Peltier devices set up with STC-1000 controller for both heating and cooling to achieve constant temperature +_0.5

Thread Starter

Steveshep

Joined Feb 6, 2017
4
I’m trying to set up a water heating and cooling system using 3 Peltier devices connected to a digital controller STC-1000 (heating and cooling). To keep water at a content temperature 18C +-0.5 so heating below 17.5C and cooling above18.5C

The point is to heat and cool using the same Peltier devices by reversing the polarity, the problem I have got is the controller switches the Pos only (the Neg is constant). So how can I make it reverse the polarity on the Peltier to change from heating to cooling.

I have the device working well manually using a 6 pole DPDT Toggle switch (on-off-on reverse polarity). My problem is I can’t get it to work of the timer because it uses the common neg. these controllers are designed to use different devices for heating an cooling switching them ion and off ndividually .. I want to reverse polarity of the same device to do the same job .. but its got me stumped.
 

Thread Starter

Steveshep

Joined Feb 6, 2017
4
I guess I really need it to control (switch) both the neg and the pos in the same way as i can manually with the 6 pole switch, but how? if not possible with the STC-1000 does anyone know of a constant temperature controller that can achieve this function?
 

Analog Ground

Joined Apr 24, 2019
448
The STC-1000 controller I find has separate output contacts for heating and cooling. Is this your controller?

https://images-na.ssl-images-amazon.com/images/I/B1kOAUuVDWS.pdf

If so, a circuit with two SPDT relay functions would do the trick or a suitable DC motor controller. Something which gives an "H Bridge" configuration.

https://en.wikipedia.org/wiki/H_bridge

Here is the concept. It could go with mechanical or solid state relays or an H bridge DC motor controller. The key is using the heat and cool contacts on the temperature controller. Just replacing your hand and your switches.

PeltierHBridgeConcept.jpg
 
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Thread Starter

Steveshep

Joined Feb 6, 2017
4
Yes that is my controller (with the seperate output for heating and cooling).... Fantastic thank you for your recommendation & diagram ... I’m going to order the parts now.
 

Thread Starter

Steveshep

Joined Feb 6, 2017
4
Thanks Mate I used a couple of automotive 5 Pole relays it worked perfectly and has the advantage of reducing the load on the controller which was in danger of being overloaded going directly.automotive relays.jpgautomotive relays.jpg
 

Raychung

Joined Jan 25, 2021
6
Thanks Mate I used a couple of automotive 5 Pole relays it worked perfectly and has the advantage of reducing the load on the controller which was in danger of being overloaded going directly.View attachment 206070View attachment 206070
Thanks Mate I used a couple of automotive 5 Pole relays it worked perfectly and has the advantage of reducing the load on the controller which was in danger of being overloaded going directly.View attachment 206070View attachment 206070
Thank you for your wiring diagram. Is neg of fan & pump connected with com neg? Right?
 

MisterBill2

Joined Jan 23, 2018
8,207
Actually, those are automotive single-pole-double-throw relays. Five terminals but single pole. Just trying to keep the terminology right in order to avoid folks like me getting confused.
The circuit is brilliant for the application, by the way.
 

MisterBill2

Joined Jan 23, 2018
8,207
I see a big problem, which is that the fan and pump connections are connecting heat and cool coils together.THAT is a problem.
Do the fans and pumps demand a specific polarity? If not, then simply connect them across the peltier device terminals.
Presently, the heating and cooling will work but the fan and pump connections are totally wrong. But the best solution is another relay to control the fans and pumps. Terminal 86 of the relay connected to terminal 30 of the heating relay and terminal 85 connected to terminal 30 of the cooling relay. Then that relay will operate for either heating or cooling and it can operate the pumps and fans.
 

Raychung

Joined Jan 25, 2021
6
I see a big problem, which is that the fan and pump connections are connecting heat and cool coils together.THAT is a problem.
Do the fans and pumps demand a specific polarity? If not, then simply connect them across the peltier device terminals.
Presently, the heating and cooling will work but the fan and pump connections are totally wrong. But the best solution is another relay to control the fans and pumps. Terminal 86 of the relay connected to terminal 30 of the heating relay and terminal 85 connected to terminal 30 of the cooling relay. Then that relay will operate for either heating or cooling and it can operate the pumps and fans.

I have so confused. Like this wring?
 

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MisterBill2

Joined Jan 23, 2018
8,207
Exactly that wiring as shown in post #10. The problem is that the red wires connecting to the fan and pump also connect to both the heat and cool outputs, which connects them to each other. The result of that would be that if either the heat or the cool switched on, both relays will operate and nothing will happen except the fan and pump running. That is why I said add another relay across the peltier devices, so that when they are powered to either heat or cool the relay will operate and power the fans and pump.
 
Due to the nature of the TEC and probably what your cooling, I think it's the wrong type of controller. the cambion controllers I use to use were based on a wheatstone bridge and a bi-polar current output. The cold sink was water. Temperature really wasn't set as a variable It worked well enough.

In other cases, we just used a power supply. One side was fan cooled and the hat load was lamps.

What you likely want is a heat/cool controller with a 0-10V output for heat and a 0-10 output for cool. better yet is on that has a digital output for mode (heat.cool) and a 0-10V (0-100%) output.

In the sophisticated controllers I used to use, there were probably 100 pages of configuration options in two books. one was a set-up guide. You might have 4-20mA, 0-20mA, 0-5, 1-5, 0-10 V outputs,

Here https://instrumentinabox.com/product/tec-controller-1-channel-unidirectional/ is a controller. i'll bet it uses PWM and not constant current. The ones I used were constant current.

Back to your problem.

You need a 0-100% type of controller not an On/Off or bang/bang controller.
You need a heat/cool type of controller.
A delta T alarm would be useful.

The final element, needs to be an "H-bridge" fed by a PWM signal. The 0-10V needs to be converted to a 0-100 duty cycle PWM. The heat/cool digital signal sets the polarity of the H-bridge. The TEC has a max delta T and that should be an alarm that shuts down the PWM.

I've seen TEC's melt.

Your only controlling at one temperature, so only heating or coolling really is necessary. In my case, water was the constant teperature sink and the thermoelectric block provided the heat.

At 16C which is below ambient. You need a cooling type of controller where 100% is max cooling. You don;t realy need a heat/cool controller except for the fact that you usually only get the cooling action with a heat/cool controller.

You need the 0 to 100% cooling, not on/off cooling.
 

MisterBill2

Joined Jan 23, 2018
8,207
From what I have experienced and the control tolerance a properly adjusted on/off controller will provide adequate control at a small fraction of the cost. The heat transfer rate is slow enough and the tolerance nand is wide enough that with a fairly constant heat load the control will work adequately. If the specification was much tighter then possibly a staged system , or even an analog control system might be needed.
 

MisterBill2

Joined Jan 23, 2018
8,207
THANKS for letting us see the whole system package! I knew it would work with the on/off control, since the response time with Peltier heating and cooling is slower than the measuring response time in this sort of system. Feedback stability is dependent on he response time of the different elements, which determines the phase shift, and in this case you got it right the first time!
And I like that insulating enclosure it is assembled in.
 
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