Generate stable moderate heat

I really don’t care how many watts it consumes as long as i can keep a stable temperature of 37 degrees C.

Watts are a measure of energy (heat) and a resistor dissipating 100W will put-out the same amount of heat as a 100W light bulb.

Power (Watts) = voltage x current
Power = voltage2/R
Power = curren2 x R

Of course, the actual temperature is not as easy to calculate - A small insulated box will get hotter than a large insulated box. You can’t warm-up a room with a 100W light bulb.

And, you get a certain heat rise so without feedback (a thermostat), if the ambient temperature changes by 1 degree, the internal “37 degree” temperature will also change by 1 degree.

wvmarle:
So... how many watts of power do you need to keep your box at that temperature?

I need 37.4 - 41.7 watts.

srturner:
As others have said, you will need some idea of the power requirement to maintain the temperature.
Also, unless the hatching box itself is located in an environment of constant temperature, you will need a temperature controller. You stated a need for a constant 37 C. Plus or minus what?
S.

A temperature control is part of what i'm building. I will measure temperature and turn on/off the heat source to maintain a stable temperature. The box will be in a room with a temperature of 22-28 degrees celsius. Inside the box, i need to keep the temperature at 37 plus/minus 0.2.

JCA34F:
What is the wattage of the "old fashioned light bulb"? 15, 25, 40, 60, 75; 100, higher?

Typically a 25 or 40 watt incandescent light bulb would be used.

weedobooty:
A temperature control is part of what i'm building. I will measure temperature and turn on/off the heat source to maintain a stable temperature. The box will be in a room with a temperature of 22-28 degrees celsius. Inside the box, i need to keep the temperature at 37 plus/minus 0.2.

How big is the enclosure?
0.2C is pretty tight, you will possibly have to make sure your heat losses are as low as possible.
Are you trying for an even heat through out the volume, if so a mat type heater would probably perform the best with some circulation system.
Can you tell us the application please?
Thanks.. Tom... :slight_smile:

TomGeorge:
Hi,
If you have some method of circulating air in the box, high wattage chassis mount resistors should do the job as heating elements.

MFG_UAL10.jpg
Tom.... :slight_smile:

I do. There will be a small fan. Trying to answer questions here, but i'm only allowed to post every five minutes.

TomGeorge:
How big is the enclosure?
0.2C is pretty tight, you will possibly have to make sure your heat losses are as low as possible.
Are you trying for an even heat through out the volume, if so a mat type heater would probably perform the best with some circulation system.
Can you tell us the application please?
Thanks.. Tom... :slight_smile:

This is an incubator box where queen cells are placed to mature and emerge. Even and uniform temperature is important I will circulate the air using a small fan. The inside of the box will be about 50x40x40 cm. This video explains it pretty well: https://youtu.be/IRz0edi2APc

weedobooty:
A temperature control is part of what i'm building. I will measure temperature and turn on/off the heat source to maintain a stable temperature. The box will be in a room with a temperature of 22-28 degrees Celsius. Inside the box, i need to keep the temperature at 37 plus/minus 0.2.

There are 2 ways to control a heater:

On and off, usually with a bit of hystereses. Advantage is it's simple, disadvantage is the temperature will always vary around the set pooint by at least the level of the hystereses.

PWM. Not as simple but more chance of getting close to and maintaining the temperature you want. With PWM you control the amount of energy going into the heater, not just on or off (well, OK, so PWM is on and off but...). You reduce towards zero the energy going in as you get closer to the desired temperature, leaving a small energy input at the set temperature to make up for losses from the enclosure. My central heating controller works this way with a cycle time of 720 seconds, I suspect you will use much shorter timescales.

A variation of PWM is burst mode if you are using AC power, burst mode just means so many cycles on, so many off in a varying ratio.

How is the current heater (the lamp) regulated?

Those IR heat lamps for terrariums may make a drop in replacement of your incandescent lamps. Add an LED light if you also want he visible light.

That temperature range is indeed very tight, especially if you want to keep it at that temperature through the whole box (near the heating element it is naturally quite a bit higher than average).

My plan is to use an on/off operation. I can tweak the hystersis since i'm controlling the heat source with an Arduino or ESP32.

I totally understand that the temperature is higher the closer to the heat source you are. The queen cells will be placed away from the heat source and the air will be circulated inside the incubator.

I also understand that having the lowest power heat source that reaches the desired temperature is preferable to have the lowest number of on/off cycles.

OK the box is 504040. The power you need depends on the heat loss from the box; which depends on
1: the thermal resistance between box inside & outside
2: the temperature difference.
(I'm assuming there is no forced convection, just a fan recirculating the air inside.)

Here is a simple heater you can build with a few components.
how it works:
TR2 & TR3 Are powwer transistors mounted on a single heat sink.
The voltage at the junction of tr2 & tr3 is maintained at half the supply voltage - so each tr dissipates the same power.
The current through them is controlled by the voltage on the base of TR1.
Suppose R1 is 0.5 ohm and there is 1.5V on the base of tr1.
Tyhen there is about 0.5V across r1, setting the current at 1A.
The total power dissipation is then 1A * 12V = 12Watts.
You can mount all the components on the heat sink.

I've used 2N3055 or TIP33 with good results, mounted on a nice big heat sink.

activeload.png

activeload.png

johnerrington:
OK the box is 504040. The power you need depends on the heat loss from the box; which depends on
1: the thermal resistance between box inside & outside
2: the temperature difference.
(I'm assuming there is no forced convection, just a fan recirculating the air inside.)

Here is a simple heater you can build with a few components.
how it works:
TR2 & TR3 Are powwer transistors mounted on a single heat sink.
The voltage at the junction of tr2 & tr3 is maintained at half the supply voltage - so each tr dissipates the same power.
The current through them is controlled by the voltage on the base of TR1.
Suppose R1 is 0.5 ohm and there is 1.5V on the base of tr1.
Tyhen there is about 0.5V across r1, setting the current at 1A.
The total power dissipation is then 1A * 12V = 12Watts.
You can mount all the components on the heat sink.

I've used 2N3055 or TIP33 with good results, mounted on a nice big heat sink.

activeload.png

Thank you.

So you need a digitally controlled egg incubator?

Why reinvent the wheel?

RIN67630:
Why reinvent the wheel?

I think there are lots of reasons. One is to build something to your own specs, not someone else's. Another is to learn. Temperature control is an interesting subject and not always as straightforward as it appears. Third is just the joy of making (provided that one has time, of course).
S.

Even a wheel may be complicated: getting the right cost, size, weight, durability and thousands of other parameters is important. IIRC the last Concorde crash was due to a faulty wheel. Maybe someone was clever enough to not waste time by reinventing a wheel and used an Aliexpress item?

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