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EV Charging - Is it realistic to simulate a battery?

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741:
So far I've had just a brief glimpse of the specs a possible project, an EV charging station. It might well not happen. So this just testing the water; I am not knowledgeable about the topic.

I gather that a test facility can use a standard circuit to evaluate 'domestic' EV charging stations. The signal side of this circuit is simple: Basically some switches, a diode, and resistors. The switches are twiddled to various positions to simulate what a car's charging unit would do (implementing the basic analog 'protocol'). The charging station responds accordingly according to some state diagrams. (An optional digital interface exists too, but I'm ignoring that here).

It would be ideal to do what a test facility would do before sending a new design off for verification.

The power side of the test circuit seems to be basically a variable load. The EV unit allows mains power (or not), via a relay - taking into account how many amps the EV unit states it wants (if the EV car wants 32A then the charger can 'refuse' for example). It also monitors the ground lead's integrity.

(1) Is it all feasible to design & build some circuit which dumps power into say two parallel domestic heaters in such a way that this looks realistic from the charge station's stance?
(2) Would it be worth doing, or would little information be gained?

MagicSmoker:
An EV charging station is basically a glorified power cord - supplies mains AC to an onboard battery charger; is that what you are designing, or the charger itself?

DBecker:
A basic EV charging control system is very simple.  It's documented all over.

The supply side is basically a GFCI, with a relay that connects the 120-240V supply when the right diode-resistor pair is connected to the "pilot" sense line.

A key point that you won't be testing with a simple setup is that the pilot waveform is strictly symmetrical, both in voltage+impedance and pulse width.  You should be able to drop the output in a bucket of water and have no DC bias.  This should be true over the full range of conductivity.  This is important for long-term corrosion resistance.  You should be able to simulate that draw and measure the bias.

And of course be able to simulate the various types of ground faults, but that's a little more obvious.


741:
Just the "glorified power cord" I think.

Thanks for the note about PWM symmetry: PWM is not mandatory, the charger is permitted to output DC instead of PWM.

Kilrah:
Those glorified power cords are pretty boring, they're common and cheap and just do a few basic measurements, some communication and fault detection that ends up switching a relay. Not very interesting as a project.

Lots of detail about those here:

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