[Ovmsdev] VDS calculated state vs. data available via CAN

Mark Webb-Johnson mark at webb-johnson.net
Fri Apr 27 16:20:18 HKT 2012

My car went in for annual service yesterday. As part of that, all power is isolated, the pem is removed, and VDS and VMS are shutdown.

When I got it back, with latest 4.6.5/40 firmware, I'm glad to say everything worked as expected. OVMS resumed and I got charging status ok - I even got a SMS alert when the Ranger stopped the test charge he was doing ;-)

Only issue was no pem/motor/fan temperatures in the App. Selecting the temperature screen on the VDS instantly brought them back, as expected.

When I got home, on the VDS, the car had lost its memory of charge time, mode and current limit. Maybe that is just a firmware upgrade issue, rather than generic VMS/VDS reset issue, but annoying as I was hoping to lose charge method/time but not current limit and mode (which is what we see on the bus).

Regards, Mark.

On 24 Apr, 2012, at 1:42 AM, Tom Saxton wrote:

> When the VDS on a v1.5 Roadster gets reset, it loses the following
> information:
>    Charge History
>    Energy History
>    Trip Meter Drive Time
>    Wh/mile history graph
> I take this to mean that these things are calculated from info on the CAN
> bus and stored in the VDS.
> In v1.5 Roadsters, the energy history got screwed up by a firmware update
> more than a year ago. The regen energy numbers shown are often ludicrous. In
> extreme examples, the day and month regen numbers can be larger than the net
> energy numbers. No doubt related to that, I see the regen number going up
> when the car is parked. (That's a nice trick!) I take this to mean that
> something on the CAN bus changed but the VDS firmware hasn't been updated.
> Things that are preserved over a VDS reset:
> Charge time, mode and current limit. (Current limit is stored by location,
> presumably by the VMS.)
> Trip distance and net energy used.
> So, presumably all of the values in this group can be queried from the CAN
> bus.
> Trip efficiency also persists. It may be calculated by the VDS or available
> on the CAN bus.
> My most recent trip meter showed 46.7 miles, 11.32 kWh, and 243 Wh/mile. If
> you do the math, 11.32 kWh / 46.7 miles = 242.398 Wh/mi, which should round
> to 242. Since the trip distance has been found on the bus at 0.1 mi
> resolution, it seems like that's the best data the VDS has. If there are
> higher resolution numbers somewhere (VMS?), then maybe the real values are
> 46.65 miles and 11.324 kWh -> 242.74 Wh/mi which rounds up to 243. So,
> perhaps the efficiency number is calculated elsewhere and broadcast on the
> CAN bus. Alternatively, the VDS either may have a higher resolution energy
> number than what it's showing or perhaps it just does math badly.
>    Tom
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