I have a 120v to 24vac transformer for a lawn sprinkler system that has
failed about 3 times since I purchased the house. This time I took the
windings apart and found the break in the 120v winding. I live in a
lightening prone area. Is this failure most likely from power surges or is
there some other possible cause.
I do not think the lightning is the cause, I think it was caused by the
overheating of the transformer itself, this happened because the transformer
is rate too low for your load. Check the voltage before applying the load,
and then apply the load to see its voltage drop. If the drop 40% or more
then, you'll need to buy a bigger transformer, do not buy the exact model.
The transformer was an original factory replacement part. Do I check the
voltage drop on the load side or the line side? The control box is outside
and in sun in the morning when the sprinklers are on, could the sun cause
The Sun could add more heat to it while in operation. You would check the
secondary (output side 24Vac)
It should not drop so much, (10% is typical 21volts) 40% = 14.4 Volts or
lower is terrible. I've seen these transformers before at Home Depot, they
look small to me for continuous operation. I have it too for door bell,
door bell is low load, that's why I don't have problem with it. Yours must
have a big and continuous load, that's why you're having a problem
statically (because in a coil, high voltage is self-generated through energy
delay release, this may be why it jumps between the wire after overheating.
I narrowed the problem to one zone using your suggestion. The voltage
dropped on one zone from around 24v to 15. All of the others had only a 1
volt drop. Next I need to narrow it down to the zone wiring or the box. I
am going to switch two zones and see what happens. If that doesn't work I
will switch the solenoid. I just hope it isn't the wire to the solenoid.
Sorry my news server was down. That's a good idea by narrowing down to a
particular zone. If one Zone took that much current then, chances are you
got a heavy load someone, plus voltage drop to 15V is not a healthy sign.
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