Lowering amperage a good thing?

[MrThreeeee]

Hi All,

I searched and didn't find this question, so forgiveness if this has been addressed. I have heard charging at a lower amperage can be better batteries long term.

I am a brand new Model 3 owner. LR RWD. I am charging from a wall charger at home on a dedicated 60 Amp breaker. If I reduce to 30 amps I charge in about 6.5 hours. Am I helping battery life by reducing the charge amperage? Your in put is greatly appreciated.

 

[nwdiver]

Hi All,

I searched and didn't find this question, so forgiveness if this has been addressed. I have heard charging at a lower amperage can be better batteries long term.

I am a brand new Model 3 owner. LR RWD. I am charging from a wall charger at home on a dedicated 60 Amp breaker. If I reduce to 30 amps I charge in about 6.5 hours. Am I helping battery life by reducing the charge amperage? Your in put is greatly appreciated.

It's unlikely that you're helping you battery much since the difference from 30A to 48A is a rounding error compared to the stress of driving, regenerative braking and supercharging. BUT... you are marginally making charging sliiiightly more efficient with lower line losses and reducing the thermal cycling of your EVSE. I usually charge at ~20A for that reason.

 

[Kuhz]

In theory yes. In real practice? Unlikely you’ll notice any difference

 

[ewoodrick]

Nope, stop worrying about the battery. Enjoy the car instead.

 

[Feathermerchan]

To the OP:
It is not a wall charger. It is a wall connector. The charger is in the car.
From the almost dawn of using LiIon batteries it has been considered OK to charge them at 1C. That is one times their capacity in Amp Hours. For example a 5 Ah battery may be safely charged at 5A.
There are 96 sets of 46 cell modules. The modules cells are in parallel. This means that the current sent to the pack by the charger is split 46 ways. Charging at 240V and 32A results in about 22A into the battery pack. Divided 46 ways that is 0.47A charge into each cell. Dropping your charge current to 20A would drop the charge current to 0.29A
So no dropping the charge current would have no effect on the battery.

 

[DriveMe]

As others, have already pointed out, home charging, even on a 60A circuit is very slow compared to Supercharging:

The maximum you can get is 48A sustained or 11.5 kW. For Model 3 that will result in a charging rate of 44 miles of range per hour of charging.
Compare that to a Supercharger. With V3 you can now get: 250 kW, a 1000 miles per hour charging rate!

So, go ahead and charge at 48A and don’t worry about the battery!

 

[jerry33]

Depends upon whether or not the electricity in your area is flakey. I charge at 33 amps for this reason (There's no fix for this because deregulated utilities have no incentive to improve the infrastructure. The rate is cheap, but it comes at a cost.) Some have postulated that charging at higher then necessary heats the cells more. There's no actual evidence that this changes the battery life. There is evidence that charging at lower than 32 amps is inefficient, and that the efficiency isn't much different between 32 amps and 80 amps.

 

[MrThreeeee]

Awesome, thanks for the feedback!

 

[dhanson865]

there was a thread back in the dual charger model S days that showed the effeciency was best at a certain number of amps, not every step down is optimal.

found it Model S Gen2 Charger Efficiency Testing

25 amps and 40 amps were the efficient choices back then, not sure how it'd go for the Model 3. You'd have to know your max rate and try various amperages around the 1/2 and 2/3 levels to figure out max efficiency. Maybe just below or just above or right at 1/2 is best, maybe somewhere near 2/3 is better or maybe not.

also he seemed to be using round numbers for amps so I assume he was turning it down from the car as my EVSE at home only does 2 amp intervals (I can do 14 or 16a but can't do 15a for example).

oh and that's about cost per charge, not battery life. Charge at any speed you like if you care about battery life.

@wk057 tested any Model 3 chargers yet?

 

[randy1200]

It appears this is not an exact science. That said, if slow charging is within your mission profile, just charge from a regular 120V wall outlet.

 

[TSLA Pilot]

It appears this is not an exact science. That said, if slow charging is within your mission profile, just charge from a regular 120V wall outlet.

NO!

The equation for energy loss includes AMPS only--the greater the amps, the worse the energy loss.

Power = Volts X Amps

If the OP charges at a 120-Volt outlet this is SUBOPTIMAL as the amps will have to maxed out; the heat/energy loss is far greater than a slow charge on a 240-Volt outlet. In a perfect world, he could reduce his amperage to whatever he desires, as long as he remains on a 240-Volt outlet.

 

[martinsfsu]

Lower amperage charging will have no effect on a battery that is designed to be charged x10+ faster at a supercharger, HOWEVER, it will protect your homes electric system. Regular and extended home charging can cause a lot of wear and tear on the circuit, wires, etc. My installer has noted seeing a lot of that a couple of years after install.

 

[Feathermerchan]

Does running your air conditioner (OK maybe not in LA) cause wear and tear on the wires? No.
Charging your car is similar to using other appliances except that it operates continuously for long periods of time. So the National Electric Code has different standards for continuous loads. So that is taken into account.
There can be issues with receptacles wearing if plugged and unplugged many times. I have had to replace a bathroom one that was worn due to hair dryer and phone charging use. Your Tesla will warn you if the plug is getting hot and slow down or stop the charge.
Reducing the amperage will increase the duration of the charge. That may help the grid depending on the local conditions.

 

[TSLA Pilot]

Lower amperage charging will have no effect on a battery that is designed to be charged x10+ faster at a supercharger, HOWEVER, it will protect your homes electric system. Regular and extended home charging can cause a lot of wear and tear on the circuit, wires, etc. My installer has noted seeing a lot of that a couple of years after install.

Have to disagree a bit on your initial sentence.

The fact that the battery can tolerate Supercharger charging does not mean it is, in any way, good for battery longevity to charge at such high rates.

Various videos (that are often quickly removed from the web) have indicated that a battery could last a lifetime+ if kept between, say, 40 to 60%, and charged and discharged at relatively low rates. Keep an eye out for anything from Dr. Jeff Dahn to learn more as he is a pioneer in the area, and he's been working with Tesla for many years now:

Advanced battery scientists join exclusive Tesla partnership at Dal in research chair roles

Chongyin Yang and Michael Metzger will both work very closely with Jeff Dahn, who is currently the NSERC/Tesla Canada Inc. Industrial Research Chair and Canada Research Chair in Materials for Advanced Batteries.

www.dal.ca

 

[Pstreicher1]

I have lowered my charge to 30a from 48a mainly to decrease the heat loss from the Telsa wall connector cable. Not that it is a big deal but I also believed it might increase battery longevity. I'm not coming across any owners that have had their battery replaced in any forums or discussions I have been on. One poster that sticks to my mind said he has a ten year old Model S with over, if I remember correctly, 200k miles or maybe it was 500k. Ten years is a long time so that sits well with me. I'm hoping by the time I need a replacement we will have even better range packs and something newer than the current 4680 batteries. Yes, I will just enjoy my ride just the same.

 

[UncleCreepy]

Pretty sure OP has figured it out almost three years after asking here.

Anyway... while it's true that charging at lower current can save a few cents on heat loss, it should be noted that the car's computer is running while you're charging, consuming about 250 W. This load does not depend on how slow or fast you charge. So if you charge at 48 Amps or 11.52 kW for 4 hours, you're losing 1 kWh. This is not a whole lot compared to the total energy drawn from the grid: 46.08 kWh (11.52 kW x 4 h).
However, if you charge at 16 Amps or 3.84 kW, it takes 12 hours to draw the same amount of energy from the grid. That means you'd be wasting 3 kWh for the car's computer instead of 1 kWh which is probably more that the heat loss could ever be.

As others pointed out, there is no significant difference in terms of battery longevity. Charging a 75 kW battery at 11.5 kW equals roughly 0.15 C which puts little to no stress on the battery.

 

[Feathermerchan]

The other place you save kWh when charging slower is in the circuit from your panel to the plug. I ran #6 about 100 ft to my plug for each pf two circuits. The insulation is noticeably hot when charging at 40A.

How do we know "the computer" draws 250W (which is over 20A at 12V)?
Maybe I should clamp on my DC current meter next time I charge.
BTW the BMS and probably DC-DC converter also run during charge. Since the BMS is in the battery as well as the charging contactors, The battery could charge with the rest of the car asleep. Unless they need cooling pumps or something elese external.

 

[TSLA Pilot]

The other place you save kWh when charging slower is in the circuit from your panel to the plug. I ran #6 about 100 ft to my plug for each pf two circuits. The insulation is noticeably hot when charging at 40A.

How do we know "the computer" draws 250W (which is over 20A at 12V)?
Maybe I should clamp on my DC current meter next time I charge.
BTW the BMS and probably DC-DC converter also run during charge. Since the BMS is in the battery as well as the charging contactors, The battery could charge with the rest of the car asleep. Unless they need cooling pumps or something elese external.

And, IIRC, those original estimates of computer power required while charging may have been based on the original Model S.

I'd guess that Tesla MAY have found a way to reduce that greatly over the M3/MY and now the next generation Model S/Y as well?

As such, I'll still be keeping my overnight charging at 10 or 15 amps as it just seems like a better idea; wish Tesla would shine some light on this for us!

 

[Pstreicher1]

I don't think it matters what the BMS or anything else in the charging circuitry in the car itself uses. TeslaFi and or a AC meter like I installed from eBay that correlates closely with TeslaFi, gives total kwh used for a charging session. That's the number we can only use to figure our costs. Now, for something a little different, why not try charging at as low a percentage as you can go and see what the current draw is. I just might have to try this to cure my curiosity. I'm anal and a nerd so I have to do it!

 

[Pstreicher1]

Some good info in this article that agrees with the Tesla manual.

Tesla Charging Limits - How to Change them and Why You Should

If the vehicle is not set to a lower current, following this rule, you will likely trip the circuit because the car will try to draw more amperage from the circuit. Trying to connect a non-Tesla adapter or cord to a Tesla provided adapter will NOT automatically change your limits. You will...

acworks.com