Probably normal. Internal transformers will get hot especially during the summer months. If it gets to hot it will blow itself out.

 

This is the reason I suggest everyone become well acquainted with multimeters and use them.

In fact I believe I placed power supply at the top of my critical path method of troubleshooting.

Kinda funny huh?

 

Well....i did check voltage at outlet it was 120...did check transformer output at around 26....
But with limited time I did not check anything else. And my expertise stops at the ac.outlet. i dont intend to test anything between the outlet and the breaker box....beyond my scope...
Everything is working fine right now....just a bit concerned about the transformer getting so hot that I can smell it and barely touch it..

 

Another thought. Could high voltage transients might break down insulation within the transformer windings? Maybe input surge protection could be added.

 

When transformers fail, many times it is heat that melts the insulation on the winding wgich shorts and causes more heat, etc. The initial short could be caused by a power side surge.

 

Strictly as a side inquiry, do they still manufacture surge protection in the form of playing card symbols? (this is not a gag - they were offered as submersible pump motor protection)

 

So a quick ohm test to see if any particular zone has a short or all zones have high resistance which causes higher amp draw. A quick inlet test on the high voltage side and outlet test. If all checks out then a quick swap of the transformer.

Since we are almost entirely residential, 2 wire is rare for me . I fried two transformers the other day tracking down my first two wire failure. The controller had an overload protection error and nothing would run. Turns out a moisture sensor for zones 34-38 had failed and was causing 2.4 Amp draw. .. I learned I should have thrown a solenoid or two in series with my transformer to eat up the load . Took me 1 hour 45 min .. It was a great learning experience for me.

 

So a quick ohm test to see if any particular zone has a short or all zones have high resistance which causes higher amp draw. A quick inlet test on the high voltage side and outlet test. If all checks out then a quick swap of the transformer.

Since we are almost entirely residential, 2 wire is rare for me . I fried two transformers the other day tracking down my first two wire failure. The controller had an overload protection error and nothing would run. Turns out a moisture sensor for zones 34-38 had failed and was causing 2.4 Amp draw. .. I learned I should have thrown a solenoid or two in series with my transformer to eat up the load . Took me 1 hour 45 min .. It was a great learning experience for me.

What's the normal draw of the sensor? Seems like a design oversight if any factory peripheral can damage the power supply.

 

So my rainy-afternoon musings have me trying to add up clues into a diagnosis. Replaced GFCIs points a finger of suspicion at the line voltage supply. If there was insulation break-through on the transformer windings, that could change the output voltage, and maybe make the transformer itself consume power from a windings short.

So, disconnect one of the transformer output wires from the controller terminal strip, and recheck the output voltage. See if the transformer cools down. At a higher degree of difficulty, would be to apply the clamparound ammeter to the primary side of the transformer.

I wonder if MOV protection (or similar) can be applied (economically) to the primary side of the controller transformer.

 

You're suggesting a no load or static measurement of the transformer.

Look again at my critical path method posts and you'll see a static voltage measurement listed.

I take these measurements for benchmarking transformers, voltage drops and field wiring.

You can actually see the voltage drop whe you perform as you've suggested.

Amperage measurements aren't near as difficult as one might think.

These 6" extensions are flat and easy to split for gaining access to a single wire for clamp meter use. They can plug in to any non hard wired system , outlet, extension cord, wall mount transformer etc.

Cool thing about this is you can measure amperage and leakage on most any appliance you can think of and it's easy.

 

Unlike the photos, I do not count on the controller being a plug-in. However, that may be the only practical means to have primary-side surge protection.

 

Unlike the photos, I do not count on the controller being a plug-in. However, that may be the only practical means to have primary-side surge protection.

No irrigation controllers were harmed posting these photos.

The top amperage measurements were of my golf cart charger resting and under load. Then my air compressor and then my MacBook.

Just a representation of how handy these $3 extension cords are.

 

I see these Hunter transformers doing this from time to time. I just replace them if I have an extra which solves the problem. If I don't have an extra, that's a new controller install. A lot of people like the app controllers so when I give them an excuse to get one, they usually do.

 

I see these Hunter transformers doing this from time to time. I just replace them if I have an extra which solves the problem. If I don't have an extra, that's a new controller install. A lot of people like the app controllers so when I give them an excuse to get one, they usually do.

I wonder if anyone pulling an overheated transformer is doing any testing on their output voltage later on. Is there any 'tell' that it has sustained electrical damage?

 

Melted/discolored insulation on windings seems like an obvious tell.

 

Funny you replied to this today Boots...I was just at another clients today that I installed a brand new Hunter Pro C a few months ago. The transformer was as hot as pork belly freshly fried in a cast iron pan.
I guess this is just the way those transformers run, but it sure makes me paranoid in fire season out here.
I bet if I put an infrared thermometer on them they'd hit 150, maybe 160 degrees.
I have strong weathered hands and I can't hold the back of my index finger on those transformers for longer than 2.5 seconds

 

I can't believe you can spend time worrying about a transformer that is warm.
I have too many that have brown yards, with a perfectly functional system, because they don't know how to water.

 

I'd be curious to see if an aftermarket or different irrigation brand transformer would put off less heat.

 

I know Rain Bird had custom transformers made. Rain Bird tried to use specs that would cover many models without increasing cost too much for the less expensive controllers, so several models might have the same transformer. But that transformer was likely made specifically for Rain Bird.
My point is that a standard off the shelf transformer has little chance of meeting the requirements closely. But perhaps one might be 'good enough'.

 

I'm wondering if standards for transformer construction have slipped. I still think of a surge/spike victim as either an inert lump (Class 2 internal fuse blown) or burnt offerings - no middle ground.

 

Multiple small surges can cause some windings to short and heat up the transformer, but not enough to cause a cascading failure. The transformer just would run hot.

 

I just don't remember older class 2 transformers running too hot. Of course, their construction might be 'clumsy' and oversized, compared to today's, and more able to dissipate heat. Could be they had better spike resistance.

Of course, controllers back when had metal faceplates helping to dissipate transformer heat. Some of them even had the transformer out of the circuit when a zone wasn't energized.

 

Well I have checked 6 Hunter Pro Cs now. Some brand new installed this year, some a year old and a couple two or three years.
Those transformers just run damn hot. I can hold the back of my index finger on the transformer for only 6 seconds before my finger starts to burn. Some have that funky hot electrical smell, some don't. I guess this is just how they run.

 

Yep, what I see too