How connect mini fan for MTB

Hi everyone It is my thirst building I building MTB 12s7p But I need some fan for my VESC the fan I have is 12v 0.4A What I have to do for connect it Use UBEC but which one Thank you

I did some math. You need a 95 Ohm resistor on your fan. Just make sure its large enough so it doesn’t let its magic smoke out right away. Hopefully I did that right haha. Here’s a pic of how I set it up

Vesc has a built in 5v 1amp for running external devices

I have the VESC from trampa And my fan is 12v 0.4A

Ok thank you man

Thank you do you have a link for buy it Thank you resistor

@Devilmycry One thing I forgot to mention is your fan is about 5 watts so you’ll want a resistor that can handle that. 95 Ohm is going to be impossible to find unless you attach multiple in series, but for simplicities sake let’s round up to 100 ohm. Here’s a link for a 5w and 20w variant. 5w is sufficient, 20w is overkill.

Idk why your using a giant resistor that’s going to create a ton of heat to then try and cool your VESC lol, quite counterintuitive. Id recommended just getting a proper UBEC or buck converter that can handle your input voltage and buck down to 12V to power the fan and anything else you need at 12V i.e. lights, more fans… more lights?

1 Like

Get[quote=“Devilmycry, post:4, topic:39411”] And my fan is 12v 0.4A [/quote]

Get a Fan for 5V , “Yeah Racing” make some really nice ones… Or use a step down converter, but dont use a resistor IMO

BTW Try it with some passive cooling like an Aluminium Plate, all i need in my MTB builds…


Your math is right, but you only did half of the calculations

R = (50-12)V / 0.4A = 95 ohm resistor needed


P = (95 ohm)*(.40A)^2 = 15.2 Watts power dissipated

Dissipating that much power is going to generate a ton of heat. 15W is a lot. As others have mentioned, either get a 12V BEC capable of 50V input, or buy a 5V fan and use the VESC to power it through a spare port on your receiver. Personally I use a 12V BEC for my fan but it also powers my lights. Go with a 5V fan if you don’t have any other accessories


I’d buy a 5v fan. They are dirt cheap.

Thanks for that correction. That’s what I get for trying to do math before bed

Everyone here has a good point, 5v fans are super cheap. If I recall you can get 10 packs from eBay for $15 or less.

just buy a 5v fan and solve the problems

Hey and instead of doing all the math on paper there’s a bunch of free calculators online that make it quite simple. I use two apps especially, Electronics Calculator and ElectroDroid both are apps on my phone. Oh and your math for the 95ohm resistor is wrong, so is @jmasta the value should actually be 125Ohm’s. EDIT: Oh and the actual wattage is 20W not 15.2 (125)*(0.4)^2 = 20

That’s not correct. You don’t need an app to calculate Ohm’s law. Blindly applying equations leads to incorrect results. I literally typed that from my phone in bed

All your app is doing is: 50/0.4 = 125, which is wrong here

The voltage drop across the resistor should be 50-12= 38V. Not 50V

The point is moot anyway. Don’t use a resistor to drop so much voltage

1 Like

@jmasta is correct. I use them to drop 8v to 5v for fans, the heat coming from it is going to cause problems in a confined space. Switching to a 5v fan and using a BEC is not the cheapest idea, but it’s the smartest, most practical, and probably cheapest long term.

God I’m an idiot lol, I guess that’s what I also get for trying to do this right before bed lol. Sorry I was thinking of using the resistor as current limiting like in an LED not for the voltage drop, my bad. Anyways I also mentioned the two apps I use not for ohms laws calculations but for more advanced stuff like, heat dissapation, SMD Codes, voltage dividers, V drop calcs, ect.