43 replies to this topic

[phildunford]

AC Fans are usually induction motors, which are brushless - can get a bit hot though...

[Caramanos2000]

Made one today with some old PC fans and an old power supply. Its a small wooden box. The hot air comes form the power supply exhaust and gets pulled through by another 80mm fan.

[dr thrust]

hmm, good idea using the waste heat from the power supply, every bit helps especially in cold dark, damp bolton!!, whilst ive got the saw, plywood and light bulbs out might aswell build a light box to sit in front of, might cheer me up

[rr22]

I was thinking of sticking a couple of computer fans in the top of somthing like this,
http://www.garden4le...il.asp?prod=125
obviously to be run away from fire hazards.
Any reason why not? I think they can be had cheaper but not researched properly yet.

[Arthur Brown]

With that propagator the airflow from a computer fan will be excessive for the 12w of heater in there, unless you use a very small fan say 15 or 20mm and maybe fit a speed reducer (resistor!). Though the sealed heater should be a sensible attribute.

[marble]

Resistors and fans don't mix

If powering with a computer supply its easy to go to either 7v or 5v

How well does calcium chloride work?

Edited by marble, 08 December 2007 - 11:56 AM.

[dr thrust]

calcium chloride works great,but keep an eye on the water trap filling up

there could be condensation problems with a plastic box, better of using wood its a great insulator!

[icarus]

computer fans are safe brushless hall effect motors but once you vent damp air you lose heat. If you put a thermostat in to stop excessive temp you would introduce sparking contacts into the box. ceramic fan heaters offer a well insulated heater element. the easiest option however is to have trays of silica gel that are exchanged and oven baked after each use in a closed cabinet .The front door is held shut by magnetic catch only so it does not form a sealed case for explosive. A computer fan runs inside the case so their is plenty of air circulation inside the case. silica gel dessicant is available in the uk from diy stores in plastic boxes to combat damp as a cheap de-humidifier . It can be oven baked and re-used many times - the computer fan can be run from any small dc power supply or 12v rechargeable battery it would run for weeks off a poor condition car battery

[Bonny]

[quote name='icarus' date='Dec 9 2007, 12:01 AM' post='41093']
The front door is held shut by magnetic catch only so it does not form a sealed case for explosive.

That's a great idea for holding the door closed! I've built a drying box but haven't put any sort of door closure on it yet.
My box uses exhaust fans only. Air is drawn in on bottom right side through furnace filters to keep out dust/cat hair etc... It then travels across light bulbs to warm it. The air then rises up on the left, travels to the right over 1st level shelf. It then rises again on the right and travels left over 2nd shelf where it is pulled out of the box through (charcoal air purifier) filters.

[dr thrust]

thanks everybody for your ideas!, job done

Edited by chris m, 30 March 2008 - 08:36 PM.

[cooperman435]

just an idea but kitchen wall cupbards will make good drying boxes and are available for about £10 to £20 dependant on the size you want. It means a well built almost airtight (completely if you use glue when assembling) and has hinges and doors ready made too.

If you ask someone replacing an old kitchen then its free too!

[leosedf]

I allready made my cabinet but i am in the procces of creating the drying controller which is a PIC microcontroller connected to a Sensirion humidity SHT sensor ( www.sensirion.com). LCD and controll buttons too.
The pic is driving two Peltier elements 136Watts each, heat sinks on the outside to cool the hot side.
For a heater i took apart an old hair dryer and took the nichrome coil and modified it to work with my 40Amp 12V power supply (for peltiers and heater).
The microcontroller's job will be just to turn on/off heater and peltier elements untill the humidity inside the cabin get's the lowest and/or maintain it in low levels.
I am still having problems to interface the sensor but i believe i will solve it in a matter of weeks.

[dr thrust]

wow that sounds amazing, goodluck with it!, keep us posted and maybe a photo?

[Bonny]

For sure some pics leosedf. My drying box is a simple wood box with 3 x 100w light bulbs and 2 small cooling fans as exhaust. Air is pulled through furnace filters and has to follow an "S" shape, in bottom right and out through charcoal filters at top left side with a middle shelf.

Edited by Bonny, 08 January 2008 - 01:20 AM.

[icarus]

high wattage wire wound resistors or the ceramic coated element out of a modern fan heater should be a good starting point dishwashers and washing machines have a thermal fuse in them to put in series with the heater element so if you lose the air flow the heater element wont get hot enough to ignite your pyro. ebay has lots of pid controllers for sale these enable you to set a precise temperature and have the advantage of remote sensor no sparking thermostat contacts in the box plumbers merchants sell pipe thermostats but bolt them on outside of a metal part of your drying box temp range around 65 to 85 c