Heating load on traction battery

I don't know the specifics, but really- if you request heat then the ICE will turn on way sooner. The electric PTC heater grids are pretty puny compared to the conventional heater. The only way for that heater to work is to run the ICE.

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The electric PTC heaters are also locked out if the car is in ECO mode. In that case, heat from the engine coolant is the only source of heat.

In modes other than ECO, the PTC heaters can contribute some initial heat, but, supporting what mr_guy_mann wrote, only about 700 watts' worth. When the engine coolant is up to temperature, the heater can extract up to 5300 watts' worth from that.

 

i would think the battery would be used less and the engine more, as you turn the temp up

 

it wouldn’t matter much, car will kick out of EV mode. EV mode won’t even last more than a minute as your driving.

 

This is interesting. So if you are Prius camping in the winter and want the engine to come on as little as possible to maintain the selected cabin temperature, then it would be best not to be in ECO mode?

 

It sounds like you might be interested in the Gen 3 hunkering thread.

Interesting question about the PTC heat for hunkering. How valuable that would be depends on a bunch of interrelated things.

During hunkering, the engine will cycle for two purposes: (1) to maintain battery charge in a target range, and (2) to maintain coolant temperature in a target range.

Some of the results in the hunkering thread showed that the ECU can adjust those target ranges depending on what it thinks you're up to. That leads to the (counterintuitive?) result that it's better for hunkering to have the heat (minimally) on than to have it off.

When the heater extracts heat from the coolant, that eventually will lead the engine to cycle to stay in the coolant temperature target range. When the PTC elements make heat electrically, that will eventually lead the engine to cycle to stay in the battery charge target range. So neither one is free.

The question might be moot because I think the PTC heaters are only active below a certain coolant temperature, which might be below the temperature range that the engine cycles to maintain, in which case the PTC heaters would be generally out of the picture anyway.

Hmm, nope, the figure is actually in the repair manual. The PTC heaters can be in play when the coolant temperature is below 65 ℃. That is lower than normal operating targets, but it is higher than the target range the ECU eventually settles into (50 to 60 ℃) if it figures out you are hunkering. That could mean that the PTC heaters might be in play the whole time.

However, I don't think that can be answered from the tests I've already done, because I think I only tested ECO mode, so the PTC heaters were never involved in my tests.

So there's room for a comparative test, ECO on and ECO off, same conditions otherwise. Want to do that? Have you got a ScanGauge or other OBD tool so you can watch the coolant temperature?

There would be two questions: (1) we know that in ECO mode, the ECU will eventually lower the coolant target range to 50 to 60 ℃ (under technique #3 conditions). Does it settle on the same coolant temperature range with ECO off?

Then (2), overall, how does the cycle timing change, between ECO on and ECO off, in otherwise the same conditions?

 

I had a chance to do that, and the result is, the ECM only settles into the lower coolant temperature range, 50 to 60 ℃, if ECO mode is on (and the heater is in use). Turn ECO mode off, and the ECM will cycle the engine more eagerly to keep the coolant temperature at or above 65 ℃.

That means the question about the PTC heaters will be moot either way. It's moot in ECO mode because ECO mode forbids the PTC heaters. It's moot out of ECO mode because the PTC heaters are normally off when the coolant is 65 ℃ or above.

It's as if they made sure that, either way, they would avoid using the engine to make electricity (conversion loss), push that into the battery (conversion loss), suck it back out of the battery (conversion loss) and use that to make heat with the PTC heaters, in favor of just giving you the heat that comes off the engine.