Discharge behavior on hw-586 (zb2L4 clone?)

I hooked up 6of these boards and ran some cells through the discharge cycle, and have decidedat least 2 of the 6 need to be either calibratedor replaced because they are reporting almost .1v different than the actual voltage. (Issue #1)

I have run a few discharge cycles on these boards in the last day or so, and wanted to share what I am seeing and see if I am operating the board correctly.





I picked the 3 boards that read the closest to the actual cell voltage and set the discharge voltage to be 3.0v. Thisis the beginning of a discharge cycle with three Samsung 2600 series cells.

While I was making notes or taking pictures, I noticed the load resistors were already heating up (Issue 2), although I had not pressed OK to start the cycle.






So I hit the OK button, and took these photos to show the current at the start of the cycle, andat some point in the discharge.




A couple of temperature measurements during the cycle.

I did not take note of the time, but eventually the display was flashing rapidly indicating the end of the cycle.




I pressed OK and it shows the mAhcapacity measured. Anotherpress of OK shows the ending voltage.... NOT 3.0v (Issue 3).

I had noticed that the cells were not stopping on the desired voltage earlier, so I used the post-it note to remind me what the setting was.

Should the boards drain the cells to 3.0v or am I mis interpreting how to use these ?

Keep in mind that the Discharge voltage will always be lower than the Resting voltage. I'm pretty sure that the device stopped at, or very close to, the 3V during Discharge voltage reading. You said you didn't notice when they stopped. So it could of been seconds, minutes, or 10's of minutes. The longer the cell rests, the further it will drift from Discharge voltage and closer to Resting voltage.

You should do the test again, have a video cam pointed at them, and see when they stop. Not sure if the voltage displays during discharging, though. Maybe you can take a DMM and connect it to the cell during discharge to show the voltage.

However, all in all, great test setup there with all the units Maybe you could do a YT video of the demonstrations

Hi Korishan,
I checked the cells a few times during discharge with my voltmeter and the voltage was within a few mv of the voltage reported by the board as it ripples through displaying Ah, A, v during the test cycle.

I tried at least one run to get it to stop at 3.92 volts, but I could only set the board to stop at 3.9v, so i ran it and was pretty sure it did not produce the expected result. Its a drag having to document everything, but I cannot remember if it was low or high or if the that test was on one of the boards i replaced... sure will be glad to have a tester that logs everything for me.

I assumed the voltage would not increase after a cell discharges.

I have replaced the two boards that seemed to be out of spec, and loaded up 6 fully charged cells and set up the camera for an overnight run. I hope the battery pack holds up in my camera... its not an 18650

SecondHandPower said:

I assumed the voltage would not increase after a cell discharges.

I have replaced the two boards that seemed to be out of spec, and loaded up 6 fully charged cells and set up the camera for an overnight run. I hope the battery pack holds up in my camera... its not an 18650

Click to expand...

Yes, there is a load voltage (which I referred to discharge voltage as this was the test) and there's resting voltage. Obviously, you want these to be as close as possible as it helps to indicate a healthy cell. If you take a charged cell and put 1A load on it, you'll see it drop from, for example, 4.18V to 4.05V, or 4.11V. The 4.11V would be a healthier cell. Now, this can change over the voltage curve. So, the same cell that did .1V drop under load at full charge, may only drop .4V under load when at 80% SOC. It can vary. But that's primarily why we watch for other things to get a more accurate reading on the cell health.

It's time to upgrade the camera's power banks

I agree...the camera has a 800 mAh battery that lasts 70 minutes. I had totesttwo batches of cells to get my timing right for the video to capture the end of the discharge cycle.

I replayed the video and sure enough, the cells all went to 3.0v, then with the load removed, they showthe higher voltages.

So in my original post, issue #3 is related to me not being aware of how the loadinteracts with the tester and thecell... NOT any problem with thedischarge boards.

< I learned something today!>

The photos below are not the greatest, these arepictures of the small screen on my camera since my laptop is out for a thermal paste makeover. Sorry, no video, but these shots show the setup and each cell hitting ~3.0 v then after a few hours rebounding to a higher voltage.






Starting voltages, setting 3.0v for discharge






Shows a few of the cells reaching the discharge level after some time...






The capacity in mAh for this test, and the voltages after a few hours shows the cells had resting voltagesfrom 3.4vto 3.7v.

So the load is pulling the cell voltage down to the 3v threshold, but the resting voltage may be higher. Stronger cells have higher resting voltages after the load is removed . (?)

Welcome to the world of realization!

Yes, the stronger cells will bounce back higher after the low voltage discharge cutoff. The ones you have to be leery about are the cells that go from >4V, drop to 3.4V or lower under load (normal, not 10W or so), and then bounce back. They shouldn't drop that low under normal load. But if a cell gradually drops to 3.4-3V over a period of time, then rebounds shortly afterwards, that's a good one.
Now, that does not mean it will have >2000mAh capacity, or even 1500mAh. That all depends on a few other properties of the cell.

We want that video, dag nab it! Great job at the capture, tho

SecondHandPower said:

I agree...the camera has a 800 mAh battery that lasts 70 minutes. I had totesttwo batches of cells to get my timing right for the video to capture the end of the discharge cycle.

I replayed the video and sure enough, the cells all went to 3.0v, then with the load removed, they showthe higher voltages.

So in my original post, issue #3 is related to me not being aware of how the loadinteracts with the tester and thecell... NOT any problem with thedischarge boards.

< I learned something today!>

The photos below are not the greatest, these arepictures of the small screen on my camera since my laptop is out for a thermal paste makeover. Sorry, no video, but these shots show the setup and each cell hitting ~3.0 v then after a few hours rebounding to a higher voltage.






Starting voltages, setting 3.0v for discharge






Shows a few of the cells reaching the discharge level after some time...






The capacity in mAh for this test, and the voltages after a few hours shows the cells had resting voltagesfrom 3.4vto 3.7v.

So the load is pulling the cell voltage down to the 3v threshold, but the resting voltage may be higher. Stronger cells have higher resting voltages after the load is removed . (?)

Click to expand...

Stronger cells (with lower internal resistance) will have lower resting voltages after the test. Weaker cells with high internal resistance are hitting 3.0V sooner and resting afterwards higher.

Stronger cells = less bounce back...