You can read
about all kinds of things people do to power their hot wire foam cutter
including things like running 110V through a light bulb in series with
the foam cutter, battery chargers, dimmer switches, Variacs, "wall
warts", batteries, and so on. There are ways that work, ways that don't,
safe ways, and unsafe ways, okay ways, and better ways.
have the potential of applying 110V to your foam cutter, it is unsafe.
Using just a dimmer switch or just a variac means that if you turn the
knob too far, you can have 110V applied to the wire. If that happens,
you will either burn out your dimmer or variac or vaporize your wire or
both and that could also cause a fire. In addition, if your were to
accidentally touched the wire or any exposed terminals, connections, or
wires on EITHER the input side or output side, you could get a shock or
if the conditions were exactly wrong, you could die from cardiac arrest.
A fuse, circuit breaker, or GFI on the input side might help but will
not guarantee the negative results above.
If you have a
low voltage requirement such as is needed for shorter or thicker wire,
you will not be able to get a low enough voltage with a dimmer switch or
variac anyway. There is a limit to the low voltage they can put out.
proper way to power your foam cutter
is with a
reduces the voltage to a lower level so you can't apply line voltage to
your foam cutter with the accompanying hazards. A transformer swaps
voltage for current. Most foam cutters take a moderate current and low
voltage. For example, with a 12V transformer, you put in 120V and you
get out 12V. That is a ratio of 120/12 or 10:1. The current is increased
10 fold and the voltage is reduced 10 fold. If your foam cutter requires
3 amps, then you are only putting in 1/10 of that or 0.3 amps into the
transformer which is slightly more than a 40 watt bulb. The voltage goes
down, the current goes up, no shock potential on the output side of the
transformer or at the nichrome wire,
You can design
your foam cutter so that all you need is the right transformer that puts
out the right voltage and is big enough to output the current you need.
(see the Calculator page and the Transformers page. That is the simplest
solution. Note that the green C-shape is representing a bow type foam
cutter with the nichrome wire stretched between the two ends. Any type
hot wire foam cutter can use the same type power supply as the rest of
this article describes.
with this overly simplified design is that it has no protection for the
transformer against short circuits and no way to adjust the voltage (and
so the current or amps) so you can't adjust the heat for the optimum
foam cutting temperature. You can calculate the proper wire gauge and
length and it will work fine but if you ever want to change the wire
size, wire length, or temperature, you have no way to change the voltage
to match it.
design will add a dimmer switch and fuse, breaker, or GFI to the circuit
above and will use the safety ground wire from the wall plug and attach
it to the transformer housing and also to the foam cutter frame if it is
components in your power supply, you have all the necessary features for
safe and adjustable features to power your hot wire foam cutter. The
dimmer switch allows you to adjust the voltage from a low value to the
maximum rated output voltage of your transformer, the transformer steps
down the voltage and steps up the current, the fuse protects all your
components against accidental short circuits, and the safety ground
connections protects against shock in the case of a component or wire
There are a lot of different kinds of dimmers and fan controls. First,
you don't need a fan control. You can't use a light dimmer to control
a fan because you will damage the motor but a hot wire foam cutter is
most similar to a light bulb -- just a hot wire, but not hot enough to
glow. Fan controls are more expensive because they have additional
circuitry in them. Don't waste the extra money on a fan control.
There are two main manufacturers of dimmers, Lutron™ and Leviton™.
There are many different types of dimmers, fluorescent,
incandescent/halogen, single pole, 3-Way, 600Watt up to 2000 watt,
white, ivory, gold, ganged, rotary on/off, push on/off, combos, etc.
Fortunately, the simplest and cheapest is also the best for hot wire
foam cutters. What you want is a 600 Watt, Single Pole, Rotary
On/Off dimmer, your choice of white or ivory knob. The Lutron
model number is D-600R-WH (white) or D-600R-IV (Ivory). The Leviton
model is 6602-I (Ivory), 6602-W (White) or 6602-IW (has both colored
The most common type of dimmer you will find in your local lighting
or hardware store is called a pre-set. What this means is that you can
set the amount of dimming and then leave it there so when you turn the
light on or off, you don't disturb the setting. This is either done
with a separate button (used with slider dimmers) or using a push
on/off action (used with rotary dimmers). You likely will not find a
rotary on/off at a local store, they will all be the push on/off style
because that is the most popular by far in the home user market.
Jacobs Online offers both types on eBay.
If you use the push on/off rotary type, then you won't be able to
tell if your foam cutter is on or off just by looking at it because
the knob switch is a toggle. It is always out. You push it in to turn
it on if it is off, you push it in again, to turn it off if it is on.
If you use the rotary on/off type dimmer, you know it is off
because it is all the way counterclockwise. It clicks when you turn it
off the same as old style radio volume controls that turned off the
radio when you turned all the way to the left. If you knob has no
marks to indicate where it is currently set, you can easily put a mark
on it with a fine tip felt pen or a scratch mark or what ever you
want. You won't know where you had it last but you can also put a mark
on the cover plate for your preferred setting so you just turn it on
and turn to line up the two marks.
IMPORTANT: A dimmer
does not turn on until it is turned up to about 50%. After it comes
on, you can then turn it down to about 15% or 20% of its full output.
It also does not turn on until a certain amount of current is flowing
through it. Just hooking up a transformer to its output does not cause
enough current to flow through it to turn it on regardless of how far
you turn the dimmer up. You MUST have a load on the dimmer. A load is
an electrical term for a device that draws current. You could connect
a light bulb to the dimmer or your nichrome wire to the output of your
transformer connected to the dimmer and then the dimmer will turn on.
If you only attach a volt meter or multimeter to the output of the
dimmer or transformer but nothing else, your voltmeter or multimeter
will register only a slight voltage. Hook up your transformer and
nichrome wire first and then clip your voltmeter to the two ends of
the nichrome wire and you will read the output voltage. Be sure your
meter is set to read AC voltage.
Indicator Light And Separate On/Off Switch
If you are
using a push on/off dimmer, each time you push the knob, you can be
changing the preset position a little. It tends to always be in the
clockwise direction for some reason. Of course, if you mark the optimum
position, you can always readjust the knob to the correct position.
enhancement, especially if you are using the push on/off style dimmer
but also just as an enhancement is to add a separate on/off switch and
indicator light as shown below. The first diagram shows the light
between the light switch and dimmer switch. In this configuration, the
light will be on full bright any time you turn the power switch on but
will not indicate whether there is power to the foam cutter or not. The
advantage is that if the light is off, you know there is no power
anywhere in the circuit downstream of the switch. That way you can leave
the dimmer switch on and at the desired position all the time and not
change it and just turn the power switch on and off separately.
light is just a standard small 110V incandescent bulb. It can be a
standard 40 watt bulb or a smaller wattage appliance bulb or better yet,
a night light that uses a small Christmas tree type bulb. You can add a
standard household outlet in a box between the on/off switch and dimmer
switch or you can put both the switch and the outlet in a double box
with a combo cover plate and then just plug the night light into the
configuration shown below is with the indicator light between the dimmer
and the transformer. In this case, the light bulb will give an
indication of the proportion of the voltage going to the transformer.
The advantage is that it shows whether the dimmer switch is on or off
which is handy if you are using the push on/off type dimmer switch. If
the dimmer switch is set too low, it may be hard to see if the light is
on at all but in that case, there isn't much voltage coming out of the
transformer, either. You could even put a light in both positions if you
As in the
configuration above, you can add a power outlet and plug a night light
into the outlet. In this case, you could put the dimmer switch and
outlet into a double box with a combo plate. This is also handy because
you can then put a standard 110V plug on the input side of the
transformer and then plug that into the second wall outlet. If you
wanted to change the transformer later or even if you wanted to use two
separate transformers for different foam cutters, you just unplug one
and plug in the other. You could mount two transformers on the same
board with the dimmer, switches, and outlets.
voltage and/or current.
monitor either the voltage or the current from the output of the
transformer. A clamp on ammeter can be used to check the current flowing
through your foam cutter nichrome wire by clamping it around either of
the wires coming out of the transformer since the output is AC. If you
have a panel type ammeter, you can splice it into one of the output
wires. You can check the output voltage by clipping the alligator clips
or touching the test probes to the two output wires.
It would be
nice to have both a digital panel voltmeter and digital panel ammeter
mounted in a metal box along with the other components for a nice
self-contained unit but there are two drawbacks. Panel meters, even
analog ones, are expensive. Also, panel meters have only one range so if
you are working in the 1 or 2 amp range, the panel meter would not be
the same as one for one in the 10 amp range. It is the same with the
voltmeter, if you are working with 3 or 4 volts, it would not be in the
same range as a voltmeter for a 12-24 volt range. Handheld multimeters
and clamp on ammeters have ranges so one instrument can be used for any
your Power Supply
You can mount
your light switch, dimmer switch, plug-in for the output from you dimmer
switch and your transformer on one board. You could then put a plug on
your input wires (primary) to your transformer and plug the transformer
into one outlet and your power indicator light into the other as
mentioned above and you will have a nice neat package. The diagram below
shows banana jacks and a panel mounted fuse holder in a blank cover
plate on the left side. The output from the transformer goes into the
left side and attaches to the banana jacks. The foam cutter would then
be plugged into the banana jacks. The 110V plug and cable also goes into
the box on the left side, the hot side goes to the fuse holder.
You could also
mount everything in a metal box with rubber feet and a carrying handle
for an even nicer package. Metal boxes heavy enough for the transformer
can be kind of expensive, though. It is also difficult to find just the
right box. If you Google electrical box or utility box or device box,
you will get the kind of boxes you use in house wiring to mount switches
and electrical outlets into. Hammond Manufacturing makes both
transformers and boxes and you might find what you want there. For
boxes, check here:
You can also
add a DPDT switch to switch between the low and high voltage outputs for
four-wire output transformers. Here is the schematic for how to