Styrofoam incubator; Thermostat with a Rheostat failsafe.

[tb144050]

Has anyone made a Styrofoam (or other type) homemade incubator and used a Thermostat ___AND___ Rheostat?

I am temp-testing a homemade Styrofoam incubator, using just the Rheostat for now:

1 styrofoam cooler
1 4"x6" rubbermaid, lid closed, filled with water
1 10-20gal zoo-med UTH, inside cooler, under the rubbermaid.
1 Rheostat
2 Digital temp probes, 1 inside cooler, 1 outside cooler (roomtemps)

(If you have to buy all these components, the $40-50 cost is comparable to a cheap incubator, but I had most of this, found some used, and REALLLLY want something with a "fail-safe")
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I am maintaining an accurate incubation temp of 83-F (actually 82-84F) in a room with temps that vary between 72 -> 78F, depending on our preference for room temp.

In our virtually temp-stable room (no extremes), the incubation temp is stable. But my question is, for those who have tried:

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Is it better to set the Rheostat, and use the Thermostat as an "overheat turnoff failsafe" (set about 2-3 degrees above preferred temp)?

or

Is it better to set the Thermostat to the desired incubation temp, and set the Rheostat to prevent "runaway high temps" if the thermostat fails?
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I am thinking that using the Thermostat as the "failsafe" and the Rheostat as the "active temp controller" will maintain a more stable temp with less variation (in a room with NO extremes).

Opinions? Experience from anyone who has tried either method? I want the most stable temp (without the cost of Proportional).

 

[scm133]

I have never made a homemade incubator before. I am sure others will chime in. Most set ups that I have seen, just use one Thermostat to control the heat. The thermostat should keep your temps at the desired range, and also should prevent overheating. Your temps really don't look bad for a homemade.

 

[tb144050]

After several days of monitoring at different room temps (around the styrofoam cooler), I see that:

Tuning the rheostat to 82F at an external room temp of 75...
-If room temp drops 5F, there IS a drop in incubator temp (-2F drop).
-If room temp increases 5F, there IS an increase in incubator temp (+2F increase).
Soooo....not the best idea if your house changes 2-5 degrees (or more) at any time during the incubation temp. My house changes 4 degrees minimum each time the central heat turns on/off.
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Instead, I am having even more stable incubator temps (+/- 1F, in room temp fluctuations of +/- 5F) with the opposite:

Tune the rheostat to (Ideal + 5F)...soooo 82F + 5F = 87F rheostat.
Tune the thermostat to 82F.
-If the thermostat ever fails, the rheostat will produce a MAX output of ~87F....protecting your eggs from cooking. :O
-The actual incubator temp is not affected unless room temp drops about 10F.
-The actual incubator temp remains more stable because the rheostat limits the heatsource, preventing excessively quick heating.
-Instead, the thermostat remains ON more that without a rheostat.
-Also, the output of the heatsource is "governed" so even though the thermostat is ON more often, the power consumption is not at "full-blast"