[cndnflyr]

That's great, thanks for the guidance

[davidmc36]

Why go to all the trouble of the somewhat mythical salt bath with associated possibility of creating hazardous gases and corroding off the connecting tabs so the battery may appear to read zero volts but only does so because of an open circuit?

http://forum.flitetest.com/showthrea...eally-bad-idea

http://www.thenakedscientists.com/fo...p?topic=1298.0

Just drain it with a resistive load and dispose of it however local regulations dictate.

[Lazy Ace]

Originally Posted by davidmc36

Why go to all the trouble of the somewhat mythical salt bath with associated possibility of creating hazardous gases and corroding off the connecting tabs so the battery may appear to read zero volts but only does so because of an open circuit?

http://forum.flitetest.com/showthrea...eally-bad-idea

http://www.thenakedscientists.com/fo...p?topic=1298.0

Just drain it with a resistive load and dispose of it however local regulations dictate.

No copper in the tabs of a lipo never had a problem discharging cells this way. If you wish to use a load so be it as long as they are discharged. Never had to slash any of the cells and I never charged up any of the cells to discharge them in a salt bath. Usually this takes place after the cells have been used and near the bottom end anyhow. I have seen cells puff up when taken down even when the load has been considered light. What ever you feel comfortable with. There is always someone who can quote someone else as to the best way of accomplishing a task. My method right or wrong has been working for me for over 15 years I'll stick with what I know thanks.

If you look on the internet there are supposedly many ways to neutralize these batteries. Pick your poison after careful reading and be careful.

Dennis

[davidmc36]

Originally Posted by Lazy Ace

No copper in the tabs of a lipo ......

Huh? The problem is the aluminum tabs rot off pretty quick.

What are the wires made of????

[kcaldwel]

I just tried the salt water bath on a damaged LiPo. I had discharged it using resistors for a couple of hours a couple of weeks ago. The voltage was 0V after discharge, but after a few weeks of sitting, the no-load voltage had recovered to about 2V per cell. I obviously need to load the batteries longer, and then maybe short the leads. I stripped the cover off so I could see what was happening at the tabs.

I mixed up a salt water bath. The resistance on an ohm meter of the salt bath was about 30k Ohms - quite high. Discharge would take a long time, probably the couple of weeks I have seen mentioned.

I put the battery in the bath, and immediately got electrolysis off the tabs. After 2 hours the positive tab had been completely eaten away. This would yield 0V at the connector, even if the battery still had charge in it.

This is the problem with the salt bath method. The battery reads 0V, but it may well not be discharged. The discharge will basically halt once the tab is eaten away, and that seems to happen very quickly if there is any life in the battery. I'm pretty sure that the tab disappearing is why the battery seems to have 0V after awhile in a salt bath.

If you don't discharge the cells to less than 1V each first, you get electrolysis off the tabs creating hydrogen, oxygen and chlorine gas from the sodium chloride (salt). Definitely do this outside. It also creates a nice toxic mess in the water with dissolved aluminum and other crud that I'm not sure what it is.

Given the need to get the cell voltage below 1V before using the salt bath, the short life of the aluminum tab in salt water, and the high resistance of the bath requiring a long discharge time, I can't see that the salt bath is really a great method. Since you have to discharge the cells with a resistance load of some type beforehand anyway, why not just leave it connected for 24 hours until the cells are completely drained?

Now that the tab is gone on this battery, I'm glad I pretty much killed it with a resistance load.

I'm not sure what to do with a pack with a damaged cell that gives you an open at the connector. I guess you have to strip the top and discharge each live cell?

I'll try an unopened pack in the salt bath for a few hours, and then open the top to see if the tab disappeared. The toxic looking water doesn't appeal to me very much either.

Kevin

[davidmc36]

Originally Posted by kcaldwel

.....Since you have to discharge the cells with a resistance load of some type beforehand anyway, why not just leave it connected for 24 hours until the cells are completely drained?...........The toxic looking water doesn't appeal to me very much either.

Kevin

About 24 hours is what I found a 12 volt tail light bulb took to get it such that the leads can just be twisted together, overnight was still showing a few tenths.

Yeah, what to do with the water after. Why not just discharge and turn the intact battery over to somebody that has the capability to deal with the materials.

[stegl]

I would go with a couple of 12v light bulbs in parallel and when down to zero volts , tie the positive and negative leads together so no bounce back up to a couple of volts. Also most voltage readings are probably just open voltage and not taken under a slight load. If slightly loaded you would likely see the voltage go to zero or pretty close.

[kcaldwel]

Some more fairly unscientific results. I took one more battery and stripped the package off it (Nanotech 1000mAh 4S), and left two more Nanotechs of similar size with the packaging on them. These three were all about 1.0 to 1.5V per cell after being drained by an 8Ohm resistance load for about 3 to 4 hours, and then left to sit for a few weeks. The voltage they show is just the recovery voltage, and I seriously doubt there is much capacity there.

I put these three in 250ml of salt water solution (not a bucket). After 3 hours last night, they were all still connected, and the tab on the stripped one's positive tab was corroded but still connected. They were all showing about 0.2 to 0.3V per cell. I decided to leave them over night before stripping the other two.

This morning the stripped one hadn't changed much. The positive tab was corroded but still connected. When I stripped the other two, they were similar, maybe a bit less corroded.

I've forgotten most of my chemistry, but it appears you need some voltage and current flow to corrode the positive aluminum tab quickly. That makes sense to me, reverse electroplating. I can't remember if there is a minimum voltage to drive aluminum into solution in salt water, or if it is just a current per area thing.

So, if the battery is essentially dead, you can put it in salt water and not much happens. If the battery has even a tiny bit of capacity left, 2V recovered per cell over a few weeks after being drained on a resistance load, then the current flow corrodes the positive terminal pretty quickly. I would suspect a battery that hadn't been drained to near empty would eat it's positive terminal very quickly. This will make it look like it is at 0V and discharged, but only because it is internally disconnected.

Current flow through salt water is proportional to the area of the electrodes divided by the distance between them I think. Once the area of the aluminum tab is gone, the current flow in the salt water bath will essentially stop.

I don't know if there is a difference in the tab thicknesses or materials between brands. The first one that the tab disappeared was a Thunderpower 850mAh 70C 850mAh.

I won't be using the salt water bath. I will be leaving my packs on the resistance load longer, 24 hours, and connecting the wires after. I will then take them for recycling.

Kevin

[stegl]

I have only had to decommission one battery so far but the auto light bulb discharge seems the way to go . When checking each lipo cell for voltage after a 24 hour discharge I think best to test voltage when light bulb still connected. If all zero then twist the pos and neg battery wires and dispose.

Earlier I mentioned using two 12 auto light bulbs in parallel so this would give twice the discharge rate. Use a meter to check to see what the amp discharge is and then decide how many bulbs to use in parallel for a given discharge rate.