Sulforaphane
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Joined: Mon Sep 02, 2019 8:29 am

Connecting a ground to 5v, is it bad?

Mon Sep 09, 2019 9:50 pm

What would happen if I accidentally connected a fans ground input to the 5v output of the Raspberry Pi?

Does it destroy the fan?

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davidcoton
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Location: Cambridge, UK

Re: Connecting a ground to 5v, is it bad?

Mon Sep 09, 2019 10:35 pm

Sulforaphane wrote:
Mon Sep 09, 2019 9:50 pm
What would happen if I accidentally connected a fans ground input to the 5v output of the Raspberry Pi?

Does it destroy the fan?
If the fan's ground is not connected to anything else, and the fan's 5V is connected only to 5V (or nothing), then no harm done.
If you short the 5V output, depending on the Pi model, you may damage the Pi. It may be temporary or permanent damage.

There are many other possibilities, ranging from "No Harm" to "Burn Your House Down" (somewhat unlikely unless something else is seriously wrong). Take care, three times a day per fan connection.
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Sulforaphane
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Re: Connecting a ground to 5v, is it bad?

Mon Sep 09, 2019 10:45 pm

davidcoton wrote:
Mon Sep 09, 2019 10:35 pm
Sulforaphane wrote:
Mon Sep 09, 2019 9:50 pm
What would happen if I accidentally connected a fans ground input to the 5v output of the Raspberry Pi?

Does it destroy the fan?
If the fan's ground is not connected to anything else, and the fan's 5V is connected only to 5V (or nothing), then no harm done.
If you short the 5V output, depending on the Pi model, you may damage the Pi. It may be temporary or permanent damage.

There are many other possibilities, ranging from "No Harm" to "Burn Your House Down" (somewhat unlikely unless something else is seriously wrong). Take care, three times a day per fan connection.
The GPIO 5v on the Pi was connected to the "Ground" on the Fan - and the GPIO ground on the Pi was connected to the 5v input on the fan. No harm has been done to the Pi. But can the same be said the other way around? - There has been no visible signs.

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davidcoton
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Re: Connecting a ground to 5v, is it bad?

Mon Sep 09, 2019 10:55 pm

OK, so the fan supply was reversed. Does the fan still work? Best to test without using a Pi. If it works, it is probably OK. If not, it's kaput.
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Sulforaphane
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Re: Connecting a ground to 5v, is it bad?

Tue Sep 10, 2019 5:46 am

davidcoton wrote:
Mon Sep 09, 2019 10:55 pm
OK, so the fan supply was reversed. Does the fan still work? Best to test without using a Pi. If it works, it is probably OK. If not, it's kaput.
How do I test it without the Pi, what tools do I need?

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davidcoton
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Re: Connecting a ground to 5v, is it bad?

Tue Sep 10, 2019 8:59 am

Connect a 5V PSU directly to the fan (right way round!). All you need is a suitable connector.
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Imperf3kt
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Re: Connecting a ground to 5v, is it bad?

Tue Sep 10, 2019 1:33 pm

davidcoton wrote:
Tue Sep 10, 2019 8:59 am
All you need is a suitable connector.
I use an old, stripped usb cable for this task myself.
Simply twist the ends of the wire and fold over themselves to thicken the connection, then insert into the connector on the fan.

It's NOT a permamant solution (though I've been doing it for months to cool my PS4), so just use it as testing.
Make sure you connect the correct wires! Usually red (positive) and black (negative) are what you would need. Do not use the white or green cables.
But beware that cheap usb cables may be wired in reverse. I learned this one by trying it on my Pi3b, thankfully the reverse polarity protection saved my Pi.
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