Granny home charging instead of Type 2?

[Shengis]

Apologies if this has already been asked but looking for advice on a thought I’ve just had.

Is it at all viable to consider not getting a home charging unit at least to begin with and instead use granny charging overnight?

My typical daily commute is 15 miles there and 15 back so 30 in total. How long would I need to charge it with a granny lead if I wanted top up the battery?

And would it be any dearer doing it that way electricity wise because it’s charging for longer than with a proper ev charger?

Feel free to say if this is a crap idea! ?

 

[siteguru]

A granny charger will nominally charge at 2.2kW. So over, say, a 10 hour period you'd get 22kWh of charge into the car. Even at a very poor 3 miles per kWh that would be 66 miles of range.

So a granny charger is certainly a feasible interim solution.

As regards cost ... it is per kWh, so the cost is based on how many kWh used, not how quickly they were delivered.

 

[Alb]

It's certainly feasible to survive with a Granny Charger but the issue is complicated if you are on a time-of-use tariff like Go where you only have 4 hours of (relatively) cheap electricity. Sticking to this means only getting around 9kWh rather than 28kWh with a proper 32A charge point.

 

[Shengis]

A granny charge will nominally charge at 2.2kW. so over, say, a 10 hour period you'd get 22kWh of charge into the car. Even at a very poor 3 miles per kWh that would be 66 miles of range.

So a granny charger is certainly a feasible interim solution.

As regards cost ... it is per kWh, so the cost is based on how many kWh used, not how quickly they were delivered.

Thanks for that. I am really struggling to get my head round this kWh thing.

You’re saying the charge is 2.2 kWh so 10 hours would be 22 kWh of charge. So surely the amount of time it takes does matter then, no? And if not, how do I know how much that will cost in electricity?

 

[Shengis]

It's certainly feasible to survive with a Granny Charger but the issue is complicated if you are on a time-of-use tariff like Go where you only have 4 hours of (relatively) cheap electricity. Sticking to this means only getting around 9kWh rather than 28kWh with a proper 32A charge point.

That’s the thing. I’m not currently on an off peak tariff. Although it is something I am thinking of switching to.

Another question then, I have a 16A (I think) commando socket in my garage specifically for a fancy high powered pressure washer I used to have. Could this be utilised with an Ohme commando cable and would it be better than a granny charger?

 

[MoDolph]

Thanks for that. I am really struggling to get my head round this kWh thing.

You’re saying the charge is 2.2 kWh so 10 hours would be 22 kWh of charge. So surely the amount of time it takes does matter then, no? And if not, how do I know how much that will cost in electricity?

kW is the rate the energy is supplied. A granny will run at 2.2kW

kWh is the total amount of energy. You calculate it by multiplying kW by time in hours.

Energy is billed in kWh.

For example you run the granny charger at a rate of 2.2kW for 2 hours:

2.2*2=4.4kWh supplied

If your electricity costs 30p per kWh then it would cost 4.4*0.3=£1.32

If you charged instead with a home charger at 7kW for 2 hours you would deliver 7*2=14kWh and it would cost 14*0.3=£4.20

The battery can store a maximum of approx 60kWh (LR) or 50kWh (SR)

 

[Shengis]

kW is the rate the energy is supplied. A granny will run at 2.2kW

kWh is the total amount of energy. You calculate it by multiplying kW by time in hours.

Energy is billed in kWh.

For example you run the granny charger at a rate of 2.2kW for 2 hours:

2.2*2=4.4kWh supplied

If your electricity costs 30p per kWh then it would cost 4.4*0.3=£1.32

If you charged instead with a home charger at 7kW for 2 hours you would deliver 7*2=14kWh and it would cost 14*0.3=£4.20

The battery can store a maximum of approx 60kWh (LR) or 50kWh (SR)

That makes sense. Apologies all for being a bit dense there!

 

[MoDolph]

That makes sense. Apologies all for being a bit dense there!

Don't worry about it. Many people get them mixed up.

 

[FiferMG4]

That makes sense. Apologies all for being a bit dense there!

It’s great to have these threads. I’m new to electric vehicles and charging myself, so learning a lot from these exchanges.

 

[Dan C]

I wouldn’t recommend using a granny cable for anything other than emergency charging, drawing that amount of power over such long period of time puts your wiring and sockets under a lot of stress, if you have any weak points in your wiring you could cause an electrical fire.

Invest in a proper EV charger and get on Octopus go tariff, yes it costs around £1k to get one supplied and installed, but we’ll worth it so you can use the cheap off peak rate of octopus go and charge your car safely.

 

[Shengis]

Anybody ken aboot commando sockets?

I’ve got a socket only with no switch beside it. Is this still safe if I was to get a commando charging cable?

I’ve found a website which says the 16A commando would give 3.6kW of output as opposed to 7kW from a 32A or full EV charger…

 

[BugEyed]

Granny chargers are the work of the devil and an accident waiting to happen. As @Dan C says above they stress the wiring in a house beyond its design level - a BS1363 socket is NOT designed for 10 Amps continuous current over a long period of time. But ignoring that major issue, there's also the issue of Earthing which granny chargers fail to deal with correctly. Most UK houses are wired PME and hence are at risk of supply faults causing the "Earth" to float up to a higher voltage and create a shock hazard. This has led to the iniquitous situation where the sensible option of installing a new circuit for even occasional use in charging an EV via a granny charger requires the same safeguards as a dedicated EVSE circuit which in turn means that customers often don't bother resulting in both the risk of a floating earth and the fire risk of a poor circuit.

Granny chargers should only be used as their name implies - for emergencies when visiting an elderly female relative and needing to get a small amount of charge that isn't available elsewhere. Frankly this is also dangerous as you are making assumptions regarding the quality of the wiring at said property which may be "unknown".

 

[MoDolph]

Anybody ken aboot commando sockets?

I’ve got a socket only with no switch beside it. Is this still safe if I was to get a commando charging cable?

I’ve found a website which says the 16A commando would give 3.6kW of output as opposed to 7kW from a 32A or full EV charger…

My dad had one fitted in his garage for when we visit and we also have a suitable granny cable so can charge at 16A. However, if using it everyday then I would recommend limiting the charge to below the maximum of the socket. So 6A on regular socket and 10A on the commando.

 

[siteguru]

Electrical Power (P) = Voltage (V) x Current (I)

As Voltage is (nominally) a constant at, say, 230V then the amount of Power is proportional to the available current.

Transposing the formula we can calculate the current based on power:

I = P / V

2.2kW (2000W) / 230V = 9.56A being drawn from your 13A rated socket

A 16A socket working at full current would provide a power output of:

16A x 230V = 3680W = 3.68kW

Whether your 16A Commando socket is rated to run continuously at 16A is another matter. Plus you'd need to regulate the power from the socket too, although the car has a setting to control (limit) the charge current. (Remember that the charger is built into the car ... what people call chargers are actually just smart charge points).

 

[BugEyed]

Anybody ken aboot commando sockets?

I’ve got a socket only with no switch beside it. Is this still safe if I was to get a commando charging cable?

I’ve found a website which says the 16A commando would give 3.6kW of output as opposed to 7kW from a 32A or full EV charger…

You are getting around the risk of the inadequate BS1363 socket but not the Earthing issues unless you have appropriate protection put in place. So it is definitely one up but still not a safe option.

Personally I wouldn't trust someone else's wiring which may not have been done to the correct standard.

 

[BugEyed]

Electrical Power (P) = Voltage (V) x Current (I)

As Voltage is (nominally) a constant at, say, 230V then the amount of Power is proportional to the available current.

Transposing the formula we can calculate the current based on power:

I = P / V

2.2kW (2000W) / 230V = 9.56A being drawn from your 13A rated socket

A 16A socket working at full current would provide a power output of:

16A x 230V = 3680W = 3.68kW

Whether your 16A Commando socket is rated to run continuously at 16A is another matter. Plus you'd need to regulate the power from the socket too, although the car has a setting to control (limit) the charge current. (Remember that the charger is built into the car ... what people call chargers are actually just smart charge points).

Care - UK voltage is often nearer 240 not 230 volts which was a fudge when adopting EU standards. For example my MG4 is currently connected at 242.3 volts.

"chargers" are little more than switches that advertise a maximum current - as @siteguru says the car is actually in charge and selects a current up to the advertised limit. Note that the power is based on the current selected and the voltage available - the example of the granny above is the wrong way around - so if the granny advertised 10 Amps and the car drew it all then at my voltage of 242.3 that would be 2.423kW, the granny would not advertise a lower current to reduce the power being taken.

 

[MoDolph]

But ignoring that major issue, there's also the issue of Earthing which granny chargers fail to deal with correctly. Most UK houses are wired PME and hence are at risk of supply faults causing the "Earth" to float up to a higher voltage and create a shock hazard.

Could you explain this in a bit more detail please as I have seen it mentioned before but do not understand it?

What makes plugging in the car different to say a washing machine into the same socket?

 

[CaptReid]

Hi, I am also using a granny charger till I get a home charger fitted, and was wondering if you have to change any settings in the car or just plug it in and lock the car and it sorts everything out.
In AC current there are a few different amp settings to choose from

 

[AndyL61]

Surely plugging in a 10amp granny charger pulling 2.2kw is less than plugging in a 3kw electric fire ?

 

[siteguru]

Is the 3kW fire plugged into the ring main, or is it on its own dedicated fused spur?