ebay aquarium temp controller modifing for SSR

WARNING: This text is addressed to electrical engineering professionals.Electricity is very dangerous and can kill you. If you decide to follow the steps below, it's on your own responsibility and i'm not responsible for and damage that may be caused to you by following these steps.

In order to convert your mechanical relay temperature controller to an improved SSR temp. controller, follow these steps:

Open the controller by removing the front side of the sticker, and pushing in the little bumps that keep the front panel in place.



Here is the controller taken outside of its box.



Here you can see the two relays. The right relay is used for cooling and the left one is for heating.



If you look on the bottom of the PCB, you will see the weldings of the relays. Pins 1 and 2 are connected to the coil of the relay, and pins 3, 4 are connected to the switch.



Use a soldering iron to carefully remove the relays.



This is the bottom side after the relays were removed.



The relay is triggered by a 14V voltage in pins 1 and 2. Connect pin 1 to pin 3, and pin 2 to pin 4.
This way, we tunnel the 14V directly to the connections 7 and 8 of the controller.



Here you can see the wiring of the heating relay. Now, when the controller triggers the relay, it actually will set a 14V voltage in connections 7 and 8 of the controller.



Here is a photo of the top of the PCB with the relays removed.



Just FYI, this is the controller's power supply.



Now it's time to put everything together. Gently put the controller back into its box and push to hear the click.





Use a voltmeter to check your work. When the controller turns the cooling element on, you should have 14V on pins 7 and 8.



Check the heating element similarly by measuring the voltage on pins 5 and 6.



Change the markings on the controller's label.



Now connect the 14V pins to an SSR. I recommend using a 40A SSR.



A SSR relay has 4 pins. Pins 3,4 are the "input" or "trigger" pins. Wire pin 3 of the SSR to pin 7
of the controller. Wire pin 4 of the SSR to pin 8 of the controller.



The brown wires in the photo are the 14V wires.
This is the complete wiring diagram (the text in the purple square means "Fermentation Fridge").


And this is the modified, improved controller, which is very reliable and extremely cheap.





Good luck!

This is so simple. I don't know why more people don't do this! I recently performed this same mod on a 120v model. I removed the relays and added jumpers from the coil voltage to the outputs and am getting a solid 18vdc. Should be perfect for my SSR control voltage. It seems like there's so much misinformation/misunderstanding about the STC-1000; it's nice to see someone break it down a little. Are you still using this unit? How has it held up for you?

Oldish thread, OP only posted three times to HBT, maybe he's still around though.

Anyway, "simple" is in the eye of the beholder, I reckon - or maybe the brain. Judging from what I've seen over the years, that's not going to be considered "simple" by most folks outside of the Automation forum.

I didn't want fried relay points to be the weak point on my keezer controller, so I drive the relays with a cheap 12V wall wart and in turn drive external relays with 12V coils. Very low current passing through the controller relays, don't have to crack open the case and hack the guts, and if it does expire it'll take just a few minutes to swap in a replacement...

Cheers!

Hello,
This modification work for me for more than 2 years with absolutely no problems.
Emanuel

All the images are gone.Anyway to restore them?