Power Needs of Battery Management System?

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brothergrimm

Member
Joined
Jun 2, 2016
Messages
12
Hi there, this is my first summer with my Spark EV in a hot location -- Sacramento, CA.

I've started hearing a fan working in there, even in the cool early morning hours. From reading other forum entries, this would seem like the battery management system keeping the battery cool and healthy.

I was curious how much power the system was drawing, so I attached a Kill-A-Watt to the included level 1 EVSE. Even after the battery has charged, I find the car drawing around 6 amps or 720 watts of power. For example, my last over-night charge needed 9kwh to recharge from half-way depleted -- but in the morning, I found that the Spark used 18kwh to charge it up and do whatever else it was doing.

Has anyone else observed this? Other thoughts? Much appreciated!
 
brothergrimm said:
Hi there, this is my first summer with my Spark EV in a hot location -- Sacramento, CA.

I've started hearing a fan working in there, even in the cool early morning hours. From reading other forum entries, this would seem like the battery management system keeping the battery cool and healthy.

I was curious how much power the system was drawing, so I attached a Kill-A-Watt to the included level 1 EVSE. Even after the battery has charged, I find the car drawing around 6 amps or 720 watts of power. For example, my last over-night charge needed 9kwh to recharge from half-way depleted -- but in the morning, I found that the Spark used 18kwh to charge it up and do whatever else it was doing.

Has anyone else observed this? Other thoughts? Much appreciated!
I live 50 miles South of Sacramento in Manteca. Last year - my first year with a Spark EV - I had the same hot-weather concerns. After a lot of data collecting using a Kill-A-Watt power meter, I figured the L1 EVSE supplied with the car was about 65% efficient in very hot weather / garage. In cooler weather I achieve about 75%. In hot weather the cooling system will be turned on as needed to maintain a safe battery temp. It is even recommended to leave the car plugged in when the weather is extremely hot or cold. I assume the 9kWh you needed came from the car's display. At 65% L1 wall-to-wheel charging efficiency, you would need, at the 8-amp charging rate (1 kWh), almost 14 kWh (14 hours) from the wall to replace that 9 kWh. At 75% efficiency, it would still take 12 hours. I suspect your car had not yet fully re-charged when you checked it.

Added note: This evening I put my 2014 Spark EV on my L1 EVSE. The car's display showed 8.3 kWh used - 32% driving, 11% climate and 0% battery conditioning. Charging started at 7pm and the car estimated charging would be completed at 8:30 am tomorrow morning. That's 13.5 hours to add 8.3 kWh back into the battery for a full charge.
 
MrDRMorgan, thanks for sharing your experience.

I'm 100% sure the car had finished charging, yet was still drawing 6 amps / 720 watts of power...at least according to the status light on the dash and the Kill-A-Watt meter.

Do you think the inefficiency is because the car is reserving amps for ongoing battery management and only then do the rest of the available amps go to charging? That's my leading theory.

I knew the charging process wasn't 100% efficient, but the battery management system is looking to me like a significant and unexpected cost of operating the car.
 
brothergrimm said:
MrDRMorgan, thanks for sharing your experience.

I'm 100% sure the car had finished charging, yet was still drawing 6 amps / 720 watts of power...at least according to the status light on the dash and the Kill-A-Watt meter.

Do you think the inefficiency is because the car is reserving amps for ongoing battery management and only then do the rest of the available amps go to charging? That's my leading theory.

I knew the charging process wasn't 100% efficient, but the battery management system is looking to me like a significant and unexpected cost of operating the car.
Interesting! At 10 pm this evening, 3 hours after I started charging, the power meter read 3.0 kWh which what I would expect. In your case, I am assuming the green dash light had switched from a steady state green light to a blinking green light state. Your power meter should have dropped to near zero and your dash display values for Drive, Climate and Battery should have all reset to zero. If this happened and you are still drawing 3/4 of a kWh of power, then I would suspect you do indeed have some strange electrical problem. The car should signal the EVSE to stop charging when a full charge state is reached. It may be possible that there is a problem with your vehicle or EVSE. What happens on the power meter when you manually terminate charging using the key FOB? Does the power meter still show power flowing even after you terminate charging and remove the plug from the car socket? You could also see if you can find another L1 EVSE to try or try an L2 EVSE at a location near you and see if it disconnects correctly. FYI - I rarely see any indication of battery conditioning on the displays of either my 2014 or 2015 Spark EV and its usually only 1% and occurs in very hot weather.
 
MrDRMorgan said:
brothergrimm said:
..... The car should signal the EVSE to stop charging when a full charge state is reached. It may be possible that there is a problem with your vehicle or EVSE. ....
Just to clear one thing: The EVSE is just a smart relay/extension cord. That relay/switch inside is either ON or OFF. It allows 120V or 240V AC to get to the car.
The only 'signaling' is the EVSE telling the car's On Board Charger to only draw 3.3kW, or whatever the max rating is for that EVSE.

If the car is plugged into the EVSE, I believe the relay should be closed because battery TMS might need to come on and do it's job.

I think I've seen mine with maybe 700 watts continuing after I got the app msg that 'Charge Complete'. I think that is TMS continuing to cool the battery for a little bit after the 'Green Light' is flashing.

My big question is: If you use 'Delayed Charge', does TMS still operate and draw some power before the 'Start of Charge'?
I missed my opportunity to measure this for myself last winter....
I want to keep the battery warm in the winter, but not charge it. I'd like to do the charging later at the free public charger across from work.
 
NORTON said:
MrDRMorgan said:
brothergrimm said:
..... The car should signal the EVSE to stop charging when a full charge state is reached. It may be possible that there is a problem with your vehicle or EVSE. ....
Just to clear one thing: The EVSE is just a smart relay/extension cord. That relay/switch inside is either ON or OFF. It allows 120V or 240V AC to get to the car.
The only 'signaling' is the EVSE telling the car's On Board Charger to only draw 3.3kW, or whatever the max rating is for that EVSE.

If the car is plugged into the EVSE, I believe the relay should be closed because battery TMS might need to come on and do it's job.

I think I've seen mine with maybe 700 watts continuing after I got the app msg that 'Charge Complete'. I think that is TMS continuing to cool the battery for a little bit after the 'Green Light' is flashing.

My big question is: If you use 'Delayed Charge', does TMS still operate and draw some power before the 'Start of Charge'?
I missed my opportunity to measure this for myself last winter....
I want to keep the battery warm in the winter, but not charge it. I'd like to do the charging later at the free public charger across from work.
Norton - I think you might be correct. 700 watts is a lot of power and, if the TMS is responsible, it would explain why I kept getting different L1 charging efficiency percentages during the hot summer last year. My Kill-A-Watt is the older EZ model and does not have some of the more important measurements the P4400 has. So it is off to Home Depot to get a P4400 and see if I can duplicate the "problem". However, I would expect the TMS to cool the battery sufficiently to stop the current draw and that would be visible on the meter. The question is how long does it take?
 
NORTON said:
...
If the car is plugged into the EVSE, I believe the relay should be closed because battery TMS might need to come on and do it's job.

I think I've seen mine with maybe 700 watts continuing after I got the app msg that 'Charge Complete'. I think that is TMS continuing to cool the battery for a little bit after the 'Green Light' is flashing.

..

You're right, it may be battery thermal management, I've seen it but I attributed it to performing cell balancing. I only see it occasionally and have not seen a correlation with warm weather.

I've also seen it with a BMW i3.

If it is cell balancing - the charge rate is reduced to a moderate level and cells that are already up to max SOC will have a bypass resistor enabled to allow other cells to catch up.

This is an example while charging from a Chargepoint EVSE at level 2.

Spark_CellBalance.PNG


kevin
 
Confirmed! I was by my car when the L1 EVSE switched the charging off. Then I heard a fan come on - I believe this is for battery cooling. I watched my power meter and found an additional 120 watts was used in 10 minutes; that's 720 watts in an hour. The fan ran for 30 minutes and then shut off. The power meter showed .40 kWh had been consumed in the 30 minutes since the EVSE disconnected and the fan turned off.
 
MrDRMorgan said:
Confirmed! ... The power meter showed .40 kWh had been consumed in the 30 minutes since the EVSE disconnected and the fan turned off.
A small price to pay for a happy, long life battery pack!!
It may have been the fan, the AC compressor and definitely the battery coolant pump running.

Do you know what a Leaf does in this situation? Nothing.
The most it can do is lower the charge rate to keep the temp from rising too high.
This is why there have been Leaf battery pack replacements on warranty.
Can you imagine a black Leaf sitting out in the sun at the Tucson airport, for weeks, with the battery SOC nearly full?
 
brothergrimm said:
Hi there, this is my first summer with my Spark EV in a hot location -- Sacramento, CA.

I've started hearing a fan working in there, even in the cool early morning hours. From reading other forum entries, this would seem like the battery management system keeping the battery cool and healthy.

I was curious how much power the system was drawing, so I attached a Kill-A-Watt to the included level 1 EVSE. Even after the battery has charged, I find the car drawing around 6 amps or 720 watts of power. For example, my last over-night charge needed 9kwh to recharge from half-way depleted -- but in the morning, I found that the Spark used 18kwh to charge it up and do whatever else it was doing.

Has anyone else observed this? Other thoughts? Much appreciated!
See posts in this thread. What you experienced is normal - I duplicated it last night and this morning. I needed 8.3 kWH and it took 11.95 kWh by the end of the cooling cycle. Last year I also had low 50% efficiency charging cycles. You will need a few charging cycles before everything settles in. Take the car out and have FUN!
 
Really appreciate the discussion guys!

So the thinking is that the car pulling 700 watts for a while after charging is normal. And it doesn't do it indefinitely, but just for a little while afterwards...perhaps 30 minutes or so based on Kevin's chart. My 18kwh over-nighter (referenced earlier) needed 9kwh for the battery, so that leaves me to conclude that there was the 700 watt process running for 12.5 hours. I'm really curious to keep an eye on things tonight.

I don't mind a 700-watt process running here or there for a short amount of time, but if it's going to be on all the time while plugged in during hot weather, that's going to really add up over the course of the summer.
 
brothergrimm said:
Really appreciate the discussion guys!
...
I don't mind a 700-watt process running here or there for a short amount of time, but if it's going to be on all the time while plugged in during hot weather, that's going to really add up over the course of the summer.

I don't know where you are based but for the first year I owned the spark I recorded every charge both the energy in (usually from Chargepoint) and energy-out (from the Energy screen). I did a few charges from 120V where I measured the energy with a KillaWatt.

My average mi/kWh was 5.7mi/kWh (based on output) and 4.7mi/kWh (based on input energy). This gives an efficiency of 83% from AC power to energy out of the battery. The efficiency for the few charges I did at level 1 was ~78%, although in view of the small number of samples is probably much less accurate.

Taking into account the expected efficiency of the AC charger (85%-90%) and battery (95%) thee can't have been much loss to battery thermal management. This was in the South SF bay (Cupertino, Sunnyvale, Los Gatos) in Sep 2013-Sep 2014.

Charging was usually done in the morning as we have chargers at work. Temperatures at that time were probably 50-80°F depending upon time of year etc.

Kevin
 
brothergrimm said:
...I don't mind a 700-watt process running here or there for a short amount of time, but if it's going to be on all the time while plugged in during hot weather, that's going to really add up over the course of the summer.
Don't worry about that.
Think 'Refrigerator'. If you had a cooling unit running non-stop at 700 watts you'd eventually have a battery pack at -20° F.

When plugged in the car's TMS runs only as required to keep the pack in a happy range of temps. Hot or cold.
My TMS needs so far have been for battery pack warming in the dead of winter. But I hear it kick in and ramp up at a DCFC for cooling too.
The pack itself is somewhat insulated so a little TMS goes a long way.

Worst case: Unplug after 'green light' flashing. Then, during your next drive you may see the 'percentage number' on the 'leaf' page rise.
I would see this in the winter. During the first ~5-10 minutes of a drive I'd see the 'Battery Conditioning' display slowly go up to ~4-5% and then not move again during a 30 minute drive.

Battery Conditioning is TMS, correct?
So use it plugged in, or use it from the battery power as you drive.
The system works, as needed, automatically to keep you pack HAPPY !!

Only time will tell how happy. We know how happy some Leaf battery packs have been with their lot in life...
 
Here's more on the continuous energy consumption from my Spark. This is what I've seen after plugging-in my fully-charged car this morning.

This represents about 2.8kwh of energy consumption over the course of 4 hours, with none of it going to actually charging the battery.

HgVqJ4O.png


I've overlaid the temperatures we're seeing in Sacramento this morning. The hours are on top with the minutes on the bottom. For example, the first bar was 200 watts and was recorded at 8:46am this morning. (I was just collecting this all from readings off a Kill-A-Watt.)

Do folks still this this is normal and intended behavior from the car?
 
I monitored charging when I first got the car about a year ago, and when the battery was full, there was no power drawn, though I disconnected when full. That was with L1 and Kill a watt. I now use L2, and did not pay attention. I don't charge to 100% at home, and always disconnect; 100% is not good for the battery.

Few things you can try:

1. Put the car on delay charging and plug it in. Does it still use power when it's not supposed to be charging?

2. After 100%, disconnect, then reconnect. Power still high after going to 100% again?

3. Does the car make noise (whirring sounds) when plugged in? When not plugged in?

4. What is your mi/kWh when going constant 55 MPH on level road with no wind? It should be over 5 mi/kWh.
 
I tried the complete disconnect and reconnect first because it was the easiest. :)

It was pretty busy in the first 30 minutes...
2:15p, 300 watts, then fan comes on, down to 120 watts
2:16p, some clicking and whirring, using 200 watts
2:18p, same noises, but watts climb in steps: 515, then 730, then 830
2:23p, heavy fan noise, 160 watts
2:25p, no noise, 100 watts
2:26p, some clicking and whirring again, using 200 watts, then up to 360
2:27p, got tired of recording things :)
2:53p, by this time the car had settled into its 640-watt continuous usage again

If I unplug the car, all noises disappear. I've been getting at least 5mi/kwh, though I'm wondering if it would do that now that it's summer.
 
brothergrimm said:
...2:53p, by this time the car had settled into its 640-watt continuous usage again....
This can't be correct TMS functioning. That is a lot of power. Where is it going? What is it trying to do?

Could it be faulty battery temp sensors? There has to multiple sensors.
Could it be faulty TMS management module? Could it be running the battery coolant loop heater and the AC compressor simultaneously?

If this behavior is happening while the hood is open there is a way to tell if the AC compressor is running by touching the 'Coolant to Freon' heat exchanger.
This is an aluminum block-like component mounted on the right side of car. It is high, near the rear with two freon lines and two coolant hoses connected to this 'block'. If it's cold to the touch the AC compressor is running. You should see the 'radiator' fans running also. (Or just unplug the car, pop the hood, when all is quiet and touch it.)

But then what if it is constantly running the cooling functions for the battery pack?

Wow, how are you going to quantify this and get Chevy onboard to fix your car?
I think GM has an 'EV Group' of specialists in customer service. When I had a Volt I had a 'Volt Advisor' assigned to me.
Good Luck trying to get them, and/or your local dealership, to listen to your evidence and take you seriously.
Please keep us informed.
 
Yeah, if no one else is seeing this, I guess it's time to speak with some service folks. I'll follow-up here with what I find out. Thanks again!
 
brothergrimm said:
Yeah, if no one else is seeing this, I guess it's time to speak with some service folks. I'll follow-up here with what I find out. Thanks again!
This looks like something is wrong. I have both a 2014 and 2015 Spark EV and neither car exhibits what you are seeing in this hot weather in Central California. Both cars charge to 100%, cool down for 30 minutes and then disconnect. I too would suggest a trip to the dealer is needed.
 
I spoke with the customer relations center this morning, and they conferred with a technical adviser twice while I was on the line. The technical adviser indicated that a continuous draw of 640 watts in warm weather is normal. They said the car is trying to maintain the battery temperature at 75 degrees or something along those lines.

When I said that other people with the Spark EV in hot climates were not experiencing this continuous draw, they didn't have anything else to add except that I was welcome to take it into the local dealership to have it checked out. Which I'll do, but probably not anytime soon. I'll just unplug it after it's charged. It's a lease, so I'm not really feeling like spending a max of $1.54/day (0.64kw x 24 hours x $0.10/kwh) to keep the battery at top health. (Not to mention that the value propositions of this car being cheap to run and better for the environment are severely impacted.)

This is my first annoyance with the car, which I've otherwise really loved. If this truly is normal behavior, I hope they change it for the Bolt EV, as it could be a PR disaster for GM and the electric car movement. Let's say you drive 14 miles to work and back, using 2.8kwh of energy. If you come home and plug it in at 6p, then leave at 8a the next morning, that's ~3kwh to charge the battery (probably a little more due to efficiency losses) and ~9kwh to run this 640-watt process for 14 hours. In this scenario the EV is 4x less efficient than previously thought. :-/
 
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