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Ideal Charge Rate??

u00mem9

Member
Jun 8, 2016
943
1,290
USA
Rate

I have a new refresh 60kWh, and I have an HPWC that can charge at 48A (seems to actually max out at 47A, but anyway)

My question is: If I charge overnight, and have plenty of time, should I slow the charge rate down to 20A or 30A? My understanding is there will be some charge rate impact to battery life, at least at the multiple 'C' level...but maybe the difference between 1/5C and 1/10C is meaningless.

Thoughts?
 

CHG-ON

Still in love after all these miles
Jun 24, 2014
3,079
648
Santa Cruz Mountains, USA
Charge rate won't affect the battery. Max charge level will. Keep it at or below 90% unless more range is needed. I have read a few engineer opinions that charging between 30-70 on a regular basis will be less stressful for the battery and make it last longer, provided that meets your needs.

Also, the higher amperage that you use to charge will use the electricity more efficiently and therefore cost you less overall: less parasitic loss. Though I would expect that it is marginal as long as you are on 240.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,765
8,346
Boise, ID
Any home AC charging rates are so relatively low that they are insignificant to the battery as far as being better or worse. Supercharging pushes it some, but they actively control it and cool the battery to keep it at an acceptable level.

So from the battery side it doesn’t matter. The only thing that may matter a little is running either the wall connector or mobile charge cable at their maximum current. They each get kind of hot doing that. A lot of heating/cooling cycles stresses materials and electronics generally, so that may shorten their lifespan some. You are running your wall connector at 48A instead of the max of 80A, so no problem. Some people (myself included) who are using the mobile cable for daily charging frequently run it at low 30’s to keep it from getting hot and not stress it.
 
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chillaban

Active Member
May 5, 2016
3,723
6,597
Bay Area
100% daily?

More and more folks are reporting that DS'es are saying it's okay to charge the 60 to 100% daily, which would make sense given the additional evidence that a 60 is locked to the bottom end of the battery.


I usually charge my SW-locked 70D to around 95% as a simulation of 90% on the 75kWhr pack. I live in an apartment and often charge the car overnight, and if I'm gonna "hog" a shared charger, I would rather get an extra hour's use out of the charger rather than wasting that time.
 

Saghost

Well-Known Member
Oct 9, 2013
8,224
7,088
Delaware
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I have a new refresh 60kWh, and I have an HPWC that can charge at 48A (seems to actually max out at 47A, but anyway)

My question is: If I charge overnight, and have plenty of time, should I slow the charge rate down to 20A or 30A? My understanding is there will be some charge rate impact to battery life, at least at the multiple 'C' level...but maybe the difference between 1/5C and 1/10C is meaningless.

Thoughts?

I'd slow the rate down. You might end up with similar overall usage - you're trading the greater overhead of keeping everything awake longer against the greater resistance losses of the high rate all through the wiring - and it puts less wear and tear on all the parts involved if there's less heating.

If you aren't keeping the car past warranty, it won't matter - and most likely everything will hold up just fine well past that.

But if you aren't gaining anything from it, why put the extra strain on the systems?
 

hacer

Active Member
Apr 13, 2016
1,156
5,257
Clarksville, MD
Your most efficient charge would be 48A.

NO!

There has been some misinformation about this for a while now (at least regarding the refreshed on-board chargers). I have been gathering data (still in progress) that clearly shows that charging efficiency is better at reduced current. The efficiency here is measured as the ratio of "charge_energy_added" as reported from the car's REST API divided by the meter reading of the meter connected to my HPWC. I've have also verrified for 2 charging cycles that the meter reading is in agreement with a time-integration of the product of "charger_voltage" and "charger_actual_current" from the REST API sampled every 3 seconds over the course of the charge duration. (This last part means that anybody can replicate these experiments entirely with the REST API even if they don't have a utility meter dedicated to the charger). Below doesn't look like many points, but in fact there are a few points lying on top of each other (at least at this scale). I'll be publishing my full spreadsheet once I've completed my experiments. I provide this preliminary sneak previous because it clearly contradicts the mantra of "highest power is most efficient". I haven't yet tested below 25A, but I suspect 25A is near peak efficiency.
pubchart
 

msnow

Active Member
Jul 14, 2015
4,951
2,394
SoCal
NO!

There has been some misinformation about this for a while now (at least regarding the refreshed on-board chargers). I have been gathering data (still in progress) that clearly shows that charging efficiency is better at reduced current. The efficiency here is measured as the ratio of "charge_energy_added" as reported from the car's REST API divided by the meter reading of the meter connected to my HPWC. I've have also verrified for 2 charging cycles that the meter reading is in agreement with a time-integration of the product of "charger_voltage" and "charger_actual_current" from the REST API sampled every 3 seconds over the course of the charge duration. (This last part means that anybody can replicate these experiments entirely with the REST API even if they don't have a utility meter dedicated to the charger). Below doesn't look like many points, but in fact there are a few points lying on top of each other (at least at this scale). I'll be publishing my full spreadsheet once I've completed my experiments. I provide this preliminary sneak previous because it clearly contradicts the mantra of "highest power is most efficient". I haven't yet tested below 25A, but I suspect 25A is near peak efficiency.
pubchart
Looking forward to seeing it but I think Tesla used to have a paper on this stating a different conclusion. If I were the OP I'd get in touch with them and confirm.
 

hacer

Active Member
Apr 13, 2016
1,156
5,257
Clarksville, MD
Looking forward to seeing it but I think Tesla used to have a paper on this stating a different conclusion. If I were the OP I'd get in touch with them and confirm.

Where can I find this paper? Anyway that paper probably pre-dates the new on board 48/72 A charger. My car is a refreshed 70D so my measurements are about the new charger. Last night I did the first 20A charge rate and the efficiency when down significantly at that current. The chart in the first post is a "published" google sheets graph, so the picture in the previous post shows the latest graph as I add more data.
 

msnow

Active Member
Jul 14, 2015
4,951
2,394
SoCal
Where can I find this paper? Anyway that paper probably pre-dates the new on board 48/72 A charger. My car is a refreshed 70D so my measurements are about the new charger. Last night I did the first 20A charge rate and the efficiency when down significantly at that current. The chart in the first post is a "published" google sheets graph, so the picture in the previous post shows the latest graph as I add more data.
I casually looked for it but couldn't find it but you are correct. As I recall it was comparing 40 to 80 A.
 

Saghost

Well-Known Member
Oct 9, 2013
8,224
7,088
Delaware
Superchargers max out at 120kW and so far there's no evidence that they noticeably hurt the battery. The difference between 48A (11.5kW) and 20A (4.8kW) is so tiny by comparison as to be irrelevant.

Agreed. I was more thinking reliability for the charger itself and the EVSE. :)
 
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jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Supporting Member
Mar 8, 2012
19,997
24,658
Texas
Agreed. I was more thinking reliability for the charger itself and the EVSE. :)
Obviously the charger will run cooler at lower amps. How much extra life you might get is another story as the charger, like the battery, is liquid cooled. The EVSE is really just a switch and it shouldn't have any heat problems. I don't charge at 40 amps with the UMC except on trips. There's definitely data that shows the UMC benefits from a slightly lower amps. The HPWC is quite a bit heavier duty and doesn't get nearly as warm at 80 amps as the UMC gets at 40.
 
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ran349

Member
Jun 28, 2016
443
301
SoCal
Any home AC charging rates are so relatively low that they are insignificant to the battery as far as being better or worse. Supercharging pushes it some, but they actively control it and cool the battery to keep it at an acceptable level.

So from the battery side it doesn’t matter. The only thing that may matter a little is running either the wall connector or mobile charge cable at their maximum current. They each get kind of hot doing that. A lot of heating/cooling cycles stresses materials and electronics generally, so that may shorten their lifespan some. You are running your wall connector at 48A instead of the max of 80A, so no problem. Some people (myself included) who are using the mobile cable for daily charging frequently run it at low 30’s to keep it from getting hot and not stress it.
Have you actually experienced your UMC heating up much? I charge at 40 amps, 240 V with my UMC and it gets only slightly warm on the cable itself, but not anywhere near hot to the touch. The warmest point I found was on the metal plate of the UMC near the green LED. I felt no noticeable warmth from the car plug or the NEMA plug end of the cable.
 

msnow

Active Member
Jul 14, 2015
4,951
2,394
SoCal
Have you actually experienced your UMC heating up much? I charge at 40 amps, 240 V with my UMC and it gets only slightly warm on the cable itself, but not anywhere near hot to the touch. The warmest point I found was on the metal plate of the UMC near the green LED. I felt no noticeable warmth from the car plug or the NEMA plug end of the cable.
Same here. It doesn't feel warm to the touch to me either.
 

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Supporting Member
Mar 8, 2012
19,997
24,658
Texas
Have you actually experienced your UMC heating up much? I charge at 40 amps, 240 V with my UMC and it gets only slightly warm on the cable itself, but not anywhere near hot to the touch. The warmest point I found was on the metal plate of the UMC near the green LED. I felt no noticeable warmth from the car plug or the NEMA plug end of the cable.
The plug gets only moderately warm, but the cable between the plug and GFI is very hot at 40 amps.
 

msnow

Active Member
Jul 14, 2015
4,951
2,394
SoCal
The plug gets only moderately warm, but the cable between the plug and GFI is very hot at 40 amps.
Yikes, hot enough to melt the wire casing? Also do you know this from experience by going inside the conduit to touch it or is it just widely known?
 

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