Charging at the lowest amperage purposely

Charging at the lowest amperage purposely

I was getting my x serviced yesterday and was talking with another x owner who said he lowers the amount of amps overnight when he knows he's not going anywhere. No reason to fully charge it so quickly if you don't need it. He said it's to preserve battery life. I look at the tech who nods his head in agreement and said yeah that's just tips and tricks you pick up from other owners.

So my question - is this true?

I did manually lower my amps last night and timed it so it's full this AM. I just want to know if I keep doing that ....

Tarla's Driver | 4 maggio 2017

I did that once, but I didn't realize that the car remembers the setting for that location, so the next time you try to charge, it will default to the lower setting. That's great if you're using a 14-30 to 14-50 converter plug so you always have to lower your amperage to 26 to avoid overloading the circuit (or overheating the wires), or if you know the wires aren't the correct gauge, but if you're just doing an intentional slow charge, it's a pain.

I don't think the slow charge really helps much. If it did, Tesla would add a charging mode where you specify the time you want charging to end (perhaps 7am for many commuters), and it would use the lowest amperage that results in that end time. I've heard it suggested to do a slow charge once in a while to clear out issues with faster charging, but I'm not sure the science for that is real. Still, if you've run the battery down a good ways and are about to leave the car parked for a weekend in your garage, you could try charging it on a 110V outlet slowly while you're gone.

I think the downside to slower charging is that the charging is probably slightly less efficient, so you'll spend more on electricity than if you charge at the regular default. This makes sense if for no other reason you're powering the charging circuitry for a much longer time. There's probably other overhead as well. | 4 maggio 2017

I'm in the camp that thinks it will extend the battery life and car life slightly by using a lower speed charging. Not enough to be concerned much about it. Here's my reasoning for only using the power rating you need:

1) Once component of battery degradation is heat. By charging at a slower rate, less heat builds up in the battery back. Now Tesla is very smart in that it limits how hot the battery gets by first cooling the battery via the HVAC system, and if that is not enough, it will automatically lower the charge current (even at a Supercharger). This last part is quite rare, but it can happen. By using a lower charge current the battery is less likely to get to the maximum temperature where cooling is required.

2) Once the cooling system is activated, that ads a slight bit of wear on the compressor and other components. The less this is needed the longer the life of these components.

Now going from the maximum home charging of 72 amps to perhaps a much lower rate of say 30 amps, is not going to make that much difference, but perhaps extends the life of the battery and components by 1% or so. Its so little difference that I wouldn't worry about it. Charge to be sure you have the range you need. | 4 maggio 2017

> ... in the battery pack.

LimawanS85 | 4 maggio 2017

I do that from time to time as well based on my reading on forum etc

campusden | 4 maggio 2017

I have never done that. I only MAX charge about once per month. It still says 262 miles when I max charge my 90D but within the first 3 miles of actual driving, the actual range drops 7 miles.

Rocky_H | 4 maggio 2017

@campusden, This is talking about how fast the charging is done based on amps, not how full to charge the battery.

Now, regarding the OP's question: Changing the amps for at home charging doesn't really make much difference for the battery pack. It can charge at levels like 90 or 100kW. On a 14-50 outlet, it can only be 9.6kW anyway at 40 amps, so as far as the battery can see, it's already "slow" no matter what. Lowering it down to 7 or 8kW isn't making much difference from the battery's perspective.

Where it can make some difference is in the charging cable hardware and maybe the AC charging converter in the car. The mobile connector is built for 40A maximum. The wall connector for 80A maximum. Running them at maximum level all the time can make them kind of hot. Heat, and especially heat cycling from cold to hot and back repeatedly wears out the life of electronics. The expansion and contraction of the metals from the heat changes can eventually break soldered connections and stuff like that. So perhaps not running the mobile or wall connector at maximum all the time every night can help to extend the device's life.

You can notice a difference in the heat level of the mobile connector for example just using amps in the mid 30's instead of 40. It's just a little easier on it.

Leeo | 4 maggio 2017

I think it's more important to keep the battery between 20 and 80% then what current you charge at.

tommyalexandersb | 4 maggio 2017

My DS told me to charge to 90%. I've always read 80% on here, and told him that but he said "no, charge to 90%", so I do. Anyone else who recently took delivery told to charge to 90%?

I usually charge at 30 amps, but only to take it easy on my old house/breaker.

Redmiata98 | 5 maggio 2017

I was told 90% at delivery for both my P90X and P85S. My battery "degradation" for both after a year and a half leveled out at 6%. I also max charge, amp wise at 72/80 on my HPWC. (My original $1500 HPWC was just replaced at just under two years use under warranty by the current $500 version. Not sure if that was a result of heat/cold rapid change effect on electronics or just normal wear on the beta version charger.)

Leli001 | 5 maggio 2017

After I installed the wiring for the 14-50 outlet, I connected the mobile charger to the car and took IR scans for the first couple of hours of charging and noticed the 6AWG wire I installed barely raised a degree or two. The mobile connector and its cable got a bit warm around 10F above ambient. The most concerning was the brand new 50A circuit breaker was over 40F above ambient (not the connections but the CB itself.. It leveled out at around 105F and was very warm to the touch.

I have read somewhere that someone mentioned a continuous duty breaker would work better but have not found that kind in the QO type for my panel.

I reduced the charge to 20A to keep the temps down as the car will be fully charged by morning anyway.

This past weekend, we had to drive into Queens from NJ and just wanted a full charge (although not really necessary) to be on the safe side as traffic is very unpredictable in the NYMA area. We have only had the car since Dec. and this was the first time we were using the 3rd row seat, so the X was almost full.

I upped the charge to 40A while I was washing it (ONR) and heard the fans coming on to cool the battery. It even got a bit warm in the garage.

I'm in the camp of reducing wear on the components as well since and it doesn't make a difference if the car will be charged by the morning or by the middle of the night.

The charger in the car is basically a rectifier. I'm in the telecoms industry where we use rectifiers at all of our sites and find the sites where the rectifiers have a higher load tend to fail prematurely. Obviously these loads are constantly on 24/7 but the cars can also be charged for quite a few hours during the day/night.

Tâm | 5 maggio 2017

Tesla's partner Professor Jeff Dahn , Waterloo Institute for Nanotechnology said slow charging is bad because you are prolonging parasitic chemical actors so the goal is to be:

"beating the clock on these time-dependent parasitic reactions"

Rocky_H | 5 maggio 2017

Regarding sales staff and delivery specialists always saying 90%, yes, they do, because it's much much easier for them to just have one consistent number to recommend to everyone. It may not be totally ideal for your situation, but it is reasonable enough to apply to everyone, and they don't have to ask and analyze about each person's unique circumstance, where then people would be arguing about why they were told different things by Tesla sales staff. And they want people to feel confident in having enough range to use, so they don't want to make people scared that they have to use a lower charge level. Having range confidence is a big deal in showing the public that electric cars are OK.

It's kind of like with Dave Ramsey advocating not doing any debt except a mortgage. That is pretty general decent enough advice because you can tell it to everyone in a wide distribution like a radio show, and it works pretty well and is good advice for almost all people in all circumstances. If you start to mention exception circumstances where it can be beneficial in some cases, it kind of opens the floodgates, and EVERYONE thinks they are that exception, and people get into debt problems. When you are having to give broad widespread advice to lots of people, it's best to give advice that is at least pretty good for everyone, rather than something that might be great for this person, but cause problems for some others.

MyXinTx | 10 maggio 2017

I am gonna go with anything Tesla recommends since they know their batteries and software better than anyone else.

Besides, they like us owners, want the batteries to last as long as possible, and have no motive to not give the best recommendations.

Besides, it makes sense to keep the charging rates at a minimum for regular charging (less heat generated), only speed it up when convenience is needed, cause the extra 15-20% time it takes on a road trip can really get old.

Vawlkus | 11 maggio 2017

Having dealt with batteries for the last 20 years or so, I feel confident in saying that slower charging DOES increase the lifespan of your batteries.

MasterT | 12 maggio 2017

@Vawlkus, can you please elaborate on "Having dealt with batteries for the last 20 years or so" - in which capacity and or function? I mean, I too "dealt" with batteries 'all my life' (using them in remote controls, watches, cars, phones, flashlights - LOL) but I'm far from being "confident" to state anything, except my super layman opinion :D

Rocky_H | 12 maggio 2017

@Vawlkus, Your statement needs parameters, though. "slow" is relative to the size of the battery and the power level. When people are talking about 6kW or 10kW charging of a battery that is 100kwh in capacity, both of those levels are already extremely slow charging for that size of battery, and going slower and slower and slower isn't always beneficial. The battery research data shows that when you are already below what would be considered "fast", there a negatives to lowering it so much that you are extending the amount of time that the battery is experiencing the chemistry changes of charging. Charging at a reasonable speed that is not really fast, but also getting it over with somewhat quickly is what helps the lifespan.

Vawlkus | 15 maggio 2017

MasterT: how does working on a non-nuclear submarine sound? Those things run on batteries (rather not say what type if it's all the same).
RockyH: I did an informal study using AA batteries. Nimah chemistry, with one set being "fast charged" exclusively on a 4 hour charger, and the other group on a 10-12 hour overnight charger. The fast charged batteries all eventually failed to hold charge, while the 'slow charged' batteries are still in service. This is over a four year period approximately, while both battery sets being discharged equally in near identical applications/apparatuses.

It's not difinitive, but it does demonstrate the point I think.

Rocky_H | 15 maggio 2017

@Vawlkus, The 4 hours versus 10 hours recharging on batteries as small as those AAs probably are a real slow versus fast difference, so it applies. My point was that 3kW versus 6kW versus 10kW are all slow rates of recharge for a battery as big as 85kWh, so it's not really comparing slow versus fast.

Leli001 | 15 maggio 2017

5kW versus 10kW is a big difference on my 50A circuit breaker. At the faster rate it gets hot around 105F while at the slower rate, it is barely warm. When the charge is complete at 3am or 6am makes no difference to me.

I mainly reduce the charge rate to keep the CB temps low on my 60+ year old panel until I can upgrade it.

Rocky_H | 15 maggio 2017

@Leli001, Well, you're talking about fast/slow relative to the circuit breaker and the mobile charge cable, where they are only built for that 10kW MAXIMUM. That 10kW is as fast as it is allowed to go, so yes, of course it can get hot. Were were talking about these rates not being fast for the battery. | 15 maggio 2017

@robynderen: As you can see, no one really knows. Dr. Jeff Dahn, cited above, is about the biggest authority on lithium ion cell charging and degradation that there is and he admits he doesn't fully understand what is going on inside the cells. Lucky for you there are more than 100,000 Tesla owners around the world following every charging regimen under the sun without seeming to hurt their batteries much. This gives you a lot a lot of latitude. I let my battery discharge to 25-30% around town and charge to 90% as fast as my little NEMA 14-50 will allow for what it is worth. If I range charge (100%), my car chastises me. Must not be a good idea...

psusi | 18 maggio 2017

Conventionally faster charging certainly does reduce lifespan of batteries, but that is probably mostly due to the heat generated, so Tesla's active cooling probably mitigates most of that. But do you really want to waste extra power cooling the pack, and making your garage warmer? And yea, at the full 40 amps, the cable that comes with the car gets rather warm, so I keep it limited to 15 amps.

teethdood | 18 maggio 2017

I saw the hour-long video by Professor Dahn. Basically he said that you want to charge the battery as fast as you can, up to C/2. So for instance if you have a 75D, you want to charge at a rate close to 37.5KW. It is different at a supercharger though because who wants to wait while on the road. Also he said individual battery cells should be charged to around 4-4.1V, which works out to around 75% State of Charge. Tesla recommends up to 90% daily charge because you may hit the road unexpectedly. However for daily short commutes, I'm keeping mine at 75% SOC.

ken | 18 maggio 2017

I max charge 100% daily on the 90D, a full charge shows 244 miles range. I drive 50k miles/yr so the car will be long done before battery warranty is over, it will be interesting to see how many yrs in the battery.

teethdood | 19 maggio 2017

what is the battery warranty anyway? I know it states 8-year unlimited miles. So for instance your X90D is rated for 257 miles at 100% SOC. What is considered battery failure? 244 like yours? 200? 150? 100? Nada?

Rocky_H | 19 maggio 2017

Degradation levels from regular use are specifically excluded in the text of the warranty from being covered, so there is no percentage. However, if one of the modules fails, where it has less range because of that, that's not degradation, and they have covered that the few times it has come up.

NumberOne | 23 maggio 2017

My experience has been that a 6-10% reduction in range is considered normal. It happens within the first 6-10k miles and then levels off. The motors are rated for at least 500k miles, so I cannot imagine the car wearing out before the warranty expires. In 10 years, I also expect the batteries to be both better and less expensive. At that point if would be nice and likely possible to upgrade a 10 year old battery pack to a newer one. It would be even nicer if one can go from a 90kW pack to something a little larger.

John | 11 maggio 2018

Thanks for that video link above (way above). I was "trickle charging" at 3AM here in Az, and to about 70% charge. Now I'm going to do max 32A, and as they say, "beat the heat" (less time for parasitic deposition to occur).

Amazing what happened with Nissan and GM (and the other one I never heard of). A 27.5% decrease in capacity on the Leaf within 1-2 years! At first I thought there goes the Big 3 intentionally sabotaging EVs, when in fact, they didn't actually test the batteries in real life over many years (and realistically couldn't). Only to learn that their accelerated battery testing caused them to pick the worst battery chemistry! Until Tesla figured out a faster feedback on experiments that accurately predicted long life characteristics. (Paraphrasing for others here, I think I understood this...) That, and the fact that they use the A/C unit to control the temperature while charging. This is real Brand Building and trust here.

This all reminds me of the Wright Brothers who invented the wind tunnel (instead of building, flying, crashing many times) to eventually discover optimal wing and propeller shapes that we all know today. Very similar story indeed.

jjgunn | 12 maggio 2018

Bottom line - heat & electronics don't mix.

Keeping your battery cool while charging will extend it's life

raffidesigns | 13 maggio 2018

For now i have the standard wall plug Nema 14-15. I get anywhere between 2-4 miles/hr. I just recently picked up my MX, I drive 60 miles a day and get around 26-28 miles in 8 hours. (from 6:00 PM - 5:00 AM) . it is plugged and charging daily.

I am still in the process of upgrading to something faster.

Rocky_H | 15 maggio 2018

@raffidesigns, That is a 5-15 outlet if you are getting 2-4 miles per hour.