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November 19, 2019, 12:26:01 pm

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Discharging LiPos ready for disposal

Started by e-flite_rules, July 26, 2019, 10:29:43 am

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e-flite_rules

It's well known that old LiPos can be disposed of as general waste PROVIDED that they are fully discharged.

I always though that soaking them in salt water was a sure fire (or non fire!) way of achieving this.  However some people have suggested that this isn't a good idea - corrosion might set up high resistance paths so that the discharge was never achieved. 

So how to discharge them?

I've seen several articles on the web saying that a pack can safely be discharged by simply connecting a resistor across the output of the cells in series.  Suggested discharge current is C/10.

S0......  Two questions.

1. Why such a low discharge rate of C/10?  Modern day cells can all cope with 10C without damage - And we're not worried about damage - we're trying to kill them! 

2. Does such a series discharge risk driving one or more cell into reverse?  What is the consequence of that?  Obviously cell damage isn't an issue.  However failure followed by a fire is!  Also if the cell went open circuit then the other cells wouldn't get fully discharged.

Given 2. above I'm thinking that the safest option is to discharge each cell individually.  But at what rate?

Thoughts please!

dickw

I don't worry too much about a particular rate.
I start by using my charger's "discharge" feature to take cells down to below normal "empty" - say about 3.5v per cell.
I then connect a 12v 20w bulb across each 3 cell portion of the balance lead and leave it to go flat (a bit under 2 amps initially). The pack can get quite warm during this so I leave it somewhere safe and non-flammable, but not had a problem yet.
Once the whole pack appears flat, I check each cell individually just to make sure nothing missed, then strip the balance leads and twist all together to make sure it stays flat.

Dick
Grow old disgracefully

pooh

From Ohms Law, you can calculate the resistance necessary to discharge the pack of any voltage at any load current, and the wattage of the required resistor.

Take a nominal 11v pack (3 x 3.7 LiPo in a 2AH pack) and a desired 10C current, say 20amps

V/I = R           or   11/20 = R = approx 0.5ohm

wattage of the resistor is  W = I x V  = 20 x 11 = 220 watts

now I doubt you have a resistor like that lying around unless you work in electronics, or are happy to buy one (a solution is 2 x 1ohm 100 watt aluminium clad resistors in parallel, mounted on a reasonable sized heatsink, total cost around £15). Bear in mind that 220 watts of heat has to dissipate somewhere, so you need good ventilation

Do the same with a larger capacity pack and/or higher discharge rates and the cost and heat dissipation rise accordingly.

do the same sums for a C/10 and you need a 56ohm 2 watt resistor , 0r perhaps 2 x 100ohm 1 watt resistors in parallel for less than £1. This time the dissipation is only 2 watts



Also, at the lower current, any reverse charging is much less likely.

NB calculations above are using approximate values, for example, 56 and 100 ohm resistors are standard components
Confucious he say "more than one aircraft in the same airspace leads to structural failure"

RobC

I thought that current wisdom is that lithium based cells should not be put in with general waste, is that to prevent lithium and cobalt getting into groundwater or just to prevent the dustmen getting incinerated? 
flying's easy - it's getting it back down in one piece that's the hard part

PDR

July 26, 2019, 12:56:17 pm #4 Last Edit: July 26, 2019, 16:43:18 pm by PDR
Quote from: e-flite_rules on July 26, 2019, 10:29:43 am
I always though that soaking them in salt water was a sure fire (or non fire!) way of achieving this.  However some people have suggested that this isn't a good idea - corrosion might set up high resistance paths so that the discharge was never achieved. 


Not so. Corrosion is itself an electrolytic process and so it cannot occur in the conductors in such a manner as to prevent a current that is already flowing. It cannot occur inside the cells themselves in any manner detrimental to discharging because the actual process which produces the current is corrosion of the cell plates, so any corrosion that can happen is already happening and it's helpful rather than detrimental.

But anyway:

Quote
1. Why such a low discharge rate of C/10?  Modern day cells can all cope with 10C without damage - And we're not worried about damage - we're trying to kill them! 


This is true, but only down to the point of no return (typically about 3.5v/cell for a modern lipo or 3v/cell for an older one). Discharging beyond thois point at ANY current very much DOES damage the cells, and we all know. If you carry on discharging below this voltage at high currents there is a very high risk of plate damage, fire and a Corbyn government, which is why when COMPLETELY discharging cells for disposal it must be done at a lower rate. If the bucket of saline option doesn't dingle your dangle then just stick a 1kohm resistor across the leads and leave them outside for a month. measure the voltage across the resistor every couple of days - when it gets down to a few millivolts they're done.

The bucket of saline thing is still the safest method though - the water keeps the cells cool and prevents significant events should the cells decide to go into a runaway melt-down or similar (rare, but not impossible).

€0.000008 supplied,

PDR
There are no shortcuts on the long, hard road to success. But if your dad's rich there could a limo service...

leckyBB

July 26, 2019, 15:12:51 pm #5 Last Edit: July 26, 2019, 15:14:40 pm by leckyBB
I have another alternative solution for you. Put battery in model and fly as normal but terminate flight in a large hawthorn tree. Leave for 24 hours while gathering the necessary equipment to retrieve model. Get scratched all over while recovering model in 40degC heat. Remove battery (in my case a new one only used once) and test it. All cells at 0.00v.
Order a new battery while tending to scratches.

ps: I normally destroy my end of life LiPo's using the salt bath method.
Life is not measured by the breaths you take, but by the moments that take your breath away.

paulinfrance

Quote from: leckyBB on July 26, 2019, 15:12:51 pm
I have another alternative solution for you. Put battery in model and fly as normal but terminate flight in a large hawthorn tree. Leave for 24 hours while gathering the necessary equipment to retrieve model. Get scratched all over while recovering model in 40degC heat. Remove battery (in my case a new one only used once) and test it. All cells at 0.00v.
Order a new battery while tending to scratches.

ps: I normally destroy my end of life LiPo's using the salt bath method.


We have a couple of members who use the 'flyaway' method, hook the plane up, turn the motor on and throw it ( hand launch ),
then loose the radio signal ( I can name the radios ) and it flies away disposing of the battery,,  :study:
Mode 2 THE only way to fly


itsme

Quote from: RobC on July 26, 2019, 12:48:57 pm
I thought that current wisdom is that lithium based cells should not be put in with general waste, is that to prevent lithium and cobalt getting into groundwater or just to prevent the dustmen getting incinerated?
Not so. As long as they are completely discharged, then its fine to put them in general waste.

frank

I know I should not say this, but couldn't resist it........... It's far more fun to take say an old worn out 3s 2200 pack outside and drive a sharp screwdriver through it !!

Most results I've had are a bit disappointing.... Smokes and fizzes a bit, then it's definitely dead, after cooling down !

Done it a few times and never had one burst into flames.

Sorry for my politically incorrect disposal method !!

AJH

If you really want "Venting With Flames" simply charge on a NiCad setting.  Having tried this in the interests of science I was encouraged that the puffing stage took several minutes but frightened by what could happen if it took place indoors:

leckyBB

Quote from: frank on July 26, 2019, 21:11:48 pm
I know I should not say this, but couldn't resist it........... It's far more fun to take say an old worn out 3s 2200 pack outside and drive a sharp screwdriver through it !

Most results I've had are a bit disappointing.... Smokes and fizzes a bit, then it's definitely dead, after cooling down !

Done it a few times and never had one burst into flames.

Sorry for my politically incorrect disposal method !

I did this on a pack which had spent a week in the salt bucket while still immersed. Just a little gas and smoke vented for a few seconds and then nothing. Proof that it was finally dead.
Life is not measured by the breaths you take, but by the moments that take your breath away.

e-flite_rules

August 01, 2019, 13:27:03 pm #12 Last Edit: August 01, 2019, 13:32:35 pm by e-flite_rules
Quote from: PDR on July 26, 2019, 12:56:17 pmNot so. Corrosion is itself an electrolytic process and so it cannot occur in the conductors in such a manner as to prevent a current that is already flowing. It cannot occur inside the cells themselves in any manner detrimental to discharging because the actual process which produces the current is corrosion of the cell plates, so any corrosion that can happen is already happening and it's helpful rather than detrimental.

But anyway:

This is true, but only down to the point of no return (typically about 3.5v/cell for a modern lipo or 3v/cell for an older one). Discharging beyond thois point at ANY current very much DOES damage the cells, and we all know. If you carry on discharging below this voltage at high currents there is a very high risk of plate damage, fire and a Corbyn government, which is why when COMPLETELY discharging cells for disposal it must be done at a lower rate. If the bucket of saline option doesn't dingle your dangle then just stick a 1kohm resistor across the leads and leave them outside for a month. measure the voltage across the resistor every couple of days - when it gets down to a few millivolts they're done.

The bucket of saline thing is still the safest method though - the water keeps the cells cool and prevents significant events should the cells decide to go into a runaway melt-down or similar (rare, but not impossible).

€0.000008 supplied,

PDR


Well I'll go with this one.  If my rubbish truck suffers a fire I'll blame PDR.

So it's dishwasher salt plus water in a plastic container.  Leave them for 2 weeks and then dispose into the general trash bin.

QED

PDR

Quote from: e-flite_rules on August 01, 2019, 13:27:03 pmIf my rubbish truck suffers a fire I'll blame PDR.

I didn't realise my wife posted here

PDR
There are no shortcuts on the long, hard road to success. But if your dad's rich there could a limo service...

Bad Raven

Late to the party I know, but:-

A LiPo that has been discharged way under the min voltage, even 0v, is not necc "dead". I am still using packs that had been so treated, and no evident loss of performance. One was stuck connected an "on" in a tree for over a month after a Rx failure, and still a period on (over two years from memory) still gives as expected performance on a hotliner type plane.


I have stated here before, the correct disposal method is the one your council states it requires. In my case they state up front about salt water etc discharge methods but their final decision was and is to dispose via battery disposal bins at tip or local car parks, NOT normal rubbish collection, etc. This due their IMO correct view that some might not BE fully discharged. 

If you get ANY reaction to shorting/puncture after salt water treatment you did not have an effective process!! (and reinforces why the council here are erring on the safety side quite correctly)
The user formerly know as Bravedan........... Well if Prince can do it....................

PDR

Quote from: Bad Raven on August 04, 2019, 07:25:41 amIf you get ANY reaction to shorting/puncture after salt water treatment you did not have an effective process!! (and reinforces why the council here are erring on the safety side quite correctly)

Sorry, but this is not true. The reaction you get when puncturing the case of a discharged lipo is simply the highly flammable electrolyte film which needs almost no encouragement to catch fire on exposure to air and will often flash nto flame spontaneously.

PDR
There are no shortcuts on the long, hard road to success. But if your dad's rich there could a limo service...

paulinfrance

Sorry to butt in :embarassed:  but after 'disposing' of 6 lipo's yesterday any idea what's going at a 'normal' price, I am looking for a few 2200/2600mah 3S for my 450 helicopter,, Opps no smileys on a quick reply,, ahh, preview and smiley's are back,,  :co
Mode 2 THE only way to fly


paulinfrance

Quote from: itsme on August 04, 2019, 11:03:26 amI know the haters will jump in, but I have had excellent results with these cheapos.
https://hobbyking.com/en_us/zippy-compact-2200mah-3s-25c-lipo-pack.html?countrycode=GB&gclid=Cj0KCQjwhJrqBRDZARIsALhp1WSdImuWBFq50sj3rLQg-vzyYsDT-2KXsZdlx45sg0bSrTaRFAsTvrAaAihHEALw_wcB&gclsrc=aw.ds&___store=en_us

2 of them were those in 2.450 mah 3s,, 2 give me 1.500 mah and 2 are to be tested, I got these for my 450 dji quad, they only gave me 5 minutes flight time, My 10 year old Voltz are the only ones that gave me satisfaction,,
Mode 2 THE only way to fly

paulinfrance

August 04, 2019, 12:36:25 pm #19 Last Edit: August 04, 2019, 14:18:54 pm by paulinfrance
This is what the last 4 look like, probably used less than 10 charges,,
Mode 2 THE only way to fly

itsme

Hard to work that out. I bought six four years ago, one went in hard when a young lad I was teaching flew behind a tree...one I lost in the North sea (Dont ask..) but the others are still working, slightly reduced in power, and four new ones I bought last year are also all ok. No puffiness.

THE BLACKBIRD

i had mine go the same Paul,5s 5000 2 out of 6 and i have two 2s that have never been in a plane gone just the same,
The man that never made a mistake
Never made anything

itsme

Its very odd, I cant say I am careful with them, but none are puffed up. Only one I have that is puffed is an Overlander one in my Align starter, but that does get some hammer.

PDR

A large number of my current [sic] fleet use one or two of the bog-standard Turnigy 40C 3s packs, either in 2200mAh or 3300mAh sizes. I have something like a dozen of each size and they're all still working. They're cheap as chips, especially if you buy them when they're in stock at the UK whorehouse, and can usually be bought with (my current preference) XT60 connectors already fitted.

The only "special" treatment I give them is that I have gotten into the habit of giving them a "storage charge" after use, and only fully charge them the night before use. I got into this habit because a colleague bought a bunch of new packs, charged them and then didn't fly for 3 weeks. Leaving them fully charged seems to have made them puff. I think this is a feature of the newer, more efficient cells because in days gone by I used to fully charge packs AFTER flying and leave them in that state until I next flew (which might have been weeks or months later). Modern cells don't seem to like this treatment.

PDR
There are no shortcuts on the long, hard road to success. But if your dad's rich there could a limo service...

paulinfrance

Maybe it's because  I charge them up the next day that they puff up, 2 of the yellow battery's in my last post were dumped, two give me 900 mah and 2 give 1500mah, and they are all puffed up, I also have a Zop power puffed up ( 1 of 3 ) and all my other battery's are normal, even my 10 + year old Voltz and Thunder tiger, I have the same problem with some mauve ( I can't spell purple )1300 mah 3s drone racer packs(nano teck)all 4 puffed up and and 2 2200 Bolt puffed but the 1300 bolt packs are all ok,, 
Mode 2 THE only way to fly

itsme

I guarantee if I look in my box of lipos, some will be fully charged and some down to 25-30%. I usually charge when I think I am going flying, mostly balance, but not always. This is what I cant understand, I am an animal with the things and dont coddle them at all. And yet no puffing! These are used in a foamy Acrowat and the slope soarer I converted to electric. Am I just lucky? I agree about the XT60s.

THE BLACKBIRD

I think Peter is right, charging them after use is bad , storage charge is the way to go,
i have always charged mine fully after use and i think that is what kills them, we cannot import any lipos into Cyprus anymore so electric flight is out for me now, the 2s i use for my big models i bring back with me when i visit the uk
I know you should not do it, but needs must
The man that never made a mistake
Never made anything

chaz2b

August 11, 2019, 15:01:29 pm #27 Last Edit: August 11, 2019, 15:03:04 pm by chaz2b
I've disposed of my liPos using salt water in a metal bucket, never had an ounce of power left in them. Cheapest and easiest method imo.
But as a foot note, none of my Methanol has ever puffed up! And it has a better smell than LiPo when it gets hot.
There are many roads to success,.....mine is currently being resurfaced! However, all detours have been removed and financial issues have been met....let's go fly!

paulinfrance

Oh come how could you tell that not an ounce of power was left, did you weigh your bucket ?. ^-^
Mode 2 THE only way to fly

Bad Raven

Purely for discussion (!), I have had the following results over time, never use storage, charge on return home :-

Loong-Max (white sleeve) - STILL got some over fifteen years old that still are OK!!
Tipple (orange sleeve) - Still have a few that are quite OK, but in modern terms the "C"  rating is low (like the Loong-Max)
Gens Ace - Nasty horrible things that went high impedance at the drop of a hat, the "30 seconds of power" specialists. Never swelled at all, they failed well before they could!! YUK!
Turnigy (Blue sleeve) - OK but not the "C" rating claimed AND they are generallly sold only in lower C options.
Turnigy "Heavy Duty" - I think these are just larger packs with lower capacity markings! (so a 2200 is effectively a 2700)
Nano-Tech - do swell minimally but do not seem affected by it, my mainstay pack type. Abused like mad, usually survive well, inc one that was below 0.1v per cell for a month plus and still works well near two years on.

Running a lot of high current drain Quads now, where 40-120A discharge from a 2200 is the norm, 30-70A from a 1500, I have found a good pack make for that use, but that is as far as I'll go, since they sell out as soon as stocked, and you have to be around when the stock notification (UK seller) comes in or wait more months.  Love you Guys, but not enough to give away my chances on supply!! 

You would not want these on planes anyway unless exploring the upper edge of EDF technology!
The user formerly know as Bravedan........... Well if Prince can do it....................

paulinfrance

'High drain quads" ?, put your battery's in a 450 sized helicopter and see what happens to your battery's,,
Mode 2 THE only way to fly