Hi,
When people start talking of glider batteries I laugh at their logic. We
have a toy that cost anywhere between 2 - 10k and upwards to keep in the
air each year(not including getting to and from the airfield and
actually getting it in the air) and they are not willing to replace a
couple of batteries each year for well under a $100.
These fancy batteries may be ok but in the vast majority of gliders the
simple still works best and is cheap and safe.
Yes I do play with these fancy batteries in my radio control toys but
withgreat care and they are always stored in a lipo safe bag. You only
have to watch this video to agree
http://www.youtube.com/watch?v=mw8jb1KmAG8 yes I know the newer ones are
better but these are only small and look at how they go up and even the
newer ones can still have problems.
regards,
Arie
On 27/02/2013 12:52 PM, Future Aviation wrote:
Hello all
It just occurred to me that I have omitted to thank John Parncutt
for his research and his willingness to share the findings with us.
Of course, in this context Mike Borgelt's professional advice must
also be mentioned. Both contributions are extremely useful to many
of my gliding friends including myself. Many thanks to both of you!
Believe it or not, the last set of SLA batteries powering the engine
circuit in my ASH 25 lasted for 10 years. At the time I opted for the
most expensive SLA batteries I could get my hands on and now it appears
that the old saying holds indeed true. You only get what you ........
Kind regards to all.
Bernard Eckey
-----Original Message-----
From: aus-soaring-boun...@lists.internode.on.net
[mailto:aus-soaring-boun...@lists.internode.on.net] On Behalf Of Mike
Borgelt
Sent: Wednesday, 27 February 2013 11:22 AM
To: Discussion of issues relating to Soaring in Australia.
Subject: Re: [Aus-soaring] LiFePo4
As I said yesterday, do proper engineering on your battery installation.
If you don't have real numbers for temperature limits, discharge curves at
various rates, charging characteristics etc etc you aren't doing
engineering, you're just guessing.
A battery designed to start a racing motorbike and then be recharged by the
alternator and floated at that voltage likely has quite different
characteristics, design and longevity from one designed for charging and
deep discharging over several hours then recharging. You can also just stop
and get off the bike when the battery catches fire.
Li batteries all need individual cell monitoring during charge and use or at
least when charging after mostly charged.
The problem with Ni MH batteries is the number of cells (10 for a nominal 12
V system). You will have at least one weaker cell which will deep discharge
more than the others and will be undercharged or more likely the other cells
will overcharge resulting in reduced battery life. Individual cell
monitoring would help but with 10 cells vs 4 for Li it is a pain.
3 years isn't bad for a NiMH battery pack.
Some people have a problem with max weight of non lifting parts and a few
kilos saved may make the difference between flying in or outside the weight
and balance envelope. For these LiFEPO4 may be worthwhile but use the
correct cells.
The cylindrical Tenergy cells sold by these people have engineering data and
are Underwriter Labs tested. The tests are published there too. Start
here:http://www.all-battery.com/lifepo4battery.aspx
I've dealt with them and they did what they said they would.
Also these people may be of interest: The batteries seem to be the same as
the Tenergy cells but with a different colour outer sleeve.
They have battery monitoring/cutoff circuitry available also. You must use a
low voltage cutoff at least.
http://lithbattoz.com.au
The old sealed lead acid batteries are OK. They are heavier although in many
installations that may not matter. The capacity is usually quoted at the 20
hour rate. In modern gliders 1 amp continuous is not an unusual load so
that's the 7 hour rate. Likely it is a 5 A-H battery at this rate. Give it a
couple of dozen charge cycles and it is a 3 or 4 A-H battery and you begin
to have problems. Note also the number of cycles you get is non linear with
depth of discharge. Small % discharge you'll get lots of cycles. Large %
discharge many, many fewer cycles.
Size the battery to handle the longest flights and then use two batteries.
Use one routinely, keep the other charged then when the first battery dies
due to low capacity you have a known good battery.
Put that one in the first position then put a new one in the standby
position. You should always have a good battery available then.
If using some new type either learn enough to do an engineering analysis or
find someone willing to do one for you. Otherwise these things may get
needlessly banned or we have fires in gliders. It would be embarrassing to
explain to your insurance compny why you had to bail out of your burning
glider.
Mike
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