HOW TO: Monitor battery voltage to watch for signs of failure

[msinger]

So say Im storing for an extended period of time. like say 7-21 days or longer..
Should I always go at like 40%-50%? Or is 30% ok?

30% is the minimum recommended battery storage level. If the battery is at 30% and you're going to fly in the next week, then I'd store it as-is. For long-term storage, charge the battery until the 3rd light starts blinking before storing it.

 

[GadgetGuy]

To clarify an earlier post, the auto-discharge feature does so without any rebalancing of the cells during the process, and large variations in cell voltage are common. This is why all batteries should be topped off just prior to flight. Doing so properly rebalances all the cell voltages so no one cell is lower than the others, as happens during the auto-discharge. If any one cell is lower than the others, the remaining battery percentage calculation will be wrong, and the battery will shut off in midflight, any time that lowest cell drops below 3.0V! This can happen, even if the remaining battery percentage displayed at launch is 87%! Simon says, "Top off your batteries before flight, if they have been stored for more than a day!"

 

[RedHotPoker]

Yup, I firmly believe that anytime you are going to be flying, top up them intelligent flight batteries. Before I left for my destination on Tuesday, I spent the time to have all four of my batteries fully charged. It gives me a certain confidence, and takes away any doubt I would have, when taking off on lower than 98% of available voltage capacity.

For the short time it takes, it may pay off huge benefits, someday.

RedHotPoker

 

[Vertigo]

OP would be even more useful than it is, if it expanded a little on lipo discharge curves and voltage sag, so people unfamiliar with lipo's get a better understanding of what these voltages actually mean. For reference, a typical lipo discharge curve (not of a phantom):

A phantom 3 can hover for ~20 minutes, so that would be a ~3C load. that shows you that 3.4V while hovering, is really cutting it close. Full throttle climb, I would guess is closer to 10C or 15C.

 

[Mocho]

It's important to monitor the battery voltage in each cell of the DJI smart battery. Be aware of the following:


4) Your battery will shut off mid-flight if the voltage drops below 3.0V.

Just to be clear, your saying that if any given cell hit's 3.0v the battery will shut off.

TIA

 

[msinger]

Just to be clear, your saying that if any given cell hit's 3.0v the battery will shut off.

That's correct. The Phantom should auto land before that happens, but you can override the auto landing by staying on the sticks. That'll eventually allow the battery to drain down to 3.0V.

 

[GadgetGuy]

Just to be clear, your saying that if any given cell hit's 3.0v the battery will shut off.

TIA

Yup! Ask me how I know!

 

[Rock Shelter]

Great info. Thank!

 

[Mocho]

That's correct. The Phantom should auto land before that happens, but you can override the auto landing by staying on the sticks. That'll eventually allow the battery to drain down to 3.0V.

Thank you

Yup! Ask me how I know!

Hmmm, I wonder

 

[royster]

A lot of great Battery info here that i;m trying to fully digest.
I think i;ve got most of it,
Am i right in thinking that after 20 -25 flights, I should do the deep discharge to 8%, I.E- Using a battery that is showing- 20-28%, which is after my average flight, let it cool & then run it in my bird, sitting on my deck, either motors running or just sitting playing with the App, until 8% battery life shows & then, once cooled down, charge her up to full?
Thanks to all for this important post.

 

[tcope]

A lot of great Battery info here that i;m trying to fully digest.
I think i;ve got most of it,
Am i right in thinking that after 20 -25 flights, I should do the deep discharge to 8%, I.E- Using a battery that is showing- 20-28%, which is after my average flight, let it cool & then run it in my bird, sitting on my deck, either motors running or just sitting playing with the App, until 8% battery life shows & then, once cooled down, charge her up to full?

Yes, but doing it this way will take awhile (it may also shut off at some point). Another way it to keep the Phantom hovering around 5'. You will need to keep ascending as the Phantom will want to land. From what I recall, this takes about 2 minutes.

 

[RedHotPoker]

They have gone & changed the duration, for you to deep cycle the Phantom 3 batteries. So from now on, after every Ten (10) full charges, not twenty (20) charges as was recomended before. ;-)

RedHotPoker

 

[msinger]

Am i right in thinking that after 20 -25 flights, I should do the deep discharge to 8%

I'm not sure this needs to be done. DJI has removed any mention of this in the most recent version of the Phantom manuals.

 

[GodFear17]

Good write up!


Sent from my iPad using PhantomPilots mobile app

 

[MotorCycle-Man]

I have been near 2 hours reading this thread...now i dont know what to do...so much back n forth here....im sure you know what i mean...one says to do this 2 others say to do that..back n forth.......In in the state of confusion LOL.

 

[GadgetGuy]

I have been near 2 hours reading this thread...now i dont know what to do...so much back n forth here....im sure you know what i mean...one says to do this 2 others say to do that..back n forth.......In in the state of confusion LOL.

Just keep using them, until either the app tells you there is a problem, or until you become aware of a problem! Nothing to obsess over any more.

 

[solentlife]

Just keep using them, until either the app tells you there is a problem, or until you become aware of a problem! Nothing to obsess over any more.

Thats about the best now ... much of the info earlier is as per recc'd previous by DJI ... with a few 'personal' modifications I noticed by some.

To satisfy my own curiosity and also various PM's / emails I rec'd - I actually tested cut-offs and voltages on my P3 batterys back last year. I've been using LiPo's for many years and felt reasonably safe that I would not damage any. I do NOT recc'd people to repeat what I did though. It can prove an expensive mistake !

These were conducted on each of the 3 batterys I have ... I did partial tests on a 4th - but that was lost after my P3S went for a swim ! All my batterys were in the 30 - 40 cycle well maintained life then ...

Note a DJI P3 battery is a 4S LiHV pack - full charge cell voltage is 4.35V each.

I charged up by usual method -> just plug battery in without switching on first. LED's did their thing ... battery charged up and board terminated charge. Voltage readings taken ... 4.3V average across cells ... and not very well balanced IMHO, Total variance lowest to highest ~0.05v. Board had terminated in my opinion safely - but early. Go reported battery as average 93 - 95%.

I discharged to reasonable level ... average about the 30% mark ... by flying. Test of cells indicated a slight increase in unbalanced voltages once rested ... but similar to what I would expect in most LiPo's use. Total variance ~0.07V. This would be due to the slight differences in Internal Resistance of the cells.

I then charged up using my normal method of switching on batterys regardless of initial charge state. This has effect of over-riding a FW code that stops you 'topping up' charge when over about 90-93%.
Full charge again as expected was terminated by the board - but this time as I usually see - the average voltage was slightly higher and in fact Go reported battery as 100% ... with better cells - but still ~0.02V total variance lowest to highest.

I then manually discharged the packs till they shut down ... DJI has set the board to do this at 3.0V per cell. but in fact the inbalance INCREASED and I had cells down to 2.85V while others were above 3.0V ... this meant that board was shutting of based on TOTAL voltage - which I had ... 12V.
Note that 3.0V is the recc'd lowest ever voltage to go to to avoid damaging cells ... but 2.85V is the actual limit with only slight damage if any between 3.0 and 2.85V. To reduce risks of damage - the batterys were used in this one by one - so I could put back on charge as quickly as possible. At 3.0V per cell - I found that the pack was difficult to read as it refused to stay powered on without repeated pressing. Once charge was with all cells at 3.0v or slightly over - the pack returned to normal. PLEASE DO NOT REPEAT THIS EXPERIMENT !!

I then charged at the usual method of battery not switched on and found similar results as previous. Balance was still not sorted.

I discharged again but this time monitored and stopped it as near 3.0V each cell as I could. I then charged up again with battery switched on .... similar results as before.

I do not say that everyone will experience same as I did back last year ... it was older battery FW but I don't think there is any difference today ... My main point is that I was disappointed to see the board work more on total voltage than individual cells. The termination before balance cycle is completed is not good in my honest opinion. There is too much reliance on a circuit board bolted onto front of the battery.

But it is good that the board goes some way toward to reducing hazards for less experienced LiPo users and also prevents excessively deep discharge ...

As to Life of the batterys - the cycle number is based on FULL cycle not partial and DJI Tech when I asked said that the 200 cycle limit was not fixed and battery could work past that if maintained in good order. So far I have not reached 200 ... so cannot verify !

Final point :

LiPo cells regardless of High Voltage as here or regular - storage is recc'd at 3.75 - 3.9V per cell. Put it another way ... that is same as the quoted nominal total voltage the packs are sold by : ~15V

Under load a LiPo can go to as low as 3.3V per cell and once rested will recover to slightly higher. It is recc'd to restrict depletion to 3.4 - 3.5V per cell as lowest ... that way most will once rested 'bounce back' to near or 3.7V per cell.

Tip : Check and clean your contacts - both sets on the battery and on the drone ... I believe that more problems occur because of grubby contacts than anything else ...

Look after your batterys - they will look after you !

Nigel

 

[GadgetGuy]

Thats about the best now ... much of the info earlier is as per recc'd previous by DJI ... with a few 'personal' modifications I noticed by some.

To satisfy my own curiosity and also various PM's / emails I rec'd - I actually tested cut-offs and voltages on my P3 batterys back last year. I've been using LiPo's for many years and felt reasonably safe that I would not damage any. I do NOT recc'd people to repeat what I did though. It can prove an expensive mistake !

These were conducted on each of the 3 batterys I have ... I did partial tests on a 4th - but that was lost after my P3S went for a swim ! All my batterys were in the 30 - 40 cycle well maintained life then ...

Note a DJI P3 battery is a 4S LiHV pack - full charge cell voltage is 4.35V each.

I charged up by usual method -> just plug battery in without switching on first. LED's did their thing ... battery charged up and board terminated charge. Voltage readings taken ... 4.3V average across cells ... and not very well balanced IMHO, Total variance lowest to highest ~0.05v. Board had terminated in my opinion safely - but early. Go reported battery as average 93 - 95%.

I discharged to reasonable level ... average about the 30% mark ... by flying. Test of cells indicated a slight increase in unbalanced voltages once rested ... but similar to what I would expect in most LiPo's use. Total variance ~0.07V. This would be due to the slight differences in Internal Resistance of the cells.

I then charged up using my normal method of switching on batterys regardless of initial charge state. This has effect of over-riding a FW code that stops you 'topping up' charge when over about 90-93%.
Full charge again as expected was terminated by the board - but this time as I usually see - the average voltage was slightly higher and in fact Go reported battery as 100% ... with better cells - but still ~0.02V total variance lowest to highest.

I then manually discharged the packs till they shut down ... DJI has set the board to do this at 3.0V per cell. but in fact the inbalance INCREASED and I had cells down to 2.85V while others were above 3.0V ... this meant that board was shutting of based on TOTAL voltage - which I had ... 12V.
Note that 3.0V is the recc'd lowest ever voltage to go to to avoid damaging cells ... but 2.85V is the actual limit with only slight damage if any between 3.0 and 2.85V. To reduce risks of damage - the batterys were used in this one by one - so I could put back on charge as quickly as possible. At 3.0V per cell - I found that the pack was difficult to read as it refused to stay powered on without repeated pressing. Once charge was with all cells at 3.0v or slightly over - the pack returned to normal. PLEASE DO NOT REPEAT THIS EXPERIMENT !!

I then charged at the usual method of battery not switched on and found similar results as previous. Balance was still not sorted.

I discharged again but this time monitored and stopped it as near 3.0V each cell as I could. I then charged up again with battery switched on .... similar results as before.

I do not say that everyone will experience same as I did back last year ... it was older battery FW but I don't think there is any difference today ... My main point is that I was disappointed to see the board work more on total voltage than individual cells. The termination before balance cycle is completed is not good in my honest opinion. There is too much reliance on a circuit board bolted onto front of the battery.

But it is good that the board goes some way toward to reducing hazards for less experienced LiPo users and also prevents excessively deep discharge ...

As to Life of the batterys - the cycle number is based on FULL cycle not partial and DJI Tech when I asked said that the 200 cycle limit was not fixed and battery could work past that if maintained in good order. So far I have not reached 200 ... so cannot verify !

Final point :

LiPo cells regardless of High Voltage as here or regular - storage is recc'd at 3.75 - 3.9V per cell. Put it another way ... that is same as the quoted nominal total voltage the packs are sold by : ~15V

Under load a LiPo can go to as low as 3.3V per cell and once rested will recover to slightly higher. It is recc'd to restrict depletion to 3.4 - 3.5V per cell as lowest ... that way most will once rested 'bounce back' to near or 3.7V per cell.

Tip : Check and clean your contacts - both sets on the battery and on the drone ... I believe that more problems occur because of grubby contacts than anything else ...

Look after your batterys - they will look after you !

Nigel

Very good in depth information and analysis. My understanding is that all DJI batteries shut off when any single cell voltage drops below 3.0V regardless of total voltage. Are you suggesting that is not the case?

 

[solentlife]

Very good in depth information and analysis. My understanding is that all DJI batteries shut off when any single cell voltage drops below 3.0V regardless of total voltage. Are you suggesting that is not the case?

I can only report what I found for my 3 batterys tested ... all 3 had a cell go below 3.0V ..... and it appeared that the FW worked on 12V total instead of individual cell ....

As I said in the post - this is what I saw. It may not correspond to what another finds. I also strongly advise others not to do the test - you could end up with a $140 brick for disposal.

I know I have had some argue with me about this and also the TOP end full charge status - again - I say what I got in testing.... others may get different.

The main thing is to maintain the batterys in reasonable manner and not over-discharge. I try to stay around the 30% mark max to land. Only if absolutely necessary do I go below that 30% warning .... and even then I avoid 20% like the plague !

Nigel

 

[N017RW]

For those folks who have used ‘dumb’ LiPos for the last 15 or so years, the rule of thumb was always learn flight times that yielded about a 30% SOC upon landing or stopping (cars).
Eventually ESCs incorporate-d low voltage alarms that could be set to produce the same result.