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Discussion Starter #1
Hi, I have bought a 6.6kW charger, which I think is a TC one.


I am building up all the EV electronics outside of the car first, in my living room, before I install it all, so I want to test the charger with the BMS and battery pack. However, I don't know how the charger decides how much current it can draw when charging.


I am in the UK, so 240V mains. I was planning to connect the charger to the mains for testing via a normal 3 pin plug but they are 13A rated, and obviously the charger doesn't know that.



So my question is - how does the charger determine what current to draw?


Is it limited by the BMS? If so, for testing, I could set the charge current to be sub-13A, but in the real world (when using a public charge point or a charging lead) how is the max current set to optimise charging time?


I am using an Orion BMS2, and the charger is controlled by CANbus.


Thanks
 

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The charger doesn't know squat.

People buy a 6,600W charger to pull 240V from a 30A minimum circuit.

If you knew you only have 3kW available, could've saved some money.

Or get a sparkie in and have an appropriate circuit installed.

That said, you say it's controlled by CAN signals, so program a mcu to send the right CAN signal and you should be all set.

Dunno if Orion BMS2 can be configured to do so, doubt it.

You did get the documentation for the charger's CAN implementation, right?

And what sort of battery pack? Don't burn the building down!
 

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Discussion Starter #3
I have no intention of burning the building down, hence the question!


Battery pack is 5 Tesla modules in series, so 120V-odd.


I can make use of the 6.6kW on the public chargers which can deliver the ampage, but clearly, for testing using a domestic 3-pin mains plug (so not even a charging lead), I need to ensure that the charger won't blow all my household fuses.


So I guess I have to temporarily set the Orion to limit the charge current the charger can draw?
 

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... in the real world (when using a public charge point or a charging lead) how is the max current set to optimise charging time?
At at charging station (public or home), the station's equipment tells the car's charger what the maximum available current is. A charging lead for use with a normal outlet is normally designed so that the attached plug tells the device what the outlet rating should be. The charger runs at that or lower, depending on its capacity and the programmed safe rate for the battery.
 

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Discussion Starter #5
At at charging station (public or home), the station's equipment tells the car's charger what the maximum available current is. A charging lead for use with a normal outlet is normally designed so that the attached plug tells the device what the outlet rating should be. The charger runs at that or lower, depending on its capacity and the programmed safe rate for the battery.

Brian, thanks, that's helpful - but how does the charging station / charging lead 'tell' the charger what the limit is?
 

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EVSE's have a +/- 12 V square wave signal at 1000 Hz. This is proportional to the maximum power it can carry. For 32 A (7.5 kW) it will put out 12 V. For 15 A it will put out 6 V and so on. Pretty sure that's right?

Some BMS's will have the means to read the pilot signal from the EVSE and interpret it as a maximum current setting. The BMS then tells the charger via CAN Bus to lower its maximum power to match the maximum available from the EVSE.

If the charger you bought wasn't CAN controlled, it will straight up draw 32 amps from the wall. Not a problem if you can only plug it into a 32 A socket, but it will be useless in a world of 10 or 15 A sockets.
 

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Brian, thanks, that's helpful - but how does the charging station / charging lead 'tell' the charger what the limit is?
This has already been answered, but I wrote a response before being interrupted, so here it is...

The various standards for charging station connections all include a way for the charging station and in-car charger to communicate (typically a couple of extra small contacts in addition to the big contacts carrying the charging power) and define a protocol for that communication. IEC 62196 is an example of one of these sets of standards.

With a mobile charging cord, the adapter plugged into the end (see Tesla's mobile charging equipment including adapters for examples) indicates to the controller in the cord what rate to use (probably with just a simple resistor built into the adapter), and that controller tells the car, just as a charging station would. Some mobile charging cords may only work with one type (and thus rating) of wall socket. The maximum current to take from a common wall socket is usually set to 80% of the rating of the socket.
 

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Example

https://www.amazon.co.uk/EVIEUN-Cable-10A-Portable-EV-Fast-Charger-IEC62196-Type/dp/B07RSRRZ5L

Limits to a 10A draw.

But rigging the input side of your charger to "speak IEC62196" is a DIY challenge.

Too bad you didn't buy a charger with a switch or knob to de-rate the current it will pull from its source.

That is what the CANbus input is for, but you need to get the documentation for its current-limiting commands, and program a mcu to send them, likely every X seconds or it will revert to default.

Alternatively, there may well be a current limiting device designed to work on 240V input and output.

But the easiest would be to just get the proper 50A circuit installed by an electrician..
 

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Orion 2 will do the Type 1/2 EVSE talking and limit the can bus based chargers on that current limit.

It just uses a simple power calculation to determing the DC limit to allow the AC limit to be obeyed.

Attached the fields in the Orion software.
 

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Discussion Starter #13
Orion 2 will do the Type 1/2 EVSE talking and limit the can bus based chargers on that current limit.

It just uses a simple power calculation to determing the DC limit to allow the AC limit to be obeyed.

Fantastic, thanks, that explains it.


So, I can enable J1772 on the Orion, and wire in a J1772 port with the control/pilot and proximity lines connected to the BMS. That will let the BMS control the charger via CAN, choosing the charge rate depending on what the EVSE or the charging lead can give.


For my testing, I can also set a charge limit of say 10A, and wire the charger's AC input to the 240V mains via 13A normal plug, bypassing any J1772 protocol, and hopefully avoid burning the house down.


Much obliged, as ever.
 

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You can build your own circuit to limit power to any CAN based charger. Code i wrote is for my friends 3kW Elcon charger. His BMS is misbehaving and i limited his max voltage for safety.
https://leafdriveblog.wordpress.com/2019/08/25/arduino-can-module/

I am in process of writing code with multiples of conditionals, so we could have like 4 buttons: Stop, 8A, 15A and max Amps.

Then you would have control of the charger and run it from the dash with whatever power EVSE is capable to deliver.

Oh... This was written with simple BMS in mind, the kind miniBMS was, that does not have its own CAN line.
 
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