I modeled a fan (link 1 has the image) and used a drone brushless motor (KV720) for this model. My goal is to reach 2500 rpm, but the dc motor drew 10+ amps at 12 volts and 1000 rpm. When I pushed a little harder without noticing it, the smell came and I stopped testing. I wonder whatever I do, will I draw 20 or 30 amps at 2500 rpm or can I get rid of this problem if I change the dc motor? (My limit goal is 12 -13 amper at 12v) If yes, How should the characteristics of the dc motor you recommend?

I looked through a car fan manufacturer's catalog. As the fan sizes increased, they used high-torque and large-sized fans. Can I overcome this problem with using a big fan with high torque dc motor? Or whatever I do will I draw extremely high current? In addition, I want to give an example which is lived. I purchased a car air conditioner fan (mini radial fan pic link2) model from this company and I modeled with the same size propeller and tested it with a brushless motor (drone motor). They drew almost the same currents at the same speed, but the dutycycle of the brushless motor was less than 50% (that is, it was actually quite efficient). So if I use a large dc motor for large fan, can I get more efficiency from a brushless motor(drone motor?

Fan 1 : Link 1: The propeller has an end-to-end length of 265mm, a height of 50mm and 10 propellers.


Fan 2: Link 2: The dimensions specified with the product I purchased are exactly the same. The only difference is a dc motor.



Brushless motor link: https://www.f1depo.com/urun/sunnysky-x3108s-kv720-fircasiz-motor

  • \$\begingroup\$ You are missing the pitch of the fan blade. With that and basic physics (or search for fan/propellor power requirement equations) you can work out the power required to spin the fan blade at different speeds. Did the drone motor data indicate the propellor size (diameter and pitch) it was designed for? \$\endgroup\$ – user_1818839 Dec 24 '20 at 15:29
  • \$\begingroup\$ @BrianDrummond Actually, I have not looked at the fan specifications for this drone motor. Recommended propeller sizes is "APC10x3.8; APC11x4.7; APC12x3.8" at datasheet.After looking at the propeller dimensions, I realized what size propeller would be suitable for this drone motor. \$\endgroup\$ – oğuz kaan çomoğlu Dec 25 '20 at 11:26
  • \$\begingroup\$ @BrianDrummond Also I test different dc brushed motor big fan(link1) the motor stuck 1000rpm and it draw 10amp. This dc motor datasheet shows 3000 -3600rpm and 0,38Nm torque.If I try different dc motor which specification is 2700 rpm 1.1Nm torque, can I get different result ? \$\endgroup\$ – oğuz kaan çomoğlu Dec 25 '20 at 11:31
  • \$\begingroup\$ First number is diameter, second is pitch. Probably in inches. Your fan is closest to 11 inches; you STILL haven't mentioned its pitch : either measure it or read its datasheet. Then compute the power and torque requirements for your fan and original prop using basic high school physics, and select a motor based on those. Yes, changing motors based on guesswork will give different results : but you'll end up with a bigger pile of useless motors than selecting the right one in the first place. \$\endgroup\$ – user_1818839 Dec 25 '20 at 12:02
  • \$\begingroup\$ And like I said : look for the basic equations. They will reveal that power requirements are related to speed cubed. So if you need 10A at 1000rpm, you'll need 2.5^3*10A to get to 2500 rpm. That's about 156A. EDIT : looked at the picture. You should have explained this is a centrifugal blower in the question. So it doesn't have a "pitch" in the sense a fan has. You'll have to hunt for the correct equation yourself. \$\endgroup\$ – user_1818839 Dec 25 '20 at 12:06

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