Probably a stupid question about charging

[coleAK]

So I just left my Tesla plugged in for 4 days while we were gone. This is the first time I had done this. Anyway today when I got in it was at 76% and when I left it was charged to 81%. It was sitting in my heated garage set to 55 degrees the entire time so no difference in temperature and it didn’t get cold. Any it was connected to my Tesla wall connector.

I’m guessing I needed to schedule a daily charge? Or should I have used the app to wake it up?

 

[Matt L]

It should have stayed topped off I think

 

[swaltner]

There’s a little hysteresis in the charging system. It lets the charge level drop several percent before topping it off. Otherwise it would wear out the battery contactor from frequent charging sessions that last a couple seconds each. Your thermostat in your home does something similar to keep the heat/air-conditioning from activating when 5e temperature changes by .01 degrees from the set point.

 

[coleAK]

I guess I assumed that since everyone says keep it plugged in (including Tesla) that any power usage while plugged in would draw from the outlet instead of the battery. In that case there should be little degradation, I wouldn’t expect 1% per day.

 

[AlanSubie4Life]

I guess I assumed that since everyone says keep it plugged in (including Tesla) that any power usage while plugged in would draw from the outlet instead of the battery. In that case there should be little degradation, I wouldn’t expect 1% per day.

What did you have your charge threshold set to?

Fairly sure Tesla does not do this continuous draw from the wall connector. They prefer to draw down the battery and then recharge it when it falls far enough below the threshold, as mentioned above. I don’t know exactly why they do this. I am fairly sure it could continuously draw 25W from the wall or whatever it needs, and leave the contactors disconnected except very occasionally. So it isn’t a contactor wear issue. In fact, their method INCREASES contactor wear - they frequently have to pop on/off for every sleep to idle transition.

Thinking about it, maybe the issue is that the charger (AC->DC) in the “penthouse” (I noticed that is what they call it in the part diagram) is not very efficient for continuous low current draw. This can be a feature of boost converters. So, it may save energy (be more efficient) to just turn on the charger periodically and recharge the battery rapidly with the charger operating at as high current as possible.

Another way to be even more efficient would be to draw less power all the time! I can only dream.

 

[EValuatED]

So I just left my Tesla plugged in for 4 days while we were gone. This is the first time I had done this. Anyway today when I got in it was at 76% and when I left it was charged to 81%. It was sitting in my heated garage set to 55 degrees the entire time so no difference in temperature and it didn’t get cold. Any it was connected to my Tesla wall connector.

I’m guessing I needed to schedule a daily charge? Or should I have used the app to wake it up?

Hi, I have seen a “mile” drop a day when parked & plugged in in my garage at similar temps and have seen others report similar. And that it takes 3 - 5 miles drop before the Battery Management System decides to top up. Maybe better to think of it in battery percentage... 1 - 2 % drop will cause the BMS to top up. BTW, had to park outside unplugged several nights during last Thanksgiving’s cold snap here in the East — our cold a relative term to yours in AK! — where it dropped to 15F overnight several times and I lost up to 8 or 9 miles a night IIRC, something I was expecting to see, so no worries.

 

[TexasEV]

Hi, I have seen a “mile” drop a day when parked & plugged in in my garage at similar temps and have seen others report similar. And that it takes 3 - 5 miles drop before the Battery Management System decides to top up. Maybe better to think of it in battery percentage... 1 - 2 % drop will cause the BMS to top up.

No I think the charge has to drop by 3% for charging to start again. At least that’s the way the Model S works.

 

[coleAK]

Thank you all. I figured it was normal just had to ask since it was the first time I’d seen it do that. Also makes me wonder if I don’t need to keep it plugged in as much as I have been.

 

[NeverFollow]

So I just left my Tesla plugged in for 4 days while we were gone. This is the first time I had done this.
Anyway today when I got in it was at 76% and when I left it was charged to 81%.

A consumption of 1% a day is what I noticed if I am not driving and not connected
So after three months, when no connected, I will get a brick!

...Any way it was connected to my Tesla wall connector.

What was the value of the threshold? I assume it was it set to 80%?

I’m guessing I needed to schedule a daily charge?
Or should I have used the app to wake it up?

This what I was thinking, why not setting a time for charging,
so the system will check the status at least once a day,
and will stop charging, if it was needed, at the selected value anyway.

One thing I noticed is that if there was a power failure (or just turning off the circuit breaker)
the charging doesn't restart.

The car plug light stay blue, and there is a message on the screen asking to re-plug the charger to the car.

 

[jdcollins5]

No I think the charge has to drop by 3% for charging to start again. At least that’s the way the Model S works.

3% drop for my 3 also.

 

[ZooSean]

3% drop for my 3 also.

Not in my case, I set it at 80% at 12am charging . And now the battery dropped to 366km but never start to charge again. Also I can’t turn charge on from app.

 

[NeverFollow]

One thing I noticed is that if there was a power failure (or just turning off the circuit breaker) the charging doesn't restart.

The car plug light stays blue, and there is a message on the screen asking to re-plug the charger to the car.

I just tested, and I was not able to reproduce the problem. After shutting down and turning the power on, the charging started again.

It might have been some problem with the car plug, but I didn't remember touching the plug or the charger.

 

[NeverFollow]

Not in my case, I set it at 80% at 12am charging .
And now the battery dropped to 366km but never start to charge again.
Also I can’t turn charge on from app.

If you have a time set for charging at 12 am, it might not start until that time?

Does unplug and plug again fix the problem and let start again?

 

[coleAK]

Yes I have mine set to 81%. For some reason I can get it to do 80%. For me it’s 79 or 81... anyway Next time we leave the 3 for a few days I’m going to leave it plugged in and schedule a charge just to see what that does.

 

[Saghost]

With scheduled charging or without, my X charges back to the set percentage every 3 days when plugged in and parked.

 

[eprosenx]

With scheduled charging or without, my X charges back to the set percentage every 3 days when plugged in and parked.

If setup for scheduled charging, does it only charge at the scheduled charging time? Or does it kick in exactly when the charge drops to the recharge point?

 

[ZooSean]

Looks like the behavior is inconsistent. I did not conclude a theory.

 

[dhrivnak]

It should have stayed topped off I think

But only within bounds. It is likely like the Roadster which wakes up once a day and if it has not been driven it goes back to sleep. Every few days it tops off but mileage will vary with 4 miles.

 

[Saghost]

If setup for scheduled charging, does it only charge at the scheduled charging time? Or does it kick in exactly when the charge drops to the recharge point?

I haven't tested comprehensively, but I believe it is when it hits the scheduled time on the third day if scheduled charging is set. (when I schedule charging, I schedule it for a couple hours before I normally get up in the winter, to mitigate the cold pack issues as best I can.)

 

[dhanson865]

I guess I assumed that since everyone says keep it plugged in (including Tesla) that any power usage while plugged in would draw from the outlet instead of the battery. In that case there should be little degradation, I wouldn’t expect 1% per day.

Degradation is normally a word used for permanent loss of capacity not a temporary loss of charge level.

Reworded a common way to say it might be "I wouldn't expect 1% SOC loss per day" or "I wouldn't expect SOC to drop 1% per day"