$5.00 variable voltage controller

[Brian Henselman]

Thanks Harvey,

Ever thought of marketing these?  You've sold the design pretty well, now
would you be interested in making some up for "electronically challenged"
people like me?  Seriously, let us know how much you would want to build
some of these puppies?  It sounds like you've found an inexpensive design
that should be very reliable.  It's just a thought.

Cheers,
Brian Henselman,RPT


-----Original Message-----
From: harvey <harvey@greenwood.net>
To: pianotech@ptg.org <pianotech@ptg.org>
Date: Saturday, October 09, 1999 12:56 AM
Subject: $5.00 variable voltage controller


>Below is a "recipe" for a low-cost, low-tech variable voltage controller
>for electric hammer irons, etc. Southern translations included where
>applicable.
>
>Disclaimer: The following is not and would not be approved by OSHA. For
>that matter, once the components are modified, the original UL approval on
>the components is also questionable, if not void. Builder/user assumes any
>and all risks. If you want certified stuff, spend the $75 or so for a
>commercial-quality unit.
>
>My local supplier, Wally World, seems to be scaling back on the hardware
>end of electrical parts. A visit to 'orphan alley' [Harveyism for where
>they stash the blow-out stuff] last night unearthed the following items and
>their discounted prices:
>
>$2.50 GE single pole, push-on, full range dimmer (#D161ULM5)
>   .50 Steel "handy box" (receptacle box)
>   .50 Steel light switch box cover (one slit -- not two-hole receptacle
type)
>
>Considering these prices, I picked up the above items, and tonight I
>assembled the controller. Additional discussion follows assembly details
below.
>
>COMPONENTS (Ingredients):
>Dimmer switch
>2-wire extension cord w/moulded ends [I used one of dozens that seem to
>create clones of themselves over time -- think I've only purchased one in
>my life]
>Handy box
>Box cover
>Misc: Rubber grommets, wire nuts (or solder and electrical tape)
>
>Leave knockouts in electrical box intact. Drill a 3/8" hole through
>existing knockout in each end of box, and DE-BURR the holes. Install one
>rubber chassis grommet into each drilled hole. (Otherwise, silicone sealant
>following final assembly comes to mind, as a variant for the grommet
impaired.)
>
>You'll need the "business" ends of the extension cord, but not necessarily
>all the wire in-between. So, cut a 6" length from the plug and extension
>ends, respectively. (Wire itself should be 6", -excluding- moulded ends).
>
>Insert cord through holes in grommets, and separate (pull apart) cord on
>each end of the box into two pigtail wires (total 4 pigtails). Cord is
>separated far enough to tie a single loop knot in pigtails, to serve as
>strain relief. Not that it matters much with AC, observing original cord
>polarity (tracer or raised edge on insulation -- style varies), reconnect
>one leg of wire back to "original" condition by either soldering and taping
>(my preference for portable use) or with a wire nut. Similarly attach each
>of remaining pigtails to each wire of dimmer switch. Screw dimmer switch
>into handy box, dressing wires out of the way of attachment screws, OR
>shorten included screws, OR use alternate screws. Screw box cover (face
>plate) onto dimmer switch, and attach dimmer knob.
>
>Total construction time: less than 15 minutes.
>
>SCALE CALIBRATION (optional):
>None is okay, since trial-and-error will also work. Otherwise, use an
>indelible marker to draw a vertical line on the side of the dimmer knob.
>With the knob in maximum counter-clockwise position, index the drawn line
>to the box cover. Making the mark adjacent to one of the cover plate screws
>is a good "zero" point. Note: the reference is only important in case the
>knob falls off or is removed at some time -- it makes placing the knob back
>in the correct position a lot easier. From the zero point, connect a load
>to the dimmer. I connected a work lamp with a 60-watt incandescent bulb to
>the output, and paralleled a digital voltmeter across the lamp's plug
>prongs to provide rough visual and voltage reference points. I then turned
>on the dimmer, and advanced the control until the meter read 50v (the first
>really viable reading), then 60, 70...and so on. At 50v and each 10v
>increment, I used the marker to draw corresponding lines on the steel cover
>plate, directly across from the line drawn on the knob. Again, really
>low-tech, but it provides a quick dial scale for repeated settings.
>
>ERRATA:
>Although I don't know how it could be made less expensively than the
>existing $5 or so, this device may certainly be improved upon and/or
>otherwise "dressed out" with additional time, components, and cost. An LED
>pilot lamp to indicate off/on status, a 2-wire w/ground "orange" appliance
>cable instead of the cheap lamp cord, even a built-in voltage meter are
>some things that come to mind. I purposely wanted short lengths on the plug
>and socket(s) outside the box, since I'll be using it in conjunction with a
>"normal" extension cord. You may wish to leave the original length on the
>PLUG side.
>
>THEORY:
>Someone in the know may explain this better (please), but trusting what
>little electronics theory remains, and without disassembling the [sealed]
>dimmer, I must assume this is what is called a 'half-wave' rectifier
>(rectal fire in Southern). It likely has a small bridging capacitor to help
>prevent RF interference and hum to TV's and radios. If this is the case,
>the resulting waveform would be a spiked DC voltage (still containing an AC
>component (Southern: half-assed DC). More expensive commercial controllers
>probably feature full-wave rectifiers, more filtering, and perhaps voltage
>stabilizing circuitry -- and hopefully a more linear (or is it
>logarithmic?) voltage pattern across the voltage range.
>
>However, the dimmer will support up to 600 watts before going thermal
>(Southern: blows up), more than adequate capacity for controlling
>incandescent lights, soldering (hammer) irons, old-style electric drills
>and Dremel Moto-tools (without built-in speed controllers), and so on. IOW,
>brush-type motors and resistive devices are okay, within the wattage
>limits. Capacitor, shaded-pole, inductance, and motors that are already
>DC-controlled do not qualify. Likewise devices requiring trigger or startup
>voltages, such as florescent lamps are also on the no-no list.
>
>Have a nice weekend!
>
>
>Jim Harvey, RPT
>Greenwood, SC
>harvey@greenwood.net
>________________________
> -- someone who's been in the field too long.
>