Safe LiPo Disposal

Hello,

I actually consider myself lucky. I've been racing with LiPo packs for two seasons and I'm about to start my third. In all that time I've not had any LiPo related problems or issues.

This weekend I broke all my electronics out of storage for their annual pre-prep for the coming race season and one of my LiPo Packs, a 3200Mah 2C pack seems to have not made it...I'm getting 4.8v on it, with one cell reading 4.2v and the other reading 0.6v - yikes.

I did contact the MFG and they no longer make this type of pack so they are washing their hands of it - which is OK, I've had it more than a year however I'm now faced with wanting to dispose of the pack safely. I'm wondering if anyone out there has actually done this - I HAVE READ plenty of posts and instructions online but I'm wondering if any of you have actually done it.

At the moment, I'm inclined to think I should carefully cut off the shrink wrap, and put the pack in a nice bath (maybe 6" deep) of salt water. Is that right? How much water? How much salt?

With all the horror stories I've heard I just want to be sure I'm doing this correctly.

Thanks,

DM

[Gustav]

I have the same situation with a flightpower pack ith one dead cell,it's been living in my shed since(away from the house).I need to get round to doing something about it.it's probably a good idea to discharge it first before the salt bath,i've heard that the salt bath won't necissarily discharge a charged pack fully.I thought about hooking up a light bulb or maybe a fan to it first.

[MetalMan]

Discharge the pack completely (a charger set to discharge in NiMh mode), and then put a resistor with a small resistance on the pack when you discharged it as far as you can with a charger. A lightbulb would also work.
Leave the pack on with the resistor (or lightbulb) for a day or so, and when that's done, then you can put that pack in salt water. If you want to have some safe fun, you can pierce the cells while they're in the salt water :).

If you only use salt water to discharge the pack, there's a chance it won't actually be discharged by the time you throw it away. One of the tabs on the cell (I believe it's the negative nickel one) will most likely dissolve before the cell is completely discharged, rendering it dangerous still.

Originally Posted by MetalMan

Discharge the pack completely (a charger set to discharge in NiMh mode), and then put a resistor with a small resistance on the pack when you discharged it as far as you can with a charger. A lightbulb would also work.
Leave the pack on with the resistor (or lightbulb) for a day or so.

How do you do the resistor trick. I would imagine you would want to discharge the pack pretty low first. What voltage is OK for resisters? I have some 150 Ohm 1/2 watt resistors. Would those work alright?

[BrianG]

If the pack is more than a 2s (which I know MacII's is only 2s), I would see if you can salvage the good cells and maybe build a smaller 2s pack or something...

Ok, so discharge and then bath...one question - I know that I've been trained to never let my pack go below 6.5v...discharge will obviously take it quite low, is the idea that a deep discharge of a LiPo will ONLY ruin the cells or is there a risk of fire/explosion?

[squeeforever]

A slow discharge like that shouldn't cause anything like that.

[MetalMan]

Discharging a Lipo battery all the way down won't cause any sort of fire issues or anything like that. The cells may puff up a little, though. It's the charging of deep-discharged cells that causes problems.
You want to deep discharge the Lipo pack/cells because that takes the energy out. Without energy, a fire can't be started, making the pack safer for garbage disposal.

[glassdoctor]

The idea is to completely drain the battery... dead... flat. AT that point there is no danger because there is no charge (energy) left that can do any damage.

Any method you want to use will work, as long as it gets the battery to 0 volts.

Again.. the saltwater bath has been way overhyped imo and is outdated. (If you can find other ways to dump it dead)

I like the idea of using a nimh discharger... that will let you dump all the way.

[squeeforever]

Personally, I would put it in a ceramic flower pot and shoot it with a staple gun or something. Hell, maybe even a 22. :p

[glassdoctor]

vidoe camera and a gun... or knife.... hook it to 12V auto battery lol

[squeeforever]

I would have fun with it, but thats just me. Of course safety first, but why not have a little fun while your at it? Just discharging it and then a salt bath is no fun. :p

[glassdoctor]

I have smoked a couple cells :) and I have some more waiting for the Dr. sometime.... muahhahahaha

I may try to get some video if I ever do some fun testing... I have 6-8 3000mah cells begging for destruction

[BrianG]

I would size the resistors so it discharges the pack at a slow 100mA. You could get different resistors depending on the size of the pack (2s, 3s, etc), or make an adaptor cable so you discharge each cell individually through the balance connector.

resistor_value = pack_voltage / discharge_current
resistor_power = discharge_current^2 * resistor_value * 3

The "* 3" is a safety margin for the resistor so it won't get too hot. So, to discharge a 2s pack (assume worst case 4.2v/cell) of 8.4v at 100mA, the resistor would be 84 ohms ( 8.4v / 0.1A). Since 84 is an odd size, choose 100 ohms. For the power, you should get a power value no lower than 3w (100mA^2 * 100 ohms *3). You can choose 3w or higher, it doesn't matter - as long as you don't go lower in power.

If you were going to discharge each cell individually through the balancer leads, just use 4.2v in your figures above. You'd need one resistor for each series cell to do the whole pack at once.

Higher value resistors will just take longer to discharge, which doesn't matter unless you are in a hurry. A full 4Ah battery will take ~40 hours to totally dump at a 100mA draw.

I need electric math for dummies!

HA, I can kind of get my way through the formula, but how do you know or get the 100mA part and what does ^ stand for. The rest of it I get, I think.

At 4s at 4.2v/cell you should go for 200 ohms at 6w?

Can you parallel more resistors?