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 Post subject: Re: Power Needs of Battery Management System?
PostPosted: Wed Nov 23, 2016 9:14 am 
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Joined: Tue Nov 22, 2016 8:47 am
Posts: 87
Location: CT
NORTON wrote:
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.

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2015 Spark EV 2LT with DCFC
2012 Volt


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 Post subject: Re: Power Needs of Battery Management System?
PostPosted: Wed Nov 23, 2016 9:28 am 
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Joined: Sun Jul 03, 2016 9:20 pm
Posts: 139
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.


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 Post subject: Re: Power Needs of Battery Management System?
PostPosted: Wed Nov 23, 2016 10:53 am 
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Joined: Mon May 25, 2015 12:19 pm
Posts: 475
EldRitch wrote:
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%.


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 Post subject: Re: Power Needs of Battery Management System?
PostPosted: Wed Nov 23, 2016 11:35 am 
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Joined: Sun Jul 03, 2016 9:20 pm
Posts: 139
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.


Last edited by EldRitch on Wed Nov 23, 2016 4:25 pm, edited 1 time in total.

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 Post subject: Re: Power Needs of Battery Management System?
PostPosted: Wed Nov 23, 2016 11:44 am 
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Joined: Sat Jun 13, 2015 1:54 pm
Posts: 243
Location: SoCal
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

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2015 Spark EV: 2LT, DCFC, Summit White


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 Post subject: Re: Power Needs of Battery Management System?
PostPosted: Tue Jun 20, 2017 10:53 am 
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Joined: Fri Mar 17, 2017 1:57 pm
Posts: 10
Location: Sacramento, Ca
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:

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2014 Blue Spark with DCFC.


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 Post subject: Re: Power Needs of Battery Management System?
PostPosted: Fri Aug 11, 2017 10:58 am 
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Joined: Thu Jun 02, 2016 12:18 pm
Posts: 12
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.


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 Post subject: Re: Power Needs of Battery Management System?
PostPosted: Fri Aug 11, 2017 11:53 am 
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Joined: Sat Jul 27, 2013 9:52 am
Posts: 125
Location: Los Gatos
brothergrimm wrote:
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

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 Post subject: Re: Power Needs of Battery Management System?
PostPosted: Wed Aug 16, 2017 9:39 am 
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Joined: Thu Jun 02, 2016 12:18 pm
Posts: 12
Looks like this balancing goes on for 30 minutes. Mine will do this all night long!


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 Post subject: Re: Power Needs of Battery Management System?
PostPosted: Wed Aug 16, 2017 9:53 am 
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Joined: Fri May 01, 2015 5:52 am
Posts: 860
Location: KC,MO
brothergrimm wrote:
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.

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Used '14 2LT w/ DCFC.
In the middle of the country.
Far from any of its sibs.


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