Li-Po Explosion!

[Lance]

This past weekend we had our annual fun-run where a disastrous event happened. I have a Seaview with the standard SubDriver, SNORT, Vislero twin 1300 mah (7.4 volt) battery pack, etc. Since it had been a long time since I used my Seaview, I ran a system check the weekend before the fun-run. I charged up the battery, checked the SD electrical system, and performed a leak check with one problem; the flap on the top of the ballast tank was sticky so it wouldn’t open to flood the tank. I lubed it up and that helped a little but it still would stay shut occasionally. It would open up after a moment or two of holding the stick to the open position. I figured I could tinker some more with it at the fun-run and recharged the battery and transmitter one more time and packed them up.
At the fun-run, I had performed the usual checkout of the SubDriver before putting my Seaview in the water and everything worked fine. I put the boat in the water and ran it on the surface along the shore for a few minutes to get warmed up. I then commanded a dive and there was no response. The motors were still running and the rudders were still responding. I tried another dive command and held the valve open as I had at home. Well, the sub started to slow down and was not responding to any command. Then there was a very significant plume of smoke coming out of the limber holes in the front of the sub. Oohs and aahs from spectators made me think of the fourth of July. Another sub buddy pulled his sub along side of my Seaview and nudged it closer to the shore. As I walked over to take her out of the water she started to sink, the bow was fully submerged to the sail. Once I pulled her out of the water and removed the superstructure I found the battery had exploded and partially blown off the battery compartment end cap. There was a strong smell of smoke and battery acid and the battery compartment was discolored (white). I brought the wreck back to my table and took out the sub driver. I noticed the battery compartment was warm to the touch, but the aft (electronics) end of the SD appeared unscathed. The end cap wiring from the on/off switch to the battery was partially melted. I had to use needle nose pliers to tug out the battery by the Dean’s plug because the battery had swollen so that it was tight in the SD. The battery was hot so I placed it away from people and property where it could either ignite or cool down safely. I took the hull and SD and rinsed them off and put them away for later inspection at home. The battery cooled down and I packaged it up for the trip home. The rest of the day I got comments from others about using Li-Po batteries and their instability. Some recommended Li-Ion instead.


Once home I found that the wiring running from the battery compartment to the ESC was also melted. Everything else appeared to be in good shape. I replaced the burnt wiring and connected the electronics to another battery to evaluate the damage to the electrical components. Everything was still working except the ESC. It wouldn’t respond to forward or reverse commands, it would sputter a little and stop. I didn’t notice any more burning smells and it didn’t feel excessively hot. I cleaned up the SD with water, baking soda and a toothbrush, sealed it back up and immersed it in the bottom of my tub for an hour to see if it was still water tight. The SD passed that test, as there was no leaking.
At this point I’m not sure what other checks I should perform. I think that the cause was a short somewhere but I found no evidence of that. I think the damage is limited to the battery and the ESC and both should be replaced. The sticky valve and the battery explosion are two separate and unrelated problems but I have some questions I hope someone can answer.

1) What could be the cause and what can I do to correct the battery problem?
2) Is there anything I should use other than water, baking soda and harsh language to clean up any residual battery acid?
3) Could the battery acid compromise the SD so it will one day weaken and fail?
4) Is there anything else that I should check for or test?
5) Are Li-Ion more stable than Li-Po batteries?
6) Is there a fix for the sticky flapper valve on top of the ballast tank?

Thanks,

Lance

[Slats]

Hi Lance,
I only comment on what I know given that I have zero experience with these batteries.

6) Is there a fix for the sticky flapper valve on top of the ballast tank?
First I am a self confessed extremely biased fan of the SD - its so bloody simple and it works. That said, the one area where it can be improved IMO is the top vent valve. I have found that this is problematic to get right in that, like your experience, it does seems to stick from time to time.

Probably best to let God Jump in here and provide his opinion - but I have found adjusting the screw underneath the valve was necessary. A bit of silicon grease also improved things. It still not perfect, and I would be keen to explore other variations like what Mike put up the other day on the site.

Best
J

[He Who Shall Not Be Named]

Lance,

Wow! I've been operating with Lithium-polymer batteries for two years now and the worst I've had happen was for one of the 1300mAh, 7.4-volt units swell up on me (I still use it, without incident so far).

Now, I have had two MTroniks ESC's blow up on me -- literally spitting solder out from the heat-cracked epoxy case! And I've suffered the occasional wiring short, something that could have been avoided had I installed, as Andy has insisted, a fuse between battery and ESC. But, so far, no Lithium-polymer battery induced fire, over-heat, or other casualty.

But that's me. You? You may have lost the lottery on this one. Might indeed be the battery. But, do look at a short somewhere that caused a high C-rate, exceeding the battery limit, precipitating the battery melt-down.

And the ESC may not be dead yet. Have you re-programmed it since the 'incident'. Might only need its ears cleaned. Just as you turn on the mission switch, while the ESC's green-red lights are alternating, press and hold the 'set' button (transmitter stick in neutral before you switch on). Still holding the set button push the transmitter throttle stick all the way to full-ahead, then down to full-astern, then back to neutral. Only then release the ESC's 'set' button. See if the ESC now works OK. If not, it's a dead-duck and has to be replaced.

If you're battery spewed electrolyte into the battery space, then the baking soda should have done the trick -- it's low pH will kill any acid in there. Hey, that begs a question: is the Lithium-polymer electrolyte an acid or base chemistry?

Andy? Kevin?

Like any SubDriver, air the thing out between runs. Read and follow your mission checks.

The vent valve problem: take the vent valve off the SubDriver and stretch the rubber element open almost to the point where you tear it free from the plastic body. That will permit it to spring more open with no contact pressure on it from the adjusting screw atop the ballast linkage arm. Re-install and apply some fresh RTV around the valve body to make it watertight.

By the way, I've looked over the pictures of your SEAVIEW. Nice work!

Here's mine:

[Slats]

The vent valve problem: take the vent valve off the SubDriver and stretch the rubber element open almost to the point where you tear it free from the plastic body. That will permit it to spring more open with no contact pressure on it from the adjusting screw atop the ballast linkage arm. Re-install and apply some fresh RTV around the valve body to make it watertight.

Thanks David - I too will keep that in mind the next time I discover it sticking.

J

[Lance]

Thanks for the complement Dave! As soon as I got your advice for the ESC I ran out to test it hoping that I can still use it. Unfortunatelly last time I used the transmitter I must have left it on, the battery was dead. I'll charge it overnight and report back with my findings tomorrow.

Lance

[roedj]

All,

The procedure for spilled LiPo electrolyte has nothing to do with pH or anything like a Lead Acid battery. All you have to do is to Google the following:

"lithium polymer battery MSDS" (without the quotes)

for a complete overview of the chemistry and its hazards.

Dan

[He Who Shall Not Be Named]

From Wikipedia:


Applications
A compelling advantage of Li-poly cells is that manufacturers can shape the battery almost however they please, which can be important to mobile phone manufacturers constantly working on smaller, thinner, and lighter phones.

3-Cell LiPo for RC-models


Li-poly batteries are also gaining favor in the world of radio-controlled aircraft as well as radio-controlled cars, where the advantages of both lower weight and greatly increased run times can be sufficient justification for the price. Some airsoft gun owners have switched to LiPo batteries due to the above reasons and the increased rate of fire they provide. However, lithium polymer-specific chargers are required to avoid fire and explosion. Explosions can also occur if the battery is short-circuited, as tremendous current passes through the cell in an instant. Radio-control enthusiasts take special precautions to ensure their battery leads are properly connected and insulated. Furthermore fires can occur if the cell or pack is punctured. Radio-controlled car batteries are often protected by durable plastic cases to prevent puncture. Specially designed electronic motor speed controls are used to prevent excessive discharge and subsequent battery damage. This is achieved using a low voltage cutoff (LVC) setting that is adjusted to maintain cell voltage greater than (typically) 3 V per cell.
Li-poly batteries are also gaining ground in PDAs and laptop computers, such as Apple's MacBook family, Amazon's Kindle, Lenovo's Thinkpad X300 and Ultrabay Batteries, the OQO series of palmtops, the HP Mini and Dell products featuring D-bay batteries. They can be found in small digital music devices such as iPods, Zunes, and other MP3 players and the Apple iPhone, as well as gaming equipment like Sony's Playstation 3 wireless controllers[2]. They are desirable in applications where small form factors and energy density outweigh cost considerations.


Explosions can also occur if the battery is short-circuited, as tremendous current passes through the cell in an instant.

[He Who Shall Not Be Named]

All,

The procedure for spilled LiPo electrolyte has nothing to do with pH or anything like a Lead Acid battery. All you have to do is to Google the following:

"lithium polymer battery MSDS" (without the quotes)

for a complete overview of the chemistry and its hazards.

Dan

Thanks Dan. But, what solvents/abrasives/acid/salt do you use to clean up Lithium-polymer electrolyte?

David,

[roedj]

Material Safety Data Sheets (MSDS) for LiPo's

David & All,

The chemistry of a LiPo is not based on a strong acid nor base. It's rather neutral but that doesn't mean it's harmless. Lead acid batteries use strong Sulfuric Acid which is a totally different animal - LiPo's are rather harmless except of course when they're burning.

In general if there is skin or eye contact with the electrolyte, flush the area with large amounts of water - seek medical help.

Clean up of spilled electrolyte consists of gathering up the electrolyte, while wearing appropriate gloves, and disposing of it. Absorbents to be used vary from sand, rock salt to unspecified absorbent. (kitty litter?) Disposal consists of placing the absorbent/electrolyte in a plastic lined metal container and throwing it away as it's OK to place in a land fill. One MSDS sheet even mentioned burning the absorbent mixture. One of the sheets said to call the local fire department which seems to me to be "ass covering" verbiage more than anything else.

MSDS sheets are all organized in a similar fashion and are easy to read. For further info ask your battery manufacturer for the MSDS sheet for his product. If the battery is sold in the USA there ought to be an MSDS.

Hope this helps.

Dan

[Subculture]

This sounds like a fault with the ESC going short circuit as you say the leads from the battery to the ESC have melted insulation- they've been trying to act as a 'fuse' (not a very good one).

Fitting a fuse protects your wiring and your wtc. It will not protect your ESC if it develops a fault (I've yet to encounter a fuse fast acting enough to blow when a semiconductor goes bad) but it will help prevent your power leads glowing red hot and your battery from becoming a potential bomb.

Lipos will supply as much energy as they can, to the point that they will destroy themselves and whatever is around them. Lithium batteries intended for the domestic market e.g. phones, laptops etc. are fitted with internal protection devices to limit the current they can supply in the event of a short.

You might ask why these aren't fitted on packs for hobby use, and the answer is- we're drawing much higher levels of current and it would limit the packs performance.

I've been using lipos for about seven years now, and I think they're amongst the very best battery technology currently available. You do need to charge these batteries right, to this end I use a balancing charger with all packs (including Li-ion packs which I use in my TX), plus it's important not to run them down beyond 3 volts per cell.

[Lance]

Thanks everyone for your input, it really helps!

Bad luck, I tried several times to re-program the ESC and it failed. I guess I'm in the market for a new one. I'll mosey on over to Mike's selection of speed controllers and pick up another one.

The good news, I guess, is that the Li-Po electolyte is relatively easy to clean up. The baking soda may have been unnecessary, but it was the only thing I could think of at the time.

Another question came to mind about the on/off switch on the end cap. Should I replace it or is this a case of testing it and if it works it's OK to use?

The idea of putting a fuse in the circuit sounds like a good idea. What type and/or size is recommended and where can I find them? Remember you are talking to someone who thinks that electricity is really black magic...

[Subculture]

Depends on the current the motor pulls, the 'C' rating of the batteries you use and the cable going to your ESC.

In my experience the cable used is usually very thick, so we don't need to worry too much about that. What's the stall rating of the motors in the Seaview SD, somewhere between 5-15A I'll wager, and if we say the Lipo's are 10C (even the humblest of Lipos are 10c) edit: I see Mike's are 15C I would fit a 15A slow blow fuse. This should be rock solid in normal use and only blow in the event of a major short circuit.

[639mpa]

Hi Guys
I'm setting up the electronics this week in my 1/96 Uss Tautog SSN639 with 2.5 sub driver(a great design). What size fuse for the battery to ESC hookup? Can I get it at radio shack?
Thanks
Two basic rules of submarine ops
1. What goes down must come up!
2. Keep the water Out of the people tank!

[He Who Shall Not Be Named]

10-15 Ampere, slow burn.

Good man. You're thinking. (I can almost see Andy nodding in agreement).

David,