Ideal or Cost Effective Home Charging

[doggy1]

Just a couple of observations.
1. You do not state what the voltage was.
2. I assume you are quoting the Pilot Signal amps rather than the actual amps?
3. I looked back at 300 charge sessions and my average, which is remarkably consistent across all charging, AC and DC is 7.3km/kW. Of course, this is rated km per nett kWHr (not gross kWHr). Very similar to your 3LR which is just one year earlier (but slightly different battery), so very consistent.
4. I have just done a number of measurements at a variety of (single-phase) currents. Whereas my low end percentage is not as bad as the figures I was quoting, it is not too crash-hot. Aircon and lights and radio all off. The DC-DC converter was pulling 320W for all sessions. The coolant pumps were running at 5.6 to 6L/M for all sessions. The AC charger will be less efficient at lower amperages (semiconductor voltage drops et al). The radiator fan was not running. However, I am betting it was running when I measured a few months ago in summer where the ambient would have been 30+ and battery cells around 35degC. Today, ambient was 23degC and mid-cell battery temperature was 25degC. Here is the data:

​	​	Tesla Model 3LR AC charging efficiency @ 23degC​	​	​	​
​	​	​	​	​	​
Pilot​	Actual amps​	Volts @ car​	Power in (W)​	Power Batt (W)​	Efficiency​
​	​	​	​	​	​
5​	5.28​	241​	1272.48​	750​	58.9%​
6​	6.16​	240​	1478.4​	980​	66.3%​
7​	7.48​	239​	1787.72​	1215​	68.0%​
8​	8.36​	239​	1998.04​	1450​	72.6%​
9​	9.46​	239​	2260.94​	1750​	77.4%​
10​	10.34​	239​	2471.26​	1940​	78.5%​
12​	12.10​	236​	2855.6​	2350​	82.3%​
14​	14.30​	236​	3374.8​	2780​	82.4%​
16​	16.11​	234​	3769.74​	3240​	85.9%​
20​	20.24​	233​	4715.92​	4000​	84.8%​
24​	24.20​	230​	5566​	4890​	87.9%​
27​	27.06​	228​	6169.68​	5450​	88.3%​
30​	29.92​	228​	6821.76​	6240​	91.5%​
32​	31.90​	225​	7177.5​	6620​	92.2%​

 

[Leeroy]

It’s an interesting data set to see compared that way, particularly as the voltage drops off the efficiency actually continues to improve.
I know that isn’t necessarily related, but I would have assumed a voltage loss/heat resistance would have dropped efficiency somewhat, but there it is.

I too charge at low amps when necessary, but do this to absorb excess solar rather than anything else. I know others charge at low amps for this reason too.

 

[doggy1]

The main voltage drop with increasing current is due to 40 or so metres of heavy duty armoured cable to my garage (nothing to do with the car). Voltage is also affected by my solar system, clouds, other power drains etc. I monitor it very closely and locally my grid voltage has been as low as 215V and as high as 278V (but not today). It does not affect the results above as low voltage does not become a measurable problem until you get down in the 120V range (as in US single phase). So, those things are outside the scope of the actual Tesla efficiency displayed in the table above.

Of course, I do have to think about the power losses in my cable and other wiring when charging because these tend to decrease the charging efficiency as the current goes up (in my case). The sweet spot for me, in my house, is about 14amps which fits nicely with my excess solar when the sun (occasionally!) shines. Then, my cable loses me less than 2%. When my excess solar amperage is low, I stuff it into the house LFP battery at high efficiency (with my own designed and built charger) then shove it into the cars at higher amperage (and higher efficiency) when convenient.

 

[Vostok]

I too charge at low amps when necessary, but do this to absorb excess solar rather than anything else. I know others charge at low amps for this reason too.

This is exactly what I do. I either charge at 5A or 6A but for me it‘s 3 phase - so either 3.6 kW or 4.3 kW. I have only 5.8 kW solar array with 5 kW inverter. So if my system maxes out (which it does for 2-3 hours each day in summer if sunny) then 4.3 kW plus typical daytime household consumption 0.7 kW matches my solar.

 

[Mashimaro]

Not sure if this is the right thread but…does anyone know why I only get a maximum of 8 amps from the standard wall plug charging at home. I have only had the car 2 weeks? Thanks.

 

[atj777]

@doggy1 How are you actually charging?

I think one reason for inefficiencies is if the car is not asleep. When I did my charge test yesterday, the car was asleep for the whole hour. This means there would have been almost no drain on the battery from the car itself.

I know if I charge with something like the Virtual Wallbox with Autarkie Manager, it keeps the car awake (as it monitors the car and changes the charging to suit). With the car awake, there would be drain on the battery while charging. That drain would be constant regardless of the charge current which means the ratio of charge rate to drain would be much lower with a lower charge current resulting in less apparent efficiency. i.e. you are putting n kWh in but taking y kWh out at the same time.

 

[atj777]

Not sure if this is the right thread but…does anyone know why I only get a maximum of 8 amps from the standard wall plug charging at home. I have only had the car 2 weeks? Thanks.

That was standard with the older UMC and tails supplied with the car. I thought the newer tails were updated to 10A.

 

[aegidius]

My Gen 1 UMC goes all the way to 10A (after 30 seconds or so ramping up) This is on Model S though, I don't know if any 3's came with the Gen 1 UMC.

 

[Leeroy]

Not sure if this is the right thread but…does anyone know why I only get a maximum of 8 amps from the standard wall plug charging at home. I have only had the car 2 weeks? Thanks.

This has come up a lot (but usually with older cars now) have a look on the actual plug itself and the text should say 10amp (or 8 amp if it’s an old one.)

 

[atj777]

@doggy1 How are you actually charging?

Actually, I think Scan My Tesla is probably keeping the car awake so it can do its measurements and is actually skewing its own results. i.e. the act of measuring is affecting the measurements.

 

[Vostok]

the act of measuring is affecting the measurements.

Schrödinger at work!

 

[doggy1]

There is some truth to this. If you can send the car "asleep", it helps. I just did a one hour test at 6 amps. The actual amperage (and power) was 3.5% higher than in the other test even though the Pilot Signal was still 6amps. The car was plugged in and asleep for 16hrs beforehand. I simply turned the EVSE from Pause to Run. The APP was off. I only turned on SmT after the one hour. What I observed was as follows:

0. Not really an observation, more a known fact: There are fixed losses associated with charging as well as dynamic ones. In general, the faster you charge the lower the percentage lost.
1. The car appears to be fully asleep but does in fact wake up to some extent. Enough to manage the charging process PLUS it connects to the internet. Screen is off.
2. This saved 140watts extra (in the hour) which went into the battery. So the efficiency went from 66.3% to 75.7%. If I extrapolate the saving to 5amps, the efficiency would rise from 58.9% to 70%.
3. Given that the DC-DC converter was using around 320W when the car was awake, having the screen off and presumably some software not running reduced this to a (guessed) 180W.
4. After the test, I turned on SmT and saw the coolant pumps still running at 6LPM. I did not hear any clicks so they were presumably running all the time and this is also presumably done by the BMS. Not sure why as temp was several deg cooler than the previous tests. Probably the same sort of logic that says if you are DC charging, no matter how slowly, the battery will be heated to 45degC.

Overall, at 6.38 amps actual charge rate and 239V, input power was 1524watts and 1150watts went to the battery resulting in a gain of 1.15kWHrs. So I was losing 374watts at the nominal 6A Pilot level.

 

[Nobody Famous]

does anyone know why I only get a maximum of 8 amps from the standard wall plug charging at home.

The car default current setting is 8A. You should be able to adjust it on the screen up to 10A.

 

[Rolond]

This has been reported before, the UMC just need to update, the way to do this is to set the charge limit to a little more than the battery charge level is at, so it charges and leave it plugged in once charging is complete, provided you have a wifi connection at home I believe, the UMC will receive a software update and the tails will then charge at 10 and 15 amps respectively

The UMC that is supplied with the cars these days should have tails that are marked 10 and 15 amps on the plugs between the pins on the plug

I got my Model 3 in June 2020, and my tails are marked as 8 and 12amp and can not be updated

 

[OzVic]

Not sure what the cars come with now, but in addition you need to be on at least 2021.12.25.7 to get the tails update.

 

[Mashimaro]

Thanks for the detailed explanation on the 8 amps charging rate. I will try the solutions provided above

 

[theappleguy]

Just adding my 50c.
I've had a Zappi V2 installed for the last year and half and been really happy with it, switching between charging only via Solar (the smart part of this charger) and doing overnight off-peak tariff charging when needed.

Currently drive a Nissan Leaf, and looking forward to my M3 later in the year. Good to hear Zappi is still working well for some Tesla owners here

 

[m3rwd]

Thanks for the detailed explanation on the 8 amps charging rate. I will try the solutions provided above

I have a 2022 with a 10a tail. Also only getting maximum of 8a charge. I've tried leaving it plugged in for hours after a charge, but still no option to increase to 10a.

 

[Nobody Famous]

I have a 2022 with a 10a tail. Also only getting maximum of 8a charge. I've tried leaving it plugged in for hours after a charge, but still no option to increase to 10a.

If you change the Current setting on screen, what are the maximum and minimum values?

 

[Maximillan]

I have a 2022 with a 10a tail. Also only getting maximum of 8a charge. I've tried leaving it plugged in for hours after a charge, but still no option to increase to 10a.

It sometimes takes a few goes to download the update. Last person that I advised this on randomness I suggested that they do a happy dance around the car to help it get to 10A, after which it did indeed get to 10A.

Correlation doesn't equal causation I know, however you've got nothing to lose by doing the dance around the car to help your chances....