After how much time is it better to turn off the vehicle, rather than idle?

As long as the key is on, the 12V battery is recharged though the HV system using the converter.

 

Sorry to hear you went through hurricane Sandy, but I'm glad to hear your Prius was able to help you get through it.

 

I agree it's a case-to-case basis, but for the average scenario, if the entire system is OFF, there's no chance draining anything unless you're in ACC mode and up.

All things being equal, for example a 60-minute wait, 60% SOC, 194F engine temp, 77F ambient temp, a Prius left in READY mode (car A) will still cool down at the same rate as one that is OFF (car B) for 60 minutes. That is until the car A discharges after 20 minutes where it will eventually fire up the ICE 3 times in 1 hour and keep a warm ICE temp well above 104F. SOC meanwhile will only be around 51% upon driving off.

When car B fires up again after 60 minutes, it will most likely still have 60% (59.5% at worst) SOC. Engine temp (from experience) would still be around 140F (104F at worst after 1 hour depending on ambient temp).

So when car B drives off, it still would have been better off than car A which consumed 3 cycles of SOC top-off to just stay above 51% SOC. Car A, meanwhile, still retained 60% SOC, consuming no gas, and driving off still above stage 2 warm-up and take off easily on traction battery only till it needs the help of ICE in gaining speed. Even if it came down to needing stage 1 warm-up, it will do so easily with a healthy SOC and covering ground already while consuming gas.

We all know the Prius is good at conserving energy, but we also have a say in how to further conserve that by powering completely OFF whenever the car will be stationary for more than 1 SOC top-up cycle.

 

if the a/c, lites and radio are off, you're pulling a miniscule amount of power. i would say more like hours than minutes. i have never powered down under any circumstances, unless leaving the car.

 

In traffic, leave it alone. But if you really want to find out, you might consider 'doing the experiment:'

• drive normally for a longish errand, say 15-20 minutes of driving
• about 5 miles from home, reset a trip meter
• park at home and leave car in "P" and "READY" -> record the trip meter numbers and time (to second)
• listen to some good tunes for 2-3 minutes -> record the trip meter numbers and time
• listen to some more good tunes 3-5 minutes -> record the trip meter numbers and time
• head into the house and wait 10-15 minutes -> come out and record the trip meter numbers and time
• head into the house and wait 10-15 minutes -> come out and record the trip meter numbers and time

You should have:

1. time stamp
2. miles (which will remain constant))
3. MPG (which should decrease slowly)
4. average speed (which should decrease slowly)

Enter these rows of data into a spreadsheet and use the following formula: miles/MPG -> fuel burned since reset

You will have a total fuel consumption for each sample. Use the time interval between samples and difference in amount of fuel burned to calculate the fuel consumption rate.

Now turn off the car and repeat the same time intervals only stopping and starting the car each time. So the time between samples, the car is OFF. Do the same set of calculations.

Now you can tell us:

• Your average fuel consumption per minute/hour in READY
• Your average fuel consumption per start/minute/hour cycling the car

Think of this experiment as a great way to document the tradeoff between starting/stopping the car manually versus just letting it sit in READY in traffic.

There is a safety issue with manually stopping the car as it takes nearly five seconds for the car to come ready. I think it is safer to be able to move at anytime in reaction of what is going on in traffic. For example, an emergency vehicle comes up and insists you have to move out of the way. If the car is in "READY", just take your foot off the brake and steer away.

There are more sophisticated ways to measure the relative effect of staying in "READY" versus manually cycling the car. But you will need a data-recording, Prius-aware scanner.

Bob Wilson

 

Just to give you an idea how long the lead acid battery could last if you're just running low powered equipment. I have one of those 12v plug in coolers that is rated 60 watts. I hooked it up directly to the 12v battery and left it running for 45 minutes by accident while my Prius was completely turned off. I was able to power up the Prius like nothing ever happened.

Another experiment that I've done a couple of years ago. I had a fully charged truck battery running a projector using an inverter. The projector is rated almost 300 watts and it ran for 1 1/2 hours and the battery didn't die. I finally shut it down since I didn't have time to wait.

 

I had my lights on, my radio on, my heater on low for about 7 minutes while I waited in line and only dropped
2 bars. I don't think turning the system on and off all the time is a good idea. The vehicle has it's own control
program and I feel it's best to let it work as designed. To much monkey business will always lead to unwanted
issue's with something. I would bet if you keep turning it on and off all the time, the relays and switches could have premature failures.
Just let the car do it's own thing and enjoy the savings.

 

According to Torque, the system pulls 0.6A current when sitting in park with "ready" on, but nothing else turned on. The battery is 6.5 Ah. Assuming only half of that is usable to discharge, it would take 5 hrs to totally discharge it from full.

 

But right there is the problem. I don't consider a 60 minute or 1 hour idle scenario an average idle scenario. I'm assuming you are sitting in your car idling....more in a Drive Thru or Traffic Jam scenario. Both scenario's where there is benefit in quickly being able to go from stop to start.

If you are in a scenario where you are not moving or just idling for what will be an hour? Certainly turn off your vehicle. If possible go further and park it first.

But basically, I'd think idle for an hour or more would most often be a camping scenario or the before mentioned usage of The Prius during a power outtage. Which weren't the scenario's I was applying.

 

Are you referring to the 12v battery located at the back? 12 x 6.5 = 78WH. That seems low for a lead acid battery that size. My little lithium battery for my grass mower is rated 140WH.

 

Of course I'm referring to the traction battery. I said when in READY.

 

The reason why I find leaving the car on to be most beneficial is that, even if the engine doesn't cool off, the car will still often run the engine (usually idling ~1,000 rpm, not generating any power) when you turn it back on after you first use the engine.

This isn't captured in the "warmup stages" that are well-known around here, there's obviously more to the warmup states that we don't really know. All I know is that if I start the car with the engine coolant >65°C, the diagram says I should be in S4 and fully warmed-up. The car will run in stealth as long as I want it to, but often after lighting up the engine (or maybe the second or third time I use the engine), it will continue to run, even as the coolant climbs past 85°C or more (normal S4 is entered at 70°C). It will happily stop when I come to a stop, it just won't stop if I try to glide.

For this reason, when you're only going to be stopped for a couple of minutes, leaving the car running is the best bet. An exception might be if, when you turn the car back on, the first thing you're going to do is accelerate to >46 mph and stay there for >5 minutes. Then you're probably always better turning the car off, since the engine will always be running for you anyway.

Certainly for the case of just waiting for a stoplight, I would leave the car running. Some of my local stoplights are even worse than the OP's in Las Vegas; about 3 minutes for a full cycle.

 

This is a good point. The ICE doesn't like to stop as easily when restarted later.

 

I agree with macman408 - if you turn off the Prius - only for a short time - any fuel savings from the time off - is burned away in the Prius' aggressive warmup cycle from a cold start. If the gas engine is still warm (>104 degrees Fahrenheit ) the aggressive warm up cycle is shorter but it is still runs for few minutes.

If you are just running into the house to fetch something and are coming right back out to drive - you'll save gas by not turning off the Prius and just parking it with the engine on while you do your short stop over...

If the outside temperature is over 70 degrees fahrenheit (then a fully warmed up Prius coolant/emission system won't lose too much heat) AND if the HV battery does not drop below 50% - a Prius HSD stop start idle tech will turn off the ICE while the Prius is idling and keep it turned off.

If the outside temperature is near or below freezing AND the Prius is idling (e.g parked in a parking lot or stuck in traffic) for over 20 minutes AND the heater/defroster is turned off (not necessary), THEN you will save gas if you turn off the Prius for over +20 minutes and restart the Prius when the traffic starts up again and you have to move.

If the outside temperature is near or below freezing AND the Prius is idling (e.g parked in a parking lot or stuck in traffic) for over 20 minutes AND the heater- defroster is needed, THEN you will not save gas if by turning off the Prius - instead keep the Prius turned on - pulse the heater for 5 minutes at high heat at hi fan then turn the heater off for 15 minutes - repeat every 20 minutes - until you start moving again. When you get moving again reset the heater to the normal position.


hope this helps
Walter Lee

 

If you want/need to shut down the Prius, go ahead. The next time you power it up, and if the engine is warm enough, you could always put it in "EV" mode to prevent it from starting. First thing this morning, my Prius allowed me to put it in EV mode after sitting in the garage for 11 hours, the indicator said outside temp was 75. I drove the car for about 1/2 a block before the ICE fired up. My speed exceeded 11 mph at that time.

The entire trip was 3.6 miles and the mpg was 54 mpg. It was a short trip but I didn't have to pay any warm up penalty.

 

Even if you start out in EV, you still pay a warmup penalty. If you do it right, you might pay the warmup penalty when the engine would've been running anyway (like going up a hill, or driving on a highway), versus when your car has fairly low power requirements, like in your neighborhood. If you do it wrong, then not only do you pay the same warmup penalty, but you ALSO end up with an empty battery, which has to be recharged next time you take the car out for a drive, costing MPGs off of that trip instead.

 

I take a ferry to work & sit on my car about a 45 mins to over a hour each trip. Depending if it's hot or cold I leave my car on. Most of the time the ICE will not come on. This is with the AC on & Radio on. If it does come on it is just for a few minutes. On the ferry you are suppose to cut your engine off. It's nice to have the car "off" and have the AC on.
My old car they would always catch me & tell me to turn off the car.