Limiting Charging Amps

[dansev]

Does anyone know if I reduce the charging amps, does that also reduce the amount of amperage available for HVAC heating when plugged in? So if I reduce the charging amps to 32 to stretch out the charging of my battery so that when I’m ready to leave, it has just finished charging, and I go to blast the heat on a cold morning 15 minutes before I get in the car, will the heat be limited by the 32 amp setting? Or is that setting only related to charging?

In other words, if it is using all 32 A to charge the battery and I turn on the heat, does it reduce the energy available to charging the battery so that it can heat the car? If this is true, I would want the full 48 A. Hope this makes sense!

 

[jjrandorin]

Does anyone know if I reduce the charging amps, does that also reduce the amount of amperage available for HVAC heating when plugged in? So if I reduce the charging amps to 32 to stretch out the charging of my battery so that when I’m ready to leave, it has just finished charging, and I go to blast the heat on a cold morning 15 minutes before I get in the car, will the heat be limited by the 32 amp setting? Or is that setting only related to charging?

In other words, if it is using all 32 A to charge the battery and I turn on the heat, does it reduce the energy available to charging the battery so that it can heat the car? If this is true, I would want the full 48 A. Hope this makes sense!

I dont know but you can test this yourself, by changing the amp setting and then turning on the HVAC and looking at the tesla app to see what it reports. When energy is not going to charge the battery the amps setting will stay the same but I am pretty sure the "miles" reported as being charged decrease while the car is using energy for something else beside charging the battery.

Rather than turning down the amp setting, though, if it were me, I would just schedule the charging time to start later, to accomplish the same thing you are doing now.

 

[GtiMart]

The car will use the energy it needs for what you ask. It always takes it from the battery. When the battery drops under your target SOC, it will start charging at the charging configuration. My understanding is that if you spend more energy than your 32A setting, the car won't charge as fast as it discharges and you'll leave in the morning with a lower SOC than you anticipate.

 

[Benito1283]

The car will use the energy it needs for what you ask. It always takes it from the battery. When the battery drops under your target SOC, it will start charging at the charging configuration. My understanding is that if you spend more energy than your 32A setting, the car won't charge as fast as it discharges and you'll leave in the morning with a lower SOC than you anticipate.

Actually, when you use HVAC and/or precondition while plugged in, it will pull power straight from the wall - as much as your amp limit will allow. I've confirmed this via multiple methods, one being the lights on the mobile connector will scroll down indicating shore power is being used. If you need more than the wall power can provide, it will take the rest from the battery.

 

[Rocky_H]

@Benito1283 has the correct answer. That amp setting is only for during the charging process, but it will pull whatever it needs for heating if you turn that on.

So let's bring up a side point here that just occurred to me. We frequently see here on the forum people installing their charging circuits in pretty sketchy ways with code violations and using a wrong type of outlet for the circuit level with just the pinky promise that it will be fine because they will just turn down the amps in the car's settings. This is yet another reason why that is a bad idea and why you should set up your circuit properly.

 

[Operator64]

@Benito1283 has the correct answer. That amp setting is only for during the charging process, but it will pull whatever it needs for heating if you turn that on.

So let's bring up a side point here that just occurred to me. We frequently see here on the forum people installing their charging circuits in pretty sketchy ways with code violations and using a wrong type of outlet for the circuit level with just the pinky promise that it will be fine because they will just turn down the amps in the car's settings. This is yet another reason why that is a bad idea and why you should set up your circuit properly.

I agree as well with it coming directly from the connector.
As far as the side point it’s astonishing to see how quickly an individual will put a price tag on their lives as well as their family’s just to save a few bucks on an install.

 

[GtiMart]

The fact that it charges doesn't prove whether the car takes power directly from the wall to operate or that it uses the battery and then uses the wall to charge the battery. It makes more sense to me that the car would always be wired to take its power from the battery, and that charging would occur when the battery goes down. Seems to make for a simpler design. But I do have to say I have no proof of what I'm advancing. The car could bypass the amperage setting in that situation and still take power from the battery. I know in the end it doesn't make a huge difference... but I would love to know with certainty.

 

[Benito1283]

The fact that it charges doesn't prove whether the car takes power directly from the wall to operate or that it uses the battery and then uses the wall to charge the battery. It makes more sense to me that the car would always be wired to take its power from the battery, and that charging would occur when the battery goes down. Seems to make for a simpler design. But I do have to say I have no proof of what I'm advancing. The car could bypass the amperage setting in that situation and still take power from the battery. I know in the end it doesn't make a huge difference... but I would love to know with certainty.

It takes it from the wall. I put an amp meter around the wires in my electrical panel and it was pulling 24 amps (max) while preconditioning. You can also see the amp draw on the screen if you open the door while HVAC/precondition is on and it’s plugged in.

 

[brkaus]

I'd be pretty surprised if the car would exceed the limit set on the display. I'll have to see if I can figure out a way to prove/disprove.

It takes it from the wall. I put an amp meter around the wires in my electrical panel and it was pulling 24 amps (max) while preconditioning. You can also see the amp draw on the screen if you open the door while HVAC/precondition is on and it’s plugged in.

What was your charge limit set to?

The car can never directly "take from the wall" because the preconditioning is all on the DC side of the power converter which is also connected to the battery. Sure, the power converter is feeding the power to the DC bus and keeping it right at/above the battery charge level but if the car can control where the power is coming from by controlling the voltage coming out of the AC->DC power converter. It can also provide a little less power from the converter and pre-conditioning would be shared between the wall and the battery.

 

[Benito1283]

My amp limit was set to 24 amps (max on a 30 amp circuit). And no, it should never exceed the set limit, whether charging or preconditioning.

 

[Rocky_H]

My amp limit was set to 24 amps (max on a 30 amp circuit). And no, it should never exceed the set limit, whether charging or preconditioning.

Well, right. We're not talking about going over 24A. It will never do that. We're talking about if you turn down the amps custom on the screen to 8 or something. It likely will draw more than 8A when you turn the heater on.

 

[Benito1283]

Well, right. We're not talking about going over 24A. It will never do that. We're talking about if you turn down the amps custom on the screen to 8 or something. It likely will draw more than 8A when you turn the heater on.

Ah, I see, not sure about that.

 

[brkaus]

Well, right. We're not talking about going over 24A. It will never do that. We're talking about if you turn down the amps custom on the screen to 8 or something. It likely will draw more than 8A when you turn the heater on.

Why is that likely?

 

[Rocky_H]

Why is that likely?

Well, by likely, I basically meant "certain", but I was taught to always leave a little wiggle room in wording in case something unusual happens because you can almost never be 100% certain all of the time forever.

But yes, when you turn on the heating up to a high level, it will draw all of that current it can from the wall connection and will be ignoring if you have a low amp limit set on the screen for charging. But of course it will be respecting the hard limit of what the circuit maximum level is.

 

[brkaus]

Well, by likely, I basically meant "certain", but I was taught to always leave a little wiggle room in wording in case something unusual happens because you can almost never be 100% certain all of the time forever.

But yes, when you turn on the heating up to a high level, it will draw all of that current it can from the wall connection and will be ignoring if you have a low amp limit set on the screen for charging. But of course it will be respecting the hard limit of what the circuit maximum level is.

You have tested this?

 

[Operator64]

You have tested this?

I have

 

[Sophias_dad]

Perhaps things have changed since the above responders did their experiments, but I just did the test myself on my 48 amp charging circuit.

Turned the car to 5A, plugged in with a cold battery/cabin. It drew 5.5A or so according to my clamp-on meter inside my main panel. Turned on HVAC, draw didn't change.

Stopped charging via the app. Was a little surprised to see the draw drop to 0, as apparently it did NOT continue using the house for power(!). I think this is a special case. I'm pretty sure if I disabled/re-enabled HVAC when plugged in it would start using house power. I'll do that test in a few hours.

 

[Rocky_H]

You have tested this?

Hmm, I don't. And it appears I should not have been so confident about that. Sorry. It looks like we're seeing some conflicting reports here.

 

[brkaus]

Hmm, I don't. And it appears I should not have been so confident about that. Sorry. It looks like we're seeing some conflicting reports here.

Probably bugs/features over time.

Personally I’d expect the car to limit to the dash/app setting and anything else would be a bug. It’s the safest implementation. But that’s just my view.

 

[dansev]

Is it me, or is it crazy that Tesla uses the battery to heat the car when plugged in to a 240v circuit? That's just unnecessary use/abuse of the precious battery that we all go to such lengths to preserve! So when I'm warming up the cabin on these 15 degree mornings in the winter, defrosting all the snow and ice off my car, I'm just sucking energy from the battery, almost no different than driving? That's not an insignificant amount of use, if this is really how it works. And it seems completely unnecessary. Am I wrong here?