REFLECTOR:Re: IVO breaker

[Wayne Lanza]

Hi John,
  The poly switch resets itself when the power is removed. Depending 
upon the way
it is wired in your airplane it might be tripping at the end of travel 
and self resetting
without your knowing. This is one of my major reservations with a poly 
switch, now
consider that when it finally fails you will either loose control of 
the prop or it will
hard fuse and you will have no protection. I am familiar with the 
physics of this type
of semiconductor and feel it appropriate as an overload protection 
device in such
products as an electric tooth brush or screw driver - not anything 
critical! This is as
kind as I will be regarding the use of a poly switch in an aircraft. 
Nuff said...
  The reason that some guys find the breaker popped is because Ivo 
recommends
using a 15A breaker which is OK, but if you keep the switch depressed 
too long after
end of travel the current will increase to over 20A thus tripping the 
breaker. The real
answer here is not a larger breaker but proper use of the prop control.

-Which brings up your next question-

  To monitor end travel you could employ a current sensing shunt on the 
prop supply
wire (+12V). With the addition of a detector circuit on the shunt, you 
could have a
light come on when the current exceeds the normal run requirements. 
This should
be simple to design and would give you the benefit of indicating both 
travel limits.

Hope this helps,
Wayne
_________________________________________________________________

On Sunday, Mar 7, 2004, at 17:48 US/Eastern, John Dibble wrote:

> Thanks, Wayne,
>  I can't find a breaker anywhere so I guess the poly switch is it.  
> Deciding
> if I am comfortable is difficult.  I don't know anything about the poly
> switch.  Does it "trip" and reset itself, or simply limit the amount of
> current?  From a non-technical, experience point of view, it has been 
> in
> service for 285 hours and trouble-free during my 80 hours experience.  
> In
> comparison, others who have a breaker report the the breaker trips 
> sometimes
> and if not watched carefully the pitch may not be where it needs to be 
> for
> takeoff.  So from a practical point of view I think the poly switch is
> better although there may be some technical reasons why a breaker is 
> better.
>
> One improvement I would like is to have an indicator when the pitch is 
> fully
> fine (at at the travel limiter where the motor stalls) so I would not 
> have
> to operate the motor in the stalled condition in order to be sure I 
> have the
> pitch fully fine.
>
> John
>
> Wayne Lanza wrote:
>
>> HI John,
>>   Unless you find an obvious breaker, I would surmise the following 
>> from
>> the picture:
>>> The red component is more than likely a surge/spike suppresser, If so
>> it will be
>>      connected between the +12V and Ground terminals on the switch.
>>> The yellow device is probably a "Poly Switch", a type of solid state
>> circuit interrupter.
>>     If so, one lead goes to the +12V terminal on the switch & the 
>> other
>> will be connected
>>     to the A/C +12 volt bus. This makes the poly switch the only
>> protection that you will
>>     have on the prop. Not too wise in my book... I don't care for SS
>> breakers in an A/C.
>>
>>   If you are comfortable with this arrangement  - fine. If you decide 
>> to
>> update your A/C
>> with a real circuit breaker, mount a 15A-20A breaker in the instrument
>> panel and get
>> rid of the poly switch.
>>
>> Fly Safe,
>> Wayne
>> __________________________________________________________________
>
>
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