pid controllers

[hedgerow pete]

well its that time again when when we all start dusting off the incubators again. i was looking at the 80 egg one i have as its home made and started looking of ideas to improve it.

does anyone here have an electricial back ground or understanding.

the idea is this, for my home brew boiler we use a pid temp controller, similar to this one, with a relay and then a heater , ok so its a tad hot for eggs but when we tried it at the lower temp it worked well enough, just needed a heater cable rather than a kettle elements or two.

whats your opinions on it basic ideals

http://www.ebay.co.uk/itm/290942960417?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

heater cable, 40w a metre
http://www.ebay.co.uk/itm/271138232218?var=570136914352&ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

relay
http://www.ebay.co.uk/itm/390628939504?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

now for my home brew set up i use all but the heater cable and it is perfect for temp controlling. i want to move away from light bulbs completely and something digital controlled would be great to have,

 

[chrismahon]

I raised a similar question to this last year Hedgerow Pete when trying to find a way to repair an existing incubator cheaply. The answer boiled down to the way incubator control circuits work. The power to the heater isn't switched on and off but is modulated so that the power is reduced and increased in pulses. The heater is never actually off, but simply operates at reduced and increased power. This maintains a smooth and constant temperature. There is a range that normal thermostats work over, not to be confused with the readout accuracy which may be very good. The switching range is typically 2 degrees, so the heater will be off allowing the temperature to fall 2 degrees before the heater comes back on again. This is too wide a range for good results with hatching. Typically a proper incubator control circuit will hold the set temperature to within 0.5 of a degree.

Brinsea do control units that have mains fan and heater outputs. 21.332 is the board code I looked at. It is a replacement part for the Octagon 20 MK111.
Unfortunately they are not cheap, but that's what you really need. Then you will need an accurate thermometer to set it against. The heater cable will be fine but you should really have a fan to avoid hot and cold spots. Hope that helps.

 

[hedgerow pete]

cheers for the posting, i was wondering what the downsides were. so heater cable is fine. we will have to look in to the controller issues seperately.

out of intrest did you find a cheaper alternative to the controller unit?

 

[chrismahon]

No I didn't Pete. But I managed to repair the original controller board on our incubator yesterday. Another thought -with a 2 degree switching range there will be an additional delay whilst the heater comes back to temperature and starts to add heat back. That could increase the effective range of temperature seen inside the incubator.

 

[hedgerow pete]

yes i was thinking that as well, i shall do some further research to see.

i did look at the ascotts set up they sell and its run on the similar lines of controller and heater wire, so i do wonder if they have the same temp fluctuations as well