Max battery charge and Max battery regeneration

Posted on Posted in ZOE

In the Dutch Renault forum, the issue came up that the maximum regenerative power allowed is higher than what CanZE reports as the Max battery charge / regen kW power. Based on a few experiments of my own only, it seems the Zoe will allow double the reported power for regeneration, capped at 40 kW DC of course. After all, it is supposed to be a short burst and the amount of energy, by definition, has already been taken from the battery.

I would appreciate your findings. Just open CanZE on the driving screen and whenever the Max battery charge / regen kW is substantially below 20 kW, try to do a serious regenerative brake (from a high speed works best, i.e. a motorway exit) and see how far the DC Power kW (or if it refreshes too slow, the blue kW in the dash) shows please. Thank you!

Edit: based on my own testing it seems there is indeed a short over-power possible. The rough formula is max_charge_power * 1.65 + 3.5. More testing by Borut suggests this seems sustainable for either roughly 40 seconds, or until the total battery voltage reaches 390 volts (4.06 volts per cell), see the comments.

It should be possible to calculate the max regen power by taking the max_regen_torque (the blue bar in the driving and consumption screen) and multiply that by the wheel speed (in rad/sec). I might implement this in a test screen.

13 Comments on “Max battery charge and Max battery regeneration”

  1. Yes, I see this every day. The max blue power on the dash is always higher than max regen on CanZE. I would not say double the value, but a few kW.

  2. I think…
    The max/regen/charge power is calculated by the battery computer ,but the regen charger work simply by constant power(40kw) or constant voltage(390 V) .
    Try loking at the battery voltage, it is always at 390 or below so the battery charger send as much power as it can to the battery until one of the criteria is meet(40kw or 390V and only then start’s to cap the power.
    On the other hand ,I live uphill and when I drive down , the observed double regen power is there for a couple of seconds and after that the regen power is exactly as the canZE shows.
    And for that reason I think ,the battery balancing is alwais on so that no battery cell ever exceedes 4.1 V

    • Well, the battery voltage can sway quite substantially, somewhere between roughly 3.6 – 4.1 V per cell (Zoe has 96 cells). Max charge certainly is calculated by the LBC, but regen is certainly not 40 kW. If the battery is full, there is almost no regen. Your observation about the regen power going down to the max charging current is an interesting one, and it makes sense: it seems like the LBC then allows a short “overpower”. Can you give me an approximation on how long this period is? I live in a totally flat country so I cannot test it 😉

      I did some experimenting on my commute this morning and a rough approximation of the short “overpower” seems to be: max_charge_power * 1.65 + 3.5

      • Hello
        the test
        SOC 95
        battery temp 9 degre celsius
        max charge/regen power reported by canZE is 5.6 kw
        it is a 25 m drop in a 400 meter span
        at the top on a hard brake the blue indicator show +13 kw
        driving down without touching the brake and speed 50 km/h (around +8kw regen until 3/4 down then the battery voltage reaches 390 V and the regen goes to 7,6,5…)
        at the end on the hard brake the blue indicator shows +5 kw.
        Don’t know second exactly, it is to many informations for one person driving 🙂

        • Thank you for your report! The numbers seems to correspond exactly with my findings this morning 🙂

          So, the 390 volts seems to be the “trigger” indeed. Learned something new today!

  3. The behavior of the Max Charge I found a bit strange. Maybe someone has an explanation here. (On a R90)
    The value seams quite volatile:
    – Higher Power on the Battery is increasing the value
    – Lower Power on the Battery is decreasing the value (incl. Regen Power)
    After the some time, the value is recovering slowly.

    Test conditions:
    T-Battery: 4°C
    SOC around 50%
    2 times driving a little bit the hill down approx. 400 Meter distance and up again
    Aircon On

    Theses are the values of the Max Charge:
    Start: 10.4kW
    Regen with 5-17kW: Value decreases 6-8kW
    Stopped and drove up again (around 40kW Power): Value rises to 19kW
    Stopped and waited: Value decreases within 2 Minutes to approx. 14kW, tendency decreasing

    Did not believe an tried again, this time only with Aircon:
    Start: 12kW
    AirCon On (2kW): Value rises to 14kW
    AirCon Off (0kW): Value decreases to 12kW

    Now with charging:
    Charging Power is 11kW on the Wall. Battery still 4°C:
    Values: Battery Power – Max. Charge

    Start: 0kW – approx. 10kW
    10 Sec: 8kW – 8.4kW
    30 Sec. 6.1kW – 6.2kW
    It stays on this value. Then charging stoped. Max Charge rises within 15 seconds to 8.2kW. After Charging Start, same story again, value decreases to 6kW.

    Specially for charging it is a bit puzzling since it seams to self limit the charge power even further, which is not very nice for charging the R90.

    But for regeneration I did not find a limitation yet. I’ll test again with 95% SOC, there the limitation should kick in since my downhill will regenerate around 3%SOC. From testing so far I can see 25kW Regen with 4.1kW of Max Charge, which does not match with the Formula stated above. Again, on a R90.

  4. Wow. Those figures are really very different compared to the 2×0 models. Also the dependency of max charge versus what is being used/charged is weird. Unfortunately I have zero “official” documentation on the 90 models :-/

    4 degrees centigrade / SOC 50% on the old battery would allow a charging rate of roughly 0.5C (11 kW, 2 hours charging). 0.5C on a 40kWh battery of roughly the same chemistry would allow 20 kW……..

    I am already hearing the 90 models are closer to the 2×0’s in charging power (in kW) limits (as opposed to charging rate in C’s). This makes totally no sense to me, especially if the regen is so high as you report.

    Could you maybe check with the wallbox if the real power taken maches roughly the Max Charge Regen?

    Confused!

  5. I don’t have a wall box allowing such measurement. However, I went tonight to drain the battery on the highway and also to heat it up. I arrived at a public charger with 35%SOC and 13°C. Then I saw these values:
    SOC – Battery Power – TBattery
    35% – 20.8kW – 13°C
    48% – 18.0 kW – 16°C
    52% – 18.1 kW – 17°C
    63% – 17.0 kW – 19°C
    70% – 17.0 kW – 19°C – Then I stopped charging.
    Before the charging (after Highway), the Max Charge Power was 29.1kW. As soon charging began, the Battery Power always matched the Max Charge Power +/- 0.3kW.
    The public charger does not give me Power, but it shows the Energy and time. It was in that time 14.2kWh within 44 Minutes which equals to 19kW average Power which would match too.
    At these temperatures, charging is ok as well.

    • Sorry for not noticing and approving your comment earlier…. So, the conclusion is that for the model 90’s, battery throttling is well underway (down to 18 kW) @ 48% SOCu and 16°C, whereas it should be able to go up to 40 kW under ideal circumstances (which is already half of the 2×0 models, given the [nearly] double size of the battery).

      I am really confused about this, as the 2×0 models only start throttling back from 40kW (=2C) at this point and the 90 models seems to be throttling back to below 20 kW (=0.5C) at the same SOC/temperature point. In other words, the model 90 battery seems to be much, much more delicately handled by the BMS, and therefor much much less willing to charge at full power. This would limit IMHO the added value of a Q90 (compared to an R90) significantly. Thank you for this data!

      • Yes, it is very confusing. The odd thing is that the new models are allowing much higher regen values at the same time which is in contradiction to the charging behavior. I assume there will be an software update in the future.
        I also gave this feedback to my dealer. He promised me to ask Renault about that.
        If I get some answer, I’ll post them here. (although I am not sure if they are even answering)

      • One more test I performed which will contribute to our confusion:

        The above Charge in short is:
        TBattery Start: 13°C, SOC Start: 35%, Power 19-17kW, Stopped @70%SOC
        One day later another Charge for testing:
        TBattery Start: 15°C, SOC Start: 60%, Power 13-11kW, Stopped @70%SOC

        so based on this two (non scientific) observations the charging power is depending on the Start-SOC Value and the Temperature. It is so weird. Another R90 driver observed the same thing, therefore I think I can post this here without getting declared as completely nuts.

    • Since we discussed, I was occasionally recording SOC/Temp/Max Charge Values of my R90. The result of the so far 100 points you find below. The values are really used when charging, but are sometimes a little lower since the Max Charge Power seams also to depend on the actual DC Power to the battery. However, I am not able to define much more to this observation.
      So far, with this diagram, all the charging curves can be explained. So having a very long “over the spec” charging cycle, the Zoe was actually cooling down the battery from 26°C to 18°C, thus extending the charge above approx. 55% SOC. In another charge, the spec was reached, there, the charging started @14°C and ended @26°C without actual cooling (as far as I can tell).
      However, I did not find any dependence of this values to the Max Regeneration Power. It seams to be limited to the Max Voltage only (but has not been tested below 4°C)

      http://www.spider.li/zoe/Max_charge_power_170406.png