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flyback diode across fuel pump

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johnbright

Joined: 14 Dec 2011
Posts: 165
Location: Newport News, VA

Posted: Thu Aug 25, 2022 6:57 pm Post subject: flyback diode across fuel pump

Someone on VAF suggested putting a flyback suppression diode across fuel pump leads like we do with contactor and relay solenoid coils. This was re an automotive fuel pump like SDS/EFII/Airflow Performance/Walbro gerotor GSL series.



What say Bob et Al?

_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

Last edited by johnbright on Wed Aug 31, 2022 5:19 pm; edited 1 time in total

user9253

Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan

Posted: Fri Aug 26, 2022 7:17 am Post subject: Re: flyback diode across fuel pump

A diode won't hurt anything as long as the banded end is connected to positive.

  Van's RV-12 schematic shows an optional 22,000 microfarad capacitor across the fuel pump.

_________________
Joe Gores

bob.verwey(at)gmail.com
Guest

Posted: Sat Aug 27, 2022 12:43 am Post subject: flyback diode across fuel pump

Why the cap Joe and not just a diode?



On 26 Aug 2022 17:20, "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)> wrote: 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 A diode won't hurt anything as long as the banded end is connected to positive.

   Van's RV-12 schematic shows an optional 22,000 microfarad capacitor across the fuel pump.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=507781#507781

 

 

 

 

 

 

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user9253

Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan

Posted: Sat Aug 27, 2022 5:03 am Post subject: Re: flyback diode across fuel pump

 	  Quote: 	
		  Why the cap Joe and not just a diode? 	


I don't know.  Perhaps a capacitor helps to reduces interference to the aircraft electrical system.  Maybe Bob N will reply.

_________________
Joe Gores

yellowduckduo(at)gmail.co
Guest

Posted: Sat Aug 27, 2022 5:18 am Post subject: flyback diode across fuel pump

My thoughts are that a diode with a finite voltage drop does nothing for 

quieting noise from the pump that is less than that finite voltage drop 

(usually 0.6 volt for silicon diode).  Comutated motors put some hash on 

the supply line.  I'm not aware of it typically causing problems but a 

capacitor should help quiet such noise somewhat.

Ken



On 27-Aug.-22 9:03 a.m., user9253 wrote:

 	  Quote: 	
		   

> Why the cap Joe and not just a diode?

 I don't know.  Perhaps a capacitor helps to reduces interference to the aircraft electrical system.  Maybe Bob N will reply.



 --------

 Joe Gores





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=507793#507793

alec(at)alecmyers.com
Guest

Posted: Sat Aug 27, 2022 5:19 am Post subject: flyback diode across fuel pump

Used to be capacitors were cheaper than diodes, I think.

Sent from my iPhone



 	  Quote: 	
		   On Aug 27, 2022, at 09:04, user9253 <fransew(at)gmail.com> wrote:

 

 

 

 

> Why the cap Joe and not just a diode?

 

 I don't know.  Perhaps a capacitor helps to reduces interference to the aircraft electrical system.  Maybe Bob N will reply.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=507793#507793

Ceengland

Joined: 11 Oct 2020
Posts: 391
Location: MS

Posted: Sat Aug 27, 2022 5:39 am Post subject: flyback diode across fuel pump

Diodes used as arc suppressors are pennies each. They 'bleed off' the large voltage spikes that happen when contacts open and load is suddenly removed from a circuit.

Capacitors wired as power supply 'filters' typically exist to smooth variations in DC levels. They store energy during low demand, and give it up when demand causes voltage to sag below their charge state. Those variations can come from the 'ripple' in rectified AC supply voltage, or from variations in DC loads. The obvious example of (huge) variation in load would be the starter, causing 'brownouts' of electronic devices, other examples are inrush current to incandescent lamps, DC motors, or for a more repetitive example, a Facet pulse pump (though I wouldn't have expected the draw of a Facet pump to have a significant effect on DC bus stability).

Charlie

On Sat, Aug 27, 2022 at 8:22 AM Alec <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: Alec <alec(at)alecmyers.com (alec(at)alecmyers.com)>

 Used to be capacitors were cheaper than diodes, I think.

 Sent from my iPhone

 > On Aug 27, 2022, at 09:04, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

 > 

 > --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 > 

 > 

 >> Why the cap Joe and not just a diode?

 > 

 > I don't know.  Perhaps a capacitor helps to reduces interference to the aircraft electrical system.  Maybe Bob N will reply.

 > 

 > --------

 > Joe Gores

 > 

 > 

 > 

 > 

 > Read this topic online here:

 > 

 > http://forums.matronics.com/viewtopic.php?p=507793#507793

 > 

 > 

 > 

 > 

 > 

 > 

 > 

 > 

 > 

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Charlie

alec(at)alecmyers.com
Guest

Posted: Sat Aug 27, 2022 6:23 am Post subject: flyback diode across fuel pump

On Aug 27, 2022, at 9:38 AM, Charlie England <ceengland7(at)gmail.com> wrote:



 	  Quote: 	
		  Diodes used as arc suppressors are pennies each. 


	


They are, now.

Ceengland

Joined: 11 Oct 2020
Posts: 391
Location: MS

Posted: Sat Aug 27, 2022 7:23 am Post subject: flyback diode across fuel pump

On 8/27/2022 9:23 AM, Alec Myers wrote:

 	  Quote: 	
		   



 On Aug 27, 2022, at 9:38 AM, Charlie England <ceengland7(at)gmail.com> wrote:



> Diodes used as arc suppressors are pennies each.

 They are, now.

How far back do you want to go? I ran a computer repair business in the 
	


1970s/80s/90s, and they were pennies each back then. Electrolytic caps 

big enough to work as legit power supply filters were a lot more 

expensive back then, too.



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_________________
Charlie

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Aug 27, 2022 10:40 am Post subject: flyback diode across fuel pump

At 09:57 PM 8/25/2022, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "johnbright" <john_s_bright(at)yahoo.com>



 Someone on VAF suggested putting a flyback suppression diode across fuel pump leads like we do with contactor and relay solenoid coils. This was re an automotive fuel pump like SDS/EFII/Airflow Performance/Walbro.



 What say Bob et Al? 	


   Did the author cite a noise problem which was

   mitigated by adding this component?



   I'm mystified by any assertion of added value.

   Rotary pumps powered by pm motors have no

   'flyback' event.  PutPut pumps like the

   Facet devices have electronically driven

   solenoids that 'cock' a compression spring.

   A cruise through the genealogy of exemplar

   patents for such pumps . . .



  https://tinyurl.com/2e6mmzyr



   . . . illustrates commonly applied 

   technology for mitigating flyback 

   energies in these devices that include

   resistors, diodes and capacitors as

   part of the designs dating back over

   30 years.



   I'm curious as to the history of

   the thread.  



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

johnbright

Joined: 14 Dec 2011
Posts: 165
Location: Newport News, VA

Posted: Sun Aug 28, 2022 5:32 pm Post subject: Re: flyback diode across fuel pump

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 09:57 PM 8/25/2022, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "johnbright" <john_s_bright>



 Someone on VAF suggested putting a flyback suppression diode across fuel pump leads like we do with contactor and relay solenoid coils. This was re an automotive fuel pump like SDS/EFII/Airflow Performance/Walbro.



 What say Bob et Al? 	


   Did the author cite a noise problem which was

   mitigated by adding this component?



   I'm mystified by any assertion of added value.

   Rotary pumps powered by pm motors have no

   'flyback' event.  PutPut pumps like the

   Facet devices have electronically driven

   solenoids that 'cock' a compression spring.

   A cruise through the genealogy of exemplar

   patents for such pumps . . .



  https://tinyurl.com/2e6mmzyr



   . . . illustrates commonly applied 

   technology for mitigating flyback 

   energies in these devices that include

   resistors, diodes and capacitors as

   part of the designs dating back over

   30 years.



   I'm curious as to the history of

   the thread.  



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?" 	




Hi Bob,



The VAF thread started as “local ground or forest of tabs for fuel pump ground?”, EFI fuel pump, and drifted at post 9 to someone recommending a diode across the pump motor to protect the pump switch. I had never heard of this so I asked here on AEL.



https://vansairforce.net/community/showpost.php?p=1629894&postcount=9

_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Aug 29, 2022 11:46 am Post subject: flyback diode across fuel pump

 	  Quote: 	
		  Hi Bob,



 The VAF thread started as “local ground or forest of tabs for fuel pump ground?”, EFI fuel pump, and drifted at post 9 to someone recommending a diode across the pump motor to protect the pump switch. I had never heard of this so I asked here on AEL.



  https://vansairforce.net/community/showpost.php?p=1629894&postcount=9 



 --------

 John Bright, RV-6A, at FWF, O-360 	


   Good show



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

Ceengland

Joined: 11 Oct 2020
Posts: 391
Location: MS

Posted: Fri Sep 02, 2022 12:19 pm Post subject: flyback diode across fuel pump

It *could* short, and if it does, it has at least some chance of opening 

the circuit protection for the fuel pump wire, before it burns itself open.



Depending on installation techniques, it could conceivably add failure 

points to the supply path to the pump.



It'll be very confusing to the guy who has to work on it at some point 

(that confused guy could even be you).



If it has no valid upside, it violates the aviation principle that if 

you throw it up and it comes down, don't install it.



On 9/2/2022 2:44 PM, Jeffrey Cohen wrote:

 	  Quote: 	
		   



 is there any downside to installing this diode across the fuel pumps? for example, can a diode short closed and prevent the pumps from operating? Is this a possible failure mode of diodes?

 Jeff





> Sent: Sunday, August 28, 2022 at 9:32 PM

> From: "johnbright" <john_s_bright(at)yahoo.com>

> To: aeroelectric-list(at)matronics.com

> Subject: Re: flyback diode across fuel pump

>

> 

> nuckolls.bob(at)aeroelect wrote:

>> At 09:57 PM 8/25/2022, you wrote:

>>   

>>> 

>>>

>>>   Someone on VAF suggested putting a flyback suppression diode across fuel pump leads like we do with contactor and relay solenoid coils. This was re an automotive fuel pump like SDS/EFII/Airflow Performance/Walbro.

>>>

>>>   What say Bob et Al?

>>     Did the author cite a noise problem which was

>>     mitigated by adding this component?

>>

>>     I'm mystified by any assertion of added value.

>>     Rotary pumps powered by pm motors have no

>>     'flyback' event.  PutPut pumps like the

>>     Facet devices have electronically driven

>>     solenoids that 'cock' a compression spring.

>>     A cruise through the genealogy of exemplar

>>     patents for such pumps . . .

>>

>>    https://tinyurl.com/2e6mmzyr (https://tinyurl.com/2e6mmzyr)

>>

>>     . . . illustrates commonly applied

>>     technology for mitigating flyback

>>     energies in these devices that include

>>     resistors, diodes and capacitors as

>>     part of the designs dating back over

>>     30 years.

>>

>>     I'm curious as to the history of

>>     the thread.

>>

>>   

>>   

>>     Bob . . .

>>

>>     Un impeachable logic: George Carlin asked, "If black boxes

>>     survive crashes, why don't they make the whole airplane

>>     out of that stuff?"

>

> Hi Bob,

>

> The VAF thread started as âlocal ground or forest of tabs for fuel pump ground?â, EFI fuel pump, and drifted at post 9 to someone recommending a diode across the pump motor to protect the pump switch. I had never heard of this so I asked here on AEL.

>

> https://vansairforce.net/community/showpost.php?p=1629894&postcount=9

>

> --------

> John Bright, RV-6A, at FWF, O-360

> Z-101 single batt dual alt SDS EM-5-F.

> john_s_bright(at)yahoo.com, Newport News, Va

> https://drive.google.com/folderview?id=1u6GeZo6pmBWsKykLNVQMvu4o1VEVyP4K

>


	




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_________________
Charlie

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Sep 02, 2022 10:07 pm Post subject: flyback diode across fuel pump

At 02:44 PM 9/2/2022, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Jeffrey Cohen <jcohen(at)post.com>



 is there any downside to installing this diode across the fuel pumps? for example, can a diode short closed and prevent the pumps from operating? Is this a possible failure mode of diodes?

 Jeff 	


   Diodes are the oldest and most reliable solid state

   devices in service. Risk of failure is exceedingly

   small. Operational benefit is on the same order as

   a paint stripe down the side of your fuselage or installing

   white sidewall tires.



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

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