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#211
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Is the 787 a failure ?
On Fri, 22 Mar 2013 16:57:55 -0000, "Keith W"
wrote: GunnerAsch wrote: On Fri, 22 Mar 2013 12:40:50 -0000, "Keith W" wrote: GunnerAsch wrote: On Fri, 22 Mar 2013 09:23:17 -0000, "Keith W" wrote: The conventional Batteries are sometimes called Sealed Lead Acid Batteries but they are actually AGM batteries. Modern passenger aircraft normally use Nickel Cadmium batteries Why havent they converted over to NmH? They have a relatively high self discharge rate and can lose up to 20% of the energy stored in the first 24 hours. This is acceptable for hybrid vehicles where the battery is primarily a temporary buffer to capture the energy from regenerative braking but not good for a system intended to initiate an aircraft startup sequence after a week in the hangar. Keith Thats not true anymore. Since Sanyo developed the Enerloop NiMH battery..they are being shipped charged from the factories. All the makers are using the new tech and have been doing so for at least 3 yrs. Ive got NiMH batteries that I only need to put on the charger ever 6 months, just to top them off. Gunner Trouble is they are not available in the size or capacity to be used in an electric vehicle, last time I checked the largest was a D size. Keith Oh, they are available a lot bigger than that. Just not readily available to the public. From the mpoweruk site: Unlike the consumer applications where NiMH has been almost completely replaced by Lithium ion, NiMH chemistry is still finding use in automotive applications where it is the technology of choice for powering HEVs and where it has accumulated over 10 years of trouble free service and can thus last for the lifetime of the car. The operating temperature range for NiMH cells has been extended to over 100 °C (-30 °C to + 75 °C) which far exceeds the temperature range currently achievable by Lithium cells making NiMH technology ideal for automotive use. NiMH can handle the high power levels typical in EV applications, the active chemicals are inherently safer than Lithium based cells and NiMH batteries don't need the complex battery management systems (BMS) essential with Lithium batteries. Early cells were susceptible to memory effect and also suffered from high self discharge, nearly ten times worse than Lead acid or Lithium batteries, but both of these weaknesses have been overcome and it is claimed that the most recent cells can hold their charge for a year. Advantages High energy density (W/kg), about 50% better than Nicads, but only about 60% of Lithium ion. Low internal impedance though not as low as NiCads Typical cycle life is 3000 cycles. Can be deep cycled. (80% to 100% DOD) Using NiMH batteries, more than 3000 cycles at 100 % Depth of Discharge (DOD) have been demonstrated. At lower depths of discharge, for example at 4 % DOD, more than 350.000 cycles can be expected. Robust - NiMH batteries also tolerate over charge and over discharge conditions and this simplifies the battery management requirements. Flat discharge characteristic (but falls off rapidly at the end of the cycle) Wide operating temperature range Rapid charge possible in 1 hour Trickle charging can not normally be used with NiMH batteries since overcharging can cause deterioration of the battery. Chargers should therefore incorporate a timer to prevent overcharging. Because of potential pressure build up due to gassing they usually incorporate a re-sealable vent valve Reconditioning is possible. Environmentally friendly (No Cadmium, Mercury or Lead) Much safer than Lithium based cells in case of an accident or abuse due to the use of more benign active chemicals, a particularly important property in high power and automotive applications. Shortcomings High self discharge rate. Can be stored indefinitely either fully charged or fully discharged. Suffers from memory effect though not as pronounced as with NiCad batteries Battery deteriorates during long time storage. This problem can be solved by charging and discharging the battery several times before reuse. This reconditioning also serves to overcome the problems of the "memory" effect. High rate discharge not as good as NiCads Less tolerant of overcharging than NiCads As with NiCads the cells must incorporate safety vents to protect the cell in case of gas generation. The coulombic efficiency of nickel metal hydride batteries could be up to 85% but is typically only around 65% and diminishes the faster the charge although this is projected to improve. While the battery may have a high capacity it is not necessarily all available since it may only deliver full power down to 50% DOD depending on the application. Cell voltage is only 1.2 Volts which means that many cells are required to make up high voltage batteries. The competing Lithium cells typically have 3 times the cell voltage (3.2 Volts to 3.7 Volts) and a much higher energy density. Lower capacity and cell voltage than alkaline primary cells. Limited supplies of rare earth element Lanthanum. Mostly in China. |
#213
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Is the 787 a failure ?
On 3/22/2013 2:59 PM, Jim Wilkins wrote:
wrote in message ... VERY common problem on "A Piece of Crap" UPS systems (as well as some cheaper ones) but when they split they don't leak. The acid in an AGM battery is Absorbed in the Glass Mat. jsw No, the Glass Matt just keeps it from sloshing around. You break open that case and the solution will leak out post haste. And you have NEVER seen an accidental leaking of an AGM battery. Now just admit it. Those that can: Do. Those that can't: Teach Daryl |
#214
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Is the 787 a failure ?
On 3/22/2013 2:54 PM, wrote:
On Fri, 22 Mar 2013 08:07:19 -0600, Daryl wrote: On 3/22/2013 7:22 AM, Jim Wilkins wrote: "Daryl" wrote in message ... ...I have never had a case break open on an AGM. Daryl Then you haven't looked very hard. http://nissandiesel.dyndns.org/viewt...60ab1 12d039d "Problem: APC UPSs sometimes have a float charge voltage that is too high and tends to cook batteries. Here's a pair of gel/AGM batteries from a SUA1000 (not an XL) that have swollen so badly that I had to disassemble the case and pry the batteries out of the metal cage: " And you haven't seen a burst case either. Bulging, deformed, etc. case but the juice is contained in the case. DAryl I've had them split from top to bottom on both ends - but they are a "dry" battery. All of the liquid is absorbed in the mat - and by the time they split they are generally baked dry anyway. I was talking about accidentally damaging the case on a good battery. They will leak if you puncture the case. You are right, many are already cooked and have that ozone smell about them. Daryl |
#215
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Is the 787 a failure ?
On 3/22/2013 3:00 PM, Jim Wilkins wrote:
"GunnerAsch" wrote in message ... D batteries are what they use in some of the electric vehicles as I recall. Some 300 of them Or was it 3000? Gunner http://www.insightcentral.net/encycl...enbattery.html You believe everything you read? Here is a quote from your very own Cite: "Its operating temperature range is -30C degrees ~ +60C degrees." I can tell you (but you won't listen) that if you operate that battery at anywhere near 10 degree or less in F, well above the -30C rating, you will be damaging your battery on a daily basis. This is why Tesla includes a battery heating blanket and an Air Conditioner for it's battery compartment. Otherwise, you have cells that are going to be damaged until, one day, you won't be able to get to the local quick stop and back. Daryl |
#216
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Is the 787 a failure ?
wrote in message
... Because they believed the air speed indicator that was lying through it's teeth. Or maybe they continued to doubt it after the ice cleared? The report didn't try too hard to reconstruct what they might have believed, beyond recounting similar incidents. The pilots do appear to have interpreted what they saw differently and acted without coordination. The Flight Data Recorder didn't capture all their displays. The report mentions that pilots fly their mental perception of the situation. AFAICT they assumed they still had adequate speed and lift and didn't understand why the instruments showed them rapidly descending although they had applied full power and pulled the nose slightly up. Apparently that aircraft just mushes down flat when it stalls. They had trouble controlling roll but not pitch. My guess is that they assumed from the abnormally high air temperature in the top of the storm that there might be strong vertical air currents and may have believed they were caught in a turbulent downdraft. The voice recording reveals mainly confusion. jsw |
#217
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Is the 787 a failure ?
"Daryl" wrote in message
... And you have NEVER seen an accidental leaking of an AGM battery. Now just admit it. Those that can: Do. Those that can't: Teach Daryl Stop trying to change your own conditions. I've seen one that HAD ruptured, but I wasn't watching when it happened. jsw |
#218
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Is the 787 a failure ?
On Fri, 22 Mar 2013 15:16:58 -0600, Daryl
wrote: On 3/22/2013 2:59 PM, Jim Wilkins wrote: wrote in message ... VERY common problem on "A Piece of Crap" UPS systems (as well as some cheaper ones) but when they split they don't leak. The acid in an AGM battery is Absorbed in the Glass Mat. jsw No, the Glass Matt just keeps it from sloshing around. You break open that case and the solution will leak out post haste. And you have NEVER seen an accidental leaking of an AGM battery. Now just admit it. Those that can: Do. Those that can't: Teach Daryl They are also called "starved electrolyte" batteries - and even when fractured they do not "leak". They are very similar in that respect to the older "gell cell" |
#219
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Is the 787 a failure ?
"Daryl" wrote in message ... On 3/22/2013 3:00 PM, Jim Wilkins wrote: http://www.insightcentral.net/encycl...enbattery.html You believe everything you read? Here is a quote from your very own Cite: "Its operating temperature range is -30C degrees ~ +60C degrees." I can tell you (but you won't listen) that if you operate that battery at anywhere near 10 degree or less in F, well above the -30C rating, you will be damaging your battery on a daily basis. This is why Tesla includes a battery heating blanket and an Air Conditioner for it's battery compartment. Otherwise, you have cells that are going to be damaged until, one day, you won't be able to get to the local quick stop and back. Daryl Have you been snorting leaded hi-test again? Try to tame those demons; it's only an example of a D sized battery in a car. jsw |
#220
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Is the 787 a failure ?
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