Glass Incubator

This simplest incubator can become a reliable helper in any household; it will spare you the annoying spring worries of buying chicks for your farm. The device is as easy to make as it is to operate. The idea for this incubator belongs to “M-K” reader V. Shopin from Belgorod region; the design work was done by the “Eureka” creative laboratory. Keeping the author’s idea, we tried to make the device more reliable and safer.

Look at the general-view drawing of the incubator. As can be seen from it, the central place in the device is occupied by… a three-liter jar — it is a kind of heat generator and, at the same time, a heat accumulator. Of course, the water in it needs to be heated, and this can be done with any household immersion heater — preferably the smallest one, rated at 300 — 400 W. The immersion heater is fastened in the jar with a bracket and a clamp cut from any sheet metal 2 — 3 mm thick. The shape and dimensions of the bracket are shown in our drawings; the clamp dimensions are chosen according to the size of the immersion-heater holder. The clamp is fixed on the bracket with a pair of M4 screws with nuts. The bracket itself is attached to a standard polyethylene lid (the kind housewives use for home canning) with a pair of M4 screws with nuts and washers. Both inside and outside the lid, rubber sealing washers must be placed under the steel washers, because the lid and the jar must join absolutely hermetically.

Besides the immersion-heater bracket, two contact terminals are also mounted on the lid — M4 studs (each with four nuts, a pair of metal washers, and a pair of rubber sealing washers), through which voltage is supplied to the immersion heater.

And finally — a metal tube is passed through the lid, reaching almost to the bottom of the jar. To fasten such a tube, a length of larger-diameter tubing with an external thread is fitted onto it, after which the joints are soldered. The tube is secured on the lid with a pair of nuts, as well as two metal and two rubber washers.

And one more of the incubator’s main assemblies is the thermal regulator. It is also homemade and consists of a plastic housing, inside which a plastic bottle-float is located.

The thermal-regulator housing is composite; it is assembled from two parts cut from detergent-packaging bottles. Note that its upper part fits onto the lower one with a small clearance. On the side surface of the upper part — the cover — two screw slots are cut, which allows it to be moved smoothly relative to the lower part to adjust the thermal regulator’s trip point. A homemade limit switch is mounted in the cover neck. Its housing is turned from any insulator (for example, textolite or acrylic glass); the side contact screws with M3 thread should preferably be copper or brass, and the center contact — an M4 screw — should be of the same materials. The latter is screwed into a pusher, also turned from any insulating material.

In the lower part of the thermal-regulator housing a through fitting is fastened, assembled by soldering from two copper tubes — an outer one with an M8 thread on its outer surface, and an inner one of 5×0.5 mm diameter.

Inside the housing there is a float — a plastic bottle whose diameter must provide a ten-millimeter clearance between the inner diameter of the lower housing part and the float.

Now a trial assembly can be made and the device checked for proper operation.

First, the heat-generator jar is filled two-thirds with water, and the assembled lid is seated tightly on it. Next, using a rubber or polyvinyl tube, the fitting on the thermal-regulator housing is connected to the fitting on the heat-generator jar lid. The immersion heater is connected to the mains through the limit-switch contacts, which are initially in the normally closed state.

So, through the contacts of the thermal relay the immersion heater is switched into the mains and begins heating the water in the jar. Of course, the air above the water surface in the jar cavity also heats up. Since the jar is sealed hermetically, the rising air pressure begins to force water out of the jar through the water intake tube into the thermal-regulator housing. At this point the float rises and eventually its lid touches the limit-switch pusher, breaking the circuit. Then the water in the jar begins to cool, and so does the air above its surface. Water from the thermal-regulator housing is drawn back into the heat-generator jar. The float descends until the limit switch closes again. The immersion heater then again begins heating the water in the jar. That, in essence, is the complete operating cycle of the heat generator.

Once the device’s operability has been verified, the final incubator assembly can begin.

For the incubator’s inner body it is best to choose an aluminum saucepan — its inner diameter should be about 300 mm and its height about 320 mm. Several holes 10 — 12 mm in diameter are drilled in the bottom and lid of the saucepan, through which the incubator cavity is ventilated.

The saucepan is placed in a casing which, in the simplest case, can be made of corrugated cardboard. Still, it is better to make the body from stronger materials — plywood or hardboard.

The space between the casing and the saucepan must be filled with any heat-insulating material — packaging or construction foam plastic, fine shavings, sawdust, or even chopped straw. In the lower part of the casing an inlet ventilation duct is provided — for example, as shown in the general-view drawing — made with a pair of battens and a plywood sheet.

The casing lid is assembled in exactly the same way as the body, and from the same materials. In the central part of the lid a cardboard ring is glued in, forming the outlet ventilation duct.

The egg trays are cut from plywood or any plastic 3 — 4 mm thick. They are fastened with four threaded studs on a plywood or plastic disc about 200 mm in diameter, as shown in the drawing. In the lower part of the saucepan body there are four water containers that help maintain optimal humidity in the incubator cavity.

After assembling the incubator, we recommend dedicating several days to adjusting the device. To do this you should arm yourself with an ordinary medical thermometer, placing it in the egg zone. Ideally it is also good to have a hygrometer — for humidity control. The baseline data for adjustments are as follows: temperature — within 37.2° to 39.5°, humidity — 55 — 70%. If the temperature inside the incubator proves insufficient, the regulator cover must be moved upward and the temperature in the incubator watched for one or two heating cycles. If the temperature is too high, the cover together with the limit switch is lowered, with subsequent temperature monitoring. During thermal-relay adjustment, a scale can be marked on its housing, and later temperature regulation can follow the experimentally obtained thermostat temperatures depending on the thermal-regulator cover rotation angle.

If the float position within the recommended temperature range does not ensure opening of the “limit switch,” it should be loaded with any loose ballast — for example, dry sand.

Chicken eggs are placed in two trays, a dozen in each. During incubation it is recommended to turn the eggs periodically (at least once a day), as a broody hen usually does. There is no need to fear that turning the eggs may drop the temperature inside the incubator — under natural conditions this happens constantly when the hen leaves the nest to take a light snack.

It should be noted that an incubator of this type is a kind of heat accumulator. Therefore even long power outages are not a problem for it — the thermos-incubator keeps the water temperature in the jar steady for a long time. And if the power supply in your home is cut for a long while, that is no disaster either: it is enough to replace the heat-generator jar with another one filled with hot water — and for several more hours the incubator will properly perform the function of a broody hen. You only need, in advance, still during device adjustment, to measure the water temperature in the jar just in case: right after the thermal regulator switches off the immersion heater, water of the same temperature should be poured into the reserve container.

«Modelist-Konstruktor» No. 10’2005