---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 03/24/14: 9 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:58 AM - Re: P-Leads for a Seawind (Robert L. Nuckolls, III) 2. 09:59 AM - Re: New Over-Voltage Protection Architecture (user9253) 3. 10:38 AM - Re: P-leads (D L Josephson) 4. 10:53 AM - New Over-Voltage Protection Architecture (R. curtis) 5. 11:05 AM - Re: Re: New Over-Voltage Protection Architecture (Vern Little) 6. 11:42 AM - Re: DIY CBOVM: variations on a theme (user9253) 7. 12:25 PM - Re: Re: P-leads (K) 8. 08:04 PM - Re: Re: DIY CBOVM: variations on a theme (Robert L. Nuckolls, III) 9. 08:10 PM - Re: Re: New Over-Voltage Protection Architecture (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 06:58:02 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Re: P-Leads for a Seawind I forgot to ask. Are your magnetos relatively new or are they the the legacy Bendix mags? The older mags have a knurled nut that holds the 'cigarette terminal' in the connection well on the back of the mag. If you build your own p-leads for older mags, those parts may be hard to find . . . but there are folks on the AeroElectric-List that can help. Bob . . . ________________________________ Message 2 _____________________________________ Time: 09:59:01 AM PST US Subject: AeroElectric-List: Re: New Over-Voltage Protection Architecture From: "user9253" There has been a recent discussion on VansAirforce about over-voltage problems. http://www.vansairforce.com/community/showthread.php?t=111102 Since over-voltage protection does not cost much or weigh much, I think that it is worthwhile having, considering the damage that could be done by too high voltage. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=420931#420931 ________________________________ Message 3 _____________________________________ Time: 10:38:18 AM PST US From: D L Josephson Subject: AeroElectric-List: Re: P-leads The concept of a "fuse" to keep faults in a tachometer from disabling an ignition needs to be stamped out, it is a dangerous misconception. I know of at least one incident where this almost caused a fatal crash. It takes very little current through a P lead from a magneto or points wire in a Kettering ignition to disrupt performance of the ignition. Can you depend on this amount of current blowing a fuse? Is the resistor going to open if there is a fault? Is the engine going to keep running well if the far end of the resistor is shorted to ground or +12? Not unless it has been tested to do so. There are many tach designs that work without an ignition pickup. VDO and other companies make programmable tachs that can be set to take a signal from one phase of an alternator output, or an inductive pickup from a flywheel or magneto case. Proper design of a tach could also yield failsafe operation but that's still putting a lot of faith in something you haven't tested. The "proof by assertion" that I've seen from a few instrument vendors isn't really confidence-inspiring. -- David Josephson ________________________________ Message 4 _____________________________________ Time: 10:53:39 AM PST US From: "R. curtis" Subject: AeroElectric-List: New Over-Voltage Protection Architecture > Since over-voltage protection does not cost much or weigh much, I think > that it is worthwhile having, considering the damage that could be done by > too high voltage. Over voltage protection is recommended for an externally regulated alternator. However, this has been kicked around for the internally regulated unit, and I am not sure that there is, as yet, a good fool proof, method for this alternator. Roger -- Do you have a slow PC? Try a Free scan http://www.spamfighter.com/SLOW-PCfighter?cid=sigen ________________________________ Message 5 _____________________________________ Time: 11:05:07 AM PST US From: "Vern Little" Subject: Re: AeroElectric-List: Re: New Over-Voltage Protection Architecture I was plagued by overvoltages on my externally regulated alternator, until I found a permanent, fool-proof solution: Schematic: http://www.vx-aviation.com/rv-9a/photos/Electrical/Regulator_relay_app.jpg This circuit bypasses the problematic alternator breaker - master switch loop - wiring loop by connecting the master bus directly to the voltage regulator through a fuselink and a relay. Since I have the battery and contactor on the firewall, the total wiring length for this is about 20", with minimal voltage drops. Ensure that you spray the relay connections with Corrosion-X or bed them in silicone grease (DC4). OVP still works normally. A side effect is that almost all alternator noise disappeared. I used to hear wig-wags and strobe noise in my headset, now it's gone. Voltage is rock-solid and does not vary with load. This design should also work with an internally regulated alternator without OVP. The ones with OVP should have a circuit breaker instead of the fuseable link. Downside to that is that the CB should be located close to the alternator and cannot be reset in flight. Cheers, Vern -----Original Message----- From: user9253 Sent: Monday, March 24, 2014 9:57 AM Subject: AeroElectric-List: Re: New Over-Voltage Protection Architecture There has been a recent discussion on VansAirforce about over-voltage problems. http://www.vansairforce.com/community/showthread.php?t=111102 Since over-voltage protection does not cost much or weigh much, I think that it is worthwhile having, considering the damage that could be done by too high voltage. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=420931#420931 ________________________________ Message 6 _____________________________________ Time: 11:42:16 AM PST US Subject: AeroElectric-List: Re: DIY CBOVM: variations on a theme From: "user9253" I built Bob's circuit. To test it, I wired it in series with an automotive lamp to a DC-DC converter like this one: http://tinyurl.com/kmpqcb8 I slowly turned the pot to increase the voltage. The lamp illuminated at almost 17 volts. Since my Rotax rectifier/regulator puts out about 13.8 volts, I decided to lower the set point of the over-voltage protector by substituting a 5.1K resistor for the 5.6K. Now the test lamp comes on at 16.2 volts. When the voltage increases above 15.8, the circuit becomes sensitive. Just touching the circuit with a digital voltmeter probe is enough to fire the SCR. Using a different voltmeter had the same affect. No doubt that in an electrically noisy environment like an airplane, the circuit will trip at 15.8 volts. That is not a problem though. 15.8 volts is 2 volts above my aircraft system voltage. If spring weather ever comes to Michigan, I will install it in the airplane. Thanks for designing the circuit, Bob. You are my mentor. Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=420938#420938 ________________________________ Message 7 _____________________________________ Time: 12:25:41 PM PST US From: K Subject: Re: AeroElectric-List: Re: P-leads Yes "Fuse" is not the terminology I'd use for such a resistor. Agree that the resistor definitely needs to be large enough value that it won't interfere if grounded and testing it should not be overlooked. Where I've seen this go bad was when a wire was run to the resistor mounted in the tach. With age and moisture the wire insulation started breaking down. The resistor should be physically at the ignition pick off point, NOT remotely located. I apply the same concept to picking off a fuel flow signal from an electronic fuel injector. Ken On 24/03/2014 1:37 PM, D L Josephson wrote: > > > The concept of a "fuse" to keep faults in a tachometer from disabling an > ignition needs to be stamped out, it is a dangerous misconception. I > know of at least one incident where this almost caused a fatal crash. It > takes very little current through a P lead from a magneto or points wire > in a Kettering ignition to disrupt performance of the ignition. Can you > depend on this amount of current blowing a fuse? Is the resistor going > to open if there is a fault? Is the engine going to keep running well if > the far end of the resistor is shorted to ground or +12? Not unless it > has been tested to do so. > > There are many tach designs that work without an ignition pickup. VDO > and other companies make programmable tachs that can be set to take a > signal from one phase of an alternator output, or an inductive pickup > from a flywheel or magneto case. Proper design of a tach could also > yield failsafe operation but that's still putting a lot of faith in > something you haven't tested. The "proof by assertion" that I've seen > from a few instrument vendors isn't really confidence-inspiring. > > -- > David Josephson > > ________________________________ Message 8 _____________________________________ Time: 08:04:04 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: DIY CBOVM: variations on a theme At 01:41 PM 3/24/2014, you wrote: I built Bob's circuit. To test it, I wired it in series with an automotive lamp to a DC-DC converter like this one: http://tinyurl.com/kmpqcb8 I slowly turned the pot to increase the voltage. The lamp illuminated at almost 17 volts. Since my Rotax rectifier/regulator puts out about 13.8 volts, I decided to lower the set point of the over-voltage protector by substituting a 5.1K resistor for the 5.6K. Now the test lamp comes on at 16.2 volts. When the voltage increases above 15.8, the circuit becomes sensitive. Just touching the circuit with a digital voltmeter probe is enough to fire the SCR. Using a different voltmeter had the same affect. No doubt that in an electrically noisy environment like an airplane, the circuit will trip at 15.8 volts. That is not a problem though. 15.8 volts is 2 volts above my aircraft system voltage. If spring weather ever comes to Michigan, I will install it in the airplane. That should not be so sensitive to probing. How is this circuit packaged? Can you send me a pucture? Bob . . . ________________________________ Message 9 _____________________________________ Time: 08:10:43 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: New Over-Voltage Protection Architecture At 01:06 PM 3/24/2014, you wrote: > > >I was plagued by overvoltages on my externally regulated alternator, >until I found a permanent, fool-proof solution: Can you post a schematic of your original installation? When you say you were plagued with over-voltages . . . was your ov protection tripping a lot . . . or were there ov events for which there was no installed protection? 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.