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Discussion Starter #1
There has been a technique that has been used by some here instead of using remote start. Instead, we would turn on the car with it still plugged in (L2) and the car would continue to charge for 15-20 min or so. Make sure all accessories are off (lights, climate control, radio, etc).

One thing I noticed is that after I topped off the charge and drove, the battery meter would drop each 10% at x.9 kWh (0.9 kWh @ 90%, 1.9 kWh @ 80%, etc) like it normally does. Keep in mind I have a 2012 Volt.

However, if I did not let the cycle complete until the green dome light started flashing (indicating charge complete), then when I drove I noticed each 10% drop of the battery meter would be at x.2 or even x.3 kWh (1.2 kWh @ 90%, 2.2 kWh @ 80%, etc), indicating I was getting an extra 0.3 or 0.4 kWh out of the battery.

Well, I finally bought an OBDII device (why did I wait this long???) and logged the data through the Torque android app, and it totally confirms my results. One thing, the SOC % only climbs by 0.39% increments. It start at 88.24%, initially drops by a small amount, then climbs about every 90 seconds or so by 0.39% to a maximum of 90.59% and when charge is complete, it drops back to 88.24%. Based on these results, I will no longer let the cycle complete and will interrupt it before it finishes. I'm not sure why this happens, maybe someone else who knows more of what is going on can explain. I did not log the motors to see if they were engaged to draw off the extra charge.

 

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The instant drop back after the charge is complete makes me wonder if there's some kind of measurement or estimation error involved. I know that measuring the state of charge of lithium batteries isn't trivial, and if the car had decided it needed to shed loss you would have seen a gradual drop rather than the spike. I can't imagine that it could/would use the motors; to my mind the most likely candidate for a sink would be the electric heater (which is on the same smaller contractor and doesn't involve risks of the car moving.) As far as I know, we've never seen an indication of the car burning off excess charge while stationary, just the two motor pad in lieu of regeneration at ultra high SoC.
 

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There have been times where I have plugged in my Volt to charge, and a few minutes after plugging in, I notice on my remotelink app that the SOC has actually decreased a percentage point or 2.....wonder if that's just the Volt doing some internal math corrections on the SOC reading....that might be what is happening to you too, ari.
 

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Discussion Starter #4
There have been times where I have plugged in my Volt to charge, and a few minutes after plugging in, I notice on my remotelink app that the SOC has actually decreased a percentage point or 2.....wonder if that's just the Volt doing some internal math corrections on the SOC reading....that might be what is happening to you too, ari.
Yes, I have seen that as well when I plug in and after a few minutes I lose a few %. However, the most important part of my test is only partially topping off the charge results in .3 or .4 kWh extra before I lose each 10%. The car does charge for an extra 15-20 min, so the electricity is going somewhere. However, whenever I let the cycle complete I can only get x.9 kWh at each 10% mark.
 

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The instant drop back after the charge is complete makes me wonder if there's some kind of measurement or estimation error involved.
Could it be related to the natural voltage drop that Lithium batteries do after charging? I know traditional SOC should be derived from amps in and amps out, but I have no idea what goes into the calculation that the volt uses. I have a SOC meter on my electric bike and it uses an algorithm for SOC that emphasizes amps in the middle but put more weighting to voltage at the ends.
 

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Discussion Starter #6
This morning before leaving for work I monitored the SOC. I did not let the charge complete and unplugged my Volt when it reached 90.59%. This was about 10 minutes. I monitored the SOC on my drive. It did not drop back down to around 88.24% until I had used 0.4kWh. Each 10% drop on the battery meter matched up with this as it was dropping at the x.3 kWh marks.

I closely monitor fix points along my drive and what the kWh usage should be. It normally takes 0.5kWh or 0.6kWh to leave my neighborhood. It was cold this morning (for Northern VA) and was 20F, so it took 0.6kWh, just as I would expect. So, the kWh usage is exactly as I would expect, however I am getting an extra 0.4 kWh out of the battery.

Yesterday, when I charged for an extra 20 minutes, I was not getting this extra 0.4 kWh. Why? I have a theory. When the Volt finishes charging, it maybe resets the SOC to a fixed value. This could explain the sudden drop. Maybe there is no more of a charge. However, the important thing is the empirical evidence. If I can drive an extra 0.4 kWh worth, then this is quite important. Well worth the $12 investment in the OBDII device and $5 in the Torque Pro App!!
 

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This morning before leaving for work I monitored the SOC. I did not let the charge complete and unplugged my Volt when it reached 90.59%. This was about 10 minutes. I monitored the SOC on my drive. It did not drop back down to around 88.24% until I had used 0.4kWh. Each 10% drop on the battery meter matched up with this as it was dropping at the x.3 kWh marks.

I closely monitor fix points along my drive and what the kWh usage should be. It normally takes 0.5kWh or 0.6kWh to leave my neighborhood. It was cold this morning (for Northern VA) and was 20F, so it took 0.6kWh, just as I would expect. So, the kWh usage is exactly as I would expect, however I am getting an extra 0.4 kWh out of the battery.

Yesterday, when I charged for an extra 20 minutes, I was not getting this extra 0.4 kWh. Why? I have a theory. When the Volt finishes charging, it maybe resets the SOC to a fixed value. This could explain the sudden drop. Maybe there is no more of a charge. However, the important thing is the empirical evidence. If I can drive an extra 0.4 kWh worth, then this is quite important. Well worth the $12 investment in the OBDII device and $5 in the Torque Pro App!!
I think I know what you're talking about. I usually go out in the morning and program all my addresses that I have to inspect into my navigation. The light goes from flashing to solid green and then charges for a while after I'm done. On those days, I've noticed that instead of the battery meter dropping to 90% at 1.0 KWH, it goes till 1.1 or 1.2 KWH.

I don't have the device you have or any of that stuff. But now, I just go turn the car on in the morning until the light turns solid green (usually within a few seconds), then turn it back off and let it top off the charge and I get the extra 0.1 or 0.2 kwh in the first 10%. I've never tried to stop it just short of a full charge. My onstar app always goes from 96% to full. I think I've seen 97% once, but never 98 or 99%. It skips those and goes to full. I've tried unplugging at 95% and the best I ever get out of the first 10% of the battery meter is 0.6 KWH, where if I let it charge another 10 minutes, I get the full 1.0 kwh.

Strange that we both have 2012 Volts. When I first bought mine and for the first 6 months or so, I consistently got 10.6 KWH of use every time. once saw 10.7. Then all of sudden, overnight, it dropped down to 10.2 kwh and has remained at that level ever since. I've read where you said you only get 9.7 most of the time? Am wondering why there is a difference. The only thing I could think of was that I waited until late 2012 to buy mine so it had the revised emissions so that it was eligible for the carpool lane stickers. Am wondering if, with that, it was programmed to use the battery more like the 2013??
 

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This morning before leaving for work I monitored the SOC. I did not let the charge complete and unplugged my Volt when it reached 90.59%. This was about 10 minutes. I monitored the SOC on my drive. It did not drop back down to around 88.24% until I had used 0.4kWh. Each 10% drop on the battery meter matched up with this as it was dropping at the x.3 kWh marks.

I closely monitor fix points along my drive and what the kWh usage should be. It normally takes 0.5kWh or 0.6kWh to leave my neighborhood. It was cold this morning (for Northern VA) and was 20F, so it took 0.6kWh, just as I would expect. So, the kWh usage is exactly as I would expect, however I am getting an extra 0.4 kWh out of the battery.

Yesterday, when I charged for an extra 20 minutes, I was not getting this extra 0.4 kWh. Why? I have a theory. When the Volt finishes charging, it maybe resets the SOC to a fixed value. This could explain the sudden drop. Maybe there is no more of a charge. However, the important thing is the empirical evidence. If I can drive an extra 0.4 kWh worth, then this is quite important. Well worth the $12 investment in the OBDII device and $5 in the Torque Pro App!!
This is what I was thinking. I believe there is some recalibration done to SOC and AER discharge window at full charge. I would e surprised if GM burns off excess charge. What would be the point of that? I'm think it recalibrates full to the current state at complete charge and full by the Volt's definition is 88.24%. Each 10% decrement is at some measured 10% reduction in capacity from there. This falls in line with the resetting that occurs with "full" charges. The Volt allows for charge above 88.24% for regen on full and there are probably measuring requirements that go along with charging that dictate a certain amount of charging occur before "full" is determined. Sounds like you figured out a way to gamed the Volt's charging system a little.

Some may warn you about battery degradation but really it is no different than someone living at the top of a hill.
 

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Discussion Starter #9
Strange that we both have 2012 Volts. When I first bought mine and for the first 6 months or so, I consistently got 10.6 KWH of use every time. once saw 10.7. Then all of sudden, overnight, it dropped down to 10.2 kwh and has remained at that level ever since. I've read where you said you only get 9.7 most of the time? Am wondering why there is a difference. The only thing I could think of was that I waited until late 2012 to buy mine so it had the revised emissions so that it was eligible for the carpool lane stickers. Am wondering if, with that, it was programmed to use the battery more like the 2013??
I honestly do not remember what I could get on a full battery when it was new. When I started paying close attention after 6 months or so it was around 9.9kWh. That is what I usually get unless it is cold and I do not warm up the battery, then it can be as bad as 9.6 or 9.7 kWh. I've asked WOT about some Volts having 10.2 and others as low as 9.8 and he said that each Volt sis a little different in regard to the battery pack and determining kWh usage. It is just an estimation. As long as you are getting a decent range then that is the important thing.

As far as having a 2013 battery, the best indication is how long does it take for a full charge at L2. If it is over 4 hrs, then most likely you have a 2013 battery. If it is more like 3:40 then it is a 2012 battery.

Some may warn you about battery degradation but really it is no different than someone living at the top of a hill.
Well, I live at the bottom of a steep driveway and use 0.1 kWh for my first 300 ft, so there is no issue with me putting any additional charge into the battery. I do not do this all the time, just when I really need an extra 0.4 kWh.
 

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I'm not an electrical engineer, so everything that follows is logic - not a refined understanding of battery technology as employed by GM.

I think the 'effect' mentioned of the SOC dropping at the end of the charge cycle is merely an artifact of the algorithms and math, and probably related to the dreaded term 'statistics' before the 'brain' arrives at the number to post on the dash.

First, if the actual SOC was reduced so quickly then ......... where did the power go?????? If nothing is 'on' then a great deal of heat (work) was created somewhere. Where? On the other hand, there is the issue of the system polling the cells of the battery to see how much charge each has - and then making an attempt to equalize the charge throughout for maximum operational efficiency - and probably to detect the possibility of a poor cell to trigger a fault alert.

Pulling the plug before the cycle ends may give a better 'reading' but I'm guessing it's really more of an illusion.

Before you torch me I'll remind you I'm making a guess here. But physics demands a plausible explanation for an outflow of energy in a very short time. Or getting more energy in less time than the full cycle.
 

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Discussion Starter #11 (Edited)
The important thing is that I can get an extra 0.4 kWh out of the battery. Before I started doing this I would almost always get a projected 9.9 kWh out of my battery. Today, I used the technique described here and returned home after using 9.9 kWh and I still had 2 miles renaming. Without this start-up technique I would have either switched to gas or would have been on the electrical equivalent of fumes.

I described this technique on the Chevrolet Volt Facebook page. This was the response from Chevrolet.

The values you are seeing for the State of Charge and the kWh used on the center energy display are both calculated values based on GM's own proprietary algorithms. The key thing to note is that they are not measuring anything physical. Physical parameters are fed into the algorithms, but those values you are watching can fluctuate and are very good estimates, not actual values. The Volt does have a small battery buffer built in for customers who live at the top of a hill, and it looks like you've found a way to over-charge the battery. While you are not doing anything that would void your warranty, it is not recommended to use this practice for such a small increase in EV range.
I don't consider getting an extra 2 miles of range small. I think it could make the difference between going 100% EV or switching to gas for some people. I won't be doing this every day, but on colder days where I need the extra range, I will.
 

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No company would endorse what you are doing given the situation but I'm sure individuals from those companies would off the record. You should have issues from it. In fact, I see this as a failed opportunity thus far on GM's part. They should make a charging feature to better take advantage of this battery capacity. Since they built in a the buffer as we surmised, and GM has now confirmed, for regenerative braking to work for those living at the top of a hill, it must be OK to use this capacity on a daily basis. Instead of only a select few being able to use this daily (without using your charging trick), GM should allow a max charge with reduced regen. If the buffer is worth only two miles of EPA range then that would give the Volt the magic 40 mile rated range and as you note it could be more. Only those living at the top of a large may choose not to take advantage so they don't have a short period of reduced or no regen. My guess is everyone would just charge to the max. This would require some programming but not a ton. Small price to pay for increased range!!!
 

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An extra mile or two of range would be a very nice bonus for me. If i can get this to work on my 2013 using a 120 plug i will be a happy camper. I dont see me using this every day but on days i know i am going to be putting on the miles this could be very useful.
Thanks, Ari!
 

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The extra 0.3 kW thanks to this technique is just 1 extra mile, so we are talking only a barely noticeable gain here.

Unlike a conventional gasoline tank gauge, a battery SoC indication is a guess based on counting the current in and out, historical data and some measurements of the voltages. There are errors in the process. In reality no electric energy gets lost. It is indeed likely that by terminating the charging prematurely the SoC algorithm does not re-calibrate itself. That seems to result in a slightly larger charge window.

Notice that in the Cadillac ELR the charge window of the same battery was widened from 65% to 72%, apparently without much effect on battery lifetime. (see this thread). The Volts EPA battery range could raise from 38 to 43 miles with this simple parameter charge.
 

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Discussion Starter #15
This morning I wanted to test out this technique using L1. I was going to log the statistics in Torque App and compare to L2 charging. Well that was not possible as it did not work for me at L1. It only charged for maybe 2 minutes and then indicated charge complete. I unplugged L1 cord and plugged in my L2 and it charged up for 10 more minutes or so.

I'll try again in a few days, but I have a feeling I will have the same results.
 

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Ari,

Do you think your technique does the same thing as "burping" the Volt. (unplugging when full and then plugging back in shortly thereafter.) I unintentionally burped my volt today. (unplugging and plugging it back in after a short loss of household power) and it drank another 0.4 kWh and the first battery bar didn't drop till 1.2 kWh on my commute today. Have you used your tools to measure what effect the burping technique has on the SOC?
 

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Discussion Starter #17
Ari,

Do you think your technique does the same thing as "burping" the Volt. (unplugging when full and then plugging back in shortly thereafter.) I
I have not tried yet. I will test this out later today or tomorrow and see how high the SOC gets using this technique.
 

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Discussion Starter #18
I tested the "burp" technique where the Volt is unplugged then plugged back in after a full charge.

It worked, but not nearly as good as using the technique where the Volt is turned on.

The "burp" method the SOC goes as high as 89.41% and lasted for 10:25 the one time I tested it. As soon as charging completes, the SOC drops back to the level it started at.

The "powered on" method the SOC goes as high as 90.58% and lasts around 16 min or so.

Clearly, both work, but the "powered on" method the charging lasts longer and the SOC goes much higher as well.
 

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In the winter I like to precondition. In many cases this makes the car comfortable enough to keep the climate off on my way to work (saving a lot more than ~0.4kWh). If I start the car (versus remote start) but do NOT turn off all the accessories (radio is off BTW) using L2 will I get the "powered on" benefit?
 

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Ari - I'm a little confused as to the technique you are using. You said you are "powering on" the Volt with no accessories running while plugged in to a L2 EVSE. But, are you then powering off and leaving it plugged in for another 10-15 minutes before unplugging, powering back on and driving away? Or are you leaving it powered on with no accessories running for 10-15 minutes before unplugging and driving away?
 
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