Problem with temperature gradient in incubator

[Amina]

I recently got a used lab incubator, with a heating element on the bottom of the unit, and I've been trying to make this suitable for hatching eggs. This is what it looks like:




I thought I had the temperature holding steady, so I put my eggs in. The next day, I realized that due to a massive temperature gradient in the incubator, I have probably cooked my poor eggs. I'm leaving them in there for now, to help me try and get the conditions right for the next eggs that I put in.

In these pictures, I have two thermometers in the incubator. You can see one of them on the top shelf. There is another one (the Brinsea Spot Check thermometer) with the probe hanging down right over the eggs in the second picture. There is about a ten degree differential between what the thermometer is reading on the top shelf, and what the Brinsea spot check probe says. If I then move a thermometer to the very bottom shelf, and leave the Brinsea one where it is, the one on the bottom shelf reads 110 and the Brinsea one right over the eggs reads 90. I also have an infrared thermometer that I can use to check egg shell temps. Doing that, the egg shells read between 91 and 100 degrees.

How can I fix the crazy temperature differential in this incubator? I do have a computer fan blowing in there. It's hard to see in the picture, but it's blowing from the left side of the incubator, across the heating element, to the right side of the incubator. We've also tried resting the fan on the bottom shelf and blowing straight up through the eggs, which also didn't fix the problem.

 

[Tabasco Jack]

First of all, you would be better off using a large shallow pan for your water. It's the surface area of the water that dictates the humidity. If the pan is too much, then cover part of it with foil to decrease the humidity level. I put a ping pong ball in mine to hold the foil off of the water.

As to the heat. What type of controls are there for setting the temperature level of the incubator? And where is the thermometer at for it? And what is the heating element like?

Is that a manufacturer and model number at the bottom of the unit? You might try googling an operating manual for it. That could tell you the operating range and temperature sensitivity of the controls.

I would set the fan so it blows across the pan of water. Old wooden incubators had curved sheet metal pieces at the rear that directed the airflow in a circle. Mine blows across the top, down the back, across the floor/water/heating element and then up the front.

Hope this helps some. I'd be glad to answer any more questions

 

[Amina]

The incubator says it's a Science Teaching Incubator from Lab Line Instruments company. I think it's the same as this one:
http://www.kroslakent.com/cgi-bin/shop/commerce.cgi?pid=932
It's so old though, that I can't find any information about it.

The temperature used to be controlled by a knob on the side, but the knob has broken off. It's hard to see, but you can change the temp using a screwdriver here:


This temperature control is very temperamental though, with a tiny turn of the screwdriver resulting in a massive temperature change in the incubator. So we added another thermostat. The red arrow is pointing to where I put the probe.



And here's the thermostat:


In this picture, we were trying to figure out what to set the thermostat at so that the eggs would be at the right temperature. Setting this probe at 92, the egg shells have temps ranging from about 95 to 99, and the bottom shelf was about 110 this morning. Maybe we should bump up the thermostat a bit, or maybe the thermostat should go closer to the heating element, so that the heating element is on frequently for short periods of time? Then we'd need to figure out again what to set the thermostat to, so that the eggs are a good temperature.

This would be much less confusing if there weren't such a huge temperature differential throughout the incubator though. We can certainly try putting a shallow pan of water on the bottom, and pointing the fan down at an angle onto the water. Are you saying that in your incubator, you have four fans? I guess we need to get three more fans to make this work?

 

[Tabasco Jack]

Quote: Is this thermostat actually controlling the heating element? It looks like the ones I have for the heating pads in starting seeds.

From what I found, the incubator has a 150 watt heating element. That should be ok for the size of the cabinet you have. It will heat up fast and cycle on and off based on your thermostat settings.

No, mine only has one fan but it's the same size as what is used in a kitchen range hood. You could try adding one more computer fan. Don't angle the fan to blow into the water, just over the top of the pan.

Is the cabinet metal? It's hard to tell from the photos but it looks like it. If it is, try adding a blanket over and around it to insulate it. That would slow down the heat loss. That could be what is causing the temperature difference between the top and bottom.

 

[Amina]

Yes, the thermostat is controlling the heating element, and yes, the incubator is metal, which is probably not good.

I added a second computer fan, and surrounded the incubator with pieces of styrofoam, which helped a little. I moved the thermostat back up to be level with the eggs. The thermostat thermometer now reads 101 (it's set to 100), the bottom shelf is 108, and the infrared thermometer says the egg shells are 98-99. I'd prefer to have the temperature more uniform in there, but at least it's better than it was??

I thought for sure this first batch of eggs was cooked... the temperature got very high for a while (not sure how long) on the first day, with the infrared thermometer saying the egg shells were 105-108. I was about to throw the eggs out yesterday and start over, but when I candled them, they almost all had embryos developing! I can't believe it. I wonder if there is any chance at all of these hatching out chicks.