Controlling Two 12v Fans off Arduino using one Power Adapter

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

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 )

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

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 ?

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

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.

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?

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)

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

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... :)

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

Great, Thanks!!!!

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