How to reduce the voltage drop?

[Murugesh_89]

Hi,
Below i put my setup with the value of voltage at the input of each board.



I am using a 12V smps. Each board in the setup draw a current of 300 mA. Now for 5 boards the current drawn from smps is 1.5 A.

Actually i need to get the supply for 20 boards using a single smps. But for now, with 5 boards itself the voltage reduce to 11.15 for fifth board. So i fear that i wont enough voltage (atleast 10.5 V as i have used 7808) at the last 20th board. Also i think when i go for 20 boards the load current will be around 6 A which cause more drop. I should not run individual wires from smps to each board.

So,
1. How can i get out from this issue so that i can get around 10.5 V at the last board.
2. How to measure the resistance in supply path. I want to know across which terminals?
3. I have regulated 5V and 8V directly from the 12V in each board, will it have anything to do with the more voltage drop issue. I mean if i regulate 5V from the output of 7808 will it be fair?

Thanks,
Murugesh

 

[godfreyl]

1. How can i get out from this issue so that i can get around 10.5 V at the last board.

Use thicker wire.

2. How to measure the resistance in supply path.

1. SMPS to PCB1:
   Voltage drop = 12.06V - 11.66V = 0.4V
   Wiring resistance = 0.4V / 1.5A = 0.27Ω
   
   
2. PCB1 to PCB2:
   Voltage drop = 11.66V - 11.42 = 0.24V
   Wiring resistance = 0.24V / 1.2A = 0.20Ω
   
   
3. PCB2 to PCB3:
   Voltage drop = 11.42V - 11.30 = 0.12V
   Wiring resistance = 0.12V / 0.9A = 0.13Ω
   
   
4. PCB3 to PCB4:
   Voltage drop = 11.30V - 11.20 = 0.10V
   Wiring resistance = 0.10V / 0.6A = 0.17Ω
   
   
5. PCB4 to PCB5:
   Voltage drop = 11.20V - 11.15 = 0.05V
   Wiring resistance = 0.05V / 0.3A = 0.17Ω

3. if i regulate 5V from the output of 7808

That will not help.

I should not run individual wires from smps to each board.

You could organize the boards into groups, with separate wires from the smps to each group. e.g. 4 groups of 5 boards.

 

[schmitt trigger]

Your schematic indicates a 0.25 mm2 wire.......that is a AWG#23 wire.....which is 67 milliohm/ meter.......your cable runs are long.

Use at least a AWG#16 wire, 1.31 mm2, or 13 milliohm/ meter.

EDIT, the actual resistance per meter is twice the value shown, as you have resistance on the positive and negative wires.

 

[wayu_ix]

You should try to increase the power supply to the Max will help.

 

[Murugesh_89]

Thanks Godfreyl..
You have calculated resistance using the voltage drop and current.
Is there anyway to measure using DMM or LCR meter. If so, across which terminals i need to measure?

Also i am using the same wire length between boards, hence why the calculated resistance is not fixed value?

 

[godfreyl]

Is there anyway to measure using DMM or LCR meter. If so, across which terminals i need to measure?

It's not easy to measure such low resistance directly with a meter.

Also i am using the same wire length between boards, hence why the calculated resistance is not fixed value?

Maybe voltage readings were not exactly accurate. The differences can be explained by errors of less than 1% in the voltage readings.

 

[Murugesh_89]

Use thicker wire.

Say if i use 2 sq mm wire. Out of single strand like coaxial cable and multi strand wire, which has low drop?

 

[amayilsamy]

You can measure the wire resistance using voltage divider circuits.

And check again what is maximum current of SMPS.

Put common capacitor output of SMPS.

 

[schmitt trigger]

Say if i use 2 sq mm wire. Out of single strand like coaxial cable and multi strand wire, which has low drop?

For DC, it doesn't matter.
For AC, as the frequency increases, skin effect and proximity effects become relevant. Google the terms.