Discharging the full battery down to below 10%, then recharging back to full again, should balance the cells again. How many charges has the battery undertaken?
Cell Deviation on the start
- Thread starter t2adze
- Start date
Cheers, I normally do that if the log has been reported at doing such and such at such and such a time and I start tapping at the various points along the way. The OP stated that the battery issues were at the beginning of the flight so I dutifully started scrolling......As an aside, here's a quick tip Tevek. If you tap the flight warning points on the map, it skips through the log to that point, thus avoiding wearing out your fingerprint...!
Ahreed
I thought about the effect of the battery electronics also, the hibernation current draw is around 2uA with 7uA powered off (i.e 0.002 to 0.007 ma) for the MCU IC.
Agreed- also IMHO.
I thought about the effect of the battery electronics also, the hibernation current draw is around 2uA with 7uA powered off (i.e 0.002 to 0.007 ma) for the MCU IC.
Either the days to discharge setting is off, your calendar is missing a few pages or you pressed the power button on the battery to check level or for some other reason between when it was charged and flown. If the pack was 3 days into the autodischarge routine it would be down around 55% charge level. Yours was at 97% at launch according to the log.
Did you press the power button on the battery between charging and flying?
And another question- what temperature where you flying in?
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But if his auto setting is one week (7 days) .... then at 4 days - the discharge should not have even started. Agreed that pressing button would reset the timer ...
Nigel
OOOP'S !!! Sorry .... got 1 and 2 flipped round !!
Agree .... if he had set it at 4 days and flew one week later .... given that time to discharge to less than 65% is estimated by DJI to be about 2 days ... then to have any reading higher than that - as he says ...
means he either pressed check button on battery - resetting timer ... or a mistake in days quoted.
Sorry again ...
Nigel
Sorry? I was confused one out of the three times I read it and took an average.
Anyway- we need to stay on this and I am looking forward to the OP response. This could be a good candidate for Helping to support the possibility that packs flown that have commenced auto discharge are a recipe for disaster. With 5% tolerance on the bleed resistors and the fact that the cells are discharged independently this is certainly a serious consideration. You would know of more than one instance where a less than 5% imbalance in cell voltages will see LVC cutout very early in the flight with the good old dumb lLiPO’s.
mmmmm .... I cannot agree on the independent discharge of cells. Sorry.
My investigation and dismantling of a DJI pack along with another more experienced in electronics than myself indicates that cells are discharged en-mass ... basically interconnection cancels any advantages.
I would see more instance of LVC cutout on a DJI pack due to cell inbalance than on a 'dumb LiPo' ... sorry to say. Reason being that I can access my 'dumb LiPo's to maintain properly.
Unfortunately the only people who have the real information are DJI themselves and they are the ones who refuse to say anything ... actually when they do - quite often its wrong !!
I have emails from their Tech Dept saying that DJI batterys stop working after 200 cycles regardless, when I questioned that - another Tech said that restriction had been lifted long time ago ... one said balancing occurs when discharging ... another said that was wrong and it occurs when charging ... another said he didn't know ...
??
Nigel
My investigation and dismantling of a DJI pack along with another more experienced in electronics than myself indicates that cells are discharged en-mass ... basically interconnection cancels any advantages.
I would see more instance of LVC cutout on a DJI pack due to cell inbalance than on a 'dumb LiPo' ... sorry to say. Reason being that I can access my 'dumb LiPo's to maintain properly.
Unfortunately the only people who have the real information are DJI themselves and they are the ones who refuse to say anything ... actually when they do - quite often its wrong !!
I have emails from their Tech Dept saying that DJI batterys stop working after 200 cycles regardless, when I questioned that - another Tech said that restriction had been lifted long time ago ... one said balancing occurs when discharging ... another said that was wrong and it occurs when charging ... another said he didn't know ...
??
Nigel
The real information is the phantom 3 intelligent board, you can see the little buggers here, R7-R10 directly in line with the balance tap leads above the connector. The circuit traces reveal a direct implementation, including semiconductors and associated passive components, of the Texas Instruments battery management solution application note. There is no provision I can see for a a bulk load to be applied across the battery for discharge purposes. Very happy to be proven wrong here.
The findings we had when causing discharge was that the discharge of cells was not even ... that they did not balance. Note I did not say it was not there as you say ... what I said is the way DJI have programmed prevents doing its job.
If DJI would alter its battery FW to allow the components to actually do their job fully - we would truly have an intelligent board - but they don't. Its like having a Ferrari and capping its RPM at 3000 !!
Nigel
If DJI would alter its battery FW to allow the components to actually do their job fully - we would truly have an intelligent board - but they don't. Its like having a Ferrari and capping its RPM at 3000 !!
Nigel
Fantastic- that is precisely my observation, the discharge is not even. We are in complete agreement. My suspicion is that the uneven discharge is directly attributed to the cells being individually bled down by out of tollerance resistors rather than being terminated to a single load across the battery pack terminals (all cells in series). I am as interested in getting to the bottom of this as you are. Firmware alteration is limited to the available config of the TI microcontroller.
The main concern I have is that testing Ri (Internal Resistance) of the cells once we opened up - was that they were more varied than most 'dumb LiPo' I see after many cycles. The DJI pack in question then was one that had only had a few cycles through it - nothing to explain its bad behaviour.
Poor Ri on cells will explain out of synch discharge. And Ri is not something you can cure.
Normal LiPo are constructed from batch checked cells before creating a pack. Factory matches cells to have an even balanced Ri ... the rejected ones often end up on eBay or downgraded in C rating ... or even with unscrupulous sellers who don't care.
Nigel
Poor Ri on cells will explain out of synch discharge. And Ri is not something you can cure.
Normal LiPo are constructed from batch checked cells before creating a pack. Factory matches cells to have an even balanced Ri ... the rejected ones often end up on eBay or downgraded in C rating ... or even with unscrupulous sellers who don't care.
Nigel
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I'm very sorry for my absence. Rough time at work.
I dont remember about pushing the button, but i remember charging the battery the night before the flight. Not sure if i topped it off before flight.
THe weather was regular. not windy. not too cold.
So what can be exactly the reason for this low deviation/ SHould i get rid of this battery?
I dont remember about pushing the button, but i remember charging the battery the night before the flight. Not sure if i topped it off before flight.
THe weather was regular. not windy. not too cold.
So what can be exactly the reason for this low deviation/ SHould i get rid of this battery?
