Extruder always-on fan keeps burning out

Question to everyone, maybe someone has some insight into what I am doing wrong.

So, this is my first 3d printer build (MPCNC or otherwise). I have the extruder on and wired per the diagrams with the extruder always on fan connected to the power plug, and the other fan on the small funnel connected to the arduino D9 port.

One motor worked for maybe 20 seconds, and then stopped and had an electrical burn smell to it. I bough another fan from a local electronics store, and it did the same thing. These are rated 12 volt, and on fan was a 750 milliamperes, and the other fan said only it is 12 volt.

Is there something I am missing ? My power supply is a standard 12V 14.6 Amp PS. Do I need to put a current limiter inline that I did not see referenced? Can I just put the extruder fan to the D9 port?

I would appreciate any ideas on this.

The fans are polarity sensitive, I would double check that.

I did. It looks like normally the red is positive, the black negative.

I had another fan, when I plug them both into D9 port on the ramps, no problem. It was when I plug them directly to the green plug, that is when they appear to fry the fan.

Are they supposed to do that?

They should work fine from the power side of the green plug, that is how most of us use it.

The heatsink fan needs to be always on or at least on when the extruder is above room temp.

That’s weird…
You shouldn’t have this kind of problem, maybe that is just bad luck, you got 2 defective fans in a row (but it’s unlikely)…

Don’t worry about your power supply Amps rating vs your fans Amps ratings, it doesn’t work that way: let’s say that your power supply is rated at 30 amps, it doesn’t mean that it will push 30 amps through your fan, it simply meant that your fan can use any current it needs, withing the maximum limit of 30amps. You can think of the power supply as a water tank, amps ratings corresponds to the total amount of water per hour that your water tank will be able to deliver without becoming empty. So even if your PSU was rated at 100 000Amps, it wouldn’t matter.
Make sure that your power supply actually delivers 12V and not 24V… but even though, fans can usually deal with twice the voltage for a while without burning up.

I would say try again with a different fan, and maybe put a capacitor in parallel with it to prevent from some voltage spikes.
That’s a very weird issue though, are you sure the fans are busted? Maybe its one of the wires going to the fan having an unstable continuity?

Or maybe show us some pictures of your setup how you had it wired when they fried.

I think I figured it out. I ran an extension wire and reversed the polarity when I hooked it up. I didn’t think that would be an issue, but I am reading that is with brushless motors.

So I am thinking that burned them out.

Does that sound like that makes sense?

Yes definitely, they are polarity sensitive.

I didn’t think it would even spin wired backwards. I do know running power through the tach wire will kill it though.