---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 12/06/19: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:54 AM - Re: OVM-14 question (racerjerry) 2. 09:04 AM - Re: Re: OVM-14 question (Robert L. Nuckolls, III) 3. 09:12 AM - Re: Re: OVM-14 question (Robert L. Nuckolls, III) 4. 10:40 AM - Re: OVM-14 question (jdpnm) 5. 12:36 PM - Re: OVM-14 question (jonlaury) ________________________________ Message 1 _____________________________________ Time: 06:54:28 AM PST US Subject: AeroElectric-List: Re: OVM-14 question From: "racerjerry" > Reason I have circuit breakers on some items is because with a momentary switch, I can short to ground items to lighten load, which will trip the breakers reducing loads. Then if appropriate I can return function to selected items as the situation permits, By resetting the individual CB. > PURPOSELY shorting out circuit breakers is generally not a good idea and will cause them to degrade. Shorting, for rare over-voltage events is acceptable, but repeated high current events could cause a circuit breaker to malfunction; even possibly welding contacts closed. A shorting switch is even more susceptible to arc damage and welding of contacts. This reminds me of an Underwriter's Laboratory report describing a homeowner that "tested" his circuit breakers yearly using a screwdriver. His house burned down as a direct result. -------- Jerry King Read this topic online here: http://forums.matronics.com/viewtopic.php?p=493726#493726 ________________________________ Message 2 _____________________________________ Time: 09:04:45 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: OVM-14 question > >PURPOSELY shorting out circuit breakers is generally not a good idea >and will cause them to degrade. Shorting, for rare over-voltage >events is acceptable, but repeated high current events could cause a >circuit breaker to malfunction; even possibly welding contacts closed. An urban technomyth completely unsupported by the physics and over a century of practice. A quality circuit breaker will find its way onto Qualified Products Lists (QPL) for government/military purchase by DEMONSTRATING anh ability to OPEN a faulted line supplied by a source current hundreds of times greater than the breaker's trip-rating. An exemplar table of qualifications for the Klixon 7274 series breakers reads as follows: Emacs! A 5A breaker upstream of a crowbar OV protection system is qualified in systems capable of up to 800 Amps of fault current. A typical ov trip current in a GA aircraft with crowbar OV management is on the order of 150 amps. Beech did crowbar OV management in a regulator I proposed for the single-engine, turbine prototype back about 1980. Of ALL the contemporary OV management systems on hand at the time, my prototype was the only one to manage a series of 50 OV events at the rate of one event every two minutes. After the test, the 'abused' breaker still tested to design specs. >A shorting switch is even more susceptible to arc damage and welding >of contacts. Do you mean a switch that closes a fault against a high current source source, or a switch used to open a a high current condition? Contacts used to 'break' a faulted circuit, such as those used in a breaker, may indeed suffer arc damage if used to open a condition beyond the device's ratings (see Endurance and Interrupt ratings above). The crowbar OVM system that flies now in thousands of OBAM and TC aircraft were designed and tested to stay will within those limits. >This reminds me of an Underwriter's Laboratory report describing a >homeowner that "tested" his circuit breakers yearly using a >screwdriver. His house burned down as a direct result. I've heard several such stories over the years . . . all of which argue with contemporary design and qualification practices for modern breakers, switches and relays. I'd need to see the published failure analysis on this . . . sounds like an urban myth to me. Bob . . . ________________________________ Message 3 _____________________________________ Time: 09:12:20 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: OVM-14 question Graybeards here on the List will recall some animated discussions about 14 years ago on the topic of 'abused breakers' in crowbar ov protection systems. Here's a white paper I generated as a contribution to those discussions: http://www.aeroelectric.com/articles/Crowbar_OV_Protection/DC_Power_System_Dynamics_C.pdf Bob . . . ________________________________ Message 4 _____________________________________ Time: 10:40:44 AM PST US Subject: AeroElectric-List: Re: OVM-14 question From: "jdpnm" thanks Bob. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=493730#493730 ________________________________ Message 5 _____________________________________ Time: 12:36:46 PM PST US Subject: AeroElectric-List: Re: OVM-14 question From: "jonlaury" nuckolls.bob(at)aeroelect wrote: > At 10:47 AM 12/4/2019, you wrote: > > ... You need one and only one low volts warning light on the main bus. If you have an LR3 regulator on your main alternator, that light is built in. Bob . . .[/quote] At the time of my installation, I thought that alternator 1 needed LVW through the LR3 reg. Didn't think that the LR3 was monitoring the main bus so installed AEC 9005 LVW for Alt 2/Ford reg. Now I have redundant LVW [Embarassed] Read this topic online here: http://forums.matronics.com/viewtopic.php?p=493732#493732 Attachments: http://forums.matronics.com//files/redundant_lvw_969.jpg ------------------------------------------------------------------------------------- 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.