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Re: [EVDL] Phd in Materials Science on LiFePO4 batteries video WAS: Lithium 60ah 144v

My 2c worth - Yes, with good initially well balanced LiFePo4 cells,
kept together or equally well insulated and thermally managed and
never imbalanced by unequal parasitic loads on one or more cells
within the pack... you can get away with just switching off the
charger at pack size (in cells) times 3.6V or whatever. But if you
are serious about your EV being a 'real' car rather than an expensive
experiment or 'grand project' - especially if you expect anyone else
to drive it - you MUST have protection against over discharge in the
form of a BMonS to provide a warning of impending doom or a BMMS to
take it out of the drivers hands.

If you go down Jack's route of basing your 'empty' pack state on Ah
counting, eventually, as the pack deteriorates, you will kill one or
more cells. It seems as obvious to me as it is inevitable. Perhaps
the cells won't ever deteriorate to the point where Ah counting
without a BMonS causes a failure. It is entirely possible if you never
discharge the cells below 70% or so (in the lifetime of the EV at
least). But one day...

Perhaps I have missed Jack's point - I'm sure he will set me straight
if I have!

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk


Collin Kidder wrote:

> Yes, if you watch the whole video from Jay Whitacre and you read and/
> or
> watch what Jack says then you'll see that the two of them really
> aren't
> actually saying the same thing. But Jack is stubborn and I do not
> see any
> way that he'll ever change his mind no matter how much anyone else
> says or
> does. In reality Jack has some good points and some of what he says
> should
> be taken to heart. But his anti-BMS rage is so strong that he loses
> all
> peripheral vision and plows straight ahead with his preconceived
> notions.
>
> For instance, Dr Whitacre says to parallel all cells and run them
> past the
> knee one way or the other. Jack says to just slap all of your cells
> together
> and not do any balancing. Which is it? Do you trust the guy with the
> PhD?
> The guy with the PhD says that, from an engineering standpoint, it
> is best
> to do cell level monitoring. In fact, he says that DIY people SHOULD
> be
> doing cell monitoring. He just says that large manufacturers do things
> differently because of their volume. Jack says it's worthless. Dr
> Whitacre
> specifically says that he used monitoring systems in the things he put
> together. (He says he monitored bundles at a time though) Jack
> apparently
> thinks he's wrong to be doing that. Some of the differences are
> subtle but
> the end result is that if you watch Jack's videos and you watch Dr
> Whitacre's video you will see that the two are not really saying the
> same
> thing. Some of the points are the same and some are not. But it
> seems like
> Jack is using the Whitacre video to claim that they agree. They
> actually
> don't seem to if you are paying attention.
>
>
> 2010/12/12 Cory Cross <[email protected]>
>
>> David Nelson wrote:
>>> This blog entry [Jack Rickard's] has an excellent video about
>>> LiFePO4
>> batteries. I
>>> recommend that every one watch it if they even have a remote
>>> interest
>>> in these batteries. Here is a quote from the blog about the
>>> professor:
>>>
>> As usual, jack went off half-cocked on his quest to prove that if he
>> can't make a good BMS, then obviously no one can. Here's a
>> explanation
>> posted on
>>
>> http://www.diyelectriccar.com/forums/showthread.php/lecture-lifepo4-cells-52773.html
>> by Dmitri:
>>



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