AC blower motor driving circuit

[teoman]

Apparently the blower motors in our cars are driven in an archaic manner by putting resistors in series with the motor where the resistor can consume quite a bit of power.

My cars blower motor just quit. It took me several hours to get it out from under the glove box. It was rather hot, I do not have air conditioning in the garage (16 apartment building) and no WiFi down there so i had to go up occasionally to google stuff.

Anyhow, I got the assembly removed and hooked up the motor to my 24V up to 5A adjustable power supply and (at 12V) it drew more than 5A and the motor works. So I think that the controller for the motor has kicked the bucket.

Doing further research I stumbled upon this thread.

https://www.benzworld.org/forums/w21...make-your.html

Where the guy builds a circuit to trigger a mosfet. Apparently the car feeds different voltages to the circuit (up to 6 Volts) and the motor driver circuit uses some fets and resistors to drive the motor. So my car may not be as inefficient as I had thought. Though seeing only 2 power connection and 2 signal connections did give me an "oh shayté!" moment thinking that the module had a canbus slave inside that would require the purchase of an original part (or spend hours reading the codes sent to the module trying to interpret the messages).


I am slightly more comfortable using micro controllers. I already have several hundred arduinos with a bunch of sensors etc (some mare deployed around the house and I teach with them). And the car is dismantled at the moment and I would like to get it to working order asap before the wife starts yapping about the state of the car and the lack of AC.

So i am thinking about using a voltage divider to scale down the input voltage to 0-5 volts so I can sense what the car controls desire. Then use mosfets to drive the blower motor. More precisely this cheapo circuit with 4 mosfets:

https://www.aliexpress.com/item/Four...ceBeautifyAB=0



Since I already have the board there, might as well use all 4 of the mosfets to power the motor so that cheapo components share the load and do not over heat.


Does anyone see any faults with my logic? Tomorrow morning I shall check the voltage output of the car for myself to determine the voltage levels (to check if there are model year discrepancies). On Thursday I should be able to build the circuit and perform some tests.

[mpg_numbers_guy]

Just delete the blower motor altogether!

[teoman]

Mmmmm...

Unfortunately that is one of the creature comforts that I am not willing to give up. I can give up power steering, radio and even give up the seats and sit on crates before I give up the AC. Heck, if I was strong enough i would go Fred Flintstone before giving up the AC. It is too hot and humid over here and I have to arrive at my destination semi respectable not dripping with sweat.


Btw, are there reusable cabin air filters much like K&N for engine air filters?

[redpoint5]

Originally Posted by teoman

Apparently the blower motors in our cars are driven in an archaic manner by putting resistors in series with the motor where the resistor can consume quite a bit of power.

Anyhow, I got the assembly removed and hooked up the motor to my 24V up to 5A adjustable power supply and (at 12V) it drew more than 5A and the motor works. So I think that the controller for the motor has kicked the bucket.

...So my car may not be as inefficient as I had thought...

When you say AC blower, you mean Air Conditioner, and not Alternating Current, right? This confused me for way longer than it should have...

What do you mean that your car is not as inefficient as you had thought? Did you measure the resistors to see how much energy is wasted at each blower setting? Would be very interesting to know.

Your plan sounds good to me, although I've not looked into the specifics.

Originally Posted by teoman

Btw, are there reusable cabin air filters much like K&N for engine air filters?

Paper filters are reusable, even more easily so than oil-based ones. Simply knock the dirt off by tapping it against a solid object like the pavement. If you really want to, use compressed air at a reasonable distance so as to not tear it and blow it out, or use a vacuum.

I never replace filters in any of my vehicles, including engine air filters, or HEPA filters in vacuum cleaners.

[teoman]

Indeed you are right. I was using AC for air conditioning. Whereas maybe I should have used climate contol. Although they do have more or less the same meening air conditioning i believe implies cooling or atleast that is the meaning it has taken over. I am not a native speaker and do not believe i have full command of the nomenclature so I could be completely wrong.

[teoman]

The blower motor circuitry has 1 output to the motor. 1 power input and one signal input.

Besides that this is all I know (from the linked thread):

“They used three FETs. I assume that the fault was in the driver stage as the FETs that i removed still were in working.”


So transistor based system should be more efficient. Unless they are using it in analog mode. I do not understand why they did not use PWM to begin with.

[mpg_numbers_guy]

Originally Posted by teoman

Mmmmm...

Unfortunately that is one of the creature comforts that I am not willing to give up. I can give up power steering, radio and even give up the seats and sit on crates before I give up the AC. Heck, if I was strong enough i would go Fred Flintstone before giving up the AC. It is too hot and humid over here and I have to arrive at my destination semi respectable not dripping with sweat.

To be great you must be like the great. Cars didn't have AC not TOO long ago!

Bring a change of clothes; also not running AC allows you to block off more of your grille.

Or there's always those solar powered AC fans you could stick in your window.

[19bonestock88]

I’m with the OP in that I won’t give up the HVAC fan... might ditch the AC compressor and power steering and all seats but mine but not giving up HVAC

[teoman]

Right now i am wearing shorts an tshirt, i am bare foot. The back side of my shirt and pants is completely wet.

[mpg_numbers_guy]

Originally Posted by teoman

Right now i am wearing shorts an tshirt, i am bare foot. The back side of my shirt and pants is completely wet.

Wow. How hot is it there? Hottest it's gotten here is 90s Fahrenheit and the hottest in my car was like 99 degrees Fahrenheit - which is tolerable on short trips. On highway trips I generally have the windows cracked or open while coasting downhill, and it stays at about 80 degrees Fahrenheit.