Yes, like that.

Ron

 

Thanks everyone for your help.
Now I have two solutions to my problem

Best regards
Anders

 

Noted.



Would the circuit look something like this?

That arrangement shown in post #18 will work IF the setup has a positive commoned (grounded) power connection. I was thinking of a circuit like the one shown in post #20. The only question then is about the unknown PWM driving source. That is because the base drive voltage needs to be applied between the base and emitter of the transistor, and the internals of the driver circuit are unknown. The circuit will work if the negative connection to the original motor is common with the 24 volts negative source.
AND, why draw the transistor on it's side like that? The analysis is simpler if the base connection points to the left and the collector and emitter are in a vertical line. That is a far more standard way of showing transistors in electronic circuits. Simulators may be different, I suppose. A standard exists that electrical circuits, like western text, are read from left to right.

 

AND, why draw the transistor on it's side like that? The analysis is simpler if the base connection points to the left and the collector and emitter are in a vertical line. That is a far more standard way of showing transistors in electronic circuits. Simulators may be different, I suppose. A standard exists that electrical circuits, like western text, are read from left to right.

Sorry about that, I didn't know.
I've no schooling in electronics, I studied to be a chef, and are trying to learn how to do stuff from what i can google and ask of forums.
I'll try to better myself but it's hard to find the time to study all the theory, standards and praxis.

 

Sorry about that, I didn't know.
I've no schooling in electronics, I studied to be a chef, and are trying to learn how to do stuff from what i can google and ask of forums.
I'll try to better myself but it's hard to find the time to study all the theory, standards and praxis.

OK, I see. If you have a meter that can measure voltage, and if the 24 volt motor is still available to be connected to the existing control board and run, then a simple test will provide the needed information.
That check will be to measure between the 24 volt motor negative side connection and that controller board common (ground) connection, which may become connected to the negative of the 12 volt supply used for the 12 volt motor. If there is no voltage then all is well. A resistance check, with power off, is also a good idea. That test should show zero or close to zero resistance.

 

The first thing I thought of was fit 2 new 12v motors and wire them in series. Don't know if you've got room for them but just an idea.

 

replacing the 24v power supply is not an option.
The intention is to have approximately the same airflow.

Is your 24V fan bad/broken? If so wouldn't the simplest thing be to just get another 24V fan?

 

I am wondering about the power rating for the original motor. My impression is that it is rather powerful: " a 12v fan instead of the stock 24v hurricane fan" implies a lot of air. A fan running on 6 watts is not really a whole lot, and if the previous bower drew a few amps then there may be some issues.
At this point I am going to change my suggestion to "Use a series resistor to drop 12 volts." That will indeed waste 6 watts, but it will be a change that can be handled by a beginner with success. That resistor should be 24 ohms and rated ten watts. I think that 24 ohms is a standard value, although it might be that 22 ohms, 10% (Red, Red, Black, silver) is the standard 10% tolerance value.

 

I think that 24 ohms is a standard value, although it might be that 22 ohms, 10%

24R 10W is a standard value
Mouser search

You'll even have a nearby fan to cool it down!

 

24R 10W is a standard value
Mouser search

You'll even have a nearby fan to cool it down!

Thanks to C.H. for verifying. I was thinking about the 10% tolerance resistor value list because they are cheaper and more available. That mindset goes back to my days of designing for production. A price difference that is not much for one part may be a big-deal for a thousand parts. Also, availability of quantities can be an issue some times.