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Inexpensive deep-discharge solution
2284 26 2015-6-3
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PeteGould
Second Officer

United States
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Use the following setup entirely at your own risk, but it's working for me.  The halogen lamp pictured below (and available via Amazon.com at this link for about $10 including shipping) is a 24v, 35w lamp.  This is the exact voltage and wattage for a safe deep-discharge of an Inspire battery.  As pictured, I purchased an extra accessory cable from DJI (the kind used to charge the remote off the aircraft battery), removed the connector for the remote, and attached the wire to the bulb's screw terminals.  When a battery is due for a deep discharge, I connect it to the bulb, turn it on, and run it until it automatically shuts off (the battery's circuitry will shut the battery off before it discharges to a level that would damage the cells).  I then recharge it using the DJI charger.  Preliminary results show 100% battery health and identical cell voltages.

Important caution: lipo batteries are completely intolerant of short circuits, even for an instant.  When the bulb is connected to the battery the metal terminals on the back of the bulb are live.  If anything causes a short circuit, the battery will be destroyed and could even catch fire (and lipo fires look more like a Fourth of July fireworks display than an ordinary fire).  Use extreme caution with exposed wires and terminals and ensure the bulb isn't sitting on or near anything conductive or anything that would be damaged by heat (mine sits on a marble slab).

With that said, I would rather discharge the battery this way than run the Inspire's electronics, fans, etc., unnecessarily just to drain the battery.

Just thought I'd share for anyone interested.


35wHalogenBulb.JPG
2015-6-3
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capalvch
lvl.4
Flight distance : 71125 ft
Venezuela
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Looks great!. Will use your idea. I was triyng to find a way to do this without waiting in front of  the drone to avoid an accident, with the propellers running.
2015-6-3
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w1der
Second Officer

Sweden
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This is a great idea ... !
I really don´t like the idea of draining the battery inside the bird as it takes a great deal of time to do it ... causing the electronics inside to heat up, possibly over heat ...
And as we know, heat is not good for the life time of any electronics.
  
I only wish that the person who engineered the software for the smart battery (not a random person from DJI support) would confirm this way is OK to do it ...

I have been thinking about this a great deal ...

Logic says ... fly the bird (hover close to the ground) until the smart battery detects "to low voltage" and shuts it down - recharge!
This really should be enough for the logic part of the battery to calculate the proper flight time (as this is the purpose of the deep discharge process).  
Anything beyond when the props stop spinning should be of no interest!?

What would happen if you connected this lamp to the battery when it was fully charged and made a deep discharge from 100% to "shut down"?
Would it glow for several hours ... and the next time you put the battery in to the bird ... the battery would estimate the new flight time based on this?

I remember a DJI rep state that after the deep discharge it is OK to "charge to 50% for storage".
This tells me the calculation for the flight time is made during the discharge cycle ... So ... what happens when we discharge the battery with something else but the bird?  

Am I making sense? ...
2015-6-3
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jon
lvl.4

United Kingdom
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Great idea.

Are we 'certain' the electronics will shut off the battery before it reaches a critically low level?

Another, maybe easier option would be two regular automotive 12V 21W (stop & turn indicator lamps) bulbs wired in series (drawing roughly 1.75A rather than roughly 1.5A). Only because they're so readily available.

Jon
2015-6-3
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daniel.frederik
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Flight distance : 10656 ft
New Zealand
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Hi Pete, a good idea is so often a simple one and yours is no exception.  I tried using a programmable charger is slowly discharge my I1 batteries but without success. There appears to be a gate across the I1 batteries eg; a volt meter indicates a very low voltage when connected to the battery terminals, this would change under the right conditions.  I suspect this gate might be to force us to use the dedicated chargers which are cooperative with this feature.
That aside, I trust your discharging system is still working well?
DF
2015-6-4
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PeteGould
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United States
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w1der Posted at 2015-6-4 15:05
What would happen if you connected this lamp to the battery when it was fully charged and made a deep discharge from 100% to "shut down"?
Would it glow for several hours ... and the next time you put the battery in to the bird ... the battery would estimate the new flight time based on this?

Highly unlikely.  Obviously I can't speak for the DJI programming department, but the calculation is almost inevitably going to be based on battery voltage and rate of discharge under load.  The cause of the sudden voltage drops is most likely that a partially used battery is going to have a certain amount of voltage rebound, causing the circuitry to estimate more remaining charge than there actually is.  It then reassesses once the battery is under full load (i.e. props spinning and bearing the weight of the aircraft).

Remember that the battery can also be discharged by using it to charge remotes or run the bird at idle (which would take a long time).  These are both approved methods of discharging the battery and likely take a bit longer than the 35w halogen lamp.  35 watts is actually a decent draw.  It shouldn't take hours to drain the battery even at full charge (it will certainly take longer than regular flight time, though).  On the other hand it's much less stressful on the battery than flying the bird (I don't know the total current draw but it's going to be significantly more than 35w).

I remember a DJI rep state that after the deep discharge it is OK to "charge to 50% for storage".  This tells me the calculation for the flight time is made during the discharge cycle.

The calculation is almost certainly not a time calculation made by measuring the duration of the discharge.  Rather, the calculation requires knowing what the minimum possible charge (what it considers 0%), so the battery has to be discharged to that point to set a baseline.  What's confusing is the difference between ACTUALLY DISCHARGING THE BATTERY TO 0%, which would destroy it, and discharging it to 0% of USEFUL CHARGE, which means it is still partially charged but not to a safely usable amount.  Note that the app never tells you anything about total charge.  It is only reporting the remaining amount of USEFUL charge.  So even when the app tells you that there is 0% remaining battery capacity, and even when the bird abruptly shuts off for lack of power, the battery is still partially charged.  However, you cannot store a lipo battery at that low charge because batteries discharge slowly just by sitting on the shelf, so if you discharge it to minimum safe charge and put it on the shelf, as it naturally discharges it will quickly be below safe minimum.  That's why you charge it to 50% right afterwards if you're planning on storing it.

I hope that makes sense...
2015-6-4
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PeteGould
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United States
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jon@thefullers. Posted at 2015-6-4 15:26
Great idea.

Are we 'certain' the electronics will shut off the battery before it reaches a critical ...

Well - that's what the electronics in the battery are intended to do.

What I have seen is that the battery switches cleanly off when the electronics decide it's at minimum safe charge.  Unlike a dying flashlight battery you don't see the bulb growing dimmer before the shut-off (which would tell you the voltage is dropping).  The lamp remains at normal brightness and then shuts off.  On recharge I show 100% battery health and identical voltages across all cells.

I agree that the battery SHOULD NOT be stored in this condition.  It should be promptly recharged either to 50% for storage or 100% for use.
Another, maybe easier option would be two regular automotive 12V 21W (stop & turn indicator lamps) bulbs wired in series (drawing roughly 1.75A rather than roughly 1.5A). Only because they're so readily available.

CORRECTION BASED ON SUBSEQUENT MESSAGES IN THIS THREAD: You could do that.  (an additional comment has been edited out as I now believe it was incorrect).
2015-6-4
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jon
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United Kingdom
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PeteGould Posted at 2015-6-5 02:37
Well - that's what the electronics in the battery are intended to do.

What I have seen is that the ...

really?

As I said two '12v' 21W bulbs, I thought that each would share the 24-ish volts, thus each would see 12V and run at their full 21W, totalling 42W of consumption.
2015-6-4
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PeteGould
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United States
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jon@thefullers. Posted at 2015-6-5 05:48
really?

As I said two '12v' 21W bulbs, I thought that each would share the 24-ish volts, thus each ...

ANOTHER EDIT BASED ON JON'S REPLY - for the purpose of not confusing readers....

In retrospect I believe you're right (and I was incorrect, and have corrected the earlier message so as not to confuse other readers).  I shouldn't write in a hurry (I was unthinkingly assuming 24 volt bulbs running at 12 volts despite your explaining your idea clearly).

Jon's explanation below is likely the correct one.
2015-6-4
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jon
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PeteGould Posted at 2015-6-5 06:13
You're half right (and I was incorrect, and have corrected the earlier message so as not to confuse ...

Do we agree that in series, each lamp will see 12v?

If we present a 12V 21W lamp with 12V potential difference, it will draw 1.75A, and consume 21W

I believe, that as both will be seeing 12V, both will consume 21W of energy, totalling 42W and the current through the circuit will be 1.75A

I Think maybe I need to actually set this up and measure it in practice.... If I set it up, and see a current draw of 1.75A (@24V) then we are indeed drawing 42W.

As I see it, these two (12V 21W) lamps, in parrallel on an adequate 12V supply will both burn brightly, drawing 21W each, totaling 42W.

To achive the same consumption in series, you would have to double the voltage across the series circuit, which we have, to near 24V.

BTW, the reason for continuing here, is not to try and be the winner, I just need to understand this stuff (which I thought I did) so need to put it to bed one way or the other.

Jon





2015-6-4
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PeteGould
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jon@thefullers. Posted at 2015-6-5 14:08
Do we agree that in series, each lamp will see 12v?

If we present a 12V 21W lamp with 12V potentia ...

Try it.  I've been away from basic electricity for a LONG time, and questions of series and parallel circuits are usually presented in terms of ohms (amount of resistance) rather that watts (amount of power consumption).  So you are likely correct given that when the two bulbs are 12v that translates to about half the resistance of 24v bulbs - something else I didn't take into account.

But again - this is why for the sake of simplicity, a single 24 volt lamp drawing 35 watts is essentially foolproof.  If I as someone who had a lot of electrical and electronic experience (albeit about 30 years ago) could get it wrong, the average completely nontechnical user mucking around with trying to get two of the right kind of bulb into a series circuit could make a mess.  I was going for ultra-simple, something anyone could do.  I didn't want to complicate it.  One cable with two wires, one bulb with two terminals, polarity doesn't matter, just tighten the two screws and don't make a short circuit.  That was what I was going for.
2015-6-5
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jon
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PeteGould Posted at 2015-6-5 21:26
Try it.  I've been away from basic electricity for a LONG time, and questions of series and parall ...

Agreed, very simple solution.

Jon
2015-6-5
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nilsblix
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Hello
http://www.ebay.com/itm/Multi-Ba ... hash=item2800e8f8c7


Is this a way to go for charging  ?

PeteGould ???
2015-6-7
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PeteGould
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United States
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I've seen one posting saying that one of those plates malfunctioned and destroyed their battery.  Since it uses the stock charger I would also be concerned that it would overheat the charger.  So my gut reaction would be to avoid it.
2015-6-7
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nilsblix
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PeteGould Posted at 2015-6-8 06:08
I've seen one posting saying that one of those plates malfunctioned and destroyed their battery.  S ...

Thank for you reply.
I have seen warning against this ( but it was from one who promote another expensive charger ).
This comes with a power supply of 400 W and 15 amp ( but can also be used with the stock charger )
http://www.ebay.com/itm/Multi-Ba ... hash=item2800e8f8c7
2015-6-7
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PeteGould
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nilsblix@gmail. Posted at 2015-6-8 06:16
Thank for you reply.
I have seen warning against this ( but it was from one who promote another exp ...

Someone will have to be the guinea pig.  Until several people have tried it successfully there's no way to know.  Keep in mind that if it DOES fry your batteries they won't be covered under warranty.  For my own part I chose to purchase additional DJI chargers rather than take a chance with a third party device, but I tend to be very conservative.  I'm not as concerned with DISCHARGING, since the 35 watt load is a known and verifiable quantity and the connection is very simple.  With the multiple charge plate I don't know what the danger of a short might be.
2015-6-7
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dbeck
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United States
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With all due respect to these very creative and workable ideas,what is wrong with after the 10th flight, just flying a long flight, (landing at 20% or less) and just letting it hover a few feet off the ground until you have around 10% left and then letting it sit on the ground until it shuts off?
2015-6-7
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PeteGould
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dbeck@promobox. Posted at 2015-6-8 10:29
what is wrong with after the 10th flight, just flying a long flight, (landing at 20% or less) and just letting it hover a few feet off the ground until you have around 10% left and then letting it sit on the ground until it shuts off?

There's nothing wrong with it at all.  However, because the mechanical parts in the Inspire (motors, fans, etc.) all have finite lives, those of us who are ultra conservative prefer not to run the aircraft under power for the additional time needed just to fully discharge batteries.  This is especially true for those with four or more batteries where fully discharging all of them involves significant run time.  But if that doesn't bother you, using the aircraft to discharge the battery is fully in keeping with the manufacturer's recommendations.
2015-6-7
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GB44
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Flight distance : 343848 ft
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Pete,

Do you know if you can get a female socket for the charger like what is in the controller.  I was thinking that maybe you could use one of these female sickest connected to some additional wires then onto a light bulb.  That way you don't destroy a perfectly good charging unit, you just plug in like when charging the controller.

Also what happens if you use a smaller watt bulb, am I correct in a assuming it just takes longer to discharge ?
2015-6-10
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PeteGould
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United States
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GB44 Posted at 2015-6-11 01:24
Pete,

Do you know if you can get a female socket for the charger like what is in the controller.  I ...

I'm sure you could get a female socket - that was my original idea.  However it would have to be ordered and I never found a specs page that told me the dimensions of the coaxial power connector (those connectors come in a nearly endless array of outer diameter, inner diameter and pin sizes).  Rather than worrying about it I just ordered and hacked a spare cable.  I figured that was still cheaper in the long run than unnecessarily running the Inspire just to run down the battery.

As far a as a lower wattage bulb is concerned - exactly.  It would just take longer.
2015-6-10
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GB44
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PeteGould Posted at 2015-6-11 02:44
I'm sure you could get a female socket - that was my original idea.  However it would have to be or ...

Pete,

Thanks for that.  I think I will take a visit to my local electronics shop for a female socket or at least see what the have.  Like you say, its probably a better way to let the battery run down.  So would a 35 watt bulb be the highest  to use.  

Was just thinking it could be connected to a small lamp, very environmentally considerate.
2015-6-10
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PeteGould
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United States
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GB44 Posted at 2015-6-11 02:53
Pete,

Thanks for that.  I think I will take a visit to my local electronics shop for a female soc ...

35 watts seems like an ideal compromise between efficiency and stress on the battery.  It's also probably on the high end of the load I'd be willing to put on the wire they're using in that cable.  Much more than that and the wire would start to heat up.
2015-6-10
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jon
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PeteGould Posted at 2015-6-11 05:04
35 watts seems like an ideal compromise between efficiency and stress on the battery.  It's also p ...

Bob would have 40A flowing down that without issue!
2015-6-10
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PeteGould
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jon@thefullers. Posted at 2015-6-11 06:51
Bob would have 40A flowing down that without issue!

Nah, he would have said the whole thing was silly and told everyone to ignore the instructions about deep-discharges.  Oh wait - that's exactly what he DID say.  
2015-6-10
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GB44
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Flight distance : 343848 ft
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Pete,

When charging the controller from a battery do you simply plug in and turn on the battery and leave it until the battery switches itself off.  Never tried charging the controller yet from the battery.

Do you think that when the battery displays 0% on the App but still shows one green led on the battery that this is sufficiently discharged or should we be looking to take the discharge beyond this point until it simply won't switch on and no led lights displayed on the battery.  I don't know why, but I have just resisted discharging until it physically switches itself off.
2015-6-14
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PeteGould
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GB44 Posted at 2015-6-14 22:34
Pete,

When charging the controller from a battery do you simply plug in and turn on the battery and ...

I would defer to Tahoe or Autumn on what is a deep enough discharge.  I have seen that when the app says 0% there is sometimes considerable charge remaining and I wonder if that difference is what needs to be recognized by the battery firmware.  As to charging the controller using the flight battery - yes, just connect the accessory cable and turn the battery on.  Keep in mind that if the controller reaches full charge it will stop draining the flight battery.
2015-6-14
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GB44
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PeteGould Posted at 2015-6-15 05:03
I would defer to Tahoe or Autumn on what is a deep enough discharge.  I have seen that when the ap ...

Pete,

Thanks for that.  I will see if Autumn or Ed chip in, but the manual does say discharge until less than 5% and if the App is say 1% or 0% then DJI can't say you are not doing things in accordance with their guidelines.  That said I want to prolong these batteries and fly without problems like everyone else so if DJI can confirm if they need to be discharged until they physically switch off that would be good information for us all.  Clear and precise information for us.

Thanks Pete
2015-6-15
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