#ask
Maybe stupid questions but i want to know what worong with my schematic? I want to power my arduino using schematic like in the picture and 12 goes in VIN and 5v just power around the device like an relay sensor etc (i make own pcb) ,,
And when i plug the input ( 24v) why the IC output of 7812 give only 5v and 7805 output only 3.3v?
And the ic 7812 become so hot ( 70 degree C)
Can you give me what's wrong with my power input?
You did not design this carefully enough, not enough basic knowledge of power dissipation and consideration of the current needed by your components.
Use a DC-DC converter. These are far more efficient than linear regulators and so will not get hot.
The problem is that linear regulators reduce the voltage from input to the desired output by burning off the extra power as heat. Let's assume your relay needs 100mA current at 5V. When regulating 24V down to 12V, the power that must be dissipated in the 7812 is (24 -12) x 0.1 = 1.2W, which will cause the regulator to heat up. For the 7805, the power dissipated will be (12 - 5) x 0.1 = 0.7W, which will also cause some heating.
With a DC-DC converter, efficiency will be around 80% or better, so when converting from 24V to 5V, the input current only needs to be 0.05A to produce an output of 0.1A and the power dissipated by the converter is only around 0.2W.
I sorry for my ignorance,, and maybe this is stupid question again,,
I have 10 relay (6 10a, 4 30a), and 2 sensor need power up by 5v
Also i have 1 valve and 2 motor, need power up by 12v, and the rest is RTC and MICRO sd logger
So that's why i make that power input.
So when the 24v pass the 7812. why the output is 5v (not supposed to be 12v)?
And when then 5v pass 7805 ( output pass by 7812 which supposed to be 12v) the output is 3.3v
Also the net "12v" i connected with VIN arduino
Using relays with 5V coils was a mistake. Consider relays with 24V coils so that they can be powered directly from the 24V supply. Alternatively consider using logic-level N-channel MOSFETs rather than relays.
What are the current requirements of the valve and motors? What are the stall currents of the motors?
To add to this, you can purchase switching versions of the 7812 and 7805
that have roughly 90% efficiency and use the same footprint. BTW, you don't need both CPIN2 and CPIN3.
However, you will probably need more current than small regulators can safely supply. A DC-DC converter is likely a better idea.
The schematic looks basically OK. I don't know why it's not operating properly.
If there is any significant load on the 12V rail, you'd expect the 12V regulator to get pretty warm - it has to dissipate 12*I watts (so if you have 200mA combined sink on 12V and 5V, that'd be 2.4W dissipated in the 12V regulator. Which would need at least some heat-sinking. (But I'd expected the output to be 12V...)
First get the 12V right and only then go further.
So you have to sum up all the current being used by the 12V devices and 5v devices. The issue is the combination of voltage across the regulator and the current through it. If you power up your circuit with nothing connected it should work right.
Regulator #1
24V input
12V output
guess at a current of 500ma (0.5A)
Power dissipated in regulator = (24-12)*0.5 = 6 watts. Consult the regulator specification sheet and see if it can dissipate 6 watts.
Keep in mind that the spec sheet may tell you the "max power dissipation" assuming that a large heatsink is attached!
The Arduino Nano is infamous for quoting power specs that are next to impossible to support with the heatsinking provided (essentially none.)
I agree. In fact nearly every spec is "qualified" by some specific condition that is unrelated by real life. So one really needs to understand the specifications before applying.
I was concerned about overwhelming the OP if I went much further.
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