I'm trying to figure why I have had two dead transformers in the last month or two or failing that, how I can start to diagnose the cause at least.
I built an irrigation controller that runs on an Arduino Mega 2560. The mega is powered via wall wart. The system operates via a 16 relay board. The board requires 12v DC power, which I get by branching off of the 24VAC to a rectifier then a buck converter. This (I believe) provides isolation between the opening and closing of the relays on the board and the delicate circuitry of the Arduino, but I suspect it may be my culprit.
For further background, I have two plugs: the wall wart and a 24VAC transformer. The 24VAC transformer feeds the irrigation valves as well as the pump start relay through the relay board. The 5v dc wall wart output and the 24VAC output share a DPST switch, isolated from each other (so I can turn the entire thing on and off with one flick).
I haven't been able to detect any faults with my MM (transformer unplugged of course), but then again, I may not be looking for the right thing. My first transformer came from an orbit system that I stripped out, with an internally hardwired plug. The second transformer was this model: 24VAC Transformer - Amazon, a direct replacement that fit all of the specs of the original.
Plugged in, I get no reading on my MM from the outputs of the transformers. Any guidance here is appreciated, before I mess up a third one!
Measure the resistance of the primary winding (the mains power prongs).
If that reads open circuit, then the temp fuse inside the transformer windings has failed.
A sign of too high load on the (750mA) supply.
Post a diagram with all the parts and their current draws (or resistance of the valves).
Leo..
Wawa:
Measure the resistance of the primary winding (the mains power prongs).
If that reads open circuit, then the temp fuse inside the transformer windings has failed.
A sign of too high load on the (750mA) supply.
Post a diagram with all the parts and their current draws (or resistance of the valves).
Leo..
Basically what I was about to write. 750 ma rating is a really small amount to power what you are doing. Don't but such small transformers!
Thanks for the replies guys. The primary is open, so the fuse is blown, as you say. I guess I assumed too much without checking figures. Thought if 750mA worked for the store bought controller it would work for mine too, though, theirs was configured with transistors, not relays. Here are links to my components first of all:
Sainsmart 12v 16-Channel Relay Board (15-20mA drive current per relay, though only two get power at any one time so, 30-40 mA for this component)
Pump Start Relay (mine is PSR-22 model. looks like 290mA holding current but 1290mA inrush. Correct me if I'm wrong about that)
Hunter PGP 1" Valve (the valves that I use, only one of these on at a time. looks like 390mA inrush and 190ma holding)
Step Down Buck Converter (the buck converter that I use to step down to 12v. runs on LM2596, spec sheet here: LM2596 looks like 10mA max operating current?)
These are all of the components on this side of the circuit. The pump itself runs on it's own line and breaker. So to do the complicated math....looks like it could range anywhere from 520mA to 1730mA...I imagine that's my answer right there. So would something like this: