2001-2003 Prius 65 mpg

Please give more information on Battery and installation. This is great. I have 2001 and I want to change it this as well.

 

Hi Dman,

Congratulations on the good performance, it does seem to reflect well on the overall mechanical condition of your car. I strongly suspect it is unrelated to the size of your auxiliary battery. There's a simple back of the envelope calculation you can do to evaluate the biggest effect the aux battery could ever have on your fuel economy.

When the car is in READY, the voltage on the 12 volt circuits is always 13.9 or so. The car's DC/DC converter regulates it rock-solid at that value. That's slightly higher than the battery's electrochemical voltage so it is always a slight flow of power into the battery, and you could measure that current with an ammeter. You don't even have to be driving to do it, it will be the same with the car in READY stationary in your driveway.

Multiply those amps by 13.9 to get watts, divide that by 746 if you want an estimate of the horsepower being consumed. I doubt you'll see more than a tenth of a HP in play at the outside, regardless of your aux battery size or model.

Cheers,
-Chap

 

is it possible for a LARGE 12v battery to feedback to the hybrid system and provide motive power, thus increasing mpg's? sort of the opposite of a bad 12v decreasing mpg's?

 

Rather than letting anyone answer that for you, I'd suggest actually working through the math as suggested above, with an ammeter if you've got one. Then you'll have answered your own question and know how you did it.

-Chap

 

arh, you sound like one of my old teachers.

 

I've measured the car overhead as about 450 W, about 450 / 745 ~= .6 HP. It is possible (not recommended) to put in a DC-to-DC converter and stored energy battery to 'off load' the .6 HP overhead. Over in ecomodder.com, there are folks who go out of their way to implement these 12V offload systems. In one case, implement a 14V battery that is plug-in, super-charged to offload this overhead. But this 450 Whr storage struck me as impractical.

Now it makes sense to consider using a solar tickle charger to keep the 12V battery topped off. There is about a 30-35 ma parasitic load for the keyless entry and controller memory: 12.5V * .035 ~= .43 Ahr. So it makes sense to have 3-4x solar capacity to handle the parasitic load and provide energy for the dark and shadow times. It would also lengthen the 12V battery life ... a lot. FYI, this is one of home projects but I don't have any results to share, yet.

BTW, this same technique works for all Prius.

Bob Wilson

 

I know this thread has some months on it, but it seems worthwhile to point out that a 100 mile trip is not a very significant sample. There are a lot of places in the US where the ground slopes significantly downhill for over 100 miles, as an example. With my 2002, I have found that the biggest impact on fuel mileage has been the tires. Depending on the brand and model, I've had it vary between 51 mpg (the original Potenzas) to 44 mpg (Michelins, I forget which). I imagine that the rolling resistance number is the biggest factor, but I've had difficulty finding the number for the limited range of tires available when I need replacements.

Scott C.