Charging currents (single phase)

After the startup sequence described in the previous posts it is now time to move on to the actual charging. Again, all the measurements come from SpeakEV user ElectricBeagle and tons of valuable info has come from user arg. If you want to check out the discussion that lead to all of this, here it is.

Let’s set the stage first. We assume single phase charging, the earth check has been performed, the mains has already been connected and, since it’s single phase charging, the relay between N and L3 has already closed. More about that later. Charging has started and as shown in the previous post, the current has ramped up to the desired level. The ramping is gradual, taking about one second.

The rather massive 100 uF capacitor is now creating that 6 A reactive current. It’s sole purpose seems to be to dampen the huge current spikes created by the switch mode power supply. Note that the capacitors are rated for 63 A. The worsening power factor is simply a side effect of that. However, at 16 A, the PF is already above 0.9, so no worries. Bottom line is: at decent currents, say at or above 16 A, the power factor is great and they do clever things with the switching to follow the voltage, see next picture, taken at a current setting of 30 A, with a very small resistor in the N line to measure current without phase shift.

At significantly lower power levels things worsen very quickly. For instance an off grid PV inverter would need to be very potent in coping with that reactive power. But I digress. Because what you really want to know is the effect of the switching. So let’s zoom in on the raggedness of the current curve.

What I wrote here before was way off, as arg argued in private…….An earlier picture suggests that the current coil produces roughly 1 volt peak-to-peak per 4 A wire current (RMS). That suggests a 10 kHz ripple current of just over 200 mA RMS. On a 10 A charge current that is give or take 2%. But this measurement was done with a current coil on the L wire at 16 A, while the previous picture was done with a resistor in N, at 30 A. I suspect the current coil is quite frequency dependent. Going back one picture, one-and-a half-dot ripple on a 26 dot amplitude is roughly 6%. At least ball park same.

Another interesting thing to look at is earth leakage, given the relatively high capacitance between the stator coils and the motor housing. One “blob” is a half-cycle, lasting 10 ms. The pattern is pretty symetrical, with a small (about 6 dots) peak to peak 50 Hz component, and a decent (about 15 dots) 10 Khz signal. The scale is 30mA/div. My rough estimate is that the 50 Hz component is 13 mA RMS and the 10 kHz part a bit above 30 mA RMS. Note that a consumer grade RCD will trip at 30 mA but as arg argued, it should not care too much about the higher frequencies (though old ones may!). All in all the stray capacitance to earth seems to be about 2nF. Note that the leakage current should not go significantly up with power, as it’s a capacitive coupling.

And this is the reason why ZOE sings. Ramping up the frequency further would progressively increase leak current up to the point where dedicated, uncompromised coils would be needed, adding quite a bit of weight if one would want to do 22 or 43 kW rectifying.

All in all I would say: not too bad really! The only thing I am not really sure about is what is meant with HF and EHF frequency in the leak currents the car can report. I always assumed 150 Hz (3rd harmonics) and 10 kHz (the switching frequency), but I am not 100% sure. If anyone knows or suspects more, I’d love to know.

EDIT: by now after more thinking and a few discussions, I am quite convinced HF means the 10 kHz domain and EHF means 10 kHz harmonics.

Oh and about the single phase relay. It can’t close before the chargepoint contactor is closed, because as long as it is open, the car doesn’t know if the chargepoint is single or three phase. However, assuming no contactor in the filter module (and I haven’t found any in the pictures of the filter and charging module), once power is switched on and it is single phase, the capacitor between L3 and N is idle, so it’s no problem to bridge it with a relay at that moment in time.

10 comments on “Charging currents (single phase)
  1. Yoko says:

    Hi there,

    Have you ever tried that when the Zoe charges with 32 Amps single phase, it stops charging every 2 minutes (exactly 2 minutes) and than resumes the charging process itself again? What kinds of tests does Zoe do during the charging process? Would it be earth leakage tests?

    I’m looking forward to your reply. Thank you very much!

    • Bob Fisch says:

      Earth leakage is the most common problem for the described symptoms.

      • Yoko says:

        So do you mean that there would be possibly an earth leakage, so the Zoe stops charging, after that when it detects no leakages, it resumes charging again?

    • Bob Fisch says:

      After that it resumes, does it stop over and over again after 2 mins or does it then continue normally? This isn’t very clear to me …

      • Yoko says:

        It would stop again after 2 minutes, it just keeps doing the same thing.

        • Yoko says:

          It would stop again after 2 minutes, it just goes on and on

        • Bob Fisch says:

          Yes, then earth leaking is very probable I would say šŸ˜‰

          • Yoko says:

            Okay, I would check my power source, since it’s quite “dirty” I would say, harmonics are everywhere and they are great in magnitude.

            Thank you so much for your answer!

          • Jeroen Meijer says:

            Be careful now. Earth leakage is a current from the mains to earth because the entire circuit has an electrical capacity to ground. This is found in the Leak Currents screen in CanZE for different frequency domains. HF should not go above 300 mA (but to be honest, I doubt it will)

            Earth line resistance is a totally different thing and is tested by the car before charging starts, so this is not your problem and checking your earth line will almost certainly solve nothing.

            Given the 2 minutes interval my bet is on the charger itself (not the car) deciding the car takes just a bit more than 32A (which is allowed by the standards, 5% I think) and stops charging. Check by going to another 32A single phase post.

  2. Yoko says:

    Dear Jeroen,

    Thanks for your reply. I have tried to add an EMI filter but I still can’t charge my ZOE normally (stil stopped after the 2-minute interval). I have checked the energy meter and checked the command from the charger, the charger output below 30 Amps, so it would be output more than 32A. I may try to keep updating you guys.

    Thanks all!

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