Charging 2 Teslas in a sequence

[eprosenx]

I don't think it's a software issue. How long did you leave them each pulling 20A? The battery heater can pull around 6kw; at those temps I've plugged a cold-soaked car into a 30A circuit, pulled 24A for a while (at least an hour or 2) without any increase in charge level. Once the battery warms it should start to charge slowly. As it continues to warm, the charge speed will improve.

The trick is to plug in and start charging as soon as you get home while the battery is still warm, or just be patient.

I wonder if that explains the issue. If the battery heater is a 6kw resistive element then it would need 25 amps just to operate. So if the HPWC only gives each car access to 20 amps, neither can get enough to fire up the heater to heat the battery pack to the point it is safe to charge it.

So if the HPWC was smart enough, it could recognize this situation and allocate all the power to one car for a while and then later to the other car and achieve charge on both. But that would require a LOT of logic and two way communication for the HPWC and I just don't know that complicating that protocol makes much sense.

Sounds like the Telsa needs better alerting to the driver/owner of what is going on (i.e. insufficient charge current available to run battery heater).

Maybe @Duckjybe could find a way to up the power on his HPWC's to a 60a breaker (or higher) which might give him the margin necessary for both cars to simultaneously warm their batteries. If he was lucky he would already have the wire of the necessary ampacity and sufficient capacity on his main service feed. Like if it was #6 AWG and run in conduit (not NM romex cable) then he could just swap the breaker to 60a and change the HPWC settings up a notch and be golden.

 

[Duckjybe]

I wonder if that explains the issue. If the battery heater is a 6kw resistive element then it would need 25 amps just to operate. So if the HPWC only gives each car access to 20 amps, neither can get enough to fire up the heater to heat the battery pack to the point it is safe to charge it.

So if the HPWC was smart enough, it could recognize this situation and allocate all the power to one car for a while and then later to the other car and achieve charge on both. But that would require a LOT of logic and two way communication for the HPWC and I just don't know that complicating that protocol makes much sense.

Sounds like the Telsa needs better alerting to the driver/owner of what is going on (i.e. insufficient charge current available to run battery heater).

Maybe @Duckjybe could find a way to up the power on his HPWC's to a 60a breaker (or higher) which might give him the margin necessary for both cars to simultaneously warm their batteries. If he was lucky he would already have the wire of the necessary ampacity and sufficient capacity on his main service feed. Like if it was #6 AWG and run in conduit (not NM romex cable) then he could just swap the breaker to 60a and change the HPWC settings up a notch and be golden.

I can’t go 60A now unless I do some rewiring (again). When I installed I put in leftover Teck #4 AL wire and inspector made me change wire to CU from the splitter box as HPWC calls for CU only. To save money I used #8 CU. I could swap it out again though but I am loathe to take everything apart again.

I can’t remember what was happening to the first car but the second car HPWC was cycling up just voltage then shutting down and repeating over and over. The charge ring kept going green then blue and then cycling and HPWC relay kept cycling. I was worried it would wear out the charge port lock. This was just after they added the battery heating indicator in the app while preheating. Interestingly, when I started cabin preheat via app or inside car, the cycling would stop and car would show something like 6/20 A. I do have video but don’t want to hijack the thread in trying to solve this issue. I just thought I’d mention it and show that it is likely a software issue that may be outstanding.

 

[Rocky_H]

I wonder if that explains the issue. If the battery heater is a 6kw resistive element then it would need 25 amps just to operate. So if the HPWC only gives each car access to 20 amps, neither can get enough to fire up the heater to heat the battery pack to the point it is safe to charge it.

No, that's not how a resistive heater works. It works at whatever level of current is flowing through it, or else it wouldn't even be possible to charge from a low power circuit like a 120V 20A outlet at all. The battery pack heater has a maximum power draw of up to 6kW, but it will still be working at levels lower than that--just with less heat output. This case of 240V and 20A is 4.8kW, so it's running the battery heater at most of it's effectiveness. So yes, it will be running the battery heater the whole time, but -35C is just crazy cold! It's probably going to sit there running the battery heater and not really charging for at least a half hour to an hour or so, and @Duckjybe probably just didn't let it go long enough to be able to get to see it get to the point where it could charge.

I suppose it's possible, though, that the heat level from 4.8kW wasn't enough to raise the temperature in -35C conditions, and the car has some logic that sees that and decides, "Unless you can give me more power, it's not worth doing this."

 

[eprosenx]

No, that's not how a resistive heater works. It works at whatever level of current is flowing through it, or else it wouldn't even be possible to charge from a low power circuit like a 120V 20A outlet at all. The battery pack heater has a maximum power draw of up to 6kW, but it will still be working at levels lower than that--just with less heat output. This case of 240V and 20A is 4.8kW, so it's running the battery heater at most of it's effectiveness. So yes, it will be running the battery heater the whole time, but -35C is just crazy cold! It's probably going to sit there running the battery heater and not really charging for at least a half hour to an hour or so, and @Duckjybe probably just didn't let it go long enough to be able to get to see it get to the point where it could charge.

I suppose it's possible, though, that the heat level from 4.8kW wasn't enough to raise the temperature in -35C conditions, and the car has some logic that sees that and decides, "Unless you can give me more power, it's not worth doing this."

If the controls for the heater are really basic (just on or off) then that is exactly how it would work. But to you’re point, I suspect the Tesla can ramp the amount of current if draws (though actually, I would not be surprised if the way they reduced heat needed was with duty cycling the element rather than actually ramping its draw down?)

We would need more details about how the heater is hooked up and controlled to be able to make good guesses as to what the issue is.

 

[tga]

I can’t remember what was happening to the first car but the second car HPWC was cycling up just voltage then shutting down and repeating over and over. The charge ring kept going green then blue and then cycling and HPWC relay kept cycling. I was worried it would wear out the charge port lock. This was just after they added the battery heating indicator in the app while preheating. Interestingly, when I started cabin preheat via app or inside car, the cycling would stop and car would show something like 6/20 A. I do have video but don’t want to hijack the thread in trying to solve this issue. I just thought I’d mention it and show that it is likely a software issue that may be outstanding.

I've never seen this behavior, but I've never used a multi-HPWC setup either.

 

[eprosenx]

I can’t go 60A now unless I do some rewiring (again). When I installed I put in leftover Teck #4 AL wire and inspector made me change wire to CU from the splitter box as HPWC calls for CU only. To save money I used #8 CU. I could swap it out again though but I am loathe to take everything apart again.

I can’t remember what was happening to the first car but the second car HPWC was cycling up just voltage then shutting down and repeating over and over. The charge ring kept going green then blue and then cycling and HPWC relay kept cycling. I was worried it would wear out the charge port lock. This was just after they added the battery heating indicator in the app while preheating. Interestingly, when I started cabin preheat via app or inside car, the cycling would stop and car would show something like 6/20 A. I do have video but don’t want to hijack the thread in trying to solve this issue. I just thought I’d mention it and show that it is likely a software issue that may be outstanding.

Do you have specs on the specific wire you used? Is it romex or SE style wire? Or is it in conduit?

You may have additional ampacity available on that aluminum wire (depending on the type), but for sure not on the #8 copper.

It does make sense that they required you to swap that since aluminum under the wrong terminals is a bad deal.

Do you have sufficient conduit size from the split point to the HPWC units for larger gauge wire?

What you describe is definitely a software bug. You should push Tesla to fix it. Even if there is not enough current to charge both cars (or either) due to how he hpwc splits power, it should fail more gracefully.

 

[wolfpet]

What kind of upgrade did you look into?

I was referring to upgrating my service from 100A to 200A. I was quoted $4.5K

 

[nwdiver]

I was referring to upgrating my service from 100A to 200A. I was quoted $4.5K

Just the service? NOT the panel? That's seems awfully high... Maybe things are different in Canada or it's a long way to your pole but my utility actually covers the cost of the upgrade. Even so... if it's an overhead line it's typically aluminum triplex which is dirt-cheap. When I got my lines upgraded it took them ~45 minutes and I doubt the materials cost >$500.

The only thing I really had to pay for is a bigger meter base which shouldn't cost >$500 including labor.

 

[wolfpet]

Just the service? NOT the panel?

It included the panel, but AFAIK the majority of the cost was related to work outside the house, including digging the tench, etc. In my city all cables are underground.

 

[nwdiver]

It included the panel, but AFAIK the majority of the cost was related to work outside the house, including digging the tench, etc. In my city all cables are underground.

Hmmm... I would try to get a second quote w/o the panel upgrade; The lines in the ground may not need replacing. My friends house was upgraded from 60A to 200A and they kept the same lines. Here in the states at least the wires on the utility side of the meter don't have the same ampacity restrictions as the ones on your side of the meter.