If plugged in but not charging, is anything happening?

[Birdman325]

Assume I follow the mantra of always plug in - (which is different than ABC - always be charging), and assume the state of charge of my car is above the set limit (e.g. my car is at 80% and the set limit for charging is 70%).

If the car is plugged in, but not charging the battery because the set limit is below the current state of charge, is the car still using shore power for "other things" - keeping the 12V active, etc (I am not sure what)?

I recall reading some posts where people are able to monitor their electrical usage in detail and are able to see that even when the car is not charging, the HPC (or plug) is still drawing some power. Curious what is actually happening.

thx

 

[DB-Cooper]

I tested this back in late 2018. When my car was fully charged 80% for example, my Sense monitoring showed reasonable power draw. I remember it being 200-300W. I’d have to test again. That’s not insignificant and would be 2.4kWh per day or almost 90 per month. I didn’t test for longer than an hour or two. I should probably revisit the testing. I’ll do it next time I charge which will probably be this weekend.

 

[CharleyBC]

Interesting. I just ran and checked Wattney, who is asleep in the garage, plugged into 240V. The green "TESLA" lights on the UMC unit are lit up steady green. But when it's actively charging, the lights march. So I always figured when they're steady it's not drawing anything except enough to light the green LEDs. As the battery slowly has phantom drains from this and that, it gets low enough that it decides to charge, and clunks to life. At least that's how I assumed things worked.

 

[Birdman325]

Interesting. I just ran and checked Wattney, who is asleep in the garage, plugged into 240V. The green "TESLA" lights on the UMC unit are lit up steady green. But when it's actively charging, the lights march. So I always figured when they're steady it's not drawing anything except enough to light the green LEDs. As the battery slowly has phantom drains from this and that, it gets low enough that it decides to charge, and clunks to life. At least that's how I assumed things worked.

Right - that is also how I assumed it worked - the car would be plugged in, and slowly losing charge over time (phantom etc) until it hits and drops below the set limit at which time it charges. If that's the case, then the benefit of being plugged in is only when it hits the set limit - there is no other benefit. But if it is doing "other things" while connected to shore power, then (i) it could slow down the time in which it takes for the battery to hit the set limit because it is drawing shore power to do some other things and (ii) maybe it keeps your 12V healthy. (I concede I have no data or technical basis for this - just curious.)

 

[GtiMart]

I've had my car plugged for a few days in a row in the garage since I'm not using it as much. Using TeslaFi to look at power usage, not a real power monitor on the wire itself. Once it's done charging, the charging stops completely. I've seen it start charging again later the same day or next day to add 0.1kWh to 0.3kWh before stopping again. It pulls the full 240V/48A but less than a minute.
TeslaFi shows the voltage of the other "minute" records at 2V and no amps, I dont know if that's valid though.

 

[ZOMGVTEK]

At least with the wall connector, when the car is done charging the relay opens and mains voltage is no longer present. The car does not use wall power when the car is idle. It will kick the charger back on when the SOC drops down a bit, and then it stops again when it’s at the set level. I assume this behavior is done due to the design of the vehicle, to mitigate lithium plating as the car can’t really entirely run off the wall. The chargers sole output is right on the battery. It would need to match charger output to consumption exactly, at every moment, otherwise electrons will flow in or out of the battery. This is effectively not possible. It can vaguely closely match, but it would mean the battery would be alternating between ever so slightly charging and discharging the entire time it’s plugged in.

If you get in and blast the heat, or preheat remotely it will start charging again. I assume it does this with A/C as well, presumably it’s looking for a minimum load before it asks for wall power.

 

[Tessaract]

When plugged in to HPWC, the car will use "shore power" for things like HVAC, even when not technical charging the battery pack.

 

[SlimJim]

It is like having the straw in the mouth from the cup of soda and not drinking it.

 

[camalaio]

At least with the wall connector, when the car is done charging the relay opens and mains voltage is no longer present. The car does not use wall power when the car is idle. It will kick the charger back on when the SOC drops down a bit, and then it stops again when it’s at the set level. I assume this behavior is done due to the design of the vehicle, to mitigate lithium plating as the car can’t really entirely run off the wall. The chargers sole output is right on the battery. It would need to match charger output to consumption exactly, at every moment, otherwise electrons will flow in or out of the battery. This is effectively not possible. It can vaguely closely match, but it would mean the battery would be alternating between ever so slightly charging and discharging the entire time it’s plugged in.

If you get in and blast the heat, or preheat remotely it will start charging again. I assume it does this with A/C as well, presumably it’s looking for a minimum load before it asks for wall power.

This is the most accurate answer in my experience. Even some very light loads (e.g. minimal heat, or seat heaters) may not even result in pulling wall power for a bit. Power draw can also exceed wall power, i.e. it can drain the battery even when plugged it if something like climate control is drawing a lot of power.

I leave mine unplugged these days. There seems to be no benefit to keeping it plugged in, and I could swear it goes into a deep sleep state more often (less vampire drain) when not plugged in.

 

[NOLADriver]

Same here. I hear the car randomly kicking on fans or motors in the garage and sometimes the wall charger relay, and I havent used it in a day or two. I dont see a need for it to consume my electricity when its holding 80% it can use for itself. I leave it unplugged.

 

[Flybyglass]

I leave mine plugged in at work and at home. At home, periodically after phantom drain drops a couple miles in range it starts charging for a few minutes. At work, Sentry is active and Cabin temp is limited to 105f. Sentry uses about 1 mile of range/Hour and if too warm the AC comes on. So charging till take place to compensate for Sentry and AC power use.

 

[vickh]

does the UMC use any power when on standby?

 

[ZOMGVTEK]

does the UMC use any power when on standby?

Yes, basically everything you plug in that does not have a physical power switch consumes some non zero power when it’s not being used. The UMC takes something like 1-2W, it’s been posted somewhere before but I don’t recall the exact number. Relative to the energy the car consumes when it’s charging, it’s insignificant so I wouldn’t worry. The wall connector takes about 4W sitting idle.