Hot air and preheating
2006-12-07 by bobysgotguns
I try to do surface mount whenever possible as I like the small size,
and nowadays a lot of the components I use are hard to find in through
hole packages. Last year I got an Aoyue 8032A++ hot air pencil (it's
self-contained, no station) along with a bunch of nozzles for about
$100, but I find that it takes a long time for solder to melt. I
though the hot air device didn't have enough power, but then I tried
the hot air station in the lab at my university with the same problem.
It turns out usually these are used together with PCB preheaters.
Unfortunately, I've not seen one under $150, so I decided to built
one. This turned out relatively simple and I present instructions
here for my version.
Since my version runs on AC, I used a dimmer to control it. With such
a configuration, I highly recomment a grounded metal chassis to serve
as shielding. I used the enclosure of a junked computer power supply.
I took apart a hot air popcorn popper I had gotten for $3 at the flea
market and removed the heating element together with its mica sheet
support. This makes the bottom of the heating well. I also had a
cylindrical mica sheeting from a hair drier, and held together with
staples, it made the side of the heating well. I cut off a
corresponding circular section in the top of the enclosure and screwed
over it a standard 120 mm fan grill. From the center of the grill, I
have a metal bold, insulated with fiberglass loom, holding the heating
well in place (it goes through the center of the circular mica sheet).
The bottom of the screw was padded with a cut cork to rest on the
enclosure bottom.
A dimmer controls the power through the heating element (i.e. infrared
range). I suggest setting it so it glows just a bit to be visible in
dim light, but not under a full light. A thermistor-based temperature
probe which controls an on-off relay (the circuit is just a two
transistor differential pair comparing the thermistor current to a
potentiometer) that's attachable to the PCB controls a relay to turn
on or off the heating. This completes the device. I didn't have a
dimmer so I built one according to the standard schematics (even
skipped the diac and it still works fine).
I don't have a digital camera so I cannot post a picture at this time,
but I'll get back my tablet soon so I'll post a sketch.
and nowadays a lot of the components I use are hard to find in through
hole packages. Last year I got an Aoyue 8032A++ hot air pencil (it's
self-contained, no station) along with a bunch of nozzles for about
$100, but I find that it takes a long time for solder to melt. I
though the hot air device didn't have enough power, but then I tried
the hot air station in the lab at my university with the same problem.
It turns out usually these are used together with PCB preheaters.
Unfortunately, I've not seen one under $150, so I decided to built
one. This turned out relatively simple and I present instructions
here for my version.
Since my version runs on AC, I used a dimmer to control it. With such
a configuration, I highly recomment a grounded metal chassis to serve
as shielding. I used the enclosure of a junked computer power supply.
I took apart a hot air popcorn popper I had gotten for $3 at the flea
market and removed the heating element together with its mica sheet
support. This makes the bottom of the heating well. I also had a
cylindrical mica sheeting from a hair drier, and held together with
staples, it made the side of the heating well. I cut off a
corresponding circular section in the top of the enclosure and screwed
over it a standard 120 mm fan grill. From the center of the grill, I
have a metal bold, insulated with fiberglass loom, holding the heating
well in place (it goes through the center of the circular mica sheet).
The bottom of the screw was padded with a cut cork to rest on the
enclosure bottom.
A dimmer controls the power through the heating element (i.e. infrared
range). I suggest setting it so it glows just a bit to be visible in
dim light, but not under a full light. A thermistor-based temperature
probe which controls an on-off relay (the circuit is just a two
transistor differential pair comparing the thermistor current to a
potentiometer) that's attachable to the PCB controls a relay to turn
on or off the heating. This completes the device. I didn't have a
dimmer so I built one according to the standard schematics (even
skipped the diac and it still works fine).
I don't have a digital camera so I cannot post a picture at this time,
but I'll get back my tablet soon so I'll post a sketch.