Charging efficiency.

[SFNM Jack]

Very interesting thread….

I’ve had my MY since the 18th of December, 2021. I love it. Her name is Jane after Jane Jetson. Hot, smart, reliable….

Anyhow, I’ve been doing a lot of research on how to most gently and efficiently charge the vehicle. I’m retired so speed of charge is not a concern for me. I’m looking for the most efficient use of power used to charge the vehicle… not for cost reasons but for environmental considerations. I averaged about 3-5 trips a week historically with my former ICE vehicle. I have a 240 14/50 dedicated circuit for level II charging which is supplied by my 8kw solar array. Based on what I’ve read during my research I’ve settled on charging at 240v 13amps with max everyday SOC of 70%. That combination seems to be a good compromise between treating the battery gently and not allowing efficiency to be badly compromised or over working the MCU and other components by overly slow charging as described here; Gently charging the Tesla battery to preserve capacity

The combination of 240v, 13amp seemed to be giving me about 93% efficiency based on the data I’m getting from the EEVE app I linked to the car. Temps were mild until a few days ago in NM. The garage was in the high fifties at night during that time. The last few days have been cold in Santa Fe…. My attached garage temp is now averaging about 50F over the last few days but temps some times are as low as 42F. Since the ambient temp drop my efficiency has dropped to 77% give or take, again based on what EEVE is telling me. Is there really a 16% drop in charging efficiency with a charging temp drop of say 10F? I plug in as soon as I park the vehicle so battery heating should not be impacting efficiency terribly. I’d be really interested in peoples thoughts on the efficiency drop as well as the the amperage I’ve chosen to charge at on my 240v circuit, which again is 13 amps.

 

[jcanoe]

When the Tesla Model Y is powered on the power usage is ~230W, with 230Wh of energy consumed per hour. I don't know if the power usage while charging is also 230W but my Tesla Model Y responds immediately when charging and I open the Tesla app so the Model Y is not in sleep mode while charging.

If you charge at 240V/13A (~3kW) hypothetically it takes 5 hours to charge from 50% to 70% (~15kWh). The Model Y is powered on consuming an assumed ~230Wh over the 5 hours or a total of 1.15kWh. 1.15kWh/15kWh is 7.6% overhead. The overhead (assumed to be ~230W) is directly proportional to the time needed to charge then reducing the time to charge would reduce the total overhead.

If you were to charge instead at 240V/30A (6kW) charging would take 2.5 hours and the overhead would 0.575kWh/16kWh or 3.8%. This may be oversimplifying things as there are other charging losses due to increased resistance in the charging cable(s) and the battery at the 6kW charging rate. Also, your solar voltaic system may not be able to provide 6kW output without depleting a battery storage array.

I don't understand the environmental consideration since the power produced by the solar array is non-polluting.

 

[SFNM Jack]

We’re a

When the Tesla Model Y is powered on the power usage is ~230W, with 230Wh of energy…

Hey, Thx for that..

On the solar…. It’s a near grid system so if it’s cloudy then its only making about 4-8 kWh across the entire day and any requirements beyond that from the car or house come from the grid. Pre-EV we averaged 20 kWh/day. there are no batteries in the system although I’m considering an LG battery solution for back up since tesla will no longer sell power walls to non-tesla solar owners. Anyhow, clouds aren’t a huge problem in NM where we average 320 days of sunshine but when we do have to pull from the grid it’s mostly coal and NG. A full sun day even in winter is producing 40+kWh. Summers longer days produce well over 50. Cost is zero always because we get credits for days we over produce which is the majority of days. That being said my excess power production reduces the amount of power the dirtier grid has to produce so I want to use what we make as efficiently as possible.

On gently charging the battery. Everything I’ve read says the compromise of slower charging between 11 and 14 amps can preserve a significant amount of battery capacity long term. Based on what you say above I guess I’m going to live with some additional overhead or up the current. Again, thx for sharing your thoughts.

I’m still interested to hear from anyone about my choice regarding lower amperage charging and it’s impact on battery capacity long term.

 

[jcanoe]

I have read that limiting charging to 1C where C is the capacity of the lithium battery will prolong the effective life of the lithium battery, i.e maintain usable capacity. All Level 1 and Level 2 charging is at most 1/7th C, only Supercharging can equal or exceed a 1C charging rate. When charging at up 11.5kW (48A) this is far below 1C. I don't know if charging at 13A provides any measurable extension to the usable life of the battery. It probably does; if the battery lasts more than 10 years does it really matter as older Tesla battery packs can fail for any number of reasons unrelated to charging rate.

 

[Benito1283]

Everything I’ve read says the compromise of slower charging between 11 and 14 amps can preserve a significant amount of battery capacity long term.

I’m interested in where you read this. I usually charge at 240v / 20A but I’m rarely pressed for time and would lower my current if it indeed helps keep the battery healthy. And I assume you mean 11-14 amps at 240v? Watts might be a more reliable unit to go by.

 

[SFNM Jack]

I’m interested in where you read this. I usually charge at 240v / 20A but I’m rarely pressed for time and would lower my current if it indeed helps keep the battery healthy. And I assume you mean 11-14 amps at 240v? Watts might be a more reliable unit to go by.

From my previous post in this thread:

described here; Gently charging the Tesla battery to preserve capacity

 

[Rocky_H]

On gently charging the battery. Everything I’ve read says the compromise of slower charging between 11 and 14 amps can preserve a significant amount of battery capacity long term.

That seems like nonsense. I went to the article you linked to, and they had one single story of one single car that had been charged exclusively at 3 kW and had really low degradation. That is called an anecdote--not data.

These are cars with very large battery packs where they can take over 200 kW of charging power. Thinking that dinking around with the difference of 3 or 6 or 11 kW makes any noticeable difference to the battery just isn't rational. That is all very slow charging. On the charging cable, though, sure--it's built for a maximum of 32A and the cable and connections can get kind of warm running at that level, and the daily hot/cold/hot/cold cycles can wear on some things over time, so I might use something like 27 to 29 amps or something just to keep it a little cooler and maybe preserve some life there.