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

Collin Kidder <[email protected]> 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.

That is why I only referenced the video. I thought they were not
exactly saying the same thing.

[snip]
> 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.

I feel the same way. I take the date he presents and form my own conclusion.

> 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.

It is much easier to take someone's words when presented in a factual
non-emotional way. Putting someone down is not evidence. What I got
was that a "real" BMS could "remove" a cell from the pack if needed,
among other things. This is what I understood was the expensive part
and that manufacturers don't do this due to cost & volume. It wasn't
clear to me whether the audience was a bunch of DIY people building
commuter conversions or building racing vehicles. I did gather that
DIY's should monitor their pack but didn't know if he was referring to
a string as parallel cells or the whole string. For example, I have a
2p20S pack of TS-LFP100AHA batteries with one monitor board per
parallel cell. Since I'm not charging up to the shunting voltage of
the boards I'm effectively not doing any more balancing since my
initial top balance so unless something goes really wrong I'm
effectively only monitoring cells (voltage only, not temperature). Is
this what Dr. Whitcare meant, monitoring strings of 2 cells in my
case?

His chemical explanation of what was going on during charge/discharge
helped me understand what went on to cause loss of capacity and why it
was impossible, or very difficult, to recover lost capacity: plating
of Li on the electrodes.

I didn't, however, hear him address charging with the cells below 0C,
only discharge down to -20 or -30C. Did anyone find any potential
problems with charging with the cells below 0C? I don't have a garage
so there are a few days each year my batteries can get below 0C even
though I have them insulated. I have enough capacity that range isn't
an issue for me but I don't want to kill my batteries because they are
too cold.

--
David D. Nelson
http://evalbum.com/1328

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