Navigation Screen

[abcdefgary]

This might be a really stupid question but can driving with the navigation screen off for a long period of time allow you to get more MPG?

[9G-man]

When you say the NAV screen do you really mean the MFD?. I don't see how a moving map could effect your gas mileage.
And the MFD is the nerve-center for all the features of the car. Is it realistic to turn it off for long periods of time.? Just turn the whole car off and save alot of gas.
Gimme-a-break.

Yeah it would save you some gas, about 100/th of a MPG. Someone quantified how many watts of electrical power used would impact a single MPG. It's a whole lotta Watts.

Learning how to drive your Prius, to exploit it capabilities, will have a far greater impact on your MPG.

[Danny Hamilton]

I think a reasonable average energy density for gasoline is about 36.6 kWh/gal. US.

So if you drive 50 MPH for one hour and get 50 MPG, you've gone through 36.6 kWh of gasoline.

In the mean time the Nav system and display probably draw less than 400 Watts altogether. After using them for that same hour, you'll have "wasted" less than 400 Wh. This works out to something less than 0.011 gallons. Assume triple that for various conversion inefficiencies (gasoline to motive to electrical) and you're looking at somewhere less than 0.033 gallons extra for 50 miles. So if you eliminate the NAV and display I suppose you might have achieved, at best, 50.03 MPG saving you 1 gallon of gasoline for every 1,500 miles.

If you drive 12,000 miles per year, eliminating the NAV and display might manage to save 8 gallons per year.

Anyone want to check my math? For some reason I'm not feeling confident about it. I expected it to come out quite a bit less than 8 gallons.

[mingoglia]

Originally Posted by Danny Hamilton

I think a reasonable average energy density for gasoline is about 36.6 kWh/gal. US.

So if you drive 50 MPH for one hour and get 50 MPG, you've gone through 36.6 kWh of gasoline.

In the mean time the Nav system and display probably draw less than 400 Watts altogether. After using them for that same hour, you'll have "wasted" less than 400 Wh. This works out to something less than 0.011 gallons. Assume triple that for various conversion inefficiencies (gasoline to motive to electrical) and you're looking at somewhere less than 0.033 gallons extra for 50 miles. So if you eliminate the NAV and display I suppose you might have achieved, at best, 50.03 MPG saving you 1 gallon of gasoline for every 1,500 miles.

If you drive 12,000 miles per year, eliminating the NAV and display might manage to save 8 gallons per year.

Anyone want to check my math? For some reason I'm not feeling confident about it. I expected it to come out quite a bit less than 8 gallons.

Are you sure they pull 400 watts together? My 62" Plasma pull 398 Watts and my 42" LCD pulls around 250 watts (from memory). I'm not sure how the MFD can pull that much?

[Danny Hamilton]

Originally Posted by mingoglia

Are you sure they pull 400 watts together? My 62" Plasma pull 398 Watts and my 42" LCD pulls around 250 watts (from memory). I'm not sure how the MFD can pull that much?

Nope. Not sure at all. Thats why I said, "probably draw less than 400 Watts". Figured there was no way they'd pull more, but wasn't sure how low I could go. If you've got a better guess, the math is simple.

If the entire system pulls 200 Watts, then divide in half. Perhaps 4 gallons per year, and an improvement from 50MPG to 50.017MPG?

[abcdefgary]

Well, I'm referring to both the NAV and MFD screen. I'm not technical with cars and this hybrid system so I don't know.

I've never owned a vehicle with a navigation screen before, but essentially in my mind, the MFD screen is a computer and it would need power to run/turn on all the time.

I assume it would need power to run the computer to help you calculate the MPG you are getting at the current moment...? And all those animations from the trip information screen? And I'm "assuming" it needs more power when it connects to the orbital satellites from the GPS to locate your position. And I also assume that it would need more power to pull data from the navigation DVD and render the images...?

Then again, that's just my little theory, with no proof to back myself up, I just wanted to see if it's true, but I guess you don't get a lot of savings when you turn the monitor off.

[mingoglia]

Originally Posted by abcdefgary

Well, I'm referring to both the NAV and MFD screen. I'm not technical with cars and this hybrid system so I don't know.

I've never owned a vehicle with a navigation screen before, but essentially in my mind, the MFD screen is a computer and it would need power to run/turn on all the time.

I assume it would need power to run the computer to help you calculate the MPG you are getting at the current moment...? And all those animations from the trip information screen? And I'm "assuming" it needs more power when it connects to the orbital satellites from the GPS to locate your position. And I also assume that it would need more power to pull data from the navigation DVD and render the images...?

Then again, that's just my little theory, with no proof to back myself up, I just wanted to see if it's true, but I guess you don't get a lot of savings when you turn the monitor off.

Since a scan gauge can pull the same info that means the info is being calculated by the onboard computer anyway and the MFD is just simply a touch screen that displays data so there probably isn't any "computing" that anything you're turning off stops (this all is a guess on my part). With regards to the tracking of satellites you may have a point there. It would be my guess that that's powered by the MFD, but then again we don't know if turning the MFD really turns much off... or perhaps it just turns the display off? Regardless, the power pulled by the tracking of satellites is probably relatively small. I'm assuming such because back when I had my external GPS receiver that hooked in to my laptop the external GPS receiver took a couple of AA batteries and they lasted a pretty long time. This was before USB external receivers that are powered by the USB...mine was a serial connection.

You make another good point about the Nav DVD. When using the DVD of my laptop to watch a movie on the plane it does drain my laptop battery much faster... but that's reading a movie sequentially off the disk non-stop. Not sure how much power the Nav DVD pulls when sporadically updating maps for the screen... part of this would probably depend on how much map info is cached elsewhere in the system.

Mike

[Danny Hamilton]

Originally Posted by abcdefgary

. . .in my mind, the MFD screen is a computer and it would need power to run/turn on all the time.

I assume it would need power to run the computer to help you calculate the MPG you are getting at the current moment...? And all those animations from the trip information screen? And I'm "assuming" it needs more power when it connects to the orbital satellites from the GPS to locate your position. And I also assume that it would need more power to pull data from the navigation DVD and render the images...?

There are many computers in the Prius. Some are necessary to operation, and others are there to provide information to the driver. The MFD screen probably isn't necessary to operation, nor is the NAV computer. Certainly there is some amount of power used to operate the NAV computer and DVD drive. As for the GPS, it doesn't need to "connect to the orbital satellites", any more that your radio needs to "connect to the radio station". The satellites transmit radio signals that are received by an antenna. The GPS computer figures out how far away from each satellite it is by timing how long it took to receive the signal from when it was transmitted, and then translates this into numbers that indicate your location.

I doubt that the total of these computers (MFD display generation and NAV) plus the MFD screen itself adds up to more than 400 Watts (and is likely quite a bit less), but I don't have any reliable information to provide on which to base that assumption. It's mostly just an educated guess.

[blamy]

Originally Posted by abcdefgary

This might be a really stupid question but can driving with the navigation screen off for a long period of time allow you to get more MPG?

No.

[abcdefgary]

But clearly something has to power the display. I'm guessing that is where the 12V battery comes in?