Will I have ground loop problems?

Discussion in 'The Projects Forum' started by djsfantasi, Feb 18, 2015.

  1. djsfantasi

    Thread Starter AAC Fanatic!

    Apr 11, 2010
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    I have a system that consists of three modules (one an Arduino), all running from 5VDC. Normally, they will be running from one power source, as shown in (A) of the diagram attached.

    However, there are times when the Arduino will be powered by another supply, as in diagram (B). In this case, a connection between grounds on the Arduino and one of the modules is made, so that communications between the modules can occur or the signals from other modules can be read on the Arduino.

    I want to leave this connection in place (for convenience), as can be seen in diagram (A). I need your expert advice on this scheme. Is it going to cause ground loop problems? Are there other issues I am not seeing?

    Thanking you for your brilliance in advance. 3modules.png
     
  2. #12

    Expert

    Nov 30, 2010
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    Why fight it? If there is any doubt, wire it correctly in the first place.
     
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  3. djsfantasi

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    Because I can't have the two supplies connected to the Arduino at the same time, as shown in your diagram. Nor do I want to. The supplies are connected via USB Type B connector. One is also used for programming and debugging and is not always connected.
     
  4. #12

    Expert

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    Well, you can understand the idea of using a separate wire for each ground and each supply line. This seems impossible while inside a USB cable. I guess you'll just have to filter the $h!t out of the power lines with capacitors.
     
  5. djsfantasi

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    Thanks. 2 of 3 modules are commercial boards and I assume their power input is filtered. The 3rd module has the $h!t filtered out of its power input.
    I was asking how likely was I to experience problems. Because in the case where everything is powered by one supply, I could manually remove the direct ground connection. It is only a jumper and is only necessary when debugging and has two power sources.
    image.jpg Click to enlarge
     
  6. #12

    Expert

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    Ground voltage bumps depend on how much current and how fast is the switching. You have provided neither of these, so I can't guess. Maybe somebody that is familiar with...you didn't name the, "modules" either. We are going to need more information.
     
  7. ScottWang

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    Aug 23, 2012
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    In your diagram (A), why you are not just disconnect the Ground wire?
     
  8. djsfantasi

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    An Arduino Mega, a Lynxmotion/Robotshop SSC-33, and my module used to get the envelop of an audio signal described here.

    The main current draw is from the SSC-32 when driving servos. The boards themselves draw less than ~200mA; the servos may draw 1.6A. The supply is rated at 8A.
     
  9. #12

    Expert

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    Ouch! 1.6 amps can cause an awful bump in the ground wire!
    You should plan a different route for that part.
    You probably already did that.
     
  10. Kermit2

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    Feb 5, 2010
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    large gauge wire will help with that ground 'bump'. 10 or 12 AWG would be my two cents. Also a old fashion iron core choke may bring relief should the other fixes be inadequate.
     
  11. djsfantasi

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    I could and have said so. It was left just for convenience. I might just use a small slide switch, to cut the connection when it is not needed.
    Yeah. The SSC-32 board is designed to control up to 32 servos, so it behaves well when there is a large current draw. Standard servos draw between .6A and 1A when stalled. Hopefully, they draw much less when NOT stalled. (hobby servo current requirements are not well documented). The power traces are separate on the board, from logic power. 3modules2.png
     
  12. #12

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    All motors draw, "locked rotor amps" at the instant of starting and decrease their current as speed increases. You can depend on less running current than starting current, but you can also depend on having a start surge for any motor that starts from zero speed.
     
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