SLA batteries opinions?

At 20:25 04 April 2018, jfitch wrote:
On Wednesday, April 4, 2018 at 12:00:07 PM UTC-7, Chris Rowland wrote:

The reservation about Lithium based batteries I have is their tendency
to
catch fire. I realise that this depends on the chemistry and
manufacture
but there have been enough instances of this that I'd be inclined to be
cautious unless the reduced mass and increased energy density is
essential.

Please relate to us the stories (with backup links) about - specifically
-
=
LiFePo4 batteries catching fire in gliders - or other similar
applications.


The more literate members of this forum will notice that I said "Lithium
based" and "this depends on the chemistry and manufacture".

A couple of links a
http://ul-segelflug.de/images/storie...017_G-GSGS.pdf

and

https://assets.publishing.service.go...-AOP_09-15.pdf

and

https://www.caa.co.uk/Commercial-ind...ium-batteries/

An experiment to try is to short out a fully charged battery and see what
happens. Wait until everything is cool and think if you want to be around
it.

Chris

Chris Rowland wrote on 4/4/2018 2:30 PM:
An experiment to try is to short out a fully charged battery and see what
happens. Wait until everything is cool and think if you want to be around
it.
For a complete study of battery chemistries, you could also try shorting an SLA
battery. They can also cause problems, and that is one reason a fuse at the
terminals is so useful.

Anyone that intends to try the "short" should probably do a YouTube search first:
all the excitement without the fire, smoke, and destroyed battery.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

On Wednesday, April 4, 2018 at 2:45:06 PM UTC-7, Chris Rowland wrote:
At 20:25 04 April 2018, jfitch wrote:
On Wednesday, April 4, 2018 at 12:00:07 PM UTC-7, Chris Rowland wrote:

The reservation about Lithium based batteries I have is their tendency
to
catch fire. I realise that this depends on the chemistry and
manufacture
but there have been enough instances of this that I'd be inclined to be
cautious unless the reduced mass and increased energy density is
essential.

Please relate to us the stories (with backup links) about - specifically
-
=
LiFePo4 batteries catching fire in gliders - or other similar
applications.


The more literate members of this forum will notice that I said "Lithium
based" and "this depends on the chemistry and manufacture".

A couple of links a
http://ul-segelflug.de/images/storie...017_G-GSGS.pdf

and

https://assets.publishing.service.go...-AOP_09-15.pdf

and

https://www.caa.co.uk/Commercial-ind...ium-batteries/

An experiment to try is to short out a fully charged battery and see what
happens. Wait until everything is cool and think if you want to be around
it.

Chris

These incidents have nothing to do with LiFePo4 batteries. Plenty of fires from SLA batteries as well, which also have different chemistry.

Regarding a BMS - this is similar to saying "lithium battery". There is a wide variety of things called a BMS, some have overcharge and/or undercharge protection, some have cell balancing, some have high current disconnects, some have more than one, or all of these facilities.

Technology is getting more complicated these days folks. Let's not throw the baby out with the bathwater by terming it all "washing".

On Wednesday, April 4, 2018 at 1:25:55 PM UTC-7, jfitch wrote:
On Wednesday, April 4, 2018 at 12:00:07 PM UTC-7, Chris Rowland wrote:
A few things about SLA batteries.

The capacity is usually defined when discharged at the C/20 rate - so for a
7Ah battery 350 mA for 20 hours. The capacity at higher rates is reduced.
If you try to take 1.4A out of a 7Ah battery it won't last 5 hours.

I have found that if you treat them well they last well. Treating them
well means not to over discharge them, or overcharge them, and to recharge
them as soon as possible.

I have had good results with a simple constant voltage charger, charging to
13.6V. This seems to be enough to recharge them overnight. I've had
batteries last for 5 years or more.

The trick is to look at your energy budget, how much current do you need?
For a fairly simple system, a LX7007 (260 mA), a radio (200 mA) and a nav
device (200 mA), that's about 7 Ah in 10 hours. That lot should run off 2
7Ah batteries with no trouble. If you have higher demands then install
enough capacity that you only use 50% on the average day's flying.

The reservation about Lithium based batteries I have is their tendency to
catch fire. I realise that this depends on the chemistry and manufacture
but there have been enough instances of this that I'd be inclined to be
cautious unless the reduced mass and increased energy density is
essential.

And regardless of what chemistry your batteries use and what other things
are in place put a fuse in the battery lead close to the battery. All
batteries have enough capacity to produce an entertaining amount of acrid
smoke in the cockpit if you get a short.

Chris


At 14:40 04 April 2018, Dan Marotta wrote:
I have to ask, then:Â* Why keep putting SLA batteries in your glider?Â* Do

you need them for weight and balance?Â* Why not just two LiFePO4?

My experience with the lithium batteries was nothing short of terrific..Â*

Prior to the switch, I couldn't power everything with two SLA batteries
for 5 hours (15 AH combined).Â* After switching (10 AH LFP), I never had
a shortage of power.

On 4/3/2018 9:05 PM, wrote:
I have flown with both an LFP and SLA battery in my ship for 5 years..
I
alternate which one is primary and which one is secondary on each flight.

A PowerSonic 12V14Ah SLA vs Powerizer 12V15Ah LFP. With all my
instruments
running the SLA voltage drops below the minimum requirements of my radio
by
5 hours. My LFP has never failed to power everything up to a 7 hour
flight. The SLA gets replaced after 3 years. My LFP is six years old
and
still working perfectly.

When I fly in very cold conditions (0C) the SLA is usually not driving
my
radio by three hours. Again, the LFP has run up to six hours without any
significant voltage drop.




--
Dan, 5J


Please relate to us the stories (with backup links) about - specifically - LiFePo4 batteries catching fire in gliders - or other similar applications.

r.a.s. is powered by lithium.

On Wednesday, April 4, 2018 at 7:16:02 PM UTC-4, Darryl Ramm wrote:
r.a.s. is powered by lithium.

- you mean the type that comes in pills? :-)

Regarding the other messages, I am surprised that the BMS does not protect from a short, I thought that was one of the stated protections officially promised. And that BMS was one major advantage of the (better) LiFePO4 batteries over SLA.

On Tuesday, April 3, 2018 at 10:12:41 PM UTC-4, Richard Pfiffner wrote:
On Monday, April 2, 2018 at 10:47:02 PM UTC-7, krasw wrote:
tiistai 3. huhtikuuta 2018 2.16.45 UTC+3 kirjoitti:
The theoretical number of times the batteries of each type can be cycled is irrelevant if they will die of old age in a number of years, even if that's 10+ years for LiFePO4 and only 3-4 years for SLA in my use.


In my experience lifetime of LFP is not better than SLA. My first battery died completely in 6 months, second had much reduced capacity after 2 seasons. Idea that chinese LFPs last thousand cycles or decade is just false.

In my experience LFP batteries are much better than SLA and deliver close to the label AH for many cycles. And if you drop them on your foot is does not hurt as bad.

Richard

Richard

What if we want to drop it on Herb's foot?
Chris

As seen on a late night TV talk show: The top reasons for using SLA/AGM batteries in gliders.
.. As tail ballast.
.. To maintain the "cheap" glider pilot stereotype.
.. Wir haben es immer so gemacht.
Jim