Conflicting Battery Readings...

[AeroJ]

Getting some contradictory readings during the latest charge of one of my Yuneec H battery packs.

Balance charger reads cels as:

4.20, 4.20, 4.17, 4.18.

Yet if I stop that balance process, when I connect one of those little LED pinout voltage reader jobbies, that tells me we have:

4.19, 4.20, 4.19, 4.27

Which one would you believe, and do you think that over-voltage on cel 4 is anything to worry about ?

Thanks

 

[Steve Carr]

You can check each cell with a digital voltmeter which might show more repeatable readings. The batteries should sit for a few hours before checking the cells.

 

[AeroJ]

Thanks Steve. Alas, I don't have one of those.

Now I've completed the balance charge, all 4 cells reported 4.2 there, but after an hour of resting the plugin reader is giving me
4. 20, 4.20, 4.22, 4.27.

Would you say that's within 'reasonable tolerances' for a safe flight ?

 

[BobW55]

How old is the battery?
Does your charger also give you the resistance of each cell?

 

[AeroJ]

The battery in question has done 54 cycles, never been flown past 14.7V, and has been kept at storage charge levels between flights. However, due to an order delay of the adapter cables, the first 40 of those charge cycles were done using the included charger.

My balance charger doesn't give me cell resistance unfortunately.

I don't know whether this has any bearing on things, but I have just got this battery back from Yuneec, which I sent to them after it did some very weird behaviour on the last charge cycle.
On that occasion all cells balanced to 4.20 except number 4 which got to 4.19, stayed there for a little while, then inexplicably dropped backed to 3.73 volts and wouldn't go higher than that. So, after some additional reading I discharged all cells at 0.2 amps until they were even, then tried rebalancing them over 5 hours also at 0.2 amps. This seemed to work initially, but then again, cell 4 would drop to 3.73 as the balance cycle neared completion. So I sent it back to Yuneec, who said they couldn't find a problem, and returned it to me, at which point tonight's charge appears to have worked as expected, apart from the minor deviation that is the reason for this post...

 

[Steve Carr]

Thanks Steve. Alas, I don't have one of those.
Now I've completed the balance charge, all 4 cells reported 4.2 there, but after an hour of resting the plugin reader is giving me
4. 20, 4.20, 4.22, 4.27.
Would you say that's within 'reasonable tolerances' for a safe flight ?

I suspect the little tester may be reading cell 4 incorrectly unless you can verify readings taken on other batteries seem correct.
A digital voltmeter from Walmart is inexpensive.

https://www.walmart.com/ip/Electric...r-Volt-OHM-Tester-AC-DC-Multi-Meter/930440347

 

[DoomMeister]

What kind of readings do you get on other batteries with the “LED plugin thingy”? As well as readings on your balance charger with other batteries?

 

[PatR]

Very good call, Doom. First determine the relative differences between devices across a spread of batteries before making a conclusion, not with just one battery. Ideally a calibrated VOM would be included in the comparison process but as calibrated tools are expensive few will have one. A relatively new VOM will do.

If the battery is being checked after cooling down from the charge cycle my only concern would be why the same battery went from having a weak cell to having a strong cell. Lipo’s don’t cycle like nicd’s and limh batteries do so the slow discharge in an attempt to break a memory should have not changed anything.

The cell voltages for the battery are all within 1/10v of each other, which is good. I seriously doubt the one being 7/100v over 4.2 is of any significance as we’re dealing with Chinese manufacturing across the batteries, charger, and measurement devices when tolerance ganging is highly suspect.

 

[DoomMeister]

Very good call, Doom. First determine the relative differences between devices across a spread of batteries before making a conclusion, not with just one battery. Ideally a calibrated VOM would be included in the comparison process but as calibrated tools are expensive few will have one. A relatively new VOM will do.

If the battery is being checked after cooling down from the charge cycle my only concern would be why the same battery went from having a weak cell to having a strong cell. Lipo’s don’t cycle like nicd’s and limh batteries do so the slow discharge in an attempt to break a memory should have not changed anything.

The cell voltages for the battery are all within 1/10v of each other, which is good. I seriously doubt the one being 7/100v over 4.2 is of any significance as we’re dealing with Chinese manufacturing across the batteries, charger, and measurement devices when tolerance ganging is highly suspect.

I agree with your layers of tolerance Pat. Even quality digital multimeters can be difficult to adjust to metrology standards. I spent time in metrology labs in both the Air Force and at AC Sparkplug (being a government contractor requires meeting higher quality standards). That aside, a decent quality multimeter will give you a better idea as to the true status of your readings.

 

[PatR]

Completely agree. I would have some doubts about the cheapest units from Harbor Freight but any of the quality brand names from hardware or electronics stores would be plenty close enough.

 

[AeroJ]

What kind of readings do you get on other batteries with the “LED plugin thingy”? As well as readings on your balance charger with other batteries?

I have checked the other 2 battery packs I have, which seem largely consistent when measured the 2 different ways. There is around 0.05v variation. As the 4.27 reading on the original pack is only slightly out of that range, and taking into account what you've all said I think that'll probably be fine, although I will keep an appraising eye on it for the next several charge cycles.

Thanks for the info everyone

 

[AeroJ]

OK, disaster has struck, but hopefully I am a bit closer to finding the answer... so just posting again to check you concur with my findings...

Since I moved from the Yuneec Charger to my old B6D clone balance charger about 10 cycles ago, my problems have started. After some successful charges, with some slightly odd readings on cell 4 as detailed above, now all 3 of my packs won't charge cell 4 past 3.73 volts. The one I returned to Yuneec was tested by them, found to be fine, and returned to me with an equal storage charge on all cells. That did 1 successful charge on the balance charger, but now exhibits the same problem as the rest of them.

If I check these batteries in the Yuneec charger, they all do a very specific error; one red light, then 4 greens and intermittent beeping. So now the balance charger is getting the full weight of my suspicion. Just checking this sounds to you too like what has gone wrong...

Thanks

 

[DoomMeister]

Sounds like it’s time for a new balance charger. What is very odd is that it thinks you are at full charge at what would be considered 0% to 1% capacity. You may have bad contacts for cell 4 and the lack of current draw may be signaling full charge capacity.