---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 12/13/10: 8 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 02:27 AM - Re: Computing a Resistor Value (BobsV35B@aol.com) 2. 06:13 AM - Re: Computing a Resistor Value (Robert L. Nuckolls, III) 3. 06:13 AM - Re: Computing a Resistor Value (Robert L. Nuckolls, III) 4. 06:13 AM - Re: Computing a Resistor Value (Mike Welch) 5. 08:03 AM - Re: Computing a Resistor Value (AlRice) 6. 08:25 AM - Re: Computing a Resistor Value (user9253) 7. 10:24 AM - "Regulated" 12 v supply (jonlaury) 8. 05:03 PM - Re: "Regulated" 12 v supply (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 02:27:16 AM PST US From: BobsV35B@aol.com Subject: Re: AeroElectric-List: Computing a Resistor Value Good Morning Al, I am sure you know more about Ohm's Law than I do, but why don't you consider using a Zener Diode? If you use a resistor, the voltage output will change as the load changes. I have no idea whether or not the load does change during operation of the AV80R but dropping resistors do not work well at all with a varying load. Happy Skies, Old Bob In a message dated 12/12/2010 8:05:24 P.M. Central Standard Time, Allen@allenrice.net writes: --> AeroElectric-List message posted by: "Al Rice" I want to install my AV 80 R GPS in my panel and wire the power lead to the bus without installing a clunky cigarette power socket on my panel. The GPS input voltage is 5 V and it draws 1.5A (at least that's what the cigarette power lead says on it). My buss voltage is 13.5V, so how do I compute the resistor ohm's and watts needed for my power lead? I know enough about Ohm's law to be dangerous. Thanks. -------- Al Rice Sky bolt 260 RV-9 A Helping with my grandson's Pi et ________________________________ Message 2 _____________________________________ Time: 06:13:19 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Computing a Resistor Value At 07:59 PM 12/12/2010, you wrote: > >I want to install my AV80R GPS in my panel and wire the power lead >to the bus without installing a clunky cigarette power socket on my >panel. The GPS input voltage is 5V and it draws 1.5A (at least >that's what the cigarette power lead says on it). My buss voltage >is 13.5V, so how do I compute the resistor ohm's and watts needed >for my power lead? I know enough about Ohm's law to be dangerous. And indeed, a total reliance on Ohm's law in this instance would be very hard if not dangerous to the GPS. You need to acquire the automotive power adapter suited for using/charging this product in the car . . . then adapt that same device to the airplane. I see that the advertising literature speaks of a USB/PC cable. Check the instruction manual to see if connection of the GPS to a powered up PC will also charge the battery. It may not . . . some USB ports on computers won't deliver 1.5A. If so, then there are dozens of "USB power adapters" designed to accept 14 volts from a vehicular power system and deliver the smooth, regulated 5v dc necessary for safe operation of the GPS. But accommodating the King automotive adapter cable in the airplane is THE 100% way to go. Bob . . . ________________________________ Message 3 _____________________________________ Time: 06:13:37 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Computing a Resistor Value At 07:59 PM 12/12/2010, you wrote: > >I want to install my AV80R GPS in my panel and wire the power lead >to the bus without installing a clunky cigarette power socket on my >panel. The GPS input voltage is 5V and it draws 1.5A (at least >that's what the cigarette power lead says on it). My buss voltage >is 13.5V, so how do I compute the resistor ohm's and watts needed >for my power lead? I know enough about Ohm's law to be dangerous. And indeed, a total reliance on Ohm's law in this instance would be very hard if not dangerous to the GPS. You need to acquire the automotive power adapter suited for using/charging this product in the car . . . then adapt that same device to the airplane. I see that the advertising literature speaks of a USB/PC cable. Check the instruction manual to see if connection of the GPS to a powered up PC will also charge the battery. It may not . . . some USB ports on computers won't deliver 1.5A. If so, then there are dozens of "USB power adapters" designed to accept 14 volts from a vehicular power system and deliver the smooth, regulated 5v dc necessary for safe operation of the GPS. But accommodating the King automotive adapter cable in the airplane is THE 100% way to go. Bob . . . ________________________________ Message 4 _____________________________________ Time: 06:13:46 AM PST US From: Mike Welch Subject: RE: AeroElectric-List: Computing a Resistor Value > The GPS input voltage is 5V and it draws 1.5A (at least that's what the >cigarette power lead says on it). My buss voltage is 13.5V=2C so how do I compute >the resistor ohm's and watts needed for my power lead?I know enough about >Ohm's law to be dangerous. > Thanks. > -------- > Al Rice Mornin' Al=2C When I first read your post=2C I didn't think the resistor was the way to go=2C either=2C same as Dick Tasker described. My thinking was you're asking quite a bit f rom just one resistor. My initial thought was "why not build a 5 volt circuit" (like this one)? http://www.tkk.fi/Misc/Electronics/circuits/psu_5v.html Recently=2C I asked this forum if they knew how I could turn my Ray Allen servo resistance output (0-5K ohms) into a visual LED indicator. Our buddy Joe Gores offere d the perfect suggestion of a circuit referenced from Mike Linse. Included in his suggestion was that really handy 5 volt circuit above=2C plus it is super easy to build. The circuit had a final voltage output of 4.96 volts=2C and when combined w ith the circuit Mike Linse talked about=2C the whole project worked exactly as I was hoping for. From the article's data points about this 5 volt circuit=2C it says it ma y be limited to only one amp=2C plus you should consider a heat sink. So I got to thinking..... .... Here's a question for for you guys that rearrange electrons for a living. ....could a guy build TWO of these 5 volt circuits=2C and combine the '5 volt output' in pa rallel? Mike Welch ________________________________ Message 5 _____________________________________ Time: 08:03:05 AM PST US Subject: AeroElectric-List: Re: Computing a Resistor Value From: "AlRice" Thanks for the advice everyone. I learned a lot with this thread. I guess I'll stick with the cigarette adapter and mount the socket behind the panel where I can't see the ugly thing. -------- Al Rice Skybolt 260 RV-9A Helping with my grandson's Piet Read this topic online here: http://forums.matronics.com/viewtopic.php?p=323176#323176 ________________________________ Message 6 _____________________________________ Time: 08:25:04 AM PST US Subject: AeroElectric-List: Re: Computing a Resistor Value From: "user9253" Al, The rating on the 5 volt adaptor is what it is capable of, not necessarily what the GPS uses. There are options: 1. Like everyone is saying, using a resistor by itself is a bad idea. 2. A resistor and a 5 volt zener diode. Without knowing the current requirements of the GPS, it will be trial and error. 7 ohms, 10W would be a starting point. 3. You could build the 5v regulator circuit suggested by Mike Welch. A 7805 in a TO-220 case bolted to the airframe and using thermal conductive paste. 4. Take apart the OEM adaptor and solder wires to it and connect to the aircraft power. 5. Buy one of these: http://www.mouser.com/ProductDetail/Murata-Power-Solutions/78SRH-5-2-C/?qs=35WhQNrE6p2lJ6BniHrImQ%3d%3d Probably generates less heat than other options. Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=323181#323181 ________________________________ Message 7 _____________________________________ Time: 10:24:16 AM PST US Subject: AeroElectric-List: "Regulated" 12 v supply From: "jonlaury" I have a video camera on my tailwheel so that I can see under the nose of my plane when taxiing. The camera calls for a "regulated" 12v, (+ or - 10%) power supply. Will a 12v inline zener diode do the job, or do I not understand how zeners work? Thanks, John Read this topic online here: http://forums.matronics.com/viewtopic.php?p=323192#323192 ________________________________ Message 8 _____________________________________ Time: 05:03:34 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: "Regulated" 12 v supply At 12:20 PM 12/13/2010, you wrote: > >I have a video camera on my tailwheel so that I can see under the >nose of my plane when taxiing. The camera calls for a "regulated" >12v, (+ or - 10%) power supply. > >Will a 12v inline zener diode do the job, or do I not understand how >zeners work? A zener works like a "smart weight" on the end of a spring. Suppose you hung a kid's swing from the ceiling on a bungee cord and with nobody in the swing, it was 3' off the floor. For the kid's safety, you want them to enjoy the swing at an altitude of 12 +/- 1 inches off the floor. Suppose the heaviest 50# kid caused the swing to assume an altitude of 16" . . . you would need to ADD weight to achieve the desired altitude. Suppose further that the lightest 30# kid pulls the swing down to 24" off the floor. Obviously, still more weight needs to be added to achieve the 12" target. 24-16 The spring rate for this example is ------ = .40 inches/lb 50-30 So added weight need to lower the altitude with the 50# kid by 4 inches is 4/.4 or 10 pounds. Added weight for the 30# kid needs to lower the swing an additional 12 inches is 12/.4 or 30 pounds. Finally, you want the swing to hang at 12" for everyone to get into our out of the swing. This means that while the swing is completely unloaded, the greatest compensating weight would have to be applied and then adjusted downward quickly and smoothly as the passenger gets into or out of the swing. The study above says a total weight of 60 pounds will hold the empty swing at the right "altitude". Okay, our zener is a "smart weight". The bungee is replaced with a resistor (R). The range of swing customers have a "weight" of 30 to 50 millamperes. The target "swinging height" or Vout of 5 volts. Emacs! Obviously, we must hang from a ceiling greater than 5 volts . . . for the purposes of this study, let's call it a Vin of 12 volts. So we need a constant differential or "drop" of 7 volts in our resistor. Let's set up the resistor so that the swing is capable of carrying passengers just above the largest anticipated demand . . . 60 mA. 8V drop at 60 mA calls for a resistor of R = 8v/.06a = 133 ohms. Our "smart weight" is a zener diode operating at 5.1 volts above the floor. Further, with no passengers in the swing, the zener needs to dissipate a total power value of 5.1v x .06 amps = 300 milliwatts. So a 500 mW or larger zener will suffice. The resistor has a constant 8v drop across it at the .06A so it dissipates worst case: 8v x .06A = .48W I'd go for a 1W resistor to run cooler. Now, with the "smart weight" maintaining 5.1 volts off the floor, any load of 0 up to and including 0.06 amps can be connected across the zener with an expectation that the 5.1 volt value will be maintained. This example is probably in the neighborhood of a best case for using a zener supply. Total power being dumped in the components is maxed at 0.78W. If one were to design a similar architecture for a 1.5A supply, the wasted power goes up to 18 watts . . . really gets things hot unless provided with HEAVY heatsinks. The architecture of choice is to utilize one of the modern DC/DC converters that yield 90 plus percent efficiencies at all load levels. HOWEVER, it's not a free lunch. There can be terrible noise generators for adf and perhaps even VHF comm radios. So as a matter of normal practice, I ALWAYS close these critters up in metallic enclosures with input and output filters. You asked about a 12 volt source. Your input can be anything from 10 to 15 volts. So you need a buck-boost DC/DC converter that provides an output from a source that may be either above or below the output. How much current are we talking about? You might want to consider a set of alkaline cells and a toggle switch to turn the system on only when actively in use. I suspect a set of dedicated batteries would last a very long time. Bob . . . ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.