[Ovmsdev] Charge Timing Feature Suggestions

Bennett Leeds bennettleeds at gmail.com
Mon May 21 05:20:01 HKT 2012

I'd like to see a "Ready By" feature that also takes into account
electricity pricing tiers and battery SOC. I see two scenarios:

1) Daily/commuter charging that leverages off-peak for saving money and
reducing demand on the grid, and also doesn't keep the battery full longer
than necessary (although this isn't really a problem I've heard).

2) Long trip charging where you don't want the car sitting at Range full
for any longer than necessary, and also want to leverage off-peak periods.

Here's how I've imagined them working:

1. You tell the car when the off-peak periods are. I think 4 params would
be sufficient:
     a. weekday off-peak start time
     b. weekday off-peak end time
     c. weekend off-peak start time
     d. weekend off-peak end time

   I know these change with the seasons, but you will just have to reset
these twice a year, not a big deal.

2. You set the maximum amperage you can actually draw at this location,
unless you've charged here before the and car remembers and OVMS has access
to that information.

3. For the commuter version, you then set the time you leave each weekday
morning - the Ready-By time. The car starts charging as late in the
off-peak period as possible that finishes either by the end of the off-peak
period or by the time you're leaving. We may want to have it finish a 45
minutes earlier to enable battery balancing. We use the SOC and max
amperage draw to figure out when to start. If we need to start before the
off-peak to make the Ready-By time, we do that - better to spend more than
not have a full battery the next day.

4. For the long-trip version, you set also set the Ready-By time, but this
should include date and time. You might be staying longer than a day and/or
only have access to 110 volt charging. The long-trip version does Range
mode charging. Here's a proposal for the logic:

   a. If the Ready-By is during an off-peak period, we start as late as
possible to finish on time. If that start isn't during the off-peak time,
we see if there's an earlier off-peak period in which we can start, stop
when that off-peak ends, then resume during the last off-peak period. If
there is no earlier off-peak time, then we start when we need to start to
finish on time.

  b. If the Ready-By is outside an off-peak period, then we first look to
see if there's an off-peak period before the Ready-By. If there is, we
charge to Standard Mode full by the end of that off-peak period, and then
start again as late as possible that still finishes the Range charge by the
Ready-By (regardless of peak periods). If this won't get us ready by the
Ready-By, then look for an earlier off-peak time to do some charging. If
there is no earlier off-peak time then we just start charging so that we'll
finish by the Ready-by. This will at least make maximum use of the off-peak
period we do have plus not have the car Range full for longer than we need.

I know this is pretty complicated. It would be simpler to ignore the tiered
pricing and just have the car ready by the Ready-By date/time in whichever
mode you want (Standard or Range). And maybe that's the first way this
should be implemented. But, for leaving from home, it'd be good to
accomodate when you're leaving with getting as much charging done off-peak
with not having the battery too full for too long. You can call it
"Bennett's Anal Trip Charge Planner."  ;^)

- Bennett
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