[Ovmsdev] Charge time prediction

Robin O'Leary ovmsdev at caederus.org
Wed May 16 18:17:27 HKT 2018

On Wed, May 16, 2018 at 08:19:13AM +0800, Mark Webb-Johnson wrote:
> If we don’t know current + voltage available from the charger, then
> how can we predict charge time? Or is the current + voltage for the
> Twizy always the same (fixed?).

It's still useful to show charge time estimate(s) even when charging
isn't in progress.  We can't be sure what will happen, but we can still
make reasonable guesses in various ways:

    - show several estimates covering a range of charger capabilities
      (this is what the Leaf does on the dash)

    - assume the charge continues with the same parameters as it left off
      (is this what OVMS did before the change discussed?)

    - use past location data and history to predict what will happen
      (wishful thinking!)

It seems to me that there is a strong case for having an "estimates"
module to off-load this kind of thing from vehicle-specific modules.
It gets so much more complicated when you go beyond what the vehicle
module can report as objective fact (the battery capacity is X, the
charger current is Y) and in to more subjective territory, where people
have different ideas of what works best for them.  We've already hit
that in the Leaf code with the SOC metric.  I think there needs to be a
clear separation.   To please everyone, the "estimates" module is likely
going to need a load of tunable parameters that shouldn't be replicated
in the vehicle modules.  Maybe it could be completely general, like the
script-driven metric generator for OBDII?

> I think it is important to clear these prediction values when they
> are no longer useful or correct, and relying on individual vehicle
> modules to do it seems incorrect.  We should be able to do this in a
> standard way. But, I see your point about an interrupted charge (I
> guess in that case we can presume a new charge would resume and the
> predictions would be roughly correct, so long as vehicle and charger
> state did not change).

Not sure I see your reasoning here.  Even when the car is not plugged in
to a charger, wouldn't you still want to see some estimated charge times?

> How about we clear these when the vehicle charge port is detected
> closed? (in addition to the existing ‘charge done’ condition)

That wouldn't help the Leaf, which doesn't seem to have a sensor for
the charge port door, so we are currently faking that from the charge
detect logic.
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