A Long Term Incubator [PDF]

Zitiervorschau

A long term incubator I have been faced with a 30 hour loss of power 2 years ago. I had a simple cooler with a heater used for fish tanks in a gallon or water, cheap but not very high tech. In order to remedy to this situation (can and will happen when you are away at work, for the weekend, etc) I decided that I needed to harden the incubator that contains what I would not want lost. Here is a picture of the device I came up with. I have tested it up to 200 C, but usually run it at 40C.

This unit is made of a popcorn tin can, lined with ceramic fiber blanket, including one layer under the lid of the can. A little trap door opens to check content. Heat losses are crucial here. The container is a bowl made of Pyrex, the brown ones that go in the oven, filled with sand. A heat resistance is lodged under the bowl. Now for the interesting part: this unit will keep temperature 6 days if power from the line goes down that long. I found this piece of equipment from the following company:

http://www.powerstream.com/CustUPS.htm

This is a Powerstream UPS (Uninterupted Power Supply). Its output is 3Amps max under 24V, so the max Power you will get is of course 72Watts. I coiled some resistance wire underneath the Pyrex dish, calculated to be 24/3 = 8 Ohms To see how to make a resistance, refer to my other post on making a quartz furnace. This unit is connected to both an outlet in the wall, and to the 2 deep cycle 12 V marine batteries connected in series for an output of 24V. When the power from the line is lost, it switches automatically to the battery supply with zero delay. I had studied computer UPSs but the best you will get is a few hours and their price was either comparable to my whole setup or much, much higher. During normal operation, the powerstream allows for 24V to be delivered to the heating element and still has a trickle charge going to the batteries, so it’s pretty much hands off when you are setup.

Here is a photo of another little incubator. I tested it up to 500 C. It can go much higher but the need was only for up to 340C. It is built on the same principle as high temp furnaces, made from a 3 gallon tin can. A glass dome allows seeing what is going on and keeps the temparature in and this requires 40Volts on the Variac to operate. The problem is that I do not have a security should the power go down. A generator is a nice thing to have but does not solve the problem when you are away. I am well aware of systems that automatically kick generators on but this is out of my financial league. The result is that I became Zen about it. LOL

The temperature controller: I buy the temperature controller, the SSR (solid State Relay needed to power the load) and the probes from a company I really like, very nice, knowledgeable and ships faster than Speedy Gonzales. www.auberins.com These temperature controllers accept all kinds of probes. For low temperatures, up to 400C, they have one called PT 10.0 that are precise to the 10th of a degree. Here is a picture of one I set up in a project box. It can also be used as simple thermometer.

Unit cost $35 for the controller, 20-25 for the SSR and 15-20 for the probe. Project box from Radio Shack. Patrice