24VAC to 5VDC using D24V3F5

I am using an example circuit from here to convert 24VAC to 5VDC.

It is driving a wemos D1 mini with relay and I have it connected to a 24VAC sprinkler solenoid valve.

I did use components on hand, so the TVS I am using is 37V and the 1000uF cap is 60 volts. I have components of the suggested ratings in the example circuit (40V TVS and 100V 1000uF) coming.

With components on hand the wemos runs a treat, when I am not turning the relay ON. When I run a script to turn the relay ON and OFF in 5 second stints the system runs for a time then crashes. I don’t have an oscilloscope so can’t check what is going on.

I am assuming the TVS is too tight and I need the 40V TVS that are still in the mail.

In any event. I will report back once I have the recommended components installed.

Has anyone else a circuit design for 24VAC to 5VDC using this Pololu widget please? The only other option I have, after TVS and maybe bumping the voltage rating of the cap, is that the circuit needs something else?


As an initial troubleshooting step, you could try using a multimeter to measure the voltage across the input and output of the power circuit when the controller crashes, although this might not give you any meaningful information if the problem is caused by a transient condition. It is hard to tell what is going on in your system without seeing oscilloscope captures, so you might consider getting one or looking for a way to access one (such as at a local makerspace or school).


Tony. Yep. I know regret all those times I didn’t buy a cheap cro at auction.

So, story so far.

The correct TVS have turned up so I ripped out the 37V component and replaced it with the 40V recommended.

Behaviour has changed. Cycles on/off 5 secondly. Still crashes BUT proceduraly will reboot and start again. Cycles 2 to 5 times between crash. ALWAYS crashes on relay opening. That is, engergize to de-energize edge.

Next thing is once I receive the 100V 1000uF caps instead of 60V, but I have feeling the farads not volts is the story. The other fix might be redesign the board to tighten up spacing between components in voltage conditioning, before the Pololu PSU.

So, did I mention I designed the board? I might solder up some components without a board (like the example) to get the component spacing the tightest.

So, still clutching at straws. I might even change the bridge I am using - though its is simpy a DIP thing with 400V 1A versus the 40V 4A.

I am more digitally than analogically inclined, and less power supply oriented.

We do not have any other suggestions for troubleshooting your system. If you do get access to an oscilloscope, please post scope captures that show what happens when your system crashes.