Wiring PWM Air Pump
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Hey guys. I'm looking to set up a PWM air pump on my printer. I picked one up online and it has 3 wires on it. A positive, a negative, and a signal. I'm not quite sure on how to hook it up. I'm guessing that the signal will go into one of the fan headers, and the positive and negative to the power supply. I don't know how to hook the pwm up to the fan header though. Any ideas?
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Are you sure the "signal" wire is a PWM control and not a tachometer output?
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I just looked at the description and it says that the purple line signal is output, so I'm guessing it is indeed a tachometer. My next dumb question, can I hook this up to a heater output instead of a fan output? I think it's going to draw too much current from the fan mosfets, so I'd rather control it with a heater mosfet. If it's an issue I can run a SSR on it.
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Yes you can connect it to a heater output and map a fan to it, using the A parameter in the M106 command.
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@dc42 Thanks. Where would I find a pinout for all the logical pins on the duet wifi and the duex5?
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@surgikill https://github.com/T3P3/Duet
Edit: if running low on fan outputs I think you could use an SSR/MOSFET board driven ftom the fan output.
Double check the heater output is protected with flyback/flywheel diodes. Probably best to add those diodes to the motors so your pump power leads don't act like a (noise) transmitting aerial with the inductive kick back.
Edit 2: I can't see any flyback protection on the heater outputs, most likely allow people to drive the heaters separately without back feeding voltage to the V_IN. Therefore flyback/freewheel diodes on the pump motor are essential.
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I put a fly back diode on my pump and run it from the heater output. Works a charm. I bought an in rush thermistor but haven't installed it and it's been fine so far. Average 7 amps inrush and settles around 1 amp when at speed
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The logical pin mapping is at https://duet3d.dozuki.com/Wiki/Using_servos_and_controlling_unused_IO_pins#Section_Logical_pin_numbers.
As others have already said, when using a heater output to drive a brushed DC motor or other inductive load, you must connect an external flyback diode. The peak current rating of the flyback diode should be at least the maximum motor current. The average rated current can be about half that.
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@dc42 This is a brushless setup. Here's a link to it.
Do I still need a flyback diode for a brushless setup?
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Brushless motors don;t normally need flyback diodes. However, they may not work well with PWM, unless you use an LC smoothing network (and then you also need a flyback diode) before the pump.