VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.


Go Back   VAF Forums > Avionics / Interiors / Fiberglass > Electrical Systems
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 01-18-2021, 10:18 AM
Chris Lunt Chris Lunt is offline
 
Join Date: Dec 2011
Location: Wiltshire, UK
Posts: 12
Question Trim and Flap Relays....to DIODE or NOT ..?

I wonder if I can lay myself open to ridicule and ask my fellow builders a really numpty question about using diodes in relays.....?

I'm using Vans' RV7 flap motor, Ray Allen Company(RAC) trim switches and pitch trim motor, and wish to incorporate servos to activate my flaps and trim motor.
I'm using AircraftExtra's servos but specific manufacturer aside, my question is far more generic.

I am trying to instal these servos in my flap and pitch trim circuits.....and good old Bob Nuckolls has provided the very schematics I need...

Flap Circuit: http://www.aeroelectric.com/articles/flaps.pdf

Trim Circuit: http://www.aeroelectric.com/articles/trim2.pdf

RAC have also been most helpful in supplying advice on their schematics, my set up uses a RAC rocker (RS2) and sticktop buttons ... shown on page 2 here: http://www.rayallencompany.com/RACme...S2withmods.pdf

I've attached my simplistic shop notes Click image for larger version

Name:	My own pictoral.png
Views:	79
Size:	930.1 KB
ID:	7104

I realise that collapsing magnetic fields around relays induce reverse current, and hence, the requirement for diodes in the RAC trim schematic and across the trim relay terminals in Bob Nuckolls' Trim wiring diagram above.

Sooooooooo, getting to my point...

Bob Nuckolls does not show diodes in his flap servo diagram above...
To my uneducated eye the flap motor uses the same servo, inherently the same problem must exist...?

I'm guessing I'm missing something somewhere....but should I instal diodes in both my FLAP and TRIM relays...?

Doffing my cap to Bob, RAC and you wonderful folks out there....
__________________
Dues auto-paid..
Reply With Quote
  #2  
Old 01-18-2021, 06:05 PM
RV6_flyer's Avatar
RV6_flyer RV6_flyer is offline
 
Join Date: Jan 2005
Location: NC25
Posts: 3,608
Default Why use a diode...

Here is an article about why a diode is used with a relay.


To make a long story short, the current flowing through a coil creates a magnetic field that activates the relay. When switched off, the magnetic field is still there and collapses. The magnetic field creates a reverse current and voltage in the opposite direction. The reverse current and voltage can damage electronic components that are getting power from the same source.

Read the article for a better explination.
__________________
Gary A. Sobek
NC25 RV-6
Flying
3,400+ hours
Where is N157GS
Building RV-8 S/N: 80012

To most people, the sky is the limit.
To those who love aviation, the sky is home.
Reply With Quote
  #3  
Old 01-19-2021, 05:28 AM
Chris Lunt Chris Lunt is offline
 
Join Date: Dec 2011
Location: Wiltshire, UK
Posts: 12
Default Bob's circuits..

Thanks Gary,

I'd garnered the gist of the reversal of flow,....

I'm confused as to why Bob Nuckolls includes diodes on his trim relay circuit, but not on his Flap relay schematic.

Many thanks for the article and your help sir.

Rgds, Chris
__________________
Dues auto-paid..
Reply With Quote
  #4  
Old 01-19-2021, 05:33 AM
fixnflyguy fixnflyguy is offline
 
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 1,319
Default What I did

I have the Ray Allen grip that has additional momentary buttons I used for flaps(one controls down, the other up). I also have aileron and elevator trim, so mine is a little different. I used the standard Ray Allen module for the 4 trim functions, but my flap switches are simply run to the VANs electric flap set-up in lieu of the rocker switch. I have been running this set up for 10 years with no issues. Pat Hatch (on here) also markets some trim/flap control boards that I understand work well. I have attached a picture with the grip I have, which is a bit different than yours.
Attached Thumbnails
Click image for larger version

Name:	Cockpit.jpg
Views:	46
Size:	278.4 KB
ID:	7132  
__________________
Bill E.
RV-4/N76WE
8A7 / Advance NC
Reply With Quote
  #5  
Old 01-19-2021, 07:02 AM
Walt's Avatar
Walt Walt is online now
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,837
Default

No diodes needed, the relay coils are generally not large enough to generate an appreciable amount of arcing.
__________________
Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154

Last edited by Walt : 01-19-2021 at 07:43 AM.
Reply With Quote
  #6  
Old 01-19-2021, 07:09 AM
emsvitil's Avatar
emsvitil emsvitil is offline
 
Join Date: Oct 2019
Location: SoCal
Posts: 436
Default

Lookup

Flyback Diode
__________________
Ed
Reply With Quote
  #7  
Old 01-19-2021, 07:20 AM
Pat Hatch's Avatar
Pat Hatch Pat Hatch is offline
 
Join Date: Jun 2006
Location: Vero Beach, FL
Posts: 885
Default

Think I'll chime in here since I'm mentioned by my good friend Bill E. Early in our relay board development we had a couple of cases where a particular brand of autopilot was being knocked off line whenever the trim button was activated. Come to find out that it was EMI from the relay coils causing this. Yes, I was very surprised, but we changed our printed circuit board to include spike suppressing diodes. Problem solved. Now, how much those diodes prevent arcing across the small switches in your grip is an open question. I suspect there is some, so the diodes will eliminate this probability. Perhaps not much, but the diodes are there and the cost is almost negligible.
__________________
Pat Hatch
RV-4 (Gone to RV heaven)
RV-6 (N44PH - Flying)
RV-7 (Sold)
RV-8 (Builder & Avionics Installer)
www.phaviation.com Trim Relay Boards/Flap Actuators
www.pathatch.com/blog (Photography)
Track Me
Reply With Quote
  #8  
Old 01-19-2021, 11:24 AM
sblack sblack is offline
 
Join Date: Dec 2009
Location: Montreal
Posts: 1,496
Default

Why change from simple Motors to servos? What is the advantage?
__________________
Scott Black
Old school simple VFR RV 4, O-320, wood prop, MGL iEfis Lite
VAF dues 2020
Instagram @sblack2154
Reply With Quote
  #9  
Old 01-20-2021, 06:35 AM
Chris Lunt Chris Lunt is offline
 
Join Date: Dec 2011
Location: Wiltshire, UK
Posts: 12
Default

Quote:
I have the Ray Allen grip that has additional momentary buttons I used for flaps
Many thanks Bill.......

I'm convinced I'm not the first to have figure this one out ��

Rgds
__________________
Dues auto-paid..

Last edited by Chris Lunt : 01-22-2021 at 02:26 AM. Reason: link to rely
Reply With Quote
  #10  
Old 01-20-2021, 06:38 AM
Chris Lunt Chris Lunt is offline
 
Join Date: Dec 2011
Location: Wiltshire, UK
Posts: 12
Default

Quote:
Now, how much those diodes prevent arcing across the small switches in your grip is an open question. I suspect there is some, so the diodes will eliminate this probability. Perhaps not much, but the diodes are there and the cost is almost negligible
Hi Pat,

Thank you for that input.

I'm no electrician for sure - but I've spent an embarrassing amount of time online reading up as best I can to make an educated guess as to how to wire up my trim relay board. As you've mentioned, the flyback voltage EMI can be significant it seems...

Sooooooo,.... it appears a couple of diodes 'across the relays' can't harm things, but may certainly help..!

Reason to persist then !

Kind Rgds
__________________
Dues auto-paid..

Last edited by Chris Lunt : 01-22-2021 at 02:27 AM.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 02:51 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.