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Power Failure Questionaire Help
I wanted to start a new thread related to my other thread "Surviving
Flight Recorder Power Failures". Thanks for all your comments. I plan on asking the SSA to allow me to give a presentation (at the next convention) on how soaring electronics all bolts together and the proper wiring techniques. I get a lot of questions on this topic as there seems to be lots of confusion on the topic. Also when I look under the "hood" of some sailplanes, I shudder at the cabling jobs that I witness. And no, contrary to popular belief, ACE hardware does not have an aviation aisle. It occurs to me that I want to put together a comparison of how popular flight recorders handle power failures. Towards that end I have come up with a few questions to ask the manufacturers. Do you have more to suggest? Multiple power sources 1) Can your device support multiple power sources? I.E. multiple batteries. 2) How do you switch between the different power sources or are the sources combined? How are they combined (diode, etc)? Backup Batteries 1) Does your device have a internal or external "backup" battery? Is it a true battery or another type of device (i.e. large capacitor). 2) How long with the backup power source last? 3) At what main battery voltage does the backup battery engage? 4) Does this battery charge itself from the main battery input? 5) What features are retained or lost when on the backup battery? a. GPS output (to PDA)? b. Output to external display? c. Internal display? d. Other? Flight Logs 1) If there is a power outage of short duration, is the flight log maintained? 2) How long of a gap in time without power is allowed and still maintain a single log file? |
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This topic is kind of funny when you think about it. We sailplane
pilots used to pride ourselves on being immune to "power failures" as opposed to power pilots who would wet their pants at the thought of losing power. We need nothing but the sun and our brains to keep us aloft. Now I can think of at least two times in the past year I've heard sailplane pilots announce over the radio they were terminating their flights because they had electrical problems and their flight computers were not functioning properly. |
#3
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On Fri, 17 Jun 2005 18:44:03 UTC, T o d d P a t t i s t
wrote: Not directly They recommend an external 22,000 mfd capacitor. Are you sure it's not 22,000uF? 22,000mF = 22F is a blinking large capacitor (not impossible, these days - I've used a 10F one). cap - less than a second, alternate battery - multiple days. 22F @ 12V is about 2As ... more than 2A seems a bit unlikely for a logger. Not trying to pick holes, just interested. Ian |
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On Mon, 20 Jun 2005 14:00:20 UTC, T o d d P a t t i s t
wrote: "Ian Johnston" wrote: On Fri, 17 Jun 2005 18:44:03 UTC, T o d d P a t t i s t wrote: Not directly They recommend an external 22,000 mfd capacitor. Are you sure it's not 22,000uF? 22,000mF = 22F is a blinking large capacitor (not impossible, these days - I've used a 10F one). Sorry, yes it's micro 10^-6 not milli 10^-3 Mind you, since capacitors in the 10F range are available, not too expensive, and about the size of an AA battery, it might be worth using one. Just be careful folks - Very Nasty Things Indeed will happen if you short one of these suckers. Stick a discharge resistor across it for a start. Ian |
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Ian Johnston wrote:
On Mon, 20 Jun 2005 14:00:20 UTC, T o d d P a t t i s t wrote: "Ian Johnston" wrote: On Fri, 17 Jun 2005 18:44:03 UTC, T o d d P a t t i s t wrote: Not directly They recommend an external 22,000 mfd capacitor. Are you sure it's not 22,000uF? 22,000mF = 22F is a blinking large capacitor (not impossible, these days - I've used a 10F one). Sorry, yes it's micro 10^-6 not milli 10^-3 Mind you, since capacitors in the 10F range are available, not too expensive, and about the size of an AA battery, it might be worth using one. Just be careful folks - Very Nasty Things Indeed will happen if you short one of these suckers. Stick a discharge resistor across it for a start. Ian The 22,000 uF cap recommendation was a very ugly hack recommended by the manufacturer, trying to respond to the rules change. Doesn't work very well, since the half second of hold time reported is somewhat short of the 5 minutes in the rules. Worse yet, it causes huge surge currents when it's connected to the battery, which could blow fuses, diodes, or damage switches. Just adding the cap is a terrible idea. I'd never do that, without additional circuitry to handle the potential problems. The supercaps would be a disaster without additional circuitry. |
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T o d d P a t t i s t wrote:
"Ian Johnston" wrote: Mind you, since capacitors in the 10F range are available, not too expensive, and about the size of an AA battery, it might be worth using one. Just be careful folks - Very Nasty Things Indeed will happen if you short one of these suckers. Stick a discharge resistor across it for a start. You also want to worry about the initial inrush current. My initial setup seemed to work fine during testing and installation. On the next day, however, the fuse blew when I turned it on as the capacitor charged. No kidding. The capacitor recommendation was an ugly hack recommended to try to do something about an ill-considered rules change, which really wasn't an actual rules change. It's been confusing people for years. Following is from a 2001 posting from the manufacturer: Hello All, after successful reinstalling my newsreader, some advice from us as the manufacurer of the Volkslogger would be useful (yes, I know, we should be more active, or active at all, at this newsgroup, and from now on we will ....): The circuit diagram in the VL manual is only a sample. In some cases (depending on the inner resistance of the Capacitor, if is an array of goldcaps or a real capacitor), a serial resistor is needed to avoid fuse blowing (but not too much resistance because of voltage drop). The Volkslogger itself draws about 120 miliamps at 12 V. You can also use an array of 10 AAA accumulator cells. Background: ------------------ When the Volkslogger got approval, the said requirement was not part of the standard. We tried to build it into our firmware during the time, but we didn't know which time frame should be used and if it would be approved by IGC/GFAC and decided to let it as it was. Until now, no firmware upgrade introduced this requirement, but now that it is a wishfull ("should") part of the standard, we will think about it over winter time. But be sure, we have much other things to develop (new ultralight plane flight information system with color map etc., see our new homepage www.ulfis.de ) I hope I helped you a little bit... best regards -- Georg Garrecht Garrecht Ingenieurgesellschaft, manufacturer of the Volkslogger Germany www.garrecht.com |
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T o d d P a t t i s t wrote:
David Kinsell wrote: The capacitor recommendation was an ugly hack recommended to try to do something about an ill-considered rules change, which really wasn't an actual rules change. I agree it's an ugly hack, but a simple one for which I already had the required components. Plus, it was successful in solving my problem. The recommendation in the manual was just to use the monster cap. That never should have found its way into the manual. Even if somebody uses a big enough fuse to avoid blowing, caps have a surge current rating which was no doubt exceeded. Having one of those things explode in your panel wouldn't be pleasant. I use a center-off double throw switch to select battery A or B. The VL is so sensitive to loss of power that throwing the switch through the center off position caused a reset half the time. I couldn't safely check battery voltages or select the new battery without risking a reset.. A better way of avoiding the problem is just having one battery. If you have room for two inadequate batteries, then you certainly could carry one battery big enough to last the whole flight. If you're not switching, then there's no problem and you don't have to use all the funny hardware that gets thrown into systems trying to fix the problem. More importantly, it avoids the need to keep guessing when the first battery is getting weak, and trying to flip the switch before the FR resets. It's sad but somehow amusing that SLA batteries adequate to solve the problem have been readily available for well over 20 years, but people seem to keep struggling with it. I fly with a Cambridge 20, which like most recorders in the field today can't tolerate a power loss for more than a tiny fraction of a second. But I've never had a single problem with multiple logs being created. Turn on the master switch, go fly, and it just works. A 5 A-H battery can power a normal panel for 6 hours no problem at all. Helps if you get the voltage right, but that's another discussion . . . Dave T o d d P a t t i s t - "WH" Ventus C (Remove DONTSPAMME from address to email reply.) |
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T o d d P a t t i s t wrote:
David Kinsell wrote: A better way of avoiding the problem is just having one battery. If you have room for two inadequate batteries, then you certainly could carry one battery big enough to last the whole flight. 1) The glider has 3 built in locations for the standard 12v 7-8AH battery. It's not designed to take larger batteries. They are large enough for 90% of my flights if fully charged. Fine. Wire them together and form one larger battery in the glider. That way you don't have to keep monitoring one battery, trying to switch before having problems with the FR. And you avoid the silly solution of a monster electrolytic. Those caps are cardboard cylinders filled with caustic liquid, and a pressure vent to hopefully avoid a rupture. Of all the components used in modern electronics, they have absolutely the worst reliability of anything. Putting one in a panel, for no good reason, is not a good idea. 2) I prefer the redundancy of two batteries. I've posted recently as to why. I know you disagree, but if you'd camped at a glider field, without easy access to electricity, as many times as I, you might prefer the dual solution too. You're missing the point. If you can carry multiple inadequate batteries, you can certainly carry one adequate battery. Switching between multiple batteries in no way extends the life, it just opens the door to failures based on funny hardware, or letting the voltage drop too low before switching. If you're not switching, then there's no problem and you don't have to use all the funny hardware that gets thrown into systems trying to fix the problem. A switch and a cap is "funny hardware"? It's about as simple as it gets. Much simpler to avoid the switching in the first place, and forget about the cap trying to hold up the system voltage as you're doing the switch. More importantly, it avoids the need to keep guessing when the first battery is getting weak, and trying to flip the switch before the FR resets. I've never had an FR reset due to low battery. The first sign is always the radio. It's sad but somehow amusing that SLA batteries adequate to solve the problem have been readily available for well over 20 years, but people seem to keep struggling with it. I fly with a Cambridge 20, which like most recorders in the field today can't tolerate a power loss for more than a tiny fraction of a second. But I've never had a single problem with multiple logs being created. Turn on the master switch, go fly, and it just works. A 5 A-H battery can power a normal panel for 6 hours no problem at all. Helps if you get the voltage right, but that's another discussion . . . Dave T o d d P a t t i s t - "WH" Ventus C (Remove DONTSPAMME from address to email reply.) T o d d P a t t i s t - "WH" Ventus C (Remove DONTSPAMME from address to email reply.) |
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