Does it draw power when plugged in, not charging?

Bigriver

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#1
I read somewhere that the car will run off outlet power when plugged in, vs. battery. So if you plug it in, it won't really discharge as much in the first place.

Usually there's a 1% per day drop, but left plugged in it might not charge for some time due to less parasitic discharge.

Is that not what you experienced?
@Toadmanor, you responded that this is true. Yet on Nov 8 you posted that your car had gone from 75% to 48% since you left it on Oct 22. So that was a 27% drop in 18 days. I’m not seeing that as any evidence of less parasitic drop when plugged in.

I ask because from my experience I’ve not seen any evidence that there is any effect of having it plugged in until the charge goes below the charging limit. I know “a plugged in Tesla is a happy Tesla” but I have wondered if that slogan was developed to get EV owners in a mindset to keep things simple -just always plug it in and don’t worry.

I don’t have my wall connector separately metered, so I do not know if it actually draws any current other than when the car is “charging.” Does anyone else have any evidence that plugging it in matters in any way when the charge is above the charge limit?

[Mod moved from other thread]
 
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Toadmanor

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#2
@Toadmanor, you responded that this is true. Yet on Nov 8 you posted that your car had gone from 75% to 48% since you left it on Oct 22. So that was a 27% drop in 18 days. I’m not seeing that as any evidence of less parasitic drop when plugged in.
Let me add information. On October 22 I did leave the car for one month. When I departed I set the charge limit to 50% and at that time the car was at 75%. So, yes, it did drop 27% but thereafter maintained a charge of 50% as set. When the level dropped to ~47% it would charge up to 50%. So I maintain that the car does charge off of the wall connector when plugged in.

"A plugged in Tesla is a happy Tesla."
 
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jdcollins5

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#3
@Toadmanor, you responded that this is true. Yet on Nov 8 you posted that your car had gone from 75% to 48% since you left it on Oct 22. So that was a 27% drop in 18 days. I’m not seeing that as any evidence of less parasitic drop when plugged in.

I ask because from my experience I’ve not seen any evidence that there is any effect of having it plugged in until the charge goes below the charging limit. I know “a plugged in Tesla is a happy Tesla” but I have wondered if that slogan was developed to get EV owners in a mindset to keep things simple -just always plug it in and don’t worry.

I don’t have my wall connector separately metered, so I do not know if it actually draws any current other than when the car is “charging.” Does anyone else have any evidence that plugging it in matters in any way when the charge is above the charge limit?

[Mod moved from other thread]
I plug mine in and schedule charging during the night. Watching the charge screen after plugging in I see the amps go up to 2 to 3 amps without charging. This is the existing car load, AC, fans, etc. Also if you preheat in the morning this load is on the charger and not the battery. Similar to an ICE alternator carrying 12V load while trickle charging the 12V battery.

When I left my car plugged in, it recharged when the SOC dropped below 3%.
 

Bigriver

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#4
Let me add information. On October 22 I did leave the car for one month. When I departed I set the charge limit to 50% and at that time the car was at 75%. So, yes, it did drop 27% but thereafter maintained a charge of 50% as set. When the level dropped to ~47% it would charge up to 50%. So I maintain that the car does charge off of the wall connector when plugged in.
I'm not questioning that it charges off the wall connector when it drops below the charge setpoint, the question is whether it got to the charge setpoint at a different time because it was plugged in when it was above the charge setpoint? Would there have been any difference in timing if it had been unplugged, and then someone plugged it in when it hit 50%?

I plug mine in and schedule charging during the night. Watching the charge screen after plugging in I see the amps go up to 2 to 3 amps without charging. This is the existing car load, AC, fans, etc. Also if you preheat in the morning this load is on the charger and not the battery. Similar to an ICE alternator carrying 12V load while trickle charging the 12V battery.
When I left my car plugged in, it recharged when the SOC dropped below 3%.
Hmm, I just went out to the garage and played with this a bit. I do see amps being pulled on the charge screen when the SOC is greater than the charge setpoint with the heater and/or seat heaters on. But when the heater is off, it stayed at 0 amps while I was watching it.

So I'm convinced that preconditioning pulls energy from the connector and not the battery. But clearly the connector doesn't supply all the energy needs of the car, as the SOC continues to decrease while it is plugged in. I'd still like to understand if anything else is also using the connector energy and not the battery -- and what real advantage is that? I do understand the benefit if you are concerned about range the following day, but few of us are pushing that envelope on a daily basis. Is there some benefit in the net energy used -- is anything drawn directly from the connector instead of the battery bypassing an inefficiency?
 

jdcollins5

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#5
I'm not questioning that it charges off the wall connector when it drops below the charge setpoint, the question is whether it got to the charge setpoint at a different time because it was plugged in when it was above the charge setpoint? Would there have been any difference in timing if it had been unplugged, and then someone plugged it in when it hit 50%?


Hmm, I just went out to the garage and played with this a bit. I do see amps being pulled on the charge screen when the SOC is greater than the charge setpoint with the heater and/or seat heaters on. But when the heater is off, it stayed at 0 amps while I was watching it.

So I'm convinced that preconditioning pulls energy from the connector and not the battery. But clearly the connector doesn't supply all the energy needs of the car, as the SOC continues to decrease while it is plugged in. I'd still like to understand if anything else is also using the connector energy and not the battery -- and what real advantage is that? I do understand the benefit if you are concerned about range the following day, but few of us are pushing that envelope on a daily basis. Is there some benefit in the net energy used -- is anything drawn directly from the connector instead of the battery bypassing an inefficiency?
You make a good point that the SOC will drop even with the connector plugged in. Mine dropped 3% before recharging.

Could it be because the car is asleep? When you are preheating you have to wake the car first.
 

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#6
I charged my car to 81% on Nov 29 and it has been plugged in since. I’ve been in and out of it numerous times with all the software updates. Today Jan 04 it is at 48%. So in 36 days it lost 33%. I have a dedicated tracker on the circuit and it has not shown any draw from the WC.
 
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#7
Not sure there are two HV DC paths on the outbound side of the 48A onboard charger? There is definitely a path to the traction battery but is there another path to other HV DC components such AC, cabin heating, DC to DC converter, traction motor via the inverter etc? It would be nice if there were two paths but that would add to complexity and cost. It is possible that the current draw being displayed on the 15" display for the cabin heat is actually being drawn from/through the traction battery and the software is smart enough to request only that much charging current from shore power (ie.. the car would technically be charging)? There is definitely another HV DC path that bypassed the onboard charger and directly connects a DC Supercharger directly to the traction battery. There is a HV connector on the top side of the penthouse that comes from the charge port and there are HV outputs out the bottom of the penthouse but all of these could be coming from the traction battery? or is there an internal path through the penthouse that connects the 48A onboard charger HV DC directly to some/all of the HV components other that the traction battery?

I have been thinking about this topic for awhile can anyone point to any documents that might answer the onboard charger TWO path HV DC output question?

Regards, Ron
 
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#8
Just performed a test. If you unlock and open the car door I hear the HV contactors close; likewise, if you access the car via the phone app, when it wakes up I also hear the HV contactors. Since these contactor closures connect the HV traction battery to the HV buss, I would conclude there is only one path. So it looks like the charger probably only charges the traction battery and all power needed by the car comes directly from the traction battery and NOT directly from the 48A onboard charger via shore power. Anyone agree?
 
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garsh

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#9
I would conclude there is only one path.
I would agree. There's no need for another.
So it looks like the charger probably only charges the traction battery and all power needed by the car comes directly from the traction battery and NOT directly from the 48A onboard charger via shore power. Anyone agree?
That's the wrong way to think about it.

Everything gets power from the high voltage bus. Usually the battery supplies the high voltage on that bus to push current. But when the charger is active, it's supplying a higher voltage on that bus than the battery, and therefore it is supplying current to everything connected to that bus.
 

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#10
I charged my car to 81% on Nov 29 and it has been plugged in since. I’ve been in and out of it numerous times with all the software updates. Today Jan 04 it is at 48%. So in 36 days it lost 33%. I have a dedicated tracker on the circuit and it has not shown any draw from the WC.
That's really strange. I often leave my car in the garage for several days; it's plugged into the Tesla HPWC whenever it is in the garage. Whenever the charge drops below 96-97% of the target (my usual target is 260mi range, around 82% charge), the car starts charging again automatically.
That's been consistent over all 7-8 firmwares I've had since June and is still the case now on 48.12.1. Did you somehow explicitly disable that feature?
 

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That's really strange. I often leave my car in the garage for several days; it's plugged into the Tesla HPWC whenever it is in the garage. Whenever the charge drops below 96-97% of the target (my usual target is 260mi range, around 82% charge), the car starts charging again automatically.
That's been consistent over all 7-8 firmwares I've had since June and is still the case now on 48.12.1. Did you somehow explicitly disable that feature?
Good point. I didn’t address that in my post. When I finished charging to 81% on Nov 29 I set the charging slider bar down to 50% and the charge time to 19:00. It took 36 days for the charge to drop to 48% and trigger the auto charge. That’s when I posted.
 

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#13
Good point. I didn’t address that in my post. When I finished charging to 81% on Nov 29 I set the charging slider bar down to 50% and the charge time to 19:00. It took 36 days for the charge to drop to 48% and trigger the auto charge. That’s when I posted.
That seems in line with what I've observed -- under 1mi of range loss per day.
 

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#14
I misinterpreted the title of this thread, since I thought I had just learned the definitive answer from a meter I installed last night on the feed to my Wall Connector.

The answer would have been 3.6 watts when the car is done charging and (I think) asleep. The WC is drawing some or all of this internally, of course. But alas, this is not germane to the question, so never mind.
 
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#15
I would agree. There's no need for another.
That's the wrong way to think about it.

Everything gets power from the high voltage bus. Usually the battery supplies the high voltage on that bus to push current. But when the charger is active, it's supplying a higher voltage on that bus than the battery, and therefore it is supplying current to everything connected to that bus.
Garsh

Thanks for your post. There are many things I still do not understand about when shore power is used and installing a power meter to monitor power usage would be helpful. When I open the drivers door, I hear the contactors close (connecting the HV traction battery to the buss) and for the purposes of the remainder of this post I am assuming they did NOT reopen or at least I did not hear them open . If the contactors DID reopen, everything would make perfect sense.

With the HV contactors closed, the traction battery, HV DC output side of the charger, and all other DC HV components are connected to the HV buss. If plugged into shore power, with the cabin heater on and the charger outputting a higher voltage than the traction battery (if it is?) why does there appear to be no current going to the traction battery? If you bring up the charging screen on the display while plugged into shore power, it shows amperage being used (apparently from shore power) when the heater is on but does not indicate that it is charging the traction battery? Maybe the onboard charger is smart enough to vary the HV DC voltage output to be lower than the current traction battery voltage so that no or very little current would flow into the traction battery? Since the cabin heater can pull significant current while active, using ALL of the available power and not charging the traction battery would make since. Is there another way, other than the HV contactors, to disconnect the traction battery from the HV buss and still have some/all the other HV components still on the buss?

Again thanks for your post response!!
Regards, Ron
 

MelindaV

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#16
I misinterpreted the title of this thread, since I thought I had just learned the definitive answer from a meter I installed last night on the feed to my Wall Connector.

The answer would have been 3.6 watts when the car is done charging and (I think) asleep. The WC is drawing some or all of this internally, of course. But alas, this is not germane to the question, so never mind.
still useful info. I installed my WC end of 2016 (when there was still the charging infrastructure federal tax credit) and it sat there powered up not being used for nearly 2 years. I considered flipping the breaker off but coming home to the little green light made it worth that 3.6w ;)
 

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#17
One thing I like about using the mobile connector at home (plugged into a new dedicated 30-amp circuit) is that I can unplug it when it's not being used to charge my car. The green lights aren't drawing much but you know the connector is drawing something when it's hanging there plugged in... because it's warm-ish. No reason to just waste it.
 

PaulK

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#18
still useful info. I installed my WC end of 2016 (when there was still the charging infrastructure federal tax credit) and it sat there powered up not being used for nearly 2 years. I considered flipping the breaker off but coming home to the little green light made it worth that 3.6w ;)
2 years at 3.6w... that’s almost enough energy to charge your car from zero to 100% :)
 

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#19
Just noticed that page 123 of the 12/20 dated owner's manual addresses this question.

"Note: Whenever model 3 is plugged in but not actively charging, it draws energy from the wall outlet instead of using energy stored in the battery"
 

ADK46

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#20
Just noticed that page 123 of the 12/20 dated owner's manual addresses this question.

"Note: Whenever model 3 is plugged in but not actively charging, it draws energy from the wall outlet instead of using energy stored in the battery"
After frequently checking the watt-hour meter I installed nine days ago, I've not spotted the car drawing power except when actively charging. That is, it reads either 9800 watts or 3.6 watts. I mean only when the car is just sitting, not "on" or with opened doors. The 3.6 watts is consumed by the wall connector, not the car.

So, I think the manual is leaving out the phrase "When and If the car requires significant power, such as for preheating or charging the 12V battery, ..."