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Best Amp charging?

Best Amp charging?

So everyone has beaten the best charge limit question to death. We all KNOW it is best for battery longevity to be between 50 and 70% charge. A little lower or higher won't make much of a difference. A lot lower or higher will decrease battery life if done routinely. But the bigger question is:

If I have a 75D and a home wall charger that is charging at 48 Amps, obviously it is no where near as fast as a supercharging station, but is it degrading the battery life? The real question is every night at home, what is the best Amps to charge it at for battery health/life? 48, 40, 30, 20, 15 Amps??? And please no comments from non-electrical engineers, non-Tesla employees, or lithium battery newbs. I have extensive knowledge of lithium batteries and know most are best charged at 1 or 2 C. Which means for a 75 pack, 1 c would be 75 Amps, 2 c would be 150 amps. Obviously only a supercharger is doing that. So even at the maximum home charge of 48 amps, even with a 75D you are charging at <1 C, more like .64 C to be exact, which is well below the optimum safe charging of 1C for a lithium battery.

tes-s | May 15, 2018

I don't think it matters to the battery. Charging at lower amperage would go easier on the onboard charger.

EVRider | May 15, 2018

So you’re only looking from comments from electrical engineers who work for Tesla and are lithium battery experts? Good luck with that. :-)

Craig1965 | May 15, 2018

Well the wall charger can put out up to 100 Amps (though most electricians run 50-60 A breakers with two 220V lines, so most home chargers are set at 48 Amps) . Obviously if you run higher breakers and higher rated wiring to get to 100 Amps, it would be harder on the onboard charger, maxing out the 100 Amp spec. But since almost EVERY home will be wired and set to 48 Amps, you are no where near being hard on the onboard charger, they are usually most efficient at 50% of max load or 50 A. I'm just wondering if charging at slower than 48A would extend battery life, but I don't think so since it is well under 1 C charging rate.

Wall Connector
Technical details Recharge speed
Miles of range per hour of charge
Circuit breaker
(amps) Maximum output
(amps) Power at 240 volts
(kilowatt) Model 3
(mph) Model S
(mph) Model X
(mph)
100 80 19.2 kW 44 52 45
90 72 17.3 kW 44 52 45
80 64 15.4 kW 44 46 40
70 56 13.4 kW 44 40 35
60 48 11.5 kW 44 34 30
50 40 9.6 kW 37 29 25
45 36 8.6 kW 34 26 23
40 32 7.7 kW 30 23 20
35 28 6.7 kW 26 20 17
30 24 5.7 kW 22 17 14
25 20 4.8 kW 19 14 11
20 16 3.8 kW 15 11 8
15 12 2.8 kW 11 7 5

tes-s | May 15, 2018

"I have extensive knowledge of lithium batteries and know most are best charged at 1 or 2 C. Which means for a 75 pack, 1 c would be 75 Amps"

Your knowledge may be a little less than you think. Or maybe mine is.

Wouldn't 1c for a 75kWh battery be 75kW? A 75amp home wall connector would be 18kW.

Craig1965 | May 15, 2018

Sorry I can't edit and reformat that table, but it is from Tesla and showing 15 to 100 A charge rates and times for each model. But like I said, VERY few people are charging over 48A at a home residence. Even destination chargers are only 40A.

tes-s | May 15, 2018

"Well the wall charger can put out up to 100 Amps (though most electricians run 50-60 A breakers with two 220V lines"

I don't think this person meets the criteria the OP asked for. AFAIK, the wall connector will only put out a maximum of 80amps. Residential power in the US is 240v - there is no 220v service available.

tes-s | May 15, 2018

"Even destination chargers are only 40A."

Many destination chargers are 80A. Here is one from the Tesla "Find Us" page.

Waterworks
60 Backus Ave

Danbury, CT 06810

Driving Directions
http://www.waterworks.com/
Phone(800) 899-6757
Roadside Assistance(877) 798-3752
Charging
2 Tesla Connectors, up to 16kW.
Available for customers. Please call ahead.

View all Tesla locations

tes-s | May 15, 2018

"But since almost EVERY home will be wired and set to 48 Amps, you are no where near being hard on the onboard charger"

Isn't the onboard charger in the 75 a 48amp charger? It is designed to operate at 48A, but that is the limit of its capability. Running equipment at the max is not necessarily a problem, but running it below its rated max might be a little easier on it.

murphyS90D | May 15, 2018

I charge at 50 amps which puts 25 amps through each of the chargers in my pre-refresh car.

Craig1965 | May 15, 2018

Sorry 240v, 220v was a typo. And yes I mean 1 C for a 75kwh pack would be charging at 75 A. I guess if you say that:

A 75amp home wall connector would be 18kW, then Tesla isn't charging the same formula as RC lipos. 18kw for a 75kw pack would be 0.24 C rate of charge at the max 48 amps, which is way way below what a lipo can be charged at which is 1C, 2C, or much higher C depending on the lipo. I have some that recomend 5C charging for helicopters. And where a RC helicopter or plane usually has 4 to 8 cells and a Tesla has thousands, it is still governed by the same chemistry and safety limitations. But I see what you are saying, the car itself will only accept 48 A regardless of how much you are able to push through up to the chargers rated 100A. You will still only get the 48A maximum with a 75D. And I don't think with that low of a (0.24 C) charge rate even at 48A you are anywhere near worrying about damaging the battery or charger, but like I said I would love for a Tesla battery expert to chime in on whether charging a 75D at < 48A is any better for the batteries or charger.

tes-s | May 16, 2018

You already answered your own question. They charge at MUCH faster rates at a superchager. Trickle charging at 48A (12kW) or 24A (6kW) makes no difference to the battery.

p.c.mcavoy | May 16, 2018

Craig1965 | May 15, 2018
Sorry 240v, 220v was a typo. And yes I mean 1 C for a 75kwh pack would be charging at 75 A. ...
--------------------------------

@Craig1965 - I feel like you are still mixing terms with some of your "C" rate references, especially when I see your statement of 1 C for a kwh pack would be charging at 75 A. Charging a 75 kWh pack at 75A would only be 1 C if that was 75 A at the pack voltage, so somewhere in the 350-400 VDC range. Given any reference to charging off a 240V AC source is not referencing the current at the pack voltage, to quote the C off the charging current is misstated and why referencing it off the charging power, namely kW is really the way to express it. You do that correctly in other parts of your post, so I think you do understand this, but your opening statement is misstated.

Now as to what's best for battery life, the best source of data I go back to is always the Tesla MaxRange crowd-sourced shared google doc dataset. It's now over 400 users around the world supplying battery degradation data from real world use. While the curator of the dataset does have people specify their daily charging power, there's not been an analysis of that. There is an analysis of impact of frequency of supercharging, which does represent higher charging rates, with that dataset saying frequency of supercharging has no significant impact. That suggests to me that if frequency of charging at 1-1.25C has no impact, then why am I worring about the difference between charging at 0.1 vs. 0.2 vs. 0.3 C.

As for concerns of charging amps and stress on the on-board charger, I know of no publicly available hard data, but what I don't see is a large number of people complaining about on-board charger failures in sites like this. In fact, it's hard for me to remember seeing many posts at all relative to the number of people commenting about main display yellow lines or door handle failures. That tells me whatever impact there is is minor and I'm not going to worry about it. I do understand conceptually that pushing electronics harder than necessary is not desirable, but I'll continue to charge my 2016 MS90D with a 48 amp on-board charger at home daily drawing 40 amps on my UMC and not lose any sleep over it.

Rocky_H | May 16, 2018

Holy cow. Well, I am an electrical engineer, so I guess I'm qualified to comment, right? *eyeroll*.

@Craig1965, Quote: " I have extensive knowledge of lithium batteries and know most are best charged at 1 or 2 C. Which means for a 75 pack, 1 c would be 75 Amps,"

"Extensive knowledge", huh? But you don't know the difference between amps and kilowatts? The 48A home charging is only about 11.5kW, so that is FAR below the charging levels at Superchargers and is a very low C rate. So any differences between 15 or 30 or 48 amps just won't make any perceptible difference from the battery's perspective.

As @tes-s mentioned, though, the onboard charger is rated for 48A max. There may be some long term reliability benefit there from using it a little below the maximum level to keep it a little cooler and put less stress on it.

italiano21uf | May 16, 2018

I have dual chargers, so is should be ok then to use the HPWC dishing out 80 amps, correct? Since it would be 40 amps per charger? Or am I mistaken?

Rocky_H | May 16, 2018

@italiano21uf, Quote: "I have dual chargers, so is should be ok then to use the HPWC dishing out 80 amps, correct? Since it would be 40 amps per charger? Or am I mistaken?"

If you are thinking 40 out of 48, that's not correct. Those older cars with actual dual chargers have two of the ones that have a maximum rating of 40A each. So running 80A total is running both of them at maximum level. Also, the wall connector cord and handle have been known to get pretty hot running at 80A all the time, so many people do run it at a lower power level (maybe in the 60's or 70's) unless the faster charging rate is needed.

Craig1965 | May 16, 2018

Thanks Rocky_H , that is what I figured, that charging at 48A versus less at home would make no difference on battery life and is well under the C that is delivered from a supercharger. But I would also have to assume that since people who supercharge every day never have a problem with their onboard charger, that part I don't understand. If a 75D has a 48A maximum onboard charger, and you are charging with 48A at home level 2 wall charger, you are saying you are at max spec. But then how in the world can a level 3 100A plus supercharging station not be going above the 48A spec for the onboard charger?

Bill_75D | May 16, 2018

DC supercharging bypasses the onboard charger.

tes-s | May 16, 2018

"If I have a 75D and a home wall charger"
You don't have a home wall charger. You have a home wall connector, which is an EVSE not a charger. When connecting to an AC power source, the charger in the car is used.

When using an external charger (like a supercharger or CHAdeMO charger), the charger in the car is not used.

Craig1965 | May 16, 2018

Ah, didn't know that. Well I guess I might set my home charger down from 48A to 40A for a little leeyway if that is easier on the onboard charger, since 40A is fast enough for me. Any benefit to running less than 40A like a computer's PSU which is most efficient at 50-70% of it's max rating?

hammer @OR-US | May 16, 2018

"DC supercharging bypasses the onboard charger."

I guess only a Tesla employee or electrical engineer would know that. ;)

Rocky_H | May 16, 2018

To clarify even a little further, basically the same sets of equipment are being used, but the location of them is different. With the home charging, you are sending AC electricity into the car, and a charger in there is converting it. With Superchargers, the AC electricity comes from the utility transformer to the big cabinets full of equipment next to the parking lot. Know what's in there? Stacks of those same chargers that do the conversion outside the car. Then, they can just pass the DC electricity straight into the battery.

As far as running less than 40A, not sure. We just don't have that level of detail to know how much benefit there would be. I wouldn't use the word "efficiency", because there doesn't seem to be much difference of that at these levels. It's more about heat changes for reliability, and you probably get most of that benefit from the first several amps below maximum, with diminishing returns where you probably don't help much more going down to something ridiculously low like 5A. Running that high current through the various connections is going to warm them up. Warming up metals makes them expand. Where you have different metals connected to each other, like aluminum versus solder, versus copper, versus silicon, versus tungsten, and whatever else may be in the circuitry, those expand at different rates, so there is some physical stress as they are pulling or pushing against each other as they try to move by different amounts. And when it cools back down, they contract and are stressed again. Eventually some of that repeated process can cause broken connections or a crack or some other kind of failure. Less extreme temperature cycling every day makes less stress on that stuff.

(And that's why I copy my text before hitting the SAVE button--stupid spontaneous logout.)

Craig1965 | May 16, 2018

Thanks for the long explanation. I think home charging at 40A makes the most sense now. I originally assumed that the AC to DC conversion was done in the wall (home) charger box. Never thought it was done in the car itself. Wouldn't it have made more sense to do it that way? Sure the home charger would be a little bigger, but it could be done, just like a computer's PSU internal vs. external.

Rocky_H | May 16, 2018

@Craig1965, Quote: "Thanks for the long explanation. I think home charging at 40A makes the most sense now. I originally assumed that the AC to DC conversion was done in the wall (home) charger box. Never thought it was done in the car itself. Wouldn't it have made more sense to do it that way? Sure the home charger would be a little bigger, but it could be done, just like a computer's PSU internal vs. external."

I know a guy on the TMC forum who very aggressively thinks that, but it doesn't make much sense. Let's go with that hypothetically. Let's say that you did need to have the conversion done outside the car by a bigger expensive unit that costs about $2,000.

That would mean if you didn't have that unit with you, you couldn't charge at a friend's house, or when visiting your parents, or overnight at a campground. All of those are regular AC outlets, and you would not have any pieces of equipment in the car that could use that readily available electricity overnight while the car is parked. That would suck.

Suckage scenario #2:
Think about public charging stations like at hotels. The hardware for a simple J1772 to pass AC electricity to a car costs a few hundred dollars, maybe $800 or so for a nice one. OK, a hotel might be willing to put in a few of those if the cars can process that energy onboard. But if the cars can't use that, and they have to rely on external conversion, then you're talk about a CHAdeMO station, which costs about 10 to 20 THOUSAND dollars for each one. No hotel is going to spring for that kind of expenditure. So that would be a huge hindrance to getting more infrastructure built out.

Craig1965 | May 16, 2018

Yeah, #1 makes a lot of sense. Once I had my home wall charger installed I put the small charging cable in the trunk for those types of emergencies where you need to charge anywhere. I just didn't think the box would be that much bigger or more expensive to make.

tes-s | May 16, 2018

"Well I guess I might set my home charger down from 48A to 40A"

Remember, you do not have a home charger. You have a home wall connector (or UMC) which is an EVSE, not a charger. When connected to AC you are using the charger in the car.

When you set the charge rate down to 40A, you are setting the car to limit the rate - not setting the "home charger" (which is an EVSE not a charger).

tes-s | May 16, 2018

"Once I had my home wall charger installed I put the small charging cable..."
You did not have a wall charger installed.

Bill_75D | May 16, 2018

Craig, write "I do not have a wall charger" 100 times on the blackboard.

murphyS90D | May 16, 2018

This is another case of acquired misinformation. People thinking that their EVSE is a charger is similar to the widely held belief that voltage in the US is 110/220 when it is in fact 120/240.

tes-s | May 16, 2018

"Craig, write 'I do not have a wall charger' 100 times on the blackboard."

Not sure it would help - he is pretty adamant about the charger thing. Remember, this is the person that was looking for precision and expertise.

"And please no comments from non-electrical engineers, non-Tesla employees, or lithium battery newbs."

italiano21uf | May 16, 2018

Based on these comments why should you use a HPWC putting out 80 amps on a new Tesla? Should I dial it down from setting D to 8? To make the output go from 80 amps to 40? It’s a 2018 75D.

p.c.mcavoy | May 16, 2018

@italiano21uf - Do you already have a HPWC on a 100 amp circuit? If so, when you charge does it show 72 amps or 48 amps?

If it is a 2018 model, then the maximum the on-board charger can handle is 72 amps. What I’m uncertain about is whether your car to actually be set up with that 72 amp charger or the 48 amp charger.

Any setting of the HPWC for a current (amperage) level above what your on-board charger capability is meaningless as the charging in the car will limit your current draw.

All refresh models when originally introduced in mid-2016 were equipped standard with a 48 amp charger with an optional 72 amp which could be specified at time of purchase. After the 100D was introduced a few months later, Tesla went to the 72 amp as the standard on the 100 packs, but my memory is the 60/75 packs stayed with the 48 amp charger as the base spec. I just checked Tesla design studio and I was not able to find details anywhere for what the spec is for the 75D.

So if you have the 72 amp charger, you’d only get 72 amps even if set at 80. You can still lower the charge current in the car to 40, 48 or something else if you want. The advantage of leaving at higher value is just shorter charging time. However, if you are always charging overnight, then higher charging rate likely has no practical value for you.

Craig1965 | May 16, 2018

Guys, I understand the difference. The cable is not a charger. But when Tesla is sending me an Elon Musk Signature Home Wall Charger, I am kind of just going to call it a charger as they do, maybe calling it a charging cable is a better idea. I get it, the charger is in the car and it is just the means to get the electricity to the car. I have about 10 lipo chargers for RC planes and helicopters. I know what a charger is. Whether it is external like the chargers I own or internal like Tesla chose to put it inside the car is just what it is. And yes the 75D's are limited to 48A.

tes-s | May 17, 2018

"The cable is not a charger. But when Tesla is sending me an Elon Musk Signature Home Wall Charger, I am kind of just going to call it a charger as they do."

I can find no reference by Tesla to a "Home Wall Charger". I have always seen them refer to it as a wall connector. AFAIK, the signature wall connector is exclusive to the rewards program. Here is what my rewards program says:

Signature Black Wall Connector
This matte black Wall Connector is exclusive to the Referral Program and includes an etch of Elon’s signature.

tes-s | May 17, 2018

Tesla calls it a connector. If you know of some place where they incorrectly refer to it as a charger, I'm sure if you post it here they will see it and make the correction.

Wall connector in the store.
https://shop.tesla.com/us/en/product/vehicle-accessories/model-s_x_3-wal...

Wall connector overview.
https://www.tesla.com/sites/default/files/downloads/charging_wall_connec...

Wall connector installation manual.
https://www.tesla.com/sites/default/files/pdfs/wall-connector-eu/wall_co...

jordanrichard | May 17, 2018

Tes-s +1.

Rocky_H | May 17, 2018

All of these people who love berating folks with “It’s not a charger” are doing this:

You go to a friend’s house to pick them up to go somewhere. The friend says, “I’m almost ready; I need to put some shoes on.”

When they come back out, you condescendingly inform them that those are NOT shoes. They are Birkenstocks, which are actually SANDALS.

(1) No one cares.
(2) Everyone knew what was meant—something to put on your feet.
(3) You’re just being annoying.

tes-s | May 17, 2018

+1 @Rocky.

But when someone says they are very knowledgable and specifically asks for replies only from engineers and experts, they should expect exact responses. That is why his statements are corrected that charging at 75A at home is not 1C for a 75kWh battery, power is 120/240v not 110/220v, it is an EVSE not a charger, wall connector puts out max 80A not 100A, almost every home is not wired for 48A charging, 50A is not 50% charger load, and all the other semi-accurate information posted.

And when someone says they are calling it a charger because Tesla calls it a charger, they are either mistaken or are looking at some Tesla materials I have never seen.

Rocky_H | May 17, 2018

@tes-s, Quote: "But when someone says they are very knowledgable and specifically asks for replies only from engineers and experts, they should expect exact responses."

Yes, @Craig certainly deserved it because of that, but in most cases it's not warranted. And yeah, that was hilarious, his saying that he was only calling it a charger because Tesla did (which they don't do). Well...except for the "Destination Charger Program".

Tesla-David | May 17, 2018

I charge our MS @80A with our HPWC. We have second onboard charger in MS to enable the higher charging rate. Works well for us to quickly charge up our MS to 70 percent, unless we are heading out on road trip, then charge to 90 percent..

Craig1965 | May 17, 2018

All over the place on the internet it is called the wall charger, but yes I see it as a wall connector at Tesla's website. In either case it's just semantics and people know what we are talking about. On top of that the Destination Charger that just got installed a month ago and I use by my home is THE EXACT same Wall Connector as I have in my garage and it is set to 40A.

tes-s | May 17, 2018

I am not aware of Tesla calling it a charger, though I'm sure they - like everyone else - has called it a charger at one time or another. But I'm pretty certain the have always referred to the wall connector as a connector and not a charger. "Tesla is sending me an Elon Musk Signature Home Wall Charger, I am kind of just going to call it a charger as they do" seems like a misunderstanding on your part. They do not call it a charger.

Tesla also does not refer to "destination chargers". They call it "Destination Charging" and "charging equipment". https://www.tesla.com/destination-charging

I even looked at the document Tesla sent us in 2014 DestinationCharging2.5.pdf about the Destination Charging program. They call the equipment High Power Wall Connector and Clipper Creek Universal. They do not refer to the EVSE as chargers. A search of the 6-page .pdf did not find the word "charger".

On the "Find-us" page you can select "Superchargers" or "Destination Charging".

I have no problem with people calling EVSE a charger, but Tesla does not do this and to say you are using the same terminology as Tesla is simply incorrect.

Tropopause | May 17, 2018

I wish I was smart enough to post here. Wait... maybe I am.

jjgunn | May 17, 2018

I had no idea we have so many electrical engineers & Tesla employees on the forums. Good to know.

Higher amps = higher heat = shorter battery life. Keep those packs cool, folks!

I'll go back to reading now as I'm not qualified to be in this thread.

tes-s | May 18, 2018

Good idea.

jordanrichard | May 18, 2018

I think the reason we “jump” on those getting the terminology incorrect is because by not correcting it, people new to Tesla will get the wrong impression. I have lost count of how many people I have talked to that thought one has to have a charger installed in their garage. I make a strong point that one just needs a standard outlet, which completely takes them by surprise.

The point is, if we are to help break down the barriers/anxiety to Tesla ownership, then we need to dispel/correct mis-information that perpetuates those barriers/anxieties.

Earl and Nagin ... | May 18, 2018

@jjgunn,
There really isn't a problem with heat since the Onboard Charging System in the Tesla monitors the temperature of the batteries and, using the thermal management part of the Onboard Charging System, cools the pack. In the event that it can't cool the pack, the current controller portion of the Onboard Charging System reduces the current drawn from the off board EVSE (Or "Charging Connector" or "Wall Charger", or . . . ) below the amount it tells Onboard Charging System it can draw to keep the batteries happy.
Therefore, the answer to the OP's question is:
The Tesla car's systems will ensure that the batteries always get "Best Amp charging", no matter what you plug in to.

jjgunn | May 18, 2018

Ahhh....very nice. Thanks. Our 100's have 72 amp high charging potential too.

tes-s | May 18, 2018

72 amp is not high charging - it is .17C which is slow charging.

Rocky_H | May 18, 2018

@jordanrichard, But I'm sure that you have sense enough to know when that is relevant or helpful, versus when it is just being incredibly annoying.

I've seen you and other do this when it is beyond obviously unnecessary. Someone already has their stuff installed and working and has been using it for months, and they have a question about, "I'm getting this pattern of LEDs flashing on my wall charger." And you fire back "That's not a charger.". That isn't helpful in any way to let anyone know how the cars or equipment works. Or someone is just asking about whether people prefer the 8 foot or 24 foot length for the "wall charger" cable. Or someone is asking about pricing of Blink versus Chargepoint "chargers". Not relevant. You should be capable of knowing that and having a little restraint. If you DO want to frequently give that impression of being irritating, that's obviously up to you, but I'm try to give a helpful suggestion to you of how to not do that.

Rocky_H | May 18, 2018

I guess the TL;DR is just to not deceive yourself that correcting people every single time is being helpful; it isn't.

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