Building a Simple and Cheap Egg Incubator

Incubating and hatching eggs is an art in itself. After some initial half hearted and failed attempts I decided to stop mucking about and built a decent incubator. In my case it is needed for quail but there is no reason why it couldn't be used for chicken eggs. (as a matter of fact i ended up doing both)

I will be describing a simple incubator that once you have all the parts you will be able to make in less than an hour, maybe even less than half an hour. In a seperate instructable I will be describing an arduino driven incubator with more functions
The simple incubator described here is an isolated cardbord box with some off the shelf electronic modules

BOM

• carton box
• polystyrene plate
• piece of glass (13x18 cm) 40cts
• incandescent lamp 60 Watt
• E27 lampfitting
• Ducttape
• Water Weasle (or make one yourself)
• Electric wire
• Fan
• some wood for the egg rack

• a thermostat, 2.58 euro
• hygrometer 1.89 euro
• Motor 1/240RPM type 49TYJ-F (optional) 8 euro

Building the housing can be simple. As I wanted it quick and cheap, rather than using wood, I opted to use a carton box that i insulated with polystyrene. Simply put a fitting plate on the bottom, against the sides and then add one as a lid. Make sure the lid fits well.Cut an 11x16 cm hole in the lid and put the 13x18 piece of glass on it. Ductape the glass to the lid

If you can get your hands on a styrofoam coolbox of proper size, use that one.

As a heater I am using a lamp, so needed to mount an E27 lampfitting. As it is difficult to attach screws in Polystyrene, I sunk the screws into a piece of wood on the outside that also functions as a handgrip.

I then bolted a small fan with spacers on the wall, aimed at the lamp. This fan is purely for internal circulation.

Make 2 holes, 1 to lead the wire of the Moisture sensor through and one to lead the wire of a temperature sensor through

Make 2 or 3 extra holes (about 1.5 cm diameter) near the bottom for ventilation. Eggs need oxygen

The simplest way to make a nearly full automatic incubator is with the following components

• W1209 Thermostat
• cheap Hygrometer
• 1/240 RPM motor 49TYJ-F (optional)

The Thermostat will control the temperature. The Hygrometer will not control the humidity but at least give info about it and the 1/240 RPM motor can be left on continuously as it will slowly turn the eggs so they make a full turn every 4 hours

This thermostat is basically an NTC with an 8 bit STM8S003F3P6 microprocessor, a display and a relay. For who is interested, there is also an ATMEGA-8 version on a Russian alcoholdistiller site.

The sensor of the W1209 is a 10kNTC. The Thermostat needs 12 Volt, mainly for the relay and has a 5 Volt regulator for the rest of the circuit.

I mounted the thermostat on a piece of cardboard that I attached to the box at an angle for easy reading.

The W1209 thermostat can be used to cool as well as to heat.
This is the way to set it:

First set the temperature:
Press the SET button for 2 sec. The measured temperature will start flashing and you can set that to the desired switching temperature with the '+' and '-' keys. Press SET again to accept the setting.
In factory setting, the device is most likely set as a cooler rather than a heater. You need to change that
Press the SET for 5 secs button until P0 appears in the display. Press SET again to confirm your choice. Most likely the display will show a 'C' (for Cooler). Press the '+' button till the 'C' becomes an 'H' ( for Heater). Press SET again to confirm
Press the SET button till you get P1: Hysteresis
The hysteresis sets the difference between the on and off temperature and has to prevent the relay to continously switch on and off. Set this at the desired value, e.g. 0.5 or 1.0 degrees.
The other P settings are best left untouched (especially P6), but here is their function

• P2 Highest temperature
• P3 Lowest temperature
• P4 calibration
• P5-Delay starting time: In this step, you set the start delay in minutes 1-10 min.If you set 1min relay is activated until one minute after reaching the set temperature.
• P6-High temperature Alarm
  The menu P6 initially turns OFF to ON and press the SET,then set the temperature at which the alarm is activated. When is alarm activated display not showing temperature only – - -.

when the display shows 'LL', the sensor is open. when it shows 'HH', the temperature is out of the measuring range, the relay will be shut down. when it shows'---', it is high temperature protecting

Once you have set the desired parameters use the relay contact to switch your heat source (lamp). The fan can either be switched together, or always be on

Basically your Incubator is now ready for use, but an egg tray/turner would be handy. I discuss that one a few steps further

So you want this fully automated to?
After you built this and are happy with it, you feel like it would be cool to also be able to regulate the humidity, rather than just monitor it, but you don't want to build the arduino version as you already have a good working thermostat.
Simple, get a DHT11 or DHT22, an Attiny85, a BC547, a 5 V relay and a USB humidifier and let the Attiny regulate the humidity get the TinyDHT lib from Adafruit.
Another possibility is a comparator opamp and a resistive humidity sensor. However, in practice it is rather easy to regulate the humidity manually

Measuring Humidity
For measuring the humidity I use a cheap hygrometer/thermometer modul

Maintaining Humidity

Key is to have a basin of water in your incubator from which water can evaporate. Remember though that water evaporates from the surface, so a larger surface will humidfy better than just a small cup of water, even if they contain the same amount of water. Some people place a tray of water under their egg rack, but of course you have to make sure none of your just hatched chicks will fall into it.
Increasing the evaporation surface can be done with e.g. a spunge in the water, or take a cup of water, make a frame with metal ware that is higher than the cup on which you can hang a piece of cloth that hangs in the water but still has a considerable surface above the water. You will see that your humidity level will rise pretty fast and your viewglass will probably fog up.

Although I do not want to really go into saying what the humidity should be, -ask 10 breeders and you get 15 different answers- I will spend some words on why the humidity is important.
If the environment of your eggs is too dry, your eggs will dry out and the chick will find itself captured in a tight sack and will most likely die.
If it is too humid, the egg cannot lose any moisture, no air pocket will develop and your chick will probably drown.
Therefore generally before the egg goes in 'lock down' breeders tend to keep the humidity below 50%.
After lock down breeders usually increase the humidity to make sure that the membranes in the egg remain soft so the chick does not have to do too much effort to free itself. Also in that last period the eggs need more air/oxygen so as the vents are open then humidity may easily go down, so thats why it is important to keep it up. You will find some more on it here.

Measuring temperature

The module I use has an NTC to measure the temperature and it seems fairly accurate. Entire books have been written about where to place the temperature sensor in an incubator. As I have a forced air incubator (read a fan blowing at the lamp), I expect the temperature to be quite even throughout the entire incubator. Nevertheless, it may be wise to measure at the egg level. Apparently a popular way of measuring temperature is in a "Water Weasle" or Ẅater wiggler" this is no more than a kids toy: a small plastic sausage shaped container filled with water. As these are some times hard to find if you are on the wrong side of the globe, it is just as easy to make one yourself: take a small ziploc plastic bag and fill it with some water (not too much) squeeze out all the air and close the zip. Then wrap it around the temperature probe, but some rubberbands a round it and you are set. The idea behind this is to mimic an egg and measure the temperature inside the 'egg'

If you are afraid that maybe the water will leak out of the ziploc bag: you can also use the gel found in modern baby diapers and add that with some water in the plastic bag

The humidity module i use also measures temperature which is a nice double check. At most they seem 0.2 degrees off from eachother

Maintaining temperature

The temperature is maintained with a lamp. I use a regular incandescent 60 Watt lamp. It should not be too close to the eggs and if you are afraid the direct radiation heat will be too large, put a panel in between the lamp and the egg rack. The fan will blow when the lamp is on. It thus cools the lamp and make sure the heat is quickly spread around the incubator. An infrared lamp may work but that is more based on the principle of direct radiation heat rather than convection heat (the incandescent lamp of course has both)

How about a different heatsource?
I am using an incandescent lamp but ofcourse there are different heat sources possible as a heating element
Power resistors would be a possibility. One will need to do some calculations though to chose the proper resistors.
The density of air at 20 degrees celsius and standard barometric pressure is 1.204 kg/m³

Suppose the incubator has a volume (l*w*h) of 20 liter, then that mass of air will be 24 gram.
Dry air has a specific heat of 1J/(g.ºC) again at normal barometric pressure

For a target temperature of 37ºC, we need to increase the temperature by 17ºC and that will cost 408J (24*17). As P=E/t and assuming we want to reach the target temperature in one minute (60s), the heat power needed is 408J/60s=6.8W.

As example suppose we have a power resistor of 20 ohm and a voltage of 12 Volt. Then the power dissipated by this resistor will be U²/R = 12²/20= 7.2 Watt. That is close enough

In a perfectly insulated incubator, once we reach the target temperature we could turn off the heat source and the temperature would remain constant over time. Obviously, this is not going to happen due to heat loss. If we can calculate the heat loss, we can determine what power is needed to keep the temperature constant. Actually we should also add this power to the power needed to heat the air, since we didn't consider heat losses in the original calculation.

To calculate the heat loss we heat the incubator to 37ºC, turn off the heat source and count the time in seconds needed to decrease (say) 5ºC. Since it's known that the energy that will be transferred to decrease that temperature is 5*24=120J, we can obtain the power needed using P(W)=E(J)/t(s). The better the insulation is, the less power will be needed.

Now before someone bites my head off... the above is only an approximation as we are not heating dry air but air with about 50-60% humidity. Humid air is less dense than dry air:

ρ = ρda (1 + y) / (1 + 1.609 y )

where

ρ=density
ρda=density of dry air
y= humidity ratio in kg/kg

If you want to do exact calculations look here.

Ofcourse one can use the same calculation for an incandescent lamp, but there power is usually not an issue. Should you want to do it do, don't forget that about 2-5% of an incandescent lamp is not generated as heat but as light (and yes that light can induce warmth again)

Eggs in an incubator need to be turned regularly. From a minimum of 2x/day to once every 2 hours. One can do that by hand, but that means opening the incubator and losing warmth. It also means you cannot go away. Therefore, an automated solution is better, although even then an eggturner can fail.

Nevertheless, in order to keep things simple, I decided to just use a push rod that is basically a piece of steelwire that goes through the wall of the box, is attached to the eggturner and enables me to push and pull the rack over the required distance.
i will be making a fully automatic eggturner for my arduino based incubator. Should you not want to wait for thet, the following may be of interest.

There are eggturners available, not too expensive, at the various chinese webshops, these are of the tilt and swing type, in which the eggs swing from one side to the other. If you make one yourself you can make it exactly according to your wishes and I have seen some true gems on the internet (here on youtube).

The easiest to make is a rolling eggturner that rolls the eggs over a certain distance so they make a 180degree turn. Moving the eggturner can be done by hand -with a wire- or by a motor that pulls/pushes the rack with eggs over that distance and after a few hours rolls them back. A clear example video you will find here, although I do not suggest you built the contraption with an attenuator -there are less space consuming ways- but it clearly shows the principle
As I will be making an incubator mainly for quails, obviously the eggs need to roll over a smaller distance than e.g. chicken eggs quail eggs need 8 cm for a full rotation, chicken eggs need abt 13 cm. A quail egg therefore has to be rolled over 4 cm (so it makes a half roll) and a chicken egg over 6.5 cm.
A popular motor to do this is a motor that makes 2.5 rpm (as pictured above) and will cost abt 6 dollars.
As we will be using an off center arm on the motor to pull the eggs 4 cm with a half rotation and then after a few hrs push them back 4 cm with the next half rotation, the arm will need to be 2 cm (it will travel 180 degrees and thus will have a pull of 2x2=4 cm. This shows that in order to cater for different size eggs you would only need to adapt the length of the motorarm (3.25 cm for chicken eggs).
The inside of my incubator is 25x35 cm I dont want to pull the eggs directly under the lamp plus i need some space for the humidifierr, so I will probably want to use 25x25 cm as I need a rolling distance of 4 cm that defines my rack as 21x25 cm. as a quail egg is abt 25x35 mm that gives space to approx 8x7=42 eggs.
Anyway, just to recap some of the measurements:
8cm = the distance to let a quail egg make a full 360 degrees roll
4cm = the distance to let a quail egg make half a roll, i.e. to turn it on its other side
2cm = the length of the motorarm
4 cm= the effective distance the motorarm moves when the motor makes half a turn