun Apr 04, 2021 9:02 am
HeidiFlowerpt Driver wrote: Sat Apr 03, 2021 11:38 am The cartridge fuse inside a standard UK 13A plug is a fairly crude device, simply a filament of wire, of appropriate gauge so that if you pass too much current through it, it will melt and break the circuit. I've often wondered, I assume that if you pass current close to its rated value through the fuse for a long period, the fuse is going to get hot but not hot enough to melt. Maybe you could experiment, immediately after a charge session, expose the fuse and feel it to see if it's the source of the warmth. Take care not to burn yourself!

It's also important that the wall socket you're plugging the charger into is in good condition (the pins of the plug make good electrical contact with the receptacles in the socket). If the wires that feed the socket, most likely a 'ring' circuit, are getting warm, you have a major safety issue and you should not use your charger until you've had it checked by an electrician.

Granny chargers generally take 10A, and the plug will likely have a 13A fuse in it. A 'proper' wallbox will take 30A and charge your car three times as fast.

I have a Zappi chargepoint, and paid over £1000 after the OLEV grant. Ouch.
Thanks for this. The granny is new from VW and wall socket also new MK IP65. Fed as a radial from a separate 32amp mcb in SWA. I will do as you say though and check the fuse and pin temperature on the VW granny next time I charge.
If the external temperature of a heavy duty rubber type plug is 32C then internally something is much hotter! How hot is ok is the question.
It sounds like your setup is right, I hope it turns out that all is well.
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Post by digital »

simonrg wrote: Fri Apr 02, 2021 8:40 pm I did originally try to get a Zappi installed as I have solar, but with quotes of around £1200 via OLEV electricians, based on internet or telephone surveys I wasn't impressed.
I, too, had after-grant quotes of £1200 for a tethered zappi from national installers who quoted using photographs.

Local installers did on-site surveys and quoted half of that.

I went with a local installer...
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BevTowcester
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Post by BevTowcester »

Hi
Dave ion says that his home supply charges at 7 to 10 miles per hour of charging.
Within the software can we see the actual charging power.
Often a charger shown as 50kw ( for example ) only charges at 30kw .due to battery status, other vehicles sharing charger or other reasons.
But we should know,
The miles per hour of charge may give a pro-rata value
But after only a few charges so far, I’ve not got the formula verified.

Question foe Dave Ion
When does it show just 7 miles per hour of charge and when 10 ?
Thanks
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Daveion
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Post by Daveion »

BevTowcester wrote: Mon Apr 05, 2021 8:22 pm Hi
Dave ion says that his home supply charges at 7 to 10 miles per hour of charging.
Within the software can we see the actual charging power.
Often a charger shown as 50kw ( for example ) only charges at 30kw .due to battery status, other vehicles sharing charger or other reasons.
But we should know,
The miles per hour of charge may give a pro-rata value
But after only a few charges so far, I’ve not got the formula verified.

Question foe Dave Ion
When does it show just 7 miles per hour of charge and when 10 ?
Thanks
I can see it as a charging status in the app when I refresh but feel sure I have seen it in the car as well when charging. The rate of 7, 8, 9 and 10mph seems to come randomly??? If there is any correlation at all it seems temperature related. Its much more likely 10mph when the batteries are warmer. When I charge via a 11kw charge point the app shows a rate around the low 40's mph.
When charging there has not been any other current draw for the car, heater, lights etc.
From other reports I have seen you cannot vary the rate of charge other than the reduced charge option which I think I read reduced charge to something like 1.4 kw even when on a 7kw charger.
Hope that helps.
Dave
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kaiz
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Post by kaiz »

Calculation: Full speed gives me abt. 56 km/h * 0,2 kWh/km (av. consumption) = 11,2 kWh/h
Reduced speed gives me abt. 23 km/h * 0,2 kWh/km (av. consumption) = 4,6 kWh/h
It is with 3ph. charger. :) Granny takes too long.
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Daveion
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Post by Daveion »

"Internally something does not have to be much hotter that 32C, to have an external temperature of 32C.

Over time the whole plug will get to nearly the same temperature as heat from the inside will be conducted to the outside through the plug. Once at the surface of the plug the heat will only be convected slowly away by the air which has a low thermal capacity and so the temperature will equilibriate towards the internal temperature"

Thanks Simonrg
Thats a really good point. As long as the temperature stabilises then there will be little difference between internal and external surfaces.
Less bothered by this now. Thank you.
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Post by HeidiFlowerpt Driver »

I just read a thread on another forum about granny chargers. The OP wanted to know how to replace the 13A plug on his granny lead. He'd cut the old plug off and was surprised to discover six wires in the lead, not the usual three. It turns out his lead had extra wires connected to thermistors inside the plugtop, likely to provide thermal monitoring to ensure the plug doesn't get too hot. If such protection is standard on granny chargers that's brilliant.
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Post by Sindidziwa »

I only get 7 or 8 mph with my granny charger. If I switch on the AC to warm the car up this then drops to 2 mph! The plug does get warm but not excessively. My Granny Charger was £165 from Screwfix - couldn't justify the Zappi chargers etc when we're mostly at home but I'm on Octopus so i use Alexa and a wifi connected plug to program the charging for the cheapest electricity - always better when it's windy. I'll soon be charging on sunny days as my PVs generate 3.6kW at full blast and I'm only charging at 2.3kW.
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Post by Daveion »

HeidiFlowerpt Driver wrote: Wed Apr 07, 2021 1:59 pm I just read a thread on another forum about granny chargers. The OP wanted to know how to replace the 13A plug on his granny lead. He'd cut the old plug off and was surprised to discover six wires in the lead, not the usual three. It turns out his lead had extra wires connected to thermistors inside the plugtop, likely to provide thermal monitoring to ensure the plug doesn't get too hot. If such protection is standard on granny chargers that's brilliant.
Thats interesting. Might explain why the cable to the smart box component is so fat. My temerature checks revealed nothing more than a plug that reaches 32C and is stable at that level throughout my charge. Longest charge so far 9 hours 35 mins.
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