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Hi,

I want to use the Raspberry pi With IO Pi Plus to control 24V load (i.e dc motor)
offcourse i need isolation between 24v circuit to the (Rpi+IO Pi) 5V - this question is about the power supply:

1. Raspberry Pi require 5V 2.5A power supply
2. I have 2 IO Pi Plus, i want to connect them to "external" 5V power supply - not from the Pi
(I'll remove the pre-soldered Link)
as recommended here: https://www.abelectronics.co.uk/p/54/IO-Pi-Plus
3. also connecting output pin from IO Pi Plus to power 24V dc motor with opto-isolator circuit
as explained here under "Driving opto-isolators with the IO Pi" :
https://www.abelectronics.co.uk/kb/article/1052/driving-relays-or-higher-loads-with-the-io-pi

How i can use only 24V 10A power supply
to supply the 5V for the RPI itself, and also to 2 IO Pi Plus boards and also to drive the opto-isolator/optocoupler
in the isolated 24v circuit that power the dc motor.

Can i do that with voltage regulators ? how ?
Which grounds need to be conneted together so they have common ground ?
Does the 5V power supply that power the IO Pi Plus need to have same ground as the Rpi or it need to be completly isolated (i think so, this is the purpose of removing the Link solder, no?)

Thanks !

Hi

You can run the Raspberry Pi and IO Pi Plus boards from the 24V power supply by using a voltage regulator to drop the 24V down to 5V. Ideally, you will want to use a DC-to-DC switch-mode regulator as they are far more efficient than linear regulators, especially with large voltage drops like 24V down to 5V. I have used the PTN78020W from Texas Instruments for several Raspberry Pi projects in the past and although they are a bit expensive they do produce a stable voltage and up to 6A capacity. You use a resistor to set the voltage for the output which you can find in the datasheet. You can also find plenty of cheaper switch-mode power supplies on places like eBay that would do the job. If you want to completely isolate the power supply for the Raspberry Pi from the motor then it is possible to get an isolated switch-mode regulator but they are a bit more expensive.

You will need to use a common ground between the Raspberry Pi and IO Pi Plus boards, the isolation link on the boards only isolates the 5V rail so you can use two separate 5V supplies and not have the IO Pi Plus supply back feed into the Raspberry Pi through the GPIO port. If the IO Pi Plus is plugged into the Raspberry Pis GPIO port then it will be connected to the Raspberry Pi ground through several of the GPIO pins so you will not need to connect separate ground wires to each board.

You only need two 5V supplies if your Raspberry Pi supply is not capable of supplying enough current to power all of the outputs on the IO Pi Plus boards but as you will be driving an optoisolator it should be safe to power the Raspberry Pi and IO Pi Plus from a single 5V supply and not remove the power link on the IO Pi boards. It may be worth using a regulator that can supply at least 3A to make sure you have plenty of spare current for the Pi and expansion boards.

Just to be sure i understand what you wrote:

let say the main power will be 24V 10A
like this:
(broken link removed)

i will use this 24v to power dc motor, relays, etc..
then using PTN78020W to "get" 5V and use it to power the RPI and the 2 IO Pi plus that connected to the Pi with the Link jumper so the IO Pi plus boards get its power also from the RPI power.

1. is what i describe here is correct ?
2. is it will be true to assume that as long the RPI is powered with "enough" current let say 5V 6A
i can use the same power also to power all my abelectronics boards stacked on RPI:
2 x IO Pi Plus -- all outputs will be connectedto opto-isolators so they draw minimal current
2 x ADC Differntial board
2 x Servo Pi
1 x RTC board
1 x Serial board
if the RPi takes about 2.5A I'll have 3.5A for all the boards, and to achive that all the outputs need to be connected to opto-isolators, and i'll not drive any load directly from the output pin, but using circuits like the example here:
https://www.abelectronics.co.uk/kb/article/1052/driving-relays-or-higher-loads-with-the-io-pi

Thanks !

What you have described is correct.

You should be able to power all of the boards from the GPIO header on the Raspberry Pi. A Pi 3 will normally draw between 280mA and 1A depending on the load and the expansion boards will not draw more than half an amp combined so a 6A supply will be more than adequate.

With the Servo Pi boards if you are using them to drive RC servos then it may be worth running separate power cables from the 5V supply to the 5V inputs on the Servo Pi and have the power jumper on the boards disconnected. Servos can draw quite a bit of current when they move so by using a separate power cable the current will go down that cable from the power supply and not through the Raspberry Pi which will reduce the chance of voltage drops.

Thanks andrew