---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 12/07/16: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:00 AM - Re: Alternator Field Circuit Fuse Blow (user9253) 2. 09:46 AM - Re: Alternator Field Circuit Fuse Blow (Robert L. Nuckolls, III) 3. 03:44 PM - Re: Alternator Field Circuit Fuse Blow (Valin Thorn) 4. 06:46 PM - Re: Alternator Field Circuit Fuse Blow (Robert L. Nuckolls, III) 5. 08:40 PM - Re: Alternator Field Circuit Fuse Blow (Valin Thorn) ________________________________ Message 1 _____________________________________ Time: 08:00:40 AM PST US Subject: AeroElectric-List: Re: Alternator Field Circuit Fuse Blow From: "user9253" A circuit breaker is best for this application because breakers take longer to trip than fuses. A breaker will tolerate short spikes of motor starting current that might blow a fuse. But since the plane already has a fuse installed, I would increase the size to 7.5 amps instead of replacing the fuse with a circuit breaker, provided that the crowbar module can handle the extra current in the event of over-voltage. If the 7.5 amp fuse does not blow, then you will know that over-voltage is not the problem, and that the alternator field draws more than 5 amps when the alternator is heavily loaded. Check the fuse holder to make sure that it tightly grips the fuse. A loose connection will make heat that will eventually blow a fuse. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=463767#463767 ________________________________ Message 2 _____________________________________ Time: 09:46:30 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Alternator Field Circuit Fuse Blow > >On both occasions the fuse blew on landing gear >extension which seems to be the least loaded >gear operation since the weight of the gear and >their gas spring struts want to deploy the gear >anyway ' the pump can barely keep up. But, we >do have a modification to our landing gear >system where the inboard gear doors close after >gear go down and the pump typically cycles very >quickly several time while it=92s closing the >inboard doors. For more background, we splurged >on expensive hermetically sealed contactors >rated for 100 A continuous for switching the >hydraulic pump motor -- Tyco Kilovac EV100 >relays with built in voltage suppression diodes. Building a 'fits all' version of a linear regulator is a real challenge. The regulator is but one component in a negative feedback control loop wherein EVERY part of the system has some effect on loop stability. The major influence on the control equation is the alternator followed by the battery and then the architecture. The symptoms you're experiencing are MOST likely a result of an overshoot transient caused by what amounts to a 'load dump' under some combination of system loads, engine rpm, alternator transfer function and battery. >I know you=92re the architect of the amazing crow >bar over voltage protection featured in our >L3RC-28 linear alternator regulator from B & C >Specialties. In talking with TJ at B&C today, >he said if the regulator sees over 32 VDC for >more than 5 milliseconds that the crow bar over >voltage will short the field circuit to trip the >CB or fuse. We=92re both wondering if using a 5A >fuse vs. a 5A CB could make a difference=85? Actually, the ov trip response is more like 50 milliseconds but it's not a strictly 'timed' function. I suspect that everything is operating as-designed but your particular combination of components and operations is giving you nuisance trips. > >Anyway, what do you think about this? It has >only happened twice. Could the field current to >drive a 100A alternator under a high load exceed >the 5A fuse limit? Should we try a 7A fuse? Is >this likely from an over-voltage condition and >if so what=92s causing it? Could it be that the >regulator isn=92t dropping the field strength fast >enough after the landing gear/hydraulic motor >stops running and causing an over voltage spike >that=92s tripping the crow bar over voltage circuit? This is not related to field current variations but simply the regulation characteristics under a load-dump situation. The 'easy' fix is to modify your regulator to extend the trip time . . . back when that product was developed, the sort of 'legacy philosophy' was to err on the short-side of trip response timing. These days, my ov protection products are configured a bit closer to Mil-Std-704 deign goals. In your 28v system, the voltage would have to remain above 32 volts for 500 milliseconds. That time interval is accurately measured in software. If the voltage drops below 32 volts any time during that 500 mS, the time resets and anohter 500 mS trip window is opened. This is well inside the 32v-for-one-second design rules for DO-160 compliance. If you would send me your regulator, I could do the mod for you. On another matter, using fuses upstream of the crowbar OVM system is not recommended. This excerpt from Z-12 Emacs! . . . shows a circuit breaker feeding the LR regulator's BUS terminal. The reason for this is based on the precise difficult you're wrestling with now . . . it's difficult (some cases impossible) to replace a nuisance tripped fuse on the OV protection system. Emacs! For other architectures where crowbar ov protection is installed in conjunction with fuse blocks, we show a FUSIBLE LINK upstream of the alternator field breaker. Modifying your regulator is probably the solution for nuisance trips . . . eliminating the ATC fuse in favor of a 5A breaker is the solution for graceful mitigation of nuisance trips. If you choose to go for the modification, coordinate it with B&C. I'll make sure they know which component needs to be swapped out for a new value. I could do the mod but they need to be on board with the process in case this situation repeat in the future. Bob . . . ________________________________ Message 3 _____________________________________ Time: 03:44:49 PM PST US From: "Valin Thorn" Subject: RE: AeroElectric-List: Alternator Field Circuit Fuse Blow Thank you Bob and Joe! For some additional diagnostic data, I've looked at my Garmin G3X Touch avionics systems flight data log for the two instances where the primary alternator fuse blew. The data is at one second intervals a there's some filtering of the data going on so I can't be sure I'm seeing true one second snap shots of the voltage and current. Here's an excerpt of the data from yesterday morning's fuse blow. Note that we have a standby alternator that kicks in when the bus voltage drops below 26 VDC. I labeled where I think the fuse blows based on seeing the voltage start to drop. I know when the gear shows down and hence when the inboard doors start closing, from a discrete in the flight data not shown in this excerpt. Here's the flight data excerpt: The first fuse blow occurrence looks similar to this one except the engine rpm was around 2100 rpm and I'd also started deploying flaps (electrical) around when the doors closed. The landing gear are down just before the inboard gear doors start closing. The inboard gear door closure takes about 5 seconds as the motor cycles on and off quickly as the hydraulic system's pressure oscillates around the pressure setting of the pressure switch. Yes, I need a higher pressure setting for the switch but the one installed now is at the limit of its range and I can't find a hydraulic pressure switch that has the needed 750 psi in the middle of its range. Anyway, it seems that it's this cycling for inboard gear door closure, when it finally closes the doors, that the fuse is blowing. Bob, I expect this probably doesn't change your conclusion that we either need to change to a CB or have the crow bar over voltage circuit adjusted to not trip so quickly with high voltage transients. Thank you so much, by the way, for offering to make that adjustment! A question before deciding our path forward, since a 5A fuse is more sensitive than a 5A circuit breaker, is Joe's suggestion to go to a 7.5A fuse in this application an option that might work? Or is that only the thing to do if the problem is that our field circuit current rides close to or higher than 5A under high loads? Thanks! Valin From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: Wednesday, December 7, 2016 10:45 AM Subject: Re: AeroElectric-List: Alternator Field Circuit Fuse Blow On both occasions the fuse blew on landing gear extension which seems to be the least loaded gear operation since the weight of the gear and their gas spring struts want to deploy the gear anyway - the pump can barely keep up. But, we do have a modification to our landing gear system where the inboard gear doors close after gear go down and the pump typically cycles very quickly several time while it's closing the inboard doors. For more background, we splurged on expensive hermetically sealed contactors rated for 100 A continuous for switching the hydraulic pump motor -- Tyco Kilovac EV100 relays with built in voltage suppression diodes. Building a 'fits all' version of a linear regulator is a real challenge. The regulator is but one component in a negative feedback control loop wherein EVERY part of the system has some effect on loop stability. The major influence on the control equation is the alternator followed by the battery and then the architecture. The symptoms you're experiencing are MOST likely a result of an overshoot transient caused by what amounts to a 'load dump' under some combination of system loads, engine rpm, alternator transfer function and battery. I know you're the architect of the amazing crow bar over voltage protection featured in our L3RC-28 linear alternator regulator from B & C Specialties. In talking with TJ at B&C today, he said if the regulator sees over 32 VDC for more than 5 milliseconds that the crow bar over voltage will short the field circuit to trip the CB or fuse. We're both wondering if using a 5A fuse vs. a 5A CB could make a difference.? Actually, the ov trip response is more like 50 milliseconds but it's not a strictly 'timed' function. I suspect that everything is operating as-designed but your particular combination of components and operations is giving you nuisance trips. Anyway, what do you think about this? It has only happened twice. Could the field current to drive a 100A alternator under a high load exceed the 5A fuse limit? Should we try a 7A fuse? Is this likely from an over-voltage condition and if so what's causing it? Could it be that the regulator isn't dropping the field strength fast enough after the landing gear/hydraulic motor stops running and causing an over voltage spike that's tripping the crow bar over voltage circuit? This is not related to field current variations but simply the regulation characteristics under a load-dump situation. The 'easy' fix is to modify your regulator to extend the trip time . . . back when that product was developed, the sort of 'legacy philosophy' was to err on the short-side of trip response timing. These days, my ov protection products are configured a bit closer to Mil-Std-704 deign goals. In your 28v system, the voltage would have to remain above 32 volts for 500 milliseconds. That time interval is accurately measured in software. If the voltage drops below 32 volts any time during that 500 mS, the time resets and anohter 500 mS trip window is opened. This is well inside the 32v-for-one-second design rules for DO-160 compliance. If you would send me your regulator, I could do the mod for you. On another matter, using fuses upstream of the crowbar OVM system is not recommended. This excerpt from Z-12 . . . shows a circuit breaker feeding the LR regulator's BUS terminal. The reason for this is based on the precise difficult you're wrestling with now . . . it's difficult (some cases impossible) to replace a nuisance tripped fuse on the OV protection system. For other architectures where crowbar ov protection is installed in conjunction with fuse blocks, we show a FUSIBLE LINK upstream of the alternator field breaker. Modifying your regulator is probably the solution for nuisance trips . . . eliminating the ATC fuse in favor of a 5A breaker is the solution for graceful mitigation of nuisance trips. If you choose to go for the modification, coordinate it with B&C. I'll make sure they know which component needs to be swapped out for a new value. I could do the mod but they need to be on board with the process in case this situation repeat in the future. Bob . . . ________________________________ Message 4 _____________________________________ Time: 06:46:31 PM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: Alternator Field Circuit Fuse Blow Anyway, it seems that it's this cycling for inboard gear door closure, when it finally closes the doors, that the fuse is blowing. Yes, when the pump motor shuts off and the bus voltage overshoots for a few tens of milliseconds. Bob, I expect this probably doesn't change your conclusion that we either need to change to a CB or have the crow bar over voltage circuit adjusted to not trip so quickly with high voltage transients. Thank you so much, by the way, for offering to make that adjustment! This is not an either/or . . . it's BOTH. (1) The fuse is an inconvenient source for crowbar ov protection that is INTENDED to open the source protection . . . better that it's a crew accessible breaker than a hard or impossible to get at fuse. (2) Adjusting the r/c time constant of the ov sense circuit will make the system less sensitive to the suspected transients. This is a good thing to do whether or not you change the bus-feeder protection. A question before deciding our path forward, since a 5A fuse is more sensitive than a 5A circuit breaker, is Joe's suggestion to go to a 7.5A fuse in this application an option that might work? Or is that only the thing to do if the problem is that our field circuit current rides close to or higher than 5A under high loads? Alternator field current is not what's opening the fuse. When the crowbar ov protection system operates, it throws a dead short on the bus feed line deliberately opening the breaker or fuse. If you made it a 15A fuse it would still pop when the ov protection system gets over=excited. See http://tinyurl.com/gs6csev for background . . . Bob . . . ________________________________ Message 5 _____________________________________ Time: 08:40:54 PM PST US From: "Valin Thorn" Subject: RE: AeroElectric-List: Alternator Field Circuit Fuse Blow Thanks Bob! I'll coordinate with B & C. We have two L3RC-28 Linear Regulators (flight and spare on shelf) -- so we'll send them both in for adjustment, one at a time so the airplane stays in service. Our fuses are crew accessible in flight. The tray pulls out from the right side of the panel with all the fuse blocks facing the pilot. The Primary Alternator Field fuse is the first one. So, we'll go ahead and stay with the fuse unless there's another reason to go CB. I can't find a good photo to show how it is set up. These two photos should provide an idea. See the face plate with a little pull ring on the right side? That's the fuse tray face plate, a two foot long fuse tray slides out from there. The second photo shows the fuse tray. Thanks again, Valin From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: Wednesday, December 7, 2016 7:45 PM Subject: RE: AeroElectric-List: Alternator Field Circuit Fuse Blow Anyway, it seems that it's this cycling for inboard gear door closure, when it finally closes the doors, that the fuse is blowing. Yes, when the pump motor shuts off and the bus voltage overshoots for a few tens of milliseconds. Bob, I expect this probably doesn't change your conclusion that we either need to change to a CB or have the crow bar over voltage circuit adjusted to not trip so quickly with high voltage transients. Thank you so much, by the way, for offering to make that adjustment! This is not an either/or . . . it's BOTH. (1) The fuse is an inconvenient source for crowbar ov protection that is INTENDED to open the source protection . . . better that it's a crew accessible breaker than a hard or impossible to get at fuse. (2) Adjusting the r/c time constant of the ov sense circuit will make the system less sensitive to the suspected transients. This is a good thing to do whether or not you change the bus-feeder protection. A question before deciding our path forward, since a 5A fuse is more sensitive than a 5A circuit breaker, is Joe's suggestion to go to a 7.5A fuse in this application an option that might work? Or is that only the thing to do if the problem is that our field circuit current rides close to or higher than 5A under high loads? Alternator field current is not what's opening the fuse. When the crowbar ov protection system operates, it throws a dead short on the bus feed line deliberately opening the breaker or fuse. If you made it a 15A fuse it would still pop when the ov protection system gets over=excited. See http://tinyurl.com/gs6csev for background . . . 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.