Question Regarding Hybrid Battery during HIGH Temps
 

Good Day; I own a 2008 Prius Touring here in Bullhead City AZ. The temps really CAN and DO exceed 120 degrees in Late July and August. Not too much but it does get there.

Is there anything I can do to help prolong the life of my batteries during the HIGH Temps?

Except for when my wife is at her part time job 3-4 days a week for 4 or 5 hours parked in the hot asphalt parking lot, the rest of the time our car is kept in the Garage.

I have an exhaust fan hooked up to help keep the heat somewhat under control. Is there anything else I should be doing?

Thanks for any input, Regards, Robert

Re: Question Regarding Hybrid Battery during HIGH Temps
 

When possible, try to park in the shade. Solar heating of the interior can be brutal. I understand there are window liners that allow them to be cracked to let the heat out and keep rain out.

The other thing is to drive so as to minimize regenerative charging of the battery. This doesn't mean doing nutty things but when you can, slow early before approaching a red light to give it time to change.

GOOD LUCK!
Bob Wilson

Re: Question Regarding Hybrid Battery during HIGH Temps
 

"...slow early...."

Does that equate to slow coastdowns as approaching a traffic light...??

Since that appears to be one of the primary techniques for more efficient recharging of the hybrid battery I don't understand your suggestion.

Re: Question Regarding Hybrid Battery during HIGH Temps
 

Actually a little more aggressive. If I see the light ahead is red or changing to red, I will start my braking down to a speed of say 20-25 miles per hour well before reaching the light. This gives the light a longer chance to change to green before I have to come to a complete stop. The goal is to preserve as much momentum as possible.
Without 'doing the math,' I'll give a verbal description. If you are interested, we can do the math for a precise answer. Understand that the kinetic energy of the car is given by:

• (1/2) * mass * (velocity*velocity)

So if I am traveling at say 40 miles per hour, the vehicle's kinetic energy is say "N" Joules. If I see the light change, I go ahead and brake to 20 miles per hour, this leaves the car rolling with 0.25*N and about (0.75*N)*charge_efficiency in the battery. However, I've just doubled the amount of time the light has to change.

Now if I win, the light changes and I accelerate back to 40 miles per hour adding (0.75*N)*discharge_efficiency. Notice that every time the energy has to pass into the battery, there is a 'charge_efficiency' and back out, 'discharge_efficiency' energy tax. These typical values are:

• charge_efficiency ~= 0.95 (generator eff.) * 0.90 (battery eff.)
• discharge_efficiency ~= 0.95 (motor eff.) * 0.90 (battery eff.)

When you do the math, charge_efficiency ~= 85%, discharge_efficiency ~= 85%. Combined charge and discharge efficiency ~= 72%. In contrast, the kinetic energy efficiency is 100%, other than rolling and a small amount of rolling drag, the kinetic energy has been preserved without heating the motor generators, battery and control electronics.

By braking early, I have increased the probability of:

• 100% kinetic energy savings of 0.25*N
• 72% regenerative energy savings of 0.75*N

Compared to a mechanical brake, our regenerative brake systems are brilliant but the built in losses are still significant. If we can, we try to preserve as much kinetic energy as possible by minimizing but not eliminating regenerative braking.

Bob Wilson

ps. In real world data, the battery efficiency decreases as they age. In some cases, I'm seeing closer to 75% charge/discharge efficiency. Also the motor generator and control electronics efficiencies are closer to 90-92% efficiency in some speed ranges. The example used 'best case' values.

Re: Question Regarding Hybrid Battery during HIGH Temps
 

I have no question regarding keeping the momentum of motion as long as possible since converting it to battery charging will always result in a net loss. But here we have a good case of which came first, the chicken or the egg..??

And timing is everything.

Say I shift into neutral to preseve my momentum and thereby prevent it from being "bled off" via regenerative braking. If I have timed things well and the light changes to green before I must make use of the friction brakes then all is well.

On the other hand if I should arrive at the decision point and the light has still not changed to green then I MUST brake, most likely brake heavily, in order to come to a quick stop.

(Was that person behind me prepared for that..??)

In any case now I have not only not saved up the kinetic energy I have almost fully exhausted it as HEAT via severe last minute braking.

Re: Question Regarding Hybrid Battery during HIGH Temps
 

Run your AC to keep your battery from getting too hot.

Batteries are like people, they work best when they are not too hot or too cold. While cold temps will not hurt a battery, hot temps can really cause failure. That's why I suggest AC when you are driving in really hot temperatures.

Yes it will lower your mpg's, but you did ask how to prolong battery life, not about increasing mpg's.

Google battery thermal management and it will give you some really good articles on how these cars operate to prolong battery life, or

http://www.mpoweruk.com/thermal.htm

Re: Question Regarding Hybrid Battery during HIGH Temps
 

If "normal" use of the Prius, anywhere it is sold, were a threat to battery longivity wouldn't Toyota have a warranty exception along the lines of brake pads or clutch discs...??

Not something that concerns me with our 2003 Prius.

Re: Question Regarding Hybrid Battery during HIGH Temps
 

I'm leaning towards "rxhybrid" on this but with one caveat, the battery thermal mass. In the case of my NHW11 Prius, it is very heavy. Although having cool air does no harm. I'd noticed that Cobasys uses water cooling in some of their larger NiMH batteries and seeing a 9C temperature increase from force charging my battery really impressed me with the thermal challenge. We are dealing with some serious heat loads for the AC to deal with.

Bob Wilson