Hey Michael,
I’ve worked first hand with lithium
ion batteries in a hybrid electric environment. You can’t over
charge them or bad things happen. I’ve seen it first hand. I
don’t know what battery chemistry that your modern EV gurus are using,
and perhaps there are Lithium chemistries (i.e. LiFe stuff we’ve been
talking about) that don’t care about a bit of over charging, but the fact
is that there are cells that will discharge faster and recharge slower than
others. I think the Toyota
is using NiMH, those don’t do bad things when that happens.
Also, balancing can take quite a bit of
time and can be impractical. One of the options is to limit charge and
discharge to protect the cells. There may be other strategies in use to
avoid problems with over charging or over discharging cells. But again,
they may be using chemistries that aren’t susceptible to damage.
There is nothing keeping you from finding
out yourself, go for it, and if you feel so inclined post your results.
Nobody here is saying don’t do it. Come to think of it, take some
video, it would be fun to watch. No one wants to destroy your fun, if we’re
wrong (and that is likely) there is some joy in proving that as well. I
don’t think anybody here knows what happens when a LIFe battery is
overcharged, I certainly don’t.
Kevin
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf
Of Michael McMahon
Sent: Wednesday, January 19, 2011
9:01 PM
To: lml@lancaironline.net
Subject: [LML] Re: Lithium
Batteries
I cannot
claim first -hand experience, but modern EV gurus claim there is not much
benefit to load balancing.
I do not
want to start an argument, but it is frustrating for people to say they
don't like ideas based on out-of-date or incomplete data. I am
building an experimental aircraft to test and learn new things, for the pure
joy of experimenting. Please don't try to stifle experimentation without
doing your research.
Just my
two cents.
On Jan 19, 2011 4:32 PM, <rwolf99@aol.com>
wrote:
>
> Concerning home-packaged lithium batteries, Hamid wrote:
>
> <<You can not just take a bunch of cells and put them in
series/parallel to make a pack and put it in your airplane to replace the lead
acid battery. You need to charge balance the pack and pay attention to the
charging voltage and over-charge/over-discharge. Better to pay some reliable
company to do the integration and testing than do it yourself and risk an
in-flight fire. The $100 you saved by doing it yourself will feel the most
expensive $100 in your wallet as you are dealing with an in-flight fire.>>
>
> I have to agree with Hamid here. I spent a very long two years as a
battery engineer in the mid 1990's and learned a bunch of stuff. Among these
was the requirement to balance the individual cells during the recharging
process (which happens at the beginning of every flight, right after you start
the engine). Screwing it up results in overcharging some cells and
undercharging others. Lead acid is rather robust in this regard, as it turns
out, but lithium is another story. In fact, the R/C model guys charge each cell
individually and discharge them in series. (They also do this in fireproof
bags, but that's the more twitchy Li-Po chemistry). I think it's the
overcharging of an individual cell that results in fires, but excessively rapid
discharge could also do it, I suppose. (Maybe due to a short in the
packaging???)
>
> WARNING! I KNOW NOTHING ABOUT MODERN BATTERIES! But I do know that lithium
batteries can catch fire and lead acid batteries don't. So I'd be reluctant to
take a chance here -- let the professional research lab do it.
>
> I also understand that this technological reticence is why I installed a
1940's Lycoming in my 360. Modern stuff is generally better but we each draw
the safety / efficiency / experimental line in different places, I suppose.
>
> - Rob Wolf
>
>
>