How to figure cost of electrical charging

that's why people are saying 3-3.3kwh.

 

Here's this mornings charge session data from ChargePoint (this is 100% typical for my daily charge) Data point- My EV range was exhausted about one mile from the charging station, so this represents a full recharge from 0 EV miles:



The graph data also shows the bulk of the recharge is completed in the first 70min...

 

This is cool to see for us non-plug in guys (but wannabe's). Why does the charging...for lack of a better word...slow down closer to the end?

 

it also drops to zero amps eight times during the charge cycle and resumes full amperage

 

it would be interesting to see if VOLT charging has the same characteristics

 

It's to avoid over voltage. Once, you get close to full charge, you're near maximum voltage. The computer slows down "charging" to avoid going over and causing damage to the battery pack. I liken it to pouring yourself a glass of water. Initially, you just pour it in. But near the end, you have to slow down so that it doesn't slosh over the edge. The battery is completely enclosed, so you can imagine what would happen if you continue to "slosh" in electricity.

 

It is also a safety issue with LiIon batteries. Overcharge them, even at the trickle level, and they outgas explosive gas (hydrogen, I believe). Add the heat from the charging, and,.... you get the picture. That is why consumer LiIon batteries like in laptops and cell phones have circuitry in the battery itself to prevent overcharging.

 

So it's the car that is causing the slowdown, not the charge point? And is that charge point 220 or 110?

 

i turned my car on today to see how much charge it had taken. it had 12.4 miles on the range meter, said it had .8 hours left to charge and was charging at 1 kwh.

 

yes, it's the charger in the car

 

It's 240v

 

Don't forget that the HV portion of the capacity can also be replenished by the plug. That's why had been rounding up when it came to per-charge estimates.

3.0 kWh is what I've been seeing quite consistently from ChargePoint, even when having dipped into HV for a bit of stealth. That works out well for simple cost math.

 

As the batteries get to be almost full, its important to reduce the charging current to protect them from damage.
Think of it as filling a glass.. if you want to get to 100% full, you slow down as you get it nearly full so you have better control.

in a Parallel battery config, as in the PiP (and Volt and Leaf), its also a time when they do some balancing between the cells in each parallel config.

I think the Drops that Prius Kitty is seeing are likely the car "checking" the current SOC to get more accurate read -- its not possible to accurately estimate charge level while charging.

 

Wow, cool to see two people make the same analogy lol.

 

or a chargepoint station.

most chargepoint stations have a 110V outlet as well if someone wants to capture a standard L1 EVSE session.

 

I'll try to grab a screen capture tomorrow. It won't be for a full charge, but it should be a complete charge.

These comparisons to overfilling the cup of water seem out of place. Isn't the PiP leaving a buffer at the top end of the SOC, about 15% or so? Do you need to throttle the current at 85% of SOC or is something else kicking in the throttle, like the temperature of the pack?

 

Generally the first 80% get charged quickly and then it goes much slower from there. So perhaps it's that final 5%?

 

Here's a pic from Apple: http://images.apple.com/batteries/images/chargechart_20090106.gif
Note how the slow charge basically takes as long as the fast charge. The ratio is not quite as even with the chart posted earlier.

 

On Long Island LIPA is about 22 cents a kilowatt for both electric and delivery combined so roughly .66 each charge. Which if you are paying avg of $4 a gallon of gas. It is probably cheaper to just not plug in. I do plug in though because I have solar electric on the house and it makes sense.

 

Since they don't get anywhere near the 100%, its not that much of a safety issue at all.

Sorry I got distracted then said filling it 100%. I ment the the analogy of trying to fill a glass to exactly 85% (Or any fixed level). If you want to hit a particular mark you need to go slower, as you repeatedly measure where you are and where you want to get. Since the act of poring fast (charging fast) is also impacting your ability to measure its better if that is slower.

Temp does make it slower and after its been charging it does accumulate more heat and need to slow down for that, but that is more of an impact on slowing down the "faster" charging part.
You can see a plot of charging data in this thread at GM-volt.com
TED 500 graph of two 10 min precond on 110v & 220v

And one with temp
Graph of data points from a remote start