Can I share 5v ground with 12v ground

Thread Starter

kenzo42

Joined Feb 26, 2014
42
Can I share a 5v ground with a 12v ground? I wanted to share the usb ground with a 12v solenoid ground. The solenoid is being powered with a 12v wall wart and the USB is being powered by the pc. Thanks.
 

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MrSalts

Joined Apr 2, 2020
1,762
Can I share a 5v ground with a 12v ground? I wanted to share the usb ground with a 12v solenoid ground. The solenoid is being powered with a 12v wall wart and the USB is being powered by the pc. Thanks.
Make sure you have a diode attached across your relay's coil to prevent any inductive kick when the coil is de-energized.
 

dl324

Joined Mar 30, 2015
14,475
Can I share a 5v ground with a 12v ground? I wanted to share the usb ground with a 12v solenoid ground. The solenoid is being powered with a 12v wall wart and the USB is being powered by the pc
In most cases, you don't have a choice.

What is the solenoid coil current? You want to do the ground wiring such that large current can't affect circuitry that would be susceptible to ground bounce. A star configuration for ground would avoid this problem, but in many cases, it's not required.
 

Thread Starter

kenzo42

Joined Feb 26, 2014
42
In most cases, you don't have a choice.

What is the solenoid coil current? You want to do the ground wiring such that large current can't affect circuitry that would be susceptible to ground bounce. A star configuration for ground would avoid this problem, but in many cases, it's not required.
It's stated 0.4A.

Fielect DC 12V 25N Push Pull Type Solenoid Electromagnet, 0.4A 10mm Stroke, Open Frame Type Solenoid, Linear Motion, JF-1039B https://www.amazon.com/dp/B07Z4JQPBN/ref=cm_sw_r_apan_i_1P4TG1N9G0089WGD6YAE?_encoding=UTF8&psc=1
 

MisterBill2

Joined Jan 23, 2018
11,900
You have two separate power supplies, each mains powered. You MIGHT have both supplies adequately isolated from the mainsso that there will be no problems. Use a meter to check for voltage between the two negative sides that you want to common. That will tell you the truth.
 

MaxHeadRoom

Joined Jul 18, 2013
25,214
You have two separate power supplies, each mains powered. You MIGHT have both supplies adequately isolated from the mainsso that there will be no problems. Use a meter to check for voltage between the two negative sides that you want to common. That will tell you the truth.
The problem with that is using a high impedance meter, it will most likely show a voltage difference, the method requires a resistor placed between the measured points, 500Ω to 1kΩ in order to create a low impedance source to see if the stray field still exists and could be a problem.
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Thread Starter

kenzo42

Joined Feb 26, 2014
42
You have two separate power supplies, each mains powered. You MIGHT have both supplies adequately isolated from the mainsso that there will be no problems. Use a meter to check for voltage between the two negative sides that you want to common. That will tell you the truth.
So you probe both negative wires with voltmeter (using voltmeter's red probe to negative and black probe to negative)?
 

MisterBill2

Joined Jan 23, 2018
11,900
So you probe both negative wires with voltmeter (using voltmeter's red probe to negative and black probe to negative)?
That is exactly what I meant. This would be measured before the two negatives would be connected. Any voltagebetween the two negatives will mean that there will be a current flowing in the negative connection. Depending on how large a current, that could be a problem. Or, if the current is quite low, it may not be a problem.
 

MaxHeadRoom

Joined Jul 18, 2013
25,214
So you probe both negative wires with voltmeter (using voltmeter's red probe to negative and black probe to negative)?
See post #9 !!
With a high impedance meter open circuit, Doesn't mean there is current flowing just a differential in voltage.
Needs the resistor to lower the impedance.
 

MisterBill2

Joined Jan 23, 2018
11,900
Max is probably right, because if the voltage is due to high impedance leakage then connecting the negatives will not be a problem. I covered that: "Any voltagebetween the two negatives will mean that there will be a current flowing in the negative connection. Depending on how large a current, that could be a problem. Or, if the current is quite low, it may not be a problem." If it is microamps or even a few milliamps then no problem. But given that we have no information about either supply, it may not be so lucky. I have seen at least one problem that way.
 

dl324

Joined Mar 30, 2015
14,475
There's an arduino connected to the USB. I'm assuming yes?
What gauge are the ground wires? How do you actually have the wiring for the MOSFET/solenoid?

If your wiring diagram depicts how things are actually wired, the area circled in red could be problematic.
1653085537009.png
 

MaxHeadRoom

Joined Jul 18, 2013
25,214
Max is probably right, because if the voltage is due to high impedance leakage then connecting the negatives will not be a problem. I covered that: "Any voltagebetween the two negatives will mean that there will be a current flowing in the negative connection.
One reason in industrial enclosure systems is the practice of equi-potential bonding, an effort to reduce and/or eliminate ground loops.
I have a Siemens paper they published on the subject.
 

dl324

Joined Mar 30, 2015
14,475
This is the actual wiring. Can you explain why the red circle is a problem?
If that section of wiring has sufficiently high resistance, it can affect any digital logic to the left. A star ground system will minimize the effects of high currents with "high" resistance interconnect.
 

MisterBill2

Joined Jan 23, 2018
11,900
The explanation of why the part of the circuit circled in red on post #16 could be a problem source is that any resistance in that section of the wire will cause a voltage drop from the solenoid current flowing through it. Because that same section of wire also carries the current to the processor module, that voltage drop will also affect the supply voltage to that processor module.
The term "Star Ground" means each circuit connection to that point called "ground" has it's own wire, with only the current from one device passing through it. "Star Ground" is an unclear term until you understand what it actually means.
 
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