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Lowering amperage a good thing?

MrThreeeee

Member
Mar 25, 2019
14
7
Middle of Nowhere, CA
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

Well-Known Member
Feb 17, 2013
8,299
10,978
United States
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.
 

Feathermerchan

Active Member
Sep 21, 2018
1,194
936
Euless, Tx
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

Member
Aug 12, 2017
752
1,278
NE OH
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

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Supporting Member
Mar 8, 2012
19,966
23,918
Texas
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.
 

dhanson865

Active Member
Feb 16, 2013
4,686
7,838
Knoxville, Tennessee
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?
 
Last edited:

TSLA Pilot

Active Member
Mar 12, 2013
1,827
2,582
United States
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.
 
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