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Author Topic: astron crowbar question  (Read 261 times)
KG6BRG
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Posts: 119




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« on: December 15, 2007, 06:29:31 AM »

My 35 amp astron supply went into over voltage protection today (crowbar).  It was on, and connected to an HF and VHF rig that were (the radios) off.  I was transmitting on my ts-520s and when I looked over at the astron's meters I thought I was seeing things, the voltage was showing 2 volts or so.  I shut it down and it reset and all seems to be well now, but I am wondering why the crowbar circuit triggered?  My only thoughts are a spike of some kind on the mains or possibly stray RF from my random wire, although I've never have a problem before with the same set up.  Any thoughts will be welcome. cheers, scott.
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KA5N
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Posts: 4380




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« Reply #1 on: December 15, 2007, 07:11:31 AM »

I think your supposition is correct.  The crowbar is triggered by a thysistor (or other kind of SCR) and all SCR's (silicon controlled rectifier) are susceptable to spikes.  Once triggered they lock on.  Not good to have a lot of RF floating about the shack.
Allen
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W5GNB
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Posts: 419




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« Reply #2 on: December 15, 2007, 07:15:41 AM »

My bet would be stray RF from your random wire antenna tripped the unit off.  If things reset ok, it would appear there was no damage done.

You probably need to check the antenna system and be sure that you don't have srtay RF in the shack or getting into the wiring of the house.

You can test things using a dummy load and see if it is perhaps a overcurrent problem that might be developing within the power supply but I would think RF from the random wire is the culprit.

73's
Gary - W5GNB
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KG6BRG
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« Reply #3 on: December 15, 2007, 10:58:16 AM »

Thanks for the conformation of my theory, and yes running a random wire into the shack is always bit of a tight rope as far as stray RF.  That being said, I've been running this current set up (with tuned counterpoise wires and a good earth ground) without any trouble before.  I was working on, and keying a TS-520 with the top off, perhaps that may have been the difference.  Since the radios connected to the Astron were off, I don't really know when it crowbared.  Well thanks again and I wonder if a capacitor across the SCR may help prevent this, or not.  cheers, scott.
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WA9SVD
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Posts: 2198




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« Reply #4 on: December 17, 2007, 06:31:53 AM »

Last things first:

    A capacitor "across" the SCR probably won't help false triggering.  Depending upon the actual circuit used by Astron to trigger the over-voltage condition, a bypass capacitor placed between the SCR gate and ground may help, but might also disrupt operation by increasing the time required to trigger; if the surge or stray RF is getting into a different part of the circuit, that might not help at all.  (A value of about 100 pf might not do any harm, but might not help.)
    You might have an intermittent or loose connection in your antenna or antenna system that may change the RF radiation pattern and cause occasional RF in the shack.  Or, it was just a fluke.  If the problem doesn't return, just chalk it up the the "ghost in the machine."
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