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Author Topic: Astron 35A power supply.  (Read 3859 times)
KB3UZF
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Posts: 21




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« on: August 05, 2010, 09:00:45 PM »

Hello all....TONS of questions here...new HAM (KB3UZF).  I bought a Astron 35A power suppply off eBay.  I'm powering a 2-meter mobile (Kenwood 7950 also off eBay) with it.  I got a voltage meter (also off eBay), digital that Installed into the face of the Astron. The Kenwood seems to operate properly. 

My question is....  When I first turn on the Astron, the voltage reads 13.83 volts.  After running with a load, the voltage drops to about 13.64 volts.  Is this a cause for concern???  Should I attempt to 'adjust' the voltage?  I have a guide on 'how to do it', but I'm not sure if it needs to be done?

Thanks for any input...

Larry
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KA5N
Member

Posts: 4380




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« Reply #1 on: August 06, 2010, 04:09:43 PM »

You are talking about 0.19 volts.  That small difference won't make any difference to any of your ham gear.  How large is the load you are powering?  Where are you measuring the voltage?  How accurate is the meter?  Does the voltage stay the same after the initial change (it might just be a warm-up thing).
You will find that the voltage at the power supply's terminals will be greater than the voltage at the input of the powered device  (voltage drop in the power cabling).
I think you are creating a problem where none exists.  Adjust the voltage if you want to, it is just a simple matter of turning a pot.  If you turn it up too much you will cause the crowbar circuit to engage and then you won't have any voltage. 
Good luck
Allen
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KB3UZF
Member

Posts: 21




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« Reply #2 on: August 06, 2010, 08:54:02 PM »

Currently I'm only powering a 2 Meter mobile rig transmitting at 5 watts.  I hooked the meter directly to the interior pos and neg posts of the Astron.  I'm not sure how accurate the meter is, it's a 'red' meter from China.  The drop from initial turn on to the 13.64 reading occurs over approx 20 mins.

This is no big deal.  I'm not 'itching' to adjust the output voltage, I was just curious if this was normal and would have any performance interactions with any connected equipment.  Picture link is below..

http://i932.photobucket.com/albums/ad165/lfeissner/0806102335.jpg

Thanks!
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K1CJS
Member

Posts: 6045




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« Reply #3 on: August 08, 2010, 12:07:21 PM »

You've got to remember a couple of thing.  Every time you have a connection where a wire is terminated to another wire or connector, you're going to have a slight voltage loss due to connection resistance.  There are a few terminations on every harness, at the ends of the wires, the fuse connectors, powerpoles or other connectors, etc.  The second thing to remember is that where there is resistance, there is a slight heating--not enough to be noticeable, but there anyway.  As the connection is heated, it may increase the resistance slightly, and the result is a slight drop of voltage.

Now that the explanation is out of the way, the simple answer is--don't worry about it.  Unless the connections are VERY sloppy or loose, nothing bad will happen.
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WA7KGX
Member

Posts: 104




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« Reply #4 on: August 11, 2010, 04:59:40 PM »

The RS-35A is a solidly built power supply that loafs along
driving a 5 watt rig.  But if you use it anywhere near full
ratings, it needs to be very well ventilated.  Don't put it
on a lower shelf. Keep it out in the open.  A small fan
might be needed for digital modes with a 100 watt radio.

The crowbar may trigger in high RF fields.  This is an
awesome event.  I added RF bypasses to mine.  Be careful
the added caps do not make the Astron unstable.
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