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#1
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"Secret" Overvoltage Protection?
I had an unusual experience last week, and figured I'd air it here for
some opinions. My Fly Baby had developed charging problems again. I wasn't sure if it was the generator or regulator, so I decided to do a bit of temporary wiring to bypass the regulator (Generator armature to +12V, ground the Field terminal). I knew that in this mode, the generator could produce high voltages that could fry my radio (ICOM IC-A5) and transponder (Microair). So I left the power switches for both off. I started the engine and watched the voltmeter. It read 8V at idle, but when the power came up, the voltage started to rise. I chopped the throttle before the voltage got much past 14V on the gauge. So, the regulator was bad. Fortunately, I'd bought a spare at a fly-market a few years back ($5). I switched regulators, buttoned up the cowl, and mounted up for a test flight. Strangely enough, neither the radio nor the transponder would power-up at first try. I cycled the power on and off, and pressed the "on" buttons on each a couple of times. The ICOM powered up about the third try, and worked normally. The Microair was more stubborn, but after about 15 minutes of power-on, it too came on when I hit the switch. The only thing I can think of is that both units have some sort of overvoltage protection that clears itself after a time. Neither has the classical "On" button with mechanical contacts that make or break the power to the unit; the "On" button undoubtedly tells some aspect of the circuit board what to do (on the Microair, one hits the power button multiple times to adjust the LCD lighting). Still, the units shouldn't have seen that direct generator output...they were turned off. So what activated the overvoltage protection? Anybody got any ideas? Ron Wanttaja |
#2
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"Secret" Overvoltage Protection?
Sorry about the top post; but I didn't want to cut your original text.
You have been tricked and, without schematics of the Com and Transponder, I really don't know exactly how they are supposed to work. However, the common problem with modern electronics is that, without an old fashoined mechanical switch, a portion of the circutry must remain powered on when the device is turned off. I am now about ten years out of date as an electronic technician, so I really don't know what additional parts reamain operational; but, at the most basic, system clocks, memory of any preselected channels (or frequencies), the on-off control circuitry, the voltage protection circuits, and possibly any crystal heaters. It is not just an aviation problem either, as I suspect that it may be a primary cause of failure in personal computers and other houshold electronics; but it is easiest to see in automotive radios--which usually have no internal batteries or capacitors to keep the memory alive when the main battery is disconnected for even a few seconds. Anyway, I'm glad that the protection circuits appear to have worked without damage. Peter "Ron Wanttaja" wrote in message ... I had an unusual experience last week, and figured I'd air it here for some opinions. My Fly Baby had developed charging problems again. I wasn't sure if it was the generator or regulator, so I decided to do a bit of temporary wiring to bypass the regulator (Generator armature to +12V, ground the Field terminal). I knew that in this mode, the generator could produce high voltages that could fry my radio (ICOM IC-A5) and transponder (Microair). So I left the power switches for both off. I started the engine and watched the voltmeter. It read 8V at idle, but when the power came up, the voltage started to rise. I chopped the throttle before the voltage got much past 14V on the gauge. So, the regulator was bad. Fortunately, I'd bought a spare at a fly-market a few years back ($5). I switched regulators, buttoned up the cowl, and mounted up for a test flight. Strangely enough, neither the radio nor the transponder would power-up at first try. I cycled the power on and off, and pressed the "on" buttons on each a couple of times. The ICOM powered up about the third try, and worked normally. The Microair was more stubborn, but after about 15 minutes of power-on, it too came on when I hit the switch. The only thing I can think of is that both units have some sort of overvoltage protection that clears itself after a time. Neither has the classical "On" button with mechanical contacts that make or break the power to the unit; the "On" button undoubtedly tells some aspect of the circuit board what to do (on the Microair, one hits the power button multiple times to adjust the LCD lighting). Still, the units shouldn't have seen that direct generator output...they were turned off. So what activated the overvoltage protection? Anybody got any ideas? Ron Wanttaja |
#3
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"Secret" Overvoltage Protection?
Peter Dohm wrote:
You have been tricked and, without schematics of the Com and Transponder, I really don't know exactly how they are supposed to work. However, the common problem with modern electronics is that, without an old fashoined mechanical switch, a portion of the circutry must remain powered on when the device is turned off. The difficulty is the lack of definitive understanding of how my airplane is wired. The original builder didn't generate a schematic. I inherited one drawn up by the third owner: http://www.bowersflybaby.com/tech/elect.gif When I ran the regulator-bypass generator test, I turned on the Master Switch, the Field Switch, and the Generator Output switch, but left off the switches for the radio and the "Aux" (which goes to the transponder). If the schematic is correct, then no +12v power should have been available to the devices unless I'd turned the breaker/switches on. However, there is the possibility the schematic is wrong...that the switches may control connection of the devices to the GROUND, and that the +12V is delivered to the radio and transponder whenever the master switch is on. Since I have a wooden airplane, there is no "ground", per se. Two wires go to each device, and whether the breaker/switch connects one wire to the ground bus or the other one to +12V wouldn't make much difference in operation. If the breaker/switch does control connection to the ground, there is a chance that the devices still see ground via their antenna ground plane. If that is the case, then an overvoltage at the +12V input *might* still be detected and reacted to. However....neither device will power-up if the breaker/switch is turned off. The ground plane for the comm radio antenna is connected to ground by the same wire that connects the radio itself to the ground. Curious.... Ron Wanttaja |
#4
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"Secret" Overvoltage Protection?
On Feb 15, 10:11*am, Ron Wanttaja wrote:
Peter Dohm wrote: You have been tricked and, without schematics of the Com and Transponder, I really don't know exactly how they are supposed to work. *However, the common problem with modern electronics is that, without an old fashoined mechanical switch, a portion of the circutry must remain powered on when the device is turned off. The difficulty is the lack of definitive understanding of how my airplane is wired. *The original builder didn't generate a schematic. *I inherited one drawn up by the third owner: http://www.bowersflybaby.com/tech/elect.gif When I ran the regulator-bypass generator test, I turned on the Master Switch, the Field Switch, and the Generator Output switch, but left off the switches for the radio and the "Aux" (which goes to the transponder). If the schematic is correct, then no +12v power should have been available to the devices unless I'd turned the breaker/switches on. However, there is the possibility the schematic is wrong...that the switches may control connection of the devices to the GROUND, and that the +12V is delivered to the radio and transponder whenever the master switch is on. *Since I have a wooden airplane, there is no "ground", per se. *Two wires go to each device, and whether the breaker/switch connects one wire to the ground bus or the other one to +12V wouldn't make much difference in operation. If the breaker/switch does control connection to the ground, there is a chance that the devices still see ground via their antenna ground plane. * If that is the case, then an overvoltage at the +12V input *might* still be detected and reacted to. However....neither device will power-up if the breaker/switch is turned off. *The ground plane for the comm radio antenna is connected to ground by the same wire that connects the radio itself to the ground. Curious.... Ron Wanttaja A lot of newer avionics have DC-DC buck/boost voltage regulators built in. This shows up on the specs as an input voltage of say, 10 - 36 V meaning the internal regulator will deliver a constant voltage to the circuit boards if the aircraft power bus is somewhere in that range. It also means that the device will work on both 12v and 24V systems. FWIW, I have a Microair 760 in my glider and find it is unusually sensitive to input voltage. Whenever the SLA battery drops to 11V, it goes totally bonkers. This brings up a slight fork to this thread and that is alternator failure. I've had three - one in hard IFR. It seems to me that modern avionics should have a UPS just like the computer I'm typing on. Modern avionics use far less power than they used to and batteries are getting better. It should be possible to have a UPS battery on the avionics bus that will power the whole panel longer than the fuel will last. |
#5
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"Secret" Overvoltage Protection?
On Sat, 14 Feb 2009 21:26:23 -0800, Ron Wanttaja
wrote: The only thing I can think of is that both units have some sort of overvoltage protection that clears itself after a time. Neither has the classical "On" button with mechanical contacts... Still, the units shouldn't have seen that direct generator output...they were turned off. So what activated the overvoltage protection? Anybody got any ideas? I wonder if it's the same problem that I've seen on a number of occasions with computers, which typically is the computer getting zapped by a static discharge (the "rubbing your feet on a carpet on a dry day" thing). The symptom is that the computer won't turn on at all, and the fix is to unplug and/or remove the battery, then press and hold down the power button for ten seconds or so to drain off any static. Plug it in and/or replace the battery, and voila! The computer works again. A transient voltage spike too fast for your gauge to register may have done the same thing to your electronics. -Dana -- There is always a law against doing anything interesting. |
#6
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"Secret" Overvoltage Protection?
On Feb 15, 9:28 am, Bryan Martin
wrote: You are correct in that some circuits in many avionics devices will be powered up anytime the master switch is on. The only way to be sure these devices are completely isolated from ship's power is to pull the fuse. But, avionics devices are not going to have any memory circuits or clocks that require a keep alive voltage unless they have a dedicated battery for the purpose. When the master switch in an airplane is off, there is no power at all getting to the avionics, all circuits are completely disconnected from the ship's power unless they have a backup power source. About the only thing in most airplanes that might bypass the master relay is an electric clock. No, some avionics have a "keep-alive" feed to them via a tiny fuse directly from the hot side of the battery contactor. Narco's MK12d + radios, for instance. If that isn't connected the memory is gone and the display will default to the lowest frequencies on system shutdown. Clocks usually have a feed through another tiny fuse. And Artex's new ME406 ELTs also have a hot feed to the panel switch, but all it does is feed the LED indicator so that power isn't robbed from the ELT's battery to do it. Kannad and some others don't use a hot wire. The hot feed is an item that adds to the installation cost, by the way. Got to find a place for the fuse and run a wire from it to the panel. Labor, man. I'm wondering if Ron's problem was a low system voltage after he installed the new regulator, until it woke up and started the generator charging. Some of these radios will drop offline if they aren't getting nearly the full rated voltage. Dan |
#7
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"Secret" Overvoltage Protection?
Dan et al ...
The "tiny fuse" you refer to is actually a single fuse mounted as close as possible to the battery box. AIVR, you can have either 3 or 5 amps directly from the battery (i.e. a 3 or 5 amp fuse) in a "keep alive" circuit that doesn't go through the master relay but is wired directly to the battery. That circuit is then wired to the clock and any other avionics that need to draw (usually microamps) current to keep memories alive and the like. In the Cessna, I mounted that fuse on the master relay bracket and got the "hot" from the master relay itself on the upstream side of the battery. Minimum wire and minimum chance for fire if the wire insulation shorts to ground. Use a rather thin wire with an extra coat of heavy shrink sleeving; if it DOES short to ground it will fuse rather than start a fire. Jim -- "It is the mark of an educated mind to be able to entertain a thought without accepting it." --Aristotle wrote in message ... On Feb 15, 9:28 am, Bryan Martin wrote: You are correct in that some circuits in many avionics devices will be powered up anytime the master switch is on. The only way to be sure these devices are completely isolated from ship's power is to pull the fuse. But, avionics devices are not going to have any memory circuits or clocks that require a keep alive voltage unless they have a dedicated battery for the purpose. When the master switch in an airplane is off, there is no power at all getting to the avionics, all circuits are completely disconnected from the ship's power unless they have a backup power source. About the only thing in most airplanes that might bypass the master relay is an electric clock. No, some avionics have a "keep-alive" feed to them via a tiny fuse directly from the hot side of the battery contactor. Narco's MK12d + radios, for instance. If that isn't connected the memory is gone and the display will default to the lowest frequencies on system shutdown. Clocks usually have a feed through another tiny fuse. And Artex's new ME406 ELTs also have a hot feed to the panel switch, but all it does is feed the LED indicator so that power isn't robbed from the ELT's battery to do it. Kannad and some others don't use a hot wire. The hot feed is an item that adds to the installation cost, by the way. Got to find a place for the fuse and run a wire from it to the panel. Labor, man. I'm wondering if Ron's problem was a low system voltage after he installed the new regulator, until it woke up and started the generator charging. Some of these radios will drop offline if they aren't getting nearly the full rated voltage. Dan |
#8
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"Secret" Overvoltage Protection?
On Feb 16, 7:32 pm, "RST Engineering" wrote:
Dan et al ... The "tiny fuse" you refer to is actually a single fuse mounted as close as possible to the battery box. AIVR, you can have either 3 or 5 amps directly from the battery (i.e. a 3 or 5 amp fuse) in a "keep alive" circuit that doesn't go through the master relay but is wired directly to the battery. That circuit is then wired to the clock and any other avionics that need to draw (usually microamps) current to keep memories alive and the like. That's where I find them and where I put the Artex's fuseholder. I don't want an always-hot unfused wire any longer than necessary. The Artex uses a quarter-amp fuse. Dan |
#9
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"Secret" Overvoltage Protection?
"RST Engineering" wrote in message m... Dan et al ... The "tiny fuse" you refer to is actually a single fuse mounted as close as possible to the battery box. AIVR, you can have either 3 or 5 amps directly from the battery (i.e. a 3 or 5 amp fuse) in a "keep alive" circuit that doesn't go through the master relay but is wired directly to the battery. That circuit is then wired to the clock and any other avionics that need to draw (usually microamps) current to keep memories alive and the like. In the Cessna, I mounted that fuse on the master relay bracket and got the "hot" from the master relay itself on the upstream side of the battery. Minimum wire and minimum chance for fire if the wire insulation shorts to ground. Use a rather thin wire with an extra coat of heavy shrink sleeving; if it DOES short to ground it will fuse rather than start a fire. Jim -- What size wire do you recommend? 22ga? |
#10
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"Secret" Overvoltage Protection?
Who is asking?
Jim -- "It is the mark of an educated mind to be able to entertain a thought without accepting it." --Aristotle What size wire do you recommend? 22ga? |
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