Electrical draw of a 2013 Model S 85

[gibbon22]

We have a 2013 Model S 85 with a 2013 residential fast charger on the wall.

Recently had Tesla solar panels and Powerwalls installed. Now, as I look at my usage in the Tesla app, we average about 1-1.5kw continuous draw. As soon as my wife gets home and plugs in the car, the draw jumps to 9-12kw. It stays that way until the car is charged to our mileage limit, then it drops away. On weekends, when it usually just sits in the garage fully charged, there will be 3-4 times per day where it seems to cycle on, draw that 9-12kw, then cycle down, maybe over a 5-10 minute period.

Just curious if this level of draw is normal, and if so, if there is a way to slow it down. When we plug it in at night, it could take a few hours to get up to charge if it wanted to.

And, are the random spikes when it is supposed to be off, normal too?

 

[PCMc]

What you're seeing 3-4 times a day is likely one or both of a couple different things.

One is the periodic recharging of the 12V battery. This has always been noted on the Model S to happen 3-4 times a day. I've never been in a situation to see the draw pulled by the car during this period to correlate it to 9-12 kW, but that seems high to me to be just the 12V.

The second, which may be more likely, is charging of the main battery kick in periodically to keep it topped up at your selected SOC. I have a 2016 MS90D which I've owned since July 2016. It used to be that if I charged and just left it plugged it, battery SOC would need to drop 2-3% below my set-point before the car would then trigger to recharge and top back up. This might only be every couple days. This behaviour seemed to change a couple software updates ago for me and now it seems like the car is wanting to kick on and do these mini top-ups much more often.

If it is this second, more frequent kicking on to top of the HVB, there are two things you can consider.

First is charge up like you normally, then when you know it will sit for a day or two unused, lower the charge limit. For example, if you normally charge to 80%, once it finishes set the charge limit down to 50%. If you see the 9-12kW periodic spikes go away, then you know it is this. You'll also get a sense for how many miles you're losing just due to parasitic drain this way. Based upon my MS90D that sits unused much of the time now, I average about 4-4.5 rated miles a day at the moment.

Now if it is the recharging the HVB, one way to reduce the peak of your 9-12 kW spikes is to reducing your charging amps. This would not eliminate the periodic usage periods, but would reduce the peak draw but last longer. For example, cut your charging amps in half, do you see the cycles reduce to say 5kW but likely last maybe 10-15 minutes and not your 5-10.

Just my two cents worth.

 

[gibbon22]

Thank you, PCMc. I'll try both of those ideas out.

I've also been thinking about kicking the battery all the way up to full, charging over weekend, letting it run down to almost nothing during the week by not even plugging it in, then charging it all the way up on the weekend. I just don't know if that is a good idea, or bad idea, for battery longevity.

 

[PCMc]

Thank you, PCMc. I'll try both of those ideas out.

I've also been thinking about kicking the battery all the way up to full, charging over weekend, letting it run down to almost nothing during the week by not even plugging it in, then charging it all the way up on the weekend. I just don't know if that is a good idea, or bad idea, for battery longevity.

@gibbon22 - Best charging strategy is somewhat dependent upon your priorities. If it is to reduce the max power demand, then simply reduce the charging allowed charging amps in the car. 240V at 40 amps is nominally 10 kw. Drop the amps down to 20 and you'll reduce peak draw to about 5 kW but your charging will take roughly twice as long.

If you're wanting to charge as much as you can on the weekend during the day when you have max solar production, then charge up to something like 90% over the weekend. I wouldn't charge to 100% unless you're going to drive shortly after charging finishes as this will add unnecessary stress on the battery. You haven't said how much range you use on a daily or weekly basis to know if charging once on the weekend will get you through the week.

I'd expect you may want to avoid any extra power draw from the grid. Depending upon how much solar and power wall capacity you have, more frequent but smaller amounts of charging may work better, essentially using the battery pack in your MS85 as extra powerwall capacity.

 

[ucmndd]

Thank you, PCMc. I'll try both of those ideas out.

I've also been thinking about kicking the battery all the way up to full, charging over weekend, letting it run down to almost nothing during the week by not even plugging it in, then charging it all the way up on the weekend. I just don't know if that is a good idea, or bad idea, for battery longevity.

Don’t do that.

5 cycles from 50-70% are much better than one cycle from 0-100%.

Keep it plugged in.