Pump for a water-bearing stove

Rolf Guest 2022-10-02 18:31 #7209791

Rate this post

•	▲ useful ▼ not useful

I have written a program for the Raspberry Pi to control a pump for a 
water-bearing stove. The program works fine - but I still need a 
computer independent safety device. If the Raspberry fails - then it 
must be ensured that the pump runs in continuous operation to avoid 
overheating of the boiler. My first approach was - to evaluate a clock 
signal to be output from the Raspberry. As long as the clock signal 
comes from the Raspberry - as long as a retriggerable monostable toggle 
stage is reset again and again. If the clock signal is missing - the 
pump goes into continuous operation. But if the clock signal remains 
HIGH - then this idea does not work. One must also evaluate the falling 
edge of the clock signal and connect it with logic. At the moment I am 
on the hose - can someone help me?

Reply Quote Edit Move Thread sperren Anmeldepflicht aktivieren Anpinnen Delete topic Thread mit anderem zusammenführen Report post

minifloat Guest 2022-10-02 20:27 #7209916

Rate this post

•	▲ useful ▼ not useful

Hi,

I suggest to address the problems from the root, in following 
priorities:

1 put an overpressure blowoff valve at the output of the boiler. This 
acts against the fault effect and prevents severe injuries, as the 
boiler tank cannot explode anymore.


2 put an overtemperature switch in series to the heater element. 
Consider also using a non-resettable type. This acts against the root 
cause and also prevents fire.


3 now it is time to think about the additional safety device you're 
planning. Simple solution is make the toggling signal AC by adding a 
capacitor in series and a resistor after the cap to GND. Then feed this 
into the input of a retriggerable monoflop. A simple form of this is the 
attached circuit. (from 
https://cpldcpu.wordpress.com/2021/02/27/the-transistorpixel/ )
Higher capacitor values have to be used, and a resistor in series to 
Q7:collector of a few hundred Ω is advisable.

br, mf

Attached files:

grafik-13.png (27 KB)

Reply Quote Edit Delete Report post

minifloat Guest 2022-10-02 20:34 #7209924

Rate this post

•	▲ useful ▼ not useful

PS.
A pressure switch of NC type in series with the heater element could 
also serve as another safety mechanism. But pressure switches could  be 
rather bulky and maybe also expensive...

Reply Quote Edit Delete Report post