Need to use a rectifier.... but where to put it?

  • #1
HelloCthulhu
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I built a high voltage ac power supply using a YouTube tutorial so I could use it in my parallel plate capacitor experiments. But since discovering that I actually need direct current to charge the plates correctly, the circuit needs to be rectified. I found a tutorial on building a full bridge rectifier out of high voltage diodes, but I was wondering if I could just use a lower voltage rectifier (say 500V) connected to the variac and still get dc at the output.

Intuitively, I'd place the fbr at the output (like in the image below) but I'm not sure what's safer/most efficient. I think I've researched most of the necessary safety precautions and always use high voltage rated safety gloves to operate the circuit as well as a high voltage resistor to discharge the capacitor. All equipment is disconnected when not in use. Any help is greatly appreciated!
rec bridge.png
 

Answers and Replies

  • #2
DaveE
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If you can't solve this yourself, then I suspect that you don't have the background in electronics that I feel is necessary to work on HV circuits safely.

There is a lot of information on the web about HV rectifiers if you research it.

I for one am not willing to help in this endeavor. Good luck, be careful.
 
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  • #3
HelloCthulhu
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If you can't solve this yourself, then I suspect that you don't have the background in electronics that I feel is necessary to work on HV circuits safely.

I apologize for my inexperience. I've designed circuits with lower voltage, but I don't have any experience rectifying voltage yet. I'm sure this is something simple, but I thought I'd ask for advice first. The warning is very appreciated!
 
  • #4
Baluncore
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That is a very dangerous circuit because it is connected directly to the mains Active and Neutral, without any isolation or fuse.

If the Active is accidentally swapped with the Neutral, the chassis will become live.

If the 3uF capacitor or the dimmer fails short, the current will no longer be limited.

The four diodes at the top right is the rectifier. That is the only place it can be, following the ignition coil = autotransformer.
Does it need a bypass capacitor across the output?
What voltage rating will it need? More than 30kV? What will that cost?

Please don't build and operate that circuit. It may kill you.
 
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  • #5
HelloCthulhu
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That is a very dangerous circuit because it is connected directly to the mains Active and Neutral, without any isolation or fuse.

Thank you for the quick response! I'm using this variac model with fuse protection. If it pops all current will drop immediately.

variac.jpg
 
  • #6
HelloCthulhu
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  • #8
berkeman
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I've learned a lot in a short amount of time, but thanks to both of your safety concerns I definitely think I should learn more about circuits and working with mains voltage before moving forward. I found one site to be especially useful, but please feel free to add any other resources. Thanks for all of your help.

https://hackaday.com/2016/05/11/looking-mains-voltage-in-the-eye-and-surviving-part-1/
Please try to find an experienced EE or similar near you so can use them as an in-person Mentor on projects like this. There really is no practical way for us to help you stay safe in working on this project, given your level of understanding and experience right now. I had such a Mentor when I learned to build AC Mains based circuits (built well enough that they could pass UL safety approvals if needed), and I suspect many of the folks here who are offering you safety advice on this project also had such an in-person Mentor.

This thread needs to be closed now. Thank you to everybody who has been trying to offer safety advice.
 
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