Controlling Two 12v Fans off Arduino using one Power Adapter

Other Hardware Motors, Mechanics, Power and CNC
1

Hey everyone,
I know this topic comes out every so often.
Just wanted to ask if I am doing the right thing, in order to avoid overheating the board and the transistors.

I am running two Fans off my Arduino Mega, they are DC12v 0.14A each.
I am using two IRF 530 transistors to drive them, I have put a diode between each transistor's drain and the positive to the Vin of the board.
The board is powered through a 12V adapter, I am not trying to control the speed, just simple on and off.
At some point I thought about using a resistor between the transistor's source and the ground of the board, but I have noticed that the fans would stop working. I tried 10k Ohm and 1k ohm, they just wouldn't work.
Can I run them without using any resistors or would I risk overheating the circuit?
The whole thing will be housed in a carton box, that's why I am trying not to overheat anything.
Also, the fans go on every 7 seconds for 3 seconds then off.

Many thanks for your help

Best

Elso

2

Can I run them without using any resistors

Yes, although the gate of a FET looks like a discharged capacitor so it is normal to put a 100R resistor in series to protect the arduino ( not the FET ) especially if you are driving it with PWM ( which you aren't )

3

Thank you dearly Grumpy Mike, do you think I should put that 100R resistor in the bunch just in case?
The fans will be working on and off for 10hours a day.
Best wishes

E

4

It's a simple circuit and we understand how it is connected but for the purpose of further discussion about modifications it would be expedient for you to draw a schematic by hand and photograph it with a cell phone and post the photograph.
Do the mosfets have heatsinks ?

5

Sure.
Here is a quick Fritzing diagram that shows what I am doing.
The Fans are represented as DCmotors and those FET Transistors in reality are the IRF530s.
Many thanks for your help
E

2fans.jpg
2fans.jpg679×697 55.7 KB

6

You should probably add some decoupling caps 0.1 to 1uF across your +5v power bus to reduce the noise spikes when the motors are running.

7

Again? When it's not TIP darlingtons then it's IRF HEXFETs. Aaack!

An IRF530 and 5V for Gate voltage isn't a match made in heaven, is it?
Who thinks that 5V is enough to get those into solid conduction?

8

Yeah, I just looked at the datasheet and you have a good point.
What do you think of the RFP30N06LE (see attached) as a replacement ?

RFP30N06LE.pdf (189 KB)

9

raschemmel:
What do you think of the RFP30N06LE (see attached) as a replacement ?

If you have them, they're acceptable.
I would suggest an NPN "switch", assuming there are a couple of NPNs and some resistors in the house, as in the attachment.
Anyone could dispute the 22K, I suppose - go for a lower value - but it would be effective.

NPN_IRF_intf.JPG

10

Hey,
thanks for feedback.
The only transistors I have lying around are:
STP16NF06 or the P2N2222A
anything I can do with that? It's the usual near deadline (tomorrow morning) and trying to make it happen by then...
:slight_smile:

11

Elso:
P2N2222A
anything I can do with that?

I would just use the NPNs. The HEXFETs are overkill.

Adding schematic (attachment). Change RB to 1K-2.2K
It has "2N3904" there, but same difference.

npn fan.JPG

12

Great, Thanks!!!!

13

So - "what's the story, morning glory?"