Rex 100-C temperature controller from Impuls to Relay output

[Nicolajbech]

Hey all

I both a Rex 100-C-V-AN temperatur controller.. I just finde out that the "V" stands for impuls output ... and i need a relay output "M" for my sous vide machine..

Does anyone know if it is possible to rebuild this Rex 100-c-v-an from impuls output to relay output?
and how to do it?

Nicolaj - Denmark

 

[cowboybob]

Welcome to ETO, niclajbech!

Get yourself an SSR (Solid State relay) with the proper rating and drive it with the "V" output.

Do you have the probe (thermocouple) for this device?

 

[Nicolajbech]

Hey Cowboybob

And thank you..

I have a SSR 40 A.. but i SSR relay i going til run a rice boiler.. and then it is flashing ( impuls output ) i dont think my rice boiler will last long... the impuls is like 1 sec on and 1 sec. of..



what I like to do is rebuild my rex 100 to a relay output.. If possible.

 

[cowboybob]

How comfortable are you constructing a small 555 timer circuit?

If you take the pulsed output of the Temp controller and use it to trigger a 555 "one-shot" timer, designed to provide, for example, a 2 second (or longer) postive pulse that is used to trigger the SSR, I think that would work.

It would assure a continous signal to keep the SSR turned on and your rice cooker with steady power, only interrupted to control its temperature.

 

[4pyros]

I don't think the pulses will hurt your cooker, it is a resistive load.
You should be able to keep your relay on between pulses with a diode and the right cap.

 

[dougy83]

If the output is changing too quickly, then change the cycle time to something larger. In the manual, https://www.mpja.com/download/rex-c100.pdf , the 'T' setting proportional cycle is the amount of time for one ON-OFF cycle of the heating element. This is by default 2 seconds for the impulse-output model; which matches your observations. If you set it to 20 seconds, your 1s-ON/1s-OFF will become 10s-ON/10s-OFF.

 

[alec_t]

I agree with 4pyros suggestion re a diode and cap, if the SSR is suitable. Can you post a link to its datasheet?

 

[dougy83]

The REX-C100 is a PID controller with PWM output. The PWM period is a settable parameter ('T'), with a range of {1 .. 100} seconds. It is much simpler just to change the parameter than to add extra circuitry.

WRT post 3, the SSR and the relay will both have similar on & off times. The flashing is due to the REX-C100 controller, not the SSR.

 

[4pyros]

The REX-C100 is a PID controller with PWM output. The PWM period is a settable parameter ('T'), with a range of {1 .. 100} seconds. It is much simpler just to change the parameter than to add extra circuitry.

WRT post 3, the SSR and the relay will both have similar on & off times. The flashing is due to the REX-C100 controller, not the SSR.

Don't think changing the parameter will stop the output from pulsing.

 

[dougy83]

It will slow down the pulse rate, and in general increase the width of the pulse.

Putting a pulse extender on the output will increase the temperature overshoot. How much are you planning on extending the output pulse?

There are other parameters in the controller; if you set the P to max, and the I&D to min, then the output should either be high for the full period, or low for the full period. The temperature control will be probably as poor as using a hysteretic controller.

 

[4pyros]

There are other parameters in the controller; if you set the P to max, and the I&D to min, then the output should either be high for the full period, or low for the full period. The temperature control will be probably as poor as using a hysteretic controller.

Its for a rice cooker don't think the OP cares.

 

[dougy83]

Its for a rice cooker don't think the OP cares.

It's for a sous vide cooker.

 

[ChrisP58]

Unless you are using purely linear power control method, I can't think of any way to control the temperature without some sort of pulsing. The only real question is what period you choose. Generally speaking, a shorter period will give you a more even temperature. For something like a heater for water, I would guess that a period anywhere from a few seconds to dozens of second should be OK. But you really need to look at the thermal characteristics of your target load.

How much water are you working with?
What is the power rating of the heating element?
What temperature delta are you trying to maintain?

There are probably a few other questions to answer to really engineer a system, but it'll probably be easier for you to just put it all together and see how it works. But unless there is something else in the system that doesn't want to be pulsed on and off (such as a fan or an existing internal temperature controller) I wouldn't worry about it pulsing.

 

[4pyros]

It's for a sous vide cooker.

I dint know what that is but the OP calls it a "rice boiler".