The programmable thermostat W1209 is erased when disconnecting

Thread Starter

curro92

Joined Sep 29, 2012
21
Hello,
I bought this programmable thermostat W1209 with display lcd. It is very cheap and easy to program, you can determine maximum temperature, or minimum temperature, etc.

https://des.gbtcdn.com/uploads/2015/image/20150908/sms_20150908151652_75165.jpg

But I have a problem: when I disconnect the power, the programming is erased. And when I connect it, I have to reprogram it again. This is normal?
I do not know what company makes it, to consult them. Does anyone use this thermostat?
 

danadak

Joined Mar 10, 2018
4,057
Its because they did not use a big enough bulk cap on power supply to keep it running while
you are changing out batteries. Or program the settings into internal EEPROM
so when power is reapplied it first looks in memory to see if settings have been
entered.

Regards, Dana.
 

crutschow

Joined Mar 14, 2008
31,091
If it doesn't have a battery backup, then you may need to add one.
The required battery size is determined by the current the thermostat draws and how long the power is off.
Since it has a LED (not LCD) display, its current consumption is likely in the tens of mA region.

Edit: I found a spec listing that states it draws 35mA (static current), and 65mA otherwise (perhaps with the relay energized or all the digits lit).
So, it will require a battery capacity of 35mAh to 65mAh per hour of operation with the power off.
 
Last edited:

DbLoud120

Joined May 26, 2014
84
Hello,
I have identical device controlling fans on my home theater amplifier.

The power to the fans and thermostat are only powered when home theater system is on.
The system is normally operated every day but may go for 24 to 48 hrs. without being used.

My set temp never needs to be re-adjusted.
I would say your device is defective or not being fed with proper voltage.
Device recomends12 VDC
 

spinnaker

Joined Oct 29, 2009
7,835
My set temp never needs to be re-adjusted.
I would say your device is defective or not being fed with proper voltage.
Device recomends12 VDC
What makes you think that? Do you have tha same device? Look at the photo the TS posted. There is no on board super cap or battery. Perhaps it has eeprom but no way to tell for sure without knowing more about the device.
 

Tonyr1084

Joined Sep 24, 2015
7,190
I have one of those atomic clocks that know what time it is. All I have to do is program the time zone. Since I so rarely have to do that I always have to hunt down the instructions just to go through the programming process. The way I got around it was to hang a hefty capacitor adjacent to the battery box. So if I remove the batteries I have about 30 seconds before the power is completely gone. Surely enough time to change the batteries without losing the programming. It's been a while since I've done that mod and couldn't tell you what exact cap I used, but my clock runs on two AA batteries. No where near the 12 volts I'm hearing your T-Stat runs on.

Someone mentioned batteries but I don't think you mentioned them (the original thread starter). If you regularly have to remove power and you lose the programming then perhaps it's time for a new controller.
 

Thread Starter

curro92

Joined Sep 29, 2012
21
Thank you all!

DbLoud120
, you're right, I managed to get the programming not deleted when the module is turned off. It must have some EEPROM. I think my problem was with two other functions of the thermostat:

- P2: Upper Limit ° C, Max temperature allowed to set
- P3: Lower Limit ° C, Min temperature allowed to set

I do not understand very well the function of these variables.

I have two identical devices. In the P0 function, one of them I programmed it as a heater (H) so that it cuts when it reaches 18ºC; and the other as a cooler (C), to connect when it reaches 25ºC

In this situation, how should I configure the P2 and P3 functions of the two devices?
 

spinnaker

Joined Oct 29, 2009
7,835
Thank you all!

DbLoud120
, you're right, I managed to get the programming not deleted when the module is turned off. It must have some EEPROM. I think my problem was with two other functions of the thermostat:

- P2: Upper Limit ° C, Max temperature allowed to set
- P3: Lower Limit ° C, Min temperature allowed to set

I do not understand very well the function of these variables.

I have two identical devices. In the P0 function, one of them I programmed it as a heater (H) so that it cuts when it reaches 18ºC; and the other as a cooler (C), to connect when it reaches 25ºC

In this situation, how should I configure the P2 and P3 functions of the two devices?
Probably so you can't set it to "unreasonable" temps when you are setting the temp for use. Say you want to use it to control heating in your home. You probably would not want it to go below ~15C and above ~25C. The min and max settings would keep you from setting it past those set points.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
13,684
Unless the controller contains a non-volatile memory device it certainly will lose memory whenever the power drops. There may not be any claim that it would have a memory. If you want memory buy a battery backed up home heating thermostat, and install the recomended battery.
 
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