NIMH Batteries

I've used NiMH cells to make my glfider battery for over 5 years now.
I always charge them with an RC Hobby charger, they have given
excellent performance.

The reason I went to 11 cells is to get 14 volts so as to insure that
my aircraft radio did not drop off due to low voltage at the end of
the day (10.5 v is the cutoff for most radios).

The reason for not using Li chemestry cells is concern for possible
overheating, bursting of cells, and resultant "Very Energetic" fire
from the release of the Lithium inside the cells. The RC hobby has
burned down well over 100 houses, apartments, cars, trucks, model
planes and garages during the learning phases of using LiPoly
chemistry cells. They require extreme care in all phases of use to
avoid catching fire when overcharged, over-discharged, or compromising
the plastic cases. Currentlfy the biggest issue is "Balancing " them
so that one or more cells don't reach full charge prematurely. This
requires a tap on each cell led out to a balancing set of circuitry.
All this information, advice and hardware information is freely
available on the RC Forums.

The Li-ion and LiFe (A123) chemistries are also suseptable to these
events, but because of the steel cases, like NiCad & NiMh, will resist
abuse better than LiPoly. In actual practice they still use
specialized charging and balancing circuits, and usually over-
discharging circuits, esp. in consumer devices such as Laptops and
Cameras.

IMHO the NiMH is the most reasonable replacement for the SLA
batteries, unless you really want to be on the cutting edge (Bleeding
Edge) of the Li technology.
I was also unaware that many others had equiped their gliders with
NiMh batteries and and had uniformly good results with their use.


BTW, I take issue with; "Both LiFePO4 series (of batteries) are
claimed to be able to be charged on most standard lead
acid chargers (set for AGM/GEL cells)", unless a complete set of
charging and balancing circuity is included in the package. And at the
prices quoted, they really should be!!

Happy thermals,

Wayne

At 19:11 04 December 2008, K M wrote:
I had similar thoughts some months ago. Being the owner of a DG glider, I
asked them for advice on NiMH & lithium based systems. The answers we

"We several times have discussed this topic.

No doubt about that you can store more electric power in the same
compartment with the same weight. But you will need a special charger and
we have to make a "Technical Note" after having tested all technical
questions with this new power system (Temperature, Danger of Fire etc.)

On the other hand the battery of a self launcher always is big enough. And
we are supplying solar cells. With this eqipment you never will have any
electric power problems.

Often we do not have any problems with the weight because the batteries
are used as a counter weight for the correct C/G.

This all is the reason why we have not made such an investigations."

and...

"You just cannot change the battery system by your own. That is a "Major
Change" and must be certified by the manufacturer.
........
When you have any additional instruments and like to have a second battery
for them - strictly separated from the main electric system - you can use
another battery-system on your own risk. Of course this system never may
supply more than 14,4 Volt.

My advice:
Don't change anything! It might be dangerous."


The British Gliding Association picked up this discussion and published
this in their newsletter:

"Glider Batteries. Several new types of battery (NiMH, Li-Po, Li-ion etc)
are now on the market, as suggested alternatives to Lead Acid (gel). There
are a number of safety risks associated with batteries and with replacing
lead acid batteries with
non-lead acid alternatives. More information is available at
http://atsipowermanagement.co.uk, http://dg-flugzeugbau.de/forum-dg0.html
(click on English language forum and follow link to non-lead acid
batteries) and http://www.caa.co.uk/docs/33/CAP562.pdf (note this is a
15Mb document). The BGA advises owners to understand fully the need to use
the correct charging system, whether installed in the glider or not, with
whatever battery type is used; different technology batteries should not
be mixed. In terms of certification, glider parts should be approved by
the type certificate holder or by modification and should either be
released or a standard part. Glider batteries are normally
considered to be standard parts. Owners should ensure that, where
batteries are replaced by alternatives, the installation, aircraft
charging system (if appropriate), weight, balance and use meets type
design approval."


So...there may be certification and insurance implictions.

Cheers

Martyn



Dear List,
It is time to replace one of the battery packs for my sailplane. I
currently use packs consisting of 7 2.5V SLA batteries to make a 14V
pack. This has worked very well for me in the past but the AH on these
cells is somewhat limited. I would like to ad a transponder and
possibly some type of collision avoidance device so I am looking to
upgrade the power supply. I have seen Nickel Metal Hydrate batteries
that come in 12V and 10 to 14 AH sized the same as the SLA batteries
alot of the glider people are using. There is a company in the UK ,
ATSI, who markets these NIMH batteries for aviation use. My question
is does anyone on the list have any experience with these or any other
12V NIMH batteries for glider use. I dont mind using the sealed lead
acid batteries but the NIMH has many advantages . And yea, I know
price isnt one of them.
Thanks

On Fri, 05 Dec 2008 09:07:56 -0800, Mike wrote:

I purchased my batteries here;

http://www.battlepack.com/NICAD-Battlepacks.asp

I notice a lot of Sanyo single cells in their catalog. If those are
anything like their NiCds, they'll do me!


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

"Free Flight 107" wrote

The reason for not using Li chemestry cells is concern for possible
overheating, bursting of cells, and resultant "Very Energetic" fire
from the release of the Lithium inside the cells.

The Li-ion and LiFe (A123) chemistries are also suseptable to these
events, but because of the steel cases, like NiCad & NiMh, will resist
abuse better than LiPoly. In actual practice they still use
specialized charging and balancing circuits, and usually over-
discharging circuits, esp. in consumer devices such as Laptops and
Cameras.

I have seen reports of burned LiPo and also some LiIo batteries and I would
not use them in my glider (apart from the LiPo in every PDA, Cellphone, MP3
Player, ....). But I have never heard of any A123 cells starting a fire, and
there are modelers who did some serious abuse testing.

BTW, I take issue with; "Both LiFePO4 series (of batteries) are
claimed to be able to be charged on most standard lead
acid chargers (set for AGM/GEL cells)", unless a complete set of
charging and balancing circuity is included in the package. And at the
prices quoted, they really should be!!

I have balancing tabs on my LiFe packs and use both, a standard lead acid
charger and a microprocessor controled charger / balancer combination.
Either way the individual cells stay pretty closely balanced.

If you want to know how some people (mis-)treat their A123 packs google for
"zip charging A123" ...

Michael