24V Pump - can I connect direct?
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Hi,
I've seen mixed reports on whether a 24V air pump can be wired directly to a Duet VIN Fan Header, or not.
The specs ripped from the product description are :
Rated voltage: 24V
No load current: 400MA
Recommended supply : 24V 2A (needs sourcing)Some confirmation would be good if I can wire direct, or if I need some sort of relay/power expander.
Thanks, Ben
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The main issue is likely to be the starting current. Measure the DC resistance of the pump several times, turning the rotor slightly between measurements, and take the lowest measured value. If it's less than 8 ohms than the starting current would exceed 3A, in which case you should connect a suitable thermistor in series with it to reduce the starting surge. Here's an example of a thermistor that may be suitable: http://uk.farnell.com/epcos/b57153s0330m000/thermistor-ntc-33r-1-3a/dp/1688797.
0Duet WiFi hardware designer and firmware engineer
Please do not ask me for Duet support via PM or email, use the forum
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1 Reply
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OK, I've been recommended a reprap Power expander which I understand opto-isolates the Duet board.
Presuming resistance is >8 ohms, or I put a thermistor in series, is there then no risk to the duet board? I'd prefer to wire it direct, simply to reduce the wiring mess needed for the power expander.
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I recommend an opto-isolator based on my own experience and killing a fan port.
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The only risk I can see is that if the pump stalls for an extended period of time (e.g. because the pump mechanism seizes up) then the mosfet and the thermistor (f you have one) may overheat - but the motor will probably burn out too.
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Based on your recommendations, is the schematic below the right one for connecting an air pump directly to the Duet ?
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Yes it is. The flyback diode is optional if the Duet is revision 1.02 or later, but having one close to the motor will help to reduce any interference generated when you PWM the motor.
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@dc42 and @benkay just wanted check with both of you my wiring before connecting to my duet 1.01. I followed the post and wired the pump accordingly. Here are the pictures:
Please let me know whether it is correct or not. I surely do not want to blow my Duet.
Cheers,
Vasan
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@sm3d seems correctly set
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Thanks @Hergonoway will update whether berd air is effective or not
Cheers,
Vasan
