Battery Cell Voltage when Charging to 100%

[FrostyCanada]

Hello fellow iMiEV owners, can someone please confirm if our batteries go beyond the 4.0 volts per cell ( when charging to full at 100%)?

I think I read a past thread saying that we have a small safety margin built into the charging protocol that avoid stressing the batteries when going to 100%?

I usually charge from 2-4 bars and stop at 14-15 bars using the stop timer on our remote.

20% - 80%

I also noticed some posting voltage readings beyond the 4.0 volts.

I'm just wondering if it's beneficial to manually charge my battery using the 20%-80% + also going from 2 bars to full from time to time.

Brian

 

[PV1]

Obviously, the closer the pack stays to 50%, the better. The max charge voltage for lithium ion is 4.2 volts. The car stops charge at 4.105 volts per cell, so there is still room to continue as far as the cells are concerned. Stopping charge at a stated 80% SoC puts you just below 4 volts per cell, which improves cycle life even further.

As to if there's benefit, of course there is. The car is programmed so that letting it go to "full" charge and stopping automatically isn't severely impacting cycle life. The spec sheet on the LEV50N cells suggests a 15-year life, cycling the battery once per day (full discharge and recharge). Whether or not that figure includes the i-MiEV's charge profile or not, I don't know, but that 15-year rating is to 80% original capacity which is very good longevity.

Personally, I always let my car charge to full, but I drive it within a few hours of full charge. It does need to go to full every now and then though for proper balancing.

 

[kiev]

...The car stops charge at 4.105 volts per cell, so there is still room to continue as far as the cells are concerned.

i was curious about this very thing a couple of weeks ago and measured this with CanIon, and got the same result. So i feel much better about letting it go to full on it's own and not worry about it holding the cells at '4.2', since in fact it never gets there.

The published data on the loss of capacity from holding at 4.2 was from a long-term test that was looking at 'storage' of a cell at the high voltage for a one-year period. That is totally different than charging to 4.2 overnight and driving the next day.

Neither Mits nor Tesla charge to the full 4.2 vpc, but i think it is for other reasons than avoiding 'storage' capacity loss, e.g. regen capability with a full pack, a safety margin during charging, etc.

 

[PV1]

Yes. If they would charge to 4.2 volts, then you would have no regen for the first few miles. The i-MiEV will allow up to 4.15 volts with regen before seriously ramping it down (measured when descending a borderline cliff coming home from 7 Springs). I'll have to look at the data to confirm that number, but I believe that's what it was.

Battery longevity and regen are the reasons, I believe.

 

[FrostyCanada]

Hello PV1, thank you for explaining this.

Have a great day,
Brian

 

[FrostyCanada]

Hello PV1, from your experience what would be the 20% to 80% mark on our battery indicator?

20% = 0 or 2 bars?

80 % = 14 bars?

Any feedback would be appreciated,
Brian

 

[PV1]

20% is 2 bars, and 80% is the boundary between 13 and 14 bars. When I leave a quick charger, I start with 14 bars, but almost immediately drop to 13 bars.

 

[blackheart]

I have a question - I have only had the car for about a month, and for a week of that I was on vacation so I have only logged about 500 miles on the car. I've been loving it - but reading items about battery health and temps, etc - have me concerned. The care is a 2012. It was a lease return with about 1700 miles on it. I have had some issues getting Canion to stay up and running. I have had some success lately and I have saved screen pics of the battery voltages.
I see .005-.01V difference between cells and the voltage is only about 3.85. If standard voltage is supposed to be up around 4, it looks like I have lost about 4% of my battery.
Can anyone help me in looking at this?
Thank you
https://www.dropbox.com/sh/9gousmxgup5g84h/AABuY8JwyH6R0QjqkanAcS9ya?dl=0

 

[JoeS]

blackheart - your readings look good to me. What happens when you slowly fully-fully charge and it shuts off? You should see 100%, 360vdc-361vdc, and all cells balanced at around 4.100v-4.105v. I would not be too fussy.

 

[blackheart]

Thanks JoeS,
I will charge it up over the weekend (when I get it back from the dealer for the recall service and programming my remote) to a full capacity. I have the EVSEupgrade so I should be able to adjust the charging down to a near trickle and "fill'er up". Then I will take a reading and see where the readings are at.

Thanks!! So much to learn ;-)

 

[Malm]

I don´t see any problem in your car. In a full a charge cells can go to 4,105/4,1V, but can be arround 4,08/4,09V too, no problem with that. And can stop charging a little behind 100%, no problem with that too.

 

[blackheart]

Well, I didn't get to trickle like I wanted to - the dealer ended up keeping the car over the weekend so I could only drive it home, plug it in, and be ready for the morning. The good news is that they were able to program the remote.
I have been trying to plug in the car when I get home, calculate how long it will take to charge for a near full battery in the morning (in case I need to do more than just run home). This morning, I was checking on the charging and I noticed this one cell being hotter than any of the others.
https://www.dropbox.com/s/f2gnayl1gotwy0f/Screenshot_2016-04-27-07-00-06.png?dl=0
Anyone have any thoughts?
It stayed up like that pretty much the whole drive up to work. I am going to go out and check at lunch. But you experienced Miev'ers, can you help me out?
Thanks
rm

 

[kiev]

Maybe that cell is close to the exhaust pipe and getting hot...lol

if it is doing this all the time and about 5 degrees above all the rest, i would suspect an instrumentation/sensor/circuit issue rather than a bad cell. The temperature sensors are located on a circuit board that is held above the cells and attached to the cell terminals with screws. i don't have any specs on what the tolerance should be for this circuit, e.g. +/- 5%.

Any sort of out-of-tolerance of resistors in the sensor circuit could give a little bias or offset from the nominal reading and produce results such as you have seen.