How Many kWh in a Full Charge?

Check out my thread:

Ok, I went to Consumers Energy ChargePoint station today. Here is the results.

Read more: http://priuschat.com/threads/attention-kill-a-watt-nerds.113900/page-3#ixzz2GqeK5NyO

 

During the summer I found that charging at home (120v) a full charge from 0.0 miles remaining would take 3.0 kwh (KAW). At work with ChargePoint (220v) it was 2.88 - 2.95 kwh. In the last 2 weeks I've seen only 2.78 kwh from the ChargePoint (3 times almost exact same results), including today when the temp was ~45F.

Some possible explanations for the change:
1. battery has less capacity now (unlikely after such a short time...only 6 months with a 10 year expected life))
2. more efficient to charge when the outside temp is lower
3. programmed behaviour based on outside air temp

Mike

 

how does all this relate to the 15% charging losses people talk about?

 

another possibility is that in the cooler temps the battery is not discharged as low before the vehicle switches out of EV mode. I suspect that at the lower temperatures the KW flow is reduced due to slower chemical reactions so the computer recognizes the lower KW output and switches out of EV.

the more I think about this, the less I think it is the case though. you should still be able to draw down the HV battery under lower loads.

 

my vehicle switches out of EV at 18% SOC

 

the SOC is not like measuring the fuel level in the gas tank. there are competing algorithms and methods for estimating the SOC of a battery like the PiPs. I think temperature affects the accuracy depending on the method. If the switch to EV is always at the "18% mark" regardless of the energy actually available, that could explain the range of kWh needed for recharges.

 

I'll have to set up my testing equipment when my EV range is at .9 miles or lower to compare results to my summer data. I'll get back to you.

 

I have noticed the charging went from 2 hours and 34 minutes last summer to 2 hours and 42 minutes the other night.

 

same voltage as the summer? I remember you had some low line voltages in the summer.

 

my data logger was about 6 volts off. I used my Battery Back up readout and a Fluke Multimeter to calibrate the logger. I did a reading with the data logger and posted it at Attention Kill A Watt Nerds thread.

 

I'm curious about this too. I charge my car at work. The charging system keeps an online record of how many kWh are going into my car each time I use the charger. I bought the car in June 2012 and started using the charger in July 2012. In July 2012, a full charge (according to data from this charging system) was around 3.4kWh. It's been decreasing slowly and steadily since then so that now it's around 3.1kWh.

 

Is this 110v or 220v. ChargePoint, Blink, or ??

3.4 kwh is a lot.

Mike

 

I don't know where the 15% number comes from. (i.e. actually measured or from some white paper). It is related, only in that one of my made up possible reasons for the decrease in kwh to do a full charge is that, maybe, the charging losses are less when the outside air temp is cooler.

For example, with 220v from Charepoint I would normally see 2.9-2.95 kwh to do a full charge. And if you accept the 2.7 kwh published by Toyota as the useful range of the battery, this would mean about 6.8%-8.4% is lost (0.2/2.9 and .25/2.95). Now I am seeing (last 3 charges) about 2.8 kwh to charge. So the losses would be .1/2.8 or 3.6%. This seems way too good. Thus my question on why the change. Maybe the battery accepts a lesser charge when it is colder, by design. Maybe the measurement isn't as accurate when it is colder.

I'm not going to heat the Chargepoint station outdoors to find out. And it seems unlikely that they would accept a watt meter design that is off by 3-4%. Certainly home utility meters must be at least within 1% at all expected temperatures...right?

Mike

 

The chargepoint measurement should be fairly accurate. The charging losses are in the vehicle, at the onboard charger, not at the chargepoint station. the losses are generated heat so at cooler temperatures you would expect some lower losses in the charging circuits but other limits in the ability of the battery to absorb the charge are probably kicking in at those lower temperatures as well. the battery warms up some during charging. some of the increased kWh consumption during summer charging may also be to run cooling fans on the charging circuit that don't need to run in the cooler temperatures.

 

15% is just what i've heard others throw around. i've been assuming 3.15 kwh/charge for the spread sheet. i.e. i've been multilying the cars reported kwh used times 1.15.

 

110V. The charging system is not chargepoint, blink, etc. I work at a university. The charging system belongs to the mechanical engineering department (which makes me think their measurements are accurate). They are studying EV infrastructure and I charge my car on their system. I get free charging and they get to further their research, so it's a win-win!

 

The battery has a lowered ability to hold a charge in cold temperatures so you see a reduction in usable range while driving. Because less battery power is available and used during driving, there is less charge required to recharge an empty battery (and it just can't hold as much because it is cold).