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PostPosted: Fri Dec 19, 2008 2:01 am 
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Superior Bird
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Neil;
In the time it would take me to look those words up in the dictionary I could probably build 3 incubators. :roll:


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 Post subject: thermostat
PostPosted: Sun Dec 21, 2008 6:05 am 
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Hatchling
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My incubator at home has a thermostat based on a UAA2016. Google the data sheet. For a really good thermostat, it might be a good place to start.

Be careful about off the shelf thermostats. I tried a flash digital one worth about $300, and even with hysteresis set to 0, the temperature varied by as much as 2 degrees, accouring to my jaycar temperature logger. (USB temp logger, highly reccomended!)

I disagree about the comments about an incubatore thermostat being set to a temperaure by the manufacturer. I am yet to see anything that confirms 100% what the perfect hatching temperature is, and certainly for me, a fair bit of tweaking is needed to get the optimum temperature.


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PostPosted: Sun Dec 21, 2008 9:22 am 
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Champion Bird
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Hi Zach
Due to the nature of how a thermostat works there will always be a degree of hysteresis, but the better the thermostat is the smaller the swing between high and low temps will be. The important temperature reading is the average between the high and low. I have a microprocessor based thermostat that has a half degree difference from hi to low (Custom designed and made by Denis) and an old style wafer that i can get set to .75 degree between hi and low (just lucky to get a good one).

With my microprocessor thermostat, I plug it in, let the incubator stabilise check the temp logging to ensure all is well and set the eggs, turn on the auto turn and forget it except to check the water trays.

Regards
Trev

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PostPosted: Mon Dec 22, 2008 4:18 am 
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Hatchling
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That seems impressive for a microprocessor type. I cannot help wondering if the polystyrene box that is my incubator adds to the hysteresis problems by not retaining any heat.

What I liked about the zero voltage controller was that is slices and dices the waveform as neccessary to maintain a constant temperature. Making a microprocessor do that would be awefully tricky


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PostPosted: Mon Dec 22, 2008 11:56 am 
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Gallant Game
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Zachypoo wrote:
That seems impressive for a microprocessor type. I cannot help wondering if the polystyrene box that is my incubator adds to the hysteresis problems by not retaining any heat.


Foam is an excellent insulator but as you mention it has zero "THERMAL MASS".
A good way to improve temperature stability is a "heat sink". Put a sealed container of water in the incubator. It will retain heat without adding to your humidity.

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PostPosted: Mon Dec 22, 2008 12:00 pm 
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Superior Bird
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Zero voltage switches are probably the most common type of electronic thermostat. Most thermostats that use an NTC would likely use the zero voltage switch. It is mostly about the component count. The Bellsouth has one.


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PostPosted: Mon Dec 22, 2008 6:57 pm 
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Champion Bird
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A conseqeunce of needed ventilation so the eggs actually hatch is that you loose heat and draw in cold air. This is why no matter how well the incubator is insulated or how much heat the material it is made of holds, the thermostat will still cycle on and off.

(Rant start)
Any company that manufactures the number of units that bellsouth or GQF do buy their components in bulk and realise the discounts that come with bulk purchases, combined with having PCB's made in 100 batches instead of 1 or 2 at a time they could equip there bators with state of the art microprocessor thermostats that are spot on out of the box.
So the question begs to be asked why do they still stuff around with wafers or crap PWM style thermostats that need calibrating, and for that matter still air and still charge a bucket load for what is essentially a peice of styro packing material?
Then the other end of the scale are the R-com style untits and others that are all singing and dancing and cost even more. (but still need to be calibrated)
(Rant end)

At the end of the day a consumer item needs to be simple to use with out all the fiddle involved b4 you even start, we all know that there is enough other stuff to worry about going wrong during the incubation period and hatch, with out the hassle of setting it up right at the start.

But on the other hand I and other's choose to build our own incubators and deal with all the bugs that come with it, but we invariably use a trusted thermostat that we dont have to mess with first. Its just one less thing to worry about.

Regards
Trev

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PostPosted: Mon Dec 22, 2008 6:57 pm 
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Junior Champion Bird
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Denis wrote:
Zero voltage switches are probably the most common type of electronic thermostat. Most thermostats that use an NTC would likely use the zero voltage switch. It is mostly about the component count. The Bellsouth has one.

What are "NTC" and "zero voltage switch"?.


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PostPosted: Mon Dec 22, 2008 7:18 pm 
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Junior Champion Bird
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Quote:
What are "NTC" and "zero voltage switch"?.


Google them and find out - they are really techie terms.

chookstarter


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PostPosted: Mon Dec 22, 2008 8:26 pm 
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Hatchling
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Location: Christchurch, New Zealand
Thanks for the 'rant' Trev.

Are you able to give a run down on how a microprocessor based thermostat controls temperature. I assume it would do the on / off thing, as opposed to modifying the sine wave to the element via an SCR. I can't help thinking an SCR controller would be the better option, as much as I try to stay away from analogue electronics.

Sure you can use a devise such as a DS18B20 to get mote accurate readings than a NTC but what do you do with the output?

One of the latest RS magazines has a really good temperature control. Can't tell you much about it as it is at work (and I am on holiday!) but well worth a look it if you see it. Would be nice to have a spare $600 to buy one of their flash controllers!


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PostPosted: Mon Dec 22, 2008 9:04 pm 
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Champion Bird
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Zach in a nut shell, the thermo uses a DS18b20 to sense the temp, a micro processor reads the sensor and according to the program it decides whether to switch a Triac on or off via a optocoupler. the triac switches on in my case 2 x 100w incandescant light globes to supply the heat to the bator.
i have also used the same micro to design a auto turner control circuit.
I blame Denis as he introduced me to these devices. :P
Regards
Trev

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PostPosted: Tue Dec 23, 2008 5:12 am 
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Hatchling
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Location: Christchurch, New Zealand
Hi, thats pretty much as I expected. I once used such a devise in an incubator alarm, which sends me a txt message via my mobile phone if the temperature goes too low.

Based on what has been discussed here, I consider such a microprocessor design inadequate for a 'polystyrene box' type incubator, hence companies like bellsouth making theirs around the zero voltage switch.

They charge $60 for such a thermostat which does make for a very expensive polystyrene box!

And despite what others have said, I like my thermostats adjustable. I seem to get better results with a slightly lower than normal temperature. May be that New Zealand chooks are used to the cold, but more likely i suspect that temperature varies inside the incubator, depending on where you measure it, as my cheap nasty (but adequate) bellsouth is a still air model.


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PostPosted: Tue Dec 23, 2008 6:44 am 
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Superior Bird
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Zach I think you may be a bit confused about how the UAA2016 actually works.

It doesn't actually do the proportional regulation by varying the on off time for each quadrant.
I think you may have seen how dimmers work which is by firing the triac using pulses of varying widths some time after a zero crossing.

The pulse width in the UAA2016 isn't controlled by the temperature but a resistor that is selected depending on the actual triac used. The pulse width needs to be such that it turns the triac ON and keeps it ON until the other parts of the circuit decide it's time to come off. But you need to be able to adjust the pulse width to suit different triacs.

The zero crossing idea is to fire the triac as close as possible to when the AC wave form is at zero volts. So that when it does come on it doesn't just suddenly go from 0 to 240V in no time flat.

The UAA2016 is actually designed for use with pretty power hungry resitive devices such as irons. You are not allowed to turn them on and off any more than once in 30 seconds. The zero crossing part is only to do with keeping RFI under control.

The proportional regulation is done using the sawtooth wave. see fig4 in this data sheet. http://www.onsemi.com/pub_link/Collateral/UAA2016-D.PDF
It's important to note that the period of the waveform is 30+ seconds.
Your incubator may respond a lot quicker than the devices this chip was designed for. I know mine certainly would.

When you look at the From Temperature Sensor (Sense Input) curve it is drawn as pretty flat and of course everything looks rosy. But the From Temperature Sensor (Sense Input) curve is actually determined by how much and how quickly your incubator temperature rises. 30 seconds may be to long to wait to make a decision.
So rather than prevent overshoot it may actually be causing it.

Hope that helps.


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PostPosted: Wed Dec 24, 2008 1:57 pm 
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Dapper Duck
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I dont know much about electronics so I bought my thermostat to make this incubator. It is Pola ll and I used a heating element from a footspa ($3 at a flea market). Turns automatically via slow turning motor (8 rpd aprox) and a water tray auto fills from the 20L container on top....Im just too lazy :mrgreen: .

Image[/img]


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PostPosted: Wed Dec 24, 2008 9:02 pm 
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Champion Bird
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Hey quailguy
please start a thread and detail how you made your bator and include lots of pics including the turner setup

Cheers
Trev

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