Cooling the Zoe battery

There are many misconceptions about fast charging. One being that “the battery should be as cold as possible when fast charging”. I mean, when hooking up the battery to a fast charger, all these fans start to run right? So it must be true. Like so many assumptions, unfortunately it isn’t. Zoe’s Batteries are very, very happy when they are over 25C and actually, when they are colder than that, the BMS will rightfully cap the maximum charging power. 43kW fast charging a pack that has been freezing overnight to 0C would almost certainly damage it beyond recovery.

Having said that, overheating the cells, that will still happily charge at a temperature of over 40C **), is a very, very bad idea. Renault implemented a pretty clever solution for that, installing an extra evaporator of the climate system in the air inlet of  the battery compartment, which is why you not only hear the battery fans kicking in, but also the climate control when fast charging.

Which of course leaves the question, why would the car do that when fast charging and the cells are way below that happy temperature of 25C and higher? Well, consider that about 10% of the energy is lost to heat *) when fast charging the battery, that is over 4kW of heat being generated, which is substantial. The car is simply using a pre-emptive strategy, blowing cooled air over the batteries. If that annoys you (those fans can really “take off”), simply put the car in ECO mode before powering it down. The climate system will not kick in now kick in at a much higher temperature. And of course, the batteries will heat up faster. Which might or might not be a good idea really. Some chargers do not appreciate the interruption of the charging process and ECO mode might avoid it.

*) some say full cycle energy loss in LiPo is 3%. While that can be true under ideal circumstances, 43kW (2C strategy) is not that.

**) Masoto Uriguchi, battery engineer at Renault states the batteries are happy up to 60C, but should not be taken above that.

Posted in ZOE
11 comments on “Cooling the Zoe battery
  1. PieterZoe says:

    Thanks for sharing insights on temperature and charging capabilities of the Zoe battery. Those of us who use CanZe have already noticed the improvement in fast-charging speed during this ‘winter period’ when the battery temperature has increased after a longer drive.

    One would expect temperature control during charging to be autonomously managed by the car. Hence it surprises me that the ECO button has an impact on the cooling management during charging. Is this deliberate choice of the manufacturer or is it simply an omission in the software design? In case of the former, what would be the rationale? ECO-mode extends the range while driving. In the colder seasons it may shorten the charging process because it allows for a faster warming up of the battery. However in warmer seasons this doesn’t make sense as the battery is already at its optimal temperature after a longer drive.

    Note that fan and cooling do work during fast charging in ECO-mode. Apparently only the preventive cooling seems to be limited in ECO-mode.

    Any thoughts on the rationale?

    • Jeroen Meijer says:

      First of all, you are right the ECO mode does not inhibit the cooling of the battery pack, but it sure seems to change the temperature setpoint at which cooling kicks in. I will change that in the main post. I do not have enough data to make a somewhat reasonable statement about the value of those setpoints. As for logic, the general idea seems to be: start cooling relatively early as the cooling can’t keep up with the rise in temperature. It makes sense, though my feeling is the normal setpoint is very low. Those batteries are happy up to a temperature of at least 40 C and charging them with 2.5C power isn’t too crazy really. It is almost like the reasoning is: well, when you’re in ECO now, you’ll probably be in ECO when you’re on your way, and as that limits your power, we can end the charging on a somewhat higher temperature. It is a bit of a far fetched reasoning, but at this moment, I can’t make up a better one.

  2. Harm says:

    Could the setting AirCo on/off also have influence on the cooling of the battery?

  3. Jeroen Meijer says:

    For sure no cooled air is send from the dash into the battery. But it has an evaporator at the battery air entrance that is connected to the primary coolant circuit. IOW, cooling capacity really IS taken from the climate system.

    As I said, I am not privy to the gory little details, but the car can decide to not use the battery fan, use it without cooling, use it with cooling, and all probably in different modes for charging an driving. The bus messages are not totally baffling, but let’s say “rather complex”.

  4. Borut says:

    In winter time Zoe should pre heat the battery from the grid, it would extend the range for 2 to 3 kwh,since that is the amount of energy lost durring battery self heating in long trip, because of high internal resistance.I’m thinking of installing a hair dryer in to batery’s air intake.
    Is someone else thinking the same ?

    • Jeroen Meijer says:

      Nice idea! Not easy to heat up 200 kg of material though 😉

    • Harm says:

      How will you make sure, the hot air is actually blown through the battery compartiment? You probably need to activate some fans to do that. Then you also need a 230V outlet that can deliver around 2000W. What about warranty?
      You can also buy the new Zoe Q90/R90, which can preheat the batteries with the more efficiënt heat pump.

  5. Bjarte Olsen says:

    My experience is that if you enable “pre-soak” at a time of more than about 3 hours from current time. The battery will also be pre-conditioned.

    Still, would be Nice if Renault would implement the new temperature management of the new 400 models into Q210/R240…

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