Dear all

I'm trying to power a switch board and several raspberry pi in parallel using this power supply :
MeanWell Power Supply 60 W 5 V 12 A RS-75–5

Unfortunatelly, after the switch and a couple of raspberry, the voltage drop from 5.04V to 4.86V.

Is there any way to fix it ? If the solution is to change the power supply, any recommandation ?

Thanks a lot for your help (this is driving me crazy for 2 weeks)

 

Hello,

How many RPI's are used and what model?
There are several models around:
https://www.raspberrypi.org/products/

Bertus

 

Hi Bertus !

Thank you for the answer. There is one raspberry 3 model b+ and one raspberry 2 model b

Thank you again.

 

Hello,

There should be no more drawn than 5 A from the powersupply.
What kind of switches do you use?
Are they rated for at least 3 A?
(I assume each RPI has its own switch).

Bertus

 

Hello,

There should be no more drawn than 5 A from the powersupply.
What kind of switches do you use?
Are they rated for at least 3 A?
(I assume each RPI has its own switch).

Bertus

And what length of what gauge wire?
Is 180mV drop really a problem?

 

Hello,

There should be no more drawn than 5 A from the powersupply.
What kind of switches do you use?
Are they rated for at least 3 A?
(I assume each RPI has its own switch).

Bertus

Hello Bertus,

There are 2 switched and they are differents models.
I have been checking in the datasheets of each and they do not specify the consumption.
Maybe I should measure it directly and get back to you with the information.

Thank you again for the help.

 

And what length of what gauge wire?
Is 180mV drop really a problem?

Hello AlbertHall,

There is small distances between each device (~5cm).
I don't know the gauge of the wires. Maybe this picture can help.

Thank you !

 

I don't know the gauge of the wires. Maybe this picture can help.

My guess is 28 AWG.

1. Have you confirmed that the drop is from the wires?
2. Is the drop significant enough to cause malfunction? 5V devices are typically spec'ed to operate down to at least 4.75V (low range of a 5% tolerance).
3. Any chance you can double up the wire to reduce the voltage drop?

You can use remote voltage sensing and compensate for voltage drop in the wire, but that will require you to design your own power supply...

 

Is there any way to fix it ?

The power supply has an adjustment pot that you can turn to increase the output back to 5 volts.
SG

 

Hello guys,

Thank you for your great help.
After some tests, you were right, dl324, the raspberry work very well under 5V. The problem was the switch which works only between 5V and 12V.

I used sghioto's tips and set my power supply to 5.23V using the adjustment pot. The raspberry can handle 5.25 and my switch is receiving now enough power to work.

I would still like to understand why the power is decreasing in this parallel circuit... But I guess there is no way to figure it out...

Thank you again to all of you for your help !

 

I would still like to understand why the power is decreasing in this parallel circuit

Probably from the resistance in the cables. Measure the voltage at the power supply terminals and then at the raspberries. Any difference would indicate a voltage drop in the wiring.
EDIT: You can also check the load regulation by reading the voltage at the power supply terminals with no load and again when the raspberries are connected. According to the specs on the supply it's + or - 1% or 50mv.
SG

 

the raspberry work very well under 5V

The last time I checked, it wasn't uncommon for RPi's to be powered by USB power supplies. Can't remember if that's spec'ed for 5% or 10% tolerance. But you were above 4.75V.