Confusion over Ground, Earth and negative connections
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I've spent a while searching for an answer and have not been able to find one, so I'm hoping someone can help me.
I have wired up two Duet 3 Mini 5+ boards successfully in an old printer and a Voron 2.4. I am now trying to wire in an external 5v Meanwell PSU to the EXT 5V header on the Duet to power some Neopixel LEDs for the Voron. Which has led me to being unsure where to connect the ground on the EXT 5V. The 5v PSU has Live, Neutral and Earth in and + and – 5v out.
This led me to look back at how I’d wired the 24v PSU when I was following this guide on the old printer. On both printers I have wired VIN to + 24v and GND to negative. https://duet3d.dozuki.com/Guide/Ender+3+Pro+and+Duet+3+Mini+5++Guide+Part+1:+Wiring/87
This has been working fine. But I want to know how I should be wiring things up to the ground connectors?
I’m not great with electronics as you can tell! I tend to get by searching and triple checking everything and I've not had any blue smoke yet! Thanks for any help!
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I've checked the continuity with my multimeter and the GND on the 5v connectors and the GND on the 24v are connected, as well as all the other GND points on the board. So I'm guessing it's not a good idea to connect the 5v negative to the 24v negative? Which is what would happen if I was to use 5v negative on the 5v external ground pin. Should I be using AC earth on the ground pins? Excuse my ignorance.
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- Connect the 24 Volt power supply -V to Duet ground connection in the main power connector.
- Connect the 5 Volt power supply -V to the Ground near the 5V external input connector.
The power supplies will have their -V connections connected together by the Duet ground plane.
THIS page shows how to add an external 5 Volt supply and where to make the connections.
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@alankilian Thanks for the reply.
I did have a look at that page in my searches but couldn't really find a definitive answer. All the articles I found said either "connect the power supply to EXT_IN" Or "connect +V to +V and GND to GND" which is a little confusing to me when I only have the options of positive and negative.
So are you saying it is safe to connect 5v negative to the 24v negative?
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@threepwood, my 3.5 cents:
Connect the chassis ground of the power supplies to earth ground from your wall outlet. Do not daisychain these connections but have each go directly to the ground wire on the main AC power ground. Connect the negatives to a single point (don't daisy chain them), use that central point to connect to to the Duet ground. connect the positives to wherever they need to go on the duet (ie ext power in and power), connect the negative power lines to the central ground point.
Lastly, and this is a point of much discussion, connect the central negative (that is not daisy chained) to the chassis ground where it connects to the incoming AC ground.
99% of the above is related to preventing differences in the ground potential and therefore ground loops and it depends on how anal you are as to how far you want to carry this. Minimum is to connect power supplies chassis grounds to AC ground, connect the two negatives of the power supplies together and connect the positives of the two supplies to power in on the Duet and the external 5V in on the Duet. The main power and ground to the Duet should be substantial (16 ga or 18 ga).
Hopefully that makes sense ... and yes, the 5V negative and 24V negative are connected together. -
@jens55
Thanks for the help. I've mocked up this very crude diagram. The positions of cables don't correspond at all to where they really are, I just tried to keep things from looking too cluttered.The distro blocks are the "Wago" type, as can be seen in my first photo.
Does that makes sense?
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@threepwood, yes, that is how I would suggest to wire it
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@threepwood I don't think that's correct, you don't need to connect mains earth to your low voltage neutral block.
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@javajoeuk I've just about finished wiring everything up and now I'm not sure if I should switch it on...
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@javajoeuk Do you think it will cause any harm? Or do you think it is just unnecessary?
I'm leaning to the side of what @jens55 recommended, because I did previously have a ground loop issue with the USB being plugged in to the PC. The PC reported an overvoltage on USB and the ports stopped working until I restarted.
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The way i have done mine is mains to both the 5v and 24v transformers. 5v to my duet3 and 24v via an SSR to the duet . The mains earth does not get connected to anything other than the mains stuff not to your neutral block.
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@javajoeuk said in Confusion over Ground, Earth and negative connections:
@threepwood I don't think that's correct, you don't need to connect mains earth to your low voltage neutral block.
That's the topic of hot debate I eluded to in my earlier post. Some people feel it needs to be connected, other people feel that it should not be connected. Either way is fine and will not cause any issues.
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@jens55 I didnt want to frighten him about connecting mains earth the neutral in case of a ground fault on the mains side of things.
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@javajoeuk, fair enough but you could say that about anything connected to ground. It's just an additional safety.
Just an additional mention to the OP - if you are using an AC mains bed heater, don't forget to connect the bed to AC earth. Some people suggest to connect the frame to earth as well but I have never gone that far.
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Thanks everyone for your help. The printer is up and running and I have 5v running through the neopixel port.
@jens55 I have already connected the bed and frame to earth, but thanks for checking!
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@threepwood .... woooo hoooooo !
