---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sun 08/10/14: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:55 AM - Re: Shunt Questions (user9253) 2. 09:50 AM - Re: Shunt Questions (Eric M. Jones) 3. 10:20 AM - Re: Re: Shunt Questions (Robert L. Nuckolls, III) 4. 10:56 AM - Re: Re: Shunt Questions (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 06:55:41 AM PST US Subject: AeroElectric-List: Re: Shunt Questions From: "user9253" See the attached picture from Dynon's installaiton manual. Is the shunt located in position A or B or C? When the shunt is located in position "A", which measures current into or out of the battery, as you know, very little current flows through the shunt when the battery is fully charged. The following pertains to a shunt in position "A". The engine needs to be off while troubleshooting. If the electrical system operates normally, the shunt must be good. If the shunt has a higher than normal resistance, then there would be a larger voltage drop across the shunt. This would show up as lower system voltage and a higher ammeter reading. Since the electrical system operates normally, I suspect a bad connection between the shunt and EFIS, or a problem within the EFIS. Even though the EFIS displays amps, it actually measures millivolts. I would test the EFIS by applying a millivolt signal to the ammeter input. This millivolt signal could be provided by a resistor network or by an almost dead flashlight battery. Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=428262#428262 Attachments: http://forums.matronics.com//files/shunt_location_143.jpg ________________________________ Message 2 _____________________________________ Time: 09:50:51 AM PST US Subject: AeroElectric-List: Re: Shunt Questions From: "Eric M. Jones" Shunts and Hall Effect sensors. Hall effect sensors seemed to be quite nice since they were small and could directly interface with other electronics. But it is harder and harder to justify their use over a simple shunt. As for troubleshooting a shunt, cracks can be very hard to detect, so bolting another in its place is a good approach. Shunts are ultra-reliable, but everything fails sometime. There is another way to measure current, and that is to measure the voltage at each end of the wire in question. This is done by running a small (like AWG 26) wire from each end of the high-current conductor (whose current you want to know) to some voltmeter. The technique works because ESSENTIALLY NO CURRENT flows in the tiny sense wires. The voltage sensor then measures the voltage drop through the fatwire. Of course, you need to know something else, like the true current/voltage drop, or true fatwire resistance. But this technique is the preferred way for really big and reasonably long power conductors. And there is no separate shunt or Hall Effect sensor. -------- Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge, MA 01550 (508) 764-2072 emjones(at)charter.net Read this topic online here: http://forums.matronics.com/viewtopic.php?p=428270#428270 ________________________________ Message 3 _____________________________________ Time: 10:20:09 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Shunt Questions There is another way to measure current, and that is to measure the voltage at each end of the wire in question. This is done by running a small (like AWG 26) wire from each end of the high-current conductor (whose current you want to know) to some voltmeter. The technique works because ESSENTIALLY NO CURRENT flows in the tiny sense wires. The voltage sensor then measures the voltage drop through the fatwire. Of course, you need to know something else, like the true current/voltage drop, or true fatwire resistance. But this technique is the preferred way for really big and reasonably long power conductors. And there is no separate shunt or Hall Effect sensor. I have used this technique in several applications where calibration is not an issue. The ammeter shunt's resistor is made from a special alloy7 called 'manganin'. http://tinyurl.com/3f79fgy This is an alloy crafted both for it's practical resistance and very low temperature coefficient of resistance. The ordinary conductors used to wire things up tend to have higher temperature coefficients. Which makes their use as an ammeter rather squirrely. As the wire heats up, it's temperature goes up, resistance goes up, power dissipated goes up, temperature rises some more and so it goes. If one plots current versus voltage drop in a wire in free- air (waiting for temperature to stabilize after each new current setting), you get a rather non-linear curve that isn't even repeatable except when the ambient conditions in which the wire operates are held constant. One practical way to use wiring as a 'shunt' is to detect lamp failure or perhaps failure in some other load like pitot heat. In this case, it is sufficient to simply know that current is flowing in the wire . . . or not. It is not necessary to know how much current flows. Bob . . . ________________________________ Message 4 _____________________________________ Time: 10:56:03 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Shunt Questions Even though the EFIS displays amps, it actually measures millivolts. I would test the EFIS by applying a millivolt signal to the ammeter input. This millivolt signal could be provided by a resistor network or by an almost dead flashlight battery. Even an 'almost dead' battery is probably too much . . . Suggest you craft a millivolt test source from a couple of resistors and a good flashlight cell. Any other combination of resistors can be used as long as you hit the 'output target' in the upper half of a 50mV full scale input to the EFIS. Emacs! This is not an 'accurate' source, only a practical source for carrying out a divide-and-conquer experiment to isolate your fault. 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.