Spin9k

This is how many 'powersports' Lithium batteries are made with the A123 cells. Anyone can do a series/parallel construction of these, the downsides are getting all the connections right that can carry the amp load, the problem of single cell failure causing a dimino failure in other cells, the difficulty of changing out a failing cell, and of course balancing during charging of the potential voltage difference between so many cells. Otherwise it's a slam dunk

TeamRX8

iTrader: (25)

and if not, a firey zoom-zoom-boom

ebb

iTrader: (7)

Team, you have seen the A123 cells catch on fire? I did not think that was a risk with the LiFeP0 batteries.

überschnell

While they are much less prone to fiery death than LiPo packs, the electrolyte in LiFePO4 cells is still flammable. As with ALL battery chemistries, care is advised (at least they don't release hydrogen gas while charging!).

Spin9k

source?

Lithium Iron Phosphate LiFePO4 - Safety & Environmental

Phosphate based technology possesses superior thermal and chemical stability which provides better safety characteristics than those of Lithium-ion technology made with other cathode materials. Lithium phosphate cells are incombustible in the event of mishandling during charge or discharge, they are more stable under overcharge or short circuit conditions and they can withstand high temperatures without decomposing. When abuse does occur, the phosphate based cathode material will not burn and is not prone to thermal runaway. Phosphate chemistry also offers a longer cycle life.

• Extremely stable - The oxidation product of lithium iron phosphate is the stable material, ferric phosphate, according to the reaction: LiFePO4 +6C → LiC6 +FePO4

• Will not overheat, catch fire or explode if inadvertently overcharged

• Can be used safely in high ambient temperatures of up to 60degC without any degradation in performance

• Inherently safe since they do not produce flammable gasses under any circumstances - even if overcharged

• The most environmentally friendly battery chemistry available today with no toxic chemicals such as lead, cadmium, corrosive acids or alkalis

• Low phosphate levels within UN Air Standards

• 99% recyclable material

sources: http://www.fero.co.nz/Agencies/LiFeBATT.html, http://www.mpoweruk.com/lithiumS.htm

TeamRX8

iTrader: (25)

He's with Lithium Pros (and apparently a new site sponsor), lol.

Welcome aboard!

It may not be a fiery death, but it can make a mess. There are pictures out there of some that have come apart. They need to be protected from both under and over charging, among other things.

.

Spin9k

uberschnell can be a vendor or whatever, but he (she) needs to be able to back up assertions, just like anyone else.

A perfect example is when you say, "There are pictures out there of some that have come apart." which is a laughable comment as well in that context.

If you can't prove your words you aren't credible.

überschnell

Do you have some reason to doubt my credibility? I find this ironic, since you give no citation for your own postings.

Of course they don't produce flammable gasses, they don't produce or emit gasses at all, at least as far as I know. The liquid electrolyte is quite flammable, I can assure you. It also smells terrible! I believe acetone/acetate is one of the main components.
Unlike LiPo, LiFePO4 chemistries do not generate a large amount of oxygen when they are venting--obviously, O2 contributes to fire. I have seen plenty of failed lithium packs, usually resulting from varying degrees of abuse. Some swell, some swell, some vent, and some do both. It is extremely rare for one to catch fire, as you need a strong ignition source when the battery is venting. Just visit any R/C forum to see the lengths those guys are going to in order to keep from burning their houses down with LiPo chemistries--charging in fireproof bags and carrying around huge buckets of sand and whatnot.

I have heard some chatter recently about testing of non-flammable electrolytes--while I'm sure this is a few years out, I'm pretty confident that lithium technology, specifically safety, will continue to advance at a rapid rate. With the push for electric cars and ever more demanding consumer electronics, there is a major push to improve performance and capacity. I've noticed the nanotechnology seems to be spurring advancements, as well.

I would challenge you to disprove my statements, rather than just questioning them.

TeamRX8

iTrader: (25)

I only need to prove things for myself, not for you. I researched the subject well before making my own choice a year ago.

überschnell

TeamRX8, my post was directed at Spin9K, not at you. Thanks for the welcome!

Spin9k

(citation now listed above).

The statement you made, "the electrolyte in LiFePO4 cells is still flammable", is what I question as a general statement for LiFePO4 batteries. There are many electrolytes in use in LiFePO4 cells, and more under development, but typically they aren't flamable or explosive in the battery. As LiPo batteries themselves don't go into thermal runaway, what electrolyte material is it you are refering to that is so flamable and under what conditions?

Digger1911

What do you guys think about MiKroh2 lightweight racing battery??

überschnell

LiPos don't go into thermal runaway? I'm sorry, you've completely lost me. Perhaps not unprovoked, although a couple of RCers who lost their cars/houses would probably disagree. Thermal runaway is absolutely possible if a cell is punctured, abused, overcharged, etc.

From http://batteryuniversity.com/learn/a...dern_batteries :

"The gas released by venting of a Li-ion cell as part of pressure buildup is mainly carbon dioxide (CO2). Other gases that form through abusive heating are vaporized electrolyte consisting of ethylene and/or propylene. Burning gases include combustion products of the organic solvents."

Tiny, highly pressurized hydrocarbon spewing out of the end of the cell; this is a fire hazard. As far as I am aware, most if not all of the lithium cells (LiPo and LiFePO4) currently made use a similar electrolyte. I would say that any pack capable of handling the discharge requirements for an automotive battery is typically (to borrow your wording) going to have enough energy density to be dangerous.

I cannot speak as to the exact composition of the electrolyte in Li cells, as I doubt any battery manufacturer can. You would have to contact a cell manufacturer directly, and even then, I doubt you'd get a straight answer.

As far as "under what conditions," LiFePO4 cells generally fail when they are overcharged. Generally, one cell reaches its finishing voltage before the rest, and continues to be overloaded with current. Without a protection system and/or stout balancing, this builds internal pressure inside the cell until the charge is complete or the cell ruptures. The damage caused by the swelling is irreversible. Normally, the cell gets quite hot and makes a gooey mess, perhaps deforming the case slightly. In a perfect storm/worst case scenario, the electrolyte mist hits a hot exhaust manifold or some other ignition source, causing ignition, which the battery continues to fuel. Heat builds, the rest of the cells swell and begin venting...a chain reaction dependent upon a lot of factors.

I certainly believe Li-Ion is safe, or I wouldn't work around them every day and use one in my personal vehicle. However, blanket statements that could lead someone to believe that they are totally harmless are dangerous with any battery chemistry.

Also, please don't mistake my posts for hostility, I enjoy the discussion.

Spin9k

Me to, I enjoy 'vigorous' discussions. So, I'm thinking perhaps the differing opinons here is due to misunderstanding of what battery types we are talking about. I'm only refering to "Lithium Iron Phosphate" batteries, not Lithium-ion batteries of any other chemistry. The LiFePO4 battery chemistry just doesn't support the catastrophic thermal runaway modes of the Li-Ion types. You mention problems with Li-Ion, but that's not the same as saying it happens with LIFePO4 cells.

At that site you mention there is a reference here in a chart http://batteryuniversity.com/learn/a...ased_batteries that gives the thermal runaway point of LiFePO4 as 270C or (512F), which would mean it would need to be exposed to that temp external heat source, like a fire!! And that's the first place I've ever seen thermal runaway associated with LiFePO4 batteries at all.

On the other hand, Lithium-Ion types are definitely unstable if misued and real problems happen when people don't appreciate the dangers. That sounds like what you've experienced and mentioned? Aren't most RC batteries just Li-Ion types?

And of course the batteries of any type can be damaged in the way you say, overcharge, and worse thermal runaway for Li-Ion. It's permanant for sure, and expensive(!)

----------------

Here's a reference that is typical for a discussion of LiFePO4 safety... http://www.iloveebikes.com/batteries.html

"The safety characteristics inherent to LiFePo4 technology result from the incorporation of phosphates as the cathode material. Phosphates are extremely stable in overcharge or short circuit conditions and have the ability to withstand high temperatures without decomposing. When abuse does occur, phosphates are not prone to thermal runaway and will not burn. As a result, LiFePo4 technology possesses safety characteristics that are fundamentally superior to those of lithium-ion batteries made with other cathode materials."

Spin9k

Checked out their site. Here's my 2c...

If you mean the "Lithium" battery, unknown type. Race battery looks nice and they talk about its use on track, specifically, so they are building to a specific purpose. It's a low cost "cells in a box" rather than a "managed cells" design, meaning no electronic nanny safeguards. That should keep cost down. External trickle charger jack is nice.

Lead acid looks good too and they sell them. Either way, looks like (it will be) a good bet if you understand how to use it. I mean the goal is to start and run your car on track and lose battery weight and this fills the bill. To bad the lithium is 'coming soon' still.

TeamRX8

iTrader: (25)

here's your citation for LiFePO4 thermal runaway

überschnell

Obviously, LiFePO4 is a type of lithium-ion. Volatility will depend on what type of cell (cylindrical vs. prismatic), energy density, age, operating conditions, etc. In my experience, no two cells are formed the same or will perform exactly the same, either.
I think that quoted number is a generalized number, probably directed at the cylindrical cells. I believe our prismatic packs are rated from the factory up to 170 or 180F? Not positive on that. We always recommend mounting batteries in a cool place, as high temps will shorten the cycle life and diminish capacity--basically, age the battery more quickly. As far as thermal runaway, I have no empirical data other than failures that I have seen firsthand.

If you have a cell that is swelling from overcharge and you keep dumping charge current into it, things will continue to get worse. However, as stated earlier, this will usually only make a mess. It takes an ignition source to create fire, but there is a LOT of energy in these cells to fan the flames.
As above, all of the batteries being discussed are lithium ion. Most RC batteries are LiPo to cope with the massively high discharge currents (at least for the size/weight) that those guys need. I don't know what cathode material is used in those packs, but it is definitely more volatile than LiFePO4. If you punch a nail through a LiFePO4 pack, it should just vent and fizzle out. If you did the same with a LiPo cell, you're probably going to have a brief, very hot fire to deal with.


Edit: That MiKroh looks like a 4S3P pack of 18650 cells. However, that would be 4.5 Ah, not 2. Not sure what kind of cells they are using.

HiFlite999

iTrader: (2)

Interesting thread! I do feel some urge to point out that in the event of battery trouble, a behind-the-glovebox mount is maybe the worst possible location. Not only do any fumes or flames go right into your lungs, access for putting out a fire or cutting the cables is difficult. YMMV, but worth consideration ...

TeamRX8

iTrader: (25)

I'm almost afraid to ask who would be dumb enough to mount one there

überschnell

^Check out the first post, hahaha.

I've seen it done plenty of times. A lot of people even put them under the seat. Honestly, your chances of catastrophic failure are pretty slim, even with the "cells in a box" construction. Of course, a real BMS is another layer of protection.

TeamRX8

iTrader: (25)

oops, well the OP can't dislike me anymore than he already does anyway

Spin9k

Unless the alternator regulator fails, the max charge voltage in the car will never exceed a nominal 13V-15V. All unregulated LiFePO4 batteries sold for cars depend on this being the case because the max charge voltage of the x4 cells is 14.8V (3.7V each). Shorting the terminals is the major concern, but that's the case for any battery.

In case of some unforseen event, the cables thru the firewall are easily available, a cutoff switch would typically be installed, and the circuit broken in an emergency. A regulated and limited battery is helpful, but is more expensive and needs a larger case.

Mounting a battery of any type inside the car is problematic, whether the concern is acid spilling, fumes, or fire, but then we are all nearly sitting on a 14+ gallon tank of explosive that is the rear seat floor aka a gas tank, not to mention on a racetrack at breakneck speeds, so calculated risks are everywhere in that environment.

I'd venture the battery behind the glovebox is in a vastly more protected place than when hanging out over the front of the car, such as it is in a stock battery install, or even in the trunk. Both those areas are crumple zones....

Spin9k

Tisk, tisk, Team.. where ever would you come up with that idea like that??? I'd really miss you as a consistent source of amusment around here

TeamRX8

iTrader: (25)

I'm pretty sure most racing organizations don't allow one in the passenger compartment without it being in some sort of containment box

Spin9k

^good point. Taking a quick look, it appears like SCCA/NHRA at least do not allow battery in passenger compartment, only "behind the rearmost seat". Hard to tell what happens in 2 seaters like a Miata.