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IVO Prop Motor Current Limiter and Electronic CB

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat May 08, 2010 12:44 pm Post subject: IVO Prop Motor Current Limiter and Electronic CB

Somebody was willing to build the circuit I proposed and

was asking about sources for the power mos-fet called out

on the drawing. I left that note on my computer in Wichita

so I'm sort of broadcasting this response in the blind . . .



I used Digikey as the first-source for any drawings I

publish. They stock an extensive collection of International

Rectifier parts. You'll be able to find the IR mos-fet

here . . .



http://www.digikey.com



Bob . . .

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Dennis Glaeser

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

Posted: Sat May 08, 2010 7:25 pm Post subject: IVO Prop Motor Current Limiter and Electronic CB

I made the original circuit that Bob posted.  I got all the parts from

DigiKey, including the IRFP 3703.

I was finally able to test that circuit today.  It worked exactly as

predicted.  With only the 0.1 ohm resistor, the current was limited to about

6 amps. This did not allow the motor to go as far as desired. So I added the

parallel 0.5 ohm resistors one at a time.  With both in place, it allows a

bit over 8 amps, which is where the motor just starts to strain. This is

also about the same place where the reed switch triggers.

The mosfet does get rather warm, but only if the switch is held longer than

normal. 



I also plan to build the Electronic CB circuit. When it was published, Bob's

said to wait until others had a chance to review and comment before

building, so I haven't begun that process yet.



Dennis Glaeser

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Dennis Glaeser

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

Posted: Sun May 09, 2010 5:16 pm Post subject: IVO Prop Motor Current Limiter and Electronic CB

The mosfet does get rather warm, but only if the switch is held longer than

normal.



    I've had a lot of folks become concerned with transistors

    that got "rather warm" but without putting some form of

    instrumentation on the device and then accounting for

    thermal resistances in the heat-energy transfer path,

    "rather warm" is a rather loose quantification term.

    There are instances where the surface temperature of

    a power device can get up to "sizzle-spit" temperatures

    and still be within operating limits. So if your finger-test

    of the device did not send you looking for the burn

    ointment, then there's a high probability that the

    transistor as installed and operated is going to be

    okay . . .



----> I didn't think to measure the mofset temp, but it definitely didn't 

	get 'sizzle-spit' hot in my tests. I'm sure it could if the switch

were

	held long enough.  I'll measure temps at my next opportunity.

-----



I also plan to build the Electronic CB circuit. When it was published, Bob's

said to wait until others had a chance to review and comment before

building, so I haven't begun that process yet.



    Go ahead an 'brass-board' it if you can. I'm still to tied

    up with table saws and paint brushes to spend time at

    the bench.



    Do you have access to a 'scope? It would be interesting

    to fine-tune/verify the value of the capacitor to make the

    circuit trip in 200-500 milliseconds after the

    green light comes on.



----> I will do that, but it will be a little while before I can get to it.

	Work and other commitments definitely get in the way of the fun

stuff.

	I don't have a 'scope, but may be able to find one in my EAA

chapter.

----



    Thanks for your help in the development effort.



    Bob . . . 



----> I'm the one who is the recipient of YOUR work 



	Dennis

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon May 10, 2010 7:41 pm Post subject: IVO Prop Motor Current Limiter and Electronic CB

At 09:05 PM 5/10/2010, you wrote:

 	  Quote: 	
		  



I may be mistaken, but I thought the Ivo prop had brushes that were 

rubbing all the time the prop was turning -- I.e. they transfer 

power from the stationary part of the engine to the rotating prop, 

which has the motor mounted on it, (which then rotates with the prop).


	


   Good questions. No doubt there are two sets of brushes.

   One that conducts power from the stationary airframe and

   rotating pitch motor assembly, a second set of brushes

   run on the commutator within the permanent magnet motor.



   So I need to expand my own question to ask which of

   the two brush sets is demonstrating a service-life

   issue.



   Bob . . .

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dennis.glaeser(at)hp.com
Guest

Posted: Tue May 11, 2010 11:11 am Post subject: IVO Prop Motor Current Limiter and Electronic CB

I will validate that it is the prop brushes, not the motor brushes that are the limited wear items.

For those who haven't seen the IVO, the contact rings behind the prop are just aluminum disks. The brushes are a metallic material impregnated with carbon/graphite.  The aluminum contact surface becomes coated with the carbon/graphite material, which improves the wear characteristics with time.



The motor assembly has a planetary gear train which drives a jack screw.  A collar on the jack screw engages pins on an arm attached to the torque tubes in the prop.  The prop is a composite material that flexes as the torque tube is twisted, providing the pitch adjustment.



IMO, the gear train is the most vulnerable part of the system, primarily because the 'pitch stops' are rubber washers that cushion the collar as it jams against the end plates!  The motor doesn't see nearly the mechanical strain that the gears do (I can't speak to the electrical strain of being mechanically stopped).  A 'motor' failure may well be a gear train failure, not a failure of the electric motor itself.  I also experienced such a failure, due to an installation interference.  I did not disassemble the unit, but I did 'loosen' things to try to peek inside.  It is a very tight assembly, so I didn't see much. I did see the motor brushes, and they, and the commutator, showed no signs of distress.  I wouldn't be surprised that special jigging/tooling is required for assembly, which would explain Ron's position.



This is why I like the idea of the electronic limiting feature of Bob's circuit.  The reed switch is a huge improvement over guessing where the prop is set, or using the provided CB as the ultimate 'stop'.  It lets the user know when the limit is reached, but doesn't prevent abuse (intentional or inadvertent).  The electronic CB prevents the abuse, and can only help improve the life of the gear train and electric motor.



The prop brushes will still wear as usual 



Dennis Glaeser



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

From: n801bh(at)netzero.com



To clarify things.....

Bob, it is the brushes that transfer the power to the prop motor on the 

hub,,, not the actual pitch change motor itself.  When the first motor f

ailed I did discuss this with Ron (at) Ivo and he was insistent not for me 

to open the motor and do an autopsy on it but to just send it back. Which

h I did and he promptly replaced it back then. I don't know if it tricky 

to open up, or there is some proprietary stuff in it he doesn't was people to see or what.

do not archive.



Ben Haas

N801BH

www.haaspowerair.com

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