---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 06/26/18: 8 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:29 AM - Re: AeroElectric-List Digest: 1 Msgs - 06/25/18 (David Josephson) 2. 05:32 AM - Re: Can a low voltage situation cause a fuse to blow? (user9253) 3. 05:52 AM - Re: Radio or Television Tower Buzz (mike>bentley) 4. 06:02 AM - Re: Can a low voltage situation cause a fuse to blow? (Eric M. Jones) 5. 06:13 AM - Re: Re: Can a low voltage situation cause a fuse to blow? (Alec Myers) 6. 06:24 AM - Re: Re: Can a low voltage situation cause a fuse to blow? (Charlie England) 7. 06:47 AM - Re: Re: Can a low voltage situation cause a fuse to blow? (Alec Myers) 8. 10:29 AM - Re: Re: Can a low voltage situation cause a fuse to blow? (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 12:29:15 AM PST US From: David Josephson Subject: AeroElectric-List: Re: AeroElectric-List Digest: 1 Msgs - 06/25/18 > On Jun 25, 2018, at 11:30 PM, AeroElectric-List Digest Server wrote: > > electrical problems with the bigger electrical units (120v - 460v), however > he told me that the reason this machine I was working on blew a fuse because > the battery was low(which it was dead when it came in). I explained to him > that according to my understanding of ohms law, that doesn't make sense. If It doesnt make sense if the load that the fuse was supplying behaves like a simple resistor, as you suggest. But you dont know thats the case. For instance, if the load is a motor and there wasnt enough current to turn it, it could very well try to draw much more than rated current while stuck on one part of the commutator, unable to move to the next. A switching power supply can draw more current as the input voltage drops as it tries to maintain regulation. This happens in aircraft avionics some times, a breaker will pop in low voltage conditions because the load is trying to pull more current. ________________________________ Message 2 _____________________________________ Time: 05:32:11 AM PST US Subject: AeroElectric-List: Re: Can a low voltage situation cause a fuse to blow? From: "user9253" A fuse holder with weak springs can create a bad connection which will make heat. Heat can blow a fuse. Not saying this is the problem in your case, but is something to check in future troubleshooting. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=481211#481211 ________________________________ Message 3 _____________________________________ Time: 05:52:17 AM PST US Subject: AeroElectric-List: Re: Radio or Television Tower Buzz From: "mike>bentley" Just an update. I rechecked all the grounds; antenna, radio, etc., made a larger ground plane (as big as I could fit under the antenna with radius just shy of the length of antenna), and tried a different coax from radio to antenna. My long distance transmission and reception is slightly better but and may have improved the interference some but it is still there. It does seem to be a characteristic of the vertically mounted antenna. I'll keep you posted if I discover anything else. Thanks for the suggestions. -------- Mike Bentley Joplin, MO N5498B Kitfox Model 4-1200 Jabiru 2200 #438 Rotec Aerosport LCH Heads Prince Prop (64 x 34) Ellison EFS-2 Throttle Body Read this topic online here: http://forums.matronics.com/viewtopic.php?p=481212#481212 ________________________________ Message 4 _____________________________________ Time: 06:02:56 AM PST US Subject: AeroElectric-List: Re: Can a low voltage situation cause a fuse to blow? From: "Eric M. Jones" First of all, low voltage IN GENERAL does not cause a fuse to blow. Look at all the cars with dead batteries for an example. Fuses are never even investigated. Two phenomena contribute to the notion: 1) Back EMF, which reduces the running current when the motor comes up to speed, and 2) Starter circuits for motors which draw large currents UNTIL the motor gets up to speed. I won't go into the details, but they are similar, and both have to do with motor starting circuits. I might add a third (rare) one: electronic circuits that try to keep an output constant. Usually these circuits have enough smarts to not blow an input fuse. For circuits that only power resistive loads, fuse-blowing at low voltage is never an issue. -------- 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=481213#481213 ________________________________ Message 5 _____________________________________ Time: 06:13:12 AM PST US From: Alec Myers Subject: Re: AeroElectric-List: Re: Can a low voltage situation cause a fuse to blow? I have a radio that requires 7.5A breakers on a 28v supply, and 10A breakers on a 12V supply. If the voltage drops the supply current requirement rises. On Jun 26, 2018, at 09:02, Eric M. Jones wrote: First of all, low voltage IN GENERAL does not cause a fuse to blow. Look at all the cars with dead batteries for an example. Fuses are never even investigated. Two phenomena contribute to the notion: 1) Back EMF, which reduces the running current when the motor comes up to speed, and 2) Starter circuits for motors which draw large currents UNTIL the motor gets up to speed. I won't go into the details, but they are similar, and both have to do with motor starting circuits. I might add a third (rare) one: electronic circuits that try to keep an output constant. Usually these circuits have enough smarts to not blow an input fuse. For circuits that only power resistive loads, fuse-blowing at low voltage is never an issue. -------- 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=481213#481213 ________________________________ Message 6 _____________________________________ Time: 06:24:28 AM PST US From: Charlie England Subject: Re: AeroElectric-List: Re: Can a low voltage situation cause a fuse to blow? 'Switcher' power supply. On Tue, Jun 26, 2018 at 8:11 AM, Alec Myers wrote: > > I have a radio that requires 7.5A breakers on a 28v supply, and 10A > breakers on a 12V supply. If the voltage drops the supply current > requirement rises. > > On Jun 26, 2018, at 09:02, Eric M. Jones wrote: > > emjones@charter.net> > > First of all, low voltage IN GENERAL does not cause a fuse to blow. Look > at all the cars with dead batteries for an example. Fuses are never even > investigated. > > Two phenomena contribute to the notion: 1) Back EMF, which reduces the > running current when the motor comes up to speed, and 2) Starter circuits > for motors which draw large currents UNTIL the motor gets up to speed. I > won't go into the details, but they are similar, and both have to do with > motor starting circuits. > > I might add a third (rare) one: electronic circuits that try to keep an > output constant. Usually these circuits have enough smarts to not blow an > input fuse. > > For circuits that only power resistive loads, fuse-blowing at low voltage > is never an issue. > > -------- > 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=481213#481213 > > ________________________________ Message 7 _____________________________________ Time: 06:47:54 AM PST US From: Alec Myers Subject: Re: AeroElectric-List: Re: Can a low voltage situation cause a fuse to blow? no doubt. but the results stand. On Jun 26, 2018, at 09:23, Charlie England wrote: 'Switcher' power supply. > On Tue, Jun 26, 2018 at 8:11 AM, Alec Myers wrote: > > I have a radio that requires 7.5A breakers on a 28v supply, and 10A breake rs on a 12V supply. If the voltage drops the supply current requirement rise s. > > On Jun 26, 2018, at 09:02, Eric M. Jones wrote: > net> > > First of all, low voltage IN GENERAL does not cause a fuse to blow. Look a t all the cars with dead batteries for an example. Fuses are never even inve stigated. > > Two phenomena contribute to the notion: 1) Back EMF, which reduces the run ning current when the motor comes up to speed, and 2) Starter circuits for m otors which draw large currents UNTIL the motor gets up to speed. I won't go into the details, but they are similar, and both have to do with motor star ting circuits. > > I might add a third (rare) one: electronic circuits that try to keep an ou tput constant. Usually these circuits have enough smarts to not blow an inpu t fuse. > > For circuits that only power resistive loads, fuse-blowing at low voltage i s never an issue. > > -------- > 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=481213#481213 > > > > > > > > > > > > ========================= > - > Electric-List" rel="noreferrer" target="_blank">http://www.matronics.c om/Navigator?AeroElectric-List > ========================= > FORUMS - > eferrer" target="_blank">http://forums.matronics.com > ========================= > WIKI - > errer" target="_blank">http://wiki.matronics.com > ========================= > b Site - > -Matt Dralle, List Admin. > rel="noreferrer" target="_blank">http://www.matronics.com/contribution > ========================= > > > ________________________________ Message 8 _____________________________________ Time: 10:29:37 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Can a low voltage situation cause a fuse to blow? At 08:23 AM 6/26/2018, you wrote: >'Switcher' power supply.=C2 > >On Tue, Jun 26, 2018 at 8:11 AM, Alec Myers ><alec@alecmyers.com> wrote: >Myers <alec@alecmyers.com> >I have a radio that requires 7.5A breakers on a >28v supply, and 10A breakers on a 12V supply. If >the voltage drops the supply current requirement rises. Breaker size isn't necessarily a 'tell' on an appliance's behaviors during a low voltage event. It has ALWAYS been the case that 28v appliances were feed with smaller wire and breakers than their 14v cousins. If you had a system that needed 100W of input energy to function, then the 14v draw was on the order of 7A, the 28v draw would be about half that. It matters not whether the appliance is a vacuum tube radio in a 1948 Stinson or a Garmin GeeWhiz in a brand new RV7. There have been many a tale citing the tripping of breakers, burning of wires and popping of fuses attributed to a reduction in supply voltage . . . tales that go back a century or more. But the laws of physics are immutable. Any system that needs more current as input voltage is reduced has some UNIQUE characteristic that seeks to maintain a constant POWER in spite of supply voltage variations. This includes many modern electrowhizzies designed to function on a wide range of input voltages. For most avionics in this class, 10-32 volts is a common design goal. To be sure, if you run such a device from a bench power supply, input current times supply voltage is relatively constant meaning that the current demand at 10v exceeds the 32v demand by a factor of about 3.2 But all other devices like incandescent landing lights, fan motors, pump motors vintage electronics, etc will draw less current as supply is reduced. Some motor driven systems MAY demand more current as the voltage drops IF the TORQUE load on the motor goes up as speed and voltage drops. Motor current is proportional to output torque. So as speed drops on things like fans, the torque will go down. A motor driving a pump at some target pressure MIGHT tend to hold a constant current as the speed/ voltage go down . . . but at some point the system can't keep up and pressure/torque/current falls. As Eric pointed out, there must be uncountable instances where some DC vehicular system went to sleep as the battery ran down . . . without blowing fuses. 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.