A Simple Question About LiFePO4 Batteries

I have a friend that built several, 4 two for him and two for me 13.2 volt 11AH lifepo4 that used round cells and a bms circuit. for about $50 each that was the same size as the standard 12volt 7ah agm. They went with my Ventus but was a great system. Now I have to talk him into building a few more for my 27 although the 27 came with two lifepo4's one K2 and one bienno both look a few years old and have great capacity so far.

CH

On Tuesday, May 15, 2018 at 11:59:54 PM UTC-4, wrote:
I have a friend that built several, 4 two for him and two for me 13.2 volt 11AH lifepo4 that used round cells and a bms circuit. for about $50 each that was the same size as the standard 12volt 7ah agm. They went with my Ventus but was a great system. Now I have to talk him into building a few more for my 27 although the 27 came with two lifepo4's one K2 and one bienno both look a few years old and have great capacity so far.

CH

The first "actual" answer to the specific question - and it only took 20 some-odd messages to get it :-)

I took apart a commercially built "drop in replacement" LiFePo4 battery a couple of years ago, and my sense was that there was a bit of wasted space. I suspect the idea was to provide a capacity and footprint that was identical to the SLA batteries they replaced. I did the same googling when I was in the market, and I didn't find anything with significantly more than 10ah stated capacity in the same footprint.

FWIW, I run a load test of my LiFePo4s at the beginning of every season. My K2s currently show about 9.4-9.5 Ah at 0.1c discharge rate. What is remarkable is how flat the voltage drop is in comparison to the old SLA/AGM batteries. (Dick's post above shows a graph).

My K2s are both 4 years old. I did have one go south, but it was stored fully/deeply discharged after a long end-of season ridge mission. K2 gave me a partial credit for a replacement even though it was stored against their recommendations.

FWIW

P3

On Thursday, May 17, 2018 at 10:38:00 AM UTC-4, Papa3 wrote:
On Tuesday, May 15, 2018 at 11:59:54 PM UTC-4, wrote:
I have a friend that built several, 4 two for him and two for me 13.2 volt 11AH lifepo4 that used round cells and a bms circuit. for about $50 each that was the same size as the standard 12volt 7ah agm. They went with my Ventus but was a great system. Now I have to talk him into building a few more for my 27 although the 27 came with two lifepo4's one K2 and one bienno both look a few years old and have great capacity so far.

CH

The first "actual" answer to the specific question - and it only took 20 some-odd messages to get it :-)

I took apart a commercially built "drop in replacement" LiFePo4 battery a couple of years ago, and my sense was that there was a bit of wasted space. I suspect the idea was to provide a capacity and footprint that was identical to the SLA batteries they replaced. I did the same googling when I was in the market, and I didn't find anything with significantly more than 10ah stated capacity in the same footprint.

FWIW, I run a load test of my LiFePo4s at the beginning of every season. My K2s currently show about 9.4-9.5 Ah at 0.1c discharge rate. What is remarkable is how flat the voltage drop is in comparison to the old SLA/AGM batteries. (Dick's post above shows a graph).

My K2s are both 4 years old. I did have one go south, but it was stored fully/deeply discharged after a long end-of season ridge mission. K2 gave me a partial credit for a replacement even though it was stored against their recommendations.

FWIW

P3

Not sure how that answered the original question. But I am intrigued with the possibility of building my own pack. Not sure I'd trust that for flying, but perhaps for earthly pursuits. It's easy to wrap up the cells in a sloppy mess of tape. But can one get a ready-made casing that is similar to the SLA batteries? Or, can somebody with a dead LiFePO4 battery send it to me so I can put new cells inside?

The wasted space issue is overcome by using prismatic shaped cells, at least in the quality units.

On 05/15/2018 01:35 PM, wrote:
I got my simple answer about the apparently non-existent larger size LiFePO4 battery.

Regarding the ensuing discussion, I didn't go the LiFePO4 route a few years ago even though the sentiment at the time seemed to "it's a no brainer; just do it." The current sentiment seems to be a bit more nuanced, which is good to know. Thx, all, for the candid inputs.

Chip Bearden


Right, some people are discovering that comparing preposterously
optimistic data sheet numbers of lithium batteries against actual
performance of SLA's isn't a valid comparison. Not everybody of course.

On Wednesday, May 16, 2018 at 4:16:35 PM UTC-7, kinsell wrote:
On 05/15/2018 01:35 PM, wrote:
I got my simple answer about the apparently non-existent larger size LiFePO4 battery.

Regarding the ensuing discussion, I didn't go the LiFePO4 route a few years ago even though the sentiment at the time seemed to "it's a no brainer; just do it." The current sentiment seems to be a bit more nuanced, which is good to know. Thx, all, for the candid inputs.

Chip Bearden


Right, some people are discovering that comparing preposterously
optimistic data sheet numbers of lithium batteries against actual
performance of SLA's isn't a valid comparison. Not everybody of course.

Some valid comparisons on this page;

http://www.craggyaero.com/lifepo_battery.htm

Richard
www.craggyaero.com

My observations were purely subjective:Â* With SLA batteries, I would run
out of power in 3-5 hours.Â* With LiFePO4 batteries, my volt meter still
showed good voltage after 5 hours.Â* No hard numbers, I know, but I got
the performance that I required.

On 5/16/2018 5:16 PM, kinsell wrote:
On 05/15/2018 01:35 PM, wrote:
I got my simple answer about the apparently non-existent larger size
LiFePO4 battery.

Regarding the ensuing discussion, I didn't go the LiFePO4 route a few
years ago even though the sentiment at the time seemed to "it's a no
brainer; just do it." The current sentiment seems to be a bit more
nuanced, which is good to know. Thx, all, for the candid inputs.

Chip Bearden


Right, some people are discovering that comparing preposterously
optimistic data sheet numbers of lithium batteries against actual
performance of SLA's isn't a valid comparison.Â* Not everybody of course.



--
Dan, 5J

I want to concur with Dan.
I fly out of Minden and we cruise between 15,000 and 17,999. It is COLD at that altitude.
My lead batteries would lose voltage as the temp dropped. After three hours at altitude they were lucky to put out 11 volts. Of course, when the batteries warmed up alter landing they had full voltage.
The LiFePO4 batteries do not seem to affected by cold soak. They work the whole flight at full voltage.

However, I can't find a LiFePO4 equivalent for it. Does such a thing exist?

How about this one?

https://www.batteryspace.com/lifepo4...assed-dgr.aspx

On Friday, May 18, 2018 at 8:24:11 AM UTC-4, wrote:
However, I can't find a LiFePO4 equivalent for it. Does such a thing exist?

How about this one?

https://www.batteryspace.com/lifepo4...assed-dgr.aspx

YES, that's the size!!! Don't know what I couldn't find this anywhere. Don't recognize the brand name but that's not necessarily an impediment. Anyone have experience with Powerizer, specifically their LiFePO4 batteries?

Chip Bearden