[AJ-ptmdy]

TorquePro sounds a lot more flexible than the OBDLink app I'm using that came free with my OBD reader.

I use OBD2 reader Veepeak BLE+ and cell-app TorquePro (I recall $5 for this app). I did get going with these tools after reading the various threads and using Telek's PIDs file and his instructions-recommendations for equipment and for procedures. I am not very IT skilled so did get stuck on details at several points along the way such as bringing in the PIDs file and then controlling the way TorquePro logs and provides data in a form I could use. Good Luck with your setting-up.

 

[do_I_want_a_used_bolt]

The article I'd cited elsewhere on this discussion board appearing in InsideEVs would suggest a root cause that's pretty subtle: My Chevy Bolt Is On Third Battery Pack: Here's Why
[-tv]

I found the linked article quite interesting as I'm looking for a used 2017 Bolt currently.

"What do you mean by compression?

We literally press them together. We put highly engineered foam between them. Then we put them all together in the cell-module assembly. Each cell has a validated pressure throughout its lifecycle for hot and cold. Even with all the monitoring we did along the way, these got through all that because the phenomenon took longer to present itself.

When you say phenomenon, you mean something in the chemistry created a diminished capacity to hold the voltage?

Yes. So instead of having a 238-mile pack, you had a 155-mile pack. "

The article seems to indicate that this problem was fixed, but it does make me wonder if the disparity between the higher vs. lower voltage cells is a problem in general over time.

"Sept. 2017 – Mar. 2018: Bolts with new battery packs appear to be reliable. GM works with LG Chem, the battery supplier, to make multiple changes to the cell manufacturing process. The company believes the problem is fixed."

Makes me think I want to look for 9/2017 or later manufactured Bolts used.

 

[Sean Graham]

Necroresponse! But I seem to have missed this the first time around - based on some other conversations, I think this is useful to clarify.

The charger is pumping juice into every cell during charging, because they are in series. There are no relays between cells, allowing them to be bypassed, to prevent this. As long as the charger is on, current is flowing through every cell.

Kinda not really. Remember that voltage is applied, and in battery charging current is drawn proportional to the square of the difference of the applied voltage and the battery's rest open circuit voltage. You don't apply both voltage and current and the circuit or battery has to figure out what to do with it.

So you can have the charger "on", applying a float voltage that is the exact same as the OCV, and no current will be drawn.

At the end of a 100% charge, using the onboard charger, the charger is putting out less than 2000 watts, at 400 volts, so under 5 amps flowing through every cell. Bleeding off 5 amps x 4.165 volts = 20.8 watts per cell, During balancing, for some length of time, every one of the 96 cells is bleeding off that much power...the whole 2000 watts.

This is entirely incorrect. As mentioned above, the cells are going to draw current based on the voltage difference, so if the "charger is putting out 2000 watts", then that's what the battery itself is drawing. Nothing is bled off. Bleeding off 2000W would certainly fry the BMS. The battery itself doesn't produce 2000W of waste heat, and it needs liquid cooling to handle that in a much larger area.

This is easy to see here where module #6, which the BMS sits on, is 9 F warmer than the others, and module #5 which is permanently attached to it is almost as warm.

While this is true, I think this is because the module 6 also takes heat from the module that it's sitting on, not from the BMS.

 

[Sean Graham]

The last portion of the charge cycle is at a constant voltage. The charger voltage is held constant and the current gradually decreases to a minimum value as the cell stabilizes at that voltage. If a cell is low, the voltage on the other cells will tend rise a bit higher and be clamped by the BMS. This will allow the low cell to be charged a bit more by allowing it to go higher.

Mostly correct - but there's no "clamping". Typically speaking, you let all cells just charge up until you hit your maximum cell limit, and then after charging is done you can selectively drain the high cells (passive) and/or charge the low cells (active) to balance it out. Based on the layout of the BMS, it's likely the former only.

One or two cells out won't be enough to affect the others in any substantial way.

The BMS is designed only to handle a small amount of power to balance out small differences. If something goes awry and this power gets too high, certainly the BMS could overheat. This could potentially start a fire in the battery pack.

Kinda not really - the BMS has a transistor and two 20 ohm resistors in series - meaning 40ohm short. So it can only drain at 105mA, or about 440mW. By the looks of it, those resistors can handle 1/4W each, so it's literally impossible for them to create too much heat that it would overheat.

EDIT: They may be 1/8W each, I'd need to measure to know for sure. If so, I suspect the IC will just throttle them at 50% duty cycle to avoid overheating - but I somehow doubt this. My point was that it will always drain at the same power, so it's either always going to overheat (obviously not), or never overheat.

 

[Sean Graham]

Sorry the for necroresponse, but I've been meaning to discuss this for a while.

I went back and watched a portion of Prof. Kelly's video and noticed that the BECM seems to monitor in 6 groups of 16 cells. I overlaid the cells from each group on top of my graph and found something that might be interesting (not sure).

I'm not following how you got here? The BMS quite clearly has 12 balance chips, meaning 8 cells each (this is common). We can also see 8 transistors per chip, backing that up. If you're referring to the harness connectors, that's just convenience, not related to how the BMS works.

He did mention that each cell at the endpoints of each group of 6 are duplicated because you need a reference voltage to measure the cells in the next group (paraphrasing). I take that to mean that given all the wiring and internals, when the BECM monitors 1-16, it monitors 16-32 next and "compares" what "channel 1" saw for 16 and compares it to what "channel 2" saw for that same cell 16. The question then becomes, what if there is a small difference?

Ok that's not quite how it works - so when you measure voltage, you need a negative reference and a positive reference, and you're measuring the potential difference between the two.

So we know that the chips work in groups of 8. It's not that chip 1 is measuring cell 8, and chip 2 is measuring cell 8, and comparing.

Chip one measures:

• ground to lead 1 - cell voltage 1
• lead 1 to lead 2 - cell voltage 2

...

• lead 6 to lead 7 - cell voltage 7
• lead 7 to lead 8 - cell voltage 8

Chip two measures:

• lead 8 to lead 9 - cell voltage 9
• lead 9 to lead 10 - cell voltage 10

...

• lead 14 to lead 15 - cell voltage 15
• lead 15 to lead 16 - cell voltage 16

Chip three measures:
- lead 16 to lead 17 - cell voltage 17
...
etc

you can see that you're always measuring the voltage between two cells. So an overlap in PCB routing is needed between the two adjacent chips of the cell voltage with multiple of 8 - but there's no need for the harness to have this.

Prof Kelley absolutely knows his stuff, but I'm quite confused about the BMS labels, leading me to believe that neither is correct. He says that both Volt and Bolt BMSes are identical, but has completely different labels on the connectors. I don't know if this was a mistake, and if so, it makes me wonder how much is assumed about the pinouts on both of them.

Volt:

1-16
16-28
28-44
44-62
62-79
79-96

Bolt:

1-16
16-33
33-48
48-64
64-80
80-96

Either way it doesn't matter - the pinout of the wires has nothing to do with the monitoring of the cells.

 

[GJETSON]

So you can have the charger "on", applying a float voltage that is the exact same as the OCV, and no current will be drawn.

While this is true, I think this is because the module 6 also takes heat from the module that it's sitting on, not from the BMS.

I have not logged a charge. Have you seen actual CC-CV charging with the Bolt, where the charger maintains a fixed current for some time, and then near the end switches to constant voltage?

This is how all the cheap chargers I have work. You get a flat constant current to about 80% SoC, and then it switches to constant voltage, and you get a natural taper to zero current. The bleeder circuit is set to a tiny faction of a volt lower than that voltage, and the resistors bleed off until all cells are at the bleeder/cutoff voltage, and it stops. After a time, the voltage settles, it will start up again, until no cells settle below that voltage...which can be 4.20 volts, despite your protests.

 

[BigMtnBolt]

2017 with 24,500mi. Nothing new to show, but more a "me too" post. SoC DIC 87.45098%. Been resting all night, but this is about 10 minutes into a pre-con. OBD Fusion iOS.

 

[Jordan Shackelford]

Why is torque showing me 3.420v exactly for every single cell in my 2019 bolt? Is that accurate?

 

[GJETSON]

Why is torque showing me 3.420v exactly for every single cell in my 2019 bolt? Is that accurate?

@Telek is the only person on this forum who might have an idea.

 

[TheLondonBroiler]

Why is torque showing me 3.420v exactly for every single cell in my 2019 bolt? Is that accurate?

Does it ever change? It sounds like somehow your .csv file ended up with the same parameter id with different labels (cell groups 1-96).

 

[Sylvain F]

I will try to post my results if it can help anyone good…I could not export csv so I typed each cell (I type fast lol)…only at 53 % SOC. Might change at lower…distance from red line to blue is .03 Volt, the (I think) acceptable range. The green line is the average.

 

[BigMtnBolt]

With all this recall business I created a PID for what they're doing with the software update anyways... namely measuring the difference between average cell voltage and minimum cell voltage. I monitor this daily just for giggles. Granted they're measuring in specific ways at specific charge levels etc. etc. and I'm just monitoring on the fly and during charging sometimes, but it's just a little extra peace of mind. The custom PID is easy to create... it's just [22C218]-[224329] and shows up like this like from my 20 minute commute this morning (sampled every 60 seconds and from 85-79% SoC). I've never seen it anywhere close to .08 in any situation so far.

 

[sendler2112]

after a charge.

View attachment 32279 View attachment 32280 View attachment 32281 View attachment 32282 View attachment 32283 View attachment 32283

What gauge style or setting is that that shows cell voltages to 3 decimal places?

 

[sendler2112]

My 2017 LT with 24,000 miles at 56% SOC had 0.0197v difference between lowest cell voltage and average. Cell #36. This car has been sitting around in various auctions and dealer lots since January and I just brought it home 3 days ago ($17,000). It had 100 miles showing on the guessometer when I drove it away and I only had it above 65% once yesterday when I went to the dealer to verify that the DCFC was functional and took it to 80% (20 kW rate at that SOC). Who knows when if ever was the last time it was fully charged to get the most complete balancing that it could have. I can charge level 1 on both ends of my 40 mile commute so don't need to get to far away from the middle for the next year? until I get my new battery. 40-70% is all I need unless I decide to push my luck next March and do a cross country trip.

 

[GJETSON]

What gauge style or setting is that that shows cell voltages to 3 decimal places?

If you pick digital gauges, then press on the gauge, you get a menu of options, press Display configuration, press and then select Number of decimal places.

 

[GJETSON]

this like from my 20 minute commute this morning (sampled every 60 seconds and from 85-79% SoC).

Nice! I am a bit puzzled though. My understanding is that it takes the car about 10 seconds to scan all 96 cells, to come up with an average, or to determine a maximum, or minimum cell reading. The battery needs to be under no variable load for this to be anywhere close to accurate. I don't see how that happens when you are driving. If you want a really clear view of the sampling process, load up the MyGreenVolt app. You will see it scanning in real time, and if you are driving, part way through a scan of the 96 cell voltages, the pack voltage will change by a lot, making the rest of the scan much higher, or lower voltage.

This one was taken at rest.

 

[BigMtnBolt]

Nice! I am a bit puzzled though. My understanding is that it takes the car about 10 seconds to scan all 96 cells, to come up with an average, or to determine a maximum, or minimum cell reading. The battery needs to be under no variable load for this to be anywhere close to accurate. I don't see how that happens when you are driving.

Yeah interesting for sure. It's just a "snapshot in time" when it's writing the log, but who knows how fast the log is written (milliseconds?) and based on whether the PID is live or from the "last 10 seconds" or whatever. I use OBDFusion app not TorquePro so... I have no idea. My commute is very consistent power-wise as I climb a mountain and then... descend that mountain (I work at a ski resort) so it's very likely, especially on the descent, that my readings are somewhat sort of "accurate" within the power load currently on the battery. In other words, like when I'm descending, it's easy for me to maintain a pretty precise kW regen for well over 60 seconds because I'm maintaining a constant speed (barring a dump truck in front of me etc. etc). But yeah... I totally get your point.

Much more importantly to me is that I've done these logs during longer periods of L2 charging as well (I put a cement block on the brake pedal to keep the computers alive) and still have never seen over .03v delta during that time and usually much closer together. I cannot say with any confidence that I have a safe battery pack, but I'm certainly not altering my lifestyle because of what's happening and will continue to monitor the cells daily and continue with HTR charging and parking outside, which I did anyways. It's all fascinating stuff... aside from the **** fires of course.

At the end of the day I love my Bolt, am never going back to ICE and hope GM can get us all sorted out expeditiously.

 

[BigMtnBolt]

If you want a really clear view of the sampling process, load up the MyGreenVolt app

Oh and thanks for this! Will download MyGreenVolt and check it out.

 

[GJETSON]

Oh and thanks for this! Will download MyGreenVolt and check it out.

Comes up very fast too. Only thing I don't like is it requires your data to be turned on, as it checks to see you bought it each time you bring it up. On another page it shows 12 volt battery voltage, and some other stuff, like battery temperature history, etc. He hasn't set it up for the Bolt yet, so the Volt/Bolt select option doesn't work.

 

[LarryO]

Yeah interesting for sure. It's just a "snapshot in time" when it's writing the log, but who knows how fast the log is written (milliseconds?) and based on whether the PID is live or from the "last 10 seconds" or whatever. I use OBDFusion app not TorquePro so... I have no idea. My commute is very consistent power-wise as I climb a mountain and then... descend that mountain (I work at a ski resort) so it's very likely, especially on the descent, that my readings are somewhat sort of "accurate" within the power load currently on the battery. In other words, like when I'm descending, it's easy for me to maintain a pretty precise kW regen for well over 60 seconds because I'm maintaining a constant speed (barring a dump truck in front of me etc. etc). But yeah... I totally get your point.

Off topic but do you see much difference in regen during cold weather?