Prius Prime - Electric Heat-Pump

All Gen4 Prius (2016-current) and PRIME (2017-current) have regular flooded 12V battery in the front engine compartment. Only Gen3 and earlier (pre 2015 modeles) had the AGM 12v battery in the rear cargo area.

 

My 2010 did. Let me tell you, it was not fun getting the rear hatch open from the inside with a dead 12v battery. I had to lay the rear seats down and crawl into the trunk area to gain access to the release that was hidden inside the plastic inside cover. Major PITA.

 

Been there. Done that. Not fun.

 

And best done when there are no pesky cameras around. No graceful way to do it.

 

I have been using my home charger port for almost three years now, making maximum use of night-rate electricity to “feed the beast.” My brand-new ChargePoint® station has given me some heretofore unavailable and interesting information to ponder:
I notice that when the traction battery is being “topped off” at the end of the charge cycle, the current draw is gradually tapered off, in stages, for the last half-hour or so. I have routinely (especially in the winter months) scheduled a warm-up prior to departure, expecting the car to use grid power to do so. But such is not the case. The car uses its traction battery to affect the warm-up (or cool-down in the summer). Then, at the scheduled departure time, it re-activates the charger to again top off the battery. During the thirty minutes or so that it takes to do this, the car's interior returns to the outside ambient temperature, making for an uncomfortable (and delayed) start to the excursion. If one chooses to start off at the scheduled departure time, the car's interior is preconditioned as requested, but at the cost of EV range. There is plenty of grid power available, even at level 1, since the charging load is being tapered off anyway. I cannot fathom the decision that was made to program the charging and loading scheme this way. Can anyone elucidate me? adTHANKSvance.

 

It seems to do the same thing on Level 2 chargers. In addition, heat pump power output is limited during pre-conditioning (according to the manual), so it takes longer than normal to melt snow and ice off the windshield in the winter (I run it for 3+ cycles with the key fob on snowy mornings), and if the car is extremely hot in the summer it doesn't make much of a difference cooling it down.

 

I tried using preconditioning a few times during winter either with a charge schedule or with the fob, but was never impressed. For one thing it does nothing in very cold winter morning below 14F. Even above 14F, it did not work to defrost. I park my car outside. I simply set the schedule charge 30 min earlier and turn on my car on the engine in HV 10 min before departure to blast the heat (and defroster) in very cold morning with a thick ice. I never had a need to precondition rest of the year (Spring, Summer, Fall).

 

My question still goes unanswered:
With at least 3.6 kW available from the (still plugged in) community grid, why not make use of that power source to run the Heat Pump (or activate resistance heating elements in extra cold temps) to accomplish "preconditioning", instead of drawing power out of the just-charged traction battery? I want my drive to start in reasonable comfort with the maximum EV range possible.

 

AFAIK, there is no resistance heating elements in PRIME, except heated seats and wheel, but they are not used for pre-conditioning. I don't have the answer to your specific question, but I suspect the heat pump can only be driven by the traction battery not directly by the grid power. In any case, for my climate, PIRME's pre-conditioning is totally useless feature.

 

Interesting. So that means, for the question of @Paul.Ivancie, the real reason Toyota does not allow the heat pump to run for the pre-conditioning by drawing power from the grid, instead using the traction battery stored power lies somewhere else.

 

The battery is plenty warm by the time it finishes charging.

To answer the question of why? No one knows. It's one of many weird design choices Toyota has made.

 

Yeah, simple reason I don't use pre-condtioning on my PRIME is because it does not work for my situations. But not only that it does not work, in my case, it also cost more than running the gas engine to pre-warm the cabin and defrost the windows before my departure.

 

Interesting. What, exactly, does the app tell you?