sniffy
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Post by sniffy on Oct 16, 2008 14:56:43 GMT -4
Do you put your batteries in the cooler?
------FAQ on batteries---------------- On the other hand, when a battery is not in use, it will slowly lose its charge as a result of leakage between the terminals. This chemical reaction is also temperature dependent, so unused batteries will lose their charge more slowly at cooler temperatures than at warmer temperatures. For example, certain rechargeable batteries may go flat in approximately two weeks at normal room temperature, but may last more than twice as long if refrigerated.
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Post by echnaton on Oct 16, 2008 15:38:51 GMT -4
Consumers Reports magazine ran a long term study on standard Alkaline batteries. Refrigerating some and leaving others on a shelf next to the refrigerator. Last time I read anything about this was two years into the test. The difference between performance in the two batches was insignificant. So for conventional batteries at least, the evidence supports those of us that leave them in a drawer.
For rechargeables, I use the new ones that will slowly self discharge to about 85% of full then hold the charge. Sure they are more expensive but when you pick up your GPS after two weeks it will work.
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sniffy
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Post by sniffy on Oct 18, 2008 14:08:27 GMT -4
How much energy can a Battery Hold? Are they maxed out?
1 Coulumb = 6.2 x 10^18 electrons or 1 A / sec Avogadro's number = 6.02 x 10^23 gram-moles
Coulumbs for a gram-mole = 6.02*10^23 / (6.2*10^18) = 97096.77419
Divide by 60*60 to get amp hours = 26.97132616
Therefore something the size or mass of a sugar cube, could give about 27 amp hours on the negative terminal.
A real battery, with separate plates and connectors might deliver 1 amp hour for a cubic centimeter.
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Post by Apollo Gnomon on Oct 19, 2008 8:26:37 GMT -4
I'm confused by your last post. Can you explain in more detail? I studied too much art and "soft science" in college, so I don't know what coulombs are and how one uses them.
I understand watts and Amp-hours, and I don't know what your imaginary battery is.
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sniffy
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Post by sniffy on Oct 19, 2008 10:10:38 GMT -4
I am saying, or didn't say:
For each electron, there has to be a molecule which will donate an electron. A battery which is ready to connect must therefore must have a weight to amp-hour ratio. This ratio will depend on the "inventory".
The upper limit is determined by many electrons/ions a mass or volume will generate. This reaction will also generate heat which cuts into the theoretical limit.
A coulumb is the quantum unit of electric charge determined by the famous Millikan experiment. 6^18 coulumbs = 1 amp-sec, energy units can be a bit confusing such as conversion of joules to eletron volts. Next, there are standard units of mass; Advogaro's number means there are 1.06*10^23 atoms in a mole. To get the mass, multiply by its atomic mass, for example O2 a mole weights 32 grams.
Perhaps you could have a peek at the first calculation to see if it makes a bit more sense.
Also you might put a battery on the scale. Divide the amp-hours by the wieght. I don't think there is a battery that will give more than 1 amp-hour per gram.
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Post by Apollo Gnomon on Oct 21, 2008 14:45:15 GMT -4
Maybe I'm still confused. I had on semester of High School chemistry back in the 80's so I'm a little fuzzy, but it seems like you are suggesting that ALL of the matter in a battery could be consumed for power. Is that even possible? I can't think it would be reversible if so, thus it would be a primary and not a secondary battery.
Am I tracking on your theory, or am I totally lost?
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sniffy
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Post by sniffy on Oct 21, 2008 18:15:56 GMT -4
If the battery has a copper plate, then there is ONE electron per molecule that can be pushed to the other terminal. Otherwise the copper molecule stays there.
I was comparing the energy of the single electron, which can be moved only ONCE, with the mass of the copper molecule which does not move.
This is rather gross oversimplification, since there is NOT a complete understanding of chemical batteries.
Knowledge of chemistry, electricity, quantum mechanics is required.
I have to poke around for some second opions, will take a few days. Those who were saying, "can't be done", or "things work just fine": Gosh I haven't heard from them.
Thank you very much for pointing out that problem of battery wieght. Would never have though of it otherwise.
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Post by Apollo Gnomon on Oct 23, 2008 17:50:21 GMT -4
Hrm. Yeah.
It's all about surface area, so you end up with a lot of mass "overhead" with both electrode and electrolyte, so the idea you have has trade-offs and unforseen issues.
Not every atom of electrode can contribute one electron - each electron has to get to the surface, through the mass of the electrode. The electrode atoms at the surface have to be "recharged" from within the electrode, and then they can react (discharge) again to the electrolyte. Each atom at the surface has to react over and over. Same thing happens with the electrolyte.
Go back to the deep-cycle vs. AGM lead-acid batteries we discussed above. Deep-cycle batteries have massive thick plates, so after they rest for a while the surface can react again and provide a bit more charge. The Cyclons have a woven-lead-mesh electrode, so they have a huge amount of surface area wetted by electrolyte. They can dump massive amounts of power out at once, and recharge really quickly.
Lead acid batteries are "discharged" at about 1.8v per cell, fully charged at about 2.2v per cell. If you fully discharge them, they're damaged, forever. You can "jump start" your car and recharge your battery after leaving your headlights on 2 or 3 times in the life of the battery.
"Primary" or non-rechargeable batteries can be discharged completely, but below a certain point they won't put out enough power to do the job required but they'll still have some "Possible" charge left in them. More overhead.
There are also internal resistance effects, involving heat. Some batteries are better than others. Gel batteries can overheat to the point that the gel liquifies, and has to cool again.
Lead-acid and alkaline batteries have Hydrogen that has to migrate through (or back into) the electrolyte.
Then there are chemical reversibility issues for rechargeable batteries. Lead-acid batteries get lead sulfide build up on the surface of the plates if left at a partial discharge for too long, reducing the surface area of the plates. NiCads develop cadmium crystals in the electrolyte, and if they are not discharged/recharged properly the crystals can get so big they reduce the amount of useful electrolyte.
I'm imagining batteries with super thin plates, to try to get to the "Ideal battery" you are talking about above. Here's where the tradeoffs happen. They would have hellacious output amperage, but not very much Amp-hour capacity. Output current would have to be limited to prevent overheating. They would either have a very high Voltage (many plates) or would be very folded to get any capacity per unit of weight.
Interesting to think about. We're both outside of our fields, here, but that's good. We can't learn things just discussing what we already know!
{edit - because I edit.}
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sniffy
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Post by sniffy on Oct 24, 2008 8:46:47 GMT -4
I am asking about this on a physics eMail list. One answer is below. Here is the point: Batteries are simply too heavy and problematic for work vehicles.
The only solution to electric vehicles seems to be "fuel cell" or some sort of constant feed
phys-l@carnot.physics.buffalo.edu Without thinking about the calculations, I can tell you that your result is a lot different than reality. A typical Nickel-Metal-Hydride rechargeable AA cell (which is considerably more energy than a AA alkaline cell) is about 2 amp hours, and it is perhaps as big as 5 sugar cubes. Therefore, your result is off by at least 50-fold.
Michael D. Edmiston, Ph.D. Professor of Chemistry and Physics Bluffton University
Edited by LunarOrbit. Please do no include personal information about other people (like their phone numbers or email addresses) in posts here. I know he is the one who shared it in his signature, but I don't think it's a good idea to put that information into the forum.
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Post by Tanalia on Oct 25, 2008 2:06:11 GMT -4
1 Coulumb = 6.2 x 10^18 electrons or 1 A / sec Avogadro's number = 6.02 x 10^23 gram-moles Coulumbs for a gram-mole = 6.02*10^23 / (6.2*10^18) = 97096.77419 Divide by 60*60 to get amp hours = 26.97132616 Therefore something the size or mass of a sugar cube, could give about 27 amp hours on the negative terminal. The math is ok, but you may be misinterpreting what it means. One mole of a metal may be able to donate 27 amp-hours worth of electrons, but that has nothing to do with 1 gram or 1 cm 3 of material (what I assume you were aiming at by mentioning a sugar cube, which is really about 4 grams and 2 cm 3). You later mentioned copper, so we'll start with that. Its atomic weight is 63.546 g/mol, so you need that many grams to get the 27 amp-hours. With a density of 8.96 g/cm 3, that mole will occupy 7.09 cm 3. Your hypothetical 1 cm 3 battery can only hold about 1/7 of a mole of copper, which means at best about 3.8 amp-hours. Of course, a block of copper doesn't make a battery. Assuming we're tying to keep the battery the same size, you need to lose copper for the other parts. First, figure on replacing half of it with something like zinc for the other terminal (zinc has very similar weight and density, so calling it half is close enough for this). Offhand, you'd think this would immediately halve the capacity, but copper and zinc both transfer TWO electrons in most reactions (unlike your later assertion of one per molecule), so the capacity is unaffected by this. The real problem comes in with the electrolyte. Depending on which chemical reactions you use, figure on replacing 75-95% of your remaining metal. This is what brings it down to the 1 amp-hour (or less) per cm 3. Physical considerations (case, insulators, ability of chemicals to migrate and react) will of course cut into the capacity further,
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sniffy
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Post by sniffy on Oct 25, 2008 8:54:04 GMT -4
Batteries are rated by the weight (aircraft) or volume (trunk space for a car). Your clarification is most helpful for someone making a choice for the application.
The plates become coated with sulfur ions in the case of lead batteries; therefore the internal resistance goes up. If the internal resistance increases exponentially; then that would be the factor that cuts into the theoretical limit.
Electrical cars, certainly construction equipment are not practical. The hybrid car uses deceleration to get back some of the energy. Unfortunately it is complex and expensive.
If I were promoting something, it would be biodiesel.
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Post by Apollo Gnomon on Oct 26, 2008 14:51:34 GMT -4
I've done a bit of looking, and found that microwave ovens are not listed at their draw, but their output. 900w ovens draw 1200w to 1400w during power-up and run cycle, so they're closer to 70% efficient for conversion of input wattage to usable heat.
Again, efficiency vs. application-specific-usefulness would have to be balanced. The advantage of using a microwave-driven flash boiler for steam (or other working fluid) would be almost instant response, no combustion, and little heatup/cooldown lag.
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sniffy
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Post by sniffy on Oct 26, 2008 23:51:43 GMT -4
Say the fluid, water, is injected, then vaporized by electromagnetic spectrum that shines through a quartz window.
The compression ratio could be more than 500 to 1. ( water to steam) Diesel is about 20 to 1. Air is injected with the "fluid" and that makes the compression ratio lower.
The main difference is that the diesel supplies the heat, while microwave supplies energy to vaporise water.
I think there is a misconception about compression ratio. Some will say that the engine head can be milled down, the compression ratio goes up and your hot rod goes faster.
Maybe there is more to this. I haven't been reading any car magazines.
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sniffy
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Post by sniffy on Oct 27, 2008 9:09:57 GMT -4
The heat of vaporization of water is 2259 joules per gram. A watt = 1 joule per second. Now if you want your gram to evaporate in a 1/10 of a second, your need a pulse of 10,000 joules for less than a gram. Lots of tech problems for microwave. Isn't it a bitch, trying to solve the energy crisis?
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Post by Apollo Gnomon on Oct 27, 2008 12:10:57 GMT -4
But which energy crisis are you trying to solve, Lunar or terrestrial?
Short answer "TANSTAFL" There Ain't No Such Thing As Free Lunch.
On earth we are currently basing our entire planetary economy on the removal an combustion or transformation of ancient carbon residue. Seems almost free, except that we're dumping that carbon into our atmosphere. That carbon is, functionally, the energy of millions of years worth of sunlight in a highly concentrated package.
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