Dgj

Shown in position to charge 4 cells

* Indicates Unmodified DrNiCad Part on Circuit Board

Fig, L Modifications to accommodate 12 cells.

Photo B. The interior, with modifico!ions* Sole the extra aluminum strips tntiwd to the heat \ink of the discharge transistot tQ3). The power supply board is mourned below the Dr. NiCad board with the transfonner to war.

supply between 12 and 14VDC capable of Lii least 1.5A. Most hams have such a supply in the shack already.

I wanted to have ihe power supply and controller all in one case. 1 also wanted to charge up to 12 cells, so I decided I would need to provide a slightly higher voltage. The instruction hook indicates some problems can be encountered when too high a voltage is utilized with a low-voltage battery pack. With this in mind, I decided to built: a supply that could provide a high or low voltage depending on uhat I intended to charge.

The circuit in Fig, 2 shows ihe power supply circuit. It will provide approximately ItV in the "low" position and !SV in the "high" position, The regulator chip, U I, should be a LM3 I7T. The "T" indicates the capability of I.5A. This is in the full-sized TO-220 case rather than Ihe ¿*MP" series with Ihe smaller tab (rated 0.5A). Use a heal sink with heat sink compound on UI.

! he transformer should be rated approximately 1SV at L5A, I used a 24V transformer (from my junk box) with some secondary turns removed to bring il down to about 20V. Radio Shack™ 273-1515, rated ai 18V and 2,0A would be ideal, If you won't be charging a pack ol more than ten cells, Lhe Radio Shack 12V, 2A transformer (RS 273-1511) will do the job for TL In this case you will not need the sw itch or R3. R2 should be replaced with a 2.0k unit, which should result in a power stippl> delivering approximate!} 12V. 11 the 2.0k resistor is increased slightly in value, the voltage will increase correspondingly.

My unit worked great when ! fireO il up. I charged up land discharged) several packs, then tried a pack that was *"dead.,h By cycling lhe pack several times over a few days, as described in the instruction book, the pack was revived!

I tried another "dead" pack. No matter how many times I tried cycling, Ihis pack remained dead. Three cells out of seven seemed to he shorted. Then I tried an old trick of applying a heavy dose of current to the three shorted cells. I very momentarily applied a full 12V from a lead-acid hatterv to each individual cell, j

This seemed to cure ihem. Then 1 c>cied them several limes with the good doctor Presto!—another pack restored. Caution: If you try the heavy-dose of-cur-rent trick, he very careful! Cells can rupture. Use long leads—and place the cells and battery around the corner, or behind something, so you're out of the line of Fire should one blow up,

1 am very impressed with Dr. NiCad. This is something that should be in every shack, My unit has paid lor itself already by restoring two dead packs—and 1 expect many more years of service from the good "Doctor/'

The Dr. NiCad kit (DN-1 @ $49,95 for the kit only) is available from Ramsey Electronics, Inc., 793 Canning Parkway, Victor NY 14564. The modification parts 1 used are: SWT - Single Pole. 12 position. Radio Shack #275-1385 T1 - Radio Shack #273-1515

Radio Shack 273 1515
Photo C\ The finished project,

D4 - One 2A, 50V bridge unit or lour RS-276-1661 (3A) UI - LM317T (Digi-Key) S3

Neuer shy die

Continued from page 5

need is to elect some new ypunger hams to the ARRL Board to kick that stodgv old or* ganizatioD in the rear to get it moving And [hat's entirely up to your club, which is probata > also run b\ a bunch ol old-timers, mired in 1930s thinking,

} our choice tor amateur radio; grow or go,

Xtal Sets

Have \ou seen any snot-no sod kids around who might be helped on their downward path in life b\ an injection of the hamitis virus.' Ibis is one \irus that not even ihe bioelcctrifier can cure, and it's simple to administer, even in full sight ol lhe parents. How about sucking lhe unsuspecting pmtonerd in with a very simple crystal radio that can be built in about an hour? The parts? Some Tinkertoy spools to support a loop antenna, wire for the antenna, ;i pair ol headphones from the kid's Walkman™, a diode and a tuning capacitor made out of aluminum foil?

Well, thai s about what led me into a lifetime of hamming. \n angel, or devil, depending on your viewpoint of me, brought a ho\ of old radio parts into the Dutch Reformed Church 1 was attending when I was 14. He gave them to m> best Friend, A Hie, who had zero interest in such junk and dumped em on me. 1 found a circuit in Popular Mechanics that used some of lhe parts to make a ei^ar box radio Unfortunately, il worked and 1 was hooked For life. You'll find 15 easy-to-build crystal radio projects in ihe new Crystal Set Projects book from The Xtal Set Society. Box 3l)2h, St. Louis MO 63130. Some great stuff here for science fairs, or even for science classes.. I he 160-page book is $17.50, including s/h. Be nn angel or devil and get busy poisoning some dirty little minds with ihis book.

Oli Oh Ozoned

A reader sent me more data on the ozone

Contifutixi on page 30

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