Film-Tech Forum ARCHIVE: Installing Kelmar AT-1200 reverse scan

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Posted by Tom Wienholt (Member # 1510) on 09-29-2003, 07:41 PM:

When installing a Kelmar AT-1200 reverse scan reader, can the existing exciter power supply be used as a power source or is it necessary to use a different power supply? Any help would be appreciated.

Posted by Mark Gulbrandsen (Member # 72) on 09-29-2003, 09:35 PM:

The Kelmar scanners are fine scanners and my 2nd choice for reverse scanners. All of them that I've installed had a seperate powersupply. There is the LED supply, and then plus and minus DC voltage for the preamp thats mounted on the pickup. I'm not aware of any other version of the Kelmar scanners than this.

The BACP scanners can be powered by the old exciter supply if desired, whoever many of them are getting old and may give problems in the not too distant future. I usually opt for the wall wart that comes with it. The BACP scanners are available through Ultra Stereo Labs dealers. A quick call to Kelmar in the morning should answer your question. Ask for Thomas.
Mark @ CLACO

Posted by Gordon McLeod (Member # 33) on 09-29-2003, 10:21 PM:

Why would one want to use the old supply
The LED is a current source and needs current limiting and the preamp is bipolar in effect

Posted by Tom Wienholt (Member # 1510) on 09-30-2003, 03:01 PM:

On the installation drawings, it shows that an exciter supply should be hooked up to the power module which then distributes power to the preamp and the LED. Am i missing something?

Posted by Matt Zeiner (Member # 1914) on 09-30-2003, 03:09 PM:

Not if the unit you are installing has the letters "DCPM" after the model number - That unit uses the existing supply with a box containing 2 add-on switchers - one for the LED and one for the bi-polar supply for the preamp. They work great as long as you are not using a USL exciter supply - The Kelmar switchers will not function unless they see at least 10 volts, and the USLs are limited to 8V. Changing R3 in the USL exciter supply to 3.9k will allow you to get the necessary 10V out of it.

Posted by Tom Wienholt (Member # 1510) on 09-30-2003, 08:08 PM:

So now im being told that the existing exciter supply is used for installation.

Posted by Mark Gulbrandsen (Member # 72) on 09-30-2003, 10:01 PM:

I checked and Kelmar now does supply an invertor PCB so one can power the sanner fomr an existing exciter supply. One would assume this is in response to the BACP design of being able to run the scanner off of just about anything except a can of beer. C.E has yet to take this approach...thankfully.

On the BACP one has to be very careful of the no-load DC level as if its over 14 volts it'll blow the preamp/inverter card out instantly.

Why anyone would want to power a modern device like this off of a sooner or later to fail DC power supply I'll never understand. Using a wall wort not only eliminates a very unreliable and possibly old power supply from the chain, but it also makes repairs easier and safer to perform.
Mark @ CLACO

Posted by Tom Wienholt (Member # 1510) on 09-30-2003, 10:15 PM:

quote:
Using a wall wort not only eliminates a very unreliable and possibly old power supply from the chain, but it also makes repairs easier and safer to perform.

What is a wall wort?

Posted by Mark Gulbrandsen (Member # 72) on 09-30-2003, 10:34 PM:

Its one of those little square plug in the wall transformers. Its also an easy way to UL listing if ya get a good one.
Mark

Posted by Tom Wienholt (Member # 1510) on 09-30-2003, 10:38 PM:

Where do you buy these plug-in transformers and what type is needed?

Posted by Matt Zeiner (Member # 1914) on 10-01-2003, 07:38 AM:

I've used Radio Shack's units in the past when the customer's existing supply is garbage - they sell a 12V 1A wall wort that will work fine. The DCPM units don't really care what you feed into them as long as you provide at least 10VDC. As for the use of existing exciter suppiles in general, I don't really see the problem here unless the customer has some REALLY old kneisley or something. The Kelmar supplies fron the AS-7200 series units are extremely reliable and common - there is really nothing in them that can go. As a matter of course we change out the 3055 transistor and capacitors before installation of the reverse scan - costs about the same as the wall wort, and will still provide AC backup power (yes - the DCPM does work nicely on AC backup) so if the wall wort goes, the whole thing has to be replaced. If you use an existing supply, at least you have backup in case of failure. The simplicity of installation can't be beat - your exciter switching is alredy in place. Also - a lot of our customers have the newer USL Supplies built into their monitors/processors - although they require slight modification, they are pretty robust units and good for 50W dissipation.

Posted by Mark Gulbrandsen (Member # 72) on 10-01-2003, 08:23 AM:

I once had ALOT of problem with Kelmar Exciter supplies. That was when the new switching version first came out though. Personally in my experience its far better to keep things simple, thats why I prefer the wall wort.
Mark

Posted by Tom Wienholt (Member # 1510) on 10-01-2003, 09:50 AM:

Thanks for your help.

Posted by Steve Guttag (Member # 268) on 10-12-2003, 11:03 PM:

I'm not a big fan of wall-warts and don't plan to start using them! The Kelmar converter unit will work off of AC or DC so even if your old supply craps out in DC mode...AC-emergency should still keep you going.

I also have a thing against DC-DC converters so I'd rather use a nice well-designed power supply...like the CE 30 or 40 series units.

Steve

Posted by Matt Zeiner (Member # 1914) on 10-13-2003, 03:08 PM:

I hear ya, Steve - I just don't trust those inverter circuits. For the most part, they seem to work reasonably reliably... Are you certain that the CE supplies don't use switchers? I think they do, but could be wrong.

Posted by Tom Wienholt (Member # 1510) on 05-09-2004, 11:26 PM:

I recently purchased a wall wort transformer to use as a power supply for an LED reader. One of the wires is white and the other is white with a gray stripe on it. So which wire is the + and which is the - ?

Posted by Michael Schaffer (Member # 1204) on 05-10-2004, 04:49 AM:

I usally plug the wall wart into the convenience outlet and then rewire that to the motor circuit so that it only comes on when the motor is running. Other ideas?

Posted by John Pytlak (Member # 331) on 05-10-2004, 05:55 AM:

quote:
I recently purchased a wall wort transformer to use as a power supply for an LED reader. One of the wires is white and the other is white with a gray stripe on it. So which wire is the + and which is the - ?

You can check polarity with a DC voltmeter.