AC on while charging

CSFTN · Jul 12, 2015

Apologies if this has already been answered - I tried to search and found nothing.

I am curious. The last part of supercharging, before balancing but during the taper - if you have the AC on, does it increase the time until full?

Another way of asking - does the car request adequate voltage/amperage to charge the battery, at its current SOC, and use the power from the same pack it is charging to run the AC, or does it request what the battery can take PLUS whatever other draws the car needs, including AC?

I understand no Tesla engineers will answer here, but perhaps there is enough collective experience to make a good, educated guess?

ecarfan · Jul 12, 2015

I doubt that having AC on during any point of the charging process makes any significant difference to the length of time it takes to reach your desired level of charge. Just a guess...

AndY1 · Jul 12, 2015

2kW of power for AC compared to 120kW of SuperCharger is negligible.

CHG-ON · Jul 12, 2015

Yes, no big difference. The car will actually kick on the compressors to cool the batteries while charging to keep them in the right temp range.

kennybobby · Jul 12, 2015

CSFTN said:
...I am curious. The last part of supercharging, before balancing but during the taper ...

i think that's a bad assumption--there is no evidence to indicate that there is any balancing done during normal CC/CV charging, but especially during supercharging in which the objective is to get a fast fill and back on the road asap.

The nature of the circuitry on the BMU boards would be ineffective at any charging current level. The BMS can send a balance setpoint voltage to the BMU at any time to initiate bleed-off balancing at about 100mA max spread across 74 cells. i suspect it is done when the car is parked and off in order to not introduce fluctuations in the Open-Circuit Voltage (OCV). Just a southern redneck with a library card here making an edjucated guess, don't know about good...

Cottonwood · Jul 13, 2015

From my informal observations, it appears that the power needed for ancillary functions such as cabin HVAC and battery heating/cooling come from the charging port while connected to shore power (whether AC or Supercharger). If shore power is sufficient, then charging will happen at the maximum rate the taper will allow, and the ancillary is added to that for power drawn from the charger. If the shore power is insufficient, then the charging power is reduced so that the ancillary power needs can be met. What is tricky in my observations is that the car displays total Current from an AC source (charging + ancillary), but while charging from a DC source (Supercharger or CHAdeMO), the car only displays the current going into the battery.

Here is a chart of AC charging power in the taper with me turning the HVAC on and off. As the power goes down in the taper, you can see how the HVAC power is added to the charging power. This was a case where I was doing a 100% charge and preheating the car before a winter hypermile adventure across the Rockies.

mknox · Jul 13, 2015

CHG-ON said:
Yes, no big difference. The car will actually kick on the compressors to cool the batteries while charging to keep them in the right temp range.

This is something I've been curious about and I want to find out more. My car never does this. It doesn't matter how hot it is, what the SOC might be, the a/c never comes on when Supercharging. All the cars around me will be humming away, but mine is perfectly silent. If I kneel down next to the front driver's side wheel, I can hear the faint sound of a coolant pump, but that's it. Otherwise, it seems to charge okay as far as I can tell.

I am wondering if this is because I have an early car with an A-pack battery that has the 90 kW Supercharging limit?

kennybobby · Jul 13, 2015

Cottonwood said:
...Here is a chart of AC charging power in the taper with me turning the HVAC on and off...

View attachment 87230

How did you get 20 kW off of 120 vac--or is that just half the voltage?

supratachophobia · Jul 13, 2015

I received an error while supercharging that stated the cabin HVAC would not be as effective as the cooling system was currently prioritized to the charging system. So it looks like 2kw does make a difference in that the cooling system can only dissipate so much heat at one time. It should be noted that the ambient temp was in the mid to high 90's.

llavalle · Jul 13, 2015

mknox said:
I am wondering if this is because I have an early car with an A-pack battery that has the 90 kW Supercharging limit?

I guess so. Mine will only do the AC sound when Supercharging at 110KW+ for more than a few minutes. If I get into a S/C stall and I gen 70 or 80kW, no AC sound.

When I pull in at 10% or less, I get the full power of the supercharge and I'll get the AC sound for quite some time : it starts around 2-3min into supercharging and last until 60-70%SOC.

beeeerock · Jul 13, 2015

mknox said:
This is something I've been curious about and I want to find out more. My car never does this. It doesn't matter how hot it is, what the SOC might be, the a/c never comes on when Supercharging. All the cars around me will be humming away, but mine is perfectly silent. If I kneel down next to the front driver's side wheel, I can hear the faint sound of a coolant pump, but that's it. Otherwise, it seems to charge okay as far as I can tell.

I am wondering if this is because I have an early car with an A-pack battery that has the 90 kW Supercharging limit?

What sort of kW charge rate are you seeing? The maximum I saw the other day in 40 degrees was 112 kW... and I thought my car was going to lift off the ground like a hovercraft... it was seriously loud with HVAC noises! I have a difficult time believing a reduction to 90 kW would have allowed my car to shut the HVAC down completely... but who knows. Have you approached Tesla about it?

Cottonwood · Jul 13, 2015

kennybobby said:
How did you get 20 kW off of 120 vac--or is that just half the voltage?

It was half the Voltage, double that and you get close to 250 Volts and that's how I get 20 kW. The is the graphical display directly off of the TED web interface.

jerry33 · Jul 13, 2015

If I have the A/C on while Supercharging the compressor goes into overdrive

tinm · Jul 13, 2015

On hot days at a supercharger I happily crank up the A/C and charge my iPhone and consider both freebies.

smilepak · Jul 13, 2015

Was at a public charger giving me a slow charge. With the AC onit gave me 14 mils per hrs charge. I turn off the AC it gave me 16 mils per hr charge.

thecloud · Jul 13, 2015

smilepak said:
Was at a public charger giving me a slow charge. With the AC onit gave me 14 mils per hrs charge. I turn off the AC it gave me 16 mils per hr charge.

Can confirm this. When I'm at a Chargepoint 30A charger which normally gives me 18-19 mph, if I remotely turn the A/C on via the app, the charging rate drops off to 14-15 mph. Not sure whether the same thing applies to supercharging, though, since that goes directly to the battery and bypasses the onboard charger(s).

mknox · Jul 14, 2015

beeeerock said:
What sort of kW charge rate are you seeing? The maximum I saw the other day in 40 degrees was 112 kW... and I thought my car was going to lift off the ground like a hovercraft... it was seriously loud with HVAC noises! I have a difficult time believing a reduction to 90 kW would have allowed my car to shut the HVAC down completely... but who knows. Have you approached Tesla about it?

I had a problem that I can't really explain last summer. I started to notice that my Supercharging rate was quite low (30-40 kW) and, at the same time, I noticed I could not get full 60 kW of re-gen. Even if doing 120 km/h and taking my foot right off the accelerator I would only see about 35 kW of re-gen max. I took it in, but Tesla reported that they could find nothing wrong and everything checked out okay. I assumed that included everything to do with Supercharging was working fine. They even took some dates/times/power levels that I had noted and sent to California for analysis. That was last August/September roughly. Then, over the winter, my main pack contactors failed and Tesla had my car for about a week while they removed the battery and replaced the failed contactors. After that, my full 60 kW of re-gen was restored and Supercharging levels seemed normal (for an A-pack) again. I figured that contactors either worked or they didn't, like a switch. But clearly something else was going on there.

Anyway, to your question, I have seen Supercharging rates just a hair under 90 kW. 88 or 89 but I don't think I've ever actually seen 90. Even in the summer heat (recent road trip to Chicago) I get absolutely no a/c action from the car even though cars in other stalls are humming away like mad. I have no idea why this is. It does make me curious and I definately will mention it when it is next in the shop.

jerry33 · Jul 14, 2015

mknox said:
Anyway, to your question, I have seen Supercharging rates just a hair under 90 kW. 88 or 89 but I don't think I've ever actually seen 90.

I'm pretty sure that those numbers are truncated rather than rounded (it was posted some time ago).

mknox · Jul 15, 2015

jerry33 said:
I'm pretty sure that those numbers are truncated rather than rounded (it was posted some time ago).

Right. I didn't recall exactly other than to say at 20% or less SOC I would see a hair under 90 kW and this will taper as the battery gets full.

beeeerock · Jul 15, 2015

mknox said:
Anyway, to your question, I have seen Supercharging rates just a hair under 90 kW. 88 or 89 but I don't think I've ever actually seen 90. Even in the summer heat (recent road trip to Chicago) I get absolutely no a/c action from the car even though cars in other stalls are humming away like mad. I have no idea why this is. It does make me curious and I definately will mention it when it is next in the shop.

Yeah, I sure would. Or perhaps even talk to them before that visit. With the complexity of the battery management system, I'd expect there would at least be an error code appear or a failsafe reduction in charging power if the cooling was called but not responding. Definitely don't want to cook the batteries.

The previous problem of low regen is also interesting and I half wonder if there is a connection. But the correction after the contactor replacement would seem to suggest 'no'.

Still seems odd though. Have you looked at the charge rate in the other cars that are blowing and perhaps noted their battery version?

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