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Re: [TowerTalk] SteppIR problem

To: <>
Subject: Re: [TowerTalk] SteppIR problem
From: "W5LT" <>
Date: Mon, 11 Jun 2007 07:06:16 -0500
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Dick makes some good points.
Cable capacitance and shunt capacitance of supressors will both increase the
transient (and over-all average) current drawn from the power supply.

A previous similar problem of motors "missing" steps (ie antenna frequently
tuned to higher than intended frequencies), was traced to extra capacitance
at the in-line supressor.

Bob, W5LT

-----Original Message-----
From: Dick Green [] 
Sent: Sunday, June 10, 2007 10:22 PM
To: 'W5LT';
Subject: Re: [TowerTalk] SteppIR problem

I remember reading on the SteppIR reflector about the driver chips being
current sources and how this makes the cable length irrelevant, except for
added capacitance. I understand that added capacitance messes up the pulse
waveform, but I don't understand how increased resistance doesn't matter. 

OK, so the chips increase the current in the face of a higher resistance,
and the load sees the same current. Fine. But the chips have to get the
extra power from somewhere, and that's the power supply. If the resistance
is high enough to cause the current draw to exceed the capacity of the
supply, the first symptom is likely to be a voltage drop. I would be willing
to bet that the controller's CPU can't tolerate less than a certain supply
voltage, so it crashes.

I saw exactly this symptom with a switching power supply feeding my Tec-Tec
Orion. The pins in the power connector at the radio got deformed, presenting
an increased resistance to the power supply. When I transmitted, the bad
connection caused a lot more current to be drawn from the supply, the
voltage dropped, and the Orion's CPU crashed.

The mystery is that apparently SteppIR believes a 500' cable run is OK. If
they've tested that length successfully, then I would be suspicious about
the cable. Perhaps it's got more resistance than it should? It might not
take much. Is the motor winding resistance + expected cable loss within
spec? I don't recall offhand, but my 300' length has resistances in the
range of 23-26 ohms (can't remember exactly, but can measure again if it
will help.) About 20 ohms of that is the motor winding. If the resistance of
the 500-foot cable is even a few ohms higher, the current draw may be
exceeding the capacity of the supply.

Can you describe the cable run? Is it interrupted anywhere between the
controller and the antenna? If so, I would worry about high-resistance
junctions. It's also possible that there's been damage to the cable. I
wouldn't worry so much about water in the conduit as damage to the cable
when it was pulled. All kinds of things can happen when you pull cable --
excessive stretch, sharp bends, damage from adjacent cables (especially
hardline), etc. The damage should show up in the resistance measurements.  

I think Bob's analysis and suggestions below are on target, but before you
start experimenting with alternate power supplies, check the cable
resistance and clear the test with SteppIR. You don't want to void your

73, Dick WC1M 
> -----Original Message-----
> From: W5LT []
> Sent: Sunday, June 10, 2007 10:20 PM
> To:
> Subject: Re: [TowerTalk] SteppIR problem
> Bill:
> I too have been following your exploits, both here and on the SteppIR
> reflector.
> I still believe the issue is related to the power supply. As Mike M.
> pointed
> out, the motor drive is via current sources, thus the length of cable
> is of
> secondary consideration. Howwever, the symptoms you describe point to a
> current limiting effect in the power supply its self. That is, the
> system
> runs fine with less than 4 motors running, kick in all four and the
> symptoms
> show up, and the symptoms suggest a drop in the supply voltage (lights
> flicker, controller shuts down, etc.).
> Can you get a power supply capable of delivering more current, perhaps
> two
> 12V regulated supplies hooked in series?
> Also, you might try to actually measure the voltage and/or current
> being
> delivered by the power supply under load.
> If the voltage remains fairly constant when all four motors are driven,
> then
> it is not the problem.
> Bob, W5LT
> -----Original Message-----
> From: Dick Green []
> Sent: Sunday, June 10, 2007 5:05 PM
> To: 'James C. Garland';
> Subject: Re: [TowerTalk] SteppIR problem
> Bill,
> I've been following your exploits on the SteppIR reflector, too.
> Jim's suggestions are excellent, and I would do all of the tests he
> recommends. They're easy to do.
> Do you have a copy of SteppIR's Yagi Troubleshooting Guide? If not, you
> can
> download it from the SteppIR site. It has all the wiring checks,
> resistances, etc. You should check the resistance across each pair, and
> you
> should make sure there's no continuity with the shield.
> But I suspect there isn't a wiring problem. I think that would have
> shown up
> when you did the individual and group motor tests. For example, if one
> of
> the wires was shorted to ground, one of the individual motors would
> have
> caused problems. But do those resistance checks anyway.
> If Jim's tests don't reveal the problem, you could try connecting an
> ammeter
> in series with the power supply output to see how much current is being
> drawn by the SteppIR controller at idle and when running the antenna.
> The
> supply has max output of 2A, so it shouldn't be close to that. The
> spike may
> be too fast to see, so you might want to borrow a logging multimeter or
> a
> storage scope.
> If you can get AC out to your tower, and if you can interrupt the
> control
> line, then you definitely should test with the controller at the tower.
> That
> would eliminate the long control line.
> If none of the above reveals the cause, then I'd discuss the problem
> with
> SteppIR again. If they feel the cable length is causing too much
> current to
> be drawn from the power supply, and it's safe to supply more current to
> the
> controller, you could try a bench supply with variable voltage of at
> least
> 33VDC and current limited output up to, say, 3A or so. But I wouldn't
> do
> anything like that without clearance from SteppIR.
> If it's not a problem with the cable being too long or the input
> voltage to
> the power supply, then it would have to be some sort of motor problem
> that's
> marginal enough not to cause a big current draw by itself, but added to
> the
> three other motors pushes the power supply over the edge. That's
> probably
> the worst-case scenario (other than miswiring at the antenna), because
> you'll have to take the antenna down to fix it.
> Been there, done that!
> 73, Dick WC1M
> > -----Original Message-----
> > From: James C. Garland []
> > Sent: Sunday, June 10, 2007 5:13 PM
> > To:
> > Subject: Re: [TowerTalk] SteppIR problem
> >
> > Bill, that's quite an interesting mystery! Evidently, you're
> > overloading the
> > power supply and it's shutting down, so I agree with Jerry's
> > assessment.
> > However, from what I understand, the stepper motors are current
> driven,
> > not
> > voltage driven. That means that even a short circuit in a pair of
> wires
> > to
> > one of the stepper motor windings shouldn't overload the power
> supply.
> > And
> > if you've checked all the resistances between pairs and they'r okay,
> > and if
> > there's no resistance across pairs, then that pretty much rules out
> any
> > problem with the antenna. If there was an antenna problem, then the
> > shutdown
> > would occur always when the same motor was energized. But that's not
> > what
> > you're seeing.
> >
> > Did you check to make sure there's no resistance between any of the
> > control
> > cable pairs and the control cable shield?
> >
> > Have you checked your AC line voltage? Your symptom could be
> explained
> > if
> > the voltage is too low. Also, by any chance is your power supply
> > plugged
> > into a GFI, UPS, or surge-protected circuit? One simple test would be
> > to
> > measure your AC line voltage when you power up the controller and see
> > if the
> > voltage sags.  Also, if the power supply is plugged into an outlet
> > strip,
> > then you could try changing it: it might be a faulty surge suprressor
> > or
> > switch in the outlet switch with some resistance that's dropping your
> > line
> > voltage.
> >
> > Let us know what you learn, and good luck!
> >
> > Jim W8ZR
> >
> >
> > -----Original Message-----
> > From:
> > [] On Behalf Of Bill Carnett
> > Sent: Sunday, June 10, 2007 9:42 AM
> > To:
> > Subject: [TowerTalk] SteppIR problem
> >
> > Greetings to all Tower Talkers,
> >
> > A very wise man and fellow TT (K7LXC) suggested I post
> > my challenge here to the group...maybe somebody will
> > have a new idea that I've not explored.
> >
> > Last week we put up a new 4L SteppIR with a 40/30
> > dipole.  The antenna is approximately 500 feet from
> > the shack.  SteppIR control line is used, continously
> > without any accessories inserted, running through 3
> > inch conduit (not that that makes any difference).
> > Prior to lifting it in the air I found that a problem
> > existed.  When attempts were made to change bands or
> > even frequency on the same band, the control box went
> > dead.  Simultaneously, as the box died, the "on"
> > indicator light on the pwr supply went out.  A second
> > later the pwr light came back on; the led "lights" on
> > the control box flashed once but the box remained off.
> >  The box could be turned back on, but the same
> > sequence occurred if a band/freq change was attempted.
> >
> >
> > Immediately all of the wiring and continuity was
> > checked with the antenna...all ok.  Spoke with Jerry
> > at SteppIR and we proceeded to change first control
> > box....before I realized the pwr supply was
> > change.
> >
> > The next step was to attempt to run each motor
> > individually and in groups.  Each motor ran
> > individually without problem.  Adding the 2nd and 3rd
> > motor caused no problems....the yagi functioned fine.
> > The addition of the 4th motor (didn't matter which
> > sequence), consistently killed the antenna. On
> > occassion it would all seem to work for a couple of
> > band changes but never more than 1 or 2 minutes - with
> > all 4 motors running. So, with up to 3 motors
> > running...all ok, with all 4, no go.  However, this is
> > a 4 element yagi.  After speaking again with Jerry, I
> > was reassured that the problem was simply a power
> > supply and all will work fine....thus the long
> > scheduled antenna raising event went forward as
> > scheduled.  Needless-to-say, the replacement power
> > supply did not correct the problem.
> >
> > Prior to erecting the yagi I extended the elements to
> > 14150 so it can be used as a monobander...but that
> > will only bring temporary happiness.  A power supply
> > (3rd) was "hand picked" by the SteppIR engineers,
> > sent, and tested this morning.  Basically the same
> > problem.  It did seem to work briefly then shut
> > down....exactly the same as before.
> >
> > So, I'm looking for ideas that have been overlooked.
> > Yes, I should have listened to my gut, rather than the
> > "experts" and canceled the raising until all problems
> > were fixed, but that can't be undone.  If this beast
> > must be lowered, I'm a bit reluctant to put it back up
> > after this experience.  Yes, all antennas have
> > problems but it would be less $$ to replace it at the
> > time of lowering rather then taking down, bring the
> > crane back and forth, etc.
> >
> > Sorry for the long-windedness of this but any and all
> > thoughts are appreciated!
> >
> >
> >
> > 73, Bill
> >
> >
> >
> >
> >
> _______________________________________________________________________
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