need to fire my wooden pellets oven , temperature switch wanted

[nashkato]

in my wooden pellets oven is a temperature switch that needs a new one every year .
everytime i ask for a new one it´s getting more expensive , even more when i tried to change the supplier .
a new on i just installed one month ago must have been faulty

the switch closes at 49 (+/- 3 ) degree celsius or higher
the switch opens at a temperature smaller 43  (+/- 3 ) degree celsius or lower

i attched a pic of how this thing looks like 

i found this one on RS that might work and costs a fraction of the "original" one .
https://at.rs-online.com/web/p/thermoschalter/2282557/

i guess my next step is to crack open the faulty one and see whats inside ?

 

[analogguru]

in my wooden pellets-oven.... (= .... in meinem hölzernen pellets-ofen...)

So when your pellets-oven is made of wood I think it would be better, when it doesn't get fired....

In the picture you attached is written that it is "recommended" to change the switch every year.  The reason is that with many switching cycles the contact can be broken and the oven will not work which is not nice when it is cold outside and you have to wait for the switch or the serviceman.  Therefore they recommend the "normal user" to change it every year before the heating period starts.

But I doubt, that one of your switches was ever broken.  The switch is the same as is used in power-amps, fog-machines etc. where they last many years.  Since you are familiar with repairing electronics I would wait until the switch gets really broken before I would mount a new one.

 

[nashkato]

;D

in my wooden pellets-oven.... (= .... in meinem hölzernen pellets-ofen...)

dont´know if that is correct ? :  in my wooden-pellets oven...
or is it just plain and simple as in german : pellets-oven

you´re completely right .
i should have made myself more clear .


the switch in my fireplace is maybe 3 or 4 years old .
during the yearly cycle in autumn of cleaning , checking , servicing , etc i thought it may  be a good idea to change that switch , and i´d still have a spare one ( the old one ) in case it´d break and i´d have to wait for replacement .

in fact , that new switch actually  broke after one month , and now the old one is in service again .
( tested it with heat/cold and ohmmeter = nothing  )

i´m sure the exact temperature isn´t that critical and the RS switch will just work fine . it just should be open when i turn it on , and be closed after the startup-procedure after 20 minutes . i´m gonna give it a try  .

 

[JohnRoberts]

You might take the old, bad thermostat apart to see why it failed.

JR

 

[PRR]

In the US: "Pellet stove".

> one on RS that might work

The low-point is significantly lower than the stove specifies. That means if it ever does go off on over-heat, it will have to cool more before it turns on again. That may be acceptable.

Yowch!! You are right-- the $5 thermo-switch is $28 at a stove-parts store!
https://pellet-stove-parts-4less.com/products/thermodisc-high-temp-by-breckwell-c-e-090-21

Also ask at the gas-furnace parts shop. I believe my high-efficiency propane furnace has similar switches. In both cases the switch protects the fan from melting/burning, so the different fuels may not be different temperatures. However gas-parts are also often over-priced. Unlike the amplifier and coffee-pot switches, the BIG fire safety switches have to be tested so your house won't burn down (in the opinion of some high-cost safety agency).

 

[Audio1Man]

The thermal switch is usually very robust and long life device. It is made of two dissimilar metal strips laminated together. The coefficient of the metals causes it to expand @ different rates and bend to open or close the contacts. You may have overloaded the contacts and burned them up. Check the load voltage & currents.
Duke

 

[nashkato]

You might take the old, bad thermostat apart to see why it failed.

this is what i found , don´t know why it failed , maybe something got stuck .

Put it back together and it switches again .
(need to find some heat resistant glue , cause i had to drill it open , maybe heat resistant silicone )

a concave dish flips when heat is applied and pushes a bolt down that connects the two contacts

 

[moamps]

I would use the old working bimetal switch you already have to drive an power relay (10€) with 230V coil.
The switch will last forever, and relay can be easily cleaned and tested every season.

 

[JohnRoberts]

this is what i found , don´t know why it failed , maybe something got stuck .

The bimetallic disc might be off some in temp but will pretty reliably click/change state.

Put it back together and it switches again .

Check for mechanical tolerances, next suspect is dirty or pitted, switch contact.  Back in the 1950s I repaired my mother's dishwasher by flipping a timer cam actuated switch contact upside down. There was a clean contact on the opposite side from the pitted one.

(need to find some heat resistant glue , cause i had to drill it open , maybe heat resistant silicone )

a concave dish flips when heat is applied and pushes a bolt down that connects the two contacts

Just guessing there may be smoke in the area that could contaminate switch contacts, so a good seal is probably useful.

Before you close it up inspect the switch contacts for pitting... high current can erode the contact quality.

If the problem is just dirty contacts, running it at lower current will not help.

Good luck, looks like a simple design, but simple is not always easy.

JR

 

[s2udio]

I would use the old working bimetal switch you already have to drive an power relay (10€) with 230V coil.
The switch will last forever, and relay can be easily cleaned and tested every season.

+1

 

[JohnRoberts]

+1

Perhaps if contact is pitted fro high current, but if just dirty (from smoke contamination) running it at lower current will not help.

JR

 

[nashkato]

the upper side of the switch is exposed to smoke in the exhaust canal , not far before the smoke leaves the stove .
there´s a heat resistant sealing beneath the switch and the housing of the stove .
contacts are reachable from the bottom side of the stove and unless the upper metal housing of the switch is leaky they and no inner parts of the switch should be exposed to smoke .

I haven´t measured it , but i doubt there´s much of current or voltage flowing through the contacts .
i ´d really have to have a look at the microprozessor control PCB and measure the voltages through the switch .

my guess though is , that it´s some small control voltage and a relay wouldn´t be of any benefit here .

stove is heating right now , and there are other things that need my attention . i guess i won´t be in there unless there´s a problem or next autumn .

 

[PRR]

On my gas furnace (I do not recall my pellet stove), some safety switches DIRECTLY shut-off Power, in case the microprocessor goes brain-dead.

A draft fan (blows or sucks the fire) is a perfect example. CPU gets stupid, fills the chamber with pellets, huge fire. Most pellet stoves will go out if the fan stops (poor natural convection). So an over-temp switch directly in line with fan motor wall-power WILL avoid melting the stove and burning the house.

 

[nashkato]

in this case that switch needs that temp of higher 49 degree C , if that temp isn´t reached stove shuts down .
in most cases it more or less checks for "wrong air" , don´t know , door open , bad (very bad ) sealing , etc
with a defective switch ( assuming it´s always open of course ) the stove will start to burn as it´s supposed to , fan will blow , everything works as it should , but will shut down once the "startup protocol " ( in which the oven pumps a lot of pellets and the stove gets hot really quick ) has run out ( app. 20 minutes )