Felix,

It is progressing. I got the car and battery screens tidied up. Now supporting suppression of the TPMS boxes if there is no TPMS installed, and grayed-out figures for those that are not currently being recently updated by the car. I even got the throbbing animation working on the charge port - very nice.

Now working on moving the Info and Control screens around as we discussed.

After that will be the MAP screen and social group support.

Regards, Mark.

On 10 Apr 2012, at 1:44 PM, felix bonnier wrote:

hi mark,

how are you doing on the UI development?  no stress!  just wondering if there is anything I can help with.........?

best

felix b. 

Sent from my iPad somewhere in our beautiful universe.......

On 9 Apr, 2012, at 22:48, Mark Webb-Johnson <mark@webb-johnson.net> wrote:


From my testing last summer (31 Celsius in Hong Kong), the efficiency loss was much worse than 5%, especially at low charge currents:


Here's were my results at around 31 Celsius:

<attachment.php.png>

Here is Tom's analysis of my log files, vs his in cool weather, at the time:

<Hot-Weather-Charging-Stats.png>

Bottom line is that ambient temperature is very important to the estimate.

Tom:

I agree that the log files would give us the best historical data for a jump-start on this. The issues are (a) getting the files, (b) ambient temperature.

I don't think (a) would be a problem. I'll submit my logs for inclusion (I've probably got 100 or 200 charges in there at temperatures from 5 Celcius up to 33 Celcius). 99% standard mode. I'm sure, that others would also submit, and we could pretty quickly build up a model.

For (b), we either need to find it in the logs files, approximate it from something in the log files, or use something like this to approximate it.

For example, I did a charge on my car at 19:31 on 30th March 2012. VMSParser shows:

03/30/2012 19:31:30 | 1333107090 | C1MB | Coolant 30C ESS 28C - 29C charging at 203.7V 0.01A
03/30/2012 19:31:30 | 1333107090 | C30M | range soc = 73%, 70A available
03/30/2012 19:31:31 | 1333107091 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.9V 0.00A
03/30/2012 19:31:32 | 1333107092 | C1MB | Coolant 30C ESS 28C - 29C charging at 221.0V 0.02A
03/30/2012 19:31:33 | 1333107093 | C1MB | Coolant 30C ESS 28C - 29C charging at 221.1V 0.00A
03/30/2012 19:31:34 | 1333107094 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.9V 0.00A
03/30/2012 19:31:35 | 1333107095 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.8V 0.02A
03/30/2012 19:31:36 | 1333107096 | C1MB | Coolant 30C ESS 28C - 29C charging at 221.0V 0.01A
03/30/2012 19:31:37 | 1333107097 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.8V 0.00A
03/30/2012 19:31:38 | 1333107098 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.8V 0.01A
03/30/2012 19:31:39 | 1333107099 | C1MB | Coolant 30C ESS 28C - 29C charging at 221.0V 0.00A
03/30/2012 19:31:40 | 1333107100 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.9V 0.02A
03/30/2012 19:31:41 | 1333107101 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.7V 0.00A
03/30/2012 19:31:42 | 1333107102 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.2V 0.04A
03/30/2012 19:31:43 | 1333107103 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.5V 0.00A
03/30/2012 19:31:44 | 1333107104 | C1MB | Coolant 30C ESS 28C - 29C charging at 221.0V 0.02A
03/30/2012 19:31:45 | 1333107105 | C1MB | Coolant 30C ESS 28C - 29C charging at 221.3V 0.00A
03/30/2012 19:31:46 | 1333107106 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.9V 0.02A
03/30/2012 19:31:47 | 1333107107 | C1MB | Coolant 30C ESS 28C - 29C charging at 221.2V 0.00A
03/30/2012 19:31:48 | 1333107108 | C1MB | Coolant 30C ESS 28C - 29C charging at 221.7V 0.01A
03/30/2012 19:31:49 | 1333107109 | C1MB | Coolant 30C ESS 28C - 29C charging at 221.7V 0.00A
03/30/2012 19:31:50 | 1333107110 | C1MB | Coolant 30C ESS 28C - 29C charging at 221.9V 0.01A
03/30/2012 19:31:51 | 1333107111 | C1MB | Coolant 30C ESS 28C - 29C charging at 222.2V 0.00A
03/30/2012 19:31:52 | 1333107112 | C1MB | Coolant 30C ESS 28C - 29C charging at 222.3V 0.23A
03/30/2012 19:31:52 | 1333107112 | C1MB | Coolant 30C ESS 28C - 29C charging at 222.3V 0.23A
03/30/2012 19:31:53 | 1333107113 | C1MB | Coolant 30C ESS 28C - 29C charging at 222.8V 0.18A
03/30/2012 19:31:54 | 1333107114 | C1MB | Coolant 30C ESS 28C - 29C charging at 223.2V 0.19A
03/30/2012 19:31:55 | 1333107115 | C1MB | Coolant 30C ESS 28C - 29C charging at 222.8V 2.23A
03/30/2012 19:31:56 | 1333107116 | C1MB | Coolant 30C ESS 28C - 29C charging at 222.9V 2.52A
03/30/2012 19:31:57 | 1333107117 | C1MB | Coolant 30C ESS 28C - 29C charging at 222.1V 5.71A
03/30/2012 19:31:58 | 1333107118 | C1MB | Coolant 30C ESS 28C - 29C charging at 220.8V 16.96A
03/30/2012 19:31:59 | 1333107119 | C1MB | Coolant 30C ESS 28C - 29C charging at 219.9V 27.05A
03/30/2012 19:32:00 | 1333107120 | C1MB | Coolant 30C ESS 28C - 29C charging at 218.3V 36.99A
03/30/2012 19:32:01 | 1333107121 | C1MB | Coolant 30C ESS 28C - 29C charging at 217.5V 46.94A
03/30/2012 19:32:03 | 1333107123 | C1MB | Coolant 30C ESS 28C - 29C charging at 216.9V 47.74A
03/30/2012 19:32:04 | 1333107124 | C1MB | Coolant 30C ESS 28C - 29C charging at 216.7V 47.75A
03/30/2012 19:32:05 | 1333107125 | C1MB | Coolant 30C ESS 28C - 29C charging at 217.3V 47.79A
03/30/2012 19:33:05 | 1333107185 | C1MB | Coolant 30C ESS 28C - 29C charging at 216.7V 47.84A
03/30/2012 19:34:05 | 1333107245 | C1MB | Coolant 16C ESS 25C - 28C charging at 217.9V 48.12A
03/30/2012 19:35:05 | 1333107305 | C1MB | Coolant 16C ESS 22C - 27C charging at 218.1V 47.96A
03/30/2012 19:36:05 | 1333107365 | C1MB | Coolant 24C ESS 25C - 27C charging at 217.7V 47.97A
03/30/2012 19:37:05 | 1333107425 | C1MB | Coolant 26C ESS 26C - 27C charging at 218.8V 48.11A
03/30/2012 19:38:05 | 1333107485 | C1MB | Coolant 28C ESS 26C - 28C charging at 217.5V 47.92A
03/30/2012 19:39:05 | 1333107545 | C1MB | Coolant 28C ESS 27C - 28C charging at 217.7V 48.06A
03/30/2012 19:40:05 | 1333107605 | C1MB | Coolant 28C ESS 27C - 28C charging at 218.5V 48.11A
03/30/2012 19:41:05 | 1333107665 | C1MB | Coolant 28C ESS 27C - 28C charging at 218.9V 48.14A
03/30/2012 19:42:05 | 1333107725 | C1MB | Coolant 14C ESS 23C - 27C charging at 217.0V 47.81A
03/30/2012 19:43:05 | 1333107785 | C1MB | Coolant 23C ESS 24C - 26C charging at 216.8V 47.74A
03/30/2012 19:44:05 | 1333107845 | C1MB | Coolant 26C ESS 25C - 27C charging at 217.9V 47.98A
03/30/2012 19:45:05 | 1333107905 | C1MB | Coolant 26C ESS 26C - 27C charging at 216.9V 47.78A
03/30/2012 19:46:05 | 1333107965 | C1MB | Coolant 27C ESS 26C - 27C charging at 218.8V 48.14A
03/30/2012 19:47:05 | 1333108025 | C1MB | Coolant 28C ESS 26C - 27C charging at 216.7V 47.77A
03/30/2012 19:48:05 | 1333108085 | C1MB | Coolant 28C ESS 26C - 27C charging at 216.3V 48.09A
03/30/2012 19:49:05 | 1333108145 | C1MB | Coolant 17C ESS 24C - 27C charging at 216.4V 47.76A
03/30/2012 19:50:06 | 1333108206 | C1MB | Coolant 22C ESS 23C - 26C charging at 218.4V 48.26A
03/30/2012 19:51:06 | 1333108266 | C1MB | Coolant 24C ESS 24C - 26C charging at 218.4V 48.26A
03/30/2012 19:52:07 | 1333108327 | C1MB | Coolant 26C ESS 25C - 26C charging at 217.7V 48.16A
03/30/2012 19:53:08 | 1333108388 | C1MB | Coolant 26C ESS 25C - 26C charging at 219.1V 48.25A
03/30/2012 19:54:08 | 1333108448 | C1MB | Coolant 27C ESS 25C - 27C charging at 218.3V 48.27A
03/30/2012 19:55:09 | 1333108509 | C1MB | Coolant 27C ESS 26C - 27C charging at 217.0V 47.95A
03/30/2012 19:56:10 | 1333108570 | C1MB | Coolant 28C ESS 26C - 27C charging at 217.0V 48.03A
03/30/2012 19:57:10 | 1333108630 | C1MB | Coolant 14C ESS 23C - 26C charging at 218.0V 48.02A
03/30/2012 19:58:11 | 1333108691 | C1MB | Coolant 24C ESS 24C - 26C charging at 217.4V 47.98A
03/30/2012 19:59:12 | 1333108752 | C1MB | Coolant 25C ESS 24C - 26C charging at 216.6V 47.78A
03/30/2012 20:00:13 | 1333108813 | C1MB | Coolant 26C ESS 25C - 26C charging at 216.9V 47.81A
03/30/2012 20:01:13 | 1333108873 | C1MB | Coolant 26C ESS 25C - 26C charging at 218.7V 48.27A
03/30/2012 20:01:30 | 1333108890 | C30M | range soc = 79%, 70A available
03/30/2012 20:02:14 | 1333108934 | C1MB | Coolant 26C ESS 25C - 26C charging at 218.4V 48.16A
03/30/2012 20:03:15 | 1333108995 | C1MB | Coolant 27C ESS 25C - 26C charging at 217.5V 47.79A
03/30/2012 20:04:15 | 1333109055 | C1MB | Coolant 17C ESS 24C - 26C charging at 217.3V 47.79A
03/30/2012 20:05:16 | 1333109116 | C1MB | Coolant 21C ESS 22C - 25C charging at 218.2V 47.85A
03/30/2012 20:06:17 | 1333109177 | C1MB | Coolant 24C ESS 24C - 25C charging at 217.3V 49.34A
03/30/2012 20:07:17 | 1333109237 | C1MB | Coolant 25C ESS 24C - 25C charging at 218.4V 45.78A
03/30/2012 20:08:18 | 1333109298 | C1MB | Coolant 26C ESS 24C - 26C charging at 220.4V 42.43A
03/30/2012 20:09:19 | 1333109359 | C1MB | Coolant 26C ESS 25C - 26C charging at 220.0V 43.13A
03/30/2012 20:10:19 | 1333109419 | C1MB | Coolant 26C ESS 25C - 26C charging at 219.6V 42.09A
03/30/2012 20:11:20 | 1333109480 | C1MB | Coolant 26C ESS 25C - 26C charging at 218.3V 43.46A
03/30/2012 20:12:21 | 1333109541 | C1MB | Coolant 26C ESS 25C - 26C charging at 218.6V 41.73A
03/30/2012 20:13:22 | 1333109602 | C1MB | Coolant 14C ESS 22C - 25C charging at 220.4V 40.81A
03/30/2012 20:14:22 | 1333109662 | C1MB | Coolant 23C ESS 23C - 25C charging at 219.5V 33.66A
03/30/2012 20:15:23 | 1333109723 | C1MB | Coolant 24C ESS 24C - 25C charging at 218.9V 36.06A
03/30/2012 20:16:24 | 1333109784 | C1MB | Coolant 25C ESS 24C - 25C charging at 220.4V 35.36A
03/30/2012 20:17:24 | 1333109844 | C1MB | Coolant 26C ESS 24C - 25C charging at 221.0V 32.97A
03/30/2012 20:18:25 | 1333109905 | C1MB | Coolant 26C ESS 24C - 25C charging at 220.9V 32.17A
03/30/2012 20:19:26 | 1333109966 | C1MB | Coolant 26C ESS 24C - 25C charging at 219.4V 33.65A
03/30/2012 20:20:26 | 1333110026 | C1MB | Coolant 13C ESS 22C - 25C charging at 218.9V 37.86A
03/30/2012 20:21:27 | 1333110087 | C1MB | Coolant 22C ESS 22C - 24C charging at 219.2V 28.58A
03/30/2012 20:22:28 | 1333110148 | C1MB | Coolant 24C ESS 23C - 24C charging at 220.6V 27.84A
03/30/2012 20:23:28 | 1333110208 | C1MB | Coolant 24C ESS 23C - 25C charging at 219.7V 27.55A
03/30/2012 20:24:29 | 1333110269 | C1MB | Coolant 25C ESS 24C - 25C charging at 221.3V 28.81A
03/30/2012 20:25:30 | 1333110330 | C1MB | Coolant 26C ESS 24C - 25C charging at 219.6V 24.53A
03/30/2012 20:26:30 | 1333110390 | C1MB | Coolant 26C ESS 24C - 25C charging at 219.1V 26.89A
03/30/2012 20:27:31 | 1333110451 | C1MB | Coolant 26C ESS 24C - 25C charging at 220.6V 26.35A
03/30/2012 20:28:32 | 1333110512 | C1MB | Coolant 26C ESS 24C - 25C charging at 220.5V 24.03A
03/30/2012 20:29:13 | 1333110553 | IDLE | range soc = 84% ESS 23C - 25C, 2.691V min, 1.205V max

and OVMS reported:

2012-03-30 18:24:07.142047 +0800 info  main: #10 C EV915 rx msg S 81,K,-1,0,done,standard,250,219,48,67,100,10,7,4,0
2012-03-30 18:24:07.144289 +0800 info  main: #10 C EV915 rx msg D 136,32,3,42,78,29,3272,65163,45,0,25,2,113,113
==> Driving PEM:42, MOTOR:78, BATTERY:29, AMBIENT:25

2012-03-30 19:23:57.730154 +0800 info  main: #10 C EV915 rx msg S 81,K,-1,0,done,standard,250,234,48,67,100,10,7,4,0
2012-03-30 19:23:57.732294 +0800 info  main: #10 C EV915 rx msg D 104,8,4,34,56,29,3284,65175,0,3379,24,2,102,113
==> Stopped PEM:34, MOTOR:56, BATTERY:29, AMBIENT:24

2012-03-30 19:33:57.348051 +0800 info  main: #10 C EV915 rx msg S 82,K,217,48,charging,standard,253,237,48,2,100,0,5,1,0
2012-03-30 19:33:57.374906 +0800 info  main: #10 C EV915 rx msg D 124,8,4,42,55,28,3284,65175,0,3986,25,2,120,120
==> Charging PEM:42, MOTOR:55, BATTERY:28, AMBIENT:25

2012-03-30 19:44:11.802571 +0800 info  main: #10 C EV915 rx msg S 84,K,217,48,charging,standard,262,245,48,12,100,2,5,1,0
2012-03-30 19:44:11.805104 +0800 info  main: #10 C EV915 rx msg D 124,8,4,43,53,27,3284,65175,0,4581,29,2,118,118
==> Charging PEM:43, MOTOR:53, BATTERY:27, AMBIENT:29

2012-03-30 19:53:11.578629 +0800 info  main: #10 C EV915 rx msg S 87,K,219,48,charging,standard,270,253,48,21,100,4,5,1,0
2012-03-30 19:53:11.582720 +0800 info  main: #10 C EV915 rx msg D 124,8,4,43,52,26,3284,65175,0,5142,28,2,120,120
==> Charging PEM:43, MOTOR:52, BATTERY:26, AMBIENT:28

2012-03-30 20:03:55.020585 +0800 info  main: #10 C EV915 rx msg S 91,K,218,48,charging,standard,282,262,48,32,100,6,5,1,0
2012-03-30 20:03:55.022789 +0800 info  main: #10 C EV915 rx msg D 124,8,4,43,51,26,3284,65175,0,5777,27,2,114,114
==> Charging PEM:43, MOTOR:51, BATTERY:26, AMBIENT:27

2012-03-30 20:14:03.376116 +0800 info  main: #10 C EV915 rx msg S 93,K,220,37,charging,standard,290,270,48,42,100,7,5,1,0
2012-03-30 20:14:03.378258 +0800 info  main: #10 C EV915 rx msg D 124,8,4,43,49,25,3284,65175,0,6374,29,2,112,112
==> Charging PEM:43, MOTOR:49, BATTERY:25, AMBIENT:29

2012-03-30 20:24:01.668658 +0800 info  main: #10 C EV915 rx msg S 95,K,221,28,charging,standard,296,277,48,52,100,8,5,1,0
2012-03-30 20:24:01.681265 +0800 info  main: #10 C EV915 rx msg D 124,8,4,42,48,25,3284,65175,0,6980,29,2,120,120
==> Charging PEM:42, MOTOR:48, BATTERY:25, AMBIENT:29

2012-03-30 20:33:59.497056 +0800 info  main: #10 C EV915 rx msg S 96,K,0,0,done,standard,299,280,48,57,100,9,9,4,0
2012-03-30 20:33:59.505736 +0800 info  main: #10 C EV915 rx msg D 108,8,4,34,47,25,3284,65175,0,7577,27,2,119,119
==> Charged PEM:34, MOTOR:47, BATTERY: 25, AMBIENT:27

I reckon the actual ambient temperature was probably 24 or 25 Celcius. It goes up during the charge, presumably because the HVAC is spewing out hot air around the ambient sensor at the front of the car (which is in the garage so will build up heat).

I think my data above is not a very good example, as I wasn't driving hard so the battery temperature was unusually low. My first instinct was that it would be good to use as an approximation for ambient, but actually not. The theory is that when the ambient temperature is hot or cold, the car has to use HVAC/heater to keep the battery at the temperature it needs, and that uses power which reduces charging efficiency. Battery temperature is a side-effect, and won't help to predict energy usage.

So, I still think ambient temperature is the correct thing to use as a predictor for charging efficiency (along with current+voltage).

The question is, looking at historical logs how can we approximate that? Only looking at charges that occurred an hour after a drive would work, but would remove 95% of my charges, like anyone else who plugs in when they get home ;-)

Regards, Mark.

On 8 Apr, 2012, at 4:22 PM, Dominik Westner wrote:

I already did some tests calculating the remaining charge time and had it implemented in the iPhone app.

First I took the simple approach to linearly estimate the remaining time by taking the charge current and voltage and calculate the energy per sec. Then take the missing energy from the current SOC. This will give you an approximation of the remaining time.

If you are looking at +/- 1 hour. This already should work from my experience.

I tried to make it better by taking into account that the charging curve is not linear, but more on a logarithmic scale. This worked a bit better. I also figured that there is some loss when charging, which I set to 5% (this probably varies by temperature).

What I did not know is the fact that once finished charging the batteries will be rebalanced for 30 minutes. Is this still shown as charging in OVMS? If yes, this would explain, why I've been off for about 30 - 60 minutes with my calculation.

I also did not take the age of the battery into account, which should be an important factor, too.

I think that it might be better to use a formula which tries to approximate the charging curve instead of using a fixed lookup table. At least it also could be fine tuned a bit easier by just setting a couple of parameters through the app to change the calculation.

Greetings

Dominik

On 08.04.2012, at 06:16, Tom Saxton wrote:

I think your model would work pretty well.

To calculate charge time, you also have to take into account the current
tapering near the top of the charge.

We can get most of the required data from log files. The only tricky bit is
getting the ambient temperature, which I don't think anyone has identified
in the log files. You could get a good approximating by only considering
charge sessions that start a least an hour of the most recent drive and then
use the starting temperature of the coolant as a proxy for ambient
temperature.

Range mode is the trickiest and the most important to time, they are also
done less often, so it's harder to get data. I'd be happy to collect logs
and extract data if we can get owners to contribute logs for a variety of
charging levels and ambient temperatures.

  Tom

on 4/6/12 5:52 PM, Mark Webb-Johnson wrote:

The core question I have here is whether it is possible to build a static
table saying that at this temperature, this available voltage+currrent, the
charging efficiency is X%? Something accurate enough to give us a charge time
prediction (given temperature, kWh needed by the pack, available
voltage+current) of +/- 1 hour?

I'm assuming the temperature should be ambient, as that is more important
overt the duration of a reasonable charge than pack temperature?

If we can have such a table, with steps of 5 degrees celcius between -10C and
+40C, and say 10 current levels, that is only 100 entries - and we would only
need 1 byte for each entry. The module could then put in the current
temperature, current/voltage level, and get out an efficiency factor. It could
estimate the kWh the pack needs (by mode and SOC/ideal-miles difference), then
multiply by efficiency factor, and get out an estimate of how many minutes is
required to achieve that.

Without this table, we could do the lookup on the server, but that would mean
having to set it _every_ night from the App/Server - as it would depend on the
SOC% the car was actually at.

If we could build this data, where could we get the data from?

Regards, Mark.

Begin forwarded message:

From: Mark Webb-Johnson <mark@webb-johnson.net>
Subject: Re: [Ovmsdev] Charge Control
Date: 6 April, 2012 8:25:51 PM GMT+08:00
To: OVMS Developers <ovmsdev@lists.teslaclub.hk>


Bennett Leeds and I have had a discussion off-list (I'm not sure if he is on
this list or not), and he brings up a valid point about balancing the pack
perhaps not occurring if we cut short the charge with a SOC limit.

Looking here:

http://www.teslamotorsclub.com/showthread.php/3848-Tesla-Roadster-Battery-Car
e?p=41995&viewfull=1#post41995

it seems that this approach may be non-optimal. For clarity, let me
cut-and-paste the Tesla reply here:

For simplicity’s sake, I will refer to all SOC (State Of Charge) numbers as a
percentage of a full (100%) charge. I cannot provide exact percentages, as
there are many variables which can cause these numbers to vary slightly,
however, I will get as close as I can.

When plugging in a nearly empty car that is set to Storage mode, the charge
will generally stop at around 20%. The car will then settle into its normal
Storage mode rhythm, topping up and discharging between 10% and 50% as the
car sees fit. Oftentimes it will keep a tighter envelope based on parameters
that I am not aware of.

Most important to remember is that Storage mode is not intended to be a
driving mode. This charge setting is primarily meant to optimize battery life
while the car is under storage conditions for two weeks or more.

Storage mode does not attempt to balance the pack, and you will cause an
imbalance in the pack by driving and charging in this mode regularly.

This will penalize you when you do occasionally charge the car fully in the
other modes, as you will not have the full range of the car available to you
until the car has a chance to balance its battery. Additionally, the car’s
range will not be as accurate if driven while in Storage mode vs. having
charged it in Standard mode after storing the car, then driving it.

Allowing the car to sit plugged in after it has finished charging in Standard
mode automatically balances the pack, and it may take a few rounds of this to
bring an imbalanced pack back to its full potential after many partial
charges. This is one of the major reasons we recommend keeping the car in
Standard mode whenever possible. Partial charges in any mode, while not on
their own bad for the battery, do not give the car an opportunity to balance
its battery, and over time can prevent you from accessing the car’s full
range potential.

When balanced, Standard mode charges the car to about 87%, with Range and
Performance modes getting the car to about 97%. These two percentages are
very much affected by the balance between bricks in the battery. An
imbalanced pack will not fill up all the way in any mode, nor will it be able
to discharge as far. Additionally, the range predictions will not be as
accurate.

Your voltages are about right.
4.10 volts = full standard mode (187-195 ideal miles)
4.15 volts = full range mode
4.20 volts = maximum of the cells that we never touch
As you may know, there is much more to it than just using voltage to
calculate range with Lithium batteries. This is something that is incredibly
complicated, and not something that I am qualified to discuss in detail, as I
do not have the full picture.

It is important to remember that SOC is not the only factor in maximizing
battery life. For instance most lithium batteries are shipped at around
30-50% SOC in consumer electronics, and part of the reasoning is that they
are less susceptible to damage from extreme temperatures at these charge
levels. It is also safer to store them at these levels. Part of the benefit
of Storage mode is that there is less work required from the HVAC system to
keep the batteryhappy and safe, and therefore, less energy is consumed while
stored.

We chose ~90% as a Standard full charge level because it offers most of the
longevity benefit of keeping the car at a lower state of charge, while still
allowing a high degree of autonomy. I understand that you are interested in
taking extra steps to maximize your battery’s life, so I do have some
suggestions for you.

I would not recommend that you continue to use Storage mode as a means of
maintaining a lower state of charge. As I explained earlier, this mode is not
optimized for this type of use.

Think of battery degradation this way. It is very much a function of time
spent at voltage and temperature. For instance, you do not want to charge a
car all the way in performance mode, and then let it sit in the sun all day.
Between the higher thermal limits and the high SOC, you are causing the
battery a relatively high amount of degradation .In fact, the car will
eventually allow itself to discharge to Standard levels if left in
Performance mode to prevent inadvertent damage to the battery. If you start
driving right away after charging in Performance or Range Mode, and don’t let
it sit, you would minimize the damage incurred, as the time spent at these
extremes is an important part of the calculation.

Similarly, if you top off to full in Standard mode, then jump in the car
right away and bring the SOC down quickly, you will minimize the small amount
of degradation that occurs at ~90%.

If you prefer to keep a lower average SOC in an attempt to maximize the life
of your battery, I would instead suggest that you stay in Standard mode and
utilize the Roadster’s built in charge timer and current limiting options to
find an average SOC that works for you. For instance, try starting your
charge at a time that allows the car to top off to a level you are
comfortable with right before you need to leave. Alternately, you can use the
Current limiting function to adjust the amount of time it takes the car
reaches a target SOC, or even a combination of these two options. The car
will remember the settings you select based on your location, so once you
find something that works for your commute, you can set it and forget it.

Just remember that the car does benefit from being allowed to sit fully
charged in Standard mode, and should be allowed to do so frequently,
especially if being used on a daily basis. Leaving the car plugged in in
Standard mode after it is done charging will initiate this balancing program
automatically. This doesn’t take much time, 30 minutes or so should do. It
may take several of these balancing cycles to bring the car back to a
balanced state if it has become imbalanced, which is something that a lack of
regular Standard mode top ups and subsequent balancing cycles can induce.

It would therefore be a good idea to set the car to “Charge on Plug In”
instead of “Charge at X time” in the charge timing menu for at least a few
Standard mode charges per week to keep the pack balanced. There are simply
too many variables for me to be able to predict how often you would need to
do this, and we do not have a recommended procedure for alternate desired
average SOC levels.

I hope this helps answer your questions, and gives you a better idea of how
to maximize battery life under your driving conditions.

Regards,

Dan Myggen

From what he is saying, it appears optimal to time the charge to bring it to
full charge in standard mode 30 minutes before you leave. That would leave
the car sitting at high charge rate for the least amount of time, but allow
enough time for balancing to occur if necessary.

This sounds exactly like our finish-charging-by approach. Rather than set the
charge start time, you set the finish time, and the system works out how long
it should take then adds on a 30-to-60 minute safety margin (which would also
allow for battery balancing to occur).

Does this make sense? Or is Dan Myggen's advise wrong?

Regards, Mark

On 5 Apr, 2012, at 7:45 PM, Mark Webb-Johnson wrote:


I'm now starting to think about the v1.3 firmware, which is intended to add
the following:

Log charge history
Log drive history
Sophisticated control of charge time

We don't really have TOU metering in Hong Kong, so not much use for me, but
part [3] would be fun nevertheless. Most charge control in EVs is pretty
basic, and it might be interesting to see how sophisticated this can be made
without complications.

I don't know if this is workable or not, so put my thoughts out into the
open for discussion.

For charge time, the consensus seems to be that people want to enter the
time to FINISH charge, vs the current time to START charge. To do that, we
need an estimate of how long the charge will take. For that, we either need
a sophisticated model or a collection of historical data we can lookup to
find something approximate. Hence item [1] on my list.

Elon talked about the car learning about you. Where you park. Where you
charge. etc. So, if always leave home at 7:00am to go to the office on
Mondays through Fridays, perhaps the car can learn? Or, at least suggest
based on what it has seen... Hence item [2] on my list.

For [1], we would store such things as temperatures, SOC start, SOC end,
charge mode, charge current, charge voltage and duration. The can bus charge
message seem to include this information.

For [2], we would store such things as date/time of drive, duration (time,
distance, and elevation change), battery usage. We seem limited in this from
what we have decoded on the can bus so far.

Regardless of the above, [1] and [2] would be useful information for any
owner, anyway.

Privacy is an issue. Two problems - (a) protection of my charge/drive
history, (b) the use of 'shared' charge history for [3]. My suggestion is to
keep drive and charge history private. Perhaps it could just be stored as
paranoid mode blobs. But, there should be an option to allow anonymised
sharing of charge history for the use of [3]. My thinking is that if you
share your data anonymously, then your lookup includes the pool of others
anonymous charge history. if you choose not to share, then your lookup is
only against your own charge history.

I did toy with the idea of using the server to control this. So, at 3am the
server sends a command to the car to start the charge, etc. That would
simplify the firmware in the car, but has a major problem of GPRS
connectivity - if the cellular signal was lost the charge wouldn't start.
Bad. So, I think it best to have the historical database in the server, the
calculations in the App, and the settings downloaded to the car while it has
cellular signal (after which it just follows them autonomously).

The Tesla Roadster currently offers you a choice of charge on plug-in, or
start charge at a particular time. It also allows you to limit charge
current and set charge mode. My thinking is to extend this by making it per
day-of-the-week for a few defined locations, and to provide an override for
the 'current' day/night. If the override is not set, and you are in one of
the defined locations, then the system looks up the day of the week and
controls charge based on what you have set. The UI for this is quite simple
- presumably a screen with tabs/selector for day or the week, and then
controls to set charge mode, current limit, and time to start/complete by.
One developer also had the good idea that a charge SOC limit would be useful
(e.g.; please stop charge when it gets to 70% / 220km ideal).

How do we handle night vs day charging? Is this only for overnight, or do we
base it on when you plugin?

Is this workable? Useful?

Really interested in people's feedback on this.

Mark.

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