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I'm working on a mini adjustable power supply that can give me a steady max of 12 volts, 3A and be able to boost to 24V when needed. Therefore, to do so I'm using a MT3608 2A DC-DC Step Up Power Supply Board Booster Module and 3A DC adjustable Current Voltage Step down converter Battery Charger LED 18650. I know Step-Up Step-Down modules do exist but it is very hard and expensive to obtain those from where I'm from. As for AC-DC power supply I'm using an old 100W computer power supply, hence using the 12V supply rail to power this. I also want to connect a Voltmeter and Ammeter to the input and output of the Buck Converter and with a flip of a switch I'm able to check either the input or the output.

This is the picture of the wiring of the Volt Ammeter that I'm using. Since I'm only limited to 2 links I will try to post the pictures of the modules in the commends. Volt Ammeter

My plan is to use one high current DPDT switch, one low current 4PDT switch and 2 relays. The DPDT switch will be use to turn on and off the boost converter and the 4PDT switch will be used to switch between measuring the input and output current and voltage. As I'm quite new to electronics I'm not entirely sure this schematic will work, and that's why I'm asking for help. enter image description here

My main concerns first of all is will this work as I came up with the design myself? The reason why I'm putting a switch to toggle the boost is the boost converter can only supply 2A and my buck converter support up to 3A so in the case that I need 3A the boost converter will bottleneck it. My other concerns are about the relay. Do I need to connect a diode in parallel to the coil of the relay to prevent current back flow? And since the the relay will be switched at a short delay after the toggle switch is flipped, during this small time delay the Ammeter will be short circuited, so can this damage the Ammeter?

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  • \$\begingroup\$ Why not use a single buck-boost converter? \$\endgroup\$ – Ignacio Vazquez-Abrams Jun 10 '16 at 1:47
  • \$\begingroup\$ Its very expensive, and where I'm staying its very hard to get. Barely any shops sell it. \$\endgroup\$ – Max Jun 10 '16 at 2:52
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Diodes are cheap using them will protect your switch. short-circuiting the ammeter will not damage anything

If you can live with a brief interruption when switching he relays aren't needed:

schematic

simulate this circuit – Schematic created using CircuitLab

"A in" is ammeter sink "ground" on your circuit. "A out" is ammeter source "ammeter" on your cricuit. "volts" is "voltmeter" on your circuit.

This only works because the buck converter has input and output grounds connected internally.

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  • \$\begingroup\$ Omg thank you so much!!! Very very helpful literally solve my problem that I have been working on for days. Just one more question where can I attach the diodes and what type of diodes to use. I'm not very familiar with using diodes. And will a toggle switch with current ratings of 3A/250Vac,6A/125Vac be able to withstand the current coming in? \$\endgroup\$ – Max Jun 10 '16 at 3:56
  • \$\begingroup\$ silicon rectifier diodes eG: 1n400x (for some digit x) but only need if you use the relays. That toggle switch doesn't say that it's suited to DC operation but the currents or or the voltages being switched are all so low that I do not exoect any problems \$\endgroup\$ – Jasen Jun 10 '16 at 4:42

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