I have assembled the MK138 kit to be used in an homemade incubator but cannot figure out how to wire up the 12v power supply and then power the 12v bulb to heat the unit which switches off when up to set temperature.
I have looked at the diagram supplied and checked all over the net and couldnt find anything that a non electrical engineer type could understand.
Currently i have the thermistor in the sensor connector as shown in the build up picture, info i now need is where to put the + and - for the 12 v power in and then to the 12v bulb.
The 12vdc connects to the terminals labeled SK2; they are next to SK1 where you put the thermistor. Connect the positive side to the SP2 terminal marked “+” and the ground to the SK2 terminal marked “-”.
The positive side of the 12vdc for the 12v bulb connects to the terminal marked “COM” on SK3; then connect the terminal labeled “NO” back to one side of the 12v bulb. Connect the 12vdc ground to the other side of the bulb.
Just out of curiosity, what is the wattage of the bulb you are using for heat? You will need to keep in mind that watts equals volts (12 in your case) times amperes, which means that the wattage of the bulb divided by 12 is the amperage drawn by the bulb. The board that I have is marked as 3A (amperes) maximum through the relay, which translates to a maximum of 36 watts. That’s not a lot of heat for an incubator, but may be enough.
By the way, I’m no expert on this, so you may want to wait for a better response from Velleman support.
Thanks for the info but to be honest still no clearer, tried a few things and cant figure this out at all.
Firstly am i right in assuming that the light i am using to heat the incubator should switch off when the relay clicks after the thermistor hits its temperature and also the little red light on the board goes out?
If that is the case alot of the wiring info i have read seems to point that the bulb is constantly wired to the 12v dc power supply anyway so cannot switch off no matter what.
To clarify for the sake of argument is we count the connections as below:-
SK1 Connection Points 1 & 2 - Used only for the thermistor
SK2 Connection Points 3 & 4 - 12 V DC Power Supply “+” to connection 3, “-” to connection 4
SK3 Connection Points 5 (NO), 6 (COM), 7 (NC) - Used by the relay
I have connected thermistor to connection points 1 & 2, 12V DC Power Supply to connection points 3 (-) & 4 (+)
In basic terms please where would i connect the 12v Bulb’s “+” and “-” connections to so that i get the desired bulb on / off depending on temperature? and are there any jumper wires used?
I am not ruling out a faulty solder or component yet , i have tried several ways to wire this up and tested the contacts and none seem to give me the desired result, does the relay on this kit break an earth to turn the bulb off or break a positive or neither, am i going in the wrong direction on this
You asked, “Firstly am i right in assuming that the light i am using to heat the incubator should switch off when the relay clicks after the thermistor hits its temperature and also the little red light on the board goes out?” The answer to that is “yes” if the power to the bulb(s) is wired correctly.
The MK138 provides no power to light the bulb(s); all power to light the bulb(s) must come from an external power supply. The relay on the MK138 simply switches the power provided by an external power supply. As I previously posted, you need a power supply with enough current capability to light the bulb(s) you are using. If you are trying to light bulb(s) whose total wattage is 36 watts, then you need a 12vdc power supply capable of supplying 3 amperes. If you try to run more than 3 amperes through the MK138, you run the risk of burning the tracks to-and-from the relay contacts. If you try to draw more power from your power supply than it is capable of, then you run the risk of damaging your power supply. If you would post the wattage of the bulb(s) you are trying to light and the output current rating of your power supply, it would be helpful.
You asked, “In basic terms please where would i connect the 12v Bulb’s “+” and “-” connections to so that i get the desired bulb on / off depending on temperature? and are there any jumper wires used?” My answer to that question follows.
If you are satisfied that the wattage of the bulb(s) does not exceed 36 watts and that your 12vdc power supply is capable of supplying all the wattage your bulb(s) require, then follow these steps. 1. Connect the bulb(s) “-” connection to the negative (-) side of your 12vdc power source. 2. Connect the bulb’s “+” connection to the NO terminal of SK3. 3. Connect the COM terminal of SK3 to the positive (+) side of your 12vdc power source.
If you do that correctly and the bulb(s) doesn’t light when the red LED comes on and the relay operates, then there is something wrong with your bulb(s) or your power supply.
Velleman support, please correct me if I am wrong, or take over and I’ll shut up.
Thanks for the reply, it makes perfect sense to me now
There must be either a faulty solder or component as goint by the wiring you described it isnt working correctly.
Will re-solder and test it all again tonight and see how it goes.
Cheers Tracecom for you detailed description on both replies, much appreciated
hi i’m also trying to set up an incubator using this thermostat, i’m running two 10w halogen bulbs its switching the bulbs but i’m finding the plug is getting really hot i’m unsure if this will work for the 3 weeks needed to hatch eggs
just wondered how you are getting on have you been able to get eggs in yet, is it running as it should, keeping temp etc.
