Power Needs of Battery Management System?

[NORTON]

bro,

Are you saying you never plug in at home and just walk away allowing it to top up to 100% SOC?
If/when you do that, and it constantly continues to pull ~700 watts (forever?) after achieving 100% SOC, your car has some sort of problem.

Unplugging at ~80% is a 'work around' on your part to avoid wasting power.
If this serves your needs, fine.

But at some point it would be great to find out what exactly is going on with your car, so you don't have to perform this 'Work Around'.
And us techno geeks want to know what the fix turns out to be !!

 

[EldRitch]

Just for another data point, I have an EVI EVSE with a display. It shows my 2016 taking 14.5a @ 245-248v while charging, and then drops to .2-.3a afterward.
I haven't caught the charger or the fan doing anything after a full charge yet, but the 50-75w draw seems to continue forever, so presumably it's keeping some of the onboard systems alive, or perhaps trickle-charging the battery for maintenance.

 

[SparkevBlogspot]

In the hottest day of the year, I plugged in via Kill A Watta and scheduled for night time charging. Even after whole day with peak at 105 degree heat, it registered no power use. Only when scheduled time came did it actually use energy. I was using L1 (120V) and set to 8A (default setting) and the car was at 4 bars / 40 miles range.

From this, I'm curious if it's due to using L1, 8A, or if it's due to mid level state of charge. LiIon supposedly is worst at high state of charge at elevated temperature. Low state of charge may not be so bad with SparkEV's NMC (2015/2016) LG cells? I wonder how 2014 with LiFe cells behave behave in such condition.

 

[MrDRMorgan]

In the hottest day of the year, I plugged in via Kill A Watta and scheduled for night time charging. Even after whole day with peak at 105 degree heat, it registered no power use. Only when scheduled time came did it actually use energy. I was using L1 (120V) and set to 8A (default setting) and the car was at 4 bars / 40 miles range.

From this, I'm curious if it's due to using L1, 8A, or if it's due to mid level state of charge. LiIon supposedly is worst at high state of charge at elevated temperature. Low state of charge may not be so bad with SparkEV's NMC (2015/2016) LG cells? I wonder how 2014 with LiFe cells behave behave in such condition.

I recently charged my 2014 Spark EV with 14.75 kWh at 8 amps using the L1 EVSE and it shut off as planned. Garage temperature was around 95 deg. F when I started and it charged all night until 10am the next morning. I have noticed the cooling fan runs for about 20 minutes after hot weather charging and then turns off.

 

[SparkevBlogspot]

BMS is active while charging. The issue for some was that BMS was taking power even when not charging. At least for me, mid level state of charge on L1/8A does not trigger BMS until charging even at very high ambient temperature. Since I never charge to 100% at home (or ever), I don't know if BMS would kick in after it's done charging.

An experiment might be to setup delayed charging such that the car won't charge much before it has to stop. If it stops charging after short charge (still mid / low level SoC), does BMS still kick in from time to time in hot weather? This might be a way to force BMS to activate if one's not comfortable with it not being active in hot weather.

Another interesting experiment with those who have power meter on L2 would be to see if delayed charging an mid/low state of charge uses power before charging begins in hot temperature. Same as my experiment, except using L2. Then one can progress to higher and higher level state of charge to see if it makes a difference.

 

[MrDRMorgan]

BMS is active while charging. The issue for some was that BMS was taking power even when not charging. At least for me, mid level state of charge on L1/8A does not trigger BMS until charging even at very high ambient temperature. Since I never charge to 100% at home (or ever), I don't know if BMS would kick in after it's done charging.

An experiment might be to setup delayed charging such that the car won't charge much before it has to stop. If it stops charging after short charge (still mid / low level SoC), does BMS still kick in from time to time in hot weather? This might be a way to force BMS to activate if one's not comfortable with it not being active in hot weather.

Another interesting experiment with those who have power meter on L2 would be to see if delayed charging an mid/low state of charge uses power before charging begins in hot temperature. Same as my experiment, except using L2. Then one can progress to higher and higher level state of charge to see if it makes a difference.

Last evening my garage was 100 deg. F. and both Spark EVs had been baking in that hot garage for many hours. When I connected my 2015 Spark EV to the Bosch L2 EVSE, I immediately heard a fan come on. Unfortunately, I cannot tell you how much power was be drawn. Same thing for my 2014 Spark EV when I connected it to the L1 EVSE. It will be even hotter the next two days and I do have a power meter available on the L1 EVSE. Is there something you would like me to try?

 

[SparkevBlogspot]

Was your L2 on delayed charging? For regular charging, fan / BMS comes on right away. I don't hear anything for 2 minutes that I'm there if it's on delayed mode. Since I don't have wattmeter on L2, I don't wait around to see if it would eventually become active before charging.

For L1, You can try the short delayed charge where it would stop charging after couple of minutes to see if BMS continue to stay on. Of note would be if it makes a different if it's high vs low SoC. Another is to redo my test to see if BMS is active before charging starts when in delayed charging mode. More data point always help. Of course, it's only if you have the time.

 

[MrDRMorgan]

Was your L2 on delayed charging? For regular charging, fan / BMS comes on right away. I don't hear anything for 2 minutes that I'm there if it's on delayed mode. Since I don't have wattmeter on L2, I don't wait around to see if it would eventually become active before charging.

For L1, You can try the short delayed charge where it would stop charging after couple of minutes to see if BMS continue to stay on. Of note would be if it makes a different if it's high vs low SoC. Another is to redo my test to see if BMS is active before charging starts when in delayed charging mode. More data point always help. Of course, it's only if you have the time.

Yesterday's L2 charge cycle was immediate. I usually run the delayed cycle to complete by 7:00am so I have no idea what goes on at night. I will see swhat I can do with L1.

7/26/2016: 2014 Spark EV 2LT: 100 deg. F right now and I just returned home from a short 4 mile trip. I plugged into my L1 EVSE and it immediately showed 965 watts - I am using the 8 amp setting. The Energy Info display did not show any battery conditioning and remaining charge was 50%. A fan came on for a few minutes and then shut off.

 

[slackinormackin]

A quick update... I didn't use the car for about 2 weeks while on vacation. My phantom power draw when battery was full issue has seemed to have corrected itself. Sorry I don't have a better solution.

 

[NORTON]

Small Note:
BMS is cell voltage balancing within the pack. Not sure what other duties it has.

TMS is Thermal Management System (Battery Conditioning on the power display) and it strictly deals with battery temp. There are probably multiple temp sensors within the pack.

We don't know the power usage of BMS.
Maybe this is where some of the 'phantom' power was going. I assume this is a once in a while procedure that runs as needed in the back ground, maybe/hopefully only when plugged in.

We can hear TMS running the fans and AC compressor at various speeds while plugged in. (They really get after it in the summer at a DCFC)
This is kind of known to be around 600-800 watts. I can see it on my Chargepoint acct. when I look at daily usage. 3.3kW then it drops to ~600 watts for a little bit.
After getting the Onstar txt msg that the car is 'Done Charging', 10-15 mins. later I'll get the Chargepoint txt saying 'Car is using little power and may be done...'.
To me, this is the important txt msg.

Smaller note:
I found how to display my Charepoint acct usage from when I bought the car. My car is now $710 less than when I bought it!
This is if I had charged at home instead of at free public charging!

 

[CCIE]

Small Note:
BMS is cell voltage balancing within the pack. Not sure what other duties it has.

TMS is Thermal Management System (Battery Conditioning on the power display) and it strictly deals with battery temp. There are probably multiple temp sensors within the pack.

We don't know the power usage of BMS.
Maybe this is where some of the 'phantom' power was going. I assume this is a once in a while procedure that runs as needed in the back ground, maybe/hopefully only when plugged in.

We can hear TMS running the fans and AC compressor at various speeds while plugged in. (They really get after it in the summer at a DCFC)
This is kind of known to be around 600-800 watts. I can see it on my Chargepoint acct. when I look at daily usage. 3.3kW then it drops to ~600 watts for a little bit.
After getting the Onstar txt msg that the car is 'Done Charging', 10-15 mins. later I'll get the Chargepoint txt saying 'Car is using little power and may be done...'.
To me, this is the important txt msg.

Smaller note:
I found how to display my Charepoint acct usage from when I bought the car. My car is now $710 less than when I bought it!
This is if I had charged at home instead of at free public charging!

Based on how the Volt BMS has been described by knowledgeable people on the Volt forum, I believe the BMS balances the individual cells using switchable resistors that bleed off charge from any overcharged cells. So, the BMS itself shouldn't draw extra energy. But, the resistors generate heat which the TMS would then have to deal with. So, cell balancing may indirectly use some energy.

 

[EldRitch]

100% on the Spark display is nowhere near 100% of the cells maximum capacity.

Chevy engineers are not idiots, and took the "don't charge Li to 100%" into account when they built the battery management software. The Spark will Never charge its batteries to 100%.

A "100%" charge is only 100% of what you are allowed by the car's battery-management software, and is just a number displayed by a computer to tell humans that the car won't take any more.

It is merely 100% of the maximum that Chevy engineers determined would support a warranteed 8-year battery life for a high percentage of buyers, and is therefore very conservative.

Thus, by limiting your charging to 80% on the display, you are actually limiting yourself to perhaps 80% of 80%, i.e. 64% of the actual maximum battery charge level (that you are not allowed to approach), and not using potential range, without extending battery life appreciably. Pointless.

 

[SparkevBlogspot]

100% on the Spark display is nowhere near 100% of the cells maximum capacity.

You can test this theory by looking at voltage at DCFC (some show voltage + current). SparkEV has 96 cells in series and 3.7 V nominal with "full" being about 4.2 volts (355 V to 403 V). I saw the voltage start about 340V and approach 400 V, which suggests to me that SparkEV does reach close to 100% capacity, not 80% that you claim. How close that's to 100% is not known, but it is certainly far closer to 100% than 80% or even 90%.

Another interesting aspect of SparkEV charging to 80% capacity is that power actually increases, because the voltage increases while the current stays the same. This is unlike all other EV; I saw i3 taper current even at 75%.

 

[EldRitch]

I was not claiming 80%, just using it as an example.

I don't know what voltage the engineers chose to use as a limit, but again - it supports an eight-year warrantee, and that seems good enough for me, as the car will be a joke by then.

I would interpret the 4.2v/cell you are extrapolating as the voltage necessary to charge a battery nearing 3.7v, since the charging voltage has to be higher than the target voltage.

 

[Zoomit]

The Spark EV charging peak power can be seen in Figure 2b, on page 8, here:
https://avt.inl.gov/sites/default/files/pdf/fsev/2015SparkDCFCAtTempBOT.pdf

80% SoC is about 15kWh and is reached at 25 minutes, and happens to be the peak with that test equipment. This is with only a 100A charger, not a 125A charger. A 125A charger might reach peak charging power, and thus start tapering, slightly earlier.

BTW, INL recently published this infographic:
https://avt.inl.gov/sites/default/files/pdf/fsev/ChevroletSparkTempInfographic.pdf

 

[boatbum11]

Well I was going to post a pic I took on the power management screen showing 3% usage for TMS, but it seems one can't post pictures from a PC directly, only via a BBS. So, no pic. :evil: :roll:

 

[brothergrimm]

A year later, I finally have an update.

I got proof of substantial current draw from this ChargePoint charging summary.

http://imgur.com/a/x38ND

In it, you can clearly see the car continue to draw ~.6kW after it reached 100% SOC.

I took this to the dealer, but they couldn't reproduce the problem. They made an update to the car regarding delayed start or something like that. I'm not sure that's going to fix it.

 

[kevin]

A year later, I finally have an update.

I got proof of substantial current draw from this ChargePoint charging summary.

http://imgur.com/a/x38ND

In it, you can clearly see the car continue to draw ~.6kW after it reached 100% SOC.

I took this to the dealer, but they couldn't reproduce the problem. They made an update to the car regarding delayed start or something like that. I'm not sure that's going to fix it.

I have also seen this:

I have seen similar profiles on Leaf and BMW i3.

I attributed it to cell balancing or possibly running the battery cooling system following a charge.

If the battery is being balanced resistive loads are put across the cells that reach the target full charge level and charging is continued at a lower rate to allow the other cells to catch up.

It would only happen occasionally - not at every charging.

kevin

 

[brothergrimm]

Looks like this balancing goes on for 30 minutes. Mine will do this all night long!

 

[NORTON]

Looks like this balancing goes on for 30 minutes. Mine will do this all night long!

I still say your car has a problem.
You need to escalate this with the GM EV Group in Customer Support,,, or whatever they call themselves.
Even then it will be hard to get one of the gals there to take you seriously. It is a technical issue.

Good luck.