DIY Load Tester
 
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DIY Load Tester

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Sticks
(@sticks)
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I am currently re-purposing an old roll top writing desk as an electronic projects workbench. It will be a place for me to store my development boards and parts in inbuilt trays. Also it will have an inbuilt development desktop pc as well as an inbuilt variable voltage power supply going to multiple output power posts either side of the bench top.

The idea is I can work on a project and then pull down the roll top and power off the bench quickly (usually when my wonderful wife tells me for the third time that dinners ready) and walk away. Then when I come back to it (usually a fortnight later) I can quickly go straight back to it.

I am thinking of following the @dronebot-workshop video to build my own power supply using a MOT that I have here. It got me thinking about the other side of the equation... power out to go with the power in. Hence the post here.

I wonder if a video on building a load tester would be a nice accompaniment to the variable power supply video. It seems that most of the Aliexpress supplied units come with a host of bad reviews relating to poor performance or, even worse, total failure and meltdown. 

If a full build is too much then maybe just a video on the theory behind the design and how they work would prove popular. I did search the forum posts, but did not locate this subject being previously submitted... but apologise in advance if it has already been considered. 


   
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Ron
 Ron
(@zander)
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@sticks I asked about interest in that sort of device a while ago and got no interest. Since then I have purchased a few of them. Due to other priorities I have not had a chance to test them all but hopefully I will be able to very soon. I will find all mine and take some pics then you can maybe point out which style you are interested in.

First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
Sure you can learn to be a programmer, it will take the same amount of time for me to learn to be a Doctor.


   
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(@davee)
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Hi @sticks,

  As Ron @zander says, he raised the question a while ago. At the time we exchanged a few forum messages on the topic, which are presumably somewhere on this site.

In essence, there is no 'universal' load requirement ... you need to specify the electrical properties you want to measure (voltage, current, etc.), are these 'static' loads (like a resistor) or 'dynamic' loads whose current demands continually vary, etc. There may also be other factors, like connectors and protocols.

For example, until fairly recently, USB power was 5V with 'optional' dynamic current limits from below 500mA to about 2.4A ... maximum around 15 Watts. Since then, new connectors, cables and prototocols have been introduced to use higher votages and current, extending it up to 240W, whilst still allowing an older USB load, which can only cope with 5V to be plugged in. All this means a comprehensive 'USB' load has to be pretty smart, as well being able to dissipate a considerable amount of power.

And, of course, there are a vast number of other supply types that you may wish to test, including the outputs from power amplifiers.

So, yes in the right circumstances, a test load can be a useful piece of kit, but you need to specify what it needs to achieve.

Best wishes, Dave


   
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Ron
 Ron
(@zander)
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@davee I think somewhere in my travels I came across a device that did load testing for a wide variety of voltages and currents but it was multiple hundreds of dollars. The load testers I have are mostly for USB but I will have to look at them again to see if they can do other voltages.

EDIT 2 The pic shows what is available in price range of $350 to $2,500. 

EDIT Just found this

Screen Shot 2022 10 21 at 10.15.42

First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
Sure you can learn to be a programmer, it will take the same amount of time for me to learn to be a Doctor.


   
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(@davee)
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Hi Ron @zander,

  The DIY box is quite a neat unit, using only cheap-ish components ... a good example of what is possible with off the shelf boards.

It really depends upon what you want or need to measure.

e.g. If you want to characterise (small-ish) batteries, then you probably want to record current and voltage over a period of time ... a box like this one could provide the basis, but would need more software, etc. ... possibly a data feed to a PC, etc.

Best wishes, Dave


   
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Sticks
(@sticks)
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@zander I won't lie... that is a bit disappointing, Ron. Obviously I agree with you that it is a good idea but understand if there isn't a broader interest in the topic.

I can always follow the advice of other YouTubers... it's just that Bill always does such excellent videos giving great details and explanations of the theory. Unlike other providers who usually offer "cut and paste" style instructables, I always walk away from @dronebot-workshop videos with a much greater understanding of the subject. 

Also, as a newbie here, I do feel it is important to contribute to the community. If I can offer up a subject that gives Bill a new video topic then I will feel that I am "pulling my weight."


   
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Ron
 Ron
(@zander)
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@sticks When I made my suggestion, I was only thinking about USB testers. @davee has opened up this discussion to the tester being a fully configurable tester. I support that, it has a much greater use case profile. The one YT example I found I quickly discovered issues with and would not recommend trying to follow it verbatim. I agree Bill would do a much better job BUT since I was originally rejected, I do wonder how many other users would be interested. I know I have no immediate plans that require one but thought it was a useful test tool to have around. Of course, somebody would then bring up logic analyzers, signal tracers, oscilloscopes as being common test tools that are probably more likely to be needed than a variable load. Hopefully Bill will read this and give us his experienced opinion.

First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
Sure you can learn to be a programmer, it will take the same amount of time for me to learn to be a Doctor.


   
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Posted by: @davee

...

In essence, there is no 'universal' load requirement ... you need to specify the electrical properties you want to measure (voltage, current, etc.), are these 'static' loads (like a resistor) or 'dynamic' loads whose current demands continually vary, etc. There may also be other factors, like connectors and protocols.

...

And, of course, there are a vast number of other supply types that you may wish to test, including the outputs from power amplifiers.

I agree totally,  @davee. It is always going to be a horses for courses subject. I suppose that is exactly why I think it is a good idea for a video topic.

If we take a look at Bill's excellent video on the linear power supply, Bill built a box to a specific specification. During the build he mentioned various considerations like current capacities of different voltage regulators and limiting frequency noise for radio enthusiast work... amongst other 

It wasn't a one box meets all needs solution by any means, but gave me the information I needed to consider my own applications and make the appropriate design decisions. Hence why I think similar approach to a video on a load tester box would be the perfect accompaniment to the linear power supply video.

By suggesting anything as a topic, I hope I never get to a stage where I'm looking for Bill to give me my specific solution. Rather I hope that it is a subject that he may think has merit and will give him a new idea to work with. I can't imagine what it is like to always be having to come up with new ideas for content.

If I can help with the odd idea that I find interesting then I'm happy to contribute. 


   
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Sticks
(@sticks)
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Posted by: @zander

...

Of course, somebody would then bring up logic analyzers, signal tracers, oscilloscopes as being common test tools that are probably more likely to be needed than a variable load.

Hopefully Bill will read this and give us his experienced opinion.

Of course. Those tools are each very important in their own way. The main downside for me is I can go buy a tool any time... but that doesn't fulfil me in the same way as understanding how the tool works. Especially if I can build my own tool to use.

Truth be told I'm looking at a variable load style solution myself... for use in designing variable voltage/current power circuits for my other projects. I have a robot vacuum cleaner in mind that will work as the experimental prototype for a robot lawn mower. Both will have a power supply circuit that draws different voltages and current loads from the same battery pack.

As I said though, my specific needs aren't as important as absorbing Bill's experience on the subject. 


   
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(@davee)
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Hi Ron @zander and @sticks,

  Please note I have no problem with a test load with a specific aim ... e.g.  USB test load

... although bear in mind, USB can mean a range of different voltages, currents, protocols .. does the tester need to cope with all of them or will a subset be sufficient?

  I was just trying to point out:

  • There is no such thing as a 'universal' load test .. it is necessary to start with a specific type or range of power source that you wish to measure
  •  
  • In addition, it is necessary to specify the type of tests it must accomplish

Best wishes, Dave


   
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