FAN control options with Duet 0.8.5

Hi there, I have a question on what would be the best way to connect the electronics cooling FANs so they could be turned on/off via G-Code or through the Web Interface?
I am not talking about the Hotend and/or Sample Cooling, since this is already been taken care of...
The reason I am asking is simple: I often print over night, or over a longer period of time. If the printer is idle, the electronics doesn't produce a lot of heat, and active cooling is not necessary. During the print it gets rather hot, and needs to be cooled actively. We all know, that over time dust will get anywhere, and would rather activate the cooling during the print only...
is it possible in any reasonable way? I have tried to use the search function, but didn't find anything useful. Perhaps something over the pwr_on terminal?

You could use a spare heater channel on the expansion connector to drive a mosfet to switch your electronics cooling fan. See [duet3d.com].

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks, good and simple idea!
But why not to use the heater output directly, if the fan power would not exceed a typical 40W what a heater would have?
Oh, I got it, you were talking about the extension header, but I have the duex4 installed, so I guess I can connect to the heater terminal detectly...

Edited 1 time(s). Last edit at 12/01/2016 04:15PM by Teilchen.

I connected the fan cooling the drivers off the same fan connector as the hotend cooling fan. So, no fan is running unless the hotend is hot.

Quote
stephenrc
I connected the fan cooling the drivers off the same fan connector as the hotend cooling fan. So, no fan is running unless the hotend is hot.

Aren't you afraid of overheating the drivers while you wait for the bed to heat up? Or do you heat up both simultaneously?

Quote
o_lampe

Quote
stephenrc
I connected the fan cooling the drivers off the same fan connector as the hotend cooling fan. So, no fan is running unless the hotend is hot.

Aren't you afraid of overheating the drivers while you wait for the bed to heat up? Or do you heat up both simultaneously?

If the machine is sitting idle while the bed heats up, then after 30 seconds the motor current will be reduced to the idle current, which will help keep the drivers cool assuming the idle current percentage is not set very high.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
o_lampe

Quote
stephenrc
I connected the fan cooling the drivers off the same fan connector as the hotend cooling fan. So, no fan is running unless the hotend is hot.

Aren't you afraid of overheating the drivers while you wait for the bed to heat up? Or do you heat up both simultaneously?

None of the motors are on until the homing starts and I use M84 in the ending code to turn them off after a print. The mount for the Duet is an open one of my design: [www.thingiverse.com]