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.

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.

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.

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.

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

T8,

Thanks for the data point. To compare apples to apples it would be interesting to test connected to a 12ohm load as I did - not that 12ohms (~1A) is somehow perfection.

Thanks, John OHM