Duet2wifi with 3-4 wire fan, wiring

Vlad

Hi guys, I just burned a pretty expensive prototype fan by following these instructions: https://duet3d.dozuki.com/Wiki/Connecting_and_configuring_fans

on connecting a 3-4 wire fans.

This article suggests to hook up PWM wire to FAN0 negative terminal, which immediately fried my fan IC. Glad I have another one as a backup, however I am not connecting it to this board unless I now know for sure what is going on over there. Basically a 24V setup for fans will output 24V PWM signal on that aforementioned terminal, while the fan PWM circuitry may expect a 5V PWM there, which is why it fried. Well, that's just my guess, since its a negative terminal anyways, and I am not super knowledgeable in such electronics.

Since I have no idea what voltage fans PWM ports usually expect as signal and google doesn't help with that, I am hoping someone can shed some light in this regard. And if the answer is 5V, maybe that article should get an update so more people don't burn their fans following those instructions. Maybe @dc42 can help?

Thanks in advance!

Phaedrux

There is no voltage (or signal) on the Fan0 negative terminal. It "receives" voltage flowing through the device from the positive terminal. The PWM is switched on the negative side so it's either allowing voltage to flow or not, but it doesn't "send" anything.

I'm not sure what happened to kill the fan, but it wasn't from receiving voltage from the Fan0 negative terminal.

Do you have a spec sheet on the fan you're using?

Vlad

@phaedrux its a custom production fan sample, they are sending me a spec sheet tonight. If the function is as you described, then what would be the point of a separate PWM input if it simply feeds 24V into the drive? This means it would function exactly as a 2wire PWM solution, which AFAIK is not the case. I have read some articles about the differences yesterday and they should be functioning differently. I have never had a fan fail in such a weird way honestly, but then I have to admit that this board does not support 3-4 wire fans, so the board could be causing that. Which is why I decided to ask on this forum basically.

dc42

@vlad the OUT- pin of the connector is an open-drain output with a flyback diode connected. So it doesn't feed voltage to the PWM pin of the fan, except for the tiny leakage current of the flyback diode (and only then if it exceeds the leakage current of the driver mosfet). This makes it suitable either to connect the negative wire of a 2-wire fan, or to connect the PWM input of a 4-wire fan, with the negative wire of the fan connected to ground in that case. If you didn't connect the negative wire of the fan to ground, then I can imagine that could damage the fan electronics.

Vlad

@dc42 Thanks David, and nope, I actually connected everything exactly according to that instruction. red and black went to always on fan, and PWM wire went to "-" lead of Fan0.... very weird, I will speak to fan manufacturer, its definitely possible that they messed some wiring up. really nice fan that is, really want to make it work with all my duet setups.

dc42

@vlad said in Duet2wifi with 3-4 wire fan, wiring:

@dc42 Thanks David, and nope, I actually connected everything exactly according to that instruction. red and black went to always on fan, and PWM wire went to "-" lead of Fan0.... very weird, I will speak to fan manufacturer, its definitely possible that they messed some wiring up. really nice fan that is, really want to make it work with all my duet setups.

Yes that's odd, assuming you didn't connect the PWM wire to the + output of Fan0 by mistake.

If you connect a multimeter between the FAN- pin of Fan0 and ground, it should register no voltage, whether Fan 0 is turned on or off. Caution! Be very careful when probing the fan output pins, because it is very easy to short both pins together, which will blow the fan mosfet if the fan is commanded on.