Most efficient way to charge traction battery while stopped in hot weather?

On a hot sunny day, occasionally I have to be stopped for extended periods with the A/C running which means the engine will come on for a few minutes out of every 10 minutes or so. to charge the traction battery. Engine comes on at 2 bars and goes off at 3 bars.

As engine efficiency at idle is low, would it be better to put it in D with the brake firmly pressed and push the accelerator so that the engine speed is in the high efficiency range so as to produce more charge for the fuel burnt and maybe also I could charge it to a few more bars on the battery indicator?

Is this line of thinking correct?

The most efficient way is to let the car make the decisions.

I think you first need to look at how you can avoid leaving the car sitting with AC on for that many minutes.

Could you elaborate.
Remember the Prius is tuned for emissions first, mpg second, but if I can charge the battery faster, the engine will be off for more time, so hopefully less overall fuel used. These long stops kill my avg mpg.

The Prius doesn't know how long I will be stopped for......at least I don't think they've incorporated the mind reading option yet.

NO! Your car engine will operate in higher temperature.

I can't imagine that pressing the brake & the gas at the same time while in D would be good for the transmission or the M1 & M2

Let your Prius do as it knows to do.

When you stop on a hot day, open all windows and shut the vehicle off. No A/C, just leave everything off, until you are ready to go again.

Imagine no more.

I believe post this answers my question. post # 1582207

I think that you can rev the engine to charge the traction and 12V battery with pressing accelerator pedal while in Park mode


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Zdenok

My post was in response to a question about how to prepare a Prius for storage. I don't recommend that you force-charge the traction battery as a routine matter as the transaxle may be stressed during this process.

Just curious, why do you need to leave it with AC on for so long?

I just can't see how putting the car in "D" and force charging with one foot on the brakes and one on the gas is going to be more efficient than letting the car manage the charging automatically. I would imagine keeping it in "P" and pushing the gas would eliminate unnecessary drive train drag that you'd have in "D". But still, how much could you possibly improve fuel economy if you still have to run the ice motor to charge the traction battery?

Actually - when the engine automatically recharges itself while stopped - the low RPM speed for hot weather is the most fuel efficient speed to recharge the battery - because it trades off time so that it can minimizes thermal lost of the ICE and the batteries itself. Running at a higher RPM speed will increase thermal lost and the higher current levels could cause the batteries/inverters to overheat. In order for the batteries to efficiently recharge - the battery temperature must stay within room temperature or be cooled by some device. Slowly recharging a battery also extends the lifespan of the battery and the battery inverters.

This powercharge myth is totally bogus... the prius is NOT idling it runs 1280RPM whe turn on to maintain the charge THIS IS the efficient way to do it (you powercharge maybe faster but surely less efficient) and it is not just the engine but all the other efficiencies... higher current higher loss over the inverter cycle ... etc IT IS DESIGNED to do this it is NOT designed to powercharge !!!

I simply shot down the car in traffic situation when I know I am going in 2 two minutes no way it will heat up during that ... I think let the car JUST recharge the battery when I am on the move soon make no sense.

Some of the comment to powercharge before storing... TOTALLY bogus (will store for years ??? maybe but for month no point)

Because he lives somewhere really hot?

Thank for the information. Immediately, after trying the power charge technique a few days ago I noticed the HSI does not show/indicate to give an idea of efficient region. Also during hot weather running the engine at higher rpm's when stopped is not doing anything to reduce heat. It makes sense that the software would not run the engine in an inefficent manner to recharge the battery. The only times a power recharge might be done is if you need to go up to a high elevation (more than a few thousand feet), you battery is at 2 bars and you require more than 98 hp to maintain speed, but then I suppose the goal of efficiency is no longer being sought if this is the intention.

And how long the battery will last in your scenario to keep you speed steady ... few dozen miles ?? and then WHAT ... totally bogus argument again ... what are you suggesting ?? stop at the side powercharge ?? and then start to clime the hill ??? 98 HP is plenty 50 years ago would have beeen a ho-trod !!!

THE ONLY valid/possible case being parked nose down in a steep down driveway .... reverse is ONLY electric ... no HV battery charge will limit your "power" to MG1 charging power ... so you MAY need to re-charge HV to get moving BUT better off letting the car decide how instead of "power charge" it ....

I think a good way to answer the question is to examine the root cause(s)

Some suggestions, if I may:

- If rush hour stop & go traffic is causing you to come to a stop frequently, simply drive the car like you would drive a manual transmission vehicle and do what people call "slow n go" avoid coming to a complete stop in traffic.
- If red lights are causing you to stop for extended periods of time, same thing, slow down way before the light and begin accelerating when it turns green again. The vehicles in front of you will generally be at the next light jamming on the brakes already anyway, as you cruise along.
- If A/C is necessary, do not use the highest fan speed, or the max A/C setting. Set it on a temperature like 74-76 at fan speed 3 or 4. If it is 100 degrees out, or 90 and humid, cooling the inside of the car down to mid 70's may be impossible on short trips anyway. On long trips set it around 74 and once you feel cool, set it to 76-78 if reasonable to do so and adjust slowly.
- If your HV battery is constantly low, either you are accelerating too slowly, too slowly up hills, or attempting to get up to speed using just the battery and I've come to find that the most efficient way to keep the ICE from turning on, is to try and never let the HV battery status bar get down to, or past 3 bars. When it gets to 3 bars, start using more ICE to accelerate.
- Since sitting at a stop light for 30-60 seconds with 3 or less HV battery bars showing may deplete the battery enough to force the ICE on, you can combat this by practicing the use of maximizing your regenerative braking efforts, especially just before the stop where you anticipate to sit for the longest.

In response to suggestions of putting the selector in "P" and revving the engine, the engine won't rev in "P" or "N" the ECU won't let it.

Mine will rev, but not for long. Just a few seconds.