"Lumping all Lithium batteries under one heading is ignoring the facts."

That is very true - but just bear in mind that the baseline for "safe for use in flight" is Lead Acid, not "safe relative to other LiIon batteries."

For those wanting to dig a bit deeper into some empirical challenge lessons learned regarding LiIon batteries that have been dealt with by other experimenters (including both success stories and "never again"), I recommend you Google "DIY Electric Vehicle Forum."  Heating, balancing, etc. are discussed in-depth by people who have converted their personal vehicles to electric, including discussion of the relative merits of the various chemistries currently available.

Be safe out there! 


Blue skies,

Bill


On 14:59, Wolfgang wrote:

"Flying is serious business. Lithium batteries are sensitive
to mishandling. Neither tolerates ignorance or arrogance well."

Lumping all Lithium batteries under one heading is ignoring the facts.

Safety is why LiFePo4 (Lithium Iron Phosphate) batteries were invented. They are a LOT tougher and safer than all other lithium batteries.

Wolfgang

----- Original Message ----- From: "Brent Regan" <brent@regandesigns.com>
To: <lml@lancaironline.net>
Sent: Tuesday, January 25, 2011 4:46 PM
Subject: Re: Lithium Batteries

Michael writes:  <<I never claimed to be an expert>>

Then perhaps you would be wise to take the council of someone who IS experienced.

<<The SECOND link in my post is a thread with several hundred posts on designing, building, and testing cells.  Have any of the naysayers read the thread, in depth, or done similar research?  >>>

Wow. Reading the anecdotal results of anonymous hobbyists is not "research", it is entertainment (for some). Reading about or doing actual experiments with the appropriate equipment and collecting reliable and repeatable data is research. My income depends on doing quality R&D so I appreciate the danger of searching the internet for data that supports your position and then taking that as evidence you are right. You can find supporting information for ANY position on the internet.

<<< I also have read <snip> that deep discharging, such as Hamid had done, is different than the minimal discharge we would expect from an engine start.  The small discharge contributes to less need to balance the cells.  Quite different from the total-loss system in an RC or solar-powered environment.>>>

Wrong, wrong and wrong.

The Wave Glider had a 10 -30 day (depending on payload power) "no sun" duration so it was a mixed cycle, not deep discharge.

Engine start is not a minimal discharge event. A 300 amp load for 30 seconds represents about a third of the available energy at those rates from a typical 20 AH battery. (careful, I set a trap here)

Cell imbalance is a function of the number of charge / discharge cycles, the depth of discharge / charge, the rate of discharge / charge, the temperature, and cell initial "matching". If you start with matched and balanced cells it will take longer to require balancing. Rate is one of the more important factors because it also effects temperature due to I^2R losses. Double the current and you get four times the heat.

<<<I'm an experimenter.  I can't just sit on the sidelines and wait for "someone else" to do the research, testing and development, then jump on the bandwagon.  That's why I'm building an experimental aircraft.  I thought this forum would be a good place to discuss development and testing of new systems rather than quickly declare it "too risky" for intelligent discussion.>>>>

I am all for experimentation, just not at 10,000 feet with peoples lives at stake. I have been a contributor on this list since the beginning and I have assisted the NTSB with several accident investigations where people died because the pilot ignored fact in favor of their own "opinion".  Flying is serious business. Lithium batteries are sensitive to mishandling. Neither tolerates ignorance or arrogance well.

Lithium batteries can and have been used in aerospace applications successfully but it requires a careful, detailed and intelligent design to mitigate the risks to an acceptable level. The risk levels that can be tolerated for an EV motorcycle or car are significantly higher than for a manned aircraft.

The word "Experimental" in Experimental Aircraft is not a directive to take foolish risks. It does mean that you and you ALONE, as a pilot and builder, are responsible for operating AND building an aircraft that is SAFE.

If I am not "intelligent" for pointing this out, so be it.

Regards
Brent Regan