Charge Losses - I'm going there!
Discussion
Hi all
I appreciate I was quite vocal about Harry's recent announcement that charge losses are a thing and what a waste of time I think it is. But my Octopus bill came in and I thought I'd at least give him the benefit of the doubt and do some maths for my i3s. Bothered but not bothered IYKWIM
Feel free to tear my maths apart (or my methodology) but I'm really struggling to work it out. Basically I have a smart meter but it's not smart enough to tell me exactly what my EV is taking. This is where my charger comes in as it does tell me what it delivered. I then have my car, which is pretty basic, so just gives kWh in whole numbers (on the app anyways).
So.
My last big charge showed the following:
Smart Meter: 30.18kWh
Charger: 28.6kWh
Car: 29kWh.
The smart meter obviously includes the rest of my house and typically I run the washing machine and diswasher during the same time period. On nights that I don't charge, I typically draw between 1-2kWh, which stacks up if you subtract the charger from the smart meter (1.58kWh).
But conservatively ignoring this completely, I'm really struggling to calculate my losses as anything near 10%. It doesn't help that my EV doesn't give a more accurate amount of power taken and clearly can't take more than the charger is delivering. If I assume the car actually saw 28kWh, that's a 0.6kWh difference (~2%).
Where am I going wrong? Is it because it's winter and it'll be worst in summer? I've an Andersen A2 2nd gen (7.2kW) on the end of 8m of cable from the CU and 5m of tethered cable.
There's a discrepancy with dates purely because I plug in before I go to bed and the car starts at midnight.
I appreciate I was quite vocal about Harry's recent announcement that charge losses are a thing and what a waste of time I think it is. But my Octopus bill came in and I thought I'd at least give him the benefit of the doubt and do some maths for my i3s. Bothered but not bothered IYKWIM
Feel free to tear my maths apart (or my methodology) but I'm really struggling to work it out. Basically I have a smart meter but it's not smart enough to tell me exactly what my EV is taking. This is where my charger comes in as it does tell me what it delivered. I then have my car, which is pretty basic, so just gives kWh in whole numbers (on the app anyways).
So.
My last big charge showed the following:
Smart Meter: 30.18kWh
Charger: 28.6kWh
Car: 29kWh.
The smart meter obviously includes the rest of my house and typically I run the washing machine and diswasher during the same time period. On nights that I don't charge, I typically draw between 1-2kWh, which stacks up if you subtract the charger from the smart meter (1.58kWh).
But conservatively ignoring this completely, I'm really struggling to calculate my losses as anything near 10%. It doesn't help that my EV doesn't give a more accurate amount of power taken and clearly can't take more than the charger is delivering. If I assume the car actually saw 28kWh, that's a 0.6kWh difference (~2%).
Where am I going wrong? Is it because it's winter and it'll be worst in summer? I've an Andersen A2 2nd gen (7.2kW) on the end of 8m of cable from the CU and 5m of tethered cable.
There's a discrepancy with dates purely because I plug in before I go to bed and the car starts at midnight.
Edited by Zero Fuchs on Saturday 27th January 13:05
Zero Fuchs said:
Hi all
I appreciate I was quite vocal about Harry's recent announcement that charge losses are a thing and what a waste of time I think it is. But my Octopus bill came in and I thought I'd at least give him the benefit of the doubt and do some maths for my i3s. Bothered but not bothered IYKWIM
Feel free to tear my maths apart (or my methodology) but I'm really struggling to work it out. Basically I have a smart meter but it's not smart enough to tell me exactly what my EV is taking. This is where my charger comes in as it does tell me what it delivered. I then have my car, which is pretty basic, so just gives kWh in whole numbers (on the app anyways).
So.
My last big charge showed the following:
Smart Meter: 30.18kWh
Charger: 28.6kWh
Car: 29kWh.
The smart meter obviously includes the rest of my house and typically I run the washing machine and diswasher during the same time period. On nights that I don't charge, I typically draw between 1-2kWh, which stacks up if you subtract the charger from the smart meter (1.58kWh).
But conservatively ignoring this completely, I'm really struggling to calculate my losses as anything near 10%. It doesn't help that my EV doesn't give a more accurate amount of power taken and clearly can't take more than the charger is delivering. If I assume the car actually saw 28kWh, that's a 0.6kWh difference (~2%).
Where am I going wrong? Is it because it's winter and it'll be worst in summer? I've an Andersen A2 2nd gen (7.2kW) on the end of 8m of cable from the CU and 5m of tethered cable.
There's a discrepancy with dates purely because I plug in before I go to bed and the car starts at midnight.
I think there are different places for the charging losses. I would expect very little between the meter and the EV, some amount in the electronic in the EV (ignoring the battery) and then some in the battery. On your charging test, is the 28kwh the amount that made it to a) the EV, b) the battery or c) the amount actually stored in the battery, i suspect it is a) but it is c) that you want. I guess to get c, you need to completely flatten the battery and then 100% charge, but given all these cars have "usable" vs "actual" battery figures, that may not be completely reliable either. I wonder if the "usable" vs "actual" is where some of the weird numbers are coming from.I appreciate I was quite vocal about Harry's recent announcement that charge losses are a thing and what a waste of time I think it is. But my Octopus bill came in and I thought I'd at least give him the benefit of the doubt and do some maths for my i3s. Bothered but not bothered IYKWIM
Feel free to tear my maths apart (or my methodology) but I'm really struggling to work it out. Basically I have a smart meter but it's not smart enough to tell me exactly what my EV is taking. This is where my charger comes in as it does tell me what it delivered. I then have my car, which is pretty basic, so just gives kWh in whole numbers (on the app anyways).
So.
My last big charge showed the following:
Smart Meter: 30.18kWh
Charger: 28.6kWh
Car: 29kWh.
The smart meter obviously includes the rest of my house and typically I run the washing machine and diswasher during the same time period. On nights that I don't charge, I typically draw between 1-2kWh, which stacks up if you subtract the charger from the smart meter (1.58kWh).
But conservatively ignoring this completely, I'm really struggling to calculate my losses as anything near 10%. It doesn't help that my EV doesn't give a more accurate amount of power taken and clearly can't take more than the charger is delivering. If I assume the car actually saw 28kWh, that's a 0.6kWh difference (~2%).
Where am I going wrong? Is it because it's winter and it'll be worst in summer? I've an Andersen A2 2nd gen (7.2kW) on the end of 8m of cable from the CU and 5m of tethered cable.
There's a discrepancy with dates purely because I plug in before I go to bed and the car starts at midnight.
Edited by Zero Fuchs on Saturday 27th January 13:05
As far as actual efficiency goes, look for heat generation. 10% on 30kwh is 3kwh, if you are losing that somewhere, it will be as heat and the equivalent of a kettle being on for an hour. I'm pretty sure you won't be getting that sort of heat loss in your house cables or EV point whereas the car fans probably come on. Overall, i suspect the best approach is to charge the car just before you leave and then the heat loss will warm up the batteries/car etc.
iom_dave said:
I think there are different places for the charging losses. I would expect very little between the meter and the EV, some amount in the electronic in the EV (ignoring the battery) and then some in the battery. On your charging test, is the 28kwh the amount that made it to a) the EV, b) the battery or c) the amount actually stored in the battery, i suspect it is a) but it is c) that you want. I guess to get c, you need to completely flatten the battery and then 100% charge, but given all these cars have "usable" vs "actual" battery figures, that may not be completely reliable either. I wonder if the "usable" vs "actual" is where some of the weird numbers are coming from.
As far as actual efficiency goes, look for heat generation. 10% on 30kwh is 3kwh, if you are losing that somewhere, it will be as heat and the equivalent of a kettle being on for an hour. I'm pretty sure you won't be getting that sort of heat loss in your house cables or EV point whereas the car fans probably come on. Overall, i suspect the best approach is to charge the car just before you leave and then the heat loss will warm up the batteries/car etc.
Yep I knew I was being stupid. Thanks! Trust me to start this inbetween jobs on a Saturday.As far as actual efficiency goes, look for heat generation. 10% on 30kwh is 3kwh, if you are losing that somewhere, it will be as heat and the equivalent of a kettle being on for an hour. I'm pretty sure you won't be getting that sort of heat loss in your house cables or EV point whereas the car fans probably come on. Overall, i suspect the best approach is to charge the car just before you leave and then the heat loss will warm up the batteries/car etc.
The usable is supposed to be 27.2kWh for my 33kWh battery. The battery was down to about 5% so 95% of 27.2kWh = 25.84kWh. The difference between my wall box and what theoretically ended up in the battery is 28.6/25.84 = 10.7%. I guess this is still approximate as I'd need to properly measure it, like you say. But we're looking at 10.7% of £2.16.
Will this be worse in winter or the same all year round? I guess 3kW sounds a lot but is massively offset by the motor efficiency when on the move. Either way it's possibly a useful exercise but if we take EV's on the whole, I'd still rather be paying the electricity bill than swiping my card at the pump.
ChocolateFrog said:
So absolute worst case you're spilling about 12p worth of electric on the metaphorical floor per charge?
I wouldn't lose too much sleep over it.
On AC home charging, yes.I wouldn't lose too much sleep over it.
On DC rapid you don't have the AC DC conversion losses but there are thermal and battery management losses. And obviously DC public chargers can be way more expensive!
Evanivitch said:
On AC home charging, yes.
On DC rapid you don't have the AC DC conversion losses but there are thermal and battery management losses. And obviously DC public chargers can be way more expensive!
Rapid charging will be different anyway.On DC rapid you don't have the AC DC conversion losses but there are thermal and battery management losses. And obviously DC public chargers can be way more expensive!
Higher current, bigger loss through many components.
vs not having conversion losses.
It's a difficult thing to measure accurately, because determining the State Of Charge before and after charging is subject to errors.
Fundamentally, a Li-ion battery charges at something like 4.2V per cell (if you're looking to charge it in a few hours) and discharges at maybe 3.75V for most of the cycle.
Exact numbers will vary with the particular chemistry, but broadly speaking that is a ~10% loss you can't escape, except at really low charge rates.
High rates of charge or discharge will make that worse.
I think Tesla claim about 85% for the efficiency of 'electrical energy going into the car, vs 'available from the battery'?
ChocolateFrog said:
So absolute worst case you're spilling about 12p worth of electric on the metaphorical floor per charge?
I wouldn't lose too much sleep over it.
This was shot down as not worth worrying about when it originated on another thread - now it has its own thread.. I wouldn't lose too much sleep over it.
Definitely just not worth even thinking about. And yes it's more £££ if you're using an expensive rapid charger, but most people do that so infrequently they won't even lose sleep over the kWh rate, let alone the losses.
Zero Fuchs said:
Yep I knew I was being stupid. Thanks! Trust me to start this inbetween jobs on a Saturday.
The usable is supposed to be 27.2kWh for my 33kWh battery. The battery was down to about 5% so 95% of 27.2kWh = 25.84kWh. The difference between my wall box and what theoretically ended up in the battery is 28.6/25.84 = 10.7%. I guess this is still approximate as I'd need to properly measure it, like you say. But we're looking at 10.7% of £2.16.
Will this be worse in winter or the same all year round? I guess 3kW sounds a lot but is massively offset by the motor efficiency when on the move. Either way it's possibly a useful exercise but if we take EV's on the whole, I'd still rather be paying the electricity bill than swiping my card at the pump.
The thing I'm not sure about, if you fancy experimenting is whether it is best to charge slowly, say at 10 amps or the full 32 amps (if your car with let you alter it). There probably is some sort of effect the temperature has too. There was some stuff online somewhere that showed 120v was worse than 240v but I think that was in the USA, which would suggest losses in the transformers i guess.The usable is supposed to be 27.2kWh for my 33kWh battery. The battery was down to about 5% so 95% of 27.2kWh = 25.84kWh. The difference between my wall box and what theoretically ended up in the battery is 28.6/25.84 = 10.7%. I guess this is still approximate as I'd need to properly measure it, like you say. But we're looking at 10.7% of £2.16.
Will this be worse in winter or the same all year round? I guess 3kW sounds a lot but is massively offset by the motor efficiency when on the move. Either way it's possibly a useful exercise but if we take EV's on the whole, I'd still rather be paying the electricity bill than swiping my card at the pump.
In answer to my question, I have used google and found:
https://teslamotorsclub.com/tmc/threads/charging-e...
Suggests 8kw is good. So maybe i've made the right decision to get a 32 amp EV wall unit rather than sticking with the granny charger - waiting currently for both car and wall unit...
TheDeuce said:
This was shot down as not worth worrying about when it originated on another thread - now it has its own thread..
Definitely just not worth even thinking about. And yes it's more £££ if you're using an expensive rapid charger, but most people do that so infrequently they won't even lose sleep over the kWh rate, let alone the losses.
I would say it isn't worth thinking about in the "do i get an EV or not" context.Definitely just not worth even thinking about. And yes it's more £££ if you're using an expensive rapid charger, but most people do that so infrequently they won't even lose sleep over the kWh rate, let alone the losses.
In a physics sense, it is kind of interesting and hopefully someone has researched this and decided that 7.2kwh is a sweet spot, or it is happy coincidence...
It is interesting in the hypothetically rather than the practical, i'm sure there are much more marginal discussions around petrol fuel efficiency
iom_dave said:
TheDeuce said:
This was shot down as not worth worrying about when it originated on another thread - now it has its own thread..
Definitely just not worth even thinking about. And yes it's more £££ if you're using an expensive rapid charger, but most people do that so infrequently they won't even lose sleep over the kWh rate, let alone the losses.
I would say it isn't worth thinking about in the "do i get an EV or not" context.Definitely just not worth even thinking about. And yes it's more £££ if you're using an expensive rapid charger, but most people do that so infrequently they won't even lose sleep over the kWh rate, let alone the losses.
In a physics sense, it is kind of interesting and hopefully someone has researched this and decided that 7.2kwh is a sweet spot, or it is happy coincidence...
It is interesting in the hypothetically rather than the practical, i'm sure there are much more marginal discussions around petrol fuel efficiency
TheDeuce said:
7.2kw is because 32a is a standard circuit, it's not because it's judged the perfect rate for frequent charging. If it was typical to have 40a circuits in single phase residential properties, and the main fuse was rated higher than at present, you'd have ~9kw as a standard.
I'm surprised of that's internationally true but fair enough. Evanivitch said:
TheDeuce said:
7.2kw is because 32a is a standard circuit, it's not because it's judged the perfect rate for frequent charging. If it was typical to have 40a circuits in single phase residential properties, and the main fuse was rated higher than at present, you'd have ~9kw as a standard.
I'm surprised of that's internationally true but fair enough. TheDeuce said:
7.2kw is because 32a is a standard circuit, it's not because it's judged the perfect rate for frequent charging. If it was typical to have 40a circuits in single phase residential properties, and the main fuse was rated higher than at present, you'd have ~9kw as a standard.
Ah, I was thinking it was 32a and that you get 40a to 50a for electric showers, hence why not more, but you need three phase to get 11kwh charger at home. I'm guessing it is something to do with 10.5 kwh showers aren't on for 7 hours at a time.So happy coincidence then!
iom_dave said:
TheDeuce said:
7.2kw is because 32a is a standard circuit, it's not because it's judged the perfect rate for frequent charging. If it was typical to have 40a circuits in single phase residential properties, and the main fuse was rated higher than at present, you'd have ~9kw as a standard.
Ah, I was thinking it was 32a and that you get 40a to 50a for electric showers, hence why not more, but you need three phase to get 11kwh charger at home. I'm guessing it is something to do with 10.5 kwh showers aren't on for 7 hours at a time.So happy coincidence then!
Obviously chargers have their own dedicated circuit but it stil makes sense to stick with a standard capacity such as 32a as all the switchgear and cabling etc is already mass produced for that standard.
Not sure you really needed to measure anything? A straight forward full wave rectifier is about 80% efficient. I know they do some fancier stuff with EVs though and have read of efficiency values in the 90-95% range.
At the end of the day you have 240V 50Hz in and it's got to be chopped up and reconstituted as 400 or 800 V DC. That takes some effort! Resistance and induction losses. And we don't have room temperature super conductors either yet.
10% loss sounds bad, but in the grand scheme of things It doesn't really dent the efficiency boost Vs ICE overall. Pretty much any device you plug in to the mains is doing the same thing. We're dribbling electrons on the floor out of every socket.
At the end of the day you have 240V 50Hz in and it's got to be chopped up and reconstituted as 400 or 800 V DC. That takes some effort! Resistance and induction losses. And we don't have room temperature super conductors either yet.
10% loss sounds bad, but in the grand scheme of things It doesn't really dent the efficiency boost Vs ICE overall. Pretty much any device you plug in to the mains is doing the same thing. We're dribbling electrons on the floor out of every socket.
Evanivitch said:
Otispunkmeyer said:
At the end of the day you have 240V 50Hz in and it's got to be chopped up and reconstituted as 400 or 800 V DC. That takes some effort! Resistance and induction losses. And we don't have room temperature super conductors either yet.
230V 
In reality virtually all areas of the UK are typically ~240v+ still, which is within the 230v + 10% agreement. I honestly can't remeber testing a supply and seeing less than 240v.
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