Transformers failing, probably due to load of multiple valves

[NOV6]

I am running Open sprinkler 3.0 with the 24 V 500 mA transformer.

In the past 2 weeks my transformer has failed twice.

There are 2 things that could be responsible:

1) running more than 2 valves at the same time.
2) running the controller with water supply turned off
Or
3) running more than 2 valves with the water supply turned off

Can I avoid this problem with a higher capacity transformer? Will a higher capacity transformer damage the controller? Where can I source a higher capacity transformer and what should the specifications be?

[Ray]

So exactly how many is ‘more than 2 valves’? The 500mA transformer might be able to run 3 or 4 at the same time, but it’s definitely pushing the limit. If you want to run more than 2 simultaneously, you should buy a 24VAC transformer with higher current capacity. We recommend jameco.com, you can search 24VAC transformer, make sure it’s ‘AC to AC’ transformer. Each open valve draws about 200mA, so if you want to open 4 at a time, you need about 1 amp current. We don’t recommend running more than 4 at the same time — if you do want that, you should get an external relay to help drive more current. The circuit on OpenSprinkler is not designed to drive a large amount of current.

Transformer with higher current rating will NOT damage the controller — as long as it outputs 24VAC. Current rating means how much current the transformer is capable of delivering. The actual current draw depends on how much the solenoids need. It’s analogous to say that just because your power socket is rated 15A doesn’t mean it’s pumping 15A all the time — how much is actually delivered depends on how much the device needs, or if a device is connected at all. 15A just means it’s capable of delivering 15A if needed.

[Author]

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