can't regulate temprature in handmade incubator

[Rod-T]

Hey I'm the one with the incubator problem I built the incubator with 1.5" space all the way around the inside of the walls are hollow and act as air duct system there are two holes in the top matching the holes in the bottom that the blue fans are sitting over the wafer thermostat is located at the top inbetween the two return air duct holes the fans blow the air across two 250 watt heat lamps straight up through the box then through the two 4" holes in the top around the box inside of the walls and back through the fans and across the lights again the problem is my brand new wafer thermostat started with a 5 degree swing in temperature then after running for a day had a 6* temp swing. After running it the last three days straight it has settled on about a 2.5* temp swing the heat turns off at 101.1and back on at 98.8 I don't know if it will hold the same over the next couple days but if it doesn't I'm going to return it and get a new one If it does hold a 2* swing should I set it to turn off at 100* after the lights go off it continues to heat to about another .5* then starts to cool very slowly The fans are on constantly circulating the air just the heat lamps turn off and on

Did you try lower watt bulbs?

 

[CBWO]

I did sorry I forgot to say that I started with two 60 watt bulbs and after 2 hrs the temp was 85* then I tried two 100 watt bulbs after 30 min the temp was 91* and very very slowly climbing so I put two 250 watt heat lamps and tithe temp gets to 100* in about 10 min. The inside measurements of the box are 18x18x45 There is a 3/8" thick plexiglass door on the front and I haven't put weather stripping around it yet because I figured the small crack around the door acts like a vent hole that a lot of people say I need

 

[Rod-T]

I did sorry I forgot to say that I started with two 60 watt bulbs and after 2 hrs the temp was 85* then I tried two 100 watt bulbs after 30 min the temp was 91* and very very slowly climbing so I put two 250 watt heat lamps and tithe temp gets to 100* in about 10 min. The inside measurements of the box are 18x18x45 There is a 3/8" thick plexiglass door on the front and I haven't put weather stripping around it yet because I figured the small crack around the door acts like a vent hole that a lot of people say I need

500 watts and it still took 10 min to get to a 100 degrees? Seems like alot.. must have some leaks. The ductwork sealed,? what made you put light bulbs on bottom? Are you following someone's design?

 

[CBWO]

It's my design after looking at a bunch of other incubators both homemade and store bought I'm just guessing at the ten minutes I never timed it There is a crack around the door because I haven't put weather stripping on it yet I figured the small crack around the door would act somewhat as a vent and was only going to worry about sealing it if the humidity control becomes a problem but because of design the entire area that has to be heated is 21x21x48" it isn't a big difference but it would make a difference overall it's a pretty big box and when it's started from outside temp the wood and everything has to heat up along with the air and the plexiglass door after it hits 100* and shuts off heat when it turns back on it takes less than 2 min to heat up to 100 again and remember that's a few degrees not just one degree

 

[Rod-T]

It's my design after looking at a bunch of other incubators both homemade and store bought I'm just guessing at the ten minutes I never timed it There is a crack around the door because I haven't put weather stripping on it yet I figured the small crack around the door would act somewhat as a vent and was only going to worry about sealing it if the humidity control becomes a problem but because of design the entire area that has to be heated is 21x21x48" it isn't a big difference but it would make a difference overall it's a pretty big box and when it's started from outside temp the wood and everything has to heat up along with the air and the plexiglass door after it hits 100* and shuts off heat when it turns back on it takes less than 2 min to heat up to 100 again and remember that's a few degrees not just one degree

Personally I think I'd had light bulbs at top. But without being there and checking each level. And can't really say.. is your size of ductwork 1.5 all 3 sides? Or just one side.. you may not have enough airflow. . I hope you get this figured out ..

 

[CBWO]

I thought the bottom was better because the heat will naturally rise didn't want the top to be hotter and the bottom colder even with the fans The duct is 1.5"x18" all the way around the box 4 sides. Two 4" fans they move a lot of air. I lit an old rag on fire while it was smoldering and smoking a lot I held the rag at the top and in just a couple seconds smoke was pouring out of both fans on the bottom after it circulated through the duct there is plenty of air circulation I think I'm just going to request a replacement wafer and hope that's the issue

 

[Rod-T]

Heat natural rises. So with radiant heat..from the bulbs underneath. . I suspect the bottom eggs are going to get more heat... at top the heat would enter the duct allowing time to blend with the air to come out bottom.

 

[MeepBeep]

After running it the last three days straight it has settled on about a 2.5* temp swing the heat turns off at 101.1and back on at 98.8 I don't know if it will hold the same over the next couple days but if it doesn't I'm going to return it and get a new one If it does hold a 2* swing should I set it to turn off at 100* after the lights go off it continues to heat to about another .5* then starts to cool very slowly

A 2°- 4° swing in air temp is perfectly acceptable... Remember it's the internal egg temp that matters not the air temp or any arbitrary air temp swing... Make a fake egg and use the temp inside the fake egg to adjust the thermostat swing, you won't see nearly as much swing as you do with air temp, if any... Generally as a starting point for air temp swing you are going to want the high and low to average 99.5°... Then you might need to adjust up or down a bit depending on the duty cycle of the heating element...

I did sorry I forgot to say that I started with two 60 watt bulbs and after 2 hrs the temp was 85* then I tried two 100 watt bulbs after 30 min the temp was 91* and very very slowly climbing so I put two 250 watt heat lamps and tithe temp gets to 100* in about 10 min. The inside measurements of the box are 18x18x45 There is a 3/8" thick plexiglass door on the front and I haven't put weather stripping around it yet because I figured the small crack around the door acts like a vent hole that a lot of people say I need

500W is a boat load of heat, how many cubic feet/inches is your incubator? And are you venting out with large holes or something?

To put that in perspective my 1.9 cubic foot (3240 cubic inch) incubator will hold temp perfectly fine with 60W bulb, at maybe 50% duty cycle and recovers plenty fast...

Even large (300+ chicken egg) cabinet incubators like the Brinsea OvaEasy line only have give or take a total of 200W maybe 300W of heating...

 

[CBWO]

A 2°- 4° swing in air temp is perfectly acceptable... Remember it's the internal egg temp that matters not the air temp or any arbitrary air temp swing... Make a fake egg and use the temp inside the fake egg to adjust the thermostat swing, you won't see nearly as much swing as you do with air temp, if any... Generally as a starting point for air temp swing you are going to want the high and low to average 99.5°... Then you might need to adjust up or down a bit depending on the duty cycle of the heating element...
500W is a boat load of heat, how many cubic feet/inches is your incubator? And are you venting out with large holes or something?

To put that in perspective my 1.9 cubic foot (3240 cubic inch) incubator will hold temp perfectly fine with 60W bulb, at maybe 50% duty cycle and recovers plenty fast...

Even large (300+ chicken egg) cabinet incubators like the Brinsea OvaEasy line only have give or take a total of 200W maybe 300W of heating...

 

[CBWO]

Mine is roughly 18,000 cubic inches or 9 cubic feet Once I get the temp regulated or at least stable I can play with the wattage of the bulbs and adjust for hot spots if there are any but first I think I need to get the temp stable so I have a constant to compare adjustments to