SLA batteries opinions?

On Wednesday, April 4, 2018 at 5:06:53 PM UTC-7, wrote:
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.

What happens is a short is way over the 15 amp max discharge current and the battery is damaged and gets hot but the BMS shuts it down at 10V before it burns.

12V 9Ah
Voltage: 12V
Capacity: 9Ah
Chemistry: LiFePO
Weight: 2.8lbs (1.3kg)
Dimensions: 5.9"(L) x 2.6"(W) x 3.7"(H), [151mm(L) x 65mm(W) x95mm(H)
Life Cycles: 2,000 @ 80% DOD
BMS YES (Internal)
Max Charge Voltage: 14.6V
Discharge Cut-off Voltage: 10V
Max Charge Current: 9A
Max Discharge Current: 15A
Operating Temperatu -22°F to +140°F, (-30°C to +60°C)


Richard
www.craggyaero.com









Richard

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 04/04/2018 04:04 PM, Richard Pfiffner wrote:
On Wednesday, April 4, 2018 at 2:31:07 PM UTC-7, kinsell wrote:
Wow. Didn't these batteries have a battery management system to prevent
damage?



On 04/04/2018 03:22 PM, Richard Pfiffner wrote:



John,

My experiences with LiFePO4

I have never heard of a LiFePO4 battery catching fire. I have had some customers connect reverse polarity. It burnt up the internal positive wire but the battery did not burn. I also just shorted a LiFePO4 12V10Ah turned it upside down and placed on a metal plate. It got hot and distorted the case near the contacts for the cells. It did not burn and was cool when I looked at it 1/2 hour later.

I had one supplier that gave me 24 Volt chargers by mistake. I charged one battery overnight and it got very large but did not catch fire.

Richard
www.craggyaero.com


I have found that BMS will not save a short.

Richard
www.craggyaero.com


A good short should bring the terminal voltage below 10 volts instantly,
strange the BMS didn't kick in before damage occured.

Also a bood BMS ought to prevent overcharging , which clearly didn't
happen with the 24 volt chargers. If I had a battery swell in my
ASH-26E, it would cause some significant damage.

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".

A fuse at the terminals is a necessary item, but that's not enough. Make
sure that the terminals are completely insulated against tossing
something metallic into the vicinity of the battery and having it fall
directly across the terminals.Â* The fuse won't help against that.

On 4/4/2018 9:36 PM, Eric Greenwell wrote:
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.Â* 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.


--
Dan, 5J

On Wednesday, April 4, 2018 at 10:16:45 PM UTC-7, kinsell wrote:
On 04/04/2018 04:04 PM, Richard Pfiffner wrote:
On Wednesday, April 4, 2018 at 2:31:07 PM UTC-7, kinsell wrote:
Wow. Didn't these batteries have a battery management system to prevent
damage?



On 04/04/2018 03:22 PM, Richard Pfiffner wrote:



John,

My experiences with LiFePO4

I have never heard of a LiFePO4 battery catching fire. I have had some customers connect reverse polarity. It burnt up the internal positive wire but the battery did not burn. I also just shorted a LiFePO4 12V10Ah turned it upside down and placed on a metal plate. It got hot and distorted the case near the contacts for the cells. It did not burn and was cool when I looked at it 1/2 hour later.

I had one supplier that gave me 24 Volt chargers by mistake. I charged one battery overnight and it got very large but did not catch fire.

Richard
www.craggyaero.com


I have found that BMS will not save a short.

Richard
www.craggyaero.com


A good short should bring the terminal voltage below 10 volts instantly,
strange the BMS didn't kick in before damage occured.

Also a bood BMS ought to prevent overcharging , which clearly didn't
happen with the 24 volt chargers. If I had a battery swell in my
ASH-26E, it would cause some significant damage.

The overcharging was a Stark Battery.

I will try the short on the famously expensive K2 battery today.

Standby for results.

Richard
www.craggyaero.com

On Thursday, April 5, 2018 at 10:52:17 AM UTC-4, Richard Pfiffner wrote:
On Wednesday, April 4, 2018 at 10:16:45 PM UTC-7, kinsell wrote:
On 04/04/2018 04:04 PM, Richard Pfiffner wrote:
On Wednesday, April 4, 2018 at 2:31:07 PM UTC-7, kinsell wrote:
Wow. Didn't these batteries have a battery management system to prevent
damage?



On 04/04/2018 03:22 PM, Richard Pfiffner wrote:



John,

My experiences with LiFePO4

I have never heard of a LiFePO4 battery catching fire. I have had some customers connect reverse polarity. It burnt up the internal positive wire but the battery did not burn. I also just shorted a LiFePO4 12V10Ah turned it upside down and placed on a metal plate. It got hot and distorted the case near the contacts for the cells. It did not burn and was cool when I looked at it 1/2 hour later.

I had one supplier that gave me 24 Volt chargers by mistake. I charged one battery overnight and it got very large but did not catch fire.

Richard
www.craggyaero.com


I have found that BMS will not save a short.

Richard
www.craggyaero.com


A good short should bring the terminal voltage below 10 volts instantly,
strange the BMS didn't kick in before damage occured.

Also a bood BMS ought to prevent overcharging , which clearly didn't
happen with the 24 volt chargers. If I had a battery swell in my
ASH-26E, it would cause some significant damage.

The overcharging was a Stark Battery.

I will try the short on the famously expensive K2 battery today.

Standby for results.

Richard
www.craggyaero.com

Need video :-).

T8

Ohhhh......lots of videos online for RC types that had an issue. Many thousands of dollars (US) went up in smoke.

Most BMS protect for charge issues, most won't prevent direct shorts at the battery or battery to load. That is why we do other fuses.
Breakers are "fine", but you typically melt/burn stuff just before they trip.

Yes, some radios play dead before hurting a LA battery, thus some add a single cell to boost voltage.
Yes, LiFe batteries tend to have a flat curve until the end, thus radios (especially when transmitting) work until the ragged end.

Your radio may be dead, other electronics may still work....at least....until you key your mic.

On Thursday, April 5, 2018 at 8:04:40 AM UTC-7, Tango Eight wrote:
On Thursday, April 5, 2018 at 10:52:17 AM UTC-4, Richard Pfiffner wrote:
On Wednesday, April 4, 2018 at 10:16:45 PM UTC-7, kinsell wrote:
On 04/04/2018 04:04 PM, Richard Pfiffner wrote:
On Wednesday, April 4, 2018 at 2:31:07 PM UTC-7, kinsell wrote:
Wow. Didn't these batteries have a battery management system to prevent
damage?



On 04/04/2018 03:22 PM, Richard Pfiffner wrote:



John,

My experiences with LiFePO4

I have never heard of a LiFePO4 battery catching fire. I have had some customers connect reverse polarity. It burnt up the internal positive wire but the battery did not burn. I also just shorted a LiFePO4 12V10Ah turned it upside down and placed on a metal plate. It got hot and distorted the case near the contacts for the cells. It did not burn and was cool when I looked at it 1/2 hour later.

I had one supplier that gave me 24 Volt chargers by mistake. I charged one battery overnight and it got very large but did not catch fire.

Richard
www.craggyaero.com


I have found that BMS will not save a short.

Richard
www.craggyaero.com


A good short should bring the terminal voltage below 10 volts instantly,
strange the BMS didn't kick in before damage occured.

Also a bood BMS ought to prevent overcharging , which clearly didn't
happen with the 24 volt chargers. If I had a battery swell in my
ASH-26E, it would cause some significant damage.

The overcharging was a Stark Battery.

I will try the short on the famously expensive K2 battery today.

Standby for results.

Richard
www.craggyaero.com

Need video :-).

T8

Video shows nothing battery gets hot and cuts out at I suspect about 10V.

Richard
www.craggyaero.com

On 04/04/2018 06:06 PM, wrote:
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.


The reason lithium batteries in all their flavors tend to have BMS
boards is that they are more sensitive to overcharge and overdischarge
problems. It's not good for SLA's to have that done to them, but but
they tolerate it much better than lithiums. Lithiums also generally
have problems with cell balancing, which is another task typically done
by the BMS. But you can't assume all bMS boards offer full protection,
RIchard's experiences tend to indicate otherwise.

For high-current batteries, disconnecting the terminals from the
internal cells is a tough problem, generally power transistors are used
to do the switching. Would you trust transistors to reliably handle the
current and voltage spikes created by a starter motor? I wouldn't.