In January of this year, inspired by some of peteroakes 's excellent tutorials I decided to begin to design and construct a DC load. I have been learning and improving my electronics ever since joining E-14 about two years ago. Those of you who are familiar with me know that I tend to be a little retro and basic in my approach to problems and projects. This DC Load unit which I have dubbed " La Carga " (named chosen by 4ringfan) will be no exception. Up until now I have always been satisfied to grab what I called a "LOAD BULB" every time I wanted to load a circuit.
While these have served my needs in simple experiments the progress of the last couple years has put me in a position where I want a little more precision and control of the load in my experiments.
As I mentioned I began in January to draw rough schematics and plans for the DC Load unit. Thanks to the inspiration offered by my friend D_Hersey I have put some effort into learning the basics of SPICE IV. For the first time in my life I am able to run simulations of many of my prototype circuits prior to bread boarding them. I also am planning so that the power supply and other circuitry is more appropriately sized to the job they are intended to do. When one is not very good at electronics there is a tendency to over build. This is why over the years many of my creations are "TANKS" when they should have been sports cars. As you will see I did not completely escape this tendency but I hopefully have made some improvements.
The plan is to use that same style enclosure that I used when I built my power supply in September of 2014.
This Case and Chasis was from a 40 year old piece of Dental Equipment called a Cavitron. Above you can see the before and after pictures of the power supply. If you have an interest in that build here is a link to the blog post: http://www.element14.com/community/people/jw0752/blog/2014/09/21/a-new-power-supply-for-john
Circuit Over View:
My plan is to build a DC Load that will cover the voltage range of 3 Volts to 35 Volts and be capable of 6 amps with a max wattage of 210 Watts. I want to have the unit sense the voltage and add or remove series current limiting resistors so that my control device, a salvaged IGBT, (Isolated Gate Bipolar Transistor) will never have to dissipate more than about 40 watts itself. I have decided to use digital LCD meters on this build so the unit will not be quite so retro, though no one will argue that I am completely out of the retro mode by any means. Something else that is new for me is that I have been inspired by waelect and I am going to blog about this build as I am doing it. Up until now I have wanted to have a finished functional unit before putting my neck out. This will give everyone better insights into some of the mistakes and wrong paths that I take while building. I do reserve the right to not talk about the really dumb mistakes.
In Episode II , a couple days from now, I will publish my schematics for the build and show pictures of some of the major components.
John
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