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July 17, 2014 at 12:52 pm #23059
Before I buy, I didn’t find power supply 24VAC that output 750mA, but found power supply that output 1000mA, it will works ?
*I know that you suggest the Orbit power supply, but I need EU plug and 220V.
Regards.July 17, 2014 at 1:19 pm #27599
Yes it will work just fine. The amperage is drawn on a need basis and the maximum for that is 1000mA. The 750 can typically run 2 stations (I believe) and more just allows the possibility of more simultaneous stations.July 17, 2014 at 2:10 pm #27600
Thanks for quick answer,
Just curious, 1.5mA also works ?
And I start only the OSPi board + Rasbperry PI without expension zone.
Regards.July 17, 2014 at 2:14 pm #27601
Do you mean 1,500mA? I know 1.5mA won’t work since a single station needs around 300mA (I am pulling this number out of my head, might not be accurate). With that said, 1,500mA would work fine based on the same principle as earlier.July 17, 2014 at 3:21 pm #27602
I mean 1500mA,
I didn’t understand your answer, can I use it or not ?
Regard.sJuly 17, 2014 at 3:41 pm #27603
Yes.July 17, 2014 at 3:44 pm #27604
Thanks for your answer.
Regard.sJuly 18, 2014 at 7:02 pm #27605
Perhaps an explanation will help.
You need about 24 Volts to run your valves and the electronics. This is produced by a transformer. The transformer does two main things.
1). It reduces (steps down) the 120 Volt AC mains power to a safer 24 Volt AC.
2). It is a transformer and is made by two separate windings of copper wire around an iron core. Which is why irrigation power supplies are fairly heavy when you pick one up. The two windings are known a primary, which connects to the mains and the secondary which produces the 24 Volts. There is no electrical connection between the primary and secondary windings. Coupling is entirely magnetic. This means that the secondary winding that you will use to power all of your irrigation system is a). at a lower and safe voltage and b). completely isolated and disconnected from the house mains supply.
The amount of power (current) any given transformer or power supply gives is measured in Amps or, milliAmps. 1 Amp = 1000 milliAmps. Thus your 1500mA transformer provides 1.5 Amps. This is more than enough to run a couple of solenoids (Main and one zone) and the OSPi electronics. Power is really measured in Watts. Watts is a number that is derived by multiplying Voltage by Amps. Therefore your 24 Volt, 1500mA transformer may also be called a 36 Watt, 24 Volt transformer (24 * 1.5 = 36). Thus the more Amps you have for a given voltage, the more power in Watts you have available and, the heavier and more costly the transformer.
I have deliberately not explored AC vs. DC voltages because the OP was asking about the power of a transformer was AC voltage exclusively. In any event the wattage calculation is exactly the same.
I hope this explanation is clear. If you need more information, please post here.July 18, 2014 at 10:38 pm #27606
rederikus gave a pretty clear explanation.
The short answer is that 1000mA and 1500mA transformers should work fine, as long as the voltage is rated 24V AC (or anywhere between 22V to 29V AC).
It’s a common misconception that higher current rating will damage the circuit — the current rating only indicates the maximum output current (i.e. how much current the transformer is capable of delivering while maintaining the rated voltage). The actual current depends on how much the circuit needs.
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