digital thermostat control for a bird brooder

[Chuck Chopp]

I have a bird brooder that is used for providing a temperature & humidity
controlled environment for baby birds until they are old enough to maintain
their own body temperatures. The brooder has a digital thermometer on it
that is accurate to within .1 degrees Celsius. The problem that I have with
the unit [and this is common to all brooder designs] is that there is an
internal light that needs to be turned on & off for various periods of time
through out the day, and the light itself produces heat that throws off the
temperature settings in the brooder.

Currently, the heating system in the brooder runs off of 110 VAC, and it
comes with a power inverter to allow it to be run off of a 12 VDC power
source [e.g. cigarette lighter in a car]. The temperature control is a
potentiometer that is used to control the electric heating elements, and
there is a fan that blows continuously to circulate filtered air inside the
brooder.

What I'm looking for is an inexpensive circuit that would allow me to set up
a digital thermostat control for the brooder. I want to use this to
calibrate the potentiometer so I know by reading the display what the
desired temperature is and then look at the digital thermometer to see what
the actual temperature is. A secondary function for the circuit would be to
compensate for the heat output of the light by stepping up the speed of the
fans [I'll get 2 speed fans], disable the light itself and sound an audible
alarm if the temperature in the brooder goes over the thermostat setting by
more than say 1.5 degrees Celsius.

Does anybody have any recommendations on a ready made digital thermostat
unit that I could adapt for this purpose, or a link to schematics for a
circuit that I could assemble from discrete components?


TIA,

Chuck

 

[SW]

Increasing speed of fans will not do any good if your unit is insulated. It
will create a more uniform temperature, but will not affect the amount of
heat in unit (unless these fans introduce and recirculate outside air or
something). As for inexpensive, there is no cheap answer as you will need
some sort of sensor and use a comparator to switch heaters on and off. Now
you introduce a whole nother set of problems such as overshoot, undershoot,
probe placement, etc.

One idea that is cheap: If you use a relay to switch between 2 different
potentiometers. One potentiometer adjusts for amount of heat to send in
when light is off. Then have relay fire form the same power light runs off
of. Then wire a different potentiometer through the relay that decreases
the heat output to the point where you will maintain the same temperature.
This will compensate for the added heat by automatically decreasing heat
form heaters.

Now here is the real question: How to wire the pots together through a
relay. Well it all depends on how the original pot is in the circuit. Is
the pot using all three wires? Is it shorted across two terminals and just
using it as a variable resistor? This will need to be found out for the
circuit to work.

I have a bird brooder that is used for providing a temperature & humidity
controlled environment for baby birds until they are old enough to maintain
their own body temperatures. The brooder has a digital thermometer on it
that is accurate to within .1 degrees Celsius. The problem that I have with
the unit [and this is common to all brooder designs] is that there is an
internal light that needs to be turned on & off for various periods of time
through out the day, and the light itself produces heat that throws off the
temperature settings in the brooder.

Currently, the heating system in the brooder runs off of 110 VAC, and it
comes with a power inverter to allow it to be run off of a 12 VDC power
source [e.g. cigarette lighter in a car]. The temperature control is a
potentiometer that is used to control the electric heating elements, and
there is a fan that blows continuously to circulate filtered air inside the
brooder.

What I'm looking for is an inexpensive circuit that would allow me to set up
a digital thermostat control for the brooder. I want to use this to
calibrate the potentiometer so I know by reading the display what the
desired temperature is and then look at the digital thermometer to see what
the actual temperature is. A secondary function for the circuit would be to
compensate for the heat output of the light by stepping up the speed of the
fans [I'll get 2 speed fans], disable the light itself and sound an audible
alarm if the temperature in the brooder goes over the thermostat setting by
more than say 1.5 degrees Celsius.

Does anybody have any recommendations on a ready made digital thermostat
unit that I could adapt for this purpose, or a link to schematics for a
circuit that I could assemble from discrete components?


TIA,

Chuck

 

[Chuck Chopp]

Increasing speed of fans will not do any good if your unit is insulated. It
will create a more uniform temperature, but will not affect the amount of
heat in unit (unless these fans introduce and recirculate outside air or
something). As for inexpensive, there is no cheap answer as you will need
some sort of sensor and use a comparator to switch heaters on and off. Now
you introduce a whole nother set of problems such as overshoot, undershoot,
probe placement, etc.

Yes, fresh air is brought inside the brooder from the outside by way of a
double filtration system. I have studied the cooling rate when the heaters
are turned off and I was able to plot the rate at which the temperature
drops simply by running the fans. The thought about getting higher speed
fans was simply to increase the airflow rate to drop the temperature quickly
if it go too hot.

In seeking a pre-built thermostat "gadget" that I could adapt for use with
the brooder [e.g. control a relay with it and let the relay turn the heaters
on/off], I was hoping that the "gadget" would have been designed with
"tuneable parameters" for handling the overshoot/undershoot issue.

I'm glad that I'm a pack-rat. I took 3 years of electronics in high school
[many moons ago], including analog electronics, digital electronics and
residential house wiring / high-voltage electricity. I have *ALL* of my
notes, still, and I find it helpful to refer to them since I was the one who
took them down when I was actually taking those classes. Somewhere in there
I have all of my lab experiments and theory notes on comparator circuits and
I'm sure those will refresh my understanding of what's involved.

One idea that is cheap: If you use a relay to switch between 2 different
potentiometers. One potentiometer adjusts for amount of heat to send in
when light is off. Then have relay fire form the same power light runs off
of. Then wire a different potentiometer through the relay that decreases
the heat output to the point where you will maintain the same temperature.
This will compensate for the added heat by automatically decreasing heat
form heaters.

That's a good idea. I could simply have the relay powered in seris with the
light bulb and if the light is turned off or the bulb burns out then the
relay would be turned off and the proper potentiometer would be used to
control the heaters. Since the wattage of the bulb is a constant, the 2nd
pot. would present a relatively effective way of compensating for the light
bulb's heat output. Of course, this does not in any way handle drastic
changes in the ambient air temperature that would in turn affect the
temperature of the air being brought into the brooder. As long as the
brooder is kept in a stable environment that wouldn't be a problem, but
these brooders are made to be portable in that you can run them from a 12
VDC source. When chicks have to be fed a frequently as every 2 hours, you
take them with you when you leave the house. This means that the ambient
air temperature may vary significantly during the operationg of the brooder.

Now here is the real question: How to wire the pots together through a
relay. Well it all depends on how the original pot is in the circuit. Is
the pot using all three wires? Is it shorted across two terminals and just
using it as a variable resistor? This will need to be found out for the
circuit to work.

I'm in the process of obtaining a damaged brooder at a very low cost so that
I can have one to experiment with. Once I have it, I can open it up and see
what the innards look like and then I'll know more about what my options are
for implementing a new control circuit for the heaters & fans.

 

[Stan]

[email protected] wrote:

}I have a bird brooder that is used for providing a temperature & humidity
}controlled environment for baby birds until they are old enough to maintain
}their own body temperatures. The brooder has a digital thermometer on it
}that is accurate to within .1 degrees Celsius. The problem that I have with
}the unit [and this is common to all brooder designs] is that there is an
}internal light that needs to be turned on & off for various periods of time
}through out the day, and the light itself produces heat that throws off the
}temperature settings in the brooder.

I assume the light is an incandescent bulb (which produces a lot of infrared
radiation)...can you put in a compatible-base flourescent, which are made
to screw into house-hold table lamps?

These lamps are usually cool to the touch. Would this help?

Stan.

 

[SW]

Best thing you could do is purchase a B-10 thermostat that goes in an oven.
The B10 series has very close differential (slow make, slow break contacts)
and you can usually adjust its range by moving the shaft stop. (Oven
t-stats are preset for very hot temp) You can Google for a B-10 Oven
thermostat and get a brand new one for say 60 dollars and you will get
ACTUAL control.

If I were you, I would wire the relay in PARALLEL as the current through
relay in series wont light the bulb very well.

Thermostat will always control a set temp and is the best idea as all the
ambient changes, if minimal, are negligible.

Increasing speed of fans will not do any good if your unit is insulated. It
will create a more uniform temperature, but will not affect the amount of
heat in unit (unless these fans introduce and recirculate outside air or
something). As for inexpensive, there is no cheap answer as you will need
some sort of sensor and use a comparator to switch heaters on and off. Now
you introduce a whole nother set of problems such as overshoot, undershoot,
probe placement, etc.

Yes, fresh air is brought inside the brooder from the outside by way of a
double filtration system. I have studied the cooling rate when the heaters
are turned off and I was able to plot the rate at which the temperature
drops simply by running the fans. The thought about getting higher speed
fans was simply to increase the airflow rate to drop the temperature quickly
if it go too hot.

In seeking a pre-built thermostat "gadget" that I could adapt for use with
the brooder [e.g. control a relay with it and let the relay turn the heaters
on/off], I was hoping that the "gadget" would have been designed with
"tuneable parameters" for handling the overshoot/undershoot issue.

I'm glad that I'm a pack-rat. I took 3 years of electronics in high school
[many moons ago], including analog electronics, digital electronics and
residential house wiring / high-voltage electricity. I have *ALL* of my
notes, still, and I find it helpful to refer to them since I was the one who
took them down when I was actually taking those classes. Somewhere in there
I have all of my lab experiments and theory notes on comparator circuits and
I'm sure those will refresh my understanding of what's involved.

One idea that is cheap: If you use a relay to switch between 2 different
potentiometers. One potentiometer adjusts for amount of heat to send in
when light is off. Then have relay fire form the same power light runs off
of. Then wire a different potentiometer through the relay that decreases
the heat output to the point where you will maintain the same temperature.
This will compensate for the added heat by automatically decreasing heat
form heaters.

That's a good idea. I could simply have the relay powered in seris with the
light bulb and if the light is turned off or the bulb burns out then the
relay would be turned off and the proper potentiometer would be used to
control the heaters. Since the wattage of the bulb is a constant, the 2nd
pot. would present a relatively effective way of compensating for the light
bulb's heat output. Of course, this does not in any way handle drastic
changes in the ambient air temperature that would in turn affect the
temperature of the air being brought into the brooder. As long as the
brooder is kept in a stable environment that wouldn't be a problem, but
these brooders are made to be portable in that you can run them from a 12
VDC source. When chicks have to be fed a frequently as every 2 hours, you
take them with you when you leave the house. This means that the ambient
air temperature may vary significantly during the operationg of the brooder.

Now here is the real question: How to wire the pots together through a
relay. Well it all depends on how the original pot is in the circuit. Is
the pot using all three wires? Is it shorted across two terminals and just
using it as a variable resistor? This will need to be found out for the
circuit to work.

I'm in the process of obtaining a damaged brooder at a very low cost so that
I can have one to experiment with. Once I have it, I can open it up and see
what the innards look like and then I'll know more about what my options are
for implementing a new control circuit for the heaters & fans.