Small scale propagation system construction

 Whenever the blog is being neglected - you can bet there's a reason for it. Work is still very demanding right now, and i've grown to really dread Monday mornings. The reason is because some equipment doesn't want to start up after being idle over the weekend, and with a couple of my maintenance employees out for medical reasons - most of my time has been spent fixing stuff. Oh well...no biggie, because that's what I do - repair equipment, or maintain it so that it doesn't breakdown....
You would think that after spending all of my days fixing stuff, using a tool of any kind would be the last thing on my mind when I get home - but, nope - building things is very relaxing, and i've been building lots of things lately. Hehe...Anyway, I decided to construct a really small propagation system for anyone that might only grow 10-12 tomato transplants each year, and hope you enjoy it.

This system was constructed from parts salvaged from a defective microwave oven, personal computer, window air conditioner, rechargeable razor, piece of scrap from a 31 gallon tote bin, 24 hour timer that was already on hand, a 5 gallon cat litter bucket, and a light socket that was picked up at Lowes.....

The first thing to be done, was to mount the light socket into the lid so that the incandescent bulb would protrude from the bottom side. A couple of wire ties were used to fasten the socket firmly into place, then connect a small 120 volt appliance cord to the screw terminals of the socket.

Next, a really small cooling fan from a computer was mounted in one end of the bucket to provide ventilation/cooling, because I knew that a light bulb in such a small space would create alot of heat within, and tomato seedlings really don't need to be exposed to more than 75-80 degrees in the early stages of growth. Several holes were drilled into the opposite side of the bucket to provide fresh intake air for the little fan, and were located toward the bottom so that the incoming air would be forced to travel across the plants on it's way to the fan. The 24-hour timer was left over from the propagation chamber that was constructed a few years ago, and will be used to cycle the light on/off at pre-determined times.

Now, here's where things get interesting.....Due to the fact that the little fan motor runs off of 12 volts d.c., a small power supply would have to be constructed that would convert the incoming 120 volts a.c. to what the motor needed. After looking at all options, a couple of items were removed from a defective microwave oven and also a personal computer. One can never have too many broken gadgets laying around, because sooner or later parts from them can be used for something. Well...at least in my experience.......

Photo below - here's a full-wave bridge rectifier rated at 5 amps and 600 volts that was acquired from a computer power supply. Although the little fan motor needs only 12 vdc @ 90 milliamps of current, this little oversized rectifier was the only option. For the record, it's constructed from 4 diodes strategically connected so that the incoming voltage is converted to direct current - and fully enclosed in a nice little package. AC voltage is applied to the 2 leads in the center, and DC voltage is then supplied from the two outer leads. I soldered various colored wires to them so that it could be connected to other things, then insulated each one with a good grade of electrical tape.

Photo below - Here's what converts the 120 volts to 12 volts a.c. It's a tiny transformer that was salvaged from a defective microwave oven, and wires were soldered to it's terminals, too....

Photo below - you can see that a small appliance cord is connected to the 120 volt side of the transformer, then white and black wires come from the other side and connect to the 2 center leads on the rectifier. So, 120 volts ac comes into the circuit, is transformed into 12 volts ac, input into the rectifier, then produced as 12 volts dc at the brown and blue wires.

Photo below - Now, something was needed to control the temperature of the enclosed propagation system - by turning on the little fan motor when a certain temperature was reached. There's nothing better than a thermostat from a defective window air conditioner to fill this need, because you can get them for free - and it's got the correct temperature range for this application. A small panel was constructed for it from a computer housing, and the transformer and rectifier were mounted inside, too. The top was cut out from a small piece of scrap tote bin, and the entire thing was then attached to the opposite side of the bucket.

Photo below - here's the sensing bulb of the thermostat mounted inside the enclosed space, which is bent to follow the contour of the inside. You can see the holes drilled into the bottom of the bucket - as this is where the intake air for the fan comes from. Controlling the path of airflow is really important, and I always take full advantage of it.

Photo below - here's a picture of the completed propagation system - which admittedly is pretty freaky looking! Haha! All that needs to be done now, is covering the terminals of the light socket with something so that someone doesn't get shocked from the exposed connection. We sure don't want that to happen....

After trying various bulb wattages, it appears that a 100 watt bulb is just right for the system. Since all of my propagation cycles take place in the shed, some warmth is needed to offset the bitter cold temperatures during the winter. Even when temperatures dip to the low 20's at night, this little fella should be able to keep the seedlings nice and cozy. A couple of 6-cell seedling packs fit perfectly inside the bucket, and I reckon we'll try some cabbage seedlings in it around the first of December. So, there ya have it....my freaky little propagation unit that was constructed for less than $10.

Take care, and happy building!

EG