Charging ahead.

I’ve spent a little effort recently watching charge rates on LeafSpy.  Rates for Screenshot_20170720-185900#JourneyCharge are set by the car and communicated to the charger.   Not all chargers are equal as it turns out.  The screen grab below shows a recent charge at the Forth Road Bridge.  The nominal DC charge rate for the Leaf is 44kW.  The value shown on LeafSpy is from the metering on the Leaf.  There is another screen available  which shows charger output against what the car has asked for.   The chargers all seem to deliver above the level instructed, but they fluctuate a bit during charging.

On the Leaf the charge tapers, the charge rate is reduced by the car as the battery nears full.  On the 24kWh Leaf this  typically begins at about 80%, on my 30kWh it is a much less aggressive taper, on a cool battery it only drops below 35kW at about 94% charge, below 6.6kW at around 98%. So that last 1.7kWh is the slow bit.

Looking at peoples experiences with Tesla batteries of various sizes a very similar set of characteristics for the last couple of kilowatts, when being range charged up to 100%.  Not surprisingly the graphs for charge rates on Supercharging show the taper beginning at a lower level, but being a very gentle reduction, not dropping below 30kW until again around 90% of charge. Simply put the bigger the battery the .the higher current can be maintained.  So a Tesla on a Chademo adapter should maintain above 10kW to about  98% State of Charge.

The BMW i3 33kW is almost identical to the Leaf, but will reach 50kW, but has a linear and slightly more aggressive taper after that.  The higher rate will mean that the i3 will win the range per minute race.Leaf vs i3

So the performance is best described in terms of the state of charge, but there will always come a point when you would be faster moving the car over onto a lower rated charge system, as the charge will actualy be maintained at a higher level longer.

The upshot of all that is that if you are using a #JourneyCharger, there is going to be point where you’d gain more driving to the next charger, somewhere between 80 and 95% for most cars with Lithium batteries.  Certainly the last couple of kW just aren’t worth waiting for.   It will save you time on your journey, with the proviso that you plan your route with options.

eva.scot

 

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njel13

Engineer, EV driver, dog owner.

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