Some LiFePO4 Battery Testing Results Manual and Automated

On Thursday, April 18, 2019 at 11:09:51 PM UTC-4, kinsell wrote:
On 4/17/19 7:58 PM, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:

Luckily with the LiFePO4 batteries when they get below ~11.0Vdc the BMS basically shuts the battery off.
True for most of them, but some of them don't actually do that. Easy to
ruin the battery that way. If I were building a battery tester, I'd
include an automatic load cutoff.

The "B6" device will stop the discharge at 2V per cell. That's only 8 volts for a 4-cell ("12V") battery. That's rather low, although supposedly does not harm the battery. But you can cheat and tell it it's a 5-cell battery, then it will stop at 10V. Just remember to change it to 4 cells for charging!!!

A "12V" LiFePO4 battery in good shape will maintain above or close to 12V for almost all of its discharge curve, then plummet rapidly at the end.

On Wednesday, April 17, 2019 at 6:58:40 PM UTC-7, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
Every year I test my two LiFePO4 batteries to gauge how long they will last during a flight. I decided to open the field a bit and also tested some soaring friend's batteries.

You can read about my simple cheap manual process (later automated - see below) here http://aviation.derosaweb.net/#batterytest which was also detailed in Soaring (Feb 2012). Yeah, I know there are automated testers on the market but I want to create something cheap that everyone can make.

My battery go/no-go is how long it will take for the battery to drop to 12.0Vdc with a continuous 12Ω (~1A) resistive load. Here is what I found;

2013 Bioenno Model BLF-1209T- 6.5H
2015 Stark Model SP-12V9-EF - 5.5h
2015 Bioenno Model HN12V9AHF- 7.0H
2017 Bioenno model BLF-1209WS - 9.0H

Full details of my results can be found here http://aviation.derosaweb.net/batter...s_04.08.19.pdf

Anyone else tested their batteries in this same way? What are your results?

Automation - Manually gathering data every 10 minutes for 6-9 hours on four different batteries is tedious at best. I watched a lot of movies. So I decided to automate the process with an cheap $10 Arduino Duo. The Arduino software takes a reading at different points of time based on the current voltage. Every one minute at the beginning and end of the test, and every 10 minutes in the middle.

It still takes 6-9 hours to run the test but recording the voltages is fully automated so running the test is a start-then-walk-away-and-come-back-later-for-the-findings kind of deal. Luckily with the LiFePO4 batteries when they get below ~11.0Vdc the BMS basically shuts the battery off. The program detects any voltage drop below 8Vdc and terminates itself.

If anyone is interested in duplicating my Arduino test rig, drop me a line and I will share the details. My Arduino code can be found at http://aviation.derosaweb.net/batterytest/arduino.

John OHM Ω

It would be helpful to modify your spreadsheet to calculate watt-hours. Comparing batteries by amp-hour capacity was ok when using the same chemistry, but is not misleading when comparing SLA to LFP.

There is a marketing ploy among the LFP manufacturers called "equivalent SLA capacity." It turns out that they are using very high discharge rates (10C) to come up with this so-called "equivalent capacity." When WH capacities are compared at a more typical glider situation, 1C, the LFP has about a 7% WH advantage at the same AH rating.

The big advantage of LFP batteries is there slower aging characteristic. SLA batteries can drop precipitously after 2-3 years of use, far beyond any datasheets I have read. They *should* be good for 400-500 discharge cycles. This would be at least 10 years of typical, non-commercial glider flying. Only once have I seen SLA batteries last more than 4 years, and most are really shot by then (50% capacity).

I encourage more sharing of battery testing of this sort. It will help us get a better handle on this annoying technology which even the big boys hate (just ask Boeing).

Tom

On Sunday, April 21, 2019 at 1:56:13 AM UTC-4, 2G wrote:
On Wednesday, April 17, 2019 at 6:58:40 PM UTC-7, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
Every year I test my two LiFePO4 batteries to gauge how long they will last during a flight. I decided to open the field a bit and also tested some soaring friend's batteries.

You can read about my simple cheap manual process (later automated - see below) here http://aviation.derosaweb.net/#batterytest which was also detailed in Soaring (Feb 2012). Yeah, I know there are automated testers on the market but I want to create something cheap that everyone can make.

My battery go/no-go is how long it will take for the battery to drop to 12.0Vdc with a continuous 12Ω (~1A) resistive load. Here is what I found;

2013 Bioenno Model BLF-1209T- 6.5H
2015 Stark Model SP-12V9-EF - 5.5h
2015 Bioenno Model HN12V9AHF- 7.0H
2017 Bioenno model BLF-1209WS - 9.0H

Full details of my results can be found here http://aviation.derosaweb.net/batter...s_04.08.19.pdf

Anyone else tested their batteries in this same way? What are your results?

Automation - Manually gathering data every 10 minutes for 6-9 hours on four different batteries is tedious at best. I watched a lot of movies. So I decided to automate the process with an cheap $10 Arduino Duo. The Arduino software takes a reading at different points of time based on the current voltage. Every one minute at the beginning and end of the test, and every 10 minutes in the middle.

It still takes 6-9 hours to run the test but recording the voltages is fully automated so running the test is a start-then-walk-away-and-come-back-later-for-the-findings kind of deal. Luckily with the LiFePO4 batteries when they get below ~11.0Vdc the BMS basically shuts the battery off. The program detects any voltage drop below 8Vdc and terminates itself.

If anyone is interested in duplicating my Arduino test rig, drop me a line and I will share the details. My Arduino code can be found at http://aviation.derosaweb.net/batterytest/arduino.

John OHM Ω

It would be helpful to modify your spreadsheet to calculate watt-hours. Comparing batteries by amp-hour capacity was ok when using the same chemistry, but is not misleading when comparing SLA to LFP.

There is a marketing ploy among the LFP manufacturers called "equivalent SLA capacity." It turns out that they are using very high discharge rates (10C) to come up with this so-called "equivalent capacity." When WH capacities are compared at a more typical glider situation, 1C, the LFP has about a 7% WH advantage at the same AH rating.

The big advantage of LFP batteries is there slower aging characteristic. SLA batteries can drop precipitously after 2-3 years of use, far beyond any datasheets I have read. They *should* be good for 400-500 discharge cycles.. This would be at least 10 years of typical, non-commercial glider flying. Only once have I seen SLA batteries last more than 4 years, and most are really shot by then (50% capacity).

I encourage more sharing of battery testing of this sort. It will help us get a better handle on this annoying technology which even the big boys hate (just ask Boeing).

Tom

Yeah, batteries, a love-hate relationship, can't live without them, but they suck. One thing about capacities: if you fully discharge an SLA repeatedly it shortens its life (as measured in years). Thus a "9AH" SLA is really about 5AH, unless you don't care if you have to replace it in less than 2 years. (They are cheap enough that you may not care.) OTOH the LFP battery you can bring right down to where it shuts itself off and no harm done. So if it is honestly rated, a 9AH LFP truly has usable 9AH, perhaps 8AH after a few years. Just don't touch any LFP rated as "xxAH SLA equivalent", those are designed for starting motors (e.g., for motorcycles) and they are "equivalent" in cranking power (peak current) but not real AH (low current for hours).

Moreover, the voltage of the LFP stays higher (say well above 12V) for a much higher portion of its discharge cycle, then plummets. That means less warning about when it will run out, but meanwhile your radio transmissions will be good. An SLA gradually declines in voltage as it discharges, and some radios (and some other devices) may not work as well on, say, 11.7V.

Albeit most modern glider-oriented devices (e.g., varios) are designed to work normally down to 10V or so. Devices with internal switching power supplies draw more current when the supply voltage is lower, roughly a constant power draw (watts). E.g., I measured the current draw of a Portable PowerFLARM and it was roughly between 100 and 200 milliamps, depending on the supply voltage, the higher the voltage the LOWER the current (very unlike a light bulb). That's why an LFP, with its somewhat higher voltage, yields a longer run time than an SLA for the same amp-hours discharged.

On Sunday, April 21, 2019 at 6:48:38 AM UTC-7, wrote:
On Sunday, April 21, 2019 at 1:56:13 AM UTC-4, 2G wrote:
On Wednesday, April 17, 2019 at 6:58:40 PM UTC-7, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
Every year I test my two LiFePO4 batteries to gauge how long they will last during a flight. I decided to open the field a bit and also tested some soaring friend's batteries.

You can read about my simple cheap manual process (later automated - see below) here http://aviation.derosaweb.net/#batterytest which was also detailed in Soaring (Feb 2012). Yeah, I know there are automated testers on the market but I want to create something cheap that everyone can make.

My battery go/no-go is how long it will take for the battery to drop to 12.0Vdc with a continuous 12Ω (~1A) resistive load. Here is what I found;

2013 Bioenno Model BLF-1209T- 6.5H
2015 Stark Model SP-12V9-EF - 5.5h
2015 Bioenno Model HN12V9AHF- 7.0H
2017 Bioenno model BLF-1209WS - 9.0H

Full details of my results can be found here http://aviation.derosaweb.net/batter...s_04.08.19.pdf

Anyone else tested their batteries in this same way? What are your results?

Automation - Manually gathering data every 10 minutes for 6-9 hours on four different batteries is tedious at best. I watched a lot of movies. So I decided to automate the process with an cheap $10 Arduino Duo. The Arduino software takes a reading at different points of time based on the current voltage. Every one minute at the beginning and end of the test, and every 10 minutes in the middle.

It still takes 6-9 hours to run the test but recording the voltages is fully automated so running the test is a start-then-walk-away-and-come-back-later-for-the-findings kind of deal. Luckily with the LiFePO4 batteries when they get below ~11.0Vdc the BMS basically shuts the battery off. The program detects any voltage drop below 8Vdc and terminates itself.

If anyone is interested in duplicating my Arduino test rig, drop me a line and I will share the details. My Arduino code can be found at http://aviation.derosaweb.net/batterytest/arduino.

John OHM Ω

It would be helpful to modify your spreadsheet to calculate watt-hours. Comparing batteries by amp-hour capacity was ok when using the same chemistry, but is not misleading when comparing SLA to LFP.

There is a marketing ploy among the LFP manufacturers called "equivalent SLA capacity." It turns out that they are using very high discharge rates (10C) to come up with this so-called "equivalent capacity." When WH capacities are compared at a more typical glider situation, 1C, the LFP has about a 7% WH advantage at the same AH rating.

The big advantage of LFP batteries is there slower aging characteristic.. SLA batteries can drop precipitously after 2-3 years of use, far beyond any datasheets I have read. They *should* be good for 400-500 discharge cycles. This would be at least 10 years of typical, non-commercial glider flying. Only once have I seen SLA batteries last more than 4 years, and most are really shot by then (50% capacity).

I encourage more sharing of battery testing of this sort. It will help us get a better handle on this annoying technology which even the big boys hate (just ask Boeing).

Tom

Yeah, batteries, a love-hate relationship, can't live without them, but they suck. One thing about capacities: if you fully discharge an SLA repeatedly it shortens its life (as measured in years). Thus a "9AH" SLA is really about 5AH, unless you don't care if you have to replace it in less than 2 years. (They are cheap enough that you may not care.) OTOH the LFP battery you can bring right down to where it shuts itself off and no harm done. So if it is honestly rated, a 9AH LFP truly has usable 9AH, perhaps 8AH after a few years. Just don't touch any LFP rated as "xxAH SLA equivalent", those are designed for starting motors (e.g., for motorcycles) and they are "equivalent" in cranking power (peak current) but not real AH (low current for hours).

Moreover, the voltage of the LFP stays higher (say well above 12V) for a much higher portion of its discharge cycle, then plummets. That means less warning about when it will run out, but meanwhile your radio transmissions will be good. An SLA gradually declines in voltage as it discharges, and some radios (and some other devices) may not work as well on, say, 11.7V.

Albeit most modern glider-oriented devices (e.g., varios) are designed to work normally down to 10V or so. Devices with internal switching power supplies draw more current when the supply voltage is lower, roughly a constant power draw (watts). E.g., I measured the current draw of a Portable PowerFLARM and it was roughly between 100 and 200 milliamps, depending on the supply voltage, the higher the voltage the LOWER the current (very unlike a light bulb). That's why an LFP, with its somewhat higher voltage, yields a longer run time than an SLA for the same amp-hours discharged.

LFP batteries are not immune from accelerated degradation due complete discharge, but may be less affected than SLA. There has been a recent report about Nissan Leaf batteries losing 10% capacity per year:
file:///C:/Users/tom_s/Downloads/preprints201803.0122.v1.pdf
These cars used a nickel manganese cobalt chemistry, so is not directly applicable to LFP. I think we will have to collect the data as there is no upside for manufacturers doing it.

Most avionics are using switching power supplies, so we should be comparing batteries on the WH capacity, not AH. LFP manufacturers are using SLA AH-equivalent comparisons for energy storage applications, not starter batteries, which have markedly lower energy storage. Motorgliders are a somewhat unique situation where you would like to do both with the same battery.

Tom

Some updates;

- I was lent a Bioenno BLF-1209WS purchased in Jan 2019. Tested and ran for 8.8h.
- Updated my Arduino automated tester by adding an "LCD Keypad Shield" display to allow monitoring of the testing. The updated code has been uploaded..
- Created a new XLS spreadsheet to parse the automated testing results and create a graph from them
- Added pictures of my test rig.

Find all this, and more, at http://aviation.derosaweb.net/batterytest.

John OHM Ω

On Thursday, May 2, 2019 at 5:11:13 PM UTC-4, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
Some updates;

- I was lent a Bioenno BLF-1209WS purchased in Jan 2019. Tested and ran for 8.8h.
- Updated my Arduino automated tester by adding an "LCD Keypad Shield" display to allow monitoring of the testing. The updated code has been uploaded.
- Created a new XLS spreadsheet to parse the automated testing results and create a graph from them
- Added pictures of my test rig.

Find all this, and more, at http://aviation.derosaweb.net/batterytest.

John OHM Ω

I get 404 not found at http://aviation.derosaweb.net/batter...g_Template.xls and the other two as well. I do see the SOARING reprint, though.

On Thursday, May 2, 2019 at 2:11:13 PM UTC-7, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
Some updates;

- I was lent a Bioenno BLF-1209WS purchased in Jan 2019. Tested and ran for 8.8h.
- Updated my Arduino automated tester by adding an "LCD Keypad Shield" display to allow monitoring of the testing. The updated code has been uploaded.
- Created a new XLS spreadsheet to parse the automated testing results and create a graph from them
- Added pictures of my test rig.

Find all this, and more, at http://aviation.derosaweb.net/batterytest.

John OHM Ω

Congratulations on building a battery tester (I wouldn't bother, myself).

But here are the shortcomings of your tester:
1. It has no discharge cutoff. It keeps discharging the battery until totally discharged. This can damage the battery, and is certainly not good for it. I would not test a battery w/o this.

2. It does not discharge at a constant current. The current decreases as the voltage drops. Modern battery testers will do this.

3. It does not discharge at a constant wattage. This is a more typical scenario where avionics will increase current as the voltage drops.

That said, it is better than sitting down for 6 to 10 hours and recording meter readings. I have switched my avionics battery from a Pb to a LiFePO4 partly because I don't want to buy a new battery every 2 years.

Tom

John,

Thanks for the yearly update on how your batteries are ageing. It's nice to see what they do under constant test conditions. (I did get a 404 not found on your 2019 pdf file link?)

In (one of)2G's directions, the modern cockpit does have those pesky switchers. I wonder if an easy alternative load might be some 12 - 5v usb chargers with light bulb loads on the 5v side. The computer rig could watch V&I on the battery side and especially the time till the BMS says lights out.

Not all K2's are the same. I have 4 of 2 different ages. One of them seems a little more tired than the others. This prompted me to setup a more complicated rig.

Depending on that the VHF and transponder are doing, one K2 will keep my bus up for around 4 hours. I added a second in parallel with it thru a low drop diode. The hope was that this would keep the batteries from circulating current, and make it about 2x longer before lights out, and let me see the switchover as the bus drops 0.4v, and work with the SH battery in parallel wiring. So far, so good. It's lasted longer than I have without needing to switch to the third, get home battery.

One of these days, I need to get around to trying them with your test plan.

Thanks again,
Stu

Just a suggestion but you might want to look at the following.
https://www.skyrc.com/BD200

Allows you to set discharge current and cut off voltage. Displays consumed mAh over discharge period.

You do have to calculate the cut off voltage per battery type X cells in series. There are many articles (and debates) on safe dishcharge cutoff voltages for various lithium batteries chemistries on line so I am not going to make a suggestion as to cut off voltage.

I just wanted to suggest the above tool as I find it useful. I fly very large scale R.C. helicopters which use rather large battery packs at high discharge currents and I find the above very useful for analyzing my packs.
YMMV

The only reason for selecting 400 mA discharge is that is as much current as my little Imax RC battery charger can sink.

400mA vs 1 A is not quite apples/apples, agreed, but for LFP batteries it's going to be very close.

T8