Traction battery heater question

Yes it does turn on even after the battery is fully charged....the brick light turns on (charge) and if you listen you can hear the inverter buzzing under the hood.....buzzing turns off when the charge light goes out.

It also works when the battery is fully charged and the bms calls for heating ....power is turned on , the charge light turn on and you hear the buzzing sound under the hood (inverter operating)

 

Indeed, you are correct about that. Now I remember that @john1701a did report that his L2 EVSE monitor showed a draw from the wall a few days after the traction battery has been fully charged. Still, I don't know what effect the traction battery heater would have on the longevity of the battery. If it is universally beneficial or vital for the health of the traction battery, then I would think Toyota would not let the user select this function to be turned on or off.

 

When a cold snap occurs for several days in my region , and not having a garage to protect the car...well I prefer having the option of turning on the battery heater and have a full charge traction battery staying above freezing temperature, than having a partially charge battery going in the sub freezing temp.
When these cold snap happens...a lot of ICE cars (no pun intended) won't start.
Since the battery heater is drawing around 200W from the 12V battery ..I think that Toyota lets you the choice to choose to pull a few amps more than what it is mentionned in the specs, and furthemore it keeps the 12Volts battery happy when it is plugged in polar temperatures.

 

Don't forget where Toyota is headquartered. The answer for the why of several Toyota decisions regarding the car could be answered by asking how it works in Japan. An outlet in Japan is 100V, and might be just 6 amps. For such households there, it takes over 10 hours to fully charge the Prius Prime, and Level 2 is not an option. For such owners, the battery heater could overload the circuit.

The battery heater is designed to keep the pack above freezing. It is also low power. Working properly, it won't overheat the battery. Since there is a fire risk from an improperly working one, Toyota won't leave out fail safes for that event. The potential risk to the battery is in charging at below freezing temps. Not in the freezing temps themselves. Maybe there is a risk for more extreme conditions, and why the heater has an extended operation mode in those markets. Toyota BMS is well done, I don't see them allowing the battery charge at a temperature that could lead to damage.

For question of the heater and battery health, it doesn't matter. When not actually being used, there isn't much risk to the battery getting chilled to the temperatures we are talking about here. There isn't any water to freeze and crystalize, which can cause damage in other chemistries. While the heater does protect the battery from charging in the cold, its real purpose is to make it convenient for us to use.

 

It's been -23C for the past 3 nights, so the battery is having lots of cold weather conditioning!

 

Oh boy...this is F... cold for november !

 

On the contrary to the west and mid-west, we are having the warmest Nov temp on our record here in the NE corner of the US. The temperature hit 70F (21C) for the past three days in a row. It is now back to normal today, but the long-term forecast is predicting a warmer winter in our region due to the La Nina effect. With the highest heating oil price in history, I am welcoming the warm winter. So far, the lowest day temp has been only in the mid 20F (-4C) a few days in Oct. With a day temp high still reaching 40F (+4C) or higher, we have not even turned on our central heating yet.

I will likely keep the Traction Battery Heater OFF on my PP for this winter again to see more accurate kWh used for charging the battery capacity for each charge session. I'm not planning to change the use and charging habit for my PP this winter.

 

@drash last time I ran a full charge and 8 amps 120 volts it took around 12 hours. It was a few years ago and iirc I also ran the 8 amp setting at 220 volt for a full charge in 4 hours. No matter what the actual times were I came away from those tests thinking 8 amps setting take approx twice as long as the max setting.
I can get the max amps in while charging from Dr Prius if that would also help confirm charge times.

 

During this whole thread nobody has mentioned whether the heater functioning increases battery range in the winter. I've been charging the car and then unplugging it when it's done. I'm thinking if I leave it plugged in I might have more range because the battery is warmer. I'm not up north technically but in Ohio where it gets 40°F in the garage.

 

A cold battery reduces its performance and ability to take a charge from regenerative braking. It can't give you as much power when accelerating than a warm one. If you run Hybrid Assistant, you'll see the draw and charge power peg won't be as high when the battery is cold.

Tesla shows this by replacing the end part of the instant power line (much like that depiction in the Prime where you see how much power is being applied, image on the right) with dots. On the Regen side of the line, it shows that the Regen power where the dots are is unavailable. On the power side, it shows that the battery cannot provide power where the dots are.

As far as range go, a blue snowflake will be shown to warn that the range will be limited until the battery heats up.

So yeah, a really cold battery will have a reduced range.

 

Heater will not kick in at 40 F ...IIRC it does kick in 1 or 2 degrees above freezing....and stops around or just below 40 F
this is the temp of the traction battery ....not the ambient temp. it takes quite some time to a 200 pound battery to cool off.