Chargepoint Starts and Stops, 14.07 kWh from one bar

[burnabyimiev]

I've had my 2012 miev for a month now. Today I pushed it to a single flashing bar for the first time before charging. Chargepoint tells me I used 14.07 kWh to fully charge (see picture). That seems lower than I expected--did I really have almost 2 kWh of power left before running out of juice completely?

Another question: after 30 minutes, this Chargepoint station stops charging for about 15 minutes, then starts up again. Has anyone else seen this? Another Miev driver experiences the same thing consistently at this station.

https://www.dropbox.com/s/i1c5zdciovo2ubg/Screen shot 2014-03-19 at 3.36.51 PM.png

Apologies, I haven't figured out how to add an image yet--I hope the dropbox link works.

 

[JoeS]

burnabyimiev, your charging curve looks very normal. The charging system normally takes a 'timeout' which can last anywhere from six minutes to over 20 minutes. It is theorized that this 'timeout' is for the battery management system to assess how much sag occurred with power removed before proceeding.

You need to recognize that there is a power conversion loss associated with charging the car. I don't remember what we finally came up with for the iMiEV, but let's say 90% using 240vac: if you measured 14.07kWh going in, you only put in 12.7kWh into the battery pack, which is even less than you thought! I wouldn't worry about it. Now that we have CaniOn, we see that there is quite a bit of 'safety' residual energy left even though the fuel gauge is down to zero. BUT - you don't want to go there, as running on empty is deleterious to battery health - think of it only as an emergency backup fuel source.

Edit:

Reflecting further, your one bar means you had less than 2kWh 'visible' left in your pack, and add that to, say, 2kWh emergency reserve and add that to the 12.7kWh you put back in and you're somewhere around the nominal 16kWh battery capacity. No worries!

Ah, found it: here is a set of Canion readings for number of bars vs. SoC: http://myimiev.com/forum/viewtopic.php?p=13018#p13018

 

[burnabyimiev]

Thanks, this is helpful and reassuring.

Chargepoint seems to have trouble with the pause in charging, though. The vehicle continues to get power, as shown by the curve, but the phone app says "vehicle not charging" as soon as the pause starts...and says that for the next 5 hours. Likewise, the chargepoint.com desktop dashboard shows the car as "charged", not "charging" after the pause.

 

[Barbagris]

Others graphs of charge I see on a quick search:

At right:

The pause is usual.

 

[Malm]

I've had my 2012 miev for a month now. Today I pushed it to a single flashing bar for the first time before charging. Chargepoint tells me I used 14.07 kWh to fully charge (see picture). That seems lower than I expected--did I really have almost 2 kWh of power left before running out of juice completely?

Another question: after 30 minutes, this Chargepoint station stops charging for about 15 minutes, then starts up again. Has anyone else seen this? Another Miev driver experiences the same thing consistently at this station.

https://www.dropbox.com/s/i1c5zdciovo2ubg/Screen shot 2014-03-19 at 3.36.51 PM.png

Apologies, I haven't figured out how to add an image yet--I hope the dropbox link works.

One bar appears at 17% SoC. I think we cannot go down to less then 4%. You had only 13% left, so 2 kWh usable. From 17% to 100% it should use 15.6 kWh from the charger. If it taked only 14, it has less 10% then the original capacity.

 

[Malm]

Now that we have CaniOn, we see that there is quite a bit of 'safety' residual energy left even though the fuel gauge is down to zero.

That's not what I saw in my I-MiEV. I allways take a look with canion. And I stopped some times with one bar left. So, I will not be so sure to have there 2 kWh to use.

 

[FiddlerJohn]

... One bar appears at 17% SoC. ... From 17% to 100% it should use 15.6 kWh from the charger. If it taked only 14, it has less 10% then the original capacity.

Checking the arithmetic:
If 100% is 16kWh
& 17% is 2.72 kWh
then 100% - 17 % = 13.28kWh

The battery could take 13.28kWh from one bar to full and some slightly larger kWh from the Chargepoint station. If the iMiEV charger is 95% efficient, the Chargepoint station should read 14 kWh for 13.28kWh into the battery.

There is also the iMiEV's 12 VDC overhead lost while charging which might be a few hundred Watts.

 

[Malm]

"If the iMiEV charger is 95% efficient". The difference with my arithmetic is that I used 85% efficiency. Maybe not so innefective. But I think less then 10% total lost cannot be true. So, one number between 10 to 15%, maybe 12,5% should be a reasonable number.

A loss of capacity of 7% in two years, in a place with medium annual temperatures over 12,5º C will be normal. I know that many of you think that i'm wrong (and i would be very happy with being wrong), well, only time will tell, but don't forget, i'm from the future.

 

[Zelenec]

When I charged from not moving car (tired turtle) to 100%, I spent 18.4 kWh, so I agree with Malm using L2 charging all losses together are more then 10%.