Energy used by the granny charger

[slmorgan42]

Hey

I have the FL with the app.

Is there a way I can see how many units of energy have been used when using the granny charger. I am going to charge at a friends house and want to offer them some cash.

Many thanks

 

[Verdigris]

Just multiply the charging time in hours by 2.3.

 

[Jomarkh]

If you know you start and finish SOC and your battery size the you can work out how many kWh have been added and multiply it by the unit rate.

 

[t509triumph]

Base it on 3kWh per hour charge. If you charge over night... say 8 hours.... that's 3*8* unit cost.
So if the unit cost was 25 pence you would take £6 of electricity

 

[kevin ellard]

Base it on 3kw per hour charge. If you charge over night... say 8 hours.... that's 3*8* unit cost.
So if the unit cost was 25 pence you would take £6 of electricity

The mg granny charger doesn't get to 3kW. I think it is only 2300W.

 

[t509triumph]

The mg charger doesn't get to 3kW. I think it is only 2300W.

OK.... offer them £5 instead

 

[kevin ellard]

OK.... offer them £5 instead

Sorry, it wasn't meant to sound like arguing. More of a planning issue for how long the car would take to charge,

 

[t509triumph]

Sorry, it wasn't meant to sound like arguing. More of a planning issue for how long the car would take to charge,

No problem.... just shows at granny charger rate, although over night charge puts in about 100 miles @ 4miles per kWh... the actual cost is small.

 

[Lovemyev]

What ever you offer in payment, the cost per mile will be significantly cheaper than petrol ️ that’s 100% for sure ! ?.
If they are an old friend, they are likely to refuse your kind offer anyway.
Just arrive with a nice bottle of wine or some beers, then you can share them together ?.

 

[slmorgan42]

Thanks everyone. Shame there isn’t a charging session summary somewhere. Would be great if it was in the app.

 

[slmorgan42]

What ever you offer in payment, the cost per mile will be significantly cheaper than petrol ️ that’s 100% for sure ! ?.
If they are an old friend, they are likely to refuse your kind offer anyway.
Just arrive with a nice bottle of wine or some beers, then you can share them together ?.

lol I always bring a bottle or three either way.

 

[Lovemyev]

lol I always bring a bottle or three either way.

I like your style !.
After sharing the three bottles of nice wine ?, I don’t suspect that you or your friend will be overly focussed on the cost of the juice used to charge the car - enjoy ?.

 

[Verdigris]

On a more serious note, take care if your friend's electrics are a bit ramshackle. You don't want to burn the gaff down.

 

[slmorgan42]

On a more serious note, take care if your friend's electrics are a bit ramshackle. You don't want to burn the gaff down.

Yeah thanks the few times I have used the granny I do consider this.

He is an electrician and has a load of power tools in the garage. Hopefully he did a good job running his power out there. lol then again he could be a cowboy electrician lol

 

[Fintious maximus]

As a matter of interest having never used the granny charger, how long would it take to charge 10%? My home charger is roughly an hour per 10% so assuming granny would be 2 to 3 hours?

 

[decrep]

If you want to be persnickety, keep in mind that the charger draws more power than it puts into the battery. At the moment my MG supplied charger is drawing 1.75 kW from the mains and putting 1.4kW into the battery.
I have a feeling that British ones may have a higher charge rate.

As a matter of interest having never used the granny charger, how long would it take to charge 10%? My home charger is roughly an hour per 10% so assuming granny would be 2 to 3 hours?

depends on the battery you have and what your home charger is. There's a difference between 64kWh and 51kWh.
Just compare the charge rating of both chargers, I for one don't know what either of them do

 

[Fluffykins]

That's prezactly the issue I had. The solution I used is discussed here:

UK domestic socket charging

I've used my granny charger a few times when away from home. Mostly when visiting my son. I bung him a few quid for the 'leccy. I use a short high current extension lead that has a single 13A socket on it, which fits thru his letterbox, and I monitor juice used with a small kWh meter mounted in...

www.mgevs.com

 

[M44LCY]

I use a power & energy monitor every time I charge with my granny charger. These tell you exactly how many kWh has been consumed by the car, Just search Amazon or anywhere else for "plug in mains power & energy monitor".

Whether you want to pay £8-10 for a unit, you have to decide. If it's for one use, it's probably not worth paying that. But I find it useful to use it as a matter of routine, so that I can keep a note of the power used in charging, hence the miles/kWh, cost/mile, etc.

The power consumed by the car isn't the same as the power added to the car - the charging process involves some losses. My meter usually says the power being drawn in about 2.23kW, but the MG app says the car is charging at about 1.8kW. In other words, although you're paying for 2.3kw while charging, you're only adding 1.8kW. The rest is used in the transfer, AC/DC conversion, etc.

I measured the difference over a period of a month, and the losses came to 14.2%. If you reckon that the power added to the car being 85% of what the plug-in meter says, you won't be far off.

 

[HazardLights]

As an aside how does a wall box compare to a granny charger for efficiency?

 

[kiwi]

The losses are not in the wall box or granny charger, the losses are in the car. The wall box and granny are just glorified relays and safety interlocks, they are not chargers. There might be a few watts dissipated there at most.

The losses are in the vehicle where the charger lives. The vehicle’s charger takes the 230VAC converts it to DC then steps up the voltage with a high frequency inverter (that also provided the isolation between the grid and the vehicle) that is controlled in such a way to deliver regulated voltage to the approx 400V battery. It’s through those steps in the vehicle where the losses occur. On top of that the energy available from the battery is always less than the energy put into the battery because the chemical conversion process is exothermic and the heat generated during charging comes from the power applied.

These vehicle losses completely dominate compared to any minor differences in a wall box vs granny.