Robert Barnard and Ray Woodriff Montana State College
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A LOW Cost Direct Current Source for the Laboratory
The need for a low cost source of variable direct current has been satisfied by the unit described in this article. Originally designed to furnish a maximum of 6 volts dc and up to 3 amps for electrodisposition experiments, these power supplies have also been used in place of batteries when performing oxidation-reduction experiments. The units require only a single 110 v outlet for operation and hencc can he carried to the students' work area. The apparatus consists of the power supply, a magnetic stirrer, and platinum electrodes. The advantage of the removable magnetic stirrer is that it can he detached for other uses and makes for a lower over-all investment in equipment, since the two units may not always be used together. The power supply consists of a full wave selenium industrial rectifier stack and selenium rectifier transformer, controlled by a powerstat auto-t.ransformer 4 A. FUSE
across the 110 v ac line input. The 3 amp output meter is protected by a 3 amp fuse. Since the ammeter is a current averaging device, no filtering of the rectified output is necessary. This reduces cost to a minimum (about $40) by keeping circuitry as simple as possible. The upright posts for carrying the dc current are made of copper tubing soldered to nuts which can be threaded onto insulated studs at.tached to the base. These can he removed for easier storage. The adjustable clips on the parts are bicycle pants clips with holes punched in them to allow them to slide on the uprights (Fig. 2). I
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Figure 2. Power supply with mounted binding port.; removable magnetic stir sits in between posts on top of cabinet and plugs into outlet on the ride. Figure 1. Circuit diagram. TI = Powerrtat autobmnrformer, Type 10. TS = Stoncor power trmwformer, RT 202. Selenium rectifler, type 310, Allied Radio #4A789. Meter 0-3 omp 21/2-in. rectangular, Simpson. Neon indicator light, Diaico Type 9 3 7 has built-in resistor for Ne 51 Neon lamp in 1 10 v oc circuit.
We acknowledge t,he assistance of the Electronic Research Laboratories at Montana State College, which contributed the circuit design of the power supply and constructed the units.
Volume 38, Number 10, October 1961
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