I'm designing a circuit for a power-on delay that powers a centrifugal water pump. When the power is switched on, it needs to be delayed by 60s before starting up the electric pump. The power source used is essentially from a wall plug: 300V max, 50Hz. The pumps themselves will typically operate between 1500 - 2000W.
I've taken multiple approaches but to no avail. I am by trade a computer-electronic engineer, so this is somewhat out of my comfort zone.
What I did so far:
- Invasive Hall effect sensor combined with a toroid to measure the current and power an IC that controls a relay. However, I realised that the AC I'm trying to delay is the AC that is needed to create the magnetic field, which I have to measure, but I can't have that because I need to delay it from ... etc ..
- Using two separate toroids, one before the relay is closed, and the other after the relay is closed. I can then generate the magnetic field while the relay is open, 60s delay, then close the relay. I can also use the second relay to monitor when the power is cut. But this approach may be too convoluted and I will still need a battery.
- Arduino nano that measures the current over a shunt-resistor/hall-effect sensor, which in turn operates the relay. I also need AC to measure this current, so again a no-go.
To 'verify' my designs I bought an Off-the-shelf Adjustable Voltage Protector (AVP) (Sinotimer SVP-912). The big realisation here is the AVP not needing another power source to operate. It only needs the AC source and gives you the 'correct' output.
There is an abundance of material for light-current delay circuits. However, I'm having a hard time finding tutorials, diagrams, material, etc for this use case.
Just as a note: I cannot use off-the-shelf AVP's, so this needs to be printable on a custom circuit board, therefore, relays, IC's, passive components, etc...