walterwoj
Posts: 28
Joined: Fri Mar 15, 2019 10:46 pm

Is it a true ground?

Wed Jul 10, 2019 10:07 pm

Are the ground pins true grounds?

That is do they go directly to ground or is there circuitry between the pins and ground. What I want to do is ground more than 3/5 volts and more amps than I'm drawing from the pi. I have a board that I will use to drive higher dcv items and it has a shared ground for everything, I can wire it separately but it would be a lot more work.

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jbeale
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Re: Is it a true ground?

Wed Jul 10, 2019 10:19 pm

I would be willing to bet all the RPi boards use a single shared ground net. HOWEVER, between any two points on the circuit board that are nominally "ground" there is a finite, non-zero resistance. If you pass significant current through any part of the R-Pi board, you are responsible for the local power dissipation, and if reaches a significant number of amps, you may have local hotspots at constriction points, vias etc. that exceed the design rules for the board in that spot.

I would not recommend passing anything more than 3.1 A (total, including board and USB device power) through any part of the board, because that is the design power. At some (unknown) level of high current, you will have a voltage offset that disrupts normal operation, and/or a constriction area (likely a via) will overheat and damage some components or the board itself.

trejan
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Joined: Tue Jul 02, 2019 2:28 pm

Re: Is it a true ground?

Wed Jul 10, 2019 10:21 pm

Using the RPi expansion header as the ground return path for something high current is a really bad idea and a good way of burning out traces or melting connectors. The return path for your external higher voltage/current devices should be a dedicated lead from your board to the PSU powering them.

walterwoj
Posts: 28
Joined: Fri Mar 15, 2019 10:46 pm

Re: Is it a true ground?

Wed Jul 10, 2019 10:32 pm

Thank you for the quick answers. I will wire it the less easy but definitely safer way.

W. H. Heydt
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Location: Vallejo, CA (US)

Re: Is it a true ground?

Wed Jul 10, 2019 11:07 pm

trejan wrote:
Wed Jul 10, 2019 10:21 pm
Using the RPi expansion header as the ground return path for something high current is a really bad idea and a good way of burning out traces or melting connectors. The return path for your external higher voltage/current devices should be a dedicated lead from your board to the PSU powering them.
Heh... Reminds me of the time we had to move a 50KVA MG set. The ground wire, to take care of stray bits of power was a 14ga. wire. The main power leads were #4/0 stranded.

boyoh
Posts: 1341
Joined: Fri Nov 23, 2012 3:30 pm
Location: Selby. North Yorkshire .UK

Re: Is it a true ground?

Thu Jul 11, 2019 9:37 am

All the ground pins on the Pi are linked no
Circuitry. Just the copper tracks on the PCB
My advice is if you are using high current on your projects, is use a separate power supply
And switch them using Opto Isolators, no need
To common the grounds, you will have total
Isolation and good noise isolation.

0v-Ground-----------Ground------------Ground

Regards BoyOh
BoyOh ( Selby, North Yorkshire.UK)
Some Times Right Some Times Wrong

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