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Full disclosure, I work at EVCables.co.uk! However, we have invested in some pretty nice test equipment and I thought it would be a shame for me to keep it all to myself.
So as an intro into the sort of topics I want to tackle I thought I start with how much power is ‘lost’ through a standard EV charging cable.
I believe this concerns people more when investigating longer cable runs and I myself have tried to find answers but was never fully satisfied with the information available on Google.
There are many tables that give estimates for power loss however none of these tables are specifically for the new EV charging flex cable. I myself created a graph using values for volt-drop per ampere per meter from this table I found at Voltage Drop Calculations

Purple Rectangle Font Parallel Pattern

Rectangle Slope Plot Font Triangle


I am sure that these values are close to real world, but that don’t include the contact resistance within the plugs themselves. Introducing our 4-Wire Kelvin tester :D
Laptop Electrical wiring Computer Audio equipment Electronic engineering


If you don’t know what 4-Wire Kelvin testing is, a brief extract from Cami-Research explains it best.
Four-Wire Kelvin measurement makes it possible to accurately measure resistance values less than 0.1 Ω while eliminating the inherent resistance of the lead wires connecting the measurement instrument to the component being measured.
What is 4-Wire Measurement?
Ohm’s law defines resistance, “R”, as the ratio of voltage “V” across a component, to the current “I” passing through it: R = V/I
To measure resistance, we apply a test current to a wire and detect the voltage drop developed. From this, we easily calculate the resistance as shown in the following figure.
Product Rectangle Font Parallel Slope


We measure the resistance of interest, RW, between the conductor ’s two mating pins. The entire circuit, however, includes the resistance of the lead wires, RL1 and RL2, so the voltage drop used in the calculation includes all three of these resistances. In many situations the lead wire resistance is much lower than the resistance of the conductor or component we aim to measure and therefore can be disregarded.
In some situations, however, the resistance of interest, RW, approaches the resistance value of the lead wires used to measure it resulting in an inaccurate reading. We correct this problem by moving the voltage measurement points out to the endpoints of the mating pins, thus, bypassing any voltage drop that may occur in the lead wires. Refer to the figure below:
Rectangle Font Parallel Slope Diagram

Now that we have a better understanding on how we get such precise measurements, we can actually take a measurement.
Product Font Line Rectangle Parallel

The cable tested is rated at 32A single phase (7kW) and is 15m long.
Power loss within a cable can also be estimated from the cable current and resistance:
Font Parallel Rectangle Graphics Logo

where:
P = power loss, W
I = cable design current, A
R = cable resistance, Ω
n = factor depending on circuit type/number of conductors
= 2 for a.c. single phase, d.c. circuits
= 3 for a.c. three phase circuits (assumed balanced)
Therefore total power loss in this cable at 32A is (I used the average resistance of the L and N leg):
Font Art Number Circle Magenta

This power loss of 88W is actually 25W less than using the bog standard voltage drop formulas!
Hope this insight is useful to some people, let me know anything else you would like me to tackle in future.

James
 

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Fortunately these losses are pretty small, compared to the efficiency loss in the actual chemistry etc of charging the battery. My own somewhat cruder measurements of "granny" EVSE charging have indicated around 10% efficiency loss on my ID.3 & Ioniq, so a 7 kW charge is going to be losing appx 700W ballpark anyway, regardless of the connecting-cable losses.
 

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Thank you for sharing this data. The collective knowledge on charging losses is quite low tbh. None of the automakers or even ozev is talking about it. At home I regularly see losses of around 12-15% with a 7.2 meter cable. Outside weather and battery temperature are the two key factors I have identified so far.

To put 12-15% in real terms my home charging EV bill was £150 last month out of which £22.5 was losses. Hilariously my direct debit for an Audi maintenance is only £22.04 indicating EVs do have a monthly charge.
 

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Thank you for sharing this data. The collective knowledge on charging losses is quite low tbh. None of the automakers or even ozev is talking about it. At home I regularly see losses of around 12-15% with a 7.2 meter cable. Outside weather and battery temperature are the two key factors I have identified so far.

To put 12-15% in real terms my home charging EV bill was £150 last month out of which £22.5 was losses. Hilariously my direct debit for an Audi maintenance is only £22.04 indicating EVs do have a monthly charge.
Charging losses (converting electrical energy to battery potential energy) is an inevitable thermodynamic fact, same as every energy conversion process. Why would OZEV have any interest in such fundamental thermodynamics. This is the realm of university research, not a government quango staffed by civil servants.
Furthermore, mention of your charging cable length, 7.2m, indicates you think the cable is the cause of the losses. If your cable was 7.0m, what do you think your losses would be?
 

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Charging losses (converting electrical energy to battery potential energy) is an inevitable thermodynamic fact, same as every energy conversion process. Why would OZEV have any interest in such fundamental thermodynamics. This is the realm of university research, not a government quango staffed by civil servants.
Furthermore, mention of your charging cable length, 7.2m, indicates you think the cable is the cause of the losses. If your cable was 7.0m, what do you think your losses would be?
Just to add, let's say that you reverted to a petrol fuelled Audi. You spend £300 per month on petrol. Of that £300, only £100 produces useful energy propelling the car, the rest is wasted as heat. Would it be a useful exercise writing to Shell and UK Treasury saying that their petrol is inefficient since I'm wasting £200 a month producing waste heat?
 

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Charging losses (converting electrical energy to battery potential energy) is an inevitable thermodynamic fact, same as every energy conversion process. Why would OZEV have any interest in such fundamental thermodynamics. This is the realm of university research, not a government quango staffed by civil servants.
Furthermore, mention of your charging cable length, 7.2m, indicates you think the cable is the cause of the losses. If your cable was 7.0m, what do you think your losses would be?
It's a tethered EVSE so I don't have the luxury to test with varying lengths. I was really hoping the makers of the EVSE, or the car makers or a regulatory body would perform these tests and assign a A-F rating. Right now it's all ooh la la la EV is so cheap and best la la la
 

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Just to add, let's say that you reverted to a petrol fuelled Audi. You spend £300 per month on petrol. Of that £300, only £100 produces useful energy propelling the car, the rest is wasted as heat. Would it be a useful exercise writing to Shell and UK Treasury saying that their petrol is inefficient since I'm wasting £200 a month producing waste heat?
The correct analogy is if while filling up the fuel there is a leak and 15% of the fuel spills away then of course I would ask for a refund. 15% is widely the losses you can expect at DC chargers. Have you ever seen any notice explaining how much actual charge you can expect when you use a particular charger? Where is the incentive for the operators of the public chargers to reduce the losses by investing in better cabling and cooling if the information is hidden away?
 

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Thank you for sharing this data. The collective knowledge on charging losses is quite low tbh. None of the automakers or even ozev is talking about it. At home I regularly see losses of around 12-15% with a 7.2 meter cable. Outside weather and battery temperature are the two key factors I have identified so far.

To put 12-15% in real terms my home charging EV bill was £150 last month out of which £22.5 was losses. Hilariously my direct debit for an Audi maintenance is only £22.04 indicating EVs do have a monthly charge.

Something is clearly wrong here, either with your measurement of cable loss, or with the actual installation. The maximum allowable voltage drop is 5% for a non-lighting load. cables must be sized so that the VD is kept to 5% or less. If you have a loss of 12% to 15% then that implies a very serious problem, as at a typical 32 A charge from a 230 VAC supply the voltage at the charge is only going to be 195.5 VAC with a 15% drop, and that should very definitely trigger some sort of error, as the lowest allowable grid voltage here is 216.2 VAC.

A 15% voltage drop on the cable also implies that the cable is dissipating about 1.1 kW during a 32 A charge, a bit over the heat from a single bar electric heater. Is the cable really glowing a dull red in use, with lots of smoke coming off the insulation?
 

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I am writing to dr
Something is clearly wrong here, either with your measurement of cable loss, or with the actual installation. The maximum allowable voltage drop is 5% for a non-lighting load. cables must be sized so that the VD is kept to 5% or less. If you have a loss of 12% to 15% then that implies a very serious problem, as at a typical 32 A charge from a 230 VAC supply the voltage at the charge is only going to be 195.5 VAC with a 15% drop, and that should very definitely trigger some sort of error, as the lowest allowable grid voltage here is 216.2 VAC.

A 15% voltage drop on the cable also implies that the cable is dissipating about 1.1 kW during a 32 A charge, a bit over the heat from a single bar electric heater. Is the cable really glowing a dull red in use, with lots of smoke coming off the insulation?
It includes multiple losses. As an end user I can see the energy sent sent at the smart meter, energy sent by pod point, and energy eventually stored and reported as available by the car.
 

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It's a tethered EVSE so I don't have the luxury to test with varying lengths. I was really hoping the makers of the EVSE, or the car makers or a regulatory body would perform these tests and assign a A-F rating. Right now it's all ooh la la la EV is so cheap and best la la la
You are getting hopelessly confused. The losses in the charging cable are small, say 10 percent of the losses in the battery and inverter.
So could we make the 10 percent smaller, yes, but it would need a heavier thicker cable. Diminishing returns. Nothing for OZEV to investigate here, it's just basic engineering.

As a thought experiment, why don't you replace your charging cable with a 6.5m long cable and save a few pennies per month?
 

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I am writing to dr

It includes multiple losses. As an end user I can see the energy sent sent at the smart meter, energy sent by pod point, and energy eventually stored and reported as available by the car.

OK, so not cable loss then.

There will be no measurable loss in the charge point (it's only a relay, switching mains on or off). There will be a maximum of 5% loss in the cable from the supply to the charge point, and in reality it should be a lot lower than that. The normal cable for runs up to around 40m is 6mm². SWA has typical losses of around 7.3 mV/A/m, so for 32 A and a 10m run from the supply to the charge point the cable voltage drop would be around 2.336 VAC. The power loss in 10m of this cable at 32 A would be about 128 W, or roughly 1.74%.

The voltage drop along the charge cable itself would be slightly less, a 7.2m long charge cable of 6mm² CSA is going to have a voltage drop of around 1.68 VAC at 32 A, so a power loss of about 53.8 W or roughly 0.73%.

That brings the total cable loss for a 10m supply cable run plus a 7.2m long charging cable to around 2.47% at 32 A. In turn that suggests that, if you are seeing a true total loss (not a measurement error) of 15%, then the vast majority of that is happening within the vehicle somewhere.
 

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You are getting hopelessly confused. The losses in the charging cable are small, say 10 percent of the losses in the battery and inverter.
So could we make the 10 percent smaller, yes, but it would need a heavier thicker cable. Diminishing returns. Nothing for OZEV to investigate here, it's just basic engineering.

As a thought experiment, why don't you replace your charging cable with a 6.5m long cable and save a few pennies per month?
Yes, I know the losses due to cable alone is small. But what is the strategy to reduce end-to-end losses? Change the car, upgrade the charger in the car, don't charge during cold weather, look for a sticker that has a symbol. Our current attitude is EV is so wonderful, just stop asking any losses related question. I wish I can start a DC public charger with 50-100% losses and become wealthy.
 

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Yes, I know the losses due to cable alone is small. But what is the strategy to reduce end-to-end losses? Change the car, upgrade the charger in the car, don't charge during cold weather, look for a sticker that has a symbol...
The major loss is in the actual chemistry & resistance of the battery, zip you can do about that, but the battery mfrs are well aware of this. E.g. Teslas latest cylindrical batteries have a different connection layout, to reduce resistance losses both during charging & discharging.

Losses in the car's charging proceess are around 10%, give-or-take a couple of %. Actual inverters & such like are doing really well if they can operate 90% efficiently, or better. Consider yourself lucky we aren't running on thermionic valves! Or even traditional transistors! And again, nothing we can do about this, the inverter & car-BMS etc systems designers are well aware of these losses. One reason for going to 800V systems is to reduce these losses, someday all EVs will be 800V probably, if not 1200V soon.for the exotica...

Losses you can control to a small extent are the mains-to-EVSE losses, and even the EVSE-to-car losses, as you can always use a 32A rated Type-2 cable on say a 16A EVSE for your PHEV etc. But that cable will cost you more to buy than the 16A rated one, will be heavier, uses more of the Earth's resources to make etc. Entirely up to you if you want to rewire your EVSE with even-heavier mains cable, but do work out the payback time first! Probably exceeds your lifetime...

... Our current attitude is EV is so wonderful, just stop asking any losses related question...
Disagree totally. There have been many threads in here where newbies arrive, asking qns about cost to run etc, and we've gently pointed out that they should allow 0% on top of what their car says they're putting into it, e.g. that 40 kWh EV their costing will in fact need more like 44 kWh from the grid, and that they need to allow about this much extra overhead when working out the monthlies. And this figure is pretty constant, my ID.3 was virtually indistinguishable on charging efficiency, whether I used granny at 6A, 10A, or wall-EVSE at 32A.

We often suggest that an EV is not suitable for a particular newbie. Towing, huge mileages, ...

... I wish I can start a DC public charger with 50-100% losses and become wealthy.
Sorry, I have no idea what you mean here.

Presumably the Rapids bill us for what they extract from the grid, and you're upset that you can only store 90% of that? Just how long do you think a Rapid operator would stay in business if you had to pay for 2x what your car actually stores, because the Rapid had itself lost the other 40%? Days, weeks at most, once the word got around...

Competition will make sure the various Rapid operators maximise the efficiency of their own kit. It reduces their costs, and some small part of that trickles down to us in turn, even if it's only by price rises happening a fewer days later ...
 

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The major loss is in the actual chemistry & resistance of the battery, zip you can do about that, but the battery mfrs are well aware of this. E.g. Teslas latest cylindrical batteries have a different connection layout, to reduce resistance losses both during charging & discharging.

Losses in the car's charging proceess are around 10%, give-or-take a couple of %. Actual inverters & such like are doing really well if they can operate 90% efficiently, or better. Consider yourself lucky we aren't running on thermionic valves! Or even traditional transistors! And again, nothing we can do about this, the inverter & car-BMS etc systems designers are well aware of these losses. One reason for going to 800V systems is to reduce these losses, someday all EVs will be 800V probably, if not 1200V soon.for the exotica...

Losses you can control to a small extent are the mains-to-EVSE losses, and even the EVSE-to-car losses, as you can always use a 32A rated Type-2 cable on say a 16A EVSE for your PHEV etc. But that cable will cost you more to buy than the 16A rated one, will be heavier, uses more of the Earth's resources to make etc. Entirely up to you if you want to rewire your EVSE with even-heavier mains cable, but do work out the payback time first! Probably exceeds your lifetime...


Disagree totally. There have been many threads in here where newbies arrive, asking qns about cost to run etc, and we've gently pointed out that they should allow 0% on top of what their car says they're putting into it, e.g. that 40 kWh EV their costing will in fact need more like 44 kWh from the grid, and that they need to allow about this much extra overhead when working out the monthlies. And this figure is pretty constant, my ID.3 was virtually indistinguishable on charging efficiency, whether I used granny at 6A, 10A, or wall-EVSE at 32A.

We often suggest that an EV is not suitable for a particular newbie. Towing, huge mileages, ...


Sorry, I have no idea what you mean here.

Presumably the Rapids bill us for what they extract from the grid, and you're upset that you can only store 90% of that? Just how long do you think a Rapid operator would stay in business if you had to pay for 2x what your car actually stores, because the Rapid had itself lost the other 40%? Days, weeks at most, once the word got around...

Competition will make sure the various Rapid operators maximise the efficiency of their own kit. It reduces their costs, and some small part of that trickles down to us in turn, even if it's only by price rises happening a fewer days later ...
Did you know that the forecourts are legally required to periodically calibrate/verify the pumps? Below is an example of one provider offering such a service.


Calibration/Verification of fuel pumps at petrol stations
Calibration pumps are used to prevent and detect potential costly fuel losses caused by leaks, temperature and vapour loss. They are vital for customer satisfaction and to Trading Standard offences due to errors in fuel dispensing.

All pumps work within a tolerance of 0.02 lpm. Our engineers test the accuracy of forecourt fuel pumps to identify if any pumps are dispensing more or less than the legal requirement. We can then adjust this manually to bring back into the suggested, recommended or required speed. The pump will then be verified and finally commissioned by the engineer.

Fuel pumps include calibration pumps, hand pumps and low-pressure calibration pumps, such as:

  • Model HP
  • Model A-396A
  • Model A-350
  • Series CHP
  • Series PCHP
You can walk to any forecourt and legally ask for this proof of calibration/verification before filling up.

There is no such verification requirement for DC public charger operators. They can technically always overcharge users by 15-20% regardless, and people would blindly accept them as DC charging losses.
 

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The amount of heat generated in a DC charger is a significant incentive to make it more efficient. Dissipating kilowatts needs big heatsinks and fans.
I'm done relying solely on competition, especially in the energy sector. By the way, not all rapid chargers bother with fans. There are many Tesla Bjorn videos that discuss the charger design aspects.
 

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I'm done relying solely on competition, especially in the energy sector. By the way, not all rapid chargers bother with fans. There are many Tesla Bjorn videos that discuss the charger design aspects.
To recap, you suggest that OZEV promote some kind of efficiency rating, presumably for both DC rapid chargers and separately for onboard chargers and the traction battery. What do you propose they measure, under what conditions. How would you use that rating information?
 

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To recap, you suggest that OZEV promote some kind of efficiency rating, presumably for both DC rapid chargers and separately for onboard chargers and the traction battery. What do you propose they measure, under what conditions. How would you use that rating information?
What the Office for Zero Emission Vehicles does
The Office for Zero Emission Vehicles (OZEV) is a team working across government to support the transition to zero emission vehicles (ZEVs). We are providing support for the take-up of plug in vehicles, as well as funding to support chargepoint infrastructure across the UK. This will contribute to economic growth and will help reduce greenhouse gas emissions and air pollution on our roads.
Yes, OZEV must be responsible for rating the efficiency of chargepoint infrastructure. The next best alternative is trading standards.

Charge point operators, EVSE providers, and even car onboard chargers should list their efficiency with a standardized test, so consumers could opt for an efficient one that would suit their budget and lifestyle.

Bjorn Nyland did a test a while ago with Tesla Model 3 and shared some loss figures. Some chargers were quite efficient and some were atrocious. I've noted down the exact timecode and some figures.

You can see out of two 50 kW chargers which one is a ripoff and which one is value for money. And notice how Ionity at 350 kW even beat some of the bad AC charge points.

- 11kW - 8.7% loss on AC
- 3.5 kW - 10.3% loss on AC (Car has to stay awake, runs some fan)
- 7kW - 6.2% loss on AC
- 50kW - 17.5% loss on DC (What a ripoff!)
- 2.3kW - 15.7% loss on AC (Ripoff!)
Charging loss on Model 3 on AC and DC - 8kW - 8.9% loss on AC
Charging loss on Model 3 on AC and DC - 350kW - 8.1% on Ionity DC (Well done!)
Charging loss on Model 3 on AC and DC - 350kW - 9.2% on Ionity DC (Battery heater not running?)

Charging loss on Model 3 on AC and DC - 50kW - 5.3% (Well done!)

tldr; Data on losses should be published and must be transparent.
 

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Yes, OZEV must be responsible for rating the efficiency of chargepoint infrastructure. The next best alternative is trading standards.

Charge point operators, EVSE providers, and even car onboard chargers should list their efficiency with a standardized test, so consumers could opt for an efficient one that would suit their budget and lifestyle.

Bjorn Nyland did a test a while ago with Tesla Model 3 and shared some loss figures. Some chargers were quite efficient and some were atrocious. I've noted down the exact timecode and some figures.

You can see out of two 50 kW chargers which one is a ripoff and which one is value for money. And notice how Ionity at 350 kW even beat some of the bad AC charge points.

- 11kW - 8.7% loss on AC
- 3.5 kW - 10.3% loss on AC (Car has to stay awake, runs some fan)
- 7kW - 6.2% loss on AC
- 50kW - 17.5% loss on DC (What a ripoff!)
- 2.3kW - 15.7% loss on AC (Ripoff!)
Charging loss on Model 3 on AC and DC - 8kW - 8.9% loss on AC
Charging loss on Model 3 on AC and DC - 350kW - 8.1% on Ionity DC (Well done!)
Charging loss on Model 3 on AC and DC - 350kW - 9.2% on Ionity DC (Battery heater not running?)

Charging loss on Model 3 on AC and DC - 50kW - 5.3% (Well done!)

tldr; Data on losses should be published and must be transparent.
Are you getting confused between different BATTERY charging efficiencies using different DC charging currents and battery temperatures? Most normal folk will choose a DC charger based on a combination of price per kWh and convenience (queuing time, other services, diversion, reliability etc). In 5 years of EV driving Ive never ever asked myself what is the conversion efficiency between AC and DC. I also don't ask myself what is the efficiency of the grid transformers feeding the DC Rapids, nor of the 400kV grid lines feeding the MV distribution.
 
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