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7kw charger limit

m3p_uk

Member
Aug 1, 2019
645
161
UK
silly question but why are most "chargers" (technically cable connectors as the ac charger is in the car) limited to 7kw output?
electric showers/cookers can go up to 11kw and so why would ev chargers not be able to do this as well?
 

VanillaAir_UK

Supporting Member
Jun 17, 2019
7,969
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Surrey, UK
The Model 3 does up to 11kW AC on 3 phase in UK. Its how the internal chargers in the car are configured for European market that limit it to 7kW AC single phase.

The Tesla wall connector (the charger is in the car) can do up to 22kW with certain vehicle models (M3 is 7/11kW) and an appropriate electrical supply.
 

m3p_uk

Member
Aug 1, 2019
645
161
UK
The Model 3 does up to 11kW AC on 3 phase in UK. Its how the internal chargers in the car are configured for European market that limit it to 7kW AC single phase.

The Tesla wall connector (the charger is in the car) can do up to 22kW with certain vehicle models (M3 is 7/11kW) and an appropriate electrical supply.
Have you got a link to where it says single phase is limited to 7kw? I didn't think it matters if it was single or 3 phase
 

VanillaAir_UK

Supporting Member
Jun 17, 2019
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Surrey, UK
By implication... Most homes are single phase

https://www.tesla.com/en_GB/support/home-charging-installation said:
Grid connection at your home
Most homes in United Kingdom allow a maximum charge rate of 7.4 kW or 19 to 27 miles/hour. This is more than sufficient for overnight charging. An electrician can determine the available power at your home during a site visit and install your Wall Connector accordingly.

Also, TWC is max 32A - which is 7kW single phase 230v, or 22kW 3 phase at 400v. Euro spec Model 3 tops out at 11kW AC.
 
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m3p_uk

Member
Aug 1, 2019
645
161
UK
By implication... Most homes are single phase



Also, TWC is max 32A - which is 7kW single phase 230v, or 22kW 3 phase at 400v. Model 3 tops out at 11kW AC.

why aren't there other "chargers" (wall connectors) which can deliver 11kw single phase at the moment?
 

VanillaAir_UK

Supporting Member
Jun 17, 2019
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Surrey, UK
There is a big difference running a 9kW shower for 10 minutes and a 48A 11kW EV charger for 6 hours. I guess the DNO's have had a say in the matter. iirc at 32A/phase, DNO need to be notified but have to give permission so can be retrospective, at more its a DNO free for all and they need to give permission - likewise with a second EV charge point I believe. Similar to PV I guess, over 16A PV single phase, DNO holds all the cards.
 
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mrbduk

Member
Sep 24, 2019
5
2
UK
silly question but why are most "chargers" (technically cable connectors as the ac charger is in the car) limited to 7kw output?
electric showers/cookers can go up to 11kw and so why would ev chargers not be able to do this as well?

7kW is about 32A on single phase which is a common MCB rating and keeps cable sizing under control. Also a lot of components in the charger probably start to get more expensive beyond 32A. Certainly higher currents are possible but that does require more expensive components and cables.
 

vitesse

Active Member
Apr 2, 2019
1,023
285
Hertfordshire (UK)
Have you got a link to where it says single phase is limited to 7kw? I didn't think it matters if it was single or 3 phase
230V * 32A = 7.4kW Can you get a domestic appliance that can draw more than 7.4kW?

EDIT: OK - looked it up and yes, 40 and even 50A switching and cabling is possible, but as already mentioned the risks of going above 32A for long periods is clearly seen as too risky for domestic applications.
 
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Jason71

Active Member
May 8, 2019
2,838
2,712
Shropshire
DNOs would probably prefer it if showers were only 7kw as well but since a 7kw shower would be pretty useless I guess it is showers that get an exception rather than EV chargers that are unfairly limited?
 

vitesse

Active Member
Apr 2, 2019
1,023
285
Hertfordshire (UK)
DNOs would probably prefer it if showers were only 7kw as well but since a 7kw shower would be pretty useless I guess it is showers that get an exception rather than EV chargers that are unfairly limited?
I'm quite sure that your average electric shower unit is far from optimal efficiency and that you could have a very good experience with showering with 'only' 7kW if the heating system was better designed. Such shower units would be more expensive though. In the long term that investment would be repaid but your average consumer is not interested in long term investment in our throw-away convenience culture.
 
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WannabeOwner

Well-Known Member
Nov 2, 2015
5,758
2,896
Suffolk, UK
EV chargers that are unfairly limited

An Overnight Charge is enough range for pretty much all situations (7kW = 22-ish MPH in a Model-S and 29-ish MPH in a Model-3), so not sure that "unfairly limited" is a real issue. The more power permitted the bigger an issue it is to sustain the grid.

The one time when more power would be handy is come-home-and-go-back-out but realistically it is unlikely that on domestic power that would give any significant range in a short "at home" interval (sure, in some instances it would be enough), so in those instances EV will need Rapid Charger anyway.

I think very few corner-cases where the extra kW is actually going to make a difference - its only going to translate into 4 or 5 MPH more.

Where 3-phase is available then higher charging rates are possible, but except for folk that happen to already have domestic 3-Phase I haven't seen any appetite for getting it installed, just for EV charging.
 
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vitesse

Active Member
Apr 2, 2019
1,023
285
Hertfordshire (UK)
An Overnight Charge is enough range for pretty much all situations (7kW = 22-ish MPH in a Model-S and 29-ish MPH in a Model-3), so not sure that "unfairly limited" is a real issue. The more power permitted the bigger an issue it is to sustain the grid.

The one time when more power would be handy is come-home-and-go-back-out but realistically it is unlikely that on domestic power that would give any significant range in a short "at home" interval (sure, in some instances it would be enough), so in those instances EV will need Rapid Charger anyway.

I think very few corner-cases where the extra kW is actually going to make a difference - its only going to translate into 4 or 5 MPH more.

Where 3-phase is available then higher charging rates are possible, but except for folk that happen to already have domestic 3-Phase I haven't seen any appetite for getting it installed, just for EV charging.

Even with only 4 hours of off-peak charging through Octopus Go I have yet to need to exceed that four hours with our MS70D.
 
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VanillaAir_UK

Supporting Member
Jun 17, 2019
7,969
5,463
Surrey, UK
And of course if anyone does exceed that 4hr at 5p, then it just slightly increases the average cost of that charge.

Say 4hr @ 5p, excess @ 15p kWh, average charge costs/kWh excluding charge losses.

4hr 5p 28kWh
5hr 7p 35kWh (50% charge LR)
6hr 8.3p 42kWh
7hr 9.3p 49kWh (close to 100% charge SR)
etc
 

m3p_uk

Member
Aug 1, 2019
645
161
UK
Electric cookers/ovens are also more than 7kw and can be left on for long periods of time so still don't get why it's not possible with ev chargers.

Fully understand that for most people they wouldn't care too much but it would be handy to top-up and go quicker.
Same argument can be used from going from a 3 pin plug to a 7kw charger for those not on a time tarrif rate. Most people travel 50 miles or less a day so on the 3 pin plug at 9 miles an hour is fine for most people overnight.
 

Jason71

Active Member
May 8, 2019
2,838
2,712
Shropshire
I'm quite sure that your average electric shower unit is far from optimal efficiency and that you could have a very good experience with showering with 'only' 7kW if the heating system was better designed. Such shower units would be more expensive though. In the long term that investment would be repaid but your average consumer is not interested in long term investment in our throw-away convenience culture.
Really? Where do you think the efficiency improvements would come from in an electric shower? Converting electricity to heat is literally 100% efficient.
 

Adopado

Active Member
Aug 19, 2019
3,798
2,908
Scotland
Electric cookers/ovens are also more than 7kw and can be left on for long periods of time so still don't get why it's not possible with ev chargers.

Actually electric cookers are not pulling their rated kW spec continuously. Yes, they are switched on at the wall but once the oven is up to temperature after a few minutes the thermostat switches off and then only tops up the heat as necessary over the longer cooking time. Same with hobs. This is very different to a solid 7kW for hours on end charging an ev.
 
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Adopado

Active Member
Aug 19, 2019
3,798
2,908
Scotland
Really? Where do you think the efficiency improvements would come from in an electric shower? Converting electricity to heat is literally 100% efficient.

The problem with a shower is that the efficient creation of heat then has to be transferred to another medium ... fast flowing water. That's where the inefficiency happens. Same as transferring heat from a domestic radiator to the air around it. The design and surface area of the radiator hugely affects the heat transfer ... same for heat exchange to water within an electric shower.
 

m3p_uk

Member
Aug 1, 2019
645
161
UK
Actually electric cookers are not pulling their rated kW spec continuously. Yes, they are switched on at the wall but once the oven is up to temperature after a few minutes the thermostat switches off and then only tops up the heat as necessary over the longer cooking time. Same with hobs. This is very different to a solid 7kW for hours on end charging an ev.

Some houses have Aircon which pull this amount continuously but that's not the point I'm making.
Doesn't matter if there is or is not something similar to this at the moment.
Just want to know why current "fast" chargers are limited to 7kw and not go up to 11kw or higher.
General consensus is that it would cost more for the parts rather than any limiting factor
 

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