Is it better to buy a bench PSU, or build one?

  • #1
theycallmevirgo
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TL;DR Summary
Are there any advantages to a commercial PSU over anything I can build from online plans?
Building a PSU is one of the few "academic" projects I'm willing to consider. I don't see it taking me too long, and I can probably make something nice to look at. However, I may consider buying one at the $300-$500 pricepoint if I'm convinced that there are major advantages. Thoughts?
 

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  • #2
Baluncore
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Do you need a PSU ?
What would you use it for ?
 
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  • #3
theycallmevirgo
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Do you need a PSU ?
What would you use it for ?


Entry level experiments/repair and electroplating.
 
  • #4
berkeman
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Summary:: Are there any advantages to a commercial PSU over anything I can build from online plans?
Since this would be an AC Mains based project, one of the primary issues is safety (shock and fire). When you buy a commercial PSU, it comes with a UL mark or similar showing that it has passed the industry standard safety regulations and inspections by the safety agency. That can be important if your setup causes a fire or gets somebody shocked down the road.

Having said that, I built my first hobby PSU while I was working a summer job at Tektronix in their R&D Lab. I had great Mentors there who patiently explained the UL safety regulations and the reasoning behind them, and checked my work as I went (this was all on my own time outside of my regular summer job there). In the end I used that PSU for probably 20 years on all kinds of hobby projects and some consulting work, and it only got a little unreliable in the end because I'd used an inexpensive slide switch to control the +/-Vout section of the PSU (I think it switched between +/-15V and +/-12V, IIRC).

So if you have good in-person Mentoring by somebody who has actually taken AC Mains projects through safety approvals, then it may be a good learning exercise to build your own. You could also have the Mentor look over the "online plans" that you've found to help you pick the best one for your projected needs.

Another thing to consider is Radiated and Conducted EMI regulations (typically by the FCC in the US). When you buy a PSU, it has also gone through that testing to be sure that it will not cause interference with other devices nearby, and will not blow up if you key up a radio nearby (don't ask me why I know about that part). If you build a design that you find somewhere on the Internet, you will not have done that testing. So if there is some issue (like stability and RF parasitic oscillations in the SMPS section), you could get a knock at your door someday from the local radio tracking folks...

https://www.physicsforums.com/threads/this-is-why-em-interference-can-be-an-issue.993976/
 
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  • #5
DaveE
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No question here. Buy a used one (eBay, swap meets, ham clubs, etc.). Since you are considering building your own, then you should be able to repair it if there's something wrong. In my experience, there is seldom anything wrong with PSs from eBay.

Don't discount the amount of money and effort that goes into the mechanical construction of these things. Even if you really want to design your own, buy a used one for all of the stuff you don't want to design and then replace whatever you think is fun or educational. You'll also learn a lot in the process by seeing the engineering choices that a pro made when they were designing a PS that had to be sold to make money; you'll be way more likely to make a safe and EMC compliant PS; and you'll end up with a better instrument on your bench when you move on to other projects.
 
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  • #6
theycallmevirgo
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it may be a good learning exercise to build your own.

My point is simply, can I build anything that will exceed either specs or capabilities of anything I can buy for, say, $80? If so, what improvements can I make? If not, it's purely an academic exercise and I can't justify the time or money. I don't have any fundamental distaste for purely academic exercises, but right now is just not a good time.

Here's an example of a unit someone on another forum suggested. Can I do better?
 
  • #7
russ_watters
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However, I may consider buying one at the $300-$500 pricepoint if I'm convinced that there are major advantages. Thoughts?
[separate post]
My point is simply, can I build anything that will exceed either specs or capabilities of anything I can buy for, say, $80?
No.
 
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  • #8
DaveE
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My point is simply, can I build anything that will exceed either specs or capabilities of anything I can buy for, say, $80?
No.
 
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  • #9
alan123hk
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My point is simply, can I build anything that will exceed either specs or capabilities of anything I can buy for, say, $80? If so, what improvements can I make? If not, it's purely an academic exercise and I can't justify the time or money. I don't have any fundamental distaste for purely academic exercises, but right now is just not a good time.

Even if you have a superb technical and theoretical basis, and do not calculate the salary cost of your own work, every part you buy is a retail price, so there is little chance of achieving your desired goal.

On the other hand, It is the responsibility of the manufacturers to ensure that the parts supplied by the suppliers and its own final products meet the safety specifications, including sending the products to the laboratory for safety certification, and rigorous testing and supervision of the production process, etc. For the average person ,even if he has a certain understanding of the safety requirements and regulations, whether he can be able to achieve the same rigorous process and safety assurance when making his own will be questionable.

All in all, ensuring safety is paramount.
 
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  • #10
dlgoff
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For $85, I'm tempted to buy one. No way would I consider trying to build a supply with the features the KD3005 has; 0.01 volt resolution, thermal protection, voltage and current overload and short-circuit protection plus you get test leads and a manual.

what improvements can I make?
What improvements do you think it needs? It's perfect the way it is.
 
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