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OV B-lead Relay
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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Apr 21, 2020 6:02 pm Post subject: OV B-lead Relay

 	  Quote: 	
		    	  Quote: 	
		  My admittedly sometimes faulty memory of the whole 'load dump' situation two decades ago was that guys were flipping their alt switches/breakers (which controlled the B lead contactor) while the alt was under load, and killing the alt. IIRC, after multiple incidents like that, the OV module/contactor circuit became a lot harder to find in the AEC docs. 	
	


    Yeah, your memory is correct. The Z24 pot boiled

    over when I think only one individual experienced

    alternator failure after cycling it. We don't know

    how fast the engine was running or what the alternator

    loads were . . . you never get that quality of data

    from someone pointing a figure at you hollering, "you

    alternator killer!"



    I think Paul M was a well entrenched advisor to

    that faction of RV fans and he was rather antagonistic

    to anything 'crowbar'. 



  	  Quote: 	
		  My solution is the He Haw Solution: 'If it hurts when you do that, DON'T DO THAT!' 	


    Exactly. If the alternator is brought off and

    on line at engine idle (standard ops) then

    there is no risk.



  	  Quote: 	
		  Here's my take: If I operate the IR alternator just like it's operated in the car, I'll never have a load dump event. If I use an OV module that is relatively immune to 'false positives', along with a relatively robust B lead contactor, the only penalty I see is carrying a few ounces of extra weight for the contactor. The contactor will never operate unless the regulator has failed (in an OV mode), in which case the 'load dump' issue is already moot. 	


   That was the spirit and intent of the design

   but I failed to include a note precluding random

   operations at high rpm. In all fairness, any

   alternator should be able to respond safely

   to on/off commands under any speed and load

   conditions.



 

  	  Quote: 	
		  This lets me use an off the shelf, *very inexpensive*, available at any auto supply, alternator. It won't be as reliable as a B&C, but based on anecdotal evidence from RV-x owners, a *lot* more reliable than a Plane Power. And I'll have about $500 left over to buy fuel. (Replacement alts, if ever needed, will be free.) If I do have to replace the alt while away from home, no mod to the alt is needed, and replacement can happen on the ramp with only a couple of wrenches. 	


   Is PlanePower having issues? I think they

   were bought out by a company that shall

   remain nameless. Has their craftsmanship

   suffered?



  	  Quote: 	
		  I have had several different 'lives' as an electronics tech, from home electronics to pro sound, to industrial gear. Even though I'd consider myself to be well above average in qualifications, I trust an 'as-built' alternator to be more reliable than one that I've modded. 	


   YEeaahh . . . with reservations. The recent

   Kitplanes article we've discussed here is

   a rather benign operation . . . with profound

   benefit.



  	  Quote: 	
		  My opinion is that if any update is made, it would be to redesign the OV module to reduce the risk of 'false positive' nuisance trips, and retain the B lead relay. Perhaps do a little testing on whether a single contact automotive cube relay can reliably open the B lead, *once*, as Bob Noffs mentioned, and treat the relay as if it's a fusible link. 	


   If we combined the crowbar feature with

   the 200A 'cube' relay, the ov sense could

   be a microcontroller that waits until the

   relay contacts are sensed to be open before

   triggering the FET. That would reduce abuse

   to the relay to insignificance for both

   an OV shutdown -AND- the normal on/off commands

   at ANY rpm.



   To be sure, MOST modern alternators including

   rebuilds should be able to stand off the load

   dump spike.



  	  Quote: 	
		   Realistically, if the OV module fires at ~16V, how much energy is really there? How much delay will there be from hitting the voltage threshold to the contacts opening? If we used a 100A cube relay (which *should*, by definition, be able to actively control a 100A load), will it really be stressed by 60-70 amps at ~20V? Or will the voltage (and energy) be much higher by the time the contacts actually start to open?  I realize that voltage will spike upward as the contacts separate, but will it be bad enough in a 'one shot' environment to weld the contacts? 	


   Yeah, an ov trip condition is asserted when

   bus voltage rises above 16v for say 500 mS.

   By this time, the energy 'spring' in the

   failed alternator is really wound up pretty

   good.  I've observed field voltages on the

   order of 1 to 2 volts for alternators carrying

   a normal running load at cruise rpm. So

   if you suddenly increase that voltage to 15v,

   the 'spring' starts winding rapidly while held

   at bay by the battery+system loads.



   This is the special condition that might be

   handled nicely with a fat-FET and relay.

   . . . I'd want to do some studies on the

   alternator test stand before running very far down

   that rabbit hole.



   But FOR SURE . . . a fat-FET and diode would 

   be a piece of cake because there's no timing

   to worry about and the b-lead never rises very

   far given that it's loaded down by the ship's

   battery. Best yet, no concerns for keeping your

   contacts out of the fire.



   For an AUX alternator in the 20-30A class,

   the diode/fet crowbar need not be very

   beefy. Maybe not so attractive for MAIN

   alternators in the 60A+ class. Voltage

   drop across the diode becomes an energy

   management issue.



   There was a time that Cessna was using

   some fat diodes in the alternator b-leads

   to orchestrate an alternator failure

   sensor some guy at Cessna dreamed up . . .

   not me!



   Here are some excerpts from a kit I wrote to

   put a 100A alternator on a USAF U17. That

   diode dropped about 0.9V at 100A for a

   dissipation the order of 90W. Needless

   to say, the heatsink was impressive. I

   seem to recall we did a similar thing

   on the C337. Had to dig pretty deep into

   the archives for those images. Wrote that

   kit in 1968!



   A Schottky b-lead diode for a 30A alternator

   would be much more manageable.



   



 

 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Apr 21, 2020 6:16 pm Post subject: OV B-lead Relay

At 02:25 PM 4/21/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Dan Fritz" <Dfritzj(at)yahoo.com>



 One of the things I've always wondered about with Z-24 was the

 impact of the B-lead contactor opening when the field switch

 is opened.  This appears to negate any positive influence of

 having a progressive switch for the master contactor and field power. 	


   Not sure how . . . the progressive transfer is an

   emulation of the 'split rocker' that simply prevents

   alternator operations without a battery on line.



   Adding the relay-crowbar ov control system doesn't

   negate that design goal.



  	  Quote: 	
		  What do you all think of the adjustment propose in the attached to

 Z-24 to re-introduce the goodness of the progressive switch while

 keeping the full protection offered by Z-24. 	


   I'm not seeing the proposed advantage. Remember

   that the "F" terminal on an internally regulated

   alternator is simply a control lead that talks

   to the internal regulator. Once the regulator

   has failed, it matters not what voltage appears

   at the "F" terminal . . . the b-lead is straining

   to take off for the moon.



  	  Quote: 	
		  One could also consider putting a TVS across the B-lead between the B-lead

 contactor and the alternator in an attempt to save the regulator

 if a nuisance trip of the Overvoltage protection were to take place. 	


   Remember that TVS (transient voltage suppressor) is

   designed to take on fairly large currents for a very

   SHORT period of time. In Z24 the alternator cannot

   be shut down hence this is no longer a transient

   event but a uncontrolled runaway that will continue

   until the field windings burn in two.



 

  	  Quote: 	
		  P.S. did this "old school" with whiteout and a pencil, excuse the messiness... 	


   fine pencil work . . .



 

   Bob . . .

Dan Fritz

Joined: 02 Apr 2020
Posts: 16

Posted: Tue Apr 21, 2020 7:45 pm Post subject: Re: OV B-lead Relay

Bob, 

Thanks for the explanation on the B-lead contactor and progressive field switch.



I like the direction you're going with the B-lead crowbar solution.  Seems like it could make the OV event much less spectacular and potentially even save a few alternators from load dumps in nuisance trip situations.  It also saves the effort to modify the alternator to eliminate the internal regulator and keeps the Autozone replacement alternator from taking up too much $time$.



That said, you've piqued my interest, I'll have to dig into my alternator to see what I've got lurking inside and determine if I want to take it on.  Sounds like there was a recent Kitplanes article that outlines a simple mod, can anyone point me to a link?



thanks,

Dan

finn.lassen(at)verizon.ne
Guest

Posted: Wed Apr 22, 2020 6:10 am Post subject: OV B-lead Relay

On 4/21/2020 8:21 PM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   ï¿½ï¿½ But given the ease with which the alternator

 ï¿½ï¿½ can be modified into a real 'aircraft'

 ï¿½ï¿½ part, any notions of a Z24 update are not

 ï¿½ï¿½ so interesting.


	


That's what I was going to do and only have a fuseable link between B+ 

and battery.



But a remark of "other possible alternator failure mode" made me 

consider putting a 80A "cube" relay in that path.



I assumed that that "other failure mode" would be a shorted rectifier 

diode (drawing current from battery). Not sure of the likelihood of such 

a failure. In my experience diodes fail open (and zeners fail shorted).



I really don't like a contactor because of weight and the current it 

draws.ï¿½ The 80A relay has a 85 ohm coil resistance. and the contactor I 

have 15 ohms. 2 W vs 12 W.



I should mention I'm putting a Mazda 13B (Renesis) in an RV-4. So in a 

battery-only (no alternator) situation, it's important to be able to 

shred all loads that are not required to keep the engine running and I'm 

designing to electrical system accordingly. The manufacturer (RWS) of 

the engine controller recommends engine-essential item be powered 

directly from battery (via one switch/breaker). However, having 

dissected a failed (open) W31- breaker/switch, I'll double that with a 

pull-breaker, and have changed from switch/breakers to a fuse block.and 

switches for pumps, injectors, coils, etc.



Finn

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Apr 22, 2020 9:58 am Post subject: OV B-lead Relay

 	  Quote: 	
		  That's what I was going to do and only have a fuseable link between B+ and battery. 	


     That works



  	  Quote: 	
		  But a remark of "other possible alternator failure mode" made 

 me consider putting a 80A "cube" relay in that path. 	


     Waaayyy back in the dark ages, during the adolescent

     years of automotive alternators, the rectifiers were

     no so robust. I first hired into Electro-Mech about

     1975. One of our products was a device you could add

     to your alternator-fitted automobile to convert it

     to a 100V dc power source to run lights and universal

     appliances 'in the field'.



     Worked okay most of the time but two many installations

     on Chrysler products were popping alternator diodes

     as a result of this installation. Had to do a messy

     recall. 30 years later, after inheriting a house from

     my father, I found one of these critters new in the box

     out in his shop. It never got installed.



     I suspect you could make this thing work

     on any modern alternator. The diodes have "come

     along way baby!" 



 

  	  Quote: 	
		  I assumed that that "other failure mode" would be a shorted rectifier diode

 (drawing current from battery). Not sure of the likelihood of such a failure.

 In my experience diodes fail open (and zeners fail shorted). 	


     Actually, both devices are most likely to fail

     shorted due to thermal destruction of the PN

     barrier.



  	  Quote: 	
		  I really don't like a contactor because of weight and the current it draws.

 The 80A relay has a 85 ohm coil resistance. and the contactor I have 15 ohms.

 2 W vs 12 W. 	


     The WR/Stancore contactor warms up pretty

     good and will stabilize at some more

     friendly current.



  http://www.aeroelectric.com/Pictures/Contactors/Battery_Contactor_Temps_1.jpg 



  http://www.aeroelectric.com/Pictures/Contactors/Battery_Contactor_Temps_2.jpg 



     It will stabilize at about 0.6A at 14V or 8.5W

     Does your load analysis show that 'saving' a couple

     of watts is useful? But the greatest savings

     are secured by not having the contactor in the

     first place.



  	  Quote: 	
		  I should mention I'm putting a Mazda 13B (Renesis) in an RV-4. So in a battery-only

 (no alternator) situation, it's important to be able to shed all loads that are not

 required to keep the engine running and I'm designing to electrical system accordingly.

 The manufacturer (RWS) of the engine controller recommends engine-essential item be

 powered directly from battery (via one switch/breaker). However, having dissected a

 failed (open) W31- breaker/switch, I'll double that with a pull-breaker, 	


  Why any breaker at all? Yeah, I worked on the team

  that wrestled with that same failure in nearly

  the entire fleet of Bonanzas and Barons. 



  	  Quote: 	
		  and have changed from switch/breakers to a fuse block.and switches for pumps,

 injectors, coils, etc. 	


   Yup, they ALL want you to tie right to the battery.

   Suggest you consider a dual feed Engine Bus as shown

   in Z101. 



 

   Bob . . .

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finn.lassen(at)verizon.ne
Guest

Posted: Wed Apr 22, 2020 2:23 pm Post subject: OV B-lead Relay

On 4/22/2020 1:54 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		  ï¿½Why any breaker at all? 	
     

Indeed, with just a fusible link between battery and engine fuse       block, why a switch-breaker?     

The only answer I can come up with: convenience.     

Powered by the engine bus are:     

Engine controller A

       Engine Controller B (yes, redundant controllers)

       Primary fuel pump

       Backup fuel pump

       Primary fuel injectors

       Secondary fuel injectors (fuel injection is staged, at certain MAP       the second set of injectors are used too)

       Leading ignition coils

       Trailing ignition coils (13B has two spark plugs per rotor)

       Engine monitor (strictly speaking not needed for engine to keep       running)

       O2 sensor (strictly speaking not needed for engine to keep       running)

       Left to right tank transfer pump (strictly speaking not needed for       engine to keep running)

       Starter relay (strictly speaking not needed for engine to keep       running)     

Put the last four items on the engine bus "because they are       engine related". 

          

After normal flight I will have to shut off 9 to10 switches       rather than just one to ensure that engine bus does not drain       battery.     

Separate switches for A & B controllers are not mentioned by       the manufacturer. He recommends just a switch/breaker directly to       battery feeding controllers and monitor. But for reason mentioned       earlier, I now prefer fuses and like the ability to disconnect a       misbehaving controller. (There is an A/B switch, so really would       be for the rare situation where voltage regulator in one       controller draws high current without blowing its fuse.) Could       have one switch, but then I would want inline fuses after the       switch.

          

Regarding diodes feeding engine bus, from the EC3 manual:

       "Also note that the use of main battery power contactors and power       distribution devices incorporating isolation diodes for backup       battery connections are not recommended for alternative engine       installations."

       I can only guess the reason is that a diode will prevent the       battery to act as a very effective noise filter.     

Thank you Bob for all you do and your advice.

          

Finn

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Apr 22, 2020 4:23 pm Post subject: OV B-lead Relay

At 05:17 PM 4/22/2020, you wrote:

  	  Quote: 	
		  On 4/22/2020 1:54 PM, Robert L. Nuckolls, III wrote:

  	  Quote: 	
		  ï¿½Why any breaker at all? 	


 Indeed, with just a fusible link between battery and engine fuse block, why a switch-breaker?



 The only answer I can come up with: convenience. 	


  The Engine Bus is part of your power distribution

  system. As a member of the FAT-wire family, no

  disconnects for the bus are called for . . . see

  Engine Bus in Z1010 



 

  	  Quote: 	
		  Powered by the engine bus are:



 Engine controller A

 Engine Controller B (yes, redundant controllers)

 Primary fuel pump

 Backup fuel pump

 Primary fuel injectors

 Secondary fuel injectors (fuel injection is staged, at certain MAP the second set of injectors are used too)

 Leading ignition coils

 Trailing ignition coils (13B has two spark plugs per rotor)

 Engine monitor (strictly speaking not needed for engine to keep running)

 O2 sensor (strictly speaking not needed for engine to keep running)

 Left to right tank transfer pump (strictly speaking not needed for engine to keep running)

 Starter relay (strictly speaking not needed for engine to keep running)



 Put the last four items on the engine bus "because they are engine related". 



 After normal flight I will have to shut off 9 to10 switches rather than

 just one to ensure that engine bus does not drain battery. 	


  10 switches? This sounds like a recipe for mis-selection

  in times of stressful ops. How will your check-list read

  for "In case of engine malfunction". If there is no

  check list included in the engine documentation, then

  CREATE ONE. You don't want to succumb to switch-flipitis

  at 8,000 feet.



 

  	  Quote: 	
		  Separate switches for A & B controllers are not mentioned by the manufacturer.

 He recommends just a switch/breaker directly to battery feeding controllers

 and monitor. 	


   but he is not a system integrator



  	  Quote: 	
		  But for reason mentioned earlier, I now prefer fuses and like the

 ability to disconnect a misbehaving controller. (There is an A/B switch,

 so really would be for the rare situation where voltage regulator in one

 controller draws high current without blowing its fuse.) 	


   How about a two pole switch. One pole for each

   controller. Each protected by a fuse AT THE BUS?



  	  Quote: 	
		   Could have one switch, but then I would want inline fuses after the switch.



 Regarding diodes feeding engine bus, from the EC3 manual:

 "Also note that the use of main battery power contactors and

 power distribution devices incorporating isolation diodes for

 backup battery connections are not recommended for alternative

 engine installations."



 I can only guess the reason is that a diode will prevent the battery to act as a very effective noise filter. 	


   Don't GUESS . . . KNOW. Call the dude up and

   get an explanation. BTW, batteries are not

   'noise filters' at any level.



 

  	  Quote: 	
		  Thank you Bob for all you do and your advice. 	


   You're most welcome my friend. That's what

   we do here . . .



   Is there a .pdf installation manual for this system

   that I could see?



 

   Bob . . .

finn.lassen(at)verizon.ne
Guest

Posted: Wed Apr 22, 2020 5:20 pm Post subject: OV B-lead Relay

On 4/22/2020 8:19 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		  ï¿½10 switches? This sounds like a recipe for         mis-selection

         ï¿½in times of stressful ops. How will your check-list read

         ï¿½for "In case of engine malfunction". 	
     

Yes, one definitely needs to be familiar with how the system       functions.     

I've been flying my RV-3B with basically the same system for 100s       of hours.     

I am developing checklists, but will be no substitute for knowing       how the system works when it comes to troubleshooting.     

Example of run-up procedure (to test that backup pump, both       controllers, all ignition coils and injectors work):

       Turn on backup fuel pump, fuel pressure should rise a bit, turn       back off.

       RPM to 3,600, adjust mixture as needed.

       Turn off primary injectors, note RPM drop, turn back on.

       Turn off secondary injectors, note RPM drop, turn back on.

       Select controller B.

       Disable leading coils ( (On)-Off-(On) switch), note RPM drop.

       Disable trailing coils (same (On)-Off-(On) switch), note RPM drop.

       Select controller A.

       RPM to idle.     

(The two switches powering the leading and trailing coil sets are       purely for troubleshooting and to turn off power to the coils. It       could be just one switch, but then would want in-line fuses after       the switch.)     

I can understand how so many switches can appear confusing, but       in practice it becomes second nature.     

"How about a two pole switch. One pole for each

         ï¿½ controller. Each protected by a fuse AT THE BUS?"     

Nope, controllers are designed to normally both be         powered on. For example, there is an option to copy tuning         parameters from A to B (should not be done in the air).     

" Is there a           .pdf installation manual for this system

           ï¿½ that I could see?"     

Emailed you the manual. Doesn't           really belong on this list, even though everything is now open           source after Tracy retired.

              

Finn

ceengland7(at)gmail.com
Guest

Posted: Thu Apr 23, 2020 4:20 pm Post subject: OV B-lead Relay

On 4/21/2020 8:59 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		                 	  Quote: 	
		            	  Quote: 	
		  My             admittedly             sometimes faulty memory of the whole 'load dump' situation             two decades             ago was that guys were flipping their alt switches/breakers             (which             controlled the B lead contactor) while the alt was under             load, and             killing the alt. IIRC, after multiple incidents like that,             the OV             module/contactor circuit became a lot harder to find in the             AEC             docs. 	
       	
       

            Yeah, your memory is correct. The Z24 pot boiled

            over when I think only one individual experienced

            alternator failure after cycling it. We don't know

            how fast the engine was running or what the alternator

            loads were . . . you never get that quality of data

            from someone pointing a figure at you hollering,         "you

            alternator killer!"

         

            I think Paul M was a well entrenched advisor to

            that faction of RV fans and he was rather antagonistic

            to anything 'crowbar'. 

         

          	  Quote: 	
		  My solution is the           He Haw           Solution: 'If it hurts when you do that, DON'T DO           THAT!' 	
         

            Exactly. If the alternator is brought off and

            on line at engine idle (standard ops) then

            there is no risk.

         

          	  Quote: 	
		  Here's my take: If           I operate the           IR alternator just like it's operated in the car, I'll never           have a load           dump event. If I use an OV module that is relatively immune to           'false           positives', along with a relatively robust B lead contactor,           the only           penalty I see is carrying a few ounces of extra weight for the           contactor.           The contactor will never operate unless the regulator has           failed (in an           OV mode), in which case the 'load dump' issue is already           moot. 	
         

           That was the spirit and intent of the design

           but I failed to include a note precluding random

           operations at high rpm. In all fairness, any

           alternator should be able to respond safely

           to on/off commands under any speed and load

           conditions.

         

         

          	  Quote: 	
		  This lets me use an           off the           shelf, *very inexpensive*, available at any auto supply,           alternator. It           won't be as reliable as a B&C, but based on anecdotal           evidence from           RV-x owners, a *lot* more reliable than a Plane Power. And           I'll have           about $500 left over to buy fuel. (Replacement alts, if ever           needed, will           be free.) If I do have to replace the alt while away from           home, no mod to           the alt is needed, and replacement can happen on the ramp with           only a           couple of wrenches. 	
         

           Is PlanePower having issues? I think they

           were bought out by a company that shall

           remain nameless. Has their craftsmanship

           suffered?

         

          	  Quote: 	
		  I have had several           different           'lives' as an electronics tech, from home electronics to pro           sound, to           industrial gear. Even though I'd consider myself to be well           above average           in qualifications, I trust an 'as-built' alternator to be more           reliable           than one that I've modded. 	
         

           YEeaahh . . . with reservations. The recent

           Kitplanes article we've discussed here is

           a rather benign operation . . . with profound

           benefit.

         

          	  Quote: 	
		  My opinion is that           if any update           is made, it would be to redesign the OV module to reduce the           risk of           'false positive' nuisance trips, and retain the B lead relay.           Perhaps do           a little testing on whether a single contact automotive cube           relay can           reliably open the B lead, *once*, as Bob Noffs mentioned, and           treat the           relay as if it's a fusible link. 	
         

           If we combined the crowbar feature with

           the 200A 'cube' relay, the ov sense could

           be a microcontroller that waits until the

           relay contacts are sensed to be open before

           triggering the FET. That would reduce abuse

           to the relay to insignificance for both

           an OV shutdown -AND- the normal on/off commands

           at ANY rpm.

         

           To be sure, MOST modern alternators including

           rebuilds should be able to stand off the load

           dump spike.

         

          	  Quote: 	
		   Realistically, if           the OV           module fires at ~16V, how much energy is really there? How           much delay           will there be from hitting the voltage threshold to the           contacts opening?           If we used a 100A cube relay (which *should*, by definition,           be able to           actively control a 100A load), will it really be stressed by           60-70 amps           at ~20V? Or will the voltage (and energy) be much higher by           the time the           contacts actually start to open?  I realize that voltage will           spike           upward as the contacts separate, but will it be bad enough in           a 'one           shot' environment to weld the contacts? 	
         

           Yeah, an ov trip condition is asserted when

           bus voltage rises above 16v for say 500 mS.

           By this time, the energy 'spring' in the

           failed alternator is really wound up pretty

           good.  I've observed field voltages on the

           order of 1 to 2 volts for alternators carrying

           a normal running load at cruise rpm. So

           if you suddenly increase that voltage to 15v,

           the 'spring' starts winding rapidly while held

           at bay by the battery+system loads.

         

           This is the special condition that might be

           handled nicely with a fat-FET and relay.

           . . . I'd want to do some studies on the

           alternator test stand before running very far down

           that rabbit hole.

         

           But FOR SURE . . . a fat-FET and diode would 

           be a piece of cake because there's no timing

           to worry about and the b-lead never rises very

           far given that it's loaded down by the ship's

           battery. Best yet, no concerns for keeping your

           contacts out of the fire.

         

           For an AUX alternator in the 20-30A class,

           the diode/fet crowbar need not be very

           beefy. Maybe not so attractive for MAIN

           alternators in the 60A+ class. Voltage

           drop across the diode becomes an energy

           management issue.

         

           There was a time that Cessna was using

           some fat diodes in the alternator b-leads

           to orchestrate an alternator failure

           sensor some guy at Cessna dreamed up . . .

           not me!

         

           Here are some excerpts from a kit I wrote to

           put a 100A alternator on a USAF U17. That

           diode dropped about 0.9V at 100A for a

           dissipation the order of 90W. Needless

           to say, the heatsink was impressive. I

           seem to recall we did a similar thing

           on the C337. Had to dig pretty deep into

           the archives for those images. Wrote that

           kit in 1968!

         

           A Schottky b-lead diode for a 30A alternator

           would be much more manageable.

         

           

         

         

                

             Bob . . .            	
     Sorry for the tardy reply; been a bit 'distracted'.

     

     RE: Plane Power alts. No personal experience, but the RV guys are a     fairly large sample (in a/c terms). If you go to the VAF forum and     search 'plane power', you'll find dozens of instances where the     brand has failed at low to very low hours. I think I've only seen     one or two B&C failures mentioned. Now this could be because it     is the one Van's offers when you buy an alt from them, so the     population is higher. But the guys who buy again seem to often     report additional failures, while those who convert to B&C     don't.  The guys who've done autopsies aren't just reporting     electronic failures; there are connector issues, failed internal     stator and/or field leads, etc etc.

     

     RE: crowbar redesign for IR alts. You wrote:

     "If we combined the crowbar feature with

         the 200A 'cube' relay, the ov sense could

         be a microcontroller that waits until the

         relay contacts are sensed to be open before

         triggering the FET. That would reduce abuse

         to the relay to insignificance for both

         an OV shutdown -AND- the normal on/off commands

         at ANY rpm."

       

       Is this the correct order for protecting the relay contacts? I       would have thought that the FET should sit between the B terminal       and relay, and fire *1st*, so that there isn't a high energy arc       at the relay contacts. I'd expect the FET to be much faster than       the relay, if the protection circuit could fire the LED at the       same instant that it crowbars the CB feeding the relay (even       without a microcontroller to do the timing).  Did I misunderstand       the goal, or circuit arrangement?

       

       Charlie

          	          		Virus-free. www.avast.com 		 	 [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Apr 23, 2020 5:00 pm Post subject: OV B-lead Relay

 	  Quote: 	
		  RE: Plane Power alts. No personal experience, but the RV guys are a fairly large sample (in a/c terms). If you go to the VAF forum and search 'plane power', you'll find dozens of instances where the brand has failed at low to very low hours. I think I've only seen one or two B&C failures mentioned. Now this could be because it is the one Van's offers when you buy an alt from them, so the population is higher. But the guys who buy again seem to often report additional failures, while those who convert to B&C don't.  The guys who've done autopsies aren't just reporting electronic failures; there are connector issues, failed internal stator and/or field leads, etc etc. 	


    Hmmmm . . . interesting. I had occasion to

    do failure analysis on another Hartzell

    alternator supplied to a UAV project.

    Again, no 'electronic' failure but a

    failure in craftsmanship.



 

  	  Quote: 	
		   RE: crowbar redesign for IR alts. You wrote:

  "If we combined the crowbar feature with

   the 200A 'cube' relay, the ov sense could

   be a microcontroller that waits until the

   relay contacts are sensed to be open before

   triggering the FET. That would reduce abuse

   to the relay to insignificance for both

   an OV shutdown -AND- the normal on/off commands

   at ANY rpm."



 Is this the correct order for protecting the relay contacts? I would have thought that the FET should sit between the B terminal and relay, and fire *1st*, so that there isn't a high energy arc at the relay contacts. I'd expect the FET to be much faster than the relay, if the protection circuit could fire the LED at the same instant that it crowbars the CB feeding the relay (even without a microcontroller to do the timing).  Did I misunderstand the goal, or circuit arrangement? 	


   You need to wait until the contacts

   were first break so that the FET wasn't trying

   to crowbar BOTH the alternator and battery. This

   is what makes the FAT diode isolator electrically

   more attractive. OV sense and reaction becomes

   a lot easier.



 

   Bob . . .

ceengland7(at)gmail.com
Guest

Posted: Thu Apr 23, 2020 5:41 pm Post subject: OV B-lead Relay

On 4/23/2020 7:55 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		                 	  Quote: 	
		  RE:           Plane Power           alts. No personal experience, but the RV guys are a fairly           large sample           (in a/c terms). If you go to the VAF forum and search 'plane           power',           you'll find dozens of instances where the brand has failed at           low to very           low hours. I think I've only seen one or two B&C failures           mentioned.           Now this could be because it is the one Van's offers when you           buy an alt           from them, so the population is higher. But the guys who buy           again seem           to often report additional failures, while those who convert           to B&C           don't.  The guys who've done autopsies aren't just reporting           electronic failures; there are connector issues, failed           internal stator           and/or field leads, etc etc. 	
       

            Hmmmm . . . interesting. I had occasion to

            do failure analysis on another Hartzell

            alternator supplied to a UAV project.

            Again, no 'electronic' failure but a

            failure in craftsmanship.

         

         

          	  Quote: 	
		   RE: crowbar           redesign for           IR alts. You wrote:

            "If we combined the crowbar feature with

             the 200A 'cube' relay, the ov sense could

             be a microcontroller that waits until the

             relay contacts are sensed to be open before

             triggering the FET. That would reduce abuse

             to the relay to insignificance for both

             an OV shutdown -AND- the normal on/off commands

             at ANY rpm."

           

           Is this the correct order for protecting the relay contacts? I           would have           thought that the FET should sit between the B terminal and           relay, and           fire *1st*, so that there isn't a high energy arc at the relay           contacts.           I'd expect the FET to be much faster than the relay, if the           protection           circuit could fire the LED at the same instant that it           crowbars the CB           feeding the relay (even without a microcontroller to do the           timing).  Did I misunderstand the goal, or circuit           arrangement? 	
         

           You need to wait until the contacts

           were first break so that the FET wasn't trying

           to crowbar BOTH the alternator and battery. This

           is what makes the FAT diode isolator electrically

           more attractive. OV sense and reaction becomes

           a lot         easier.

           

                

             Bob . . .            	
     Ah...yes. Forgot that the battery would try to drive the short.

     

     Thanks for clearing my head.

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