Re: Best rechargeable batteries for electric motors

Doug McLaren wrote: 
In article <bbydnVcwg5yAY0LfRVn-jg@xxxxxxxxxxx>,
Bob Monsen  <rcsurname@xxxxxxxxxxx> wrote:

| The Natural Philosopher wrote:
| > Bob Monsen wrote:
...
| Here is a link describing the problems fedex has had with them:
| | http://www.findarticles.com/p/articles/mi_qa3864/is_200505/ai_n13642120

From your link --

   In the past several years there have been incidents involving lead
   acid (20), NiCd and NiMH (4), lithium primary (5), lithium-ion (1),
   and dry cell (8) batteries.

So, from the numbers, which battery sounds the most dangerous?  Which
battery sounds the safest?


Are you really trying to argue that nicad packs are as dangerous as liion or lipo packs? The article above is talking about both primary and secondary cells.

Here is a quote:

"M. Sudduth of FedEx related their experience in shipping batteries. Because of the recent incidents, they require shippers of lithium batteries to go through a qualification process before accepting shipments from them. They accept only shipments from the qualified list, and they are taken as Class 9 hazardous goods. Their two recent incidents involved medical primary lithium batteries and 78 Li-ion batteries intended for HEV application. Both incidents were detected before the aircraft took off. The Li-ion cell fire melted the plastic shipping container. It was taken off the aircraft when a worker smelled smoke. It appeared that the cells were not packaged properly and were touching one another. The fire started in one cell and then spread domino fashion to nearby neighbors. He did not identify the source of the cells."

The li-ion batteries were huge ones, of course, as implied by their HEV usage. The link was mainly included to point out the danger of lithium fires. The link indicates that fires in lithium batteries cannot be put out using the typical fire extinguishers that are used on aircraft.

In case it's not clear, lithium primary = lithium batteries that
cannot be recharged.  These are not what we use in our planes, though
your transmitter may have one to retain it's memory when the primary
battery is discharged.

Granted, these figures do not mean that lead acid batteries are 20x
more dangerous than li-ion cells, but only that they (it's not really
clear who `they' is, however) had 20x the problems with them recently.

| Here is an article outlining the requirements for charging LiION and | LiPoly batteries:
| | http://www.hobbyjapan2000.com/li-po-li-ion-batteries.html

We are all pretty much aware of these instructions.


Even people who are asking what the best rechargable battery is, like the OP?

Note that many of these instructions apply to other types of batteries
as well.  For example, looking at these instructions, only #2, #3, #6
and #7 don't apply to NiCd or NiMH cells.  (For #1, the rule changes
considerably, but the gist is still there -- use only the appropriate
charger.)

Some of the other rules aren't quite as important for NiCd or NiMH
cells, but they are still good ideas.  Like #4, #5, #9, #10.

| Again, they are completely safe if you charge them and use them | properly.

That's not entirely true of any battery.  Safe perhaps 99.999% of the
time (pick an appropriate number of 9's) but not 100%.  And I'm not
counting things like crashes which can cause fires, be it with NiCd or
LiPo cells.


There are recently documented cases of exploding cellphones, and spontaneous laptop combustion, which are directly attributable to mishandling lithium secondary cells. I can't remember a similar widespread problem caused by nicad or nimh batteries.

As I've continued to assert, these batteries are safe, but one must simply take more care in using and charging li-ion and li-poly batteries than nicad or nimh batteries.

| However, the RC community is into charging speed, and so tends | to 'fast charge' batteries with huge currents. Who wants to wait?

I'm perfectly willing to wait if that means I don't ruin my batteries.

And the RC community is really into _dis_charging speed, not charging
speed.

| My little hitec charger puts more than 3C into a 600mAH nicad pack

And you let it?  Bad idea.  You're ruining your NiCd pack.

SubC cells tolerate higher charge rates, and that's mostly what the RC
car community uses.  But your AA (?) pack should never be charged at
over 2C.

| and would probably put more in if it weren't for the external
| current limits I use.

Lovely.  You'd abuse your batteries even more if you could.


Well, no, that isn't what I said. I was complaining about the hitec charger, which was included in an ARF plane. It also included 600mAH nicad pack. The charger instructions indicates it wants a 5A, 12V supply, but I only give it 2A, using my bench power supply. The charger claims to be designed to charge 600mA to 1800mA packs.

| This is ok for Nicad or nimh packs, since it only wears them out | more quickly.

Most of the time, yes.  But if something goes wrong, they can catch
fire or cause fires as well.

| It's a fire hazard for liion, and possibly lipoly packs, | particularly homemade packs made from free cells.

Where did this bit of wisdom about homemade packs come from?


As I understand it, commercial packs which are designed for comsumer devices are required to have current limiting electronics built into them. Since packs made out of individual cells may not have this current limiting built into them, there is nothing preventing them from producing too much current, resulting in a fire. For example, if you inadvertently cause a short in your charged, homemade, unprotected liion pack, (after a crash, or by shoving the pack into a backpack with something that might short it) the current will not cut out as they heat up, and the pack could well explode, or burst into flames.

--
Regards,
 Bob Monsen

If a little knowledge is dangerous, where is the man who has
so much as to be out of danger?
                                 Thomas Henry Huxley, 1877
.

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