Author Topic: Driving bigger fans in my 3D printer...  (Read 752 times)

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Offline Bug2k17Topic starter

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Driving bigger fans in my 3D printer...
« on: July 23, 2019, 04:18:12 pm »
The board in my ctc 3d printer has a port for adding an extra fan, I've used it with a small 40mm 24v fan without problems for a while.

I am trying to power 2 80mm 12v fans (in series) from this output. It does work but heat and smell produced tells me this is not going to work long term.

Measuring the voltage at the socket with the fan off gives, +24.2v and +22.3v, with the fan switched fully on gives +24.2 and ~+0.4v.

I though perhaps something like a tip120 or tip125 (as I already have some of these!) might be able to drive the fans, but I really can't get my head around how this is going to work. I would appreciate any advice on how drive the fans from an output like this.

Thanks.
 

Offline Siwastaja

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Re: Driving bigger fans in my 3D printer...
« Reply #1 on: July 23, 2019, 04:59:13 pm »
You can't drive fans (or any motors, for that matter) in series. The current never balances properly, and one ends up getting too much voltage.

Use two 24V fans in parallel instead.
 
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Offline james_s

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Re: Driving bigger fans in my 3D printer...
« Reply #2 on: July 23, 2019, 06:23:12 pm »
While it's generally not advisable, I don't think that's the problem here. It sounds to me like the driver is overheating due to the current draw of the larger fans. Do you have a schematic? What controls the fans in the existing setup?
 

Offline Bug2k17Topic starter

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Re: Driving bigger fans in my 3D printer...
« Reply #3 on: July 23, 2019, 07:39:25 pm »
This socket has the part 7R030 next to it, a quick google brings up this https://www.nexperia.com/products/mosfets/power-mosfets/PSMN7R0-30YL.html which looks like the correct package.That spec looks like it should handle a couple of fans easily?
« Last Edit: July 23, 2019, 07:43:43 pm by Bug2k17 »
 

Offline james_s

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Re: Driving bigger fans in my 3D printer...
« Reply #4 on: July 23, 2019, 09:12:13 pm »
Assuming it's being driven into saturation it should. Is that the part that's getting hot?
 
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Offline Bug2k17Topic starter

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Re: Driving bigger fans in my 3D printer...
« Reply #5 on: July 24, 2019, 09:36:45 am »
Ok, I've run the printer with the board out, it seems the cause of the heat seems to be an adjacent connector starting to melt! This one drives the heated print bed. It seems the extra cooling is causing the print bed heater to work much harder in order to keep it at target temperature. I've taken the connector sockets off the board and soldered the wires for the heater directly onto the board. After running a small print, there appears to be no overheating and it works fine.

It does seem that these boards are not capable of adjusting the fan speed, the gcode to run them works with an M106 S0 switching it off and other values 1-255 just power it on a full speed.

Thanks for the help, much appreciated. My fault finding skills need work!
 


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