Warning for those charging using 120v

[pdx_m3s]

I'm not an expert but curious where you got that number? There are optimal ranges for lithium batteries. My experience is in the RC field and 70 might be too low for a battery in active use. I think between 80-90 is ideal. Take it with a grain of salt. These batteries are different than the ones I've used.

Well, the "Daily" range for setting the charging limit goes all the way down to 50%, FWIW.

 

[stonelance]

How do we reconcile this with the manuals recommendation to plug in as often as possible?

The manual also says that the soc of charge prior to charging the battery does not affect battery health.

So I understand that it is not the manual's recommendation, but based on my experience and of many other owners on these forums, the method I described is the way to keep the range display more accurate. Keep in mind the manual was likely written before they even started selling the car. They learn a lot about it as it is used and they get data back. The particular part you quoted was likely more concerned about keeping it plugged in so that the battery doesn't drain to nothing when the car isn't used for a couple weeks. Keeping it always charged also makes it less inconvenient if you suddenly need to go on a long trip.

This isn't really about battery health. The battery health is likely fine whether you do this or not. This method just increases the accuracy of the SOC estimate. I can tell you that leaving it plugged in after it gets to 90% will not make a difference as that is exactly what I have always done. After owning the car several months the "range" was down 15 miles. You can always just avoid all the worry and confusion by switching the battery display to % instead of range, which is what I recently did.

 

[srs5694]

To me, it's like discussing strategies for how to fill up your gas tank. What temperatures make the fuel more dense and when should you pump? How do you reduce water condensation in the tank? Do you fill up more frequently to reduce vapor space, or do you let it run down to keep sludge from accumulating? Do you top off? Etc., etc. Just doesn't matter, for the most part.

It's interesting you should mention that. I once owned a diesel-powered VW Golf (and got burned by Dieselgate), and VW diesel forums had threads discussing fueling issues such as the ones you mention. Any remotely unusual fuel will provoke such discussions, and I wouldn't be surprised to see them (although likely at lower frequency) even in forums for gas-powered cars.

Keep in mind the manual was likely written before they even started selling the car. They learn a lot about it as it is used and they get data back.

I'm pretty sure that Tesla updates its manuals as new features are released, so as to cover those new features. That said, unless there's a new feature that affects charging or engineers discover something about the batteries that they hadn't known before, it's unlikely they'd revise the manual's charging recommendations, so your point is still valid.

 

[raptor5244]

The particular part you quoted was likely more concerned about keeping it plugged in so that the battery doesn't drain to nothing when the car isn't used for a couple weeks. Keeping it always charged also makes it less inconvenient if you suddenly need to go on a long trip. This isn't really about battery health. The battery health is likely fine whether you do this or not.

Agreed. If you read the manual it makes it sound like anytime you are not driving your model 3 it should be plugged in. Like you mentioned I think this is just Tesla trying to cover itself from owners that forget to plug in or go on a month long vacation or something and drain the battery to 0.

 

[vickh]

So, my take is that this is simply a bad indication and not given the batteries a chance to equalize.

I dare say that if you charge to 80 or 90% and then periodically, every few months, let it got to 100% and stay there for a little, that you'll battery will be happy.

I think that the SC was stretching it a little when the blamed it on the short cycles (which is kinda stupid, since I'm assuming that they were actually long cycles at slower speeds).

My numbers are still showing great after a year and I generally go to 100% just by having a trip to go on and charging to 100% before a trip.

Basic rules from my playbook.

• Don't charge to 100% every day, unless you absolutely need to do so, because you drive that far.
• Don't take it to near 0% to try to balance the batteries, that's old school concepts. Of course, like above, it's okay if you need to because of drive.
• 80-90% is probably some of the better places to charge to,
• Charge to 100% every few months.
• Stop worry about the battery so much!

Can the indicator be reset by service?

Would you recommend that for the SR it doesn't matter about 100% (b/c it's locked SR+? )

Also is SC it to 90% say once/twice a week overkill? (close to work)

 

[israndy]

I'm not an expert but curious where you got 70%

It's that what was said at the Tesla Autonomy Day? I seem to remember someone said 70% for the first time and I was thrilled as I had already been charging only to this point

 

[djroberts]

It's that what was said at the Tesla Autonomy Day? I seem to remember someone said 70% for the first time and I was thrilled as I had already been charging only to this point

I've researched since then and agree 70 does look like a good long term limit.

I charge to 80% in my SR which has a top locked battery so it's more like 73%.

 

[darth_vad3r]

So, all that is to say: for those of you using 120v to charge on a daily and/or consistent basis, charge to 90% as often as possible; if not, attempt to find a different charging solution (e.g. installing a 240v). If you've experienced "degradation" try recalibrating by leaving the car charged in at 90% for 1-2 hours consistently for several weeks. Or, try charging to 100%, draining to ~10%, then charging back up to 100%, and then driving down below 90%.

Or just ignore the ”degradation” because it’s not real.

 

[peakshaving]

My charging schedule (work only) means I get to 90% maybe once every two weeks and I'm still balanced.

Only 4000 miles on the odometer though.

 

[mknox]

What I take away from this is that the battery management system is still “working” the battery (balancing, calibrating, etc) even after a charge is completed, so it’s best to ensure a couple hours of buffer between charge completion and unplugging.

I had an S and now drive an X so there might be a difference with the 3 but.... I've heard the same argument for S and X as well, but have no evidence that this is actually happening. I have a sub-meter on my car's charging circuit and as soon as the car reaches it's set point, current from the wall drops to zero and stays there. The only time power comes from the wall is if the car is actively charging, running HVAC remotely, or if you get in and turn things on with the car still plugged in. At any other time, it draws exactly zero from the wall. So if it is doing some sort of balancing or calibrating, it's not using any shore power to do it. My sub-meter logs go back to early 2013 when I got my first S.

 

[darth_vad3r]

I had an S and now drive an X so there might be a difference with the 3 but.... I've heard the same argument for S and X as well, but have no evidence that this is actually happening. I have a sub-meter on my car's charging circuit and as soon as the car reaches it's set point, current from the wall drops to zero and stays there. The only time power comes from the wall is if the car is actively charging, running HVAC remotely, or if you get in and turn things on with the car still plugged in. At any other time, it draws exactly zero from the wall. So if it is doing some sort of balancing or calibrating, it's not using any shore power to do it. My sub-meter logs go back to early 2013 when I got my first S.

Good info, but so many ways to hand-wave it away

2 easy ones are (1) “It’s not a 3” (which you stated), and (2) the car could just be using the fact that it is plugged in after a charge purely as a signal to proceed with some extra recalibration/balancing process that requires no actual shore power (which you also stated) ... it just uses this opportunity to perform the procedure, and maybe only in some rare case would it require power.

I also recall @wk057 mentioning that the bleeding for balancing is tiny, like microwatts.

 

[mknox]

2 easy ones are (1) “It’s not a 3” (which you stated), and (2) the car could just be using the fact that it is plugged in after a charge purely as a signal to proceed with some extra recalibration/balancing process that requires no actual shore power (which you also stated) ... it just uses this opportunity to perform the procedure, and maybe only in some rare case would it require power.

Could be that it is just using the "I'm plugged in" signal, but to me, seems unlikely. When I say the car is drawing zero, I really mean zero... not even a mA of current.

However... I have seen instances of the car continuing to "charge" (at the full amps I have it set for) for some time after it seems to reach the setpoint. Then it finally will go to Charge Complete state and wall power drops to zero. That is more likely the "balancing". But I have only seen this once or twice since early 2013.

 

[darth_vad3r]

However... I have seen instances of the car continuing to "charge" (at the full amps I have it set for) for some time after it seems to reach the setpoint. Then it finally will go to Charge Complete state and wall power drops to zero. That is more likely the "balancing". But I have only seen this once or twice since early 2013.

How do you gauge “reach the set point”?

When the SoC reaches 89.5%, the display shows “90%”, but it still has a half percent left to charge to reach 90.0%.

 

[mknox]

How do you gauge “reach the set point”?

When the SoC reaches 89.5%, the display shows “90%”, but it still has a half percent left to charge to reach 90.0%.

Fair enough. Typically the time interval between 87-88, 88-89 and 89-90 will be roughly the same and it will click off and go to Charge Complete fairly soon after hitting 90. In those rare instances I mentioned, the car would sit at 90% (on the display) for considerably longer (once for almost an hour) before clicking off and going to Charge Complete.

 

[darth_vad3r]

Could be that it is just using the "I'm plugged in" signal, but to me, seems unlikely. When I say the car is drawing zero, I really mean zero... not even a mA of current.

ps. 1 microwatt at 240V is only ~4 nanoamps

Anyways, I think bleeding doesn’t require input power at all. Any “extra recalibration” it wants to do could simply be triggered by being at 90 and being plugged in. Or not at all we don’t know what it’s doing in there on its own without shore power

 

[darth_vad3r]

Fair enough. Typically the time interval between 87-88, 88-89 and 89-90 will be roughly the same and it will click off and go to Charge Complete fairly soon after hitting 90. In those rare instances I mentioned, the car would sit at 90% (on the display) for considerably longer (once for almost an hour) before clicking off and going to Charge Complete.

Oh well an hour is something alright

 

[darth_vad3r]

Fair enough. Typically the time interval between 87-88, 88-89 and 89-90 will be roughly the same and it will click off and go to Charge Complete fairly soon after hitting 90. In those rare instances I mentioned, the car would sit at 90% (on the display) for considerably longer (once for almost an hour) before clicking off and going to Charge Complete.

What power rate do you charge at? An hour at 120V could be explained by the apparent up to ~1 kWh of regen capacity that could be hidden from the battery gauge distance displayed on the dash if it had been depleted by -1 kWh from lots of say flat or uphill driving without regen before charging. I dunno. If it was drawing 6 or 11 kW for an extra hour though ... that’s a lot of power getting “burned off” with bleeding or being added in to the pack because the % was way off when it first said “90”. If it’s the latter, maybe these are cases they want you to leave it plugged in at 90. Although I think the recommendation is to keep it plugged in “after complete” and your scenario seems to have been a pre-completion thing. Who knows

Interesting stuff.

 

[CharleyBC]

After this conversation, I'm looking forward to a feature in an upcoming update. It will let you select a choice that tells the car to pick the charge level that will make the battery happy. If you're going on a trip tomorrow, you can set to 90% or whatever just like we do today. If it's just normal commuting and errands, let the car decide, perhaps subject to some minimum you can live with for daily use. (I started this as a joke, but I actually kinda like it.)

 

[israndy]

I believe I recently saw a post suggesting that charging slowly was actually BAD for the car. At the time I didn't care because I have 40 amps at home and 48 amps at the cabin, plus supercharging.

This week, however, I started charging on solar, and I don't generate anywhere NEAR that many amps, so I am plugging into 120v. I am Charging on Sunshine only, at 12 amps. Obviously, this takes time, but I am retired. It's MUCH cheaper than generating now and charging later as I am not Net Metering (got in too late). That means I pay 28¢ for each kWh but only earn 7¢ for each kilowatt I don't use, so charging when the sun is shining is best.

So I don't care if it's inefficient to charge at 120 volts, it's free. The question is: is it bad for the car to charge at 1440 watts every time?

Interestingly the 4kW PV system I bought COST me $1440 used, co-winkie-dink

 

[wk057]

Admittedly didn't read the whole thread... but will point out a few things.

Charging from 120V will in no way hurt the battery. The lower the charge rate, the better. It's not statistically significantly better to charge at 1kW vs say 5kW. But slower is always better for the pack, but don't go out of your way to charge slowly. Just know it won't hurt the cells.

Lower rate charging is less efficient, so keep that in mind, but not harmful to the car, battery, etc... just your wallet. You'll actually probably save money in the long run installing even a 30A 240V outlet.

Now, the issue is that the current shunts used by Tesla are not as accurate at lower current. So over time, calibration of the pack capacity can drift one way or another. This isn't real degradation though, and a couple of supercharges from low SoC to 85+% or so should get it back in line quickly enough. This is just literally a rounding error with the prolonged low currents that's easily corrected with higher power charging.

As for shore power, the car doesn't always keep shore power engaged when plugged in. It will draw from the wall when changing, preconditioning, if you're in the car while it's plugged in and using accessories, etc. Otherwise it will just use the battery for vampire drain and such. Once it loses more than a few % below the charge set point, it'll kick back on to top the pack off again.

You don't need to be plugged in for balancing, and balancing is completely independent of charging in the latest hardware/software. Balancing is continuous as needed and should be transparent. You should never need to do anything specific to balance your pack.

Think that's all the relevant notes for here.