Model S Battery Heating discussion

[sandpiper]

I guess another difference is the heater in the S&X is single "speed", ~5kW, while in the Model 3 they can control the amount of power used. (Which should allow pack heating on lower powered EVSEs, which has been a problem in cold climates for the S&X.)

There's no reason that they can't control the power going to the resistance heater in the S, unless they control it by a mechanical relay and are worried about wear on the contacts. Is that the case? I can't see it.

Assuming it's a solid state relay of some sort, they can switch it on and off as quickly as they like.

 

[MP3Mike]

There's no reason that they can't control the power going to the resistance heater in the S, unless they control it by a mechanical relay and are worried about wear on the contacts. Is that the case? I can't see it.

Assuming it's a solid state relay of some sort, they can switch it on and off as quickly as they like.

That doesn't change how much power it draws. It only changes the duty cycle. Which doesn't help. (Not to mention you would have to cycle the charger electronics in unison to prevent charging the battery when it is too cold.)

It will still draw ~5kW anytime you turn it on. And if your EVSE only provides 3kW that means the remaining 2kW comes from your battery. And the problem is that you could run the battery dead before you manage to heat it enough to be able to charge it. And then you are worse off than you started. (So they refuse to heat the battery when connected to an EVSE that can't provide enough power to power the heater.)

 

[sandpiper]

That doesn't change how much power it draws. It only changes the duty cycle. Which doesn't help. (Not to mention you would have to cycle the charger electronics in unison to prevent charging the battery when it is too cold.)

It will still draw ~5kW anytime you turn it on. And if your EVSE only provides 3kW that means the remaining 2kW comes from your battery. And the problem is that you could run the battery dead before you manage to heat it enough to be able to charge it. And then you are worse off than you started. (So they refuse to heat the battery when connected to an EVSE that can't provide enough power to power the heater.)

Huh? Sure you draw the excess from the battery but so what? If you’re running 5kw at 20% duty cycle, switching a few times per minute, you’ll be drawing from the battery part of the time and charging part of the time. Neglecting minor efficiency effects, the net effect is the same as if you were drawing a continuous 1kw.

You wouldn’t run the battery dead in either scenario as long as your average heating power draw is less that what you can draw from the wall.

 

[MP3Mike]

uh? Sure you draw the excess from the battery but so what? If you’re running 5kw at 20% duty cycle, switching a few times per minute, you’ll be drawing from the battery part of the time and charging part of the time. Neglecting minor efficiency effects, the net effect is the same as if you were drawing a continuous 1kw.

No, you can't charge the battery when it is that could without permanently damaging it. So Tesla will not turn the heater on unless your EVSE can supply at least 5kW to cover the entire heater demand. It is a real problem in cold climates, as if you don't have enough range to get to a high power EVSE you can't heat the battery and you can't charge it; so all you can do is tow your car to a high powered EVSE or wait for the weather to warm up.

 

[sandpiper]

No, you can't charge the battery when it is that could without permanently damaging it. So Tesla will not turn the heater on unless your EVSE can supply at least 5kW to cover the entire heater demand. It is a real problem in cold climates, as if you don't have enough range to get to a high power EVSE you can't heat the battery and you can't charge it; so all you can do is tow your car to a high powered EVSE or wait for the weather to warm up.

Huh. I live in Canada and charge my car in the winter all of the time - often down to -30. It’s just life around here. Certainly it doesn’t start out at 80 amps, but I’ve never seen it limit anywhere near as low as a couple of kw.

 

[ucmndd]

Huh. I live in Canada and charge my car in the winter all of the time - often down to -30. It’s just life around here. Certainly it doesn’t start out at 80 amps, but I’ve never seen it limit anywhere near as low as a couple of kw.

Go read a bit in the Model 3 forum about trying to supercharge (or any charge really) a completely cold soaked battery in sub-zero temps. The first 30-60 minutes do basically nothing other than heat the battery.

 

[sandpiper]

Go read a bit in the Model 3 forum about trying to supercharge (or any charge really) a completely cold soaked battery in sub-zero temps. The first 30-60 minutes do basically nothing other than heat the battery.

I don’t have to read. I live it. Yes, if it’s cold soaked supercharging is very slow at first. I’ve seen it as low as 10-15kw. And as it warms up, so the current increases.

But Mike is talking about a couple of kw. I’ve never seen anything close to that.

In any case, I’m sure that Tesla hadn’t programmed the system to pulse modulate the heater. But that doesn’t mean it’s not doable. Internal resistance in the cells warms them as well( just more slowly.

 

[sandpiper]

No, you can't charge the battery when it is that could without permanently damaging it. So Tesla will not turn the heater on unless your EVSE can supply at least 5kW to cover the entire heater demand. It is a real problem in cold climates, as if you don't have enough range to get to a high power EVSE you can't heat the battery and you can't charge it; so all you can do is tow your car to a high powered EVSE or wait for the weather to warm up.

In any case, the early debate was around whether they would just update the motor without doing the whole drive train. I think we will see the whole train. You think just the motors. Fair enough, let’s watch and see what happens. If I’m wrong, I will humbly accept any public floggings that are due.

 

[MP3Mike]

I don’t have to read. I live it. Yes, if it’s cold soaked supercharging is very slow at first. I’ve seen it as low as 10-15kw. And as it warms up, so the current increases.

But Mike is talking about a couple of kw. I’ve never seen anything close to that.

You weren't reading what I said. I said with a cold battery and a low powered EVSE you can't charge at all. Not even a couple kW. If you haven't seen that than they you:

• Don't have a Model S or X
• Didn't have a cold soaked battery
• Or were using a EVSE, or Supercharger, capable of ~5kW or more.

The situation that was the most problematic for people was say they arrive at a hotel late and the destination charger/EVSE was in use. The decide no problem I will get up early and move the car to charge it before I shower, eat, etc. With the car being cold soaked and the EVSE being a low power, i.e. like a ChargePoint 207v 24A, unit they could neither charge nor heat their battery.

 

[sandpiper]

You weren't reading what I said. I said with a cold battery and a low powered EVSE you can't charge at all. Not even a couple kW. If you haven't seen that than they you:

• Don't have a Model S or X
• Didn't have a cold soaked battery
• Or were using a EVSE, or Supercharger, capable of ~5kW or more.

The situation that was the most problematic for people was say they arrive at a hotel late and the destination charger/EVSE was in use. The decide no problem I will get up early and move the car to charge it before I shower, eat, etc. With the car being cold soaked and the EVSE being a low power, i.e. like a ChargePoint 207v 24A, unit they could neither charge nor heat their battery.

Please point to a case where this has happened. It makes no sense. I haven't had that exact scenario, but a 5kw heater takes time to heat a half ton battery. I've had plenty of cases charging a cold soaked battery on 40amp/220V chargers, which do meet your minimum criteria. In those cases I've been gaining km right away - certainly well before the heater can make any appreciable difference.