Hey guys,
I am writing to ask if you would know how I could solve an issue I am having with my current setup for a project. I am using a Raspberry Pi to turn on an air pump through a relay board. Previously, the air pump was setup such that power was supplied from:
230V (AC) -> Computer ATX Power Supply (Switchmode AC to DC) 12V -> Air Pump DC Motor.
The first air pump was rated at 12V 8A. The power supply can output 36A at 12V. Although,I had issues with this air pump as it would trip the power supply over-current protection. To overcome this problem I am using this circuit (found on this forum: https://www.electro-tech-online.com/threads/cheap-and-cheerful-dc-motor-soft-start.30314/) to “soft start” the motor to reduce the inrush current when starting the motor from idle as I believe the initial current spike is shutting down the power supply.
So initially, the current is limited by the 0R5(10W wire wound resistor) resistor for a short amount of time, when the capacitor is charged the MOSFET(IRF540N) allows the current to flow through it instead. This effectively reduces the current to the motor for a short amount of time at the start.
I changed my air pump recently as it wasn’t delivering enough air flow. The new pump is a higher current pump, it requires 14A at 12V. I thought the previous slow start circuit would work but it appears the MOSFET is now overheating when turned on in the first few seconds. Previously I could hear the motor was running at a slower rate then spread up, now the motor just starts and runs without the lower voltage initially for 0.5sec then being fully powered after. Do you think this is due to the motor it self? (I measured a resistance close to 0.5 ohm across the terminals, and the previous motor had a resistance of 0.7 ohm).
What do you think I should do to solve the problem?
I was thinking of:
Image of Air Pump:
Image of soft starter circuit:
Image of Relay:
Image of ATX power supply:
I would really appreciate any help with this issue, thank you!
I am writing to ask if you would know how I could solve an issue I am having with my current setup for a project. I am using a Raspberry Pi to turn on an air pump through a relay board. Previously, the air pump was setup such that power was supplied from:
230V (AC) -> Computer ATX Power Supply (Switchmode AC to DC) 12V -> Air Pump DC Motor.
The first air pump was rated at 12V 8A. The power supply can output 36A at 12V. Although,I had issues with this air pump as it would trip the power supply over-current protection. To overcome this problem I am using this circuit (found on this forum: https://www.electro-tech-online.com/threads/cheap-and-cheerful-dc-motor-soft-start.30314/) to “soft start” the motor to reduce the inrush current when starting the motor from idle as I believe the initial current spike is shutting down the power supply.
So initially, the current is limited by the 0R5(10W wire wound resistor) resistor for a short amount of time, when the capacitor is charged the MOSFET(IRF540N) allows the current to flow through it instead. This effectively reduces the current to the motor for a short amount of time at the start.
I changed my air pump recently as it wasn’t delivering enough air flow. The new pump is a higher current pump, it requires 14A at 12V. I thought the previous slow start circuit would work but it appears the MOSFET is now overheating when turned on in the first few seconds. Previously I could hear the motor was running at a slower rate then spread up, now the motor just starts and runs without the lower voltage initially for 0.5sec then being fully powered after. Do you think this is due to the motor it self? (I measured a resistance close to 0.5 ohm across the terminals, and the previous motor had a resistance of 0.7 ohm).
What do you think I should do to solve the problem?
I was thinking of:
- Trying to make the circuit again with new calculated R,C values
- Add high inductance in series to the motor terminals to slow down the rate of current change (I got a 470uH ferrite core inductor but it gets warm and I am not sure about the usual temperature range, so I haven’t explored this option further)
- Add a 12V 1.3 Ah lead acid battery in parallel to the +12V line from the power supply, which will be charged by the the computer ATX power supply, this should provide the required current to start the motor if it too demanding for the power supply.
- Starting capacitor?
Image of Air Pump:
Image of soft starter circuit:
Image of Relay:
Image of ATX power supply:
I would really appreciate any help with this issue, thank you!
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