My contribution to the battery aspect of this thread is to question why we are so infatuated by 12 volts? [I once wrote Standards, and Standards often impede innovation]
I also agree that the electrical systems must be designed and implemented taking into consideration volts, amps, temperature high and low, wiring, insulation, noxious gases, fusing, short circuit and thermal runaway, G load, weight and many other factors At Oshkosh 2006 the Blue Mountains Avionics presentation said for light aircraft the move to 24 volt systems was a no brainer, just so logical. Most instrumentation and radio's require 10 volts and a 12 volt system decays to 10 volt reasonably fast. Microair's need probably 10.5 before the transmitter goes garbled, Cambridge falls over at about 8 volts. Mike could perhaps comment on the minimums for Borgelt instruments. PDA's and XCSoar have a USB 5 volt input so may work longer on a 12 volt system? Some avionics are designed for 35 volt DC maximum input [but XCOM and Microair apparently have 16 ~ 17 volt maximum input specification] But starting with 24 volts gets much more out of the battery before avionics fail. Even moving to say 16 volt to keep within radio specification could lead to increased useful battery life. Cranking amps for starter motors is at the high drain end of the drain spectrum but arguably is early in a batteries discharge cycle in the glider application. So why not have 16 ~ 24 volt systems in gliders? Alan Wilson [ARMIT Comm Eng] Canberra From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Wednesday, 27 February, 2013 8:58 PM To: Discussion of issues relating to Soaring in Australia. Subject: Re: [Aus-soaring] LiFePo4 Nice one Arie. You do bring a bit of costing perspective into the argument here. The YouTube footage is interesting (horrific?), but I suspect basically irrelevant. I think that any glider pilot who knows anything about the problem, does not want to experience an inflight cockpit fire UNDER ANY CIRCUMSTANCES. I know of one example, where the pilot was VERY happy to have survived the experience - without having to bail out. He reported that fire - as in burning - was NOT the problem. He reported that the amount of fumes and smoke generated in an incredibly short time from the ignition of the plastic wire covering due to shorting of the electrical system was in fact the primary problem. For this unfortunate pilot, there were really two problems: first he had to be able to breathe, and secondly he had to be able to see what you are doing - basically impossible in a cockpit filled with smoke! Re your statement "willing to replace a couple of batteries each year ...." Probably a slip of the pen: As Bernard has pointed out a high quality SLA gel cell type battery MAY last up to 9 or 10 years, but this is hardly likely to be the norm. Five - seven years seems to be much more realistic estimate. As far as I can tell, the life of the LiFePo4 batteries is not claimed to be any better than this latter figure. At this point in time, LiFePo4 batteries are MUCH more expensive. However I expect that in a few years time the price will have fallen, and many glider pilots will be using these "new fangled" devices,. I suspect that I will need to replace my current glider batteries in the near future. I do not have a max AUW of the non-loading bearing parts problem - one valid argument for lighter batteries - and my power consumption figures - high power consumption requirements are another valid argument for using LoFePo4 - are relatively modest, so I have no intention of using LifePo4 batteries for the replacement. What this whole discussion has crystallised for me is the requirement, regardless of the type of battery selected, is to always use a high quality battery manufactured by a reputable factory who stands behind their product. [I have in the past tried "cheap" batteries, and regretted it.] Regards, Gary ----- Original Message ----- From: Arie van Spronssen <mailto:[email protected]> To: Discussion of issues relating to Soaring in Australia. <mailto:[email protected]> Sent: Wednesday, February 27, 2013 6:56 PM Subject: Re: [Aus-soaring] LiFePo4 Hi, When people start talking of glider batteries I laugh at their logic. We have a toy that cost anywhere between 2 - 10k and upwards to keep in the air each year (not including getting to and from the airfield and actually getting it in the air) and they are not willing to replace a couple of batteries each year for well under a $100. These fancy batteries may be ok but in the vast majority of gliders the simple still works best and is cheap and safe. Yes I do play with these fancy batteries in my radio control toys but with great care and they are always stored in a lipo safe bag. You only have to watch this video to agree http://www.youtube.com/watch?v=mw8jb1KmAG8 yes I know the newer ones are better but these are only small and look at how they go up and even the newer ones can still have problems. regards, Arie On 27/02/2013 12:52 PM, Future Aviation wrote: Hello all It just occurred to me that I have omitted to thank John Parncutt for his research and his willingness to share the findings with us. Of course, in this context Mike Borgelt's professional advice must also be mentioned. Both contributions are extremely useful to many of my gliding friends including myself. Many thanks to both of you! Believe it or not, the last set of SLA batteries powering the engine circuit in my ASH 25 lasted for 10 years. At the time I opted for the most expensive SLA batteries I could get my hands on and now it appears that the old saying holds indeed true. You only get what you ........ Kind regards to all. Bernard Eckey -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Mike Borgelt Sent: Wednesday, 27 February 2013 11:22 AM To: Discussion of issues relating to Soaring in Australia. Subject: Re: [Aus-soaring] LiFePo4 As I said yesterday, do proper engineering on your battery installation. If you don't have real numbers for temperature limits, discharge curves at various rates, charging characteristics etc etc you aren't doing engineering, you're just guessing. A battery designed to start a racing motorbike and then be recharged by the alternator and floated at that voltage likely has quite different characteristics, design and longevity from one designed for charging and deep discharging over several hours then recharging. You can also just stop and get off the bike when the battery catches fire. Li batteries all need individual cell monitoring during charge and use or at least when charging after mostly charged. The problem with Ni MH batteries is the number of cells (10 for a nominal 12 V system). You will have at least one weaker cell which will deep discharge more than the others and will be undercharged or more likely the other cells will overcharge resulting in reduced battery life. Individual cell monitoring would help but with 10 cells vs 4 for Li it is a pain. 3 years isn't bad for a NiMH battery pack. Some people have a problem with max weight of non lifting parts and a few kilos saved may make the difference between flying in or outside the weight and balance envelope. For these LiFEPO4 may be worthwhile but use the correct cells. The cylindrical Tenergy cells sold by these people have engineering data and are Underwriter Labs tested. The tests are published there too. Start here:http://www.all-battery.com/lifepo4battery.aspx I've dealt with them and they did what they said they would. Also these people may be of interest: The batteries seem to be the same as the Tenergy cells but with a different colour outer sleeve. They have battery monitoring/cutoff circuitry available also. You must use a low voltage cutoff at least. http://lithbattoz.com.au The old sealed lead acid batteries are OK. They are heavier although in many installations that may not matter. The capacity is usually quoted at the 20 hour rate. In modern gliders 1 amp continuous is not an unusual load so that's the 7 hour rate. Likely it is a 5 A-H battery at this rate. Give it a couple of dozen charge cycles and it is a 3 or 4 A-H battery and you begin to have problems. Note also the number of cycles you get is non linear with depth of discharge. Small % discharge you'll get lots of cycles. Large % discharge many, many fewer cycles. Size the battery to handle the longest flights and then use two batteries. Use one routinely, keep the other charged then when the first battery dies due to low capacity you have a known good battery. Put that one in the first position then put a new one in the standby position. You should always have a good battery available then. If using some new type either learn enough to do an engineering analysis or find someone willing to do one for you. Otherwise these things may get needlessly banned or we have fires in gliders. It would be embarrassing to explain to your insurance compny why you had to bail out of your burning glider. Mike _______________________________________________ Aus-soaring mailing list [email protected] To check or change subscription details, visit: http://lists.internode.on.net/mailman/listinfo/aus-soaring _______________________________________________ Aus-soaring mailing list [email protected] To check or change subscription details, visit: http://lists.internode.on.net/mailman/listinfo/aus-soaring _____ _______________________________________________ Aus-soaring mailing list [email protected] To check or change subscription details, visit: http://lists.internode.on.net/mailman/listinfo/aus-soaring _____ No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2238 / Virus Database: 2641/5635 - Release Date: 02/26/13
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