December 31, 2012

Project: PAiA P60 Regulated Power Supply Kit

Over the  years, we have built a number of electronic devices that require a 9v DC power source.  We typically keep a box of 9v batteries on-hand though more often then not we find our cache of batteries depleted.  During a recent trip to the local grocery store we were shocked to see name-brand 9v alkaline batteries selling for nearly $5/each.  This inspired us to build a dedicated 9v power supply for use on the bench with goal of reducing our use of overly expensive 9v batteries in the coming year.  Perhaps that is a worthy New Year resolution for us all.

Regulated or unregulated?
An unregulated DC output power supply (e.g. most common wall-warts) delivers voltage without voltage control.  The DC output voltage is dependent on a couple of factors: 1) the voltage reduction transformer; 2) the amount of current used by the device receiving the power (also called load).  An easy way to identify if a wall-wart is unregulated is to simply measure the voltage without a load.  If the voltage is several volts higher than the rated voltage on the device then it is unregulated.  The typical wall-wart is often also unfiltered making it unsuitable for radio related projects.

A voltage regulator controls a power supply such that it delivers a constant voltage output over a variety of load currents (up to a maximum load).

We have a junk box full of transformers and could have had an unregulated power supply for next to nothing.  However, the ability of delivery exactly 9v for our creations was appealing and not very costly ($10 to $25 depending on the kit).  The cost of building a 9v regulated power supply is quickly recovered by simply avoiding the purchase of a few 9v batteries.

Linear or switched regulator?
Regulated power supplies can be built with linear or switched regulators.  We decided we were indifferent regarding this question.  Either would work fine for our simple needs.  We did a quick search of various kit makers to see what was offered in the way of regulated power supplies.

PAiA P60 Regulated Power Supply Kit
As a youth in the 1980's we had always enjoyed looking through the PAiA catalog of kit electronic musical instruments.  In our eyes, PAiA had the coolest looking gear hands down; though we lacked the means necessary to buy and build it.  So during our search of kit manufacturers, we were delighted to find that PAiA is still in business offering a variety of electronic kits.  A quick review of the PAiA website is all it took to find a low-cost little regulated power supply kit that fit our needs perfectly: PAiA P60 Regulated Power Supply Kit

The P60 kit provides a circuit board and all components except for the 3-pin (TO-220 package) voltage regulator.  This allows the builder to select the specific regulator / voltage that meets his needs (5v to 24v).  Input voltage can be either AC or DC and needs to be 2v or 3v higher than the target output voltage (depending on the regulator chosen).  We liked the fact that terminal blocks were provided for both input and outputs.  This would make it very easy to connect and disconnect from various projects.  We also appreciated the on-off switch and power-on LED indicator.  The power supply is rated for up to 1A which would be more than enough for our 9v projects.  We had a couple of 7809 voltage regulators on-hand so this kit would be a perfect fit.

The kit was a breeze to assemble following the guidance provided by the kit product sheet.  We decided to substitute a blue LED for the one that came with the kit out of personal preference.  We are Anderson PowerPole connector enthusiasts so it was natural to wire up an Anderson PowerPole to the input block.  This would make it easy to connect the to our 13.8v DC Astron RS-35M power supply that we use in the shack or in the car using our home-brew car power to Anderson PowerPole adapter.

On the output block we connected one of our home-brew 9v battery clips.  This would make it easy to connect to our electronic 9v creations.  To use a battery clip as a power source (simulated battery) requires reversing the polarity.  That way when two clips are married together the voltage polarity will be correct. 

The power supply has worked flawlessly in our shack since it was built.  We really appreciate the convenience and economy of powering up our 9v creations free of the hassle and expense of 9v batteries.  We are using our 9v power supply at the time of this writing to power KC2VSR's 3D Xmas Tree which gives a little holiday charm to the shack.  We haven't mounted it in a case so far.  Looking for something that is both free and suitable to repurpose.

By the way, we found an excellent resource for power supply terminology.  It is interesting to browse through the page.

Good DX and 73, NJ2X

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