Posts: 237
Joined: Mon Jun 06, 2016 12:24 pm
Location: Bottom right hand corner of Wales

Re: DC Rapid Charging - sort of a quiz question

Wed Jun 07, 2017 10:08 pm

Appreciate that Bob.

The point of asking was that I wasn't aware of circumstances where the car would ask for less power than was available (other than at the full end of the charge cycle) and replies I've got here and elsewhere show many examples of cars charging flat out from as low as 6% SoC.

The unit was a 50kw Rapid DC on CCS and I therefore expected it to deliver accordingly. It appears it didn't.

What I am trying to understand is whether the provider's information has any merit and should I be thinking of more regular charging stops on warm days with long journeys or is that a complete red herring.


Posts: 2121
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: DC Rapid Charging - sort of a quiz question

Wed Jun 07, 2017 11:09 pm

A warm day in Wales would be a mild day in many southwest U.S. locations where E.V.'s flourish and reports of slower than expected DC fast charging are rare. The i3's battery pack cooling system should totally prevent heat-related slow charges in milder climates like in Wales. The charger itself could overheat, but in a milder climate, that would almost certainly be due to a fault.

Battery pack protection occurs at high, not low charge levels (at least according to the charging power vs. charge level charts I've seen). So that excuse seems bogus.

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

Posts: 5034
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: DC Rapid Charging - sort of a quiz question

Thu Jun 08, 2017 1:34 pm

A hot battery should not be rapidly charged. The i3's logic won't let it happen. Charging does create heat, and the faster and longer you do that, the more heat is generated. Rapid or sustained high charge and discharge rates warms the battery pack.

Even if the CCS unit is in the high 90% efficiency range, if it has 50Kw output, it will be making some serious heat! They, like the internal components in the car, must manage their temperature. Assuming the CCS unit's cooling fans and filters are not compromised, depending on how hot it is, it just may end up overheating and reducing its output. THrow a solar load on it, that can just complicate the issue. Whether the thing had just finished a charging cycle on someone else when you arrive, could be a factor verses it sitting there idle for hours.

Much higher current rates are coming, and that will just make it even harder. Newer battery tech seems to have less internal resistance, so that bodes well since it won't create as much heat. THe future looks more promising when it all starts to come together. Ideally, you'd draw power from the electric roadway, and never need to stop and recharge the vehicle. That too, may happen outside of test tracks.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above

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