Re: Li-Polymer Batteries

That, like any other thermal insulator, will increase the internal temperature of the battery, thus increasing the risk of earlier expiry.

Jan Panteltje wrote on 10/17/2017 5:47 AM:

I seem to recall a number of professional designs from companies who have much reputation to loose which burst into flames.

So no, I don't have tons of confidence in Lithium batteries to the extent that I want to strap one on my kayak with no physical protection against the boat catching on fire.

On a sunny day (Tue, 17 Oct 2017 06:18:09 -0400) it happened rickman wrote in :

Was it not Liion?

Well just roll.

Jan Panteltje wrote on 10/17/2017 6:26 AM:

I seem to recall Lithium doesn't do so well in contact with water.

On a sunny day (Tue, 17 Oct 2017 06:33:15 -0400) it happened rickman wrote in :

Have not had any Li fires, so don't know, but youtube has the answer:

So what can you do in a kayak? water proof bottle:

Interesting to see how far people will go to ignore the total system and focus on one ill-conceived component. The devil is in the details, and we have few.

Do the math. How much energy is released in a battery fire? If you insulate it, how hot will it get inside, since you've guaranteed thermal runaway? How much energy is released as heat if you discharge the battery at maximum current allowed by your current limit strategy? What does that do to the cell temperature if you insulate it?

How often are you gonna use this kayak device? Can you not throw it overboard if it catches fire? I submit that the release mechanism is far more likely to jamb than the battery is to catch fire. ;-)

Given your paranoia, might a NiMH or Alkaline AA cell pack be more cost effective and weigh less and take up less space than your protection vault and fire suppression apparatus and floating burn unit to treat the injured? Maybe you should have two burn units just in case one of the doctors has a heart attack.

I surmise that there are some devices sold on EBAY that are made from tested/fully compliant components and do what they say. Problem is that you can't tell which.

Battery protection built into the battery won't solve your problem. It's there as a backup to your own carefully crafted redundant battery management system. I'm not saying you shouldn't have it. I'm saying that you shouldn't rely on it.

The good news is that you are very much more likely to drown than to catch fire.

Here's the authoritative report of one example of an *aerospace* qualified battery fire. The pilot was dead (ho ho) lucky the fire only occurred after landing.

The pictures in the report are informative.

Jan Panteltje wrote on 10/17/2017 11:31 AM:

There are so many things wrong with this I have to assume you are joking with me.

Lithium is highly reactive with water. It is stored in oil or under Argon to exclude water. Take that seriously.

Jan Panteltje wrote on 10/17/2017 11:31 AM:

Oh yeah, Lithium sometimes fools the experts.

Not sure what you mean about ignoring the "system"?

A lithium batter will release a *lot* more heat than just what is stored in the battery. Even discharged lithium batteries have to be stored safely.

Don't care, the concern is to prevent the China syndrome where the battery burns its case and melts though my boat. High density polyethylene won't stand up to a lithium fire, or any other type of fire for that matter.

The unit won't be drawing the maximum current. There will be protection to prevent this. The load will be relatively light compared to the C value. I'm interested in a long discharge time.

Not very easily. It will be securely affixed to the bow of a 17 foot kayak with me in the middle. My arms aren't 8 foot long.

A great reason to prevent a fire from becoming catastrophic.

That would be a good idea, but NiMH cells don't have the density. But that might not be a significant issue. But the circuits to use NiMH in a device like this aren't so common.

Yes, and the battery charger/step up circuit also incorporates protection.

I'd hate to hear the bad news.

Yes, you understand the problem...but what's the number? I suspect you can't contain a fire in any container you're willing to paddle around in a kayak. Depends on that number.

Ok then that's something you can change in your "system approach".

slight modification of the requirements can make a huge difference in the "system" solution.

Looking at the overall system requirements can reveal if this is a viable option. It does address your major fear. It's all about the weighting of constraints. Was it the Rolling Stones???You can't always get what you want.. But the circuits to use NiMH in

Do you care what's common? You building more than one? If you can accommodate the voltage variation of lithium, you can probably figger out how to substitute Lithium.

Yes, changing the problem can make the solution much easier to find. So what change are you proposing?

The way you talk, you sound like you are familiar with formal project management. What drives the requirements in the systems you work on?

I recall someone's tag line saying engineering is about making what you need with the materials you can get. In this case I am not looking to design a board and solder chips. I wish to use commonly available and low cost board level components to fabricate this system. So yes, I care what's available. What's common usually means low cost. So I care about that as well. So far I have not seen a single board that will serve as a power bank using a single NiMH cell the way I can with a lithium cell.

I don't see where you are making any effort to help. You seem to want to nitpick rather than assist. I was hoping someone here had been down this road and could help with recommendation of what to use or what to avoid.

On a sunny day (Tue, 17 Oct 2017 16:52:07 -0400) it happened rickman wrote in :

No, not joking.

If you are worried about it, why not take an old lipo and throw it in the water? Just spend the 4 $ or so for a test.

When I charge liion and lipo I always have safety procedures in place, basically it is 2 to 3 meters from the door to the tiled terras, and I have HUGE pliers to grab a burning one and put it outside, and a hose to stop any collateral fires it may have caused.

But some _advice_ IF you are so WORRIED why not use Lifepo4? I have some lifepo4 cells in AAA form (about 3V per cell, in one keyboard, and in my temperature meter), and those are safe, and have hardly any self discharge. Lifpo4 high power is used in ships, and if you type lifepo4 in the ebay search window you find many variants and sellers. It is MUCH safer than lipo or liion.

On a sunny day (Tue, 17 Oct 2017 16:53:07 -0400) it happened rickman wrote in :

I know, it is the intro on my website:

See also:

Jan Panteltje wrote on 10/18/2017 3:12 AM:

For starters I'm not going to use a glass container in an outdoor, rugged environment. It would not be long before it bumped against something hard enough that the glass broke and parts are everywhere, not to mention glass shards. Then there is the problem of the seal not lasting. The one in your photo looks like the *rubber* is about shot. Rubber is a terrible material to use unless it can be kept from the sun and air or specially treated.

Again, I think you are joking with me. Tossing a sealed battery in the water would do nothing to test the results when it is on fire and hits the water. As long as the lithium is sealed inside it would be fine. Otherwise spilling a drink on your cell phone would result in a fire.

I've given that some thought. The charging would not be on the boat unless from a solar cell. But that would not be at a high rate. The solar cell of a size that would fit in the case only put out around 150 to 200 mA in bright sunlight and this may be an exaggeration by the vendors. I have one on order I will be testing. I wouldn't expect 200 mA into a 3000 mAHr cell to be stressing it at all. Otherwise it will be charged off the boat.

Same reasons I'm not using NiMH.

I find much lower capacity other than the 26650 size cell which is too large. The flat form factor of the polymer cells is very handy.

I wonder why I can't find anything similar to the charger, step up boards to make one of these cells into a power bank? The one board I do find many sellers of is the protection board.

A sealed plastic bag of water either side of the battery could work, The bag absorbs heat, melts, then extracts the heat turning into relatively harmless fire extinguishing steam. But once you do that you're better off going to NiMH :)

NT

On a sunny day (Wed, 18 Oct 2017 04:58:54 -0400) it happened rickman wrote in :

OK, I dont't know what you are doing, sure glass can break. But you would not be throwing it around againt rocks..

This is a very old bottle, new ones are cheap and last >10 years with al sorts of things conserved in it.

OK, use your imagination now for a moment and do that short or overload thing you mention, and THEN toss it in the water, or while it is in the water, else the discursion becomes endless. Put a camera on it and upload the result to youtube. That is real, the rest is mainly paranoia. Again, do you bring walky talkies? Those use lipo too, at least my baofeng has, would not put it in the water tough. You need a waterproof bag or something.

'Same' means less capacity? lifepo4 has a lot more capacity that NiMh, is more reliable too in my experience (real experience), has much lower self discharge (THAT is important in the boonies, take out your radio, camera, batteries empty...)

Too large with or without all the external safety wrap you were going to put on the other batteries?

Specify size, voltage, mAh, form factor.. Ebay is full of boost - and buck converters for about 5$.

I was wondering until I saw who was posting this. Try learning something about putting out a lithium fire.

The point is to limit temp rise to minimise likely harm to the boat.

states that for secondary lithium cells "you may use a standard ABC fire extinguisher or water to put out a lithium ion battery fire." whereas for primary cells, which contain elemental lithium, "Only Class D fire extinguishers that contain a copper powder are approv ed for combating a lithium fire" It also explains why. Are you saying they're wrong? If so, on what basis?

NT