Combi boiler fan controller

Thread Starter

mally

Joined Feb 4, 2016
36
Hello , I have my hands on I working combi boiler fan , and I have a project where I need to control the speed of the fan , the fan has a pcb on the back of it with 230acv in and a socket with 5 other pins I have searched the net trying to find out what they do and from what I understand 2 are for pwm and the other three are for sensors .I have tried wiring a Potentiometer but it doesn't do anything , I have also tried adding a pwm to the two pin but still no joy . As anyone any idea if these fans are possibly variable? Or is there something and not doing correctly. Here is a picture of the pcb.any more pictures just let me no.
 

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Thread Starter

mally

Joined Feb 4, 2016
36
Hello , I have my hands on I working combi boiler fan , and I have a project where I need to control the speed of the fan , the fan has a pcb on the back of it with 230acv in and a socket with 5 other pins I have searched the net trying to find out what they do and from what I understand 2 are for pwm and the other three are for sensors .I have tried wiring a Potentiometer but it doesn't do anything , I have also tried adding a pwm to the two pin but still no joy . As anyone any idea if these fans are possibly variable? Or is there something and not doing correctly. Here is a picture of the pcb.any more pictures just let me no.
 

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Hymie

Joined Mar 30, 2018
976
When the combi-boiler detects a demand for DHW or central heating, it spins up the exhaust fan which draws in air past the gas burners. Before the gas valve opens and the gas is ignited, the boiler uses a pressure sensor to detect that the fan is producing an air flow sufficient for the operation of the boiler. Should your proposed modification cause the incorrect operation of the motor, you would then be relying on the pressure switch alone to protect the boiler from potentially producing deadly carbon monoxide.

Therefore I would recommend not modifying the fan speed control if it is to remain operational in the combi-boiler.

That said, often fans provided with some form of external speed control (like the one you have) use a 5Vdc signal (0V to 5V), making the external speed control signalling fairly simple. Your problem is finding which are the 0V and 5V pins.
 

Hymie

Joined Mar 30, 2018
976
Some speed control fans go further and provide the 0V and 5V, allowing control via a potentiometer with the wiper input voltage controlling the fan speed. Check whether there is a 5V output on one of the pins.
 

Thread Starter

mally

Joined Feb 4, 2016
36
When the combi-boiler detects a demand for DHW or central heating, it spins up the exhaust fan which draws in air past the gas burners. Before the gas valve opens and the gas is ignited, the boiler uses a pressure sensor to detect that the fan is producing an air flow sufficient for the operation of the boiler. Should your proposed modification cause the incorrect operation of the motor, you would then be relying on the pressure switch alone to protect the boiler from potentially producing deadly carbon monoxide.

Therefore I would recommend not modifying the fan speed control if it is to remain operational in the combi-boiler.

That said, often fans provided with some form of external speed control (like the one you have) use a 5Vdc signal (0V to 5V), making the external speed control signalling fairly simple. Your problem is finding which are the 0V and 5V pins.
Hiya and thank you for your reply, this fan will not be going into a combi boiler , I was hoping to use it to suply air to a home made oil burner , to start the burner the air suply needs to be slow and as the burner heats up as does the air flow . I would like to make a controller and if I get it all working fine then modify to some kind of self thermostat control? So I need to work on the circuit board that's I already have on the fan , and try work out what needs power or not ...
 
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