Li-Polymer Batteries

Looks like the outside dimensions, 3.5 x 70 x 90 vs 3.5 x 70 x 95.

Mark Storkamp wrote on 10/16/2017 1:47 PM:

Duh! Thanks. Now to figure out why they are a different size. Could that be the protection circuit board? They say these cells include protection, but maybe that is not entirely accurate?

rickman wrote on 10/16/2017 10:16 AM:

I got an answer to the question above.

One thing that concerns me about lithium cells is their nature to catch fire and the way they are almost explosive when they do. I'm thinking of making a box for them of aluminum sheet. This will contain a fire if a cell ruptures, but not the heat. I don't have a lot of space to add insulation, but I could add a layer of something that would absorb the heat at least on the side that would be in contact with anything. I'm wondering what would be a good insulating or heat absorbing layer. In the old days I would wrap the box in an asbestos cloth, but I expect they aren't used any more.

I found some half inch thick Ceramic Fiber Blanket on eBay for $10. This looks like it could help insulate a run away battery. But when I look at a data sheet, I'm not sure it will keep the outer plastic case from melting and/or catching fire. They give a temperature rise, but don't say how long they allowed before taking the measurement. They cite ASTM Test Procedure C-177, but I haven't dug that up yet to see how it is done.

What else would be an option? It should be cheap and available.

rickman wrote on 10/17/2017 1:30 AM:

This looks interesting and it would be easy to install. They say it will

On a sunny day (Tue, 17 Oct 2017 01:30:45 -0400) it happened rickman wrote in :

It has build in chips to protect it, very unlikely to cath fire if you use a decent charger chip.

Jan Panteltje wrote on 10/17/2017 4:13 AM:

"Very unlikely" is fine when it is sitting on your desk. If that happens you get an appropriate fire extinguisher and put it out or at least let it burn and put out anything else it has ignited. If you are in a vehicle where you have no means of escaping and no way to deal with the fire, you are SOL. "Very unlikely" isn't good enough for me.

Also, I'm not convinced all of these units have protection. The two model numbers would seem to indicate one is 5 mm longer than the other. I expect this is exactly the size of the protection board, so one might have protection and the other might not. It is not all that unusual for an eBay listing to contain errors and complete lies^H^H^H^H^H alternate facts.

On a sunny day (Tue, 17 Oct 2017 05:21:15 -0400) it happened rickman wrote in :

Na, wrap your nuclear plants in ..

True, I only looked at the link, you can see the protection board, I have some like that, but only 1000 mAh, marked 'Varta'. From China nevertheless.

I have some without protection board too...more RC type single cell lipos. And then I have the 3 cell ones, 30C ... no protection either. Danger all around me, Oh and the box with LiIon super powerfull forgot how many C.

Gotta run :-)

Think about it, you find lipos everywhere, even in those blutooth earplugs / headsets for your cellphone, and happily plug it in your ear and wear it on your head. Cars have gasoline, bad things can happen... There is a mad dog president in control of the button, I would worry about that first. Probabilities.

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.

SNIP They say that the battery is fully protected internally... over voltage, undervoltage and over current so should be perfectly safe....

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.

"They" say the battery protected, yes. I don't recall anyone assuring that makes them "perfectly safe". I recall certain cell phones made be a major manufacturer (with a great deal of reputation at stake) who had a rash of battery fires while the phone was in people's pockets.

NiMH might be the right way to go. Four Enloop AAs would give 4.8 volts nominal at around 2000 mAHr and no real circuitry required. Because they are charged in pairs I've always had trouble keeping them balanced. So my preference is for the single cell Lithium Polymer if I can make it safe enough.

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.