Prius NiMH Ovonics Batteries
- Hello Mike
Thanks for taking the time to post your results with the Prius packs. Sorry
to say I would have been surprised if it was much different.
About six months ago Noel was putting a pack of Ovonics in. Anyone know how
he is doing with them?
In a message dated 12/25/2007 9:03:13 A.M. Pacific Standard Time,
There are a few directions to approach the Prius packs for use in an EV.
Energy content is about 1.0-1.2 kwhrs per pack from the testing that I
did. Five in parallel give you 5.0-6.0 kwhrs of energy. That might get
you 20-25 miles of range if you drain the pack dead. I'm assuming 250
watt-hours per mile. Following the rule of thumb to not go lower than
50% state of charge, you might have a range of 10-12 miles. Imagine
having this kind of range after spending the time it takes to
mechanically restrain every module so they don't expand and wiring it
all up. A 1 amp charge rate will ruin an unrestrained Prius module.
Then there is how to charge nimh in parallel. Some say it's
impossible. Ask them how many times they have tried it. It can be done
but requires even more of a complicated pack. The built in relays in
the Prius packs make parallel charging and it's associated maintenance
possible. Every now and then the pack needs to be separated into
individual packs and charged separately.
Then there is the cooling issue. That's an entire page all by itself.
The Prius modules are rated to last 150k miles because they do in fact
run in a narrow band of soc. I forget the exact number, if I ever knew
it, but guessing at 40-80% is pretty close. That tight band is how
they get millions of very shallow charge/discharge cycles. In an EV
one hopes to get to 1000 cycles. The plates that make up each module
are just thinner looking to me, than say the EV95 in the RAV4/Ranger
nimh cells. That relates to being more efficient at accepting
regen energy. Not all batteries are good at taking short dumps of
energy and actually converting it chemically and storing it as
electrical energy. Some of it is absorbed and turned into heat instead.
Having several packs in Parallel will help distribute the load. But
you only get a very short range for all of your work. I can tell you
that having 5 Prius packs in parallel gave me the lowest pack
impedance I will ever have. My regen was so severe it would almost
break the rear tires lose on deceleration.
Anyway, it sure is fun to tell your friends that your EV drives on
Prius batteries. Unless the EV is something light like a golf cart, I
suspect the lifetime will be short. If nothing else the range is just
not worth the effort, to me anyway. I started to figure this out after
spending weeks making up fan control circuits and lots of testing.
The guy I sold all of my perfectly good packs to, smoked several of
them right off the bat. I can promise you he is much more educated
than I am. A professor in fact. The bottom line is that these
different versions of nimh batteries, Cobasys, Prius, Sanyo, are so
different in chacteristics that each should be considered a completely
Here is a pic of the packs in the bed of my truck. There are more in
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