Need idea for PWM fan controller for remote AC condenser

[casias]

Hello,

I have a Derale 16926 fan that has a 23.4 amp draw. It is on a automotive remote-mount air conditioner condenser. It pulls way more air than I need for this application. I would like to manually slow the fan speed until the high-side pressure rises slightly, then leave it there.

**broken link removed**

**broken link removed**

I tried a PWM motor controller from ebay that was supposed to be rated at 800w, but it toasted within seconds. It looked like this

**broken link removed**

I am looking for a good quality controller that will do the job. It is also exposed to the elements under the vehicle.

Any ideas?

Scott

 

[MikeMl]

Re: Need idea for PWM fan controller for remote AC condenser by poster casias


Fan Motor specs?
Power source?
Speed control method?

first time I posted an answer that became the first post in the thread????

 

[schmitt trigger]

Many posters, when queried with basic information to properly answer their requests, simply do no longer reply. This happens here in almost all forums I attend.
But this is the first time I see someone deleting the post.

 

[ericgibbs]

But this is the first time I see someone deleting the post.

hi schmitt.

The OP's post is not deleted, somehow its 'stuck' in the Moderation queue.

Electromaster will have to do whats necessary, the Mods have tried to Approve it without success.

Eric

 

[casias]

I didn't delete anything. I haven't had a chance to respond. The fan motor is 12v, automotive, probably a bosch, with 23.4 amp draw according to the specs. My question is whether I need to oversize the PWM controller to say a 30 or 35 amp and if there is a better quality controller than the chinese one I purchased on ebay that toasted immediately. This cools an ac condenser, and really needs to be reliable.

Any info would be appreciated. Are you guys not able to see my original post? If not here it is

Derale 16926 fan on remote mount ac condenser. I would like to decrease fan speed by about 40-50 % manually. My first PWM controller was from ebay, rated at 800w, but toasted within seconds. It was only $20.

Any info would be appreciated.

Scott

 

[casias]

Re: Need idea for PWM fan controller for remote AC condenser by poster casias


Fan Motor specs?
Power source?
Speed control method?

first time I posted an answer that became the first post in the thread????

When I first read this, I thought you were goofy. This info was in my post. Now as I read further, I think you guys can't see my post.

Scott

 

[schmitt trigger]

Confusion understood.
The fan...is it a brushed or brushless type?

Many of the brushless DC motors do not like to have their input voltage PWM'd. It drives (no pun intended) their internal H-bridge drivers nuts.

 

[ericgibbs]

hi,
The OP's opening post should now be visible.

E

 

[casias]

No its brushed. But it has been recommended to me that I get a "Soft start" feature on the PWM controller?

 

[KeepItSimpleStupid]

I know this https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_120539_-1 isn't good enough, but it can give you a place to start. I have used it for both a speed control and a shutter solenoid driver. The motor I used for the speed control whined using the controller.
Note: I like presenting stuff without justification to provide a "basis" for a design even if the idea is quirky.

It does include soft-start.

There are a few problems with this application:

1) Engine compartment (Environmental)
So, you might have to use a diecast aluminum case with an "O-ring" seal. Another possibility is doing it in two pieces.

2) The automotive electrical system.
Transients of -200 to +50 are common. You have to protect against that.

3) You may have to reduce the electrical noise made by the device into the 12V system

4) You have to be able to handle the short-circuit current, at least for a short time.
So, te 25A is probably while running. the surge might be considerably higher

5) The Velleman kit gives you a place to start and you have a scematic, so you have these problems to solve.I'd try to get it to work with the ignition off and without paying attention to environmental issues first. You MUST add a negative voltage and positive voltage clamps. Transorbs and a 1N500x diode with a PIV greater than 200 V should work with a fuse. It would be handy to know the DC resistance of the motor. Measuring that might require a 4 terminal technique. e.g. Current through the motor and voltage across it at a low voltage.


1. Frequency of operation
2. The FET output should be selected and properly heatsinked.
3. Add the OVP and transient protection.

Now work on environmental.

I'd suspect that the case of a large diecast Aluminum box will work as a heatsink. A finned sink could also be added.

The magazine NutsandVolts always has PWM modules for sale.

I did some searching (minimal) and found this: https://www.avayanelectronics.com/Products/AE-7960/ae-7960.html Note, that it says "proper heatsinking".

 

[casias]

Thanks for the info. I didn't think about the power surge and noise issues that would call for a regulated power supply. I did find this kit from Painless Wiring that is what I need, and is designed for this application, but it modulates the fan speed from 50% to 100 % based on a linear relationship with a temperture probe in the cooling system. My application for an AC condenser would not need this.

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But I think I could maybe replace the temperature sensor in this diagram with a rheostat or potentiometer? that would allow me to modulate the sensor voltage and adjust the fan speed that way. I really don't need a specific speed, just a way to slow it down until the pressure in the high side of the AC system rises slightly.

**broken link removed**

How would I determine the size of potentiometer I need?

 

[KeepItSimpleStupid]

You don;t need a regulated supply for a controller, just supression of transients. See this article: https://www.google.com/url?sa=t&rct...uHIAxs5k59lgO0g&bvm=bv.48705608,d.aWc&cad=rja

I think what you found is a good choice.

In one case, you could try to contact the manufacturer.

I do agree that most sensors are thermister or resistor based, but for some reason the automotive sector doesn't like to give out specs.

The thermister itself is somewhat non-linear, but is passed through some amount of linearization.

I think all you really need to do is measure the resistance vs temperature of te sensor.

I once did this by starting out with hot or even boiling water. Put in a temp sensor. Add cold water and stirr. Wait for the temperature to settle and take a resistance and temp reading.

Wattage is going to be small. I'd take a look at the voltage across the resistor and use P=V^2/R to give you an idea in watts what you should use. I would even expect 1/2 Watt. Once you have determined the value, replace wit a fixed resistor enclosed in heat shrink tubing.

You could even look at two points. 25 C and boiling 100C or slightley less. The resisto needed would be either higher or lower than the 212 F value, depending on whether R increases or decreases with temperature.

Sensors are usually specked with the value at 25 C.

You can use https://wiki.answers.com/Q/What_is_the_normal_engine_temperature_for_a_car_engine as a guide.

The car is a pressurized system, so wather boils at a higher temperature; 212 F is te normal boiling point of water, Pressures are somewhere between 7 and 14 PSI, I think.

 

[casias]

Thanks for your information. I will order one of these and try it.

Scott

 

[casias]

As an update to this. I did find a 50 amp fan controller that has adjustable speed. It came from ebay **broken link removed**. I put it in a rubbermaid container and punched holes in the side to pass wires through grommets. It will slow the fan from 100% down to about 40%, and restarts smoothly with soft-start. This fan draws about 25 amps, but does well on a 30 amp fuse.

 

[KeepItSimpleStupid]

Thanks for the feedback.