# Forums

## I want to know how to calculate the time that is needed to charge a 85 kWh battery using 230 Volt home outlet, charge at 1 Amps?

Maybe somebody can tell me how to calculate this?

The 85 kWh battery of a Tesla Model S is totally empty.
This EV is parked in a garage, next to a house.
In the garage there is the normal 230 Volt outlet, just like in any house in The Netherlands.
The standard single charger is used (not the twin charger).

On the touchscreen you can select the level of amperage that you want (from 1 up to 40 Amps).
Suppose that I choose to charge at 1 Amp.
Then there is the difference between the standard charge, which is 80% of the full range charge.
Is that correct?

How much time will it take to do a standerd charge?
How much time will it take to do a full range charge?
And how do I calculate that?

Timo | February 14, 2013

85kWh using 230W would be a bit under 370 hours. Can't say I recommend that.

Benz | February 14, 2013

@ Timo

I forgot to mention that the Tesla Model S is not going to be used for about a month due to vacation.

And would it matter to the outcome of 370 hours if this would be done during winter (freezing conditions of -10 degrees Celcius)?

I am 3146 | February 14, 2013

@Benz...the best way to leave it for that period of time and at that temperature is fully charged and plugged in. Model S will keep its battery warm and will draw the current it needs as the car requires the charge. The colder the environment the more that is required to warm the battery and protect it from freezing.

Benz | February 14, 2013

@ I am 3146

I do understand that it is required to warm the battery and protect it from freezing. Therefore I would leave it plugged in. But would it be OK if I set the level of amperage to 1 Amp? Would that be enough to keep the battery warm during that about 30 day period?

Timo | February 14, 2013

Make it two just in case :-P

Benz | February 14, 2013

@ Timo & I am 3146

OK. So, the Tesla Model S will automatically stop charging when the battery will have been fully charged (but the connector will still be attached to the charging port)?

And because of freezing conditions, the will need energy to keep the battery warm, and therefore it will use some energy and the level of stored electricity in the battery will decrease. We already know that the connector will remain attached to the charging port, so the car will automatically start charging again?

But is it harmful to the battery that the connector will be attached to the charging port for a month?

Will it not lead to decreasing the capacity of the battery, and will it not lead to a quicker degradation of the battery life than the battery normally would have decreased?

Brian H | February 14, 2013

No. Connection doesn't hurt. 1 amp probably is below the minimum protection and warming and losses level, though. Anyway, the next app release (4.3?) is rumored to permit commencing the charging on a timer, so a higher level could be chosen, starting closer to pick-up time.

Benz | February 14, 2013

@ Brian H

A moment ago, I had a great idea.

Would it not be super practical, if there would be some kind of a App on your smartphone via which you could see if the battery of your EV is being charged or not (at a certain moment), and to what the level the battery will have been charged (at a certain moment).

And even better, if you could also change the level of amperage that the battery is being charged at (at a certain moment), while your are sitting in a chair and enjoying the sun on the other side of the planet!

July10Models | February 14, 2013

You have to think of the worst case scenerio. The very worst case is that you just completed a 300mi run and the car is completely depleted when you plug it in only to have the power go out(as a power failure blackout situation). The electronics in the car are designed to manage the batteries and will restart charge when it is necessary so you should let the car have its fill and if the power goes out it should be more than capable of riding through the outage. In the example above so you have to on vacation and power is already out. Plug the car in and go on vacation, when the power returns the car will fill up. Don't complicate a simple situation. If you are worried about the burning down your house, well that is a wiring problem and maybe your house is not ready for an EV or any other high load appliance.

Benz | February 14, 2013

No, I am not worried about "burning down" anything. I did not mention any of that. You are making that up yourself. But maybe I should have mentioned in my first post of this thread that the house is ready for an EV. I will give you that. Thanks anyway, and be well.

jat | February 14, 2013

I would worry that 1A might not be enough to counter battery heating losses. The car will automatically heat the battery when needed, and automatically charge to replace lost charge -- why wouldn't you just let it do its job? The software is already designed to maximize the life of the battery, so there is no need to try and out-guess it. Just charge to standard, leave it plugged in, and when you come back it will be near the standard charge and the battery protected against getting too cold.

The mobile app lets you see the state of the battery, whether it is charging currently, and lets you stop/start it. It does not let you set the charge rate.

DouglasR | February 14, 2013

@jat +1

Dropping the current down to 1, 2, or even 5 amps is a bad idea. If an unplugged battery loses 8 miles of rated range per day, that works out to about 2.4 kWh per day. It would require over 10 amps just to stay even.

Benz | February 14, 2013

OK. Just plug in, let it do a standard charge, and let it plugged in for the whole month. So, it actually is easier than I thought it would be.

I saw in a youtube video that somebody was actually changing the level of amperage manually. So therefore I thought that maybe I should be doing that as well. And therefore I was wondering what would be the best thing to do.

Will I be able to see on the touch-screen how much electricity the Tesla Model S has "consumed" during that month?

riceuguy | February 14, 2013

@Benz, also remember that if for any reason you want, you can use the mobile app to start and stop charging manually while you are gone. There's no need to do so, but if you wanted to you could!

Osiris | February 14, 2013

So actually batteries "like" it warm, when they are in operation. But if stored colder temperatures are prefered. One should not go below 0°C. Storing fully charged batteries normally can't be recommended. The regular storage conditions are somewhere between 30-50 % SOC. But it depend on the mancfacturer.

Easiest way to go, use a timer, whcih swiches an for 2 or 3 h a day. With the app you can controll the chargecurrent in this time from your location. I just would keep the rangemeter at around 50%. With this you will certainly prevent deep discharge or idle charging.

Hope I could help

Salman | February 14, 2013

@DouglasR, is my math wrong: 230V * 1A * 24 hrs = ~5.5kWh ? So the OP would actually be ok, assuming only 2.4kWh loss per day (I suspect it could be more in extremely cold weather, though). Still, I agree there's no need to go through this math exercise when the simpler option is to just plug in and let the battery management system do its job.

@Benz, the car has two trip meters which track mileage, energy usage, etc., so you could set one to the beginning of the period you want to track, but I'm unsure if it tracks "vampire load" or not (i.e. it might only show energy usage while driving).

DouglasR | February 14, 2013

@Salman

My bad. I computed a per hour rate of charge instead of a per day rate.

Benz | February 14, 2013

@ Salman & DouglasR & Osiris & jat@jaet.org

Best thing to do is to just plug in and let the Tesla Model S do all the work. But besides that, it now appears that charging at just 1A would be possible as well.

Brian H | February 14, 2013

The problem with "letting the MS do all the work" has been that the top-up occurs after the battery has discharged to lower levels than you might want to start out with, and that it often happens that it wasn't just before leaving, so the battery is cold and low then. Timing allows co-ordination so that the battery is warm and full just when you want it to be. Trickle-charge accomplishes the about the same thing, in absence of timing control (so it's just a workaround being used till timing is available.)

Curmudgeon | February 14, 2013

The only reason to lower the charge amps is when you
are using a circuit that is not rated for 40 amps.
My garage 220 circuit is only rated for 20 amps.

Hills | February 14, 2013

I have NEMA 14-50 Outlet that allows Model S to draw 40 A. I routinely dial down the current to below 20A, often as low as 5 to 10 A. If I use 40A and the car finishes charging 7-8 hours before I leave the house, a few miles are usually lost. By allowing the car to finish charging less than one hour before I leave, Model S leaves with 240-242 rated miles. Anyone has a better idea?

Brian H | February 14, 2013

Even if it finishes (would finish) just after you leave, you'd only be missing 2-3 miles. That gives you more flexibility.

jat | February 14, 2013

@BrianH - that doesn't matter if he is gone for a month. If he really cares about it being completely full when he gets back rather than possibly 10 miles down, he can manually start a charge from the mobile app while he is on the way back.

@Hills - I start up the heater about 15min before I leave, and I start a charge then as well (flipping it briefly to max-range to get it started if I need to). Both the car and battery are warm when I get in the car, and the car is fully charged (not that it matters given my normal commute).

Brian H | February 14, 2013

jat;

some have found it as much as 80 miles down. The automatic recharging seems to be quite infrequent, tailored to keeping at least a 50-60% SOC for battery health. Not the same objective as being full on departure.

DTsea | February 14, 2013

Benz- yes, the Tesla app for iOs has a charging screen that shows state of charge. You can pick regular or extended range, and also command it to start charging (or stop). You can even tell it to turn on the heater (maybe good if car covered with snow) which is very nice in the morning.