Slow vs "Fast" charging confusion

Hi folks,

I'm trying to understand the differences between all types of chargers and on the surface it seems the main difference is how fast electrons flow into the battery. Thus slow (7KWh) < fast (22KWh) < rapid (50KWh).

However, when I connect to a slow charger at work (at least back when this was possible) I'd get an average of about 5.6KWh. I appreciate the car can only take so much AC power so you'll never get the full 7KWh. However for "fast" chargers, although the car is capped at 10 or 11KWh, I'd still expect faster rates than those from a slow charger when plugged in to those so I was really confused when my charging session on Tuesday at a fast charger only drew an average of 4.2KWh. This was a bay of 4 with, as far as I could tell, no one else plugged in (I wasn't keeping an eye on the car the whole time). While the work slow chargers are a row of 6 with often all chargers being in use.

I know DC will vary greatly depending on the state of your battery when you first plug in (something I'm still not understanding) so getting the full 50KWh from a rapid charger is not likely to happen much. But my experience with AC seems to be that the flow rate varies very little over time once you're plugged in, I'm just not sure why "fast" chargers get slower than slow ones. If anyone has a straightforward explanation I'd be grateful, thanks

What cable are you using - you need 32A 3 phase to get 11Kw from a fast charger - I think you have the single phase 16A version - you would in effect only be charging on a single vs 3 phase

You need a different cable to take full advantage of the speeds provided by a fast charger??? I suppose that makes sense but how come no one told me this before? Specifically why didn't my dealership mention this when they bundled the cable with my car purchase?

What happens when you use a 32A 3 phase cable on a slow charger then?

Fast EVSE are AC type2 connections.
Rapid are DC CCS.
Some Type 2 EVSE can supply 22kW via a three phase connection. check which on board charger you have.
The Granny EVSE can be referred to as Slow.

Yes I know the difference between AC Type 2 both slow (7K) and fast (22k) and DC CCS. The latter is typically tethered anyway so that's not an issue. I use the same charging cable on 7k and 22k chargers, I don't know if it's a 3 phase. Though looking at evcables.com and how much a 3 phase costs, I'd have thought that's what we have but I'll have to check our paperwork as I had not heard until today that there were 2 types of cables

jeanloup said:

You need a different cable to take full advantage of the speeds provided by a fast charger??? I suppose that makes sense but how come no one told me this before? Specifically why didn't my dealership mention this when they bundled the cable with my car purchase?

What happens when you use a 32A 3 phase cable on a slow charger then?

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My Understanding is if you have a single phase cable and plugged into a 3 phase charger you would only draw from 1 phase so roughly a 3rd of the speed.
Think it might also effect speed depending on rating of cable if you plug a 3phase cable into a single phase charger, that the speed could be reduced if each phase isn't capable of the full speed the charger is.

Agreed. A 32A single phase (~7kW) cable connected to an 11kW charge point will only deliver ~3.6kW charge rate. (1/3 of 11kW, minus losses).

the rating of the cable should be stated on it. Plus look at the connectors - if there are pins/receptacles in the L2 and L3 "holes" then it is a 3-phase cable, otherwise it is single phase.

Also, look at the port on your car ... only the Phase 1 (MY22, no rear wiper) LR cars came with 3-phase onboard chargers (in the UK).

I get 6.5 kw on a 7 kw type 2 public charger. I don't think the SR cars can do any more no matter what cable you use.

Some fast chargers can be set to lower speeds. Some kerb side chargers in London are limited to 5kW for example.
If your car was switched on with you sat in it and the HVAC was running, that can account for 1 to 2kW of load therefore you will be charging your battery at a lower rate of charge.

Rolfe said:

I get 6.5 kw on a 7 kw type 2 public charger. I don't think the SR cars can do any more no matter what cable you use.

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The single phase onboard charger is rated to 6.6kW, so that's why.

Thanks for the response everyone.

I'm gonna assume 32A-SP means 32 amps single phase? Excuse my French but this shit is way more complicated than it should be...

If the manufacturer says I can draw up to 11KWh on AC then I would expect to be able to get that with the cable I was sold not a fraction of this because I should have 3 phase instead of single phase (is there even a double phase??). But it looks like if you want to make the most of your car charging abilities you need a PhD in electrical engineering (I have similar complaints when it comes to dealing with my solar array but that's not for this forum)

siteguru said:

Also, look at the port on your car ... only the Phase 1 (MY22, no rear wiper) LR cars came with 3-phase onboard chargers (in the UK).

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This is important to check. Look at the charge port on your car. If it is 3 phase there will be metal pins in the L2 and L3 sockets. If it doesn't have metal pins there, then it is not 3 phase and will not support 11kW charging whatever cable you use.

Exactly this - the 2nd release (not to use the word phase) of cars, only have single phase chargers, so 7kw is going to be maximum, even if the charger (3ph charger supplied by a 3ph power supply) and the cable has the rating and internal connections to do it.

Easy way to tell is looking at the bottom two corners of the charging socket on the car... if there are pins, that are phases 2 and 3... no pins mean no can do.

Just think of it as AC or DC. AC charges at 6.6kWh (single phase) and DC charges at high speeds.
Note: Some MG4s can charge at a faster rate on 3 phase AC but not all and you need the 3 phase cable.

PeteC said:

This is important to check. Look at the charge port on your car. If it is 3 phase there will be metal pins in the L2 and L3 sockets. If it doesn't have metal pins there, then it is not 3 phase and will not support 11kW charging whatever cable you use.

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They all seem to have pins in them so is it just a case of getting a three phase cable or something?

And I tried to check the manual of the car or the website and nothing specifies what category of AC charger is installed on the SE long range, unless it's buried in an appendix somewhere.

I'm assuming you're all electricians or related professionals as I've no idea where the average user would even find out about any of this stuff. I barely understand it myself... Actually scratch that, I've no clue what the difference between single phase and three phase is and why you need it or don't need it...

You don’t really need to worry anyway. If you are charging using your own cable is likely because you will charge for several hours or are t popping up at the supermarket. It will charge slowly no matter if it’s 3, 6, or 9 kW that you get in that battery.
If you need to charge rapidly you go to a rapid charger.

It’s like with petrol: you want the correct octane for your car, but if you then start looking at the fuel quality, additives, and ethanol content it gets overly complicated.

I don't see the relevance with petrol sorry. We're talking about how fast the car gets charged. With petrol whether you use ethanol, unleaded, diesel or whatever your combustible of choice is, it'll take more or less the same amount of time to fill all cars of equal size (I'm not comparing city cars to cargo ships here).

"Rapid" still takes the best part of an hour if you want your battery as full as possible and when you're like me and can't charge at home, I go with charge as much as possible as infrequently as possible instead of little but often. Different philosophies I guess but with this change of paradigm, we all adapt in our own ways. So yes if getting 10KWh means charging the car in 4h instead of 8h at 5KWh then it does matter. It's all the more relevant when you use public chargers which have a cap on how long you can have your car plugged in before being charged exorbitant amounts of money for overstaying your welcome...

jeanloup said:

). But it looks like if you want to make the most of your car charging abilities you need a PhD in electrical engineering (I have similar complaints when it comes to dealing with my solar array but that's not for this forum)

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I was referring to this statement of yours.
If you want to make the most out of your car’s charging abilities surely you need to also consider ambient temperature, the battery temperature, the state of charge of the battery, the quality of the charger’s liquid cooling in the cable, the charging losses within the charger, the total capacity of the grid supply, and possibly more.

It truthfully isn’t that complicated when it comes to AC charging. You mention you can’t charge at home so you must choose your slow charger carefully and are interested in knowing what speed you are meant to get.

All you need to know at this point is that your car can charge at a maximum of around 6.5kW on any AC charger rated 7kW and above.

If you get less than that, and it’s not the charger the limiting factor, and it’s really important you know whether reason is, then maybe what would help is for you to share the time of day when you were charging, how long the charging session was for, the site you were using, whether the car was switched on or off, and what the peak was. Also would help if you are including the final half an hour to two hours charging at far less than 1kW when the battery is balancing at 100% in your calculations.

I don't do calculations. I just expect a fast charger to be faster than a slow one. Surely that's not an unreasonable assumption to make?

It's not unreasonable, but there are particular situations where it might not be true.