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Zoe ZE50 R135
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Discussion Starter · #1 ·
I'd like to understand better how the charge current is determined. On a 2KW domestic charger cable there's a box that I guess limits the current to 10A and also I understand takes a control signal from my Zoe and switches on the supply to the car at the programmed time. My Zoe can charge at 22KW so if I connect it to a 7KW outlet presumably the outlet limits the current to 32A? So am I right in saying that the mains outlet always needs to have a current limiting function?
I never tell my Zoe which charger I'm on so I guess it has to be the supply end that limits the current and the Zoe just sucks in as much as it can (up to 32A). Or is it that the supply end tells the car how much to take and the Zoe limits the current?
 

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MG5
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When you connect a type2 cable the car, via the CP wire, tells the EVSE to supply 230V AC to the car and also via the CP what the max current available to be used by the cars on board charger.
 

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Each part of the charging 'chain' has its own limit. The wallbox will only send up to its maximum design limit. The cable will only transfer up to its own limit. And the car will only accept the limit it has been designed to take.

This means that in any configuration of any combination of wallbox, cable, and car, the lowest rated amperage in that 'chain' will be what happens.
 

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Each part of the charging 'chain' has its own limit. The wallbox will only send up to its maximum design limit. The cable will only transfer up to its own limit. And the car will only accept the limit it has been designed to take.

This means that in any configuration of any combination of wallbox, cable, and car, the lowest rated amperage in that 'chain' will be what happens.
That's 99% true. The last 1% is that the car's on-board charger (OBC) is the place the limits are combined and applied. The wallbox and the cable each tell the car their maximum allowed current, but don't limit anything themselves. (The cable is completely dumb: it just connects the power and CP wires straight through from one end to the other, with a resistor on the PP at the end to signal the cable's rating to the car.)

Understanding the limits is slightly complicated in that some AC charge points, cables and car OBC are capable of 3-phase power, and others only single-phase. The OBC does the best it can with whatever phase pattern arrives at its power connector. The Zoe's 22 kW charger needs 3-phase 32 A at 230 V to run at full power.
 

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That's 99% true. The last 1% is that the car's on-board charger (OBC) is the place the limits are combined and applied.
I was trying to break it down so that a non-techy person can understand the basic logic to apply.

Once much more nerdy concepts are introduced, whether for 100% accuracy or because such things interest someone more than most people, I think that a lot of new EV owners glaze over and could forget the basic message.

As in this paragraph in your message. Totally accurate and important. But well over the head of most new EV owners.

"Understanding the limits is slightly complicated in that some AC charge points, cables and car OBC are capable of 3-phase power, and others only single-phase. The OBC does the best it can with whatever phase pattern arrives at its power connector. The Zoe's 22 kW charger needs 3-phase 32 A at 230 V to run at full power."

Your extra 1% may well be correct but if you just state that without the context of how the OBC makes that decision then the 'weakest link' aspect might be missed by someone not as tech-savvy as yourself.
 

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Cup ball, ball Cup, just like that.

It's not magyck but in simple terms there's a clever component in the car which determines how much power it can safely take when presented with any supply equipment and cable combination.

So the granny lead presents itself to the car as being able to supply 10 amps whilst the 7kW chargepoint states that it can provide 32 amps.
If a separate cable is also used the car reads a value from that to ensure it's able to supply the 32 amps. If it's only rated for 16 amps then that's what the car will draw.

Of course, the bit of equipment in the car (the OBC or onboard charger) doing all the deciding is hugely expensive and has to look after itself.

It takes away the risk of someone doing something silly.

HTH

Gaz
 
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I believe it's different for DC rapid charging, in which case isn't it the car communicating to the rapid charger what it can take and then it's the charger doing the limiting (if the charger can output more power than the car can handle)
 

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Zoe ZE50 R135
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Discussion Starter · #9 ·
Pierpoint: "If it's [the cable] only rated for 16 amps then that's what the car will draw. "
What sort of cable might that be I wonder? Something like this I guess - a cable with intelligence in its control box.
 

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Pierpoint: "If it's [the cable] only rated for 16 amps then that's what the car will draw. "
What sort of cable might that be I wonder? How does a cable declare its rating?
(Edit; sorry, based on diagram linked below, I have to amend my understanding of this)

There are resistors in the lead that modifies a carrier signal. The A carrier signal is generated by the EVSE you plug into, which 'broadcasts' what it is capable of, passes that signal through the lead, and to the OBC on the car. If the car sees the signal has been modified by the lead, it de-rates itself to what the lead can deliver. If the OBC sees the unmodified EVSE signal it will regulate its current drawn to what the OBC says it can deliver.

So it is under the control of the car's OBC entirely. The OBC dictates the charge rate, but receives the EVSE signal via the lead and interprets that.

If you were minded to want to manipulate the current your car charges at, you can manipulate the resistance in that signal path to ground, via the lead, and make the car charge at whatever you want it to charge at. Some portable EVSE leads have this feature built in, and you can press buttons on it for different charge levels (what you are doing is altering the broadcast charge setting from the EVSE to the OBC).

If the OBC goes wrong it could draw high currents through the lead and EVSE that they are not capable of. I've never head of that happening. If it did, the EVSE would likely throw its relay in error, or the lead 'may' have a thermal fuse in it. Not sure if they do.
 

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Pierpoint: "If it's [the cable] only rated for 16 amps then that's what the car will draw. "
What sort of cable might that be I wonder? How does a cable declare its rating?
The cable has a resistor set into the connector which the car can measure and different resistances denote a different type and quality of cable.
There are a number of people who have a 3 phase cable which is only rated at 16 amps but has more connections so the car can charge faster if connected to a 3 phase chargepoint.
The problem occurs when the cable is used for a single phase chargepoint and the car can only draw 16 amps down one line at the rate the resistor suggested was safe.
I have heard of older cables being supplied that were rated at 16 amps but only single phase but presume they are no longer about.

To clarify what cable you have you should find writing on the outer sheath of the cable itself plus looking down the end of the connector you may well see that the pins or otherwise are marked as p1, p2, p3 you'll see metal inside or no metal or no connector at all for p2 and p3.
The wording and the connected pinout will give some insight into which cable you have.

Gaz
 

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Zoe ZE50 R135
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Discussion Starter · #12 ·
The cable has a resistor set into the connector which the car can measure and different resistances denote a different type and quality of cable.
There are a number of people who have a 3 phase cable which is only rated at 16 amps but has more connections so the car can charge faster if connected to a 3 phase chargepoint.
The problem occurs when the cable is used for a single phase chargepoint and the car can only draw 16 amps down one line at the rate the resistor suggested was safe.
I have heard of older cables being supplied that were rated at 16 amps but only single phase but presume they are no longer about.

To clarify what cable you have you should find writing on the outer sheath of the cable itself plus looking down the end of the connector you may well see that the pins or otherwise are marked as p1, p2, p3 you'll see metal inside or no metal or no connector at all for p2 and p3.
The wording and the connected pinout will give some insight into which cable you have.

Gaz
So the car measures the resistance value - that I can understand. More believable than some other comments about the resistor modifying the signal from the charge point - like, how could a simple resistor do that!?

And I've been looking at a Commando socket 32A cable that has selectable charge ampage. Presumably it switches in different resistors.
 

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What sort of cable might that be I wonder? Something like this I guess - a cable with intelligence in its control box.
Not necessarily. A few years ago many EVs only had a 16 amp charger on board so the owner fitted a wallbox that could deliver that. And bought a 16 amp type 2 to type 2 cable that was 16 amp rated as they were cheaper and much lighter to handle. Then, as discussed above, if that cable was used at a public charger capable of up to 22 kW it would still only deliver 16 amps for two reasons. First of all the car would only accept 16 amps, and secondly the cable would also restrict to that level. Weakest link in any chain of power levels would always apply.

Rather than the cable you showed, a 16 amp OBC just needs a cheaper 16 amp cable like this.

Type 2 to Type 2 Charging Cable - EV Cable Shop
 

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[Apologies for more technical detail.]
The type 2 or type 1 lead does not modify the CP signal sent by the charge point. It announces its own capability using a resistor (in the plug at the car end) between PE (earth) and PP. That resistance also serves to tell the car that there's a cable plugged in, even if there's no power connected at its other end. A non-tethered cable has another resistor at the wall box (EVSE) end to give the same capacity and connection information.

Here is Wikipedia's connection diagram - R6 codes the cable's capacity.

16A single-phase cables do exist. Here is an example.

I've been looking at a Commando socket 32A cable that has selectable charge ampage. Presumably it switches in different resistors.
That "cable" includes the EVSE circuit, the stuff normally inside the wall box, and which sends the square wave signal with a wide range of current capabilities.
 

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[Apologies for more technical detail.]
The type 2 or type 1 lead does not modify the CP signal sent by the charge point. It announces its own capability using a resistor (in the plug at the car end) between PE (earth) and PP. That resistance also serves to tell the car that there's a cable plugged in, even if there's no power connected at its other end
I stand corrected.
 

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MG5
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So the car measures the resistance value - that I can understand. More believable than some other comments about the resistor modifying the signal from the charge point - like, how could a simple resistor do that!?

And I've been looking at a Commando socket 32A cable that has selectable charge ampage. Presumably it switches in different resistors.
Many shy away from those things as they do not include protection that may come into play if there is a specific type of earthing fault.
Usually referred to as an Open PEN fault.
Anyway, if it's the ability to select which amperage you are using then the Wallbox Pulsar Plus is good at that, providing a 5 metre tethered cable is long enough. If you need a 7 metre cable then you'd need the Max version.

Gaz
 
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