I wanted to see the dragon eye back light of the Manker MK34 in red, meaning battery is low. So I used the flashlight until the back light changed from purple to red. Then I just left the light with the red back light for a couple of days to enjoy the sight of it. An hour ago I decided to charge the batteries again. Two cells were exactly 3.084V, but the third one was 3.424V. Seriously what?
Although it shouldn’t matter I use Manker wrapped high drain cells (Sanyo NSX). How on earth is it possible that all three cells are not equal in voltage in this state?
They went in @ what charge? Are the cells “matched”?
I got the three cells out of the light at different voltages (before charging) after using the light only with back light on for less than a week. A couple of weeks ago I used the light with freshly charged 4.20 cells. The three cells are matched, however this shouldn’t matter I believe. 3P should result in identical voltages and that is not the case.
Edit:
Even if you have three different cells all at three different voltages, the end voltage of all three cells should become identical after a while in a parallel configuration.
It should indeed result in the same voltage across all 3 the cells.
Maybe if one or more cells have different internal resistance it can be different?
only if the cells have different internal resistance to get em off the flashlight with different voltage you need to run the flashlight on a very high mode
and then while the light is running pull the batteries from the flashlight
as soon as you turn out the light the 3 batteries in parallel get to their resting voltage, so the one with higher resistance has a bit higher voltage, so this bad cell starts to charge up the 2 better cells and the voltage evens out after a short time
That is for example if one of the cells is like a NCR18650B instead of UR18650NSX (=actual cell). But I think this shouldn’t matter. It’s like water going from a higher level streams to lower level. That’s the case with electrons moving from higher voltage to lower voltage. The amount of (internal) resistance only alters how fast (current) the electrons move. Eventually steady state is achieved where there is no voltage difference. The three cells were in the MK34 with only the back lit button on for extreme low current draw for about three or four days, which is plenty of time for the three cells to have identical voltage…
+1
That’s the way I see it too.
Well I’m just going to put back the cells back in the light, everything switched off, and let’s see what happens in a couple of hours.
Edit:
One hour later I checked voltages again. All three cells are 3.308V. Apart from the value, this is what the cells are supposed to do. The dangest thing: the back lit button is purple again now. Apparently 3.3V results in purple, so when the back lit button was red it was reading 3.1V from the two cells instead of 3.4V.
Really odd…
It wasn’t bounce back?
The 3,4V was not the last you measured?
3.4V was the voltage of only one cell an hour ago. The two others were 3.1V. I put them all back in the MK34, and an hour later (did not use the light), all cells were equaled to 3.3V.
The latter is normal, and is what’s supposed to happen. But the question is how on earth I got different values to begin with…
you measured after letting them all rest for a while?
The initial values of 3.1V and 3.4V I got when I just took them out of the light. However, I haven’t used the light (strained the cells) in two weeks time: only the backlit button was on, so the current was very low. After I read the measurements, about an hour later, the voltage increased (bounced) just a bit to my surprise by a couple of thousandth of Volt. But the voltages roughly remained the same, as well as the difference.
There may be some voltage bounce, but I don’t think this explains the difference in voltages.
That cell could be damaged, or having bigger resistance then other two, I’ve seen this before with some older cells that have big internal resistance, after discharging them to the point where flashlight start to blink or shows red warning, measured voltage shows 3,7V…
If you could check that out you might have a clue?
One cell was not making contact and when you took them out then put them back in it did make contact?
Cheers David
That’s indeed how it should work.
I thought that he had used the light prior to the measurement, so in that case a different ir could result in a different voltage reading.
But you haven’t used the light for a long time before measuring the voltages, so the cells should be equal.
And now, after putting them back in they all read the same?
Could it be a faulty connection? (Like pommie said)
I understand this behaviour, but this should not be the case here as explained by Lexel in post #5
This is very plausible. But this never happened before. I checked cell height, and all cells stick out of the battery tube equally, and also sufficiently for good compression when battery tube is tightened.
I have observed for some time a bit of gunk on the positive side of the cells. I have always thought it was residue from the grease on the driver cathode for lubrication purpose. This also means that this grease should conduct electricity. Maybe this is not the case, and the more this grease oxidises, the more electrical resistance it creates?
This situation is correct. Somehow a connection problem seems most logical…
I think I’ll just have to monitor my light more closely; check whether it’s the same cell or bay etc…
Clean that gunk and check the welding of the springs
I was thinking about leaving everything as is, and then “hope” problem will repeat… But eventually I will clean it for sure.
It seems to me that one cell is making poor or intermittent contact. My guess would be a partially collapsed spring or a cold solder joint at one spring.
Spring height for all three cells are identical. Poor contact of a spring is easily traceable, as the cell with higher voltage will occur in that bay only. And I will monitor this as well.