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Flap motor draw for Rv-7A

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airlincoln(at)sbcglobal.n
Guest

Posted: Fri Mar 12, 2010 9:21 am Post subject: Flap motor draw for Rv-7A

Anyone know how many amps the flap motor draws on an RV-7A?  I don't see it listed on the motor itself or on any of the documentation I've got and Van's doesn't know offhand either.  I was going to use a 10A fuse and 14AWG wire (total wire run of about 15 feet) which seems very conservative, but I'd still like to know what the amperage draw is so I can calculate the total "worst-case peak" amperage that my alternator & battery will need to produce.  Thanks.



Do not archive

Lincoln Keill

RV-7A

 [quote][b]

wgill10(at)comcast.net
Guest

Posted: Fri Mar 12, 2010 9:46 am Post subject: Flap motor draw for Rv-7A

Lincoln, 

  

I used 16AWG and a 3-amp fuse. That worked great for 2 years, but this winter the 3-amp fuse occasinally blew when really cold outside (-5F). I suspect the cold grease did not allow the motor to run its normal speed. I upped the fuse to 7.5 amp during the winter and have since returned to the original 3-amp without further problems. 

  

Bill 

  

 

---

sarg314(at)gmail.com
Guest

Posted: Fri Mar 12, 2010 10:06 am Post subject: Flap motor draw for Rv-7A

I've been using a 5 amp fuse.Â  I used fairly light wire - 20 or 22 I think - because the use of the flap motor is very intermittent. It's just on for a few seconds once or twice and then you don't use it again for an hour.Â  You can tolerate a wire which, under continuous use, would have a noticeable temperature rise. 

-- 

Tom Sargent

  [quote][b]

Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Fri Mar 12, 2010 10:51 am Post subject: Flap motor draw for Rv-7A

True as far as it goes, BUT the voltage drop on the small wire, depending on its length, may mean that the full design power of the motor is not available. This may or may not be significant depending on, amongst other things, your airspeed. It's also a little hard on the motor running it at reduced voltage. Generally wires feeding motors should take voltage drop into consideration so that the motor receives, as near as possible, full design voltage during operation however short or intermittant that operation may be.

  

 Bob McC

 

  Date: Fri, 12 Mar 2010 11:03:16 -0700

Subject: Re: Flap motor draw for Rv-7A

From: sarg314(at)gmail.com

To: aeroelectric-list(at)matronics.com



I've been using a 5 amp fuse.  I used fairly light wire - 20 or 22 I think - because the use of the flap motor is very intermittent. It's just on for a few seconds once or twice and then you don't use it again for an hour.  You can tolerate a wire which, under continuous use, would have a noticeable temperature rise.

-- 

Tom Sargent

[quote]



-List">http://www.matronics.com/Navigator?AeroElectric-List

ronics.com

ww.matronics.com/contribution



[b]

_________________
Bob McC
Falco #908
(just starting)

jef.vervoortw(at)telenet.
Guest

Posted: Fri Mar 12, 2010 10:59 am Post subject: Flap motor draw for Rv-7A

I’m struggling with the same these days.  

I found yesterday on www.ametektip.com \technical documents\Product Catalogs\Product Specification for the Pittman motor 9234 series, from Vans, at 12 Volts: current (at) continuous torque: 3,53 A and peak current 14,5.  

Cold weather could weaken the battery.  

   

Jef in Belgium;91031.  

   

         

  

Van: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] Namens wgill10(at)comcast.net

 Verzonden: vrijdag 12 maart 2010 18:45

 Aan: aeroelectric-list(at)matronics.com

 Onderwerp: Re: AeroElectric-List: Flap motor draw for Rv-7A  

  

     

Lincoln,  

   

I used 16AWG and a 3-amp fuse. That worked great for 2 years, but this winter the 3-amp fuse occasinally blew when really cold outside (-5F). I suspect the cold grease did not allow the motor to run its normal speed. I upped the fuse to 7.5 amp during the winter and have since returned to the original 3-amp without further problems.  

   

Bill  

   

 

 ---

jef.vervoortw(at)telenet.
Guest

Posted: Fri Mar 12, 2010 11:36 am Post subject: Flap motor draw for Rv-7A

I’m struggling with the same these days.  

I found yesterday on www.ametektip.com \technical documents\Product Catalogs\Product Specification for the Pittman motor 9234 series, from Vans, at 12 Volts: current (at) continuous torque: 3,53 A and peak current 14,5.  

Cold weather could weaken the battery.  

   

Jef in Belgium;91031.  

   

         

  

Van: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] Namens wgill10(at)comcast.net

 Verzonden: vrijdag 12 maart 2010 18:45

 Aan: aeroelectric-list(at)matronics.com

 Onderwerp: Re: AeroElectric-List: Flap motor draw for Rv-7A  

  

     

Lincoln,  

   

I used 16AWG and a 3-amp fuse. That worked great for 2 years, but this winter the 3-amp fuse occasinally blew when really cold outside (-5F). I suspect the cold grease did not allow the motor to run its normal speed. I upped the fuse to 7.5 amp during the winter and have since returned to the original 3-amp without further problems.  

   

Bill  

   

 

 ---

mprather(at)spro.net
Guest

Posted: Fri Mar 12, 2010 12:04 pm Post subject: Flap motor draw for Rv-7A

My hazy recollection is that running reduced voltage being hard on motors

depends on the type of motor..  I looked up what appears to be the

replacement motor and found a link here:



http://www.clickautomation.com/PDF/items/9234S004.PDF



I believe the peak current at 12V is found when stalled (RPM=0).  Reducing

the Voltage should lower the current, reducing the temperature.



Again, my hazy recollection is that AC induction motors may not like

running with sagging voltage.  Hopefully someone can remind me how this

works..

Matt-



 	  Quote: 	
		  

 True as far as it goes, BUT the voltage drop on the small wire, depending

 on its length, may mean that the full design power of the motor is not

 available. This may or may not be significant depending on, amongst other

 things, your airspeed. It's also a little hard on the motor running it at

 reduced voltage. Generally wires feeding motors should take voltage drop

 into consideration so that the motor receives, as near as possible, full

 design voltage during operation however short or intermittant that

 operation may be.



 Bob McC

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 12, 2010 4:01 pm Post subject: Flap motor draw for Rv-7A

At 02:02 PM 3/12/2010, you wrote:

 	  Quote: 	
		  



My hazy recollection is that running reduced voltage being hard on motors

depends on the type of motor..  I looked up what appears to be the

replacement motor and found a link here:



http://www.clickautomation.com/PDF/items/9234S004.PDF



I believe the peak current at 12V is found when stalled (RPM=0).  Reducing

the Voltage should lower the current, reducing the temperature.



Again, my hazy recollection is that AC induction motors may not like

running with sagging voltage.  Hopefully someone can remind me how this

works..


	


    A DC motor doesn't really have a "hard" voltage rating.

    I.e., the nameplate only speaks to performance at the

    nameplate voltage. In the case of the motor specs cited

    above, you won't find all that good stuff on any nameplate.



    I've purloined the speed/torque/amps curve from the

    data sheet cited above and added a few more features

    which can be seen here:



http://www.aeroelectric.com/Pictures/Curves/Speed-Torque-Current_Curve.jpg



    The 12v speed/torque plot is shown in brown along with

    the current torque curve shown in blue. Note that

    the output of a DC motor is proportional to current

    so ONE plot suffices for all conditions. The speed/torque

    curve is bounded a the left end by applied voltage

    divided by Ke (back EMF constant). With 12v applied and

    zero load, we see about 6200 rpm. 9V applied yields

    about 4600 rpm. 6V applied drops the no-load speed

    to 1/2 the 12v value or 3100 rpm.



    The right end of these curves is bounded by the internal

    resistance of the motor. At zero rpm, the current that

    flows in the motor is volts/ohms. 6V yields 1/2 the

    locked-rotor current of 12V. Since output torque is

    absolutely proportional to current, it holds further

    that stall torque is proportional to applied voltage.



    Now, suppose it takes 20 oz-in to move your flaps

    a the top of the white arc on your IAS display.

    Let's assume further that your alternator is working

    and there's about 14 volts applied to the motor.



    14V applied to this motor gives you a no-load speed

    of about 7600 rpm and a stall torque of 48 oz in.

    Let's say your 20 oz-in working load slows the motor down

    to about 4300 rpm and the motor will draw just under

    7.5 amps. Now, battery only the bus drops to 12v and

    the speed comes down to about 3000 rpm. It will now

    take about 1.5 times longer to extend the flaps. But

    the current is still 7.5 amps. If your battery is

    on its last legs and the applied voltage drops to

    9V, 20 oz-in of load runs the motor at 1500 rpm.

    Flap extension time is now 5 times longer than

    at 14v. Guess what? The current is still 7.5A. As

    the battery continues to die, by the time the

    voltage drops to 6 volts, the motor speed goes

    to zero, flaps stop moving and gee whiz, the current

    is still 7.5 amps.



    Obviously in this simplistic case, current required

    to extend flaps is never constant over full stroke

    of the mechanisms. When you have the performance

    curves for the motor, you can deduce behavior

    at what ever voltage and load you wish bounded only

    by speed bounded by potential damage to motor, torque

    (current) bounded by risks of smoking wires/brushes,

    and ability to move at all bounded by applied voltage

    divided by internal resistance which yields a stall

    current (or torque at which speed drops to zero).



    Now, when picking a wire size to drive the motor,

    any resistance EXTERNAL to the motor is in series

    with INTERNAL resistance which serves to reduced

    stall current. Suppose your wiring resistance reduces

    14v stall current from 48 amps down to 43 amps. Just

    draw in a new line (yellow) to account for the motor's

    'new' loop resistance. You can draw any number of

    additional lines parallel to the 14v curve to predict

    performance at the full range of applied voltages

    as described above.



    Want to know how your installation particulars

    influence motor performance? Get the motor performance

    curves at any voltage, get out your pencil and straight

    edge, and plot it out.



    Understand too that the efficiency/power curves for

    EACH voltage/loop resistance combination will need

    recalculation.



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 12, 2010 7:00 pm Post subject: Flap motor draw for Rv-7A

At 11:17 AM 3/12/2010, you wrote:

 	  Quote: 	
		  Anyone know how many amps the flap motor draws on an RV-7A?  I don't 

see it listed on the motor itself or on any of the documentation 

I've got and Van's doesn't know offhand either.  I was going to use 

a 10A fuse and 14AWG wire (total wire run of about 15 feet) which 

seems very conservative, but I'd still like to know what the 

amperage draw is so I can calculate the total "worst-case peak" 

amperage that my alternator & battery will need to produce.  Thanks.


	


    As described in the posting of a few minutes ago,

    wire size increases total loop resistance. This

    has an easily predicted effect of reducing

    stall current (translates to slow acceleration

    of motor) and reduces speed of the motor.



    At the same time, huge variability of voltage,

    air loads and wiring resistance had have

    MEASURABLE effects that may not even be

    noticed by the pilot. How often do you check

    flap travel times with a stop-watch?



    Knowing the worst-case peak values are useful

    only to the extent that you don't nuisance trip

    your circuit protection. Using fuses to protect

    a PM DC motor suggests some consideration for

    weakening a fuse with repeated but infrequent

    inrush values on the order of 30-50 amps . . . but

    light guage wire goes a long way toward mitigating

    that effect. Keeping voltage drop low improves on

    motor performance but exacerbates inrush effects.



    The 10A fuse and 14AWG wire is as good as any for

    some reasons . . . upsizing to a 15A fuse is

    good for other reasons. But one fellow talks

    about pretty small wire and fuse . . . The motor

    probably draws very low average current. Small

    wire mitigates inrush. If this particular motor

    seems sluggish during some portion of flap extension,

    the pilot has no measured/considered reason to

    attribute the effect to really high air loads,

    small wire, undersized motor, or some combination

    of those.



    In the final analysis, it comes down to perceptions.

    If it's been "doing the job" for some period of

    time with no nuisance trips . . . well, it's

    hard to argue with success! Doing what ever has

    been installed in a few thousand RVs wouldn't

    be a bad idea.



    The point is, performance points for flap motors

    in OBAM aircraft are all over the map. We could

    spend a lot of time worrying about it . . . ultimately

    fine tuning a decision that has no operational

    benefits.



    Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Mar 13, 2010 7:19 am Post subject: Flap motor draw for Rv-7A

Some private emails on the flap motor thing

      have prompted some further expansion on the

      topic of powering and sizing motors . . .



Anyone know how many amps the flap motor draws on an RV-7A?  I

don't see it listed on the motor itself or on any of the

documentation I've got and Van's doesn't know offhand either.



      Up until now, we've only discussed the capabilities

      and performance of DC motors as described in their

      performance data. This discussion says NOTHING about

      what the motor is expected to do as-installed in

      the airplane.



      Just because a motor has some particular nameplate

      rating does not automatically set the operating point

      as installed. Looking at the data plots I published

      yesterday . . .



http://www.aeroelectric.com/Pictures/Curves/Speed-Torque-Current_Curve.jpg



      . . . suppose your flap system extension from 0-10

      degrees required only 4 oz in of torque from the

      motor. During this portion of the stroke it would

      draw about 2A and run at 6800 rpm. Assume from 10-

      20 degrees, air loads are building on the panels

      and the current averages 6 oz in. Now current rises

      to about 2.5 amps and speed drops to 6600. From

      20-30 degrees, the air loads are at max. Torque might

      rise to 10 oz-in at end of stroke with the current

      surging up to 3.5A



      This may be typical of what an RV or many other

      OBAM aircraft demand of their flap extension systems.

      This does not amount to much power. Indeed if we

      compare the effort required to extend flaps by hand

      with a "Johnson Bar", the horsepower developed during

      a 30 pound pull through a arc length of 2 feet over

      say 10 seconds really isn't much. The motor's task

      is no greater except that SOME flap systems may

      incorporate some form of worm gear reduction which

      can have an efficiency of 30% or worse.



      But even then, the power needed to extend flaps

      is small. A HP is 550 lb-ft of work per second.

      Our 60 lb-ft in two seconds is only 30 lb-ft/second

      or 1/20th HP. A really lousy mechanism efficiency

      might push that up to 1/5th HP.



      In the hypothetical extension scenario I cited

      above, electrical power into the flap extension

      system peaked just before the haulted at the

      fully extended position. 3.5A x 14v = 49 watts.

      49w / 746w/hp = 0.06 HP



      If these numbers are in the same reality ball park

      with the system in an RV, then it's easy to see

      how motor ratings on the side of the motor can

      be VERY misleading with respect to real performance

      numbers. Van's has had no particular reason to

      go get the real numbers. In the airframe/power-plant

      integrator's world, detail of electrical system

      performance become useful ONLY when things are not

      working and some investigation is launched to fix

      the problem. Even then, the investigators may come

      out of the exercise only having UPsized some

      obviously undersized component (motor, breaker,

      attach hardware, etc) and may STILL be uninformed

      as to the real numbers.



      I hope this exchange has shed some light on the

      difficulty of answering questions like the one

      that started this thread. Unless somebody has

      taken the time and tools to go measure the performance,

      the answer's will always be shallow and tend toward

      the conservative. Certainly, wiring and fusing the

      flap motor cited in the data plots at say 10A and

      wiring with commensurate wire will eliminate any

      possibility of nuisance tripping.



      But understand that just because there's a 10 or

      15A breaker protecting your hangar-mates flap

      circuits doesn't say diddly-doo about what that

      system really demands in terms of electrical

      energy.



      A pretty sharp cookie once opined,



"If you want to know, measure! When you can measure what you are

speaking about, and express it in numbers, you know something

about it, but when you cannot measure it, your knowledge is of

a meager kind." - Lord Kelvin 1824-1907



      So after all this 'discussion' we're still unable

      to answer the original question. Anyone got an

      RV and a data acquisition system who would be

      will to gather some real flight test data?



      Bob . . .

lrsecaldwell(at)earthlink
Guest

Posted: Sun Mar 14, 2010 4:54 am Post subject: Flap motor draw for Rv-7A

[quote]                              Normal   0               false   false   false      EN-US   X-NONE   X-NONE                                                     MicrosoftInternetExplorer4                                                   <![endif]-->                                                                                                                                                                                                                                                                                                                                                                                                                                <![endif]-->          /* Style Definitions */  table.MsoNormalTable 	{mso-style-name:"Table Normal"; 	mso-tstyle-rowband-size:0; 	mso-tstyle-colband-size:0; 	mso-style-noshow:yes; 	mso-style-priority:99; 	mso-style-qformat:yes; 	mso-style-parent:""; 	mso-padding-alt:0in 5.4pt 0in 5.4pt; 	mso-para-margin:0in; 	mso-para-margin-bottom:.0001pt; 	mso-pagination:widow-orphan; 	font-size:11.0pt; 	font-family:"Calibri","sans-serif"; 	mso-ascii-font-family:Calibri; 	mso-ascii-theme-font:minor-latin; 	mso-fareast-font-family:"Times New Roman"; 	mso-fareast-theme-font:minor-fareast; 	mso-hansi-font-family:Calibri; 	mso-hansi-theme-font:minor-latin; 	mso-bidi-font-family:"Times New Roman"; 	mso-bidi-theme-font:minor-bidi;}  <![endif]-->My measured current for my RV-& with the model 92345 motor was 2.0 Amps when at the stop, ie stalled.  I discount the theory that when the lube is cold that the current could be higher since the motor has an over ride clutch which slips at the end of travel and if the mechanical load was higher in the middle of travel then at the stops the clutch should slip.  Of course the starting current could be higher but I doubt if it would be briefly more than 4 amp..  I have been using a  5 amp fuse without problems.

   

 Roger

       	  Quote: 	
		  Time: 09:21:37 AM PST US

From: Lincoln Keill <airlincoln(at)sbcglobal.net>

Subject: Flap motor draw for Rv-7A



Anyone know how many amps the flap motor draws on an RV-7A? -I don't see 

it listed on the motor itself or on any of the documentation I've got and V

an's doesn't know offhand either. -I was going to use a 10A fuse and 14AW

G wire (total wire run of about 15 feet) which seems very conservative, but

 I'd still like to know what the amperage draw is so I can calculate the to

tal "worst-case peak" amperage that my alternator & battery will need to pr

oduce. -Thanks.

Do not archive

Lincoln KeillRV-7A

  	
   

 [b]

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Mar 14, 2010 7:38 am Post subject: Flap motor draw for Rv-7A

 	  Quote: 	
		  	
 

 At 07:13 AM 3/14/2010, you wrote:



 My measured current for my RV-& with the model 92345 motor was 2.0 Amps when at the stop, ie stalled.  I discount the theory that when the lube is cold that the current could be higher since the motor has an over ride clutch which slips at the end of travel and if the mechanical load was higher in the middle of travel then at the stops the clutch should slip.  Of course the starting current could be higher but I doubt if it would be briefly more than 4 amp..  I have been using a  5 amp fuse without problems.



    Thanks for taking the time to do some real

    measurements and share them with us. I'm having

    trouble visualizing the electrical and mechanical

    features of your flap extension system.



    Normally, a motor that is powered up but not

    turning will draw some value of current limited

    only by its internal resistance. This would be

    close to the data sheet stall current . . . on

    the order of 30A or more. In this case, we would

    expect the supply protection device to operate.

    This is another reason why the proper adjustment

    of limit switches is important.



    I seem to recall that the RV flap actuator

    was a ball-screw with free-wheel clutches

    at each end of travel. If this is the case,

    then the current you measured wasn't a "stall"

    current in the conventional sense, but an

    motor unloaded value that is a by-product

    of the free-wheeling mechanisms.



    Drag of the free-wheeling clutches at ends of

    a ball screw are relatively insensitive to

    temperature variation as you've guessed.



    Were these measurements taken in flight

    - airloads on the flaps during extend cycle?



    Bob . . .



     [quote][b]

wgill10(at)comcast.net
Guest

Posted: Sun Mar 14, 2010 5:52 pm Post subject: Flap motor draw for Rv-7A

You can surmise all you want about cold temps and  related current draw, but there is a relationship. Don't think so, test at -5F  and report. Otherwise, you're smply guessing. 

  

  

 [quote]   From:    Lapsley R. and Sandra E. Caldwell (lrsecaldwell(at)earthlink.net)    

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

   Sent: Sunday, March 14, 2010 7:13  AM

   Subject: Re: Flap    motor draw for Rv-7A

   

    	  Quote: 	
		                      Normal   0               false   false   false      EN-US   X-NONE   X-NONE                                                     MicrosoftInternetExplorer4                                                   <![endif]-->                                                                                                                                                                                                                                                                                                                                                                                                                                <![endif]-->     (at)font-face { 	font-family: Cambria Math; } (at)page Section1 {size: 8.5in 11.0in; margin: 1.0in 1.0in 1.0in 1.0in; mso-header-margin: .5in; mso-footer-margin: .5in; mso-paper-source: 0; } P.MsoNormal { 	FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman","serif"; mso-style-unhide: no; mso-style-qformat: yes; mso-style-parent: ""; mso-pagination: widow-orphan; mso-fareast-font-family: "Times New Roman" } LI.MsoNormal { 	FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman","serif"; mso-style-unhide: no; mso-style-qformat: yes; mso-style-parent: ""; mso-pagination: widow-orphan; mso-fareast-font-family: "Times New Roman" } DIV.MsoNormal { 	FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman","serif"; mso-style-unhide: no; mso-style-qformat: yes; mso-style-parent: ""; mso-pagination: widow-orphan; mso-fareast-font-family: "Times New Roman" } .MsoChpDefault { 	FONT-SIZE: 10pt; mso-style-type: export-only; mso-default-props: yes; mso-ansi-font-size: 10.0pt; mso-bidi-font-size: 10.0pt } DIV.Section1 { 	page: Section1 }     /* Style Definitions */  table.MsoNormalTable 	{mso-style-name:"Table Normal"; 	mso-tstyle-rowband-size:0; 	mso-tstyle-colband-size:0; 	mso-style-noshow:yes; 	mso-style-priority:99; 	mso-style-qformat:yes; 	mso-style-parent:""; 	mso-padding-alt:0in 5.4pt 0in 5.4pt; 	mso-para-margin:0in; 	mso-para-margin-bottom:.0001pt; 	mso-pagination:widow-orphan; 	font-size:11.0pt; 	font-family:"Calibri","sans-serif"; 	mso-ascii-font-family:Calibri; 	mso-ascii-theme-font:minor-latin; 	mso-fareast-font-family:"Times New Roman"; 	mso-fareast-theme-font:minor-fareast; 	mso-hansi-font-family:Calibri; 	mso-hansi-theme-font:minor-latin; 	mso-bidi-font-family:"Times New Roman"; 	mso-bidi-theme-font:minor-bidi;}  <![endif]-->My measured      current for my RV-& with the model 92345 motor was 2.0 Amps when at the      stop, ie stalled.  I discount the theory that when the lube is cold      that the current could be higher since the motor has an over ride clutch      which slips at the end of travel and if the mechanical load was higher in      the middle of travel then at the stops the clutch should slip.  Of      course the starting current could be higher but I doubt if it would be      briefly more than 4 amp..  I have been using a  5 amp fuse without      problems.



Roger

 	  Quote: 	
		  Time: 09:21:37 AM PST US

From: Lincoln Keill <airlincoln(at)sbcglobal.net> (airlincoln(at)sbcglobal.net)

Subject: Flap motor draw for Rv-7A



Anyone know how many amps the flap motor draws on an RV-7A? -I don't see 

it listed on the motor itself or on any of the documentation I've got and V

an's doesn't know offhand either. -I was going to use a 10A fuse and 14AW

G wire (total wire run of about 15 feet) which seems very conservative, but

 I'd still like to know what the amperage draw is so I can calculate the to

tal "worst-case peak" amperage that my alternator & battery will need to pr

oduce. -Thanks.

Do not archive

Lincoln KeillRV-7A

  	






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[b]

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Mar 14, 2010 6:53 pm Post subject: Flap motor draw for Rv-7A

At 08:51 PM 3/14/2010, you wrote:

  	  Quote: 	
		   You can surmise all you want about cold temps and related current draw, but there is a relationship. Don't think so, test at -5F and report. Otherwise, you're smply guessing. 	


  Gently my friend. He DID come forward with some observed

  current readings . . . and might be induced to go get some

  more. Yeah, temperatures can have a huge effect on currents

  because copper resistances go down and the grease (especially

  on worm gears) gets stiff. But let's not scare him off. He

  has hardware, test equipment, a demonstrated curiosity and

  a willingness to share!



  Bob . . .    [quote][b]

lrsecaldwell(at)earthlink
Guest

Posted: Mon Mar 15, 2010 8:06 am Post subject: Flap motor draw for Rv-7A

I guess I did not make myself clear.  I believe the clutch in the RV-7 is a friction clutch.  In other words the motor never stalls, but the clutch slips.  Thus max steady state current draw is set by the breakaway torque not any air loads.



Of course the current draw varies with temp, but I will still claim the peak current will be the starting current.  That too varies with temp.  I would futher claim that the peak starting current will occur if the flap is at the stop, and you attempt to restart the flaps in that same direction, thus starting the flap motor at max torque.  However this would be a transient and mat not blow the fuse.  It does not blow my 5 amp fuse, admittedly at benign temps.



Since I do not have a environmental chamber at home I will be unable to meet your request to measure at -5 deg.



Roger

Time: 06:52:10 PM PST US

From: "William Gill"<wgill10(at)comcast.net>

Subject: Re: Re: Flap motor draw for Rv-7A



You can surmise all you want about cold temps and related current draw,

but there is a relationship. Don't think so, test at -5F and report.

Otherwise, you're smply guessing.

   From: Lapsley R. and Sandra E. Caldwell

   To:aeroelectric-list(at)matronics.com

   Sent: Sunday, March 14, 2010 7:13 AM

   Subject: Re: Flap motor draw for Rv-7A

     My measured current for my RV-&  with the model 92345 motor was 2.0

Amps when at the stop, ie stalled.  I discount the theory that when the

lube is cold that the current could be higher since the motor has an

over ride clutch which slips at the end of travel and if the mechanical

load was higher in the middle of travel then at the stops the clutch

should slip.  Of course the starting current could be higher but I doubt

if it would be briefly more than 4 amp..  I have been using a  5 amp

fuse without problems.



     Roger

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