Can You Ground a 3D-Printed Plastic Chassis for Electronic Projects Safely?

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Discussion Overview

The discussion centers around the safety considerations of grounding a 3D-printed plastic chassis for electronic projects, particularly when using AC mains power. Participants explore various aspects of grounding, insulation ratings of transformers, and the materials suitable for constructing a safe chassis.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about the proper grounding methods for a 3D-printed plastic chassis when using a transformer with multiple outputs.
  • Another participant emphasizes the importance of the transformer’s safety rating, questioning whether it is single or double insulated, and suggests using a metal chassis connected to Earth Ground if it is single insulated.
  • A participant mentions their lack of experience with AC mains projects, having previously only worked with low voltage DC systems.
  • Concerns are raised about the availability of safety ratings and datasheets for transformers sourced from online marketplaces.
  • Suggestions are made to keep high voltage wires short and organized within the chassis to minimize risks, including the use of heat shrink sleeving and cable ties.
  • One participant shares their experience of learning about AC mains safety through mentorship and encourages seeking local hobby groups for support.
  • There is a mention of the challenge of avoiding mains hum in the circuit design.

Areas of Agreement / Disagreement

Participants express varying levels of experience and knowledge regarding AC mains projects, with some advocating for safety measures while others share personal anecdotes. No consensus is reached on the best approach to grounding the chassis or the necessity of using a metal box.

Contextual Notes

Participants note the importance of adhering to safety standards, such as UL Safety rules, but there is uncertainty regarding the specific requirements for grounding and chassis materials based on transformer ratings.

Who May Find This Useful

This discussion may be useful for hobbyists and students interested in electronics, particularly those exploring projects involving AC mains power and safety considerations in circuit design.

William123
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Hello

The Chinese were kind enough to send me a "music mixer" (XH-M164) and apparently these sell for about 8-11 dollars so I thought I might as well build something cool with it. I found an amplifier aliexpress (http://bit.ly/2nTD8VX) and the recommended transformer for that is a 32v 200VA toroidal transformer. Luckily there are transformers out there that are specifically made for what I'm going to make. They have 3 outputs, 6V, 12V and 32V so the music mixer will be powered by the 12V output and the amplifier will be powered by the 32V output.

Anyway, this is the first time I'm building something that is powered from the wall and I want to stay safe. How does one go about grounding a 3D-printed plastic chassi? Should I just make every effort to isolate everything and leave the grounding wire alone? The transformer has 3 wires for for every output and both the amplifier and music mixer has 3 inputs, but I don't see how that third wire is grounded. The 6V output is an exception, that one is just two yellow wires.

Thanks
 
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William123 said:
Hello

The Chinese were kind enough to send me a "music mixer" (XH-M164) and apparently these sell for about 8-11 dollars so I thought I might as well build something cool with it. I found an amplifier aliexpress (http://bit.ly/2nTD8VX) and the recommended transformer for that is a 32v 200VA toroidal transformer. Luckily there are transformers out there that are specifically made for what I'm going to make. They have 3 outputs, 6V, 12V and 32V so the music mixer will be powered by the 12V output and the amplifier will be powered by the 32V output.

Anyway, this is the first time I'm building something that is powered from the wall and I want to stay safe. How does one go about grounding a 3D-printed plastic chassi? Should I just make every effort to isolate everything and leave the grounding wire alone? The transformer has 3 wires for for every output and both the amplifier and music mixer has 3 inputs, but I don't see how that third wire is grounded. The 6V output is an exception, that one is just two yellow wires.

Thanks
If you are wanting to use AC Mains input voltage for this project, you need to do a number of things to make this safe. What is the safety rating of this transformer? Is it rated as "single insulation" or "double insulation"? Can you post a link to the datasheet?

If the transformer is single insulated, or if you cannot be sure, you need to use a metal box for the chassis, and connect that metal box to Earth Ground from your 3-prong power plug (assuming you are in the US). The :Line input needs to go through a fuse and then to the power switch, and then to your transformer.

Is this the first time you've built a project with AC Mains input power?
 
berkeman said:
The :Line input needs to go through a fuse and then to the power switch, and then to your transformer.
Sure
berkeman said:
Is this the first time you've built a project with AC Mains input power?
Yes it is. I've only built low voltage DC driven things before. I'm more on the arduino side of things.
berkeman said:
If you are wanting to use AC Mains input voltage for this project, you need to do a number of things to make this safe. What is the safety rating of this transformer? Is it rated as "single insulation" or "double insulation"? Can you post a link to the datasheet?

If the transformer is single insulated, or if you cannot be sure, you need to use a metal box for the chassis, and connect that metal box to Earth Ground from your 3-prong power plug (assuming you are in the US)
I didn't know that the transformer rating determines the chassi material but it makes sense now that I think about it. The transformers I have been looking at are from china (aliexpress again) and I don't really know if you'll find either datasheets or safety ratings on these things. Here are two examples: http://bit.ly/2nPxjri http://bit.ly/2oRwqgY

I do have a metal chassi from a power supply that crapped out on me. I could 3D-print just the front so that I can turn the knobs and all that and ground the chassi.
 
William123 said:
Sure

Yes it is. I've only built low voltage DC driven things before. I'm more on the arduino side of things.

I didn't know that the transformer rating determines the chassi material but it makes sense now that I think about it. The transformers I have been looking at are from china (aliexpress again) and I don't really know if you'll find either datasheets or safety ratings on these things. Here are two examples: http://bit.ly/2nPxjri http://bit.ly/2oRwqgY

I do have a metal chassi from a power supply that crapped out on me. I could 3D-print just the front so that I can turn the knobs and all that and ground the chassi.
It's really best if you have a Mentor who can work with you in-person on a project like this, so you can learn how to build such projects safely. Basically you need to comply with all of the UL Safety rules that you would if you were designing a real product and submitting it to UL for approval.

Here is a good tutorial website (notice the disclaimer about AC Mains Safety):

http://www.markhennessy.co.uk/articles/power_supplies.htm

I was lucky enough to build my first AC Mains powered project (a lab power supply) in my spare time while I was working a summer job as an intern at Tektronics in Oregon. Several of the very experienced engineers and technicians in our group gave me hints and watched as my project progressed, and were able to help me build it as if I were going to submit it to UL in the end. That power supply lasted a very long time. :smile:

For liability reasons, we are limited in how much help we can give you on a project like this. Please look around your area for a hobby group or similar that you can link up with.
 
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berkeman said:
It's really best if you have a Mentor who can work with you in-person on a project like this, so you can learn how to build such projects safely. Basically you need to comply with all of the UL Safety rules that you would if you were designing a real product and submitting it to UL for approval.

Here is a good tutorial website (notice the disclaimer about AC Mains Safety):

http://www.markhennessy.co.uk/articles/power_supplies.htm

I was lucky enough to build my first AC Mains powered project (a lab power supply) in my spare time while I was working a summer job as an intern at Tektronics in Oregon. Several of the very experienced engineers and technicians in our group gave me hints and watched as my project progressed, and were able to help me build it as if I were going to submit it to UL in the end. That power supply lasted a very long time. :smile:

For liability reasons, we are limited in how much help we can give you on a project like this. Please look around your area for a hobby group or similar that you can link up with.

Thanks for the article, I'll read it tomorrow when I have more time.

An internship like that must be absolutely golden. I'm moving to Gothenburg this summer to start studying computer science (which is not without some electrical engineering but maybe not so much about AC mains circuits) and it would be awesome to do an internship like that.
 
Keep all the high voltage wires short and in the same area/corner of the case. Cable tie wires together so that should one become disconnected (eg from the switch) it cannot reach any other components (such as mounting screws for the switch). Use lots of heat shrink sleeving. If possible put all the high voltage stuff in a "case within a case" so you can work on the rest of the circuit with less risk to yourself.

One of the hardest things to avoid is introducing mains hum. Avoiding that is a whole other story.
 
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CWatters said:
Keep all the high voltage wires short and in the same area/corner of the case. Cable tie wires together so that should one become disconnected (eg from the switch) it cannot reach any other components (such as mounting screws for the switch). Use lots of heat shrink sleeving. If possible put all the high voltage stuff in a "case within a case" so you can work on the rest of the circuit with less risk to yourself.

One of the hardest things to avoid is introducing mains hum. Avoiding that is a whole other story.

Really good suggestions. Thanks!
 
No problem. Some years ado I was involved in designing set top boxes and similar IT equipment that had to meet BS EN 60950.
 

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