What is the usable power in KWh ?

Your calculation is correct. But, the 6.5Ah figure is the total capacity of the cells. Mind you, prius limits the usable capacity to only one third of that to maximize battery life. There is a trade-off between depth of discharge and total life cycles in every type of battery.

 

KWh is a unit of energy, not power. Which do you want: power or energy?

Tom

 

Regen back into a PHEV add-on pack is very much a second-order efficiency gain, and possibly even would result in reduced MPG if you never plug it in. Once your PHEV pack is depleted, then charging it via regen means that you are charging it with the ICE. You want a plug to charge your PHEV pack, not the ICE. Let regen go into the smaller traction battery instead. Plan on charging the kit as often as possible, and plan on having lower MPG than you do now if you don't plug it in. The added weight will offset the increase in regen capture efficiency due to slightly more favorable Peukert's constant.

These systems work best with you use the ICE for acceleration and hills, then try to cover ground with the ICE off on flat and downhill.

 

No-plug Prius has 1.31 kWh and it uses only 40% of it. Usable is 0.524 kWh.

 

in watts, not watts/second. watts/second does not have a meaning for the kind of questions you are asking.

Lets say you are pushing a big rock. Are you interested in how fast you can push the rock, or how far ?

 

201.6V x 6.5Ah = 1.31 kWh

HV Battery full 8 green bars is ~80% SOC and one purple bar is ~40% SOC. Prius maintains that range to prolong the battery life.

 

It's a common mistake. This is the brief explanation:

Force is how hard you push on something. Generally this is expressed in units of pounds or newtons.

Work is when you exert force over a distance, such as skidding a box over the floor. Work is a form of energy, so it is usually expressed in units of joules or calories.

Power is how hard you work, or work per unit time. It is usually expressed in units of watts or horsepower.

Power is no indication of the amount of work. Something can be very powerful, but only for a brief instant, and therefor do little work. Or it can work slowly but continuously, producing a lot of work but not much power.

So when you talk about putting energy back into the battery you want units of work or energy, not power.

Much of the confusion comes from the electrical distribution industry, who insists on measuring electrical energy in compound units. They like to use watt-hours, which is power times time, which equals energy. It's a round-about way of doing it, and causes no end of confusion to non-engineers.

Tom

 

Let me attempt to correct your misconceptions.

The added weight to include that 10x capacity, that you have to lift over the hills, as well as expend energy to bring up to speed, will cause lower MPG. Can you at least acknowledge that fact?

So, after paying a weight penalty in your efficiency, you can perhaps capture slightly more energy. But you need to be coming down a seriously long mountain grade for it to make any difference. And if you are coming down from the top of Pike's Peak, for example, you would have expended more energy than you could capture by lifting the weight of the pack to the top.

"Occasionally full" means that there is not a lot of energy going to waste. And I can't see you losing out on much if any energy from regen, living in Oceanside, NY. For comparison, I have a 54 MPG tank going right now in my Gen II, which is less efficient than your Gen III, and I live in the Rockies, and I see 80% SOC daily.

If you are on the highway, there is a constant dance between battery charging and discharging. When you accelerate or go up even the slightest incline, the battery will discharge. When you slow down, the battery will charge. Otherwise, the HV computer attempts to manage state of charge (SOC) to maintain 60%. On the highway, there is generally not enough power from the battery system to overcome wind resistance, and so the ICE must be used. There is no excess energy that is lost on the highway, other than a second order effect like the ICE operating at an output level that is less optimal. But how do you tell the ICE to operate at a higher output, most optimal level, simply because you have a PHEV kit?

The PHEV will help you on the highway by keeping SOC above 60%. Then the HV computer will preferentially use battery power and keep the ICE at lower power output. That's called blending, and that can get you fairly high MPG.

Yes

Think about the Plug-in Prius drivers. They get 13 miles of EV range per charge. That's about 1/4 gallon of gas saved. If they plug in once per day, six days a week, the most gas that they will save is 78 gallons per year. If you decide to PHEV, think about your driving pattern and see if it would be possible to plug in two or even 3 times per day. That's the only way it even begins to come close to being worthwhile.

Also, the remarks of PiP drivers that don't charge (i.e. a long trip) is that they generally get 50 - 60 MPG. These are generally very experienced Prius/hybrid drivers already in a car with a brand-new pack. They can't get 70-80 MPG simply because the battery pack is larger and can capture more regen. Your non-plugging-in results could be worse than theirs, because your car is not optimized for regen with a large add-on pack.

 

I think from the start this thread has missed the point. The Prius IS NOT an electric vehicle! The fact you -can- be propelled by electric only is just "window dressing". The hybrid electric part is there so the Atkinson cycle engine is usable, it's not there to drive the vehicle down the road.

Remember, if you were to use electric only you would be severely limited in how much power you could use. The fact the battery -contains- a certain amount of energy doesn't mean you can actually -use- that energy. You are limited in several ways on how much energy you can use and how fast you can use it. First, current you can draw is limited to protect the battery. Then you are limited in how much current over time (usually the limit is time) you can use, as the battery heats up and that will shut you down. Next, the system will only let you run the battery from about 80% to about 30% of the 6.5 A-Hrs. Finally, the electric motor is only so powerful (around 40 HP) so that will limit you. I -suspect- you would eventually overheat that as well if you had enough battery power that you could use, but currently it's the battery that is the limiting element. And that's because it was -never- intended to propel the car on its own.

 

Just a bit of additional information:

1. The actual Prius HV battery voltage varies with SOC so the available energy is a bit higher than the nominal calculation stated earlier in this thread.
   1. About 200v at 40% SOC (low end of usable energy)
   2. About 220v at 80% SOC (high end of usable energy)
2. The modules in Gen3 Prii have a lower series resistance than those in the Gen2 Prii so the power (watts) available is higher in a Gen3.
   1. Gen2: 100A max current rating
   2. Gen3: 130A max current rating

JeffD

 

Nope. Neither of those is in fact a loss of energy to the car system, one is a conversion to potential energy the other a conversion to kinetic energy. Both can be recovered, or used as a substitute for chemical energy later. Energy losses (to the system) are brakes and air resistance.

 

I've wondered about this. It seems like you have more get up and go (pardon the layman's way of thinking about this) using the battery when the battery is fuller. I presume this explains it.

 

You also have a larger, more powerful engine in the Gen3.

JeffD