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Some LiFePO4 Battery Testing Results Manual and Automated



 
 
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  #21  
Old October 16th 19, 11:05 AM posted to rec.aviation.soaring
krasw
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Posts: 520
Default Some LiFePO4 Battery Testing Results Manual and Automated

On Wednesday, 16 October 2019 05:44:35 UTC+3, 2G wrote:
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


1. BMS does the cutoff inside battery anyway
2. Voltage does not drop much with LFP
3. How is this relevant, most just want to know if their battery capacity is 10Ah or 7 Ah, not 9.998 Ah.
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  #22  
Old October 16th 19, 02:38 PM posted to rec.aviation.soaring
[email protected]
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Posts: 104
Default Some LiFePO4 Battery Testing Results Manual and Automated

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
  #23  
Old October 17th 19, 01:51 AM posted to rec.aviation.soaring
kinsell
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Posts: 243
Default Some LiFePO4 Battery Testing Results Manual and Automated

On 10/16/19 4:05 AM, krasw wrote:
On Wednesday, 16 October 2019 05:44:35 UTC+3, 2G wrote:
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


1. BMS does the cutoff inside battery anyway


Unfortunately, not all LFP batteries have a BMS, and of those that do,
not all have low-voltage cutoff. Of all the misinformation that gets
spead about on LFP's, that right at the top of the list.

Given how easy it is to add a low-side power switch, I wonder why you
would build an automated, computer controlled tester that lacks this.
Adding it would make it useful for a wide range of batteries.



  #24  
Old October 17th 19, 02:40 AM posted to rec.aviation.soaring
John DeRosa OHM Ω http://aviation.derosaweb.net
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Posts: 90
Default Some LiFePO4 Battery Testing Results Manual and Automated

On Wednesday, October 16, 2019 at 7:51:15 PM UTC-5, kinsell wrote:

Unfortunately, not all LFP batteries have a BMS, and of those that do,
not all have low-voltage cutoff. Of all the misinformation that gets
spead about on LFP's, that right at the top of the list.

Given how easy it is to add a low-side power switch, I wonder why you
would build an automated, computer controlled tester that lacks this.
Adding it would make it useful for a wide range of batteries.


Kinsell - You have me thinking now.

While both my Stark and Bioenno batteries has a BMS that cuts off at 10Vdc, it wouldn't be too difficult to add an Arduino relay shield to the mix. It could remove the load for non-BMS lithium batteries and for SLA's.

These shields contain four 3A 24Vac relays and cost about $4.50 (cheap! see https://www.ebay.com/itm/323801575423). The neat thing about these shields is that they stack and make a nice tidy package. I would have a stack of;

LCD Display
-----------
Relay Shield
-----------
Arduino

Once the battery charge drops to the low volt trigger point, I would remove the load (turn off the relay) from the battery via coding. One relay rated at 3A should be ok but I might use two relays in parallel to be sure.

I just ordered a couple of the relay shields and will report back.
  #25  
Old October 17th 19, 03:25 AM posted to rec.aviation.soaring
Charlie Quebec
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Posts: 226
Default Some LiFePO4 Battery Testing Results Manual and Automated

It’s 2G he has to whine and contradict people, it’s all he has got.
  #26  
Old October 17th 19, 03:56 AM posted to rec.aviation.soaring
2G
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Posts: 673
Default Some LiFePO4 Battery Testing Results Manual and Automated

On Wednesday, October 16, 2019 at 3:05:58 AM UTC-7, krasw wrote:
On Wednesday, 16 October 2019 05:44:35 UTC+3, 2G wrote:
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


1. BMS does the cutoff inside battery anyway
2. Voltage does not drop much with LFP
3. How is this relevant, most just want to know if their battery capacity is 10Ah or 7 Ah, not 9.998 Ah.


1. No, the BMS will not cutoff discharge - I know.
2. Relevant when comparing different battery chemistry's.
3. It's relevant when comparing lithium batteries to lead-acid.

As a former electrical engineer, I strove to minimize error sources as much as feasible because until you know the answer, you don't know which error is going to bite you in the butt. Nothing worse than having your glass panel go dark in the middle of nowhere because you under-estimated.

Tom
  #27  
Old October 17th 19, 03:58 AM posted to rec.aviation.soaring
2G
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Posts: 673
Default Some LiFePO4 Battery Testing Results Manual and Automated

On Wednesday, October 16, 2019 at 7:25:24 PM UTC-7, Charlie Quebec wrote:
It’s 2G he has to whine and contradict people, it’s all he has got.


CQ, go **** off...
  #28  
Old October 17th 19, 02:37 PM posted to rec.aviation.soaring
kinsell
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Posts: 243
Default Some LiFePO4 Battery Testing Results Manual and Automated

On 10/16/19 7:40 PM, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
On Wednesday, October 16, 2019 at 7:51:15 PM UTC-5, kinsell wrote:

Unfortunately, not all LFP batteries have a BMS, and of those that do,
not all have low-voltage cutoff. Of all the misinformation that gets
spead about on LFP's, that right at the top of the list.

Given how easy it is to add a low-side power switch, I wonder why you
would build an automated, computer controlled tester that lacks this.
Adding it would make it useful for a wide range of batteries.


Kinsell - You have me thinking now.

While both my Stark and Bioenno batteries has a BMS that cuts off at 10Vdc, it wouldn't be too difficult to add an Arduino relay shield to the mix. It could remove the load for non-BMS lithium batteries and for SLA's.

These shields contain four 3A 24Vac relays and cost about $4.50 (cheap! see https://www.ebay.com/itm/323801575423). The neat thing about these shields is that they stack and make a nice tidy package. I would have a stack of;

LCD Display
-----------
Relay Shield
-----------
Arduino

Once the battery charge drops to the low volt trigger point, I would remove the load (turn off the relay) from the battery via coding. One relay rated at 3A should be ok but I might use two relays in parallel to be sure.

I just ordered a couple of the relay shields and will report back.


Good, that would be a nice addition to your project. You can also
Google "low-side power mosfets" for a different option that takes less
power to drive. Probably available in a stackable module also.


  #29  
Old October 18th 19, 11:07 AM posted to rec.aviation.soaring
krasw
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Posts: 520
Default Some LiFePO4 Battery Testing Results Manual and Automated

On Thursday, 17 October 2019 03:51:15 UTC+3, kinsell wrote:
On 10/16/19 4:05 AM, krasw wrote:
On Wednesday, 16 October 2019 05:44:35 UTC+3, 2G wrote:
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


1. BMS does the cutoff inside battery anyway


Unfortunately, not all LFP batteries have a BMS, and of those that do,
not all have low-voltage cutoff. Of all the misinformation that gets
spead about on LFP's, that right at the top of the list.

Given how easy it is to add a low-side power switch, I wonder why you
would build an automated, computer controlled tester that lacks this.
Adding it would make it useful for a wide range of batteries.


I have built tester that uses coulometer and low voltage switch, I have a car tail light bulb as a load (10 or 20W). Parts for this can be bought from ebay for next to nothing. Search ebay for "battery coulometer" and "DC12V Battery Low Voltage Automatic Cut off Controller". You get automatically reading for your battery capacity. Mine can be installed between charger and battery so that you can also read how much capacity was charged.
  #30  
Old October 18th 19, 12:17 PM posted to rec.aviation.soaring
Tango Eight
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Posts: 801
Default Some LiFePO4 Battery Testing Results Manual and Automated

My latest $0.02 on topic...

Bought a Bioenno BLF-1209WS (9 AH rated) in August, and it delivered 10.2 AH on an Imax battery charger (discharge @ 400 mA). It was still at 12V when I terminated the test for reasons not related to the battery.

T8
 




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