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TickTock
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Re: Active EV-CAN sampling: cell voltages, pack temperatures

Mon Jan 06, 2014 12:12 pm

GregH wrote:
TickTock wrote:
GregH wrote:With the help of a few LeafDD customers in colder climates, we can now extend the temperature translation table (first post of this thread) down to 0C.. and soon hopefully confirm down to -10C..

Very nice! These remain surprisingly linear - looks like extrapolation should be valid outside this range.


I know! Personally I'm shocked it's still 10 clicks per degree C all the way down to 0C.. I would have thought for sure the nonlinearity of the thermistor would have resulted in 12 or 13 clicks per degree C down in the colder realm (as it is confirmed 8 or 9 on the hot side). Could it be the Leaf's own temperature calcs are lazily linear? And in the end, do we care what the real temps are or what the trigger points for things like temp bars and battery heaters is?

I suppose the curvature may be there but Nissan decided a linear fit was good enough. We should sanity check the result against an independent thermometer at several points.

GregH
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Re: Active EV-CAN sampling: cell voltages, pack temperatures

Mon Jan 06, 2014 4:15 pm

TickTock wrote:
GregH wrote:I know! Personally I'm shocked it's still 10 clicks per degree C all the way down to 0C.. I would have thought for sure the nonlinearity of the thermistor would have resulted in 12 or 13 clicks per degree C down in the colder realm (as it is confirmed 8 or 9 on the hot side). Could it be the Leaf's own temperature calcs are lazily linear? And in the end, do we care what the real temps are or what the trigger points for things like temp bars and battery heaters is?

I suppose the curvature may be there but Nissan decided a linear fit was good enough. We should sanity check the result against an independent thermometer at several points.

Check the published thermistor curve in the service manual EVB-19 (2013) or EVB-22 (2012)... Sure doesn't look flat from 0 to 10C to me!
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TickTock
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Re: Active EV-CAN sampling: cell voltages, pack temperatures

Wed Jan 29, 2014 8:43 am

GregH wrote:Check the published thermistor curve in the service manual EVB-19 (2013) or EVB-22 (2012)... Sure doesn't look flat from 0 to 10C to me!

I appears the ADC and degreesC value on the canbus are linearized but the value displayed on the eyebrow has been curvature corrected. I shut the passenger door on a thermocouple such that it sits about 1cm away from the door just above the side mirror. Monitoring with my Fluke which has 0.1 deg accuracy, I can say that the eyebrow readout matches very well with the Fluke *once equilibrium is reached*. It takes about 10 minutes for the dash readout to settle, but when it does it is within 1 degree of the Fluke measurement (the Fluke responds very quickly, within seconds) however the canbus readout is often as much as 5 degrees off. For example, this morning, after being on the road for about 20 minutes, I measured 43F outside and read the same on the dash, but got 38F from the canbus. I think we need to start collecting some more datapoints of *real* temperature to fill out our lookup table properly. My data suggests the dash is a good measurement - as long as it has been at reasonably constant temperature for at least 10 minutes. So if any of the folks living the the north can grab a datapoint or two along with the canbus temp at the low extreme, I can get the upper extreme here in a few months and we should be able to fit a curve. Remember, only to trust the dash after you've been driving at least 10 minutes.

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TickTock
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Re: Active EV-CAN sampling: cell voltages, pack temperatures

Wed Jan 29, 2014 10:10 am

Greg, maybe you can start tracking this, too, in the OP. The 3C entry, then, would be:

3 degrees C starts at 690 (6 degrees C actual)

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Re: Active EV-CAN sampling: cell voltages, pack temperatures

Thu Jan 30, 2014 1:21 pm

TickTock wrote:Greg, maybe you can start tracking this, too, in the OP. The 3C entry, then, would be:

3 degrees C starts at 690 (6 degrees C actual)

Hmm.. you mean based on our eyeball reading of the thermistor curve?
A few people with LeafDD have the new software that shows temps under 0C, and I have a few readings, but not enough yet to confirm the -2 to -1 or -3 to -2 transitions. I'd like to think this was just sloppy software (on Nissan's part) down to 0C and there's a different slope below 0C but I have yet to confirm that.
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TickTock
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Re: Active EV-CAN sampling: cell voltages, pack temperatures

Thu Jan 30, 2014 7:43 pm

GregH wrote:
TickTock wrote:Greg, maybe you can start tracking this, too, in the OP. The 3C entry, then, would be:

3 degrees C starts at 690 (6 degrees C actual)

Hmm.. you mean based on our eyeball reading of the thermistor curve?
A few people with LeafDD have the new software that shows temps under 0C, and I have a few readings, but not enough yet to confirm the -2 to -1 or -3 to -2 transitions. I'd like to think this was just sloppy software (on Nissan's part) down to 0C and there's a different slope below 0C but I have yet to confirm that.

No, that was measured using a Fluke multimeter with a thermocouple probe outside the cabin (see my previous post).

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Re: Active EV-CAN sampling: cell voltages, pack temperatures

Sat May 03, 2014 12:16 pm

About Group 6,

I've been having a bit of disassembly fun.

I was trying to find adequate shunt resistors on the BMS board and I didn't see any.

Image

Image


https://www.flickr.com/photos/jaesin/sets/72157644497791245/

The wires are also quite small for shunting.

Am I missing something?

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gbarry42
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Re: Active EV-CAN sampling: cell voltages, pack temperatures

Sat May 03, 2014 4:34 pm

How much current are you expecting? It's pretty low, from what I heard.
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garygid
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Re: Active EV-CAN sampling: cell voltages, pack temperatures

Sun May 04, 2014 8:29 am

Each of the 12 main chips has four 430 ohm ("431") resistors, so those might be the
shunt resistors for 48 modules or 48 cell pairs. Is there another BMS board to handle the
other 48 cell pairs? Are there any parts on the other side of the board?

A shunt of 10 ma is not much current, and 240 mah per day is
only about 1 watt-hour per day, so not very rapid equalization, but maybe they thought
that 0.3 kWh a year would be sufficient?

Just an uninformed guess.
See SOC/GID-Meter and CAN-Do Info
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Jaesin
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Re: Active EV-CAN sampling: cell voltages, pack temperatures

Sun May 04, 2014 12:19 pm

No second PCB but the bottom is populated as well if I remember correctly.

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