Energy Capacity of the Hybrid Battery

(amphours x volts)/1000 = kwh

 

It seems to me that I've heard it is 1.2 or 1.3 KWH.

 

As stated above the capacity is 6.5watt-hours*200volts = 1.3 kwatt-hours. Only about 1/2 of that is actually available for use to protect the battery from early failure. The capacity will slowly degrade over the life of the car so mine may be down to as low as 50% of its original capacity at this time (4 years and 107,000 miles.

My Prius still gets the same great MPG now as it did when new so the battery is still doing the job.

JeffD

 

A small correction, 6.5Ah * ~200V = ~1.3kWh. In general for DC systems, Volts * Amps = Watts, and similarly Volts * Amp hours = Watt hours. AC can be trickier.

You can find more info on the Prius battery here:

Toyota Prius Battery Specs - EAA-PHEV

Rob

 

You only get 600Wh of that to play with, though, due to the SOC
limits. Which allows you to suck up about 600 vertical feet
of drop, coincidentally. Here [in the second part] are some
experiments and commentary that you might find amusing.
.
_H*

 

From Toyota's Prius spec:
Traction Battery

Battery Type
Sealed Nickel-Metal Hydride (Ni-MH)

Battery Power Output
28 hp (21 kW)

Battery Voltage
201.6V

Capacity
6.5Ah or 1.31kWh

 

OP asked for energy capacity, not power output.

Power = energy/time, or energy = power * time

The power rating of battery tells you how fast it can deliver the energy contained in it, but tells you nothing about the total energy stored in the battery. Energy density and power density of a battery are two different properties of a given battery technology, but both are important in automobile powertrain applications. In greatly simplified terms, they dictate how far you can go and how fast you can go. Two different things.

That ends today's 8th grade physics lesson.

 

So, if you extracted all of the effective HV battery capacity of 1.31kWh at the maximum power output of 21kW, it would maintain that power level for 1.31/21 x 60 = 3.74 minutes. That assumes the quoted 1.31kWh capacity is the effective allowed capacity between the upper and lower charge limits.

Not a lot of time, eh! Which is why you need that ICE sucking, squeezing, banging and blowing that hi-energy fossil fuel in parallel. There's a lot more energy in that stuff, which is just as well; most of it gets lost before it gets to the road-wheels.

 

The battery is kept between 40 and 80% of its capacity. Because of this, my understanding was that the capacity is barely affected over time... If your battery only had 50% of its original capacity, wouldn't it show in your mileage? (especially in city driving where regenerative braking is so important)

 

Yes it might impact a bit on the mileage but I've seen tests that have shown up to 50% loss of battery capacity gives surprisingly little MPG loss under normal driving conditions. The reason is that the vast majority of the time (in normal driving situations) you're not using all of the available SOC (state of charge) swing anyway. For example the nominal SOC is somewhere around 60% and you'll find that most of the time it's staying within +/- 10% of this value. As the battery capacity declines the SOC swings will typically increase, so a 60% to 70% swing for a new battery might result in say a 60% to 80% SOC swing for a battery that was nearly worn out.

Anyway, what I'm trying to say is that it's because fairly small SOC swings (typically < +/- 10%) are very common whereas large SOC swings that use close to the full available SOC swing (40% to 80%) are relatively rare. If the battery lost 50% capacity then sure those occasional large SOC swings would not be possible, but the more common smaller SOC swings would be unaffected.

 

So it's 6.5Ah which is equal to 1.31kWh. How does it compare to
- Tea Kettle 2000W
- Smartphone battery 2000mAh?

My guess:
2000mAh = 2Ah. So Prius battery has merely 3 times the capacity of smartphone battery ?!?! Why is it so big then?
2000W*1h = 2kWh. So Prius battery is not enough to hold an hour long tea party with a boiling kettle all the time?

General logic says the Prius battery must be quite powerful. I must be wrong somewhere.

 

spidgorny,

On the first count, you are wrong in the respect that the important figure of merit is energy capacity (Watt-hours), not charge capacity (Coulombs = Amp-seconds = Ah*3600). You get Wh from Ah by multiplying by the voltage. A cell-phone battery is only a few volts -- mine is rated at 3.7V and they converted it for me to 4.44 Wh. That's compared to the 1300 Wh of the Prius battery which is at a nominal 200V. Also, your smart phone is Li-ion, which can hold a higher energy density than the NiMH Prius battery.

On the second count you are correct. A 2000W tea kettle running for an hour will indeed suck down 2 kWh of energy. That's the same amount of energy you need to move your whole Prius about 10 miles down the road on pure EV (if you figure 200 Wh/mile for a Gen2). That's why you don't see many battery-powered tea kettles!

 

Well The formula is simple as was stated already The formula is fairly straight-forward.
kilowatthours = (amphours * voltage) / 1000

 

thanks, i've been waiting 3 years for that!