Battery status

[Offroader]

I have a couple of batteries that have a few score flights on them but they show yellow on their voltages when viewing in @msinger's LogViewer. Voltages are at or below 3.5V.

Question is: how low does a cell have to go before I have problems?

PhantomHelp LogViewer

 

[With The Birds]

I have a couple of batteries that have a few score flights on them but they show yellow on their voltages when viewing in @msinger's LogViewer. Voltages are at or below 3.5V.

Question is: how low does a cell have to go before I have problems?

PhantomHelp LogViewer

At what % capacity are you seeing 3.5V. How far out of balance are the cells? What flight time are you getting compared to when new? What is the current reported capacity and life %? In the absence of more detail it’s hard to know if you have a problem.

 

[Offroader]

34% remaining, about 14.5 minutes into the flight (near the end). Cell deviation is between .045 and .08 V. There are times during the flight where all 4 cells are below 3.5V. Holding the power button down for 5 seconds shows 2 LEDs on, 1 flashing, one off.

Probably time to retire this one.

 

[With The Birds]

From memory that LED sequence suggests 70%+ remaining life. Balance and flight time seems good. No real issue here. Retire why?

 

[solentlife]

3.5V per cell when rested is too low for storage - that's first item. Storage voltage range is 3.7 - 3.85V per cell ...

It is not unusual in flight when heavy demand comes on - that a battery dips much lower than it would when not loaded or light demand. As the flight battery depletes in flight - the voltage drop per action increases as it still has to supply the watts per that action. Its a vicious circle. Demand for xx watts ... but battery is part discharged ... means amps are increased to compensate. This then gets Internal Resistance fighting it and voltage drop increases ... amps go up to compensate ...

As batterys get near to discharged level - they really do have a very hard time of it.

As WTB says .. why retire it ? The indicator to say retire or not really comes down to flight duration ... if you are still getting reasonable flight times - then why retire ?

Viewers of data are great tools IF you understand the data they give you. Sorry to say ... but too many people pick up utilities from forums / online etc and then are worried because they have not the understanding.

 

[Waylander]

Hi offroader
If I remember correctly, I thought there was a deep discharge routine, where cells could be re-balanced, try this link there is some discussion on the topic.

CRITICALLY LOW POWER AT 35%

Waylander

 

[Offroader]

The reason for my concern is that I had a battery fail where cell 1 went bad over time and the AC quit running and fell to the ground. I have been keeping the flight logs tagged with the battery number (I have all my batteries labeled) and store them with the videos/pictures so I can monitor their performance. After the failure, I went back and reviewed the logs for that failed battery and could see the degradation during each flight.

Now, whenever I see this kind of indicator, I get freaked out. This is why I want to know what the safe low cell voltage was.

As far as retiring the battery, I have more confidence in it, just take it easy and keep the flights short with this one. I have 5 much more reliable batteries for the longer flights.

Thanks for the input.

 

[solentlife]

Hi offroader
If I remember correctly, I thought there was a deep discharge routine, where cells could be re-balanced, try this link there is some discussion on the topic.
Waylander

LiPo's should be balanced at full charge level for good reason. There is ZERO evidence that a DJI battery balances in deep discharge - its a myth that gets repeated and so becomes 'accepted fact'.
Deep discharge does nothing except reset capacity counter. It does not recover any capacity whatsoever.
All that happens is that the counter which has got out of step is re-aligned. In fact capacity never changes - except when physical change or damage occurs to cell or cells. What does happen is that when Internal Resistance increases with age and us of the battery - its flight time reduces due to the extra work to overcome this internal resistance causes higher voltage drop.

OK ... back to balancing. All reputable LiPo chargers do balancing at full charge level. Very good reason for this. Balancing involves bleeding off the higher charged cells till they all are similar. Charger then shoots another charge burst in ... checks balance and bleeds again if necessary ... this is a repeated cycle until charger detects common levels.
If its done at deep discharge level - it can result in damaged cell or cells ...

The DJI charge control board has another way to try and correct inbalance but in reality is not a good way to do it. As the battery charges - it monitors the cells and trys to alter each cells charge rate to arrive at balanced full charge. Unfortunately this same board detects a full total voltage and shuts off BEFORE any real balancing can take effect. That full voltage could be unbalanced cells that total the 17.4V required.
Usually the board does manage to keep cells reasonably in step - but as they age and gets harder - the board will not keep up with it. You can get a short reprieve by deep discharge and charge up full - this gives charger opportunity to try balance through a longer charge run ... but its a temporary item and will soon revert to unbalanced again.