Safety of batteries

[Delbert]

I understand that connecting batteries in parallel is not recommended, if not quite dangerous. Because any small difference in voltage will result in an equalizing current following between the batteries - possibly a very large equalizing current.

 

But is not a single battery effectively an infinite number of batteries in parallel? Or, expressed another way: how close do two batteries connected in parallel need to be to be viewed as one larger battery?

 

And even if it isn't considered an infinite number of batteries, chances are there'll be uneven voltages over the plate(s) area during discharge. Which surely must mean equalizing currents within the battery - possibly quite high equalizing currents. Possibly exacerbated by uneven working temperature (like the centre of a battery is likely to be hotter that the periphery).

 

Yes, I'm thinking of that plane that seems to have penchant for fire.

 

[studiot]

It is not recommended to connect batteries in parallel because special (=expensive, bulky and power dissipative) circuitry is required to equalise them in use. It is, however possible and done on occasion, usually in fixed locations (eg remote radio transmitting stations), where large banks of accumulators are required.

 

An accumulator (eg a car battery) has its cells in series, not in parallel. That is how you can obtain 6 volts, 12 volts or 24 volts as standard in this type.

Battery powered portable equipment normally has its voltage supply made up from several cylindrical batteries connected in series.

 

Picture 2 here clearly shows the series connection.

 

http://www.progressivedyn.com/battery_basics.html

Edited July 13, 2013 by studiot

[EdEarl]

It is not recommended to connect batteries in parallel

....

 

http://www.progressivedyn.com/battery_basics.html

The link provided by studiot says, "Lead acid batteries can be connected in parallel to increase the total AH capacity."

 

I looked at a number of pages on the internet, and all agreed that batteries may be connected in parallel. However, it is possible that a one can short circuit and discharge all the others quickly. If a short circuit does occur, it is possible for the one with the short circuit to overheat and cause damage to things near it, especially if the shorted battery leaks. It is also possible wiring will be damaged. Overheating of batteries or wiring can be a fire hazard. Remove flammable objects from battery compartments.

 

Moreover, batteries should not be recharged while wired in parallel without special parallel recharging circuits.

[Delbert]

Yes, I know batteries should not be connected in parallel!

 

To summarise, the point of my query was questioning whether or not a single battery is in effect an infinite number of very much smaller batteries in parallel?

 

And with this in mind, I offered the thought question as to how close ('close' as in theoretical imagination) two batteries would need to be to end up as one larger battery?

 

Like, if one could simply solder the plates together of the two smaller batteries, thus making one large battery. The batteries were two batteries, but now very closely joined in parallel to make one bigger battery. In other words, a large battery - or any battery - is a smaller number of (infinite number of) batteries joined in parallel.

 

If the above is a reasonable conclusion, is it also reasonable to take the view that since batteries should not be joined in parallel there's a fundamental underlying problem with batteries - in particular, large batteries.

[John Cuthber]

"To summarise, the point of my query was questioning whether or not a single battery is in effect an infinite number of very much smaller batteries in parallel?"

Yes, it is (well, not strictly infinite- you can't have a battery with half a molecule or half an atom), but the number is huge).

However,unlike getting a bunch of batteries in separate boxes and connecting them, the individual parallel cells are small, so if one reverse charges another it's not going to matter much.

All of them are very nearly identical.

(if you are going to put batteries in parallel, make sure that they are all the same brand, same age and so on.

 

Also they all share the same thermal environment.

If one part of the cell starts delivering more than its share of the current then the electrolyte in the vicinity is heated up and so it is held in check a bit.

If you have two separate cells and one warms up a bit its internal resistance falls a bit and so it delivers more current so it warms up a bit more.

At the least, this means it goes flat before the other one, and that's a problem.

[ewmon]

Delbert, the difference in the configurations you describe is rather subtle, but very important.

 

Many cells combined in parallel electrically are parallel in the electrical sense.

Many "cells" combined in parallel chemically/physically are parallel in the chemical/physical sense as well as in the electrical sense.

 

Consider the simple demonstration with cells consisting of two electrodes in a solution, like a typical lead-acid automobile battery cell.

 

Battery A is one huge cell (that is, many small cells combined in parallel chemically/physically). Battery A can compensate for imbalance in its reactions both chemically/physically (within its solution and reactions) as well as electrically (within each electrode).

 

Battery B is many small cells combined in parallel only electrically (through circuitry). Battery B can compensate for imbalance in its reactions only electrically (within the parallel circuitry between the cells), and not chemically/physically because its cells do not share a common solution.

 

This is why multiple separate parallel cells/batteries and their circuits are more prone to high currents and the dangers that follow than are large singular cells/batteries.

[Enthalpy]

Parallel connection depends on how sensitive the battery current reacts on the voltage. With 1.5V alkaline of nearly the same history, they may get a bit warm, you may lose some capacity, nothing spectacular. With Cd-Ni accumulators: boom, either at the cells or at the cables, and that's brutal. So in case of doubt, it's better not to try.

 

A single cell is many locations in parallel, sure... but

- They were produced at the same time from the same material

- They have always been charged or discharged together

so no imbalance has a chance to develop during use.

 

As for the Dreamliner, the dangerous kind of lithium accumulator was the wrong choice, but now they're stuck because this bird relies so heavily on electricity to replace hydraulics, and safer chemistries weigh more. The ironic bit is that passengers aren't allowed to board with dangerous materials, whose list includes many lithium batteries. The response by the manufacturers has been to wrap the batteries in a fireproof envelope: less than perfect, but it's a response, and it should have been done from the beginning. Some design mistakes are just bad luck, this one was a bit coarse to my taste.

 

One 787 has caught fire recently, after the corrective measure was recommended, yes... But I haven't read whether this particular plane had already received the modification, nor if the fire relates with the battery. Also keep in mind that competition is rude.

[Delbert]

A single cell is many locations in parallel, sure... but

- They were produced at the same time from the same material

- They have always been charged or discharged together

so no imbalance has a chance to develop during use.

 

Presumably the first requires tight control during manufacturing - possibly very tight with what might be referred to as large batteries.

 

With the second being dependant on a number of factors, I'd have thought. Like evenly spread operating temperature throughout the plates perhaps being one. Because the discharge characteristics will doubtless be different at different temperatures. And with larger, higher capacity, batteries the temperature differences over the plate area may presumably become significant.

 

As for the Dreamliner, the dangerous kind of lithium accumulator was the wrong choice, but now they're stuck because this bird relies so heavily on electricity to replace hydraulics, and safer chemistries weigh more. The ironic bit is that passengers aren't allowed to board with dangerous materials, whose list includes many lithium batteries. The response by the manufacturers has been to wrap the batteries in a fireproof envelope: less than perfect, but it's a response, and it should have been done from the beginning. Some design mistakes are just bad luck, this one was a bit coarse to my taste.

Electricity replacing hydraulics! Didn't realise that one. Seems a radical step.

 

From what I can ascertain, what I would call a fundamental problem with batteries as I tried to outline above, is unsolvable. And is especially significant with large batteries. If this is true, then frankly, I'm hoping they don't fly over my house!

 

I might add that the lead acid jobs in cars (which I think could be classified as high capacity and discharge) are probably far more reliable because of the liquid acid. The liquid being able to conduct heat around the battery to even out any thermal effects and prevent significant temperature differences during heavy use.

 

I've got both a lawn mower and strimmer powered by these Li-iron batteries. They work well but get hot!! Hot during operation and charging. Also, they seem to work at 100% power right up to the point where they're discharged. One moment they are going at full throttle, and the next nothing! Motors don't seem to slow down a bit as the battery nears discharge.

 

P.S. the built-in spellchecker doesn't seem to know about 'strimmer'.

[Enthalpy]

Electricity replacing hydraulics: this is very tempting, because:

- Hydraulics needs maintenance but still fails. Electricity hopefully improves that; to be seen.

- Electric actuators may become lighter than hydraulics. For slow movements, and after an industrial effort.

- With big batteries, the aeroplane can shut down its power generator on the ground, which more and more airports demand.

 

Though, this switch is less than easy, and aircraft producers and operators are conservative, by nature and for some good reasons. The Dreamliner is the first to push electric actuators so much, more so than the contemporary A-380 for instance, which could change the chemistry of its smaller batteries.

 

The Dreamliner keeps some hydraulic actuators, but I suppose electric ones will replace them all on future aeroplanes. The aeroplane industry has pushed for quick electric machines for two decades, especially with a steel sleeve to retain permanent magnets; my suggestion with graphite fibers or with wound steel band should improve

http://www.scienceforums.net/topic/73798-quick-electric-machines/

[Delbert]

Electricity replacing hydraulics: this is very tempting, because:

- Hydraulics needs maintenance but still fails. Electricity hopefully improves that; to be seen.

- Electric actuators may become lighter than hydraulics. For slow movements, and after an industrial effort.

- With big batteries, the aeroplane can shut down its power generator on the ground, which more and more airports demand.

 

Can't say I would agree with that.

 

The number of failure points, modes or however one likes to refer to them, in electrical or electronic actuators and associated paraphernalia, must be legion.

 

Presumably you'd be happier if the brakes on your car were electronic (and also the other cars approaching you)? You know, with some sort of sensor or sender device under your foot, sending a signal or power to some sort of motor driven actuator at the brake pads. All this presumably powered via plugs/sockets, battery, alternator generator and all the other paraphernalia possibly including computer control?

 

Power steering is bad enough when that fails!

 

I seem to recall one TV prog investigating a plane crash whereby the investigating team managed to isolate the problem to a multi-pin plug and socket. But they never managed to isolate the precise failure mechanism, i.e. dodgy contact, iffy soldered connection and so on.

 

And I think I've been involved in something very similar, whereby we had some kit that was working 24hrs a day. Changes then required it to work only 18hrs a day. The kit was therefore switched off for 8hrs. Upon switching on it failed to work, but after an hour or so it would work okay. Unfortunately that was before the engineer arrived, therefore no fault found. I got involved and set up a plan to catch the bugger! Pouncing on it upon switch-on I isolated the problem to a soldered joint on a circuit board, which upon examination, had clearly never been soldered! It had obviously been like it since new with no consequence to the equipment that anyone noticed, such that it was considered to be a perfectly reliable piece of kit. But with a magnifying glass it was clear that the pin was so close to the circuit-board hole that a tiny miniscule movement due to heat and contact became sound enough to have lasted at least 5 years of 24hrs working without fail.

 

As for hydraulics, push a liquid down a pipe and it'll come out the other end or the piston (or whatever) will move.

 

Anyway, and not to put too fine appoint on it, it is clearly only luck and good fortune that this plane thing with electrical control that's so reliable hasn't dumped the relevant number of souls into the ocean or land at great speed.

[Enthalpy]

Reliability can't be inferred from impressions of complexity. It's really a matter of observation, and hydraulics do fail. To become half-way reliable, they need intense and regular maintenance, and they still fail.

 

Do you believe the airliner pilot creates hydraulic pressure with his feet? I regret the disappointment... He acts on sensors, other sensors observe the position of the control surfaces, and in between, a computer tells a servovalve what flow to send to the actuator.

 

Worse: on present airliners, the pilot's action doesn't determine the position of the control surfaces. The pilot tells the computer what the plane is supposed to do, and the computer deduces the action on the control surfaces.

 

It's much the same with car brakes. Since the ABS, the driver acts on a sensor, a computer decides what to do.

 

In this context, an electric actuator introduces no more software and electronics than a hydraulic one.

[arc]

These are the first steps to an eventual takeoff to landing pilot-less commercial airline industry. They will save a fortune in not having to pay pilots to fly. But they will have to supply a "pseudo" pilot for many decades to transition the public into the concept. Most crashes occur during takeoffs and landings, with pilot error being the primary cause.

 

Time will eventually show that the pilot-less planes are safer with less fatalities and the airlines are able to maintain services without pilot fatigue and human error lurking on every flight. The pseudo pilots of the future may instead be answering passengers questions via email and reassuring them the turbulence is nothing to worry about. With an occasional coming out to deal with passenger safety issues. Flight attendants may be the true indispensable human component, having the job of being the face of the airline while assuring emergency evacuations are carried out correctly.

 

 

[Delbert]

Reliability can't be inferred from impressions of complexity. It's really a matter of observation, and hydraulics do fail. To become half-way reliable, they need intense and regular maintenance, and they still fail.

 

Do you believe the airliner pilot creates hydraulic pressure with his feet? I regret the disappointment... He acts on sensors, other sensors observe the position of the control surfaces, and in between, a computer tells a servovalve what flow to send to the actuator.

I never said hydraulics never fail.

 

And at what point did I say or imply that a pilot creates hydraulic pressure with his (or her) feet?

 

The pressure with feet was related to an example with motor vehicles, and since you seem to indicate that electrics or electronics are so reliable, I asked would you prefer the braking system your car or the oncoming vehicle to be operated by an electrical or electronic system?

 

It's much the same with car brakes. Since the ABS, the driver acts on a sensor, a computer decides what to do.

Don't think it's as you describe. Inasmuch as I believe you will find it's a pressure release and restore system, and the driver's foot is not on a sensor as you seem to imply, but is applying the relevant pressure. There is the vacuum assist - which is vacuum operated air system from the inlet manifold.

 

Further to this battery business, such a cause has not been ruled out for the recent fire on the ground. Apparently it's the ELT device employing a battery, which according to a news report yesterday evening, it was the battery. And similar, if not the same, devices are used on other planes!

 

And I've just read this morning that another Dreamliner plane had to make an abrupt return because of a 'maintenance issue'! Sounds like bovine manure baffles brains or something not to frighten the horses.

 

I'm sorry, but for the reasons I've outlined at the beginning of this topic, I'm of the view that batteries are fundamentally flawed. The AA or AAA jobs are probably acceptable, even a car battery because of the liquid content, but with these other high power jobs, the inherent flaw could well be paramount.

Edited July 19, 2013 by Delbert

[Enthalpy]

[...] would you prefer the braking system your car or the oncoming vehicle to be operated by an electrical or electronic system?

It is already the case, for a long time:

http://en.wikipedia.org/wiki/Anti-lock_braking_system

the driver provides the pressure (my mistake) whose use is fully controlled by software.

 

Same for airliners since the A320 in 1984:

http://en.wikipedia.org/wiki/Fly-by-wire

software decides everything and overrides the pilot's inputs in many modes.

 

If electronics and (gasp!) software are already in the loop, I do prefer to stay with power electronics and electric actuators than make the final step with hydraulics - where it's possible. I used both for crash-test technology, and too often to our taste, hydraulics was unreplaceable.

 

About the battery's defects, I strongly doubt the explanation is "too big elements". Much bigger batteries have already been operated.

 

But knowing that some lithium chemistries have already caught fire in laptops, I'd have strongly favoured others, or to the very least I'd have encased the elements from the beginning. Certification should have demanded it as well.

 

Serious worries in a new plane design? Sure. Other planes, not all as innovative as the Dreamliner, have had more.

[Delbert]

It is already the case, for a long time:

http://en.wikipedia.org/wiki/Anti-lock_braking_system

the driver provides the pressure (my mistake) whose use is fully controlled by software.

 

Same for airliners since the A320 in 1984:

http://en.wikipedia.org/wiki/Fly-by-wire

software decides everything and overrides the pilot's inputs in many modes.

 

I think you're reading it wrong. In a car the pressure comes from the driver's foot assisted by inlet manifold vacuum. ABS is a pressure release and restore system.

 

As for aircraft, I think you will find that the relevant control, fly by wire, or whatever, is duplicated at least twice, if not four times in some aircraft. And what's more, I believe the duplicated computer hardware is of different design. Also, the control software is also duplicated and written by different software houses. Even more, each software house has no communication or possibly any knowledge of who the others are! This I understand is to prevent accidental exchange of information and resultant duplication of errors!!

 

I understand things are taken to such lengths because of the undoubted errors that permeate computer software. That's not to mention the dreaded virus!

 

Anyway, you've kindly answered my question in being quite happy and in favour for more, if not total, electronic systems in vital areas.

 

 

About the battery's defects, I strongly doubt the explanation is "too big elements". Much bigger batteries have already been operated.

 

But knowing that some lithium chemistries have already caught fire in laptops, I'd have strongly favoured others, or to the very least I'd have encased the elements from the beginning. Certification should have demanded it as well.

 

Serious worries in a new plane design? Sure. Other planes, not all as innovative as the Dreamliner, have had more.

It's clear to me that they don't know - or more to the truth they don't want to admit - what the problem is. And so they stuff the thing in a steel case!!

 

It is plainly clear they haven't and can't solve the problem. Haven't and can't because it is a fundamental flaw - as I stated.

 

And as for other planes having more problems, am I to assume this safety thing is a numbers game? As I said previously, it's only luck and good fortune that a number of souls haven't perished already because of a battery known to catch fire - examples of which I understand can be seen on the internet. A manufacturer willing to take that sort of risk with the lives of others is not to be trusted - something I think you've indicated by suggesting it should've been encased from the start.

 

Doubtless they will continue with bodge ups (encasing it in a steel box is a bodge) to get around the problem with sufficient confidence to convince the regulatory authority they can continue to fly. I believe someone once referred aviation to: tombstone technology.

 

I rest my case.

[Enthalpy]

I happily read you agreement that software has full control over present ABS car brakes. Which removes the objections against electric actuators to replace hydraulic ones, since software already controls hydraulic actuators, in aeroplanes as well.

 

Fireproof case: I prefer this to a lithium battery supposed to be safer.

 

Your style is incredibly presumptuous. You probably have only press reports, come with a bizarre theory about big batteries - though they've been around for years - and allege the companies working on it can't solve it and must not be trusted.

 

Fact is that engineering comes with surprises, be it errors, unknown terrain or plain bad luck. Aeroplane manufacturers are not "willing" to risk your life: they're just surprised by where and how problems occur.

 

Aeroplane accidents can be deadly, yes. So is electricity - which you probably use to write here. Risks don't suffice to reject changes.

 

In case you're suggesting that Boeing willingly ignored the risk of this lithium battery chemistry: Airbus had chosen the same on the 380... Airbus have changed the chemistry since the batteries caught fire on the Dreamliner. I wish they encased them, in addition.

[Delbert]

I happily read you agreement that software has full control over present ABS car brakes. Which removes the objections against electric actuators to replace hydraulic ones, since software already controls hydraulic actuators, in aeroplanes as well.

 

Sorry , I'm confused. My car's brakes are not operated by an electronic actuator. They are operated by my foot assisted by vacuum from the inlet manifold. It has ABS which if the wheel slows down or stops under very extreme conditions it momentarily releases the pressure and then restores it. If those conditions are not met - which is all of the time for me - then the ABS does nothing. That means nothing, nothing at all. The actuation is my foot with vacuum from the inlet manifold - no electronic actuation is involved.

 

Fact is that engineering comes with surprises, be it errors, unknown terrain or plain bad luck. Aeroplane manufacturers are not "willing" to risk your life: they're just surprised by where and how problems occur.

 

Aeroplane accidents can be deadly, yes. So is electricity - which you probably use to write here. Risks don't suffice to reject changes.

 

In case you're suggesting that Boeing willingly ignored the risk of this lithium battery chemistry: Airbus had chosen the same on the 380... Airbus have changed the chemistry since the batteries caught fire on the Dreamliner. I wish they encased them, in addition.

Well, you've said they should have put the thing in a box from the start? Why on earth should they do that one might ask? Answer: because they catch fire unpredictably! My words would be: bloody dangerous.

 

If they didn't ignore this fire problem, then that means they didn't know about it. Which indicates to me that not knowing about the fire hazard says they shouldn't be making planes. After all, even you knew when you said you would've encased the thing from the start.

 

In other words they doubtless did know, which means they took a chance.

 

Your style is incredibly presumptuous. You probably have only press reports, come with a bizarre theory about big batteries - though they've been around for years - and allege the companies working on it can't solve it and must not be trusted.

Such ripostes tell me all I need to know. I do not wish to continue.

Edited July 22, 2013 by Delbert

[Enthalpy]

My car's brakes are not operated by an electronic actuator. They are operated by my foot [...]. It has ABS which [...] momentarily releases the pressure and then restores it. If those conditions are not met - which is all of the time for me - then the ABS does nothing. The actuation is my foot [...] - no electronic actuation is involved.

Which means exactly that your life depends directly on the electronics and software that controls the ABS. If that software plays crazy, it can stop braking altogether. Or it can let your car slip when you need ABS action.

[The lithium batteries] catch fire unpredictably! My words would be: bloody dangerous.

 

If they didn't ignore this fire problem, then that means they didn't know about it. Which indicates to me that not knowing about the fire hazard says they shouldn't be making planes.

You don't know under which circumstances they chose this battery chemistry and decided not to encase it. Maybe the battery manufacturer believed to have solved this issue. Remember the time when lithium batteries caught fire in laptops? This seems to be over.

 

Possibly the environment of an aeroplane has raised a failure mode that wasn't known on terrestrial uses.

 

Again, I find your style presumptuous. You ignore the context that brought the trouble, propose a very doubtful explanation, seem to imagine that engineering can run without surprises, and claim "they shouldn't make planes". That's hard.

[Delbert]

Which means exactly that your life depends directly on the electronics and software that controls the ABS. If that software plays crazy, it can stop braking altogether. Or it can let your car slip when you need ABS action.

I don't know why I'm answering this - being the presumptuous so-and-so that I am.

 

I can't quote the mechanism, but I think you will find the ABS actuation is some sort of catch and release mechanism (If anyone has the inclination, perhaps it's worth visiting a breaker's yard). Whereby the thing releases at the end of each cycle of movement - irrespective of whether the electronics releases it or jams on.

 

 

Possibly the environment of an aeroplane has raised a failure mode that wasn't known on terrestrial uses.

 

From what I recall reading the things caught fire on the ground. And thanks be to whoever that they were on the ground.

 

I read further that the extinguishers they carry whilst in the air wouldn't have been able to deal with said fires.

 

Also, unlike a full tank of fuel, a battery (of whatever type) contains all the ingredients for overheating, fire or whatever should a defect cause some internal discharge - 'local action' I think it's called. Unlike a full tank of fuel, which needs another ingredient to be mixed with it, namely: oxygen. And before you attempt to shoot me down, I not saying that there is no combustion danger whatever with fuel tanks.

[Enthalpy]

The ABS decides the force applied on the brake pads while braking. Passenger's life depends fully on the electronics.

 

Dreamliner battery: several caught fire in flight, forcing to land in emergency, and no extinguisher is meant to reach them...

 

The Airbus 380 had the same battery chemistry. Airbus' response was "we'll replace the chemistry, we can because our batteries are smaller". But is some people start to argue that the battery's size lets them overheat, I wonder if Airbus considers keeping the dangerous battery chemistry. This would not be an "error" any more, and Internet has memory.