Toyota Seeks Battery-Price `Sweet Spot' for Plug-Ins

[miscrms]

Originally Posted by Flying White Dutchman

Sorry for the offtopic qs : but 15C? whats that

There may be more than one convention, but I believe 1C indicates a discharge in Amps equal to the capacity in Amphours. Ideally this would be the current draw required to fully discharge the battery in one hour, although that is not often the case in reality. You can think of it as a measure of how "hard" a battery is being worked. Putting out 100A might be no big deal for a 100Ah battery, as its only 1C, but a smaller battery will have to work harder to put out the same amount of current. The Prius batteries are rated at 6.5Ah capacity, and from what I have read a full electric drive acceleration can draw 100A or more. 100A/6.5Ah =~15.4C. 15C is considered quite a high rate of discharge. This would generally have a negative impact on battery life, but the PanasonicEV cells used have been specifically designed for these conditions.

To put that a little bit in perspective, consider a traditional lead acid starter battery. Most of us would think of these as very powerful batteries, optimized to deliver very high currents for a short period of time. These are often 40-50Ah in capacity, and capable of putting out short bursts of 400-500 Amps to start a cold car. So they would be running at around 10C (400-500/40-50).

Rob

[Flying White Dutchman]

but the prius 6.5ah are based on a 6h rating
for example a 12 volt lead acid battery is rated 20amp hours. ( 20h )
so where is this fitting in?

[miscrms]

Originally Posted by Flying White Dutchman

but the prius 6.5ah are based on a 6h rating
for example a 12 volt lead acid battery is rated 20amp hours. ( 20h )
so where is this fitting in?

Yeah, thats where it gets complicated, and I'm not honestly what the proper convention is (or if there is one agreed upon). The 20 hour rate is where most PbA are specified, and this is often referred to as the C/20 (1/20*C) rate. As you rightly point out, under that definition a PbA battery will last much less than an hour at 1C (usually about 30 minutes) due to the non-linearity of the Peukert effect. If you are talking about capacity, I think most people do scale the current such that at 1C it really does last an hour. If you are just talking about discharge rate relative to capacity I think people often don't scale it, and just use the 20 hour capacity. Fortunately the whole thing gets simpler for Li-ion and NimH as they generally do not exhibit Peukert effect and are much more linear over discharge rate.

Rob

[Flying White Dutchman]

so a lead acid battery with a discharge rate of 12ah over 20h and 8ah over 6 hours = NiMh prius battery rated 6,5ah over 6 hours?

[DaveinOlyWA]

Originally Posted by Shawn Clark

I do a 1.1 mile stretch once or twice a week (tested in both directions) on battery only and don't recall moving more than 1 bar on the SOC display. On the flat the battery range appears to be several miles, recognizing that the display is non-linear. Climbing hills would be another matter entirely, and one of the reasons a lot more battery will be required.

daniel,

I don't see battery swaps as impractical at all, but fast recharging is dicey. Battery swaps will require design with that in mind, a different kind of filling station. There is no reason that specific form factors can't be designed for use among all manufacturers (several sizes). Besides, paying for the battery on installments rather than necessarily owning it from the start makes sense as it would speed adoption.

i wouldnt comment on this post with a 10 foot pole

[bedrock8x]

Clett,

Don't be fooled by BYD's advertising hype.

The quoted price for raw cells is $1843/kWh delivered to US with only 1 yr warranty.

See quote below.

Originally Posted by clett

"Toyota's number of $5k/10 mile Li-ion"

Toyota are grossly overestimating the cost of lithium-ion. BYD and others are already selling LiFePO4 for $300 per kWh, which at 5 miles per kWh is just $60 per extra EV mile range. Assume $100 per EV mile to allow for shallow discharging.

What they mean is their lithium-ion (ie from Panasonic EV) is still uncompetitive in terms of cost.