$5.00 variable voltage controller

[Brenda Mamer]

On a similar note.  Several years ago  I hooked up my single speed Dremel tool, to
a sewing machine foot pedal.  It was convenient to operate with my foot, leaving
both hands free.
                                                        Brenda Mamer, RPT  WI

harvey wrote:

> 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.