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Re: Phoenix Range Test Results, September 15, 2012

Posted: Fri Sep 21, 2012 7:21 am
by WetEV
kolmstead wrote:drees wrote:

There's only two things that might cause one car to turtle at 350V and another to turtle at 290V.

1. A software problem. No further explanation needed here.
2. At least one cell-pair with significantly lower capacity than the rest - one cell-pair hit the low-voltage limit and the BMS shut the party down. Should be easy to check with a Consult by taking this car down near turtle.
-----

If we know the voltage at which a battery with all good cell pairs goes to turtle, then anyone with Gary's SOCmeter can run to turtle and check pack voltage. If it's significantly higher than normal, you have one or more bad cell pairs, which would be a warranty issue.
Or that the pack is out of balance. Need to charge and not drive right away, at least occasionally.

Re: Phoenix Range Test Results, September 15, 2012

Posted: Fri Sep 21, 2012 7:22 am
by azdre
kolmstead wrote:drees wrote:

There's only two things that might cause one car to turtle at 350V and another to turtle at 290V.

1. A software problem. No further explanation needed here.
2. At least one cell-pair with significantly lower capacity than the rest - one cell-pair hit the low-voltage limit and the BMS shut the party down. Should be easy to check with a Consult by taking this car down near turtle.
-----

To me, this could be the most exciting news from the Tempe test. If we do have one or two cell pairs failing, all it will take to demonstrate this is to run the car down to VLBW or better still, turtle, and have the dealer perform a cell pair voltage check. But it is crucial that the car not be charged before this is done. My experience has been that the first thing the dealer does with a low SOC car is charge it up. My car, which turtled on the way to the dealer in January, was up to 70% SOC before they did cpvc.

If we know the voltage at which a battery with all good cell pairs goes to turtle, then anyone with Gary's SOCmeter can run to turtle and check pack voltage. If it's significantly higher than normal, you have one or more bad cell pairs, which would be a warranty issue.

-Karl
We did this on one of our 362 battery tests that were done (one of 2 cell tests). I drove the car into the dealership, hit VLBW as I was pulling in to the service drive. This was also a day when some engineers, techs, and middle managers were in town back in July, and I think there were there to observe the test. The variance was 23 mV. I think the acceptable tolerance is 50 mV.

Re: Phoenix Range Test Results, September 15, 2012

Posted: Fri Sep 21, 2012 7:40 am
by RegGuheert
azdre wrote:We did this on one of our 362 battery tests that were done (one of 2 cell tests). I drove the car into the dealership, hit VLBW as I was pulling in to the service drive. This was also a day when some engineers, techs, and middle managers were in town back in July, and I think there were there to observe the test. The variance was 23 mV. I think the acceptable tolerance is 50 mV.
Thanks for that data point!

Perhaps at that time your pack was degraded but no cells were failing or perhaps the dealer did not do the test properly. If they charged the car before the test, that could cause the result they reported. The Nissan LEAF battery is top-balanced, which means that if there is a difference in the capacity of the cells, it will not show up near the top of the range but it will show up near the bottom. (The test procedure specifies discharging the pack before the test, but that doesn't mean they always do it properly.)

BTW, what was the voltage of your battery at turtle in the recent test?

Re: Phoenix Range Test Results, September 15, 2012

Posted: Fri Sep 21, 2012 9:23 am
by turbo2ltr
There's only two things that might cause one car to turtle at 350V and another to turtle at 290V.

1. A software problem. No further explanation needed here.
2. At least one cell-pair with significantly lower capacity than the rest - one cell-pair hit the low-voltage limit and the BMS shut the party down. Should be easy to check with a Consult by taking this car down near turtle.

I'm not sure why people are connecting voltage with capacity.

I can show you a pack that has 400V but won't get you down the block, and one that has 290V and will drive for 100 miles.

Who told you the BMS shuts the party down when one cell pair hit a low voltage limit? How do you know the whole pack doesn't have a much higher internal resistance and just has a higher open circuit voltage? Is the voltage we get from the BMS correct? Is it calculated? Does it compensate for temperature drift? Did you see the BMS code? Do you know what it's doing?

And I'm saying "you" as in everyone.


I'm getting tired of all these theoretical and speculative discussions. Batteries are not an exact science. Calculating open circuit voltage and coulomb counting is not easy. There are more variables than you can ever imagine. Nobody knows anything. Things are much more complex than everyone thinks they are. There are a few people on here that know this...and they are the quietest.

I can't believe how much time people waste arguing stuff they have no clue about.

Re: Phoenix Range Test Results, September 15, 2012

Posted: Fri Sep 21, 2012 9:43 am
by RegGuheert
turbo2ltr wrote:Who told you the BMS shuts the party down when one cell pair hit a low voltage limit?
I think Phil did, but perhaps I am remembering incorrectly. Let's just say that the car measures it, so let's hope that's what it does.
turbo2ltr wrote:How do you know the whole pack doesn't have a much higher internal resistance and just has a higher open circuit voltage?
That's another possibility. It might explain the fact that Azdre's car did not fail the CELL VOLTAGE LOSS INSPECTION.
turbo2ltr wrote:Is the voltage we get from the BMS correct?
Yes. Phil has verified that it is within about 0.5 volts of a calibrated high-accuracy Fluke voltmeter each time he has measured it, including once this week. He also stated that the high-voltage voltmeter in the LEAF cross-checks itself against the low-voltage meters and the car throws codes if there is disagreement.
turbo2ltr wrote:Is it calculated? Does it compensate for temperature drift? Did you see the BMS code? Do you know what it's doing?
It might do all of those things, but the number coming out through the meter apparently matches absolute voltage very well.

Re: Phoenix Range Test Results, September 15, 2012

Posted: Fri Sep 21, 2012 10:00 am
by TonyWilliams
RegGuheert wrote:BTW, what was the voltage of your battery at turtle in the recent test?
Before you guys get too excited about the partial information I gave, two of the cars did not hit turtle (that was my command decision as the last cars were arriving, and we'd already damaged 4 during tows). Not all the drivers got the final voltage, because the Gidmeters were set on Gid # or %.

Here's the list:

LEAF --- CapBars- miles-M/kWh-Volts ---GOM
Red429 --- 10 --- 71.8 - 4.3 - ----------74
Blue494 ---- 8 --- 59.3 - 3.7 - ----------56
Blue534 --- 10 --- 75.7* - --- - 315.5----74 (ECO=84) (*Data edit 75.7 for typo)
White530 -- 10 --- 69.7 - 4.0 - ----------73
White272 -- 10 --- 66.1 - 4.4 - ----------68
Red500 ---- 9 ----73.3*- 4.4 - -342.5*---66 (*No turtle; 2 miles >VLB: Added 4 miles)
White626 --12 ----73.5 - 4.3 - -317.5----73 (CapBars were 10, reset 12, now 11)
Blue842 ---12 ----79.6 - 4.1 - --------- 76
Silver679-- 10 ----71.8 - 4.2 - -303.5--- 75 (18.2 miles after LBW)
Blue917--- 10 ----72.5 - 4.1 - -310.5 ---67
Black782-- 12 ----76.6 - 3.9 - -295.0 ---88ECO (Out4.0/In3.8; LBW 6.9, VLB 6.5)
Blue744 ---9 -----72.3*- 4.4 - -352.0*-- 63 (*No Turtle; 1 mile after VLB; added 5 miles)

Re: Phoenix Range Test Results, September 15, 2012

Posted: Fri Sep 21, 2012 10:03 am
by RegGuheert
TonyWilliams wrote:Before you guys get too excited...
Thanks, Tony! We'll try to contain ourselves! :)

Re: Phoenix Range Test Results, September 15, 2012

Posted: Fri Sep 21, 2012 10:34 am
by TickTock
Did we fail to capture mpkwh on Blue534?

Re: Phoenix Range Test Results, September 15, 2012

Posted: Fri Sep 21, 2012 11:24 am
by DaveEV
turbo2ltr wrote:How do you know the whole pack doesn't have a much higher internal resistance and just has a higher open circuit voltage?
An increase in internal resistance doesn't change voltage at rest. It will result in a decrease in voltage under load and an increase in voltage when charging.
TonyWilliams wrote:Before you guys get too excited about the partial information I gave, two of the cars did not hit turtle (that was my command decision as the last cars were arriving, and we'd already damaged 4 during tows). Not all the drivers got the final voltage, because the Gidmeters were set on Gid # or %.
The cars who did not hit turtle should have their results removed. If you want to show the data that was obtained, it should be with a huge * that those cars did not go to turtle and their results have been adjusted. Adding some arbitrary distance to their results is misleading at best unless you've performed a study on these low-capacity cars that conclusively shows the distance a car with the same number of bars will travel between VLBW and turtle.

If you were basing your earlier comments of 60 volt difference between cars at turtle by including these cars, then that's completely misleading since voltage of the pack starts dropping rapidly after VLBW is reached.

Re: Phoenix Range Test Results, September 15, 2012

Posted: Fri Sep 21, 2012 11:33 am
by RegGuheert
drees wrote:
turbo2ltr wrote:How do you know the whole pack doesn't have a much higher internal resistance and just has a higher open circuit voltage?
An increase in internal resistance doesn't change voltage at rest. It will result in a decrease in voltage under load and an increase in voltage when charging.
I'm pretty sure you are both saying the same thing. (I was about to write what you wrote, drees, but then I reread what turbo2ltr said and I saw it can be interpreted pretty much the same way.)