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Posted: Wed Dec 06, 2006 7:51 am
There are a lot of right answers here. Chris is right about the mixture being fairly precise or no explosion. For gasoline the ratio is between 14 and 15 to 1. This is widely known among those that understand how engines work. This is also how I debunk the 80 miles per gallon carburetor myth.
Storing batteries on concrete does not "suck the charge out". The temperature of the battery will usually be lowered sapping available power but it is not the concrete that does this.
You DO NOT want to seal a battery in a bag or any sealed container. You want to dissipate the hydrogen gas produced during a charge cycle.
Dacflyer has an interesting thing with the wheelchair batteries that are exactly the opposite of my experience. I have along the lines of 50 UPS units in networking closets. About every three years we replace the batteries and every six we replace the entire UPS. Sooner if the unit fails after the first set of batteries has been replaced. When replacing batteries I have noted that when replacing batteries on failed units the batteries have swelled to the point that I have to disassemble the unit and pry the batteries free. If I get to the unit before the batteries completely fail it is not nearly as bad. The interesting thing is using the same type of batteries, in the same type of UPS, getting fed from the same power mains, I will see batteries that can potentially last five or six years. Others fail after only two years. Three being the average and our decided cutoff before replacing them.
Posted: Wed Dec 06, 2006 8:06 am
Oh, I've learned a few things recently but not from some of the hand waving inaccurate physics claims made here. More from verifiying that some of the calims were inaccurate half truths. Not exactly a friendly way to learn, I'd rather be challenged by clear explanations than by the hubris so well demonstrated in this thread. It seems too many degrees makes one hot under the collar and saps ones diplomacy (puns intended). It also seems age and experience result in the formation of explosive gases with lots of flash (read on).
If being annoyed by someone who supports his factual calims by bosting about their experience rather than by posting links to reputable pages which support their claim makes me part of a Clique, then so be it. Y'all can guess at my formal education age and experience, I prefer to let my remarks stand by themselves.
Half truth: Hydrogen is corrosive. While gassious Hydrigen is associated with corrosion it does not in itself cause it, it is more commonly associated with embrittlement of metals and stress cracking. Now H+ in solution in an ionic form is what makes an acid, so hydrogen sulphide and other compounds certainly do cause corrosion.
Half truth: plastic bags are hermetic. Close enough for a human nose but ask any hound (particularly a drug sniffing one) and he'll tell you most plastic is not (though ellegedly oven baking bags come very close). In fact no plastics or epoxies are considered hermetic for semiconductor packaging. Gasses particularly hydrogen (being the smallest) do diffuse through these materials at a measureable rate (though not plastic, think of a shrinking helium filled baloon, its not leaking, its lost directly through the wall). Given the relative atomic weights of oxygen and hydrogen, I would expect any long term enviornment to be a bit oxygen rich as compared to an ideal Brown's Gas (2:1 H:O).
Now, getting back to the actual subject (and not to pick on one person), I would like to ask Lenp to describe "explode" a little better. Was it a vigorous pop, a significant bang or a long hot meltdown. I can imagine some ignitions might be entirely contained in the battery and unannounced. Did you see it go or are you going by the aftermath.
I am aware that a major failure mode of any battery is thermal runaway as a result of a direct short internally (think exploding laptop or cell phone battery). Low electrolyte levels, age and infrequent use all encourage dendrite growth (lead sulphide I think) which will ultimately result in a shorted cell. A short in a fully charged cell can easily generate enough heat to melt the battery case and cascade to the remaining cells. High vapor pressure from boiling electrolyte and softened plastic Could make quite a mess when it lets go. Low electrolyte levels allows for a larger gas volume which can be compressed for a bigger effect.
Most (if not all) sealed batteries still have a vent to prevent catestrophic failure in this event, it's just not intended to be opened for inspection. A vent is not necessarily a one way valve (which might allow acid to escape thus not being sealed), more often they are like fuses, they operate once and can't be reset. Frequently it is just an engineered weak spot in the package or lid.
As for Dacflyers meter wiggle, it just sounds like a characteristic of the smart charger interacting with the batteries particular charge rate which is determined by the internal resistance which generally changes with age and manufacturing method. Meter wiggle at the beginning of the charge cycle might indicate the formation and fusing open of dendrites which form more readily in dead or low batteries but that's not what you describe. I say the beginning because charging would decompose the dendrirtes unless they were not submerged in electrolyte.
I find it hard to imagine even a liter of gas(and there is far less than a liter of volume in an empty single battery cell) at a perfect 2:1 ratio contained inside the heavy duty plastic body of a car or marine battery having enough energy to do all that much damage but I am far from saying it can't happen. A better description would sure help.
I would also expect electrolyte loss to result in a reduction of cell voltage and capacity signaling demise before it should get to explosive. Certainly if a portion of the plates are not immersed in electrolyte, they cannot produce current.
Furthermore, a cursory examination of the remains of a damaged battery might not be sufficient to distinguish between failure modes. Unless you witnessed the pale blue flash (or was it red) of a water forming bang of course. Do you see split sides and popped off caps without thermal damage (supporting the explosion failure mode) or do you see signs of severe heating or melting of the plastic case (supporting an internal short). Thermal runaway would persist until either the originating short fused open or the electrolyte leaked out and the current flow ceased. In the latter scenario, the shorted cell could still be measured as a short after the fact. Failure analysis would involve gently flushing the acid with DI water then inspecting the plates as well as observing the character of the resultant damage to the case and terminals.
Also, my understanding of the danger of car battery explosions was more a hazard of acid being ejected or getting flash burned rather than mechanical failure of the battery package itself. Most of the hazard occured when using an external charger and unsealed lead acid batteries especially if you were careless and checking electrolyte levels (caps off) while charging or especially when disconnecting the charger (as H2 concentration is highest during and immedietly after charging rather than before). THese explosions generally did not occur under a closed hood, running or not. Now many if not most car batteries are SLA and contain dendrite growth inhibitors making them much safer.
Batteries are a bit like water heaters. don't expect them to last much longer than their warranty particularly with traditional charging methods (as opposed to smart chargers)
If you really want to put the subject to bed, spend ten bucks on the report on battery failure modes http://www.batterycouncil.org/FAILUREMO ... erForm.pdf
And this link is quite informative if not so much about SLA it covers other exploding battery types pretty well
I wanted to add some links from Wiki but its blocked here in china, go figure. For that matter so it seems is google after 10pm and my company website too. Surfing is hit or miss here. Can't wait to get home, nuff 4 now.
Posted: Wed Dec 06, 2006 8:40 am
Its always funny to watch the Google over actual experience, as if the degree is speaking and can be picked on?
The degrees led me to my experience, and all of it is still just as valid as it was spoke. And I still work with them and see their results which beats the google any day.
Explosions donâ€™t occur in a mis match of gasses, while hydrogen is highly corrosive and can be checked in any sealed battery condition, and so the jokes are still here which is why this is the comedy club.
And how I teach, you can bitch at, but over the years the ignorant does do their fact checking before they engage their mouth, while silence is always preferred over their ignorance which is what has been learned as a known lesson that soo many here complain about.
How you learn is unimportant to me, but learn you have done even if you still claim indigence.
But we will always have the Google expert so your choices are clear, get an education or get a Google, its up to you, or even better, get off your butts and learn for your self.
False inexperienced claims will get you no where, and neither will google with out getting off your tush.
And PS, battery acid which contians sulfuric acid freezes at a relatively high temperature, and IS altered by cold objects like the concrete floor over "time" causing its balance to settle, altering the condition of the battery.
Cars and freezing batteries is also a known fact where the acid becomes frozen and canâ€™t crank the battery until its electrolyte warms up.
While cold, the cranking amps are not the same as a warm battery and left long enough the battery will discharge and alter the electrolyte.
There are no pure reactions in a battery environment like pure hydrogen, which is why the out gassing eats up everything
And brittle metals is a great Google experience, if your only looking for and finding the ignorance you seek.
Posted: Wed Dec 06, 2006 12:35 pm
Hackelsup, welcome to the thread!
Other opinions are always important.
The exploding batteries I have associated with were in two different environments, so, at the risk of redundency, here's the information .
The battery with no cell access, was installled on a garden tractor, operating in the open air, but had just been taken off of a high rate charger since it would not crank. After the charger was disconnected, the tractor was started and all seemed normal. After a few seconds running the headlights suddenly flared up, way too bright then the battery exploded with a loud and sudden report. I did not wittness any flame since I was getting off the tractor at the time. The top of the battery was fragmented, pieces went airborne and one battery post disconnected from its internal connection. The plates in the battery were in a crumbled state and there was hardly any electrolyte expelled A new battery was installed, charging was checked and the tractor has been in service for over a year with no battery issues.
This battery was likely 5-6 years old and was kept on a 100 ma charger when not in use. I think the battery had a momentary internal open connection and it unloaded the generator, hence the increase in voltage and the flaring headlights. The explosion was caused when the open circuit reconnected. Likely the electrolyte was too low because of the long term charging and the inability to service the battery.
This battery was in an industrial environment, installed on a pallet jack. Power is used to lift the load, not to move or lower it, so the duty factor is quite low. The jack has an internal charger that must be manually connected when charging is required. The operator said the battery was on charge for several days and the full charge light did not illuminate. The charger was disconnected, the jack pulled out from the parking area and the switch to operate the hydraulic pump was pressed. At that time there was an explosion. The battery is encased in a metal housing with downward pointing louvers and the operator saw no flame. A minimal amount of electrolyte leaked from the battery. I removed the housing and the battery had a cracked case and the top was fragmnted with pieces inside the compartment and the plates appeared to be deteriorated. This battery was determined to be approximately 7 years old. Interestingly this battery appeared to be way overrated for the service. The pump draws less than 10 amps and the battery was a 550CCA deep discharge Sears Diehard. With that low of a load the battery probably had quite diminished capacity but it did not noticably affect the pallet jack's performance. The battery was to be replaced by in-house personnel Because of the difficult access to the battery, the electrolyte was never serviced.
Neither battery showed any case bulging, distortion or melting, only fragmented top and cracked sides from an obvious outward pressure. In both batteries there was an obvious lack of lost electrolyte or spray.
Hope this helps
Posted: Wed Dec 06, 2006 2:04 pm
Im unaware of any actual completely sealed batteries.
Not even Nicads which are "sealed" will hold back the out gassing once it exceeds a limit.
[And pull back into the battery, the undesired air]
Even lead acid sealed cells have vents, and they stop the battery gas from over expanding [breaking] the case, and they do draw back pressure.
They all equalize with air once the gas is pushed out. SOP
What you see and how its made is not the same thing.
Just for your reading...[eng note]
http://www.engineersedge.com/battery/se ... attery.htm
Posted: Wed Dec 06, 2006 6:56 pm
Posted: Wed Dec 06, 2006 9:07 pm
HacklesUp & Lenp
KUDOS on a very indepth and informative posts. This is what we need here - good solid and logical information.
Posted: Thu Dec 07, 2006 2:45 am
Thanks RR, I chewed on that one for a few days till I got time to answer.
I do want to comment on the implication that my knowledge (or anyone else for that matter) comes mainly from google. If you have ever read a scholarly paper in a journal or symposium proceeding you would know that they contain, without fail, a long list of references which support all of the factual claims not already supported by the data in that paper. I already had my opinions, the links and my other surfing were just due diligence in verifying my statements would be accurate. While I'm not aiming to write symposium papers here, I do aim to support my claims when possible rather than resting on my laurels.
Also I would like to reconsider my assessment that such a small volume of gas could produce a large explosion. I failed to consider the gas may have been under substantial pressure thereby increasing the number of atoms available to react as compared to 1 atm.
Additionally the page I linked calims that an internally shoted battery can go volcanic in a blink of an eye. Given that the liquid electrolyte would act as a heat sink for a while at least, melting and heat damage might not be very apparent (without complete dissection of the battery). Therefore, I wouldn't conclude on which failure mode occured based only on the description of the resultant damage without further examination. In fact, it may have been some combination of thermal runaway which generates copious amounts of gasses and creating explosive conditions. I would expect (spring-valve) vents to clog and fail at least once in while and fuse type vents as well.
FWIW, many pages I surveyed claimed that Hydrogen explosions from lead acid batteries are rare at best and that (unspecified) design changes have made them safer than in the past. I didn't dig enough to understand that completely though.
I do agree though that so called SLA (sealed) batteries are not really sealed up tight, they just aren't intended to be opened and can be operated in any position.
Some good info here, especially section 4 http://www.repairfaq.org/ELE/F_Car_Battery.html
Posted: Thu Dec 07, 2006 9:17 am
Ill bet they even give credits and then a degree for reading the NET Google.
.....is the oldest saying in the book, but Im sure its easier than a class room full of years, books, professors, and on the job training?
But they did get one completely right that I saw on google, type in the word â€œutter moronâ€
Posted: Thu Dec 07, 2006 5:29 pm
In Regards to Google
Or any of the major search engines for that matter. Google isn't a pin poiunt source of information, but rather a culmination of knowledge from millions of web sites. For the most part, these come fom very knowledgable people and manufacturers around the world. That is quite a diversification to say the least. I think these sites are great for knowledge and learning and use it quite often when confronted with complex problems. As engineers we cannot possibly know or retain all the electronics knowledge we have learned . However, our "mighty weapon" is that we are aware of such knowledge and know where to look for it, wheather that be past textbooks, Google or under any rock if neccessary. The important thing is that once found, we have the ability to not only understand it but to quickly learn it or relearn it. I have learned things from text books that I have never seen in web searchs, I have also learned things from web searchs that I have never seen in text books. I guess the point I am trying to make is that knowledge is where you find it. To confirm anything, I like to cross check one against the other. And when on the web sites, sometimes I will run thru a hundred sites on the same subject just for confimation. Sooo --Viva La Google!
Posted: Thu Dec 07, 2006 6:54 pm
I agree, they are great for the numbers and formulae we all forget. [Google and such]
However, they are not a substitute for knowledge, experience, or any thing else.
Its like looking up a encyclopedia and seeing an answer, then proclaiming to know it all based on just one answer.
It doesnâ€™t matter how accurate the answer is, it Doesnâ€™t work that way.
[ I know too many wives that would try to disagree, especially here]
You need experience in the subject, perspective, and experience long before you will ever â€œget a clueâ€
Posted: Fri Dec 08, 2006 5:54 am
Chris, This may be too personal. If it is, please just ignore me (yeah right!). Speaking of wives.... are you married? Just curious. Sorry to be off topic here
Posted: Fri Dec 08, 2006 10:36 am
13 years of bliss.
But Now I stay away from all the stress, rat race, world travels, cities, and the hustle and bustle others call life. Gets you no where quick.
Give me the million acres of noiseless out doors any day, where if I pay attention real hard I might hear one truck a day, some where off on some lone distant highway.
The artificial world was plenty enough in my youth, but then I grew up and stopped.
Posted: Sat Dec 09, 2006 12:08 am
I worked in industry where "sealed maintenance free" batteries were used. Most were gel cells ranging in size from 2Ah to 100Ah. All of these batteries have vent caps inside. I think that sealed simply means it is not able to be opened by the end user.
This is an interesting thread especially with all of the laptop battery issues lately. Have you guys seen the exploding laptop lithium ion battery that was sent into thermal runaway?
http://hackedgadgets.com/2006/11/26/lap ... tery-fire/