Small Switching Power Supply

helio neves's picture

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Joined: Nov 22, 2019

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Small Switching Power Supply
December 11, 2019 - 10:28pm

Hi everybody!

I have a water level controller, which uses a transformer to energize a 24V DC relay which switches on and off a pump. The transformer burned off, and I wonder if I can make a small switching power supply instead of use a linear one...

The relay resistance is about 1100 ohms; doing the math, the all circuit requires about 27 milliamps @ 24 Volts DC... how can I make a switching power supply in place of the transformer?circuito.gif

Sourav Gupta's picture

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Joined: Feb 12, 2018

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Whats is the controller in that image?
December 12, 2019 - 12:31am

The controller uses the BC546. What is the current consumption of that controller?

What is the purpose of this circuit? Outdoor or indoor? What is the input AC rating?

helio neves's picture

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Joined: Nov 22, 2019

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The controller gets no more
May 21, 2020 - 4:57pm

The controller gets no more than ( 24V -12V )/2700 ohms = 4.4mA.

I already mention the purpose, read it again more carefully. It´s mounted in a watertight frame ( maybe the reason why the transformer got burned ).

I don´t know the AC 230V consumption ( I didn't measure before the transformer get burn! ), but I estimate it's about 9mA.

 

Sourav Gupta's picture

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I dont see any reson for the
May 22, 2020 - 7:33pm

I dont see any reson for the burned transformer as per the above circuit.

However, you can use small VAC to 100mA 24V switching power supply module that is readily available to purchase. You can surely try it out.

helio neves's picture

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Note that the schematic is
May 21, 2020 - 5:12pm

Note that the schematic is incomplete; there's more parts missing: the probes to the well, a varistor hanged between the transformer and rectifier bridge...; but I guess it makes no difference to the matter