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#31
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A Simple Question About LiFePO4 Batteries
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 |
#32
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A Simple Question About LiFePO4 Batteries
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? |
#33
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A Simple Question About LiFePO4 Batteries
On Thu, 17 May 2018 07:57:20 -0700, moshe.braner wrote:
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? If you're reasonably handy with a 'Junior hacksaw' or similar fine- toothed tool and with using rapid setting epoxy, then making a container with the same dimensions as the SLA you're replacing is fairly easy. Make it from 1/16" (1.5mm) epoxy plate), possible with hardwood of epoxy rod in the corners. If you can't find it locally, epoxy plate can be sourced from: http://www.cstsales.com/ -- Martin | martin at Gregorie | gregorie dot org |
#34
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A Simple Question About LiFePO4 Batteries
If you'd like to build your own, BatterySpace.com seems a good place to start.
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#35
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A Simple Question About LiFePO4 Batteries
The wasted space issue is overcome by using prismatic shaped cells, at least in the quality units.
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#36
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A Simple Question About LiFePO4 Batteries
Greg used two flat clear pvc plates for top and bottom hot glued the round cells, 8 I believe, in stagared with two end clear pvc and bms board large shrink tubing over it all for the long sides and . It has held up now for two seasons without problems. He also bought a battery welder to connect the cell together.
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#37
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A Simple Question About LiFePO4 Batteries
On Thursday, May 17, 2018 at 5:29:29 AM UTC-7, wrote:
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. This LiFPO battery shows a significant a temperature dependence of voltage: https://www.batteryspace.com/prod-specs/9055.pdf Basically, all chemical reactions are very temperature dependent. Tom |
#38
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A Simple Question About LiFePO4 Batteries
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 |
#39
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A Simple Question About LiFePO4 Batteries
Interesting - the discharge voltage goes down with lower temperatures - isn't that the opposite of lead-acid? At the least, lead-acid needs higher CHARGING voltages when it's cold.
How well does a microAir radio, which is finicky at low SLA voltages, do with a "12V" LFP battery, which offers a slightly higher voltage on the discharge curve? |
#40
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A Simple Question About LiFePO4 Batteries
On Friday, May 18, 2018 at 8:05:47 AM UTC-7, wrote:
Interesting - the discharge voltage goes down with lower temperatures - isn't that the opposite of lead-acid? At the least, lead-acid needs higher CHARGING voltages when it's cold. How well does a microAir radio, which is finicky at low SLA voltages, do with a "12V" LFP battery, which offers a slightly higher voltage on the discharge curve? I have a MicroAir and it works great with a LIFEFO4 battery. Richard www.craggyaero.com |
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