---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 07/22/26: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:31 AM - Galloping alternator - Piper Warrior (Alec Myers) 2. 11:03 AM - Re: Galloping alternator - Piper Warrior (Alec Myers) ________________________________ Message 1 _____________________________________ Time: 06:31:48 AM PST US From: Alec Myers Subject: AeroElectric-List: Galloping alternator - Piper Warrior Hi Bob et al I have been reading Aeroelectric resources on the cause of the galloping alternator issue, and how to fix. I just want to verify that the circuit where a too-high resistance will cause an oscialltion is this one (yellow): And that a differential diagnosis is that the problem goes away on temporary connection of the red wire - have I understood that correctly? ________________________________ Message 2 _____________________________________ Time: 11:03:36 AM PST US From: Alec Myers Subject: Re: AeroElectric-List: Galloping alternator - Piper Warrior Another question for Bob, about the galloping alternator issue. The aircraft alternator field coils have (typically) resistance of 4 ohms and inductance 0.25 henrys. That gives a time constant of 62 milliseconds, or equivalently a 90 degree phase shift at 2.55Hz. Values are of course approximate but order-of magnitude is useful. If the oscillation is about 3 Hz (from memory) theres a second parasitic pole at about 3.5Hz. This means the phase shift at 3Hz has hit 180 below the frequency at which the magnitude of the loop gain is below 1. Hence the oscillation. I understand that a field circuit resistance of 200 milliohms is likely to be troublesome. An RC circuit with a R value of 200 milliohms needs a C value of 0.225 Farads. Which is enormous. So - the question - is it the chemistry in the aircraft battery thats acting as a capacitor with that sort of value? On Jul 22, 2026, at 09:30, Alec Myers wrote: Hi Bob et al I have been reading Aeroelectric resources on the cause of the galloping alternator issue, and how to fix. I just want to verify that the circuit where a too-high resistance will cause an oscialltion is this one (yellow): And that a differential diagnosis is that the problem goes away on temporary connection of the red wire - have I understood that correctly? ------------------------------------------------------------------------------------- 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.