SG57
Former Vendor
This is a very interesting problem you've identified with adding end-time charge scheduling and likely why Tesla was hesitant to implement it. Starting a temporary, pilot charge to get the charge rate is unreliable as you don't know how long to wait until you're at the full charge rate. A few minutes may suffice in some places, but not in others and especially cold places.Where would they get the charge rate which is crucial to know how long it will take to charge? Would they use history from charging at a given location? Would they do a pilot charge for a minute or two to test the charge rate?
I've solved this problem though as best I can by using a hybrid charge rate.
If the car's charge state provides a charge rate (or better yet, time to full charge), then I use that value to make my calculations. If not, then I use a manual, user-entered charge rate to make my scheduled charge start time calculation. I poll occasionally once charging to get actual charge rate and re-do my calculations for safety.
A not-so-bad downside to this method - if the manual charge rate is too low, then charging may start prematurely and require stoppage and a restart later to hit your desired completion time. No big deal.
Another not-so-bad downside to this method - if the manual charge rate is too high or your charge rate slows at any point, then charging may start too late to hit your desired completion time and there's nothing you can do about it. This isn't that big of a deal unless your users seriously botch the manual charge rate.
I can vouch that this method has worked for me and my testers successfully for nearly a month. I've grown quite fond of having regenerative braking in the morning again despite the single-digit weather.