L2 Charging Profile

[v_traveller]

Below is a screen capture from a Chargepoint charging session; it's typical of what I've been seeing on a daily basis. Charging station is 208/240V 30A.

Max charge rate is at ~5.8 kW, starts dropping just about when myfordmobile reports 99% charged. Takes about 20-25 minutes to drop to ~0kW. From the time is drops from 5.8kW to 0kW, Chargepoint shows ~1.2kWh consumed, but myfordmobile only shows an increase of 1% (to 100%) and an increased range of 2 to 3 miles (typically 100-110mi total range is indicated), so apparently there seems to be some inefficiency in getting that last 0.2-0.5kWh or so into the battery.

This means that at $1.00/hr while hooked up to the Chargepoint at work, I'm paying about $0.50 for that last 2 to 3 miles of charge. Not very cost effective - equivalent to about $1/kWh.

I don't need a full charge to get home, so now I unplug before the rate of charging starts dropping, unless I'm stuck in a meeting or something.

Just food for thought for those of us that have to charge away from home and pay for it, especially if you find yourself stuck using a $2/hr charging station (i.e. Walgreen's)...

 

[francishsu]

Your findings are interesting, because a couple of days ago I had plugged it in when it was already at 99%. For some reason, MyFord Mobile kept reporting it at 99% after quite some time (more than 30 minutes) with a "Waiting to charge" status, even though I had it set at Charge Now. Also, the light on the Ford EVSE was blinking, indicating it was still charging the car. Tried disconnecting and reconnecting the charger, but it wasn't making a difference. Finally just disconnected it thinking (hoping) it was just a glitch, and later drove it. When I plugged it back the charging behavior returned to normal. i.e. MyFord Mobile reported it as "Charging" and it reached 100% eventually.

 

[WattsUp]

It would be interesting to know if this "slow down" phase is somehow important to the battery charging process, on the off-chance that purposely circumventing might do more harm than good.

 

[v_traveller]

I figured it's safe to cut off charging before reaching 100% because (1) there's nothing in the owner's manual that says doing so is detrimental, and (2) one of the prevailing tips for prolonging Li-ion battery life (whether the battery is for an EV or handheld device) is to avoid fully charging if you can afford to do so.

See Tip #5 of the following:
http://insideevs.com/understanding-battery-capacity-loss-from-a-four-year-bmw-electric-trial-veteran/

Also, for an explanation of that "slow down" phase (referred to as "saturation charge"):
http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries