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Hova Bator and Little Giant Tests

Low cost Styrofoam-box-type, table-top incubators are made by Miller Industries (Little Giant) of St. Paul, MN and by GQF (Hova-bator) of Savannah, GA.
In this study, a sample of each was purchased locally and tested for temperature consistency with laboratory quality temperature recording equipment.

The Little Giant was procured off-the-shelf at a farm discount department chain in Wisconsin (Mills Fleet-Farm) for about 10% less than factory advertised prices.
The Hova-bator was available from a competing store (Blain's Farm and Fleet) at a similar discount.

Prices


Sanitation is often an issue with the use of Styrofoam enclosures. Besides cleaning with an appropriate germicide, periodic replacement of the enclosure bottoms may be desirable.
Hova-bator offers a replacement bottom with a plastic liner for $11.75 in its catalog.
Little Giant lists a replacement incubator bottom (part #5210) in its care-and-use leaflet but did not respond to my e-mail request for price.
Note: the above prices are often exceeded significantly in e-bay or other auction sites.

Technical Discussion

Little Giant
The Little Giant uses a 42 watt "rope" heater connected to a solid state temperature control. It features integrated circuit, CA3079, which is frequently used in similar applications. Interested parties can find the IC specifications on the Intersil/Harris Semiconductor web site.
The temperature control is of the "proportional" type. This means that it can use a fraction of, or all of, the heating unit's wattage, as required.
Temperature is set by means of a volume-control type adjustment.

The fan kit includes an 8 watt, motor-driven fan with crimp-type wiring connectors. It is attached under the top of the incubator with two screws.

The egg-turner is a 6 revolution-per-day, continuously running gear motor linked to six pivoting galvanized steel bars. The bars are drilled to accept plastic baskets into which the eggs are placed. There is space for 48 2"-3" eggs. The eggs are tilted approximately 30 degrees in each direction every 4 hours.

Hova Bator
The Hova-bator uses a slightly lower power 27 watt "rope" heater controlled by a micro-switch and brass-bellows-style thermostat similar to that found in many brooders. An adjustment screw extends through the top of the incubator.

The fan kit was not available for testing. However, it is appears to be almost identical to the fan tested on the Little Giant. The fan kit for the Little Giant probably could have been installed in the Hova-bator.

The egg-turner is functionally similar to the one just described with a 6 rotation per day continuous gear motor linked to six plastic bars with cup-shaped depressions molded into them. There are cups for 42 2"-3" eggs.

Both incubtors
Both incubators have Styrofoam housings with a 15" X 15" screen floor upon which to place the eggs. Water pans are molded into the base under the screen for humidity augmentation. A pair of clear plastic windows is set into the top for observation.

The egg-turner for the Hova-bator is not quite as tall as the Little Giant's and will fit into either incubator. However, the Hova-bator egg turner is a snug fit in the Little Giant; you have to be careful not to damage the Styrofoam base.

Neither incubator included a hygrometer or calibrated thermometer; although, the thermometer provided by GQF is much easier to read.

Temperature Regulation Testing

Because hatching charts suggest the need for a half-degree Fahrenheit accuracy, the temperature regulating performance of the two incubators was examined with this expectation. (All temperatures discussed in this report will be degrees Fahrenheit.)

Six thermocouples calibrated to measure temperature to a tenth degree C accuracy were attached to a 7" x 14" wooden frame. When set into the incubator, the frame occupies one half of the available space with thermocouples spaced seven inches apart and one and one-half inches off of the screen floor.
The thermocouples were numbered channels 1 through 6 on the accompanying temperature charts. Their location can be visualized by imagining a tic-tac-toe grid with the bottom of the grid along the "cool" edge of the enclosure. (The cool side was deemed to be the side along which the heating element was connected to the wiring.) Reading the grid left to right and top to bottom, the thermocouples are numbered: 6, 5, X, 4, 3, X, 2, 1, X (where "X" denotes a grid with no thermocouple). Because of the symmetry of incubator we get by with six rather than nine thermocouples because the temperatures at location "X" of the top row would be expected to be the same as the temperatures at thermocouple 6, and so forth.

Prior to each of the three tests, the incubator was allowed to stabilize for several hours. Recordings were then logged every fifteen seconds first for two hours of constant operation.
Next the cover of the incubator was lifted for one minute to simulate opening the incubator for inspection or manual egg turning. The cover was replaced and temperatures were recorded for an additional hour.
Finally the air stream from a small table fan was directed across the incubator to simulate air drafts, and temperature was recorded for another half-hour.

Hova-bator still air incubator Test ResultsView Chart

The wafer-style thermostat was fairly easy to adjust; each turn of the adjustment screw altered the set-point by a few degrees.
However, it required more than an hour to reach stable operation.
With a load of cool eggs (not tested) the temperature could easily take a lot longer to stabilize.

During the two hours of constant operation, the temperatures at all 6 measurement sites rose and fell from one to two degrees at approximately ten-minute intervals, corresponding to the cycling of the thermostatic switch.
The desired temperature is actually the average of this fluctuating temperature. The fine adjustment of temperature is likely to be very frustrating to the user because it constantly changes.

During this, or any other test, there was a considerable range of temperature from site to site. The average temperatures in the corners of the rectangular hatching area were almost 4 degrees cooler than the warmest average temperatures at the center and at the top of the measurement grid.

When the cover was opened and replaced, the incubator required almost 30 minutes to recover to within a half a degree of its original setting.

When the incubator was subjected to drafty conditions, the average temperatures were all lowered by about 2 and a half degrees.

The Little Giant still air incubator TestView Chart

When used as a still air incubator, the Little Giant was a little more difficult to adjust due to the sensitivity of the one turn control.
I later hot glued a disc of wood to the slender control shaft to make adjustment easier.
The incubator did stabilize in less than an hour, probably because of the higher wattage heat unit in combination with the electronic control.

The continuous two-hour test revealed none of the periodic temperature fluctuation that the thermostatic unit (Hova-Bator) demonstrated.
However there was a steady drift in all temperatures of almost a full degree over the two-hour period.
This may have been in response to changes in room temperature or some other cause.

The temperature consistency from site to site was a little worse than that of the Hova-bator.
The center thermocouple read almost two full degrees higher than any other measurement site and almost five degrees higher than the corners.

Recovery from removal of the cover to half a degree of the original temperature was accomplished in about ten minutes.
The electronic control is clearly superior in this regard.

When the incubator was placed in a draft, all temperatures dropped by two to three degrees. The drop was more pronounced at the sides than at the center.

Little Giant with Forced Air Fan TestView Chart

With the forced air fan kit installed in the Little Giant, WITHOUT readjusting the thermostat control, the incubator's temperature at egg height was about 20 degrees higher than it measured as a still air incubator. This demonstrates that the sensors, which are located near the tops of incubators, were surrounded by a layer of warm air approximately 20 degrees higher than the air around the eggs.
This warm air layer, moves around and oozes out of the incubator's top vent holes. This makes the whole system sensitive to outside air currents and everything else. It is little wonder then that air currents or changes in room temperature alter the temperatures surrounding the eggs so easily without the fan installed.
Equalizing the temperature of the internal air with the fan kit for can therefore be expected to stabilize either the Hova-bator or the Little Giant substantially.

I readjusted the thermostat for temperatures around 100 for the actual test.

The continuous two-hour test showed very steady temperatures and better uniformity of temperature at the various sites.
However the lower corner remained almost two degrees lower than any other site.
The other five sites showed a temperature spread of about two degrees with the warmest locations being the side and top edges.
The center, the top corner and the bottom edge locations stayed within a degree of each other.
Though not perfect, this was the most uniform temperature profile of any of the three tests.

The recovery from the top being lifted took a little over 10 minutes with a surprising temporary 4 to 5 degree temperature overshoot.

The effect of the outside draft was a drop of less than 1 degree.
This improvement is consistent with the above discussion on temperature stability.

Recommendations

The corners of the still or circulating air incubators show drastic drops in temperature. I would suggest clustering eggs near the center and not filling the incubator to more than 2/3 capacity.

As a still air incubator, the Hova-bator seems more stable and uniform if you can live with the fluctuations as the thermostat cycles every ten minutes.

As a circulating air incubator, the Little Giant is preferable because it does not cycle and seems to stabilize more quickly.

The circulating air option is highly recommended with either incubator.

For my own purposees, I decided to use two Little Giant incubators with the fan kits.
One of the incubators is equipped with the Hova-bator egg turner which I feel is easier to clean and is less likely to cause injury should a chick hatch with the egg turner present.
I am using calibrated thermistor-type temperature probes with digital readouts.
I expect to be able to maintain the temperature regulation to plus or minus a half degree of the desired temperature for two dozen eggs clustered near the center.

FOLLOW UP 4/00

Follow up on the thermocouple study I did a while back. I corresponded with a couple of folks about temperature regulation in the Little Giant (Miller) temperature control so I thought the following observation might be of general interest.  

I highly recommend that anyone using an incubator with an electronic control run it for about a week before setting eggs. On the two Miller's I said I would use, the temperature drifted downward for about five days then remained so steady that I just check them in the morning and hardly ever adjust them again. Once "broken in" they worked quite well the next time. I can't even guess what component ages in them. I have little trouble maintaining plus or minus a half degree F.  

To repeat a previous comment. Glue a 1" disk (with an indicator line drawn on it) to the control shaft of the Little Giant incubator or you'll go crazy trying to adjust it.

The author, Jim Utzerath is an independent consulting engineer residing in Wisconsin and has no association with any of the suppliers mentioned in this report.
E-mail utzerath@execpc.com










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