How to pick a MOSFET?

Hello, I am currently working on a project that uses an arduino uno R3 to run a 24v DC motor that pulls 4.5A. My question is, how do you determine what MOSFET to use?

I tried to use http://www.digikey.com/product-search/en?x=-1147&y=-73&lang=en&site=us&KeyWords=huf75639p3-nd but it quickly over heated.

the max gate voltage applied is 4v. (ranges from 2-4v). attached is a crudely drawn (sorry) section of the schematic dealing with the motor.

any help would be appreciated.

thanks,

-Jim

24V motor controller drawing.pdf (12.7 KB)

That parts looks capable.
Try lowering the gate resistor to 150mA so the MOSFET is switched on/off faster.

Hello, I am currently working on a project that uses an arduino uno R3 to run a 24v DC motor that pulls 4.5A. My question is, how do you determine what MOSFET to use?

I tried to use http://www.digikey.com/product-search/en?x=-1147&y=-73&lang=en&site=us&KeyWords=huf75639p3-nd but it quickly over heated.

the max gate voltage applied is 4v. (ranges from 2-4v). attached is a crudely drawn (sorry) section of the schematic dealing with the motor.

any help would be appreciated, I posted this in general electronics, but I figured motors may be a better place to post this.

thanks,

-Jim

24V motor controller drawing.pdf (12.7 KB)

That part looks capable. Try lowering the gate resistor to 150 ohm so the MOSFET switches on/off faster.
P=I^2R = 4.54.5*.025 = 500mW, maybe put a heatsink on it as well.

Thanks, I will try that now.

Thanks for replying to this one as well!

I am in the middle of lowering the gate resistor. I am a little confused as to where the R = .025 came from though?

I have a beefy heatsink on it at the moment http://www.digikey.com/product-search/en?x=-1147&y=-73&lang=en&site=us&KeyWords=ra-t2x-51e-nd

sorry for the noob question, still learning.

im sorry, i see the 25 Mohm on the part now.

mOhm (0.025), not MOhm (25,000,000). Units matter.

A flyback diode would be appropriate as well.

Thanks for the correction, I will be more careful.

I am very new to MOSFETs how would you go about lowering the gate resistor to 150 ohm.

Would I add a resistor from the gate pin to the source pin? Should I calculate it like the resistors are in parallel?

You show a 1K in your diagram from Arduino pin 3 to the MOSFET gate. Change it to 150.

thanks, I actually do have a flyback diode attached, I just failed to draw it in. //fail

Thanks for all the help!

Sorry, that part is definitely not suitable for driving direct from the Arduino, because it's not a logic-level mosfet. You need to pick a mosfet that has a low Rds(on) quoted at Vgs=4.5V (not 10V as for that part), such as IRLU8726pbf. And you definitely need to use a flyback diode.

// slaps forehead.

Thanks, sorry for the silly question. I have been way overthinking this.

Trying it now, will have results in a few min

Ok, will check later, gotta run.

I let the motor run for a while, I used a infrared thermometer and the mosfet/heatsink was reading around 190 F =(

thanks, I see that Digi-Key has IRLU8726pbf in stock, will order a few now.

I do have a flyback diode, I just forgot to draw it in the schematic, my bad.

I did notice that the max power for the IRLU8726pbf is 75W. Is that going to be enough? I thought I would need something over 100W. 24v * 4.5A = 108W

or does the max power mean something else?

No the power is what it will dissipate not what it switches.
Find the power from I²R where R is the on resistance of the FET.

You know cross posting pisses people off here. It is bad MANNORS.