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Rex C100 temperature controller - changing settings Answered

I recently ordered a REX C100 for my electric melting furnace project.
As it came already with a SSR and temp sensor I only added a sensor capable of reading more than 400° of the supplied one.
These controller are dirt cheap and have lots of support in the modding community - although you now can get them new in all variations so no more modding required.
Internally they run on 12V DC, so even mobile use is possible (but this time after modding).

My problem with this controller started with the not included manual.
As it is no China clone but an original from RKC Japan, I downloaded their manual and tried to adjust the max temp settings as well as changing to the thermocouple.
To my surprise the menus for that simply did not exist on my model.
Reading a few more manuals showed that to get to the "initial or factory setup" you need to change the lock code.
Here things get confusing:
Once in the lock menu setting most manuals state to enter "0000" to activate the hidden menus.
(Mine was alreay on 0000)
Others state to set the code to "0100".
In any case you have to hold the setup key for a few seconds to store the changes and after that hold the settings and shift key for about 5 seconds to enter these factory menus.
After being close to send the unit back I tried different code combinations and finally found that "1000" actually activates the hidden menu on my model!
But again there was no joy as several vital settings still did not show up.
To finally get all settings another step is required:
The first item in the hidden menu is "CODE" and it shows as "0000".
After changing this to "0001" the setup key can be used to get to the settings to change the max and min temps.
Once all this done the controller actually shows the selected sensor and if Celsius or Fahrenheit is used at the start and from now on simply by clicking through the hidden menu with the setup key you can get to the min and max temp settings again.

I hope this info will help someone running into the same brick walls as I did...

28 Replies

sandeep kumars1 (author)2018-03-12

I have REX C100. But the temparature does not stop as desired. It keeps on increasing. I have tried changing the PID and the SSR in case any manufacturing issues. But not able to solve the problem. Any help please....

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Dear Sandeep, you need to tune your PID controller. The default settings are pretty much useless, unless you're quite lucky.

You can try manual tuning, a very simplified and crude procedure is as follows: if the temperature overshoots a lot, decrease the proportional (P) and integral (I) constant. If the temperature is oscillating a lot, decrease the I constant. If the regulator is switching on and off rapidly, increase the derivative (D). If the controller is unable to reach the designated temperature, i.e. undershoots, first increase the P constant and/or I constant, but not a lot, in order to prevent oscillations.

You can also check out the Ziegler-Nichols PID tuning method, there are a lot of resources on the web about it. It requires a bit of experimenting and calculating, but should provide you with a very good set of parameters to setup your controller.

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Col68 (author)2018-03-31

Hello planet,

i ordered a cheap REX-C100FK02-V * AN DN on Aliexxx and here is the received PID :) the main chip is a HY16F88VB, according to my research on the internet it is not a chip PIC16Fxx , in short considering the PCB it makes me think about security, do you think it is possible to use it ? all information would be very appreciated, Thank you in advance, cordially.

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priest77 (author)2016-04-14

I've ordered from ebay my second c100 but this one is "Berne REX-C100" and the menu differs from my old "RKC REX-C100".

Problem is that I need it to show me decimals of °C because I am using it in my egg incubator. I have PT100 (thermocouple) and I want to use it instead of the K type thermocouple that came with C100.

When I power it on in shows me:


and then



Then when I enter in settings menu I have this (all with only 3 digits values):

AL1 (050)

SoH (999) this one is locked

ATU (000) this one is locked

P (030

I (240)

d (060)

Ar (025)

T (020)

SC (000)

LCK (000)

When I change LCK to (100) I get:

SL1 (000)

SL2 (000)

SL3 (000)

SL4 (001)

and here in SL(x) everthing is locked except SL4. I think that if I could unlock SL1 that I can change the thermocouple type, but how?

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Bricola55 (author)priest772016-07-27

Hello, I've recently bought a Berme REX-C100FK02-V*AN by Banggood and got the same settings and same problem. They do not really answer to all my questions, especially what is this SoH parameter for. By me the SoH is not locked, and I can change the value, but I do not see a significative changing if I set it to 000 or 999. I have to dig a bit more on it.

The model I've got can not work with resistive sensor like Pt100, it is
normally fixed for TC sensor and is calibrated to the K sensor provided with it. The SL1 can not be change. For this, as fare as
I've seen, a hardware setting must be done. I'm going to try this way to
see how it will work.

Anyways, by trying key combination, I found the sensor calibration (I assume it is). Be careful to not do it unless you know what you are doing, otherwise you are going to lost the calibration made in the factory ! If you have some mV generator it might be possible to change this calibration for an other TC type (not tried yet).

Only for info, again do not make it if you can not correctly recalibrate the unit !

Sensor calibration :

Push Down and Set key together >3s. At this time you will see LAS, which I assume is the Lower Analog Span calibration point, on the upper display (red) and a value on the green display which is the actual reading value from the sensor (you can see changing if you heat or cool the sensor). Generate the 0°C correct value (see bellow) and push Set key to accept and go to the HAS parameter, which I assume is the Higher Analog Span calibration point. Here the correct mV value should be generated (see below). Key Set to accept and come to a CAS parameter that I do not know what it means. Key Set again and come to the normal display.

I've been playing a bit with those parameters and saw how they change the calibration. 1st the LAS and HAS value are figure value and not the real temp.

The LAS does not give 0 when the input is 0mv, but it shows 64 (in my case). To have a 0°C displayed in normal mode, the LAS value, for my instrument, is 83, means an input of 1.3mV. For the HAS, it seams the target value is 430°C (don't ask me why, but it's what I've found). So a K sensor type at 430°C gives 17.667mV (regarding TC tables). If you put a 17.6mV, HAS shows 395, and this will display 428°C in normal mode. We are quite near. The CAS does nothing for this instrument.


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GustavoS65 (author)Bricola552017-01-31

Bricola55, how are you generating this mV input to the PID, mine it's not calibrated, this SET + DOWN, mess with all the calibration and guess what: I found this hidden menu before knowing what it does.

I'm planning to generate this aproximate temperatures to try to roughly calibrate the PID again.

Please, can you describe your equipment?

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Downunder35m (author)Bricola552016-07-27

Thanks for sharing!
I know chinaman changed the REX100 models a few times but the latest changes seem to affect what we were able to do before.
Anyway, I can not really recommend a manual "calibration" of the sensor values, this should be performed through the automatic routines where possible.
Only if you have all vital parameters for a probe you might be able to find the corresponding values through the manual calibration.

I am still quite sure there is a way to get to the code settings as in previous models but now it might be required to use software or at least access to the programming.
Why do I make this statement if it seems noone is able to do so?
Quite simple: I have seen these newer Rex models with different sensors and temp ranges offered online.
One even for incubator use with a temp range of just 25-45°C...
I am reluctant to order one as I don't really need one right now and would not know what model variation I get.
It could be as simple as pressing the right buttons together or doing so while switching on - quite a few devices alow access to hidden parameters only during startup.
Could also be that two testpoints need to be shorted on the circuit board (or extended outside to a switch).
Worst of course would be the real need to access the programming part.
But maybe your insight will make other people try, try again, and then some more to find out how we can access them.

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Bricola55 (author)Downunder35m2016-07-28

Hello, as you can see on the picture of my Breme Rex-C100FK02-V*AN, the selection between TC and RTD is now made at the hardware level. I'm going to test this to see if only the bridge selection is enough or other adaptation must be performed.

I've also been trying a lot of key combination at start-up and during normal running without finding the Grail. I won't give up, but chances to find out begins to fade.

I think they really have made thinks more complicate and lock access. There is may be a possibility to come into the program itself, look at the 4 pins contact near U3 (that is of course without type, number or code on it). I'm not at the right level to go into, may be someone else can.

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JoachimS9 (author)Bricola552016-11-05

Hi, did you test this? I have the exact same problem, and after opening it up I'm very tempted to just go ahead and cut the three TC bridges and soldering up the three RTD bridges. I'm kinda worried about calibration, though, as RTD Pt100 probes come in a variety of ranges, and I'm not sure if the kind I have (-50C-500C, 1/2" NPT threaded detectors) would even give a temperature in the ballpark of what's correct.

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nixmit (author)priest772016-09-21

After the LCK setting my Berme Rex-C100 gives:

oH (002)
According to some manuals it sets the differential gap

In my understanding it's about the limits of regulation.

Factory setting is 002, which should mean SV plus or minus one degree.

Anyway my system overshoots sometimes more than 1 degree; enough reason to order a genuine RCK PID with Pt100 probe.

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Downunder35m (author)nixmit2016-09-21

Overshooting can be a simple cause of a wrong PID setting.
I would try the autotune function first.
After changing settings it is often required to do this.
Especially if the object in question is quite big or heats very fast.

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nixmit (author)Downunder35m2016-09-21

My comment was about the Berme Rex-C100, which is a (too) cheap imitation of the original RKC PID.
As you can see in priest77's post, the Atu setting is blocked.
So I fumbled around with some other settings, but the final solution must come from my newly ordered RKC Rex-C100. ;-)

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Downunder35m (author)priest772016-04-14

There might be a similar way to unlock the menu on your model but:
Even with a different type of thermocouple it won't be any good for eggs.
Been there done that, moved on.
Even with modified pid values the controller will have over 2° of fluctuation, which is pretty good for heating other things but not nearly good enough for incubating.
You need betwwen 37.8 and 38.2°C for the eggs with changing temps during the different stages - no chance to get that accurate with a REX.

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priest77 (author)Downunder35m2016-04-15

Actually my old "RKC REX-C100" can hold the temperature very steady on my forced air incubator. I am using it with PT100 thermocouple with tree wires, and after changing it in settings to PR100 I've got decimals. I also think the hysteresis is set to 0 and the fluctuation is 0.2°C, and very seldom goes to 0.3°C.

I think I will order another one but with RKC label, because this "Berne" I can't unlock to modify settings.

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Quanny (author)priest772016-04-24

Hi, I was wondering if you have managed to fix the problem, as I am having the exact same thing happen to my c-100

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priest77 (author)Quanny2016-04-25

I gave up from it and I ordered another one on ebay but now with "RKC" label.

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Downunder35m (author)priest772016-04-15

Thanks for that info, I think it will be usefull for quite a few people.
Was not aware that you can this too as I only needed a much higher temp range.
Have you tried other code combinations like 1100 and such?
Although the menu changed there might be a chance they left the inner workings similar.
But sadly it also shows that the guys don't want us to play with them to get better features. :(

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Bakwegesa (author)2016-05-19

Hi, I have a REX C400
PID and SSR40 DA relay and a K type thermocouple. I am applying it with 60W
heating light globes for temperature control of a chicken egg incubator system.

The challenge is that everything is all wired up well and I set the SV temperature
at 370C. The SSR does not switch on and the PV temperature appears
high even when the ambient temperature is low.

My question is would there be anything wrong with the PID control output which fails
to furnish the right Voltage and trigger to turn on the SSR.

Please urgently


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Downunder35m (author)Bakwegesa2016-05-20

370°C might be slightly too high I would use 37.8 the first day, then 38 for the next week, after that 37.6 till hatching.
Takes a day longer but at least for me give a female/male ratio of 7/3.
But I guess you know that and had a typo...
I don't have the C400 but if the set temp is within what the thermocouple has show it should work fine.
There are different types available, the standard ones are for up to 400°C, mainly for water use are to around 150°C, the good ones for your purpose are only rated to about 75°C and offer a much higher sensitivity.
Test you system with some water.
Drop the thermocouple in and start heating, the lights should come on long before boiling - if the do when the water is not even really hot you might just have to run the PID tuning.
No clue about the procedure on the C400 but it should be stated in the online manual.
If it allows for it do the PID tuning for a temp of 40°C.

But there should be also a LED indicating if the thing is switching, so you might not need to drag the heating lamps to the hot water for testing, just check the LED ;)

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Bakwegesa (author)Downunder35m2016-05-20

Thanks for the advice, 370 Deg Centi was erroneously typed but I meant 37 Deg Centigrade.

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KimJ42 (author)2016-02-14

Hi, I have the same setup, but I cannot enter 1000 in the setup menu since my pid only shows 3 digits in the display - 000, can only enter 100!!

Any sugestions or is it maybe a bad pid

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Downunder35m (author)KimJ422016-02-14

They change the "trick" to get into the hidden menue.
But the Rex 100 always has 4 digits to my knowledge - you are certain it is the same model?

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KimJ42 (author)Downunder35m2016-02-15

yes it is the same model, just ordered a new one, then I must Compare them and see

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Quanny (author)KimJ422016-04-25

hi, were u able to solve the problem, same thing happening here, i only have three digits, but i had four.... i don't know what i did

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KimJ42 (author)Quanny2016-04-25

Hi, no I haven't solved it, and the second one I received is doing exact the same, just as priest77 is writing

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RobbT3 (author)2016-01-25

Hi, I have a REX c100 PID and SSR 40 AMPS relay and a thermocouple. I bought the whole lot from amazon about 2 weeks ago and got my head around it today.
I am using it with a heating element.

Now my problem is : when everything is all wired up together ( including heating element) and I choose a temperature for the heating element. The relay comes on and off, which is kinda normal, but when it does so, the temperature obtained by the thermocouple goes up, then when the SSR stops, it goes back to the right temperature....

Two questions, would there be anything wrong with my wiring which causes the thermocouple to not record the right temperature? ( which i think is right) or might it be the thermocouple that is malfunctionning?


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otakon87 (author)2016-01-06
Downunder35m (author)otakon872016-01-06