Prevent explosion, battery compartments, Lipo batteries

Waterproof Housing, Frames, and Buoyancy Methods.
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Jaman42
Posts: 94
Joined: Nov 3rd, 2014, 4:19 am

Prevent explosion, battery compartments, Lipo batteries

Post by Jaman42 »

Again I have been thinking about the potential danger of keeping lipos in a closed off aluminum tube, I don't want it to explode on me. I have been reading a lot on the subject and life batteries seems to be a good alternative, for my requirements however I have to pay a bit more for a bit less capacity.

Faulty life batteries will also most likely puff (expand) but I guess it's the reaction with air that make lipos less safe. The life batteries most likely won't catch fire but that is not my main concern. I already got all the lipos so I am using those for now and perhaps when they are depleted I get something else.

I wrote about a pressure release valve I found in another post, the low pressure is around 55$ which I believe is resonable price but it is rated for a depth of 100m and I am aiming for a bit more so everything else is designed for a depth of 300m. The high pressure ones are ridiculously expensive so they are not an option. So here are my options as I see it.

1. Remove the endcaps of the battery compartments when out of water. Potential fire hazard but at least there will be no explosion with flying endcaps as a result. As long as the endcaps are on there is a potential of an explosion however. I do believe most accidents happen when the cell(s) are discharged to much or when charging so it might be resonable safe.
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2. Buy the 55$ pressure release valves or make a weak spot on the battery compartments and make them in to silicon oil filled pressure compensating compartments. I've read people claim that Lipos handle pressure very well but I haven't seen any figures on how well. I have no idea if a lipo can handle 450 psi.
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3. Buy a ball valve or similar that can handle 450 psi and manually open it when out of water. A concern could be that I forget to open it. A advantage is that there will be a hole straight into the compartment so pressure building up would escape immediately. No tools required and no flying projectiles, might get a bit bulky and perhaps cause a jet of flames shooting out if the batteries ignite.
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4. Make my own pressure release system that can handle the pressure. I was thinking a bit how the design would look and thought about the base principle. It need to brake easily when force is applied from the inside and withstand force from the outside. I made a simple design to get the thoughts going realizing that it could turn into a bullet if an explosion would to occur.
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5. Fill the compartments with silicone oil (it's non-flammable) to remove the air to decrease the risk of an explosion. The expansion of the battery cells would still build up a pressure but without the fierce reaction when in contact with air it might not cause a problem.

6. The danger of lipos is overrated, just put the batteries in the compartments. Monitor the voltage carefully when charging, discharging and operating and there won't be any issues. I mean poring the floor full of gasoline and lighting a match will also burn down your house, I wonder on how many occasions "the batteries just exploded" without the user doing something wrong. Alternatively: The force of the batteries expanding won't be enough to make the compartment explode.

So that's my current thoughts on the matter, all ideas seems potentially dangerous. Any comments or other ideas?
Bindo
Posts: 112
Joined: Apr 7th, 2015, 4:42 pm

Re: Prevent explosion, battery compartments, Lipo batteries

Post by Bindo »

A little misleading if #2 is an unknown :(

i wouldn't be pressurising LIPO's thats for sure
Jaman42
Posts: 94
Joined: Nov 3rd, 2014, 4:19 am

Re: Prevent explosion, battery compartments, Lipo batteries

Post by Jaman42 »

Yesterday I unintentionally turned my lipo into a welder for a split second. I was charging one of my packs to use for testing the electronics. Instead of disconnecting the battery connectors I did the silly mistake of disconnecting the plugs from the charger first leaving two hot wires dangling. For a split second they hit the stainless steel bench on which I was working on, a small bit of the tip of the connector melted of and stuck to the bench. Gave me an idea on how much current these batteries can deliver, it's quite impressive.

Well lesson learned for the next time, I'm not gonna charge batteries on a surface that is conductive and from now on I will always disconnect the battery connectors instead of the extension going to the charger.

Like I said it was only for a split second so the battery pack seems to be alright, no puffiness and all the cell voltages where the same. I'm gonna keep my eyes on it but nothing obviously wrong with it. Just thought I share my experience so perhaps someone else could avoid doing the same mistake.

I guess it got me thinking so I hade to do some more research on lipos and finally came to the conclusion that they are pretty safe. I also came to the conclusion that almost all "lipo accidents" on for example Youtube are intentional, made to prove how dangerous they can be if mistreated, and boy are they being mistreated. I mean if you light a candle and it tips over you could burn your house down, perhaps an aerosol can standing nearby could even cause an explosion. You probably charge your cellphone on the nightstand while you sleep? Lithium-ion and lithium-polymer "accidents" are very similair in how they behave. Considering how many batteries are out there and how few the real accidents are I feel comfortable using them. When following the guidelines and using the right equipment I feel it's safe.

Most of the accidents seems to be caused from overcharging the cells, usually by having the wrong setting on the charger, for example charging a 3S battery with 4S setting, by having a faulty cell and not balancing charging or simply by having an old charger. Nothing against old chargers but the development has been moving forward and I can safely say based on what I have read that modern chargers are much more reliable when it comes to these safety features. When in storage you should discharge the batteries to storage capacity for two reasons. First of all your battery will last longer and second, more importantly if the battery would magically short-circuit the reaction wouldn't be anything close to what you can see in the "Lipo accident" videos on Youtube. Batteries that magically short-circuit seems to be rare thou :), consider how many stores and hobbyists that have lipos in storage without bursting into flames all the time that makes perfect sense.

I will always balance charge, some people say that it's only necessary to do that once in a while but it's an unnecessary risk to take. If a cell dies your charger will still keep on charging the other cells to try and reach the voltage of all of the normally healthy cells combined resulting in overcharged cells. If you balance charge your charger will stop charging when it detects a dead cell or even too big of a voltage difference between the cells, it's a no-brainer. I also read that it is good practice to only charge at 1C, for me charging a single battery would mean 5 ampere, when charging all the batteries in parallel it would mean 40 ampere but I would need a much bigger charger to be able to do that. My charger can only do 10 ampere so it would take a bit longer but other than that there is no disadvantage of charging at a lower current.

So I have learnt to always balance charge my batteries at the correct settings on a non conductive surface, to remove the battery connectors first, not to over charge or over discharge them and to always store them at storage voltage. I might charge the batteries in open battery compartments or disconnect them first, still undecided. I would probably store them with the battery compartments opened as well because I am not sure how much punch there is in a 4S lipo at storage voltage. There aren't much videos on how lipos at storage voltage react for a reason I suppose, it might not be that spectacular to watch a battery just sitting there :). One day i will make a watertight battery compartment with the same design as I use and at a safe location short circuit a 4S lipo inside of it at storage voltage and see what and if something happens.
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