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IvoProp current limiter -revisit

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Mike Welch

Joined: 13 Feb 2011
Posts: 272

Posted: Tue Jun 21, 2011 11:01 am Post subject: IvoProp current limiter -revisit

Bob N,



  Quite a while back I built and installed the IvoProp current limiter circuit you desgned.

By all account, it appears to work, with one significant exception; it cuts out very quickly

when cycling in either direction.  In other words, the blades barely move at all.



  Yes, the LEDs light up, and all other aspects of the circuit appear to function properly.

The only weakness is the extreme shortage of blade movement.  I know the obvious, question

is; do we know if the blades are free to mover properly?  As far as I know, yes, they 

used to work just fine, prior to the installation of the current limiter circuit.



  Bob, is it possible to "vary" the circuit's current limitation.  Example....if the present resistors

that control the circuit's current to "top out" at such and such amps, would it be reasonable to 

redesign the circuit to allow for 'differing" overloads.  Do you get what I'm trying to say?



  By watching the entire system (circuit, prop blades/motor, etc), the circuit appears to 

operate as it was designed, except that it appears to cut out at 1, maybe 2  amps.



  I have to run off to Minneapolis for a few days, but when I get back, I'll hook up a

highly accurate ammeter in the present arrangement, and see exactly how much current 

shuts it off.



  Any ideas, or suggestions are highly appreciated.



Thanks,  Mike Welch

 		 	   		  

  [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jun 21, 2011 11:28 am Post subject: IvoProp current limiter -revisit

At 02:56 PM 6/21/2011, you wrote:

 	  Quote: 	
		  Bob N,



   Quite a while back I built and installed the IvoProp current 

 limiter circuit you desgned.

By all account, it appears to work, with one significant exception; 

it cuts out very quickly

when cycling in either direction.  In other words, the blades barely 

move at all.


	


   Okay, just so folks know what we're talking about here's a recap

   of the circuit and design goals for the system Mike has crafted:

-----------------------



http://aeroelectric.com/Pictures/Schematics/IVO-Prop_Pitch_Controller.pdf



Design goals:



Provide absolute current limit on the order of 9A:



   Q114 is a power FET that saturates with bias

   through R104, R105 and D109 when power is applied

   through "M" connections that sense motor power.



   Voltage drop across R117/R118 is monitored through

   R116 causing Q115 to turn on when drop across the

   R117/118 exceeds Vbe of Q115. This is approx .6

   volts. When Q115 turns on, it starves Q114 of gate

   drive and causes it to become a constant current

   generator with calibration set by the combination

   of R117/R118.



   Any time the constant current loop is active,

   LED D109 will be illuminated. D109 will flash

   each time the prop pitch motor is energized

   and the system becomes an active inrush current

   limiter.



Limit the duration of the current limit mode to

100-200 mS whereupon the system goes open circuit

and removes power from the motor:



   At any time the current limiter is active,

   Q115 collector current through R105 will turn

   on Q103 causing the collector to pull up to

   the supply rail. This causes C112 to charge

   through R106 until zener D110 conducts at about

   8V. This event will occur approximately 120 mS

   after onset of current limit.



   When D110 conducts, it pulls the base of Q115

   more positive causing the Q115/Q103 pair to

   "latch up" not unlike an SCR. When the latching

   event occurs, the collector of Q115 pulls to

   a few millivolts above ground depriving Q114

   of all gate drive.



Normal operation:



   D109 will flash each time the motor control switch

   is closed due to motor inrush current being

   electronically limited. D109 will also flash a

   bit longer (about 120 mS) when the prop pitch motor

   reaches the mechanical stop and the current limit is

   invoked.



   As long as the prop pitch motor is powered

   D108 will be illuminated. When the prop

   pitch system reaches a mechanical limit and

   the control switch is NOT relaxed,  D019 flashes

   for about 120 mS and D108 goes dark.



   Releasing the motor control switch removes

   power from the latching loop and discharges

   C112 through R119, R104, BC junction Q103,

   and R106.



   The system spends so little time in I-limit

   mode that Q114 does not require a heat-sink.

   D109 and D108 staying on together indicates

   a malfunction and the motor control switch

   needs to be released within a second or so

   to avoid over-heat damage to Q114.

--------------------

 	  Quote: 	
		     Yes, the LEDs light up, and all other aspects of the circuit 

 appear to function properly.

The only weakness is the extreme shortage of blade movement.  I know 

the obvious, question

is; do we know if the blades are free to mover properly?  As far as 

I know, yes, they

used to work just fine, prior to the installation of the current 

limiter circuit.


	


    The green LED should be illuminated when the

    pitch motor is being commanded and the system

    is NOT in a current limited mode.  If the

    motor hits the stop and current spikes, the current

    limit mode kicks in. The green LED should dim or

    go dark . . . the amber LED should illuminate

    saying that current limiting operation is in

    effect. One should release the switch quickly

    after the amber LED comes on.



 	  Quote: 	
		    By watching the entire system (circuit, prop blades/motor, etc), 

 the circuit appears to

operate as it was designed, except that it appears to cut out at 1, 

maybe 2  amps.


	


    Had you tested this before? With the values selected

    for R117 and R118, current limit should be on the

    order of 10 amps. If your 'stalled' current is

    2A, then the current limit is kicking in MUCH to

    low.

 	  Quote: 	
		     I have to run off to Minneapolis for a few days, but when I get 

 back, I'll hook up a

highly accurate ammeter in the present arrangement, and see exactly 

how much current

shuts it off.


	


    Good lick. But be cautious about this measurement.

    The TIME that the Q114 can stand to run at 10A

    (140 watts) is limited by the size of heat-sink it

    enjoys. Normal operations will have you releasing

    the switch within a second or so of having the amber

    light come on so when things are working right, a

    large heat-sink is not needed. Experimental measurements

    are another matter. Be quick.

 	  Quote: 	
		     Bob, is it possible to "vary" the circuit's current 

 limitation.  Example....if the present resistors

that control the circuit's current to "top out" at such and such 

amps, would it be reasonable to

redesign the circuit to allow for 'differing" overloads.  Do you get 

what I'm trying to say?


	


    Yes but . . .  this does not appear to be the

    root cause of symptoms you're observing.

   Bob . . .

Dennis Glaeser

Joined: 10 Jan 2006
Posts: 53
Location: Rochester Hills, Michigan

Posted: Tue Jun 21, 2011 5:15 pm Post subject: IvoProp current limiter -revisit

Bob and Mike,

 

I have been using Bob’s circuit on my IVO and it works flawlessly.  It’s a simple and foolproof way to protect the gear train that drives the blade pitch mechanism.

 

When I finished the circuit, Bob asked if I had access to an oscilloscope in order to verify it’s operation.  One of my EAA chapter members has one and we captured the traces per Bob’s specs.  Perhaps Mike could do the same thing and that might provide a clue as to what is (or isn’t) happening.

 

Bob’s description says that when the current limit is reached, D108 (amber LED) flashed for 120 ms and D109 (green LED) goes dark.  In my implementation, the amber LED stays lit as long as I hold the switch (the motor stops) – the green LED does go dark.  I don’t know if that is significant, but thought I’d mention it.    When the motor is running, the green LED is on, but the amber LED is off (except for the flash at startup).

 

If there is anything I can do to help, just let me know.

 

Dennis Glaeser

   [quote][b]

Mike Welch

Joined: 13 Feb 2011
Posts: 272

Posted: Tue Jun 21, 2011 5:59 pm Post subject: IvoProp current limiter -revisit

Bob,



  Thank you for the highly informative description of the circuit.  I know to keep the 

toggle switch testing very brief, however, I did mount the FET on a 1 1/2" X 2" piece

of aluminum for a heat sink.  The heat sink, and complete circuit is contained in a 

neat plastic box.



  After I get back from my mini-vacation, I'll do my best to test the circuit...carefully.



  I also verify the correct LEDs are lighting as you described.



  Thanks a bunch, I'll get back ya early next week.



Mike Welch



PS.  Do they have fish in Minnesota?



 		 	   		  

  [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jun 21, 2011 6:24 pm Post subject: IvoProp current limiter -revisit

At 09:12 PM 6/21/2011, you wrote:

  	  Quote: 	
		  Bob and Mike,

  

 I have been using Bob’s circuit on my IVO and it works flawlessly.  It’s a simple and foolproof way to protect the gear train that drives the blade pitch mechanism.

  

 When I finished the circuit, Bob asked if I had access to an oscilloscope in order to verify it’s operation.  One of my EAA chapter members has one and we captured the traces per Bob’s specs.  Perhaps Mike could do the same thing and that might provide a clue as to what is (or isn’t) happening.

  

 Bob’s description says that when the current limit is reached, D108 (amber LED) flashed for 120 ms and D109 (green LED) goes dark.  In my implementation, the amber LED stays lit as long as I hold the switch (the motor stops) – the green LED does go dark.  I don’t know if that is significant, but thought I’d mention it. 	


  You bet. I'd forgotten how that thing was supposed to work.



  Q103/Q115 form a time-delayed latching switch that switches

  ON as soon as C112 charges up enough to cause D110 to

  go into conduction. Once the latch triggers, Q115 is held

  on 'saturated' until power is removed. 



  	  Quote: 	
		     When the motor is running, the green LED is on, but the amber LED is off (except for the flash at startup). 	


  So the amber LED flashes at start up indicating that

  the current limiter did its job while the motor spins

  up. When the system hits mechanical stops, the led

  will light again when current limit becomes active.

  A few milliseconds later, the latch trips and the

  motor current goes to zero. Green led goes dark. 

  Amber LED stays lit.



  So my earlier admonition about being quick on the switch

  to avoid overheating Q114 is all wet. The time-delayed

  shut-down latch protects Q114.



  	  Quote: 	
		   

 If there is anything I can do to help, just let me know. 	


  You just did. Thanks!



  If there's enough interest in this device, it could

  be packaged up nicely in a box like this:



 [img]cid:.0[/img]



   Since you guys did all the development and proof of concept

   work, it would only take a couple hours to package it up

   and add it to the product line. We could also make this

   a DIY project and sell the ECB, case and connector hardware.



 

 

   Bob . . .

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dsleepy47

Joined: 15 Dec 2007
Posts: 41

Posted: Tue Jun 21, 2011 6:45 pm Post subject: IvoProp current limiter -revisit

I will take 2



Deems

  If there's enough interest in this device, it could

  be packaged up nicely in a box like this:



 [img][/img]



   Since you guys did all the development and proof of concept

   work, it would only take a couple hours to package it up

   and add it to the product line. We could also make this

   a DIY project and sell the ECB, case and connector hardware.



 

    Bob . . .



 		 	   		  

  [quote][b]

_________________
dsleepy47
N1491R

Mike Welch

Joined: 13 Feb 2011
Posts: 272

Posted: Tue Jun 21, 2011 7:21 pm Post subject: IvoProp current limiter -revisit

Thanks for the responses, guys.  I really wish I had more time to try and figure it out

right now, but I'll have to wait until next Monday or so, after I get back.



I went out and did a quick cycle or two of the circuit, and the LEDs appear to turn on and off

as Dennis describes.  The pitch motor obviously is twisting the prop blades, but the whole 

thing still seems to be working exactly as it should, except it only has a one second range, 

from switch on to circuit off, maybe at most, two seconds!



I did see that if I keep switching in the same direction, over and over, I can get the opposite

direction to stay "lit" longer, getting it to twist for 3-4 seconds.  I even kept "pressuring it", 

and the 10A circuit breaker popped.  I reset it, and everything still worked fine...just briefly.



I'll know more after I get back.



Thanks,  Mike W

 		 	   		  

  [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jun 21, 2011 8:15 pm Post subject: IvoProp current limiter -revisit

At 11:17 PM 6/21/2011, you wrote:

 	  Quote: 	
		  Thanks for the responses, guys.  I really wish I had more time to 

try and figure it out

right now, but I'll have to wait until next Monday or so, after I get back.



I went out and did a quick cycle or two of the circuit, and the LEDs 

appear to turn on and off

as Dennis describes.  The pitch motor obviously is twisting the prop 

blades, but the whole

thing still seems to be working exactly as it should, except it only 

has a one second range,

from switch on to circuit off, maybe at most, two seconds!



I did see that if I keep switching in the same direction, over and 

over, I can get the opposite

direction to stay "lit" longer, getting it to twist for 3-4 

seconds.  I even kept "pressuring it",

and the 10A circuit breaker popped.  I reset it, and everything 

still worked fine...just briefly.


	


   Okay, if your 10A breaker popped, the motor/gearbox

   combo is drawing way too much current . . . for reasons

   as yet unknown. The limiter may well be doing what

   it was designed to do. Try taking it out of the circuit

   as described earlier and then measure the current.



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jun 21, 2011 8:15 pm Post subject: IvoProp current limiter -revisit

At 10:42 PM 6/21/2011, you wrote:



 	  Quote: 	
		  I will take 2



Deems


	


   noted. thanks.

   Bob . . .

n801bh(at)netzero.com
Guest

Posted: Wed Jun 22, 2011 5:41 am Post subject: IvoProp current limiter -revisit

I can add some insight into why the device might be inconsistant.... 

I run the Ivo Prop on my V-8 experimental. I switch back and forth from the regular Magnum series tapered blades to the Paddle blades depending on if I am cruising or hitting the back country strips where leading edge protection in needed. Both are cut down to 76" dia. The regular magnum ones twist alot easier then the paddle ones simply because of the mass of the blades. Maybe one person has the tapered blades and the device works great and the other guy had the paddle blades and that makes it trip the circuit ????. I do find the idea you guys are crafting quite novel and useful. With a BIG disclaimer, I admit I am old school and on my experimental I run a non shunted ammeter gauge. Yeah, I know possible radio noise but I crafted my install using as many safeguards as I could and my set up is bone quiet... I like the idea of a quick glance to see if my charging system is working or not. Voltmeters are good but it takes a moment to do the math and the ammeter shows instantly whether I am keeping up with the load or not.. My choice, I know........ The best part of the ammeter gauge is when I change pitch I can look at the gauge and see the neddle deflection.   Slight movement shows it is twisting the prop. When I get to the end of the travel, which is pretty easy to guess when that happens, I see the major needle deflection, which is indicative of a locked rotor, then  I know I am at my stop. If I don't quickly get off the switch, in about 2 seconds the Ivo provided CB will trip.  Also keep in mind during the blade bending event the greatest load is when the prop is at each end of its twisting. The load on the motor is not linear at all throughout the entire range so that needs to be taken into consideretion.. IMHO. .02 cents worth.<G> 

Ben.

Ben Haas

N801BH

www.haaspowerair.com



--------

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