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Revision to Connecting and configuring fans

Tony

Mixed-voltage setups are not directly supported, but the Duet switches the fans' connections to ground, so you may be able to connect each fan's positive side to the appropriate voltage and its negative side to the appropriate pin on the Duet. Each controlled fan can be configured in firmware as a gcode controlled fan or as a thermostatically-controlled fan.
 
'''Caution:''' Duet 06 and 085 boards, and Duet WiFi boards priorWe recommend no more than 1.5A continuous current draw from each fan output, although 3 to PCB revision 1.02, do not have built-in flyback diodes on4A for a few seconds while the fan outputs , because standard brushless fan motors dostarts up will not needharm them. If you connect a ''brushed'' DC motor to a fan output, you must connect a flyback diode in parallel with the motor. A 1N400x diode (where x = any digit in 1..7) is suitable. Connect the cathode of the diode (the end with the stripe) to the positive fan wire (the V_FAN terminal on the Duet) and anode to the negative fan wire (the FANx- terminal on the Duet).
'''Caution:''' Duet 06 and 085 boards, and Duet WiFi boards priorWe recommend no more than 1.5A continuous current draw from each fan output, although 3 to PCB revision 1.02, do not have built-in flyback diodes on4A for a few seconds while the fan outputs , because standard brushless fan motors dostarts up will not needharm them. If you connect a ''brushed'' DC motor to a fan output, you must connect a flyback diode in parallel with the motor. A 1N400x diode (where x = any digit in 1..7) is suitable. Connect the cathode of the diode (the end with the stripe) to the positive fan wire (the V_FAN terminal on the Duet) and anode to the negative fan wire (the FANx- terminal on the Duet).
 
Each=== Cautions when connecting brushed DC motors e.g. air pumps ===

* Duet 06 and 085 boards, and Duet 2 (WiFi/Ethernet) boards prior to PCB revision 1.02, do not have built-in flyback diodes on the fan outputs , because standard brushless fan motors do not need them.
** If you connect a ''brushed'' DC motor to a fan output, you must connect a flyback diode in parallel with the motor.
** A 1N400x diode (where x = any digit in 1..7) is suitable. Connect the cathode of the diode (the end with the stripe) to the positive fan wire (the V_FAN terminal on the Duet) and anode to the negative fan wire (the FANx- terminal on the Duet).
* Brushed DC motors may have high start currents, which may exceed the rating of the mosfet.
** Before connecting a brushed DC motor to a
fan output on the Duet, use a multimeter to measure its DC resistance several times.
** Rotate the motor shaft slightly between readings and take the lowest reading you see (ignore any transient readings while the shaft
is rated for 1.5A continuousbeing rotated).
** Divide this value into the V_FAN voltage (typically you will use V_IN) to get the peak
current draw, although 2A forat startup.
** If this peak current is greater than 3A then you should connect
a few seconds whilesurge reducing thermistor in series with the fan starts up will not harm themto reduce the startup current. Here is an example of a thermistor that may be suitable: http://uk.farnell.com/epcos/b57236s0250m000/thermistor-ntc/dp/9751904.
Each=== Cautions when connecting brushed DC motors e.g. air pumps ===

* Duet 06 and 085 boards, and Duet 2 (WiFi/Ethernet) boards prior to PCB revision 1.02, do not have built-in flyback diodes on the fan outputs , because standard brushless fan motors do not need them.
** If you connect a ''brushed'' DC motor to a fan output, you must connect a flyback diode in parallel with the motor.
** A 1N400x diode (where x = any digit in 1..7) is suitable. Connect the cathode of the diode (the end with the stripe) to the positive fan wire (the V_FAN terminal on the Duet) and anode to the negative fan wire (the FANx- terminal on the Duet).
* Brushed DC motors may have high start currents, which may exceed the rating of the mosfet.
** Before connecting a brushed DC motor to a
fan output on the Duet, use a multimeter to measure its DC resistance several times.
** Rotate the motor shaft slightly between readings and take the lowest reading you see (ignore any transient readings while the shaft
is rated for 1.5A continuousbeing rotated).
** Divide this value into the V_FAN voltage (typically you will use V_IN) to get the peak
current draw, although 2A forat startup.
** If this peak current is greater than 3A then you should connect
a few seconds whilesurge reducing thermistor in series with the fan starts up will not harm themto reduce the startup current. Here is an example of a thermistor that may be suitable: http://uk.farnell.com/epcos/b57236s0250m000/thermistor-ntc/dp/9751904.
 
== Always-on fans ==

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