When those controllers were returned did they test good, or were they
blown?
I asked him to do ohmmeter measurements to eliminated direct shorts and
remove all extraneous devices from the lines. If he does that and the
controller has been changed and survived as good, and there is still a
problem, I would bet on an excessive amount of stray capacitance. The
current going into stray capacitance to ground is not measured by the
driver IC. It measures only differential current. It is possible that
it is small enough to not damage the IC but add just enough extra load
to current limit the supply causing it to drop voltage. This stray
capacitance is most likely in a transient suppressor he has added which
is the reason I suggested removing these. The effect of cable
capacitance is something that can be simulated very easily. I haven't
done that. It would require some measurements to characterize the cable.
Jerry, K4SAV
Jerry Keller wrote:
> Jerry.... we already tried another controller... and the same thing
> happens. Not only that, but it's reapeatable, time after time,
> according to the customer. Same thing happening on two different
> controllers says to me it's not the controller. Also, I don't think
> it's the antenna. I can't quite see what it is, or how it's
> happening, but I think it's something to do with the control cable or
> how that is routed. Capacitance, shorts, ground loop, not sure....
> but something like that kicks in when the load on the controller /
> power supply is ramped up to 4 EHUs. Than bring anything to mind?.
> 73, Jerry K3BZ
>
> ----- Original Message ----- From: "K4SAV" <RadioIR@charter.net>
> To: <towertalk@contesting.com>
> Sent: Sunday, June 10, 2007 10:53 PM
> Subject: Re: [TowerTalk] SteppIR problem
>
>
>> Don't take that antenna down just yet. It is much more likely that the
>> problem is on the ground.
>>
>> First some basic operational details that may help you understand
>> possible causes. Maybe if I give you enough information you will think
>> of something that you didn't describe and didn't think about as being
>> the problem. This is kinda long, but maybe it will be useful. You
>> probably don't need to know all this, but I don't know which part you do
>> need.
>>
>> It is true that the motors are current driven, and this current
>> regulation will work correctly provided there are no shorts on any of
>> the control wires. (It may work correctly if the short is only across a
>> motor winding.) There is no current limiting or any other control
>> mechanism to save a driver IC should there be a short of one of the
>> control lines to ground or to any other line. Without the controller to
>> radio serial cable there is no direct connection between power supply DC
>> ground and the case, however excessive current can be pulled going thru
>> the capacitance inside the power supply (about 15 nf between AC ground
>> and DC ground) should an output line be shorted to ground. With this
>> serial cable there is a direct connection between DC ground and earth
>> ground so blowing the driver is much easier. A faulty surge suppressor
>> can also be a problem. Usually what happens when there is a short of
>> any kind, the driver IC will blow, and the control box will go off. If
>> the box was on when this happened, the box will go off and may then come
>> back on. If the short occurred while the box was off, when turning the
>> box on, the LEDs will blink one time and the box will shut down. The
>> control box can be made to come back on, but there will no longer be any
>> control of the element that has the problem. Other elements may
>> continue to function.
>>
>> A DC voltage applied by a ground loop in the system should have no
>> effect on the controller if there are no improper loads on the control
>> lines out to the antenna. However if you have a transient suppressor in
>> the system and that loop voltage becomes high enough to break down the
>> transient suppressor, then it may damage the driver because then the
>> driver can dump excessive current thru the transient suppressor (kinda
>> unlikely).
>>
>> The box shutting down is usually the result of power supply overload,
>> causing the voltage to drop to a level which makes the control box
>> electronics malfunction. You should have a 33 volt power supply. If
>> that overload is a result of an improper load on one of the output
>> lines, you can bet that the box now has a dead driver IC. This load on
>> the supply is usually removed when the driver IC blows (so it shouldn't
>> shut down again), however I wouldn't rule this out entirely. It is
>> possible that the driver IC failed in a shorted state and did not burn
>> up traces inside the IC which is more common. The shut down could also
>> be the result of a bad power supply in which case the driver IC may
>> still be good.
>>
>> A cable that is too long or has a too high resistance should not cause
>> the controller to shut down. If the cable is long enough to drop enough
>> voltage such that the driver IC that does the current regulation has no
>> headroom left, and therefore cannot produce current regulation, the
>> element may not move to the proper position. If the length is marginal,
>> it might be intermittent, sometimes moving to the right position, or
>> maybe close. Settings may not be repeatable. This can cause some real
>> head scratching. This should not cause the control box to shut down.
>>
>> A similar condition can result if there is too much capacitance on the
>> control lines, such as may happen when someone uses a surge suppressor
>> that also contains a bypass cap. The current is regulated dynamically
>> by the IC. It pulses the lines by shorting them to the supply, measures
>> the differential current being drawn, and then opens the connection when
>> a preset current limit is exceeded. This is done a relatively fast rate
>> (I forget the frequency). The IC is expecting this current to gradually
>> ramp up as it should do when driving an inductor. If there is a cap on
>> the line, the current will rise very quickly causing the driver to turn
>> off, leaving the motor winding with not enough drive current. This will
>> cause the element not to go to the correct position, or it may only go
>> part way to the correct position. An MOV that has too low of a rating
>> or is shorted (even temporarily) will blow the driver IC.
>>
>> Now that you know a little more about how it works, maybe this will help
>> in diagnosing the problem. Now a few suggestions.
>>
>> 1. When you say that the addition of the fourth element "killed" the
>> antenna, do you mean it didn't work properly, or the controller box shut
>> down? If the control box is shutting down, then the problem can be
>> either the power supply or the controller. Since you have replaced the
>> power supply that leaves the controller. A one-time shut down of the
>> controller usually indicates a controller driver IC failure due to a
>> control line short, but a repeated shut down can indicate some other
>> problem inside the controller. The reason for this may become more
>> obvious after you read the other info below.
>>
>> 2. Disconnect the control box and do an ohmmeter test of all the
>> control lines to make sure there is an open circuit between all control
>> lines and ground, and check for an open between each line and ALL OTHER
>> lines except for the mate for that line.
>>
>> 3. Remove any surge suppressors or other devices you have attached to
>> the control lines.
>>
>> 4. You can check to see if elements are moving by going to the
>> Create/Modify menu and moving only one element at a time and observing
>> that the SWR changes when each element moves. The second director
>> should only cause a small movement in SWR, but any change at all
>> indicates that the element is moving.
>>
>> 5. If you have an oscilloscope, you can verify that the control box is
>> still working. Disconnect the control cable. Each motor is driven with
>> only two wires. Locate the pair used for the element you suspect may
>> have a problem. Put a load on the back of the control box on the lines
>> to be tested. Don't use the full load like the resistance of a motor
>> (it will get hot), all you need is something like 1K ohm between the two
>> lines. With the scope, measure the differential voltage on these
>> lines. You will see some funny looking waveforms with a peak amplitude
>> of twice the supply voltage. (The driver IC automatically switches the
>> polarity on the two lines, so the voltage measured differentially will
>> be twice the supply. ) If you don't have a scope, you can do a primitive
>> test with an AC voltmeter and measure the AC voltage on these lines and
>> compare what you get to other line pairs. If it is significantly
>> different, then it is likely that the driver IC is bad. It will be hard
>> to measure with a voltmeter because the average value changes a lot when
>> you switch bands (peak values are constant). If it doesn't change then
>> you know the driver is definitely bad. CAUTION: DO NOT LET THESE LINES
>> SHORT TO THE CASE. It will blow a driver IC! And don't connect the
>> scope ground lead to either of these lines, connect the scope ground to
>> the controller case. You need two probes.
>>
>> If you sent the original control box back to SteppIR, maybe you could
>> call them and ask if the returned box was good or had a bad driver IC.
>> If it had a bad driver IC, chances are that the one you have now also
>> has a bad IC due to a condition that has not been corrected. Oops, I
>> see you didn't indicate that you changed it or that one was sent one
>> back. Maybe it is time (after you check other stuff).
>>
>> 6. Now let me take a best guess at the problem. Since you have already
>> eliminated the power supply, if you do the tests to make sure you don't
>> have any shorts on the control lines, remove surge suppressors and other
>> devices, and it still shuts down, then it has to be the controller box.
>> Reason: The voltage to the control electronics is dropping too low or it
>> will not operate without a higher than normal input voltage. With no
>> shorts, there should not be an excessive load. So something inside the
>> controller is malfunctioning.
>>
>> Jerry, K4SAV
>>
>>
>> Bill Carnett wrote:
>>
>>> 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
>>> faltering....no 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
>>>
>>>
>>>
>>>
>>> ____________________________________________________________________________________
>>>
>>>
>>> Moody friends. Drama queens. Your life? Nope! - their life, your
>>> story. Play Sims Stories at Yahoo! Games.
>>> http://sims.yahoo.com/
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
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>>> TowerTalk@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>
>>>
>>>
>>
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>>
>>
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