Incubator with resistance wire

[PortugalBreeder]

Many people use incandescent light bulbs as their incubator's heating elements, but I really think resistance wire is better and I was wondering if anyone has already tried it before (in home made incubators off course)?

All commercial incubators use resistance wire. In the next picture do you see the rounded square on the top part? Is resistance wire.

Resistance wire is a low resistance conductor, classified by Ohms/feet (Ohm is the unit for electrical resistance), that heats up when crossed by an electric current, it is usually used for high temperature applications but if properly chosen and controlled it can have several advantages over light bulbs. (Do not produces light, do not wreck suddenly creating a risk of loosing all the eggs, reacts very fast to applied voltage, last for a life in you incubator and more that I don't remember now)
Disadvantages only can think about the price which is higher than a regular light bulb.


Now the trick part, choose the correct wire,
I know I need between 200 and 500W for my incubator,
P = [200,500] watts

And my power supply is 220 Vac,
V = 220 Vac

Electric power formula (derivation from Ohm's law),
P=VI <=> I=P/V

I=[200,500]/220=[200/220,500/220] A (amperes)

Ohm's Law,
V=RI <=> R=V/I

R=220/[200/220,500/220] = [220^2/500, 220^2/200] = [96.8, 242] Ohm

Now you have the resistance your wire should have between 96.8Ohm and 242Ohm to produce between 200W and 500W under 220Vac applied voltage. So if you find a wire for sale that have 50Ohm/feet, you need to buy approximately between 2 feet=100Ohm and 5 feet=250Ohm.

For last but not least, you should check you wire Max Watt per feet value to know if it can handle the power you are going to put in.
Example:
The 50Ohm/feet wire we found on the shop can handle up to 150W per feet, so if I'm going to buy 2 feet the wire will be able to handle 300W which is less than the power you you are going to want, 200W, so its safe to apply 220V at this 2 feet of wire getting 200W of heat for my incubator!

Hope you all understood it, any questions/corrections please post bellow.

 

[Clay Valley Farmer]

200 to 500 watts is a huge amount of heat, must be one big unit. and if you put that much power though a wire a couple feet long it will be red hot and cook the eggs from radiated heat alone. I would think you could keep a good sized well insulated bator up to temperature with 1/10 that power. Wire will be somewhat more efficient than a bulb as more of the energy will be in IR range rather than visible light.


Old toasters are a good source for the wire.

 

[PortugalBreeder]

This is suposed to be a tutorial, and the values are as round as possible so that people can understand formulas, and their logic.

 

[PortugalBreeder]

This is the power ratings I use for my incubators,

Power Type of incubator (chicken eggs)

around 20Watts Table top from 1 to 20 eggs
around 40Watts Table top from 20 to 100 eggs
around 100Watts Cabinet incubator 100 to 200eggs
around 200Watts Cabinet incubator 200 to 300eggs


Thank you Clay Valley Farmer for pointing that out.

 

[Clay Valley Farmer]

Cool, good tutorial to understand the calculations. Just the example seems extreme to me and could misslead someone trying to figure things out for the first time.

Far more practical and safer to have a well insulated space and less heat input over a longer wire or possibly lower voltage. For example 10 times the length of wire such that the wire only rises to 200F max. On the downside the more mass in the heating elements the greater the hysterisis effect (overshoot). A good thermostat though can solve that problem.

This way there will be less cycling and a more constant temperature. Also less radiated heating problems creating hot spots.


On a side note, I think the on/off switch aproach used in many cheap incubators is where someone building their own can improve the end product and hatch.

I'm thinking a dimmer switch (pulse width or duity cycle control) added to the circuit in addition to the cycling thermostat to control will be the ideal, with this the unit can be brought up to temperature quickly then back the dimmer switch down until cycling is minimal. I know it throws a curve into the ohms law example but from a practical prespective a far superior design can be had controling both how often the heating element switches on and off as well as how much power (voltage and duty cycle) is availible to be put into the element.

 

[rebelcowboysnb]

Ill stick with my light bulbs an hairdryers. No math to confuse an not as much open current.

 

[PortugalBreeder]

Quote:
Great you are already using resistance wire, and that a great suggestion from were people can get it!

The red coiled thing.

 

[rebelcowboysnb]

I just use the whole hair dryer.

 

[bigdawg]

gqf sells the heating wire that fits there sportsmans, that what i have in my homemade cabinet bator and two wafer thermostats

 

[ga_goat]

I use ni-chrome wire mostly salvaged from central heating / air units that have been replaced , I like it bacause it is hot and then when it goes off it cools down quickly a light buld has the glass shell that stays hot longer so the theromostat is harder to set . I don't use math , I just use screws to hold the insulators stretch the wire around them cut it at the terminals , squeeze on a hi-temp end on it and push it on the connector , if the lights go dim in the shop when it comes on I shorten the wire . built 4 this way and all work fine .