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Re: [TowerTalk] SteppIR cable

To: "'shack'" <noddy1211@sbcglobal.net>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] SteppIR cable
From: "Joe Subich, W4TV" <w4tv@subich.com>
Date: Mon, 11 Jun 2007 02:45:01 -0400
List-post: <mailto:towertalk@contesting.com>
Mike, 

I would bet that the switching supply is shutting down because 
of a highly capacitive load and very high current peaks. 

The stepper motors operate on square wave drive.  The controller 
is feeding 8 pairs of wire all with capacitance and all in 
parallel as far as the power supply is concerned.  

A 500 foot control cable is certainly long enough to act as a 
transmission line since we have an "RF" control signal.  I do 
not know what the pulse frequency so I can't guess what kind of 
impedance transformation might be happening. 

If it were me, I would replace the switching supply with a 
simple analog/linear supply using a 24 volt transformer, 
a 5 Amp bridge rectifier and 2000 uF of filter capacitance. 
With no electronic shutdown/foldback one could confirm that 
the problem is higher than expected peak currents causing 
the switching supply to shut down. 

73, 

   ... Joe, W4TV 
 




> -----Original Message-----
> From: towertalk-bounces@contesting.com 
> [mailto:towertalk-bounces@contesting.com] On Behalf Of shack
> Sent: Sunday, June 10, 2007 11:12 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] SteppIR cable
> 
> 
> I still think it is the length of the cable. Has anyone tried 
> to measure
> current and voltage when under load e.g. when all four elements are
> being adjusted?  I think there is a voltage drop, which is why the
> controller malfunctions.
> 
> Wire has resistance and a lot of wire has more resistance which has to
> be overcome.
> 
> Have the Steppir folk actually tried driving a four element with 500
> feet plus of wire?
> 
> Mike
> 
> -----Original Message-----
>  
> Several mentions were made that it was related to the 500 feet of
> control 
> cable, but SteppIR's engineers say the longer cable would 
> actually help 
> reduce the load, so cable length has been ruled out.
> 
> I dont know how the longer cable would help.
> I would look at the size of the cable. SteppIR makes two size, one for
> short runs and one for long runs.
> 
> GL  K4WZ   Ron
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