I am working on a project that uses a Ulka water pump rated at about 0.5A. I will ultimately want to control the pump using an Arduino, however before I attempt that to start with I am just using a push button switch wired up as the schematic diagram shows:


From what I have read here, an inductive load (which I believe the Ulka pump to be) requires a random switching Solid State Relay (SSR).

So first I tried a random switching SSR rated for 5A, which didn't work, but I could hear the pump humming all the time.

Just in case, I then tried using a zero-crossing SSR rated for 10A to switch the active (hot) wire, which worked, except the pump hummed when not in use. This made me think maybe I need to switch both active (hot) and neutral wires, but I thought that since its a single phase switching just the active (hot) would be sufficient.

Should I be switching both wires?

I also tried using an electromechanical relay rated for 15A, I heard the relay switch, but the pump did not turn on.

Could I potentially use a zero-crossong triac driver to accomplish this?

  • \$\begingroup\$ Solving this is probably going to require developing an understanding of these pumps - apparently they are vibratory solenoid things that include a rectifying diode, which may complicate things. But it's unclear why the electromechanical relay did not work, unless there is an error in your wiring, the pump has become damaged, or requires something you are overlooking in order to operate, like priming or a specific orientation or input/output pressure. \$\endgroup\$ Commented Jan 3, 2017 at 0:26
  • \$\begingroup\$ Thanks for your reply Chris, I have tested the pump after each attempt and it works as expected. I think I may need to buy another electromechanical relay tomorrow. To confirm the wiring is correct I tried shorting the leads on the AC side of the relay to each other and the pump works, however the humming still occurs. I think you're right in that I will need to do a lot more reading about these types of pumps. \$\endgroup\$ Commented Jan 3, 2017 at 0:56
  • \$\begingroup\$ I'm having a lot of difficulty finding a schematic for the Ulka pumps. I metered across the terminals and conformed that there is indeed a internal diode. Would I be correct to think that the power to the pump is rectified, but not filtered, AC? \$\endgroup\$ Commented Jan 3, 2017 at 1:41
  • \$\begingroup\$ Just to clarify, I meant an electrical schematic \$\endgroup\$ Commented Jan 3, 2017 at 1:42
  • \$\begingroup\$ I tried using a triac with snubber circuit this morning and the pump is now controlled by a 5V push button . However the pump still has an electrical hum when turned off and leaks a little when off. Should I maybe be switching both hot and neutral wires? \$\endgroup\$ Commented Jan 3, 2017 at 17:20

1 Answer 1


I finally found the cause.

The hum was coming from the 3 way valve, which is also activated when the brew switch is flipped. When I activated the hot wire of the pump and the hot wire of the 3 way valve using a relay, the pump worked as it should.


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