Scullcom Hobby Electronics #45 - Electronic DC Load Part 1

[@PeachState112]

How could anyone dislike this? It's the best diy electronic DC load on KZbin. I always look forward to your videos. Keep up the good work.

[@scullcomhobbyelectronics1702]

Thank you.

[@mancelprince7426]

Jealousy made them do it.

[@Todestelzer]

It’s very detailed. Probably too much for some folks.

[@TheDrewker]

@@Todestelzer It's bots. They like/dislike to appear real. If all they did was click like, YT's algorithms would know it was a bot

[@danielb8197]

I have made this unit, with all 9 episodes combined and LOVE this thing. Thank you VERY much for all your hard work. ( ps I'm in New Zealand). Cheers

[@borayurt66]

Am I the only one who watched this like an action movie? Very good project, very informative video. Thank you sir!

[@scullcomhobbyelectronics1702]

Thanks Bora :)

[@ivanreynoso3849]

Damn. i Miss this guy, i wonder what hes been up to.

[@anurasenarathna1703]

The best DIY Electronic Load video with lots of bells and whistles. Thank you very much.

[@BryanByTheSea]

Thank you. You put your heart and soul into these projects and videos. Ticks me off that people have the nerve to give a thumbs down.

[@scullcomhobbyelectronics1702]

Thanks Bryan.

[@MrMickjbriggs]

What a superb. tutorial, a rare treat to find someone on KZbin that actually knows their subject.

[@scullcomhobbyelectronics1702]

Thanks Mick.

[@sexysmeksi]

I'm subscribed to a lot of electronic hobby channels and I must say that you are the only one whose videos are informative for a guy who doesnt have big knowledge in electronics. Great Great videos!

[@scullcomhobbyelectronics1702]

Hi Ivan, Thanks for your kind comments. Glad you find my videos helpful. Regards, Louis

[@Matlus]

I have been watching a lot of your videos lately, and became an instant fan! It's very clear to me that you thoroughly enjoy this stuff. The care with which you plan out these videos, the time, thought and effort you put in to the projects, including the video production is truly commendable. There are dime a dozen channels on KZbin, but none that I've seen do anything close to what you're doing here. Tip of the hat to you sir! Please do keep this up. Can't wait for part 2.

[@scullcomhobbyelectronics1702]

Thanks for you kind comments. I am working on Part 2 at the moment which will have some improvements with the software.

[@ufohunter3688]

I want to build one for my lab with the following chnages; I will connect the heat pad of the MOSFET directly onto the heat sink and place the insulator on the 0.01 Ohm resistor (if I had one), for better cooling of the FET? I have a few 0.001 Ohm 1W surface mounts on hand, which i intend to use, instead of the 0.01 Ohm you are using. I don't want to connect it to the heat sink, as it will add complexity in calculating the junction temperature of the FET, from the LM75 readings. Thanks for this practical project. Sick of all the LED blinking projects everyone else makes. You have excellent lab quality designs that are very reasonable to build, and above all, it's open source. Merry Christmas to you and all the people of Earth.

[@scullcomhobbyelectronics1702]

Thanks for your comments. You could do what you suggest but be careful as the body of the Mosfet is connected to the drain and so the metal of the heatsink will be at the full load potential which could be dangerous as we progress to higher load voltages. My recommendation would be to still isolate the Mosfet and use good quality heatsink compound and instead bolt the LM35 (temp sensor) directly on the heatsink as its case is already at ground potential. The body of the power resistor I used is already isolated so that does not need isolation. Good luck with your project. Regards, Louis

[@ufohunter3688]

Good point. Will do. Any discrepancies in the actual junction temperature compared to what L35 reports, should be a constant (or a linear slope) that could be calibrated for, and stored in the EEPROM. Thanks again.

[@RobB_VK6ES]

Going too low with the sense resistor will make it hard to get reliable current readings at low currents. The S/N ratio will be terrible.

[@rolandleusden]

Adding a battery capacity test function with programmable cut-off voltage would make it even more universal.

[@scullcomhobbyelectronics1702]

One of the add-on options for this project will be a battery capacity test function particularly for LiPo batteries.

[@lordmarshall1139]

+Scullcom Hobby Electronics hay Hobby could build a 30000 watt e m p device will copy it after ward I am going wait for your response cool man keep up the good Work

[@PapasDino]

Nice project Louis. I'll share this with my ham radio club's Builders Group as several folks have expressed an interest in building their own electronic loads for their workbenches when we start up again in the spring.

[@scullcomhobbyelectronics1702]

Thanks Dino. This project still requires some refinement which I will cover in the other parts of this project as we progress.

[@ufohunter3688]

Please consider the option of using an ESP8266-based chips, so you can have WiFi and OTA (over-the-air) firmware update facilities like future IOT connections, or firmware extensibility, by software updates alone. WiFi is everywhere now. The code needs minimum changing since it is Arduino-based.

[@RobB_VK6ES]

Looking very versatile Louis. I like the design goals. I did not see any precision voltage reference in the schematic. Adding one for the ADC and DAC stages might be worth investigating. Also a second PCB dedicated to the heatsink mounted components will help with current handling as well as making it easier to package the unit into different cases and use of different heatsinks. As a final wish, perhaps the ability to add more mosfet stages to increase the power handling. Low tempco sense resistors are expensive so your 35W unit looks to be a useful hack to avoid drift. Looking forward to the progress on this project.

[@scullcomhobbyelectronics1702]

Thanks for your comments, only just seen it since for some reason google put it in the spam box! I will be giving a more detailed look at the ADCs in part 2 - the one's I choose have a built-in voltage reference. As far as the DAC is concerned we could add a voltage reference if required. It looks like I may take the power mosfet, Temp Sense (LM35) and Power Sense Resistor off the PCB and hard wire with heavy gauge wire. I am looking at adding additional power Mosfet's in parallel to increase power handling.

[@TheFunkman]

Almost done building mine. Outstanding PCB Louis! Just waiting on a few parts. Got all you sent in the mail today. I'll send you some pics when it's done. Thanks for a great project. This will replace my DC load I built from a guy down under. No support from him at all.

[@scullcomhobbyelectronics1702]

Thanks Rudy, Nice to hear. If you need any further help let me know. I am just uploading a update video on this project. Regards, Louis

[@grahamhall2662]

Brilliant. I know time has moved on but really, Wow I understood this , excellent teaching and demonstration. Thank you.

[@mfierst7326]

This is an interesting project. Thanks a lot for your video's. I like your video's because you are showing the thinking behind the designing process of the project and not just the project itself. As far as this this particular project is concerned, it would be even more interesting if it could be turned int a version of which the CR function could be used as a load for low frequency AC signals, for instance as a test load for audio amplifiers, but that would, amongst other things, require measurements of negative voltages and currents as well.

[@scullcomhobbyelectronics1702]

Thanks for your comments. Not sure if the CR function of this would be suitable for AC operation, but worth looking in to. Regards, Louis

[@gopalinc]

This is how a product is designed and developed. Well explained with minute details.

[@budude2]

Absolutely perfect timing - - Santa did not get the load generator I had on my list so this will make a perfect project!

[@scullcomhobbyelectronics1702]

Thanks Brain. Have fun with this project as we progress.

[@First2ner]

Two things to think about: * Since your current sense resistor is higher value and on same heatsink as power mosfet, fet will heat up resistor and its resistance will go up, you can see that on this video, where you had CR, current went down. maybe think about lower value resistor with x10 or something op amp. OR add function in software to compensate this live (but you may need to fix oscillations that you could get from adding this in software) * Also think about adding energy measurement, when you would like to know capacity of battery

[@scullcomhobbyelectronics1702]

Thanks for your comments and suggestion. I plan to add a battery capacity option as we progress with this project. Also we could look at a lower value sense resistor. Regards, Louis

[@Barbouri]

Another great video! I have been wanting to build a DC load for some time now, and your video has given me the inspiration to finally build one. Thanks, Greg C.

[@scullcomhobbyelectronics1702]

Thanks Greg. The prototype PCB I made was using KiCad. But I have also designed a double sided PCB using Eagle which I was thinking of sending to OSH Park for production. But as the project is still in progress I thought I would wait a while as I may make some changes. Also it gives me more time to get use to using Eagle CAD software - I was inspired to use it following your excellent work on the PCB's you designed for my Milliohm and Millivolt Meter projects. Regards, Louis

[@bloguetronica]

This is a very good project! The 2 channel, 18 bit ADC sure offers a very good resolution for voltage and current measurement (perhaps overkill), and the 12 bit DAC is fine enough to provide control over the pass MOSFET. Three devices on the same I2C bus, and that's it! Love the simplicity.

[@scullcomhobbyelectronics1702]

Thanks for your comments. The dual ADC is a 16 bit version. Regards, Louis

[@qzorn4440]

o my with the neat Arduino and the serial port you can even write test programs to control the load and bench power supply settings to test different customer devices automatically 🥳👌🧞‍♀ another super project 🌷🦤☕🧁 thanks a lot ♨ excellent description

[@firozextc]

Dear Sir, Your accomplishing this while maintaining a home and raising three children is a marvelous achievement.I need to design similar constant current/ power Electronic Load for 500W.

[@rodneyjaygarrett]

WOW, Nice Christmas video. Excellent video, concise and great explanations. I do look forward to your videos. I plan on building this. I have been looking for a DC load project that had this same criteria that a novice like I could follow. Thank you for taking the time to share your knowledge!

[@scullcomhobbyelectronics1702]

Thanks Rodney for your kind comments. Have fun with this project. Regards, Louis

[@vll1976]

You should swap linear region and saturation region on your board at the beginning of video. Saturation region is used for switching, when drain to source voltage is at minimum, so power dissipation at the transistor is low. All linear power supplies and electronic loads use linear region of the transistor, so DS has some voltage drop, and as a result of it we shall provide heat dissipation.

[@scullcomhobbyelectronics1702]

Hi, In my diagram I show the "Linear Region" as the region of operation where the drain current (Id) rises at a linear rate in relation to the voltage applied across the drain and source (Vds). This region is also referred to as the "Ohmic Region" as the Mosfet behaves like a voltage controlled resistor. This is how you will see it explained in electronic text books. However, this reference to "Linear Region" here is different from "Linear Region" from the overall circuit perspective point of view. In the "Saturation Region" the Mosfet is acting like a current source. This is also often also referred to as the "Linear Region", "Linear Operation" or "Linear Mode" in electronics when the device is between states where the Mosfet is neither fully on or fully off. It is this middle so called "Linear Region" where the Mosfet will dissipate significant power. Unfortunately the term "Linear Region" is the most inconsistently used term when it comes to its use when referring to MOSFET's. It can mean exactly the opposite depending on your point of view. In short the diagram on my board is technically correct. Regards, Louis

[@stanilastefan1687]

Love your videos. Your projects not only are very useful but are also very good explained. I want you to know that your work is highly appreciated. Thank you for your effort.

[@scullcomhobbyelectronics1702]

Thanks for your kind comment.

[@Wilson84KS]

Amazing, explained just perfectly, can't await to see all other parts.

[@chrisalpha2354]

happy i discovered your channel.one of the best if not the best dc load i've seen.well explained and implemented.

[@johnh1353]

Love the backdrop of keithley bench meters ... fine taste sir very fine taste

[@peterfielden-weston7560]

Nice to see you back again. I'm very interested in this project and will most likely build one myself. Merry Christmas.

[@scullcomhobbyelectronics1702]

Thanks Peter. Merry Christmas and all the best for 2017.

[@richardgrier4721]

I have designed a somewhat similar project. It also used an Arduino Nano. I like your hardware design better than my somewhat simpler version (I used the Arduino A/D inputs instead of separate A/D's, and I did no temperature monitoring). One thing that I did that on my project was to use a PC application that communicated with the Arduino over the USB Virtual Serial port, both for parameter setting and display. This allowed me to add real-time charting and the ability to log data to a CSV file for archival/data logging purposes. Automated testing is practical, and something like MPP is easy to calculate. Another implication is that the Arduino code only needed to deal with raw data associated with setting current and associated control functions and the PC software could do other calculations needed. I appreciate the flexibility that a PC application provides -- I can add software and UI features without having to go through the, somewhat painful (at times), Arduino code/debug/test cycle. All of the PC code was done using the free Microsoft Visual Studio Express edition, so there was no extra cost for that part of the project. If you have any interest in collaborating, by having me write a PC display application, I'd be happy to hear from you (www.hardandsoftware.net). The initial application would be display and data logging only, but control code could be added fairly simply. I'd start with display only, because the Arduino code changes would be trivial.

[@scullcomhobbyelectronics1702]

Hi Richard, Thanks for your comments. I had a look at your website, interesting. At the moment I am concentrating on getting the project to a good operating level with some additional features. There is already some means of logging using the Arduino Serial Monitor which if you look at my code I used that in some of the initial testing of this project. I have been considering adding some form data logging but using a SD Card or IC memory, but initially I want to add some functionality for battery capacity testing. Thanks for the offer and if I decide to go that route I will let you know. Regards, Louis

[@richardgrier4721]

Yes, it is relatively easy to parse the serial data stream from the Arduino and to display various results in a PC application. I recommend the free Microsoft Visual Studio Express edition for this, because it has powerful, built-in, controls for charting and for adding control functions as the project develops. Code to automatically detect which port is being used for the load is a useful addition; this would allow the program to be used with no user configuration, in its simplest form.

[@ZEROSTATIC72]

You may want to watch the dissipation on the MOSFET the one you've chosen looks to have a maximum of 70W. Thanks for the great videos.

[@scullcomhobbyelectronics1702]

Thanks for your comment. Yes this particular Mosfet has a maximum power rating of 70 watt. This is something I want to discuss in part 2 as we could either parallel several Mosfets to increase the power or use a different one with high power ratings.

[@sufzoli]

Hi, I like this project, I'm considering to use it as a base design for my own. On the other side, I'd like to add some comments on the MOSFET selection. The 70W maximum dissipation (when you need 150W) is not the only problem with this MOSFET. The Trench MOSFETs not really designed to operate in linear region. It suffer the same thermal instability in linear mode as the BJTs. In addition the MOSFET in question hasn't got FSOA characterization, what is essential for such stressful operation. May I suggest to read this paper about the linear mode? www.digikey.com.au/Web%20Export/Supplier%20Content/microsemi_278/pdf/microsemi-power-an-make-linear-mode-work.pdf You should consider to either use MOSFETs designed for linear mode from IXYS or Microsemi: www.microsemi.com/product-directory/mosfet/732-linear ixapps.ixys.com/family.aspx?i=5 Or check the FSOA characterization of the IRF MOSFETs: www.irf.com/product-info/hi-rel/alerts/fv5-p-09-01-a.pdf Zoltan

[@cncdavenz]

Looks like its going to be an interesting 2017 on the Scullcom Hobby electronics channel. Thanks

[@scullcomhobbyelectronics1702]

Happy New Year.

[@drulli1]

Thank You for this projecct. I will build it when it will be in a mature state. On my whishlist is an "interface" which allows to read the main KPIs (ampare, voltage, time) to an external device (i.e. PC with a program like Matlab or similar). With that information a battery discharge curve could be displayed and it would be easy to test and compare differnet batteries and check if they provide the offered capacity.

[@scullcomhobbyelectronics1702]

Thanks for your comments. I will be adding additional features which will include Battery Capacity testing (discharging) in mAh.

[@jlegen]

Thank you for this great video! Just in case some arduino gpios need to be saved for other purposes: using only one analogue input together with some resistors on the buttons would laos do the job, and probably would also ease the wiring. I'd also use separate wires to measure the output voltage to avoid the voltage drops...

[@scullcomhobbyelectronics1702]

Thanks for your comments.

[@symik3]

I have started almost the exactly project about a half year ago, but i gave up with programming, i have the hardware laying in a box, soldered together as modules from China, I hope i can finish it, i will review my work based on your video, and hopefully finish it.

[@scullcomhobbyelectronics1702]

Thanks. Hope you succeed.

[@EnriqueVetere]

Nice project. You could implement some acceleration detection in the rotary encoder so you don't need the cursos. The amount increased/decreased is defined by the speed of rotation.

[@scullcomhobbyelectronics1702]

Thanks, I will be looking at further options as this project progresses.

[@elektrotechnik2011]

Brilliant and simple circuit. Thank you for sharing!

[@Roy_Tellason]

A couple of things come to mind. I'd have gone for a MOSFET in the bigger TO-247 case rather than in TO-220. Also, you might want to put a bend in the leads of the devices that are mounted to the heatsink, which will flex them slightly as temperatures change. Leaving them straight will eventually pull them out of the device packages. I know of one manufacturer that got into trouble with this. :-) Also, I see that you started out with 3 wires on that fan, presumably the 3rd wire being what some computer motherboards use to show me the speed that the fan is running at. This would be useful to monitor that the fan is indeed running, and you could have the software do a shutdown if that signal were absent. In the case of either the fan or the MOSFET, you could allow for both footprints on the board, so one could use whichever device was handy.

[@enginstud8852]

Do you know what he put a buffer before the opamp and after the DAC ? OPAMPS have high input impedance so is a buffer really needed ?

[@makerKID5]

You're back with another fantastic video! Very good content.

[@scullcomhobbyelectronics1702]

Thanks.

[@fritzt0815]

Nice project. A very good starting point for me. I need a DC load to test my own PCB design. I have some rotary encoders, an Arduino Pro Mini (without USB), some 2x16, 2x20 and one 2x24 LCD. the only thing missing is a usable FET - maybe I could salvage an appropriate one out of the many PC power supplies lying around here. I'll give that a try.

[@scullcomhobbyelectronics1702]

Thanks. I am working on Part 2 and I will cover additional info on choosing a Mosfet for this project. I have now found a better Mosfet to use. Hope to upload Part 2 in the next few days.

[@SatyajitRoy2048]

Nice initiative for a product that most of the peoples are in need of. Please do an extensive testing video where you could show the dynamic performance of this load on CP and CR modes when voltage changes rapidly. Also low voltage performance testing is needed. Say for example, someone wants to test a battery discharge performance of a 1.5V AAA battery with very minimal load of around 10mA or less. So, the load should work at its best till 0.8V which should be the cutoff voltage of the battery of this kind. Hence its essential to have a performing electronic load at that point. The software could have a feature to show consumed watt hour / ampere hour when battery discharge test is done. It seems, the ADC you have used doesn't have enough throttle for decent performance on CR and CP modes when load voltage changes fast. You need to measure the voltage across the sensing spot of the ADC and then need to calibrate the reading. Otherwise you will have very bad error when jumping from 10V to 20V with a moderate load. YES!!! PCB design doesn't look to be proper for a design with 5 Amp capabilities. Traces are very narrow. You need to fill those narrow traces intended to carry higher currents with solder bumps to have better performance. AND!!! I dont see proper grounding plan for intricate measurements.

[@scullcomhobbyelectronics1702]

Thanks for your extensive comments. I will be adding battery capacity testing as the project progresses. The PCB will also change and I may take the power components off the PCB and hard wire with heavy gauge wire. The final PCB version for this project is likely to be a double sided PCB with grounding. Also more testing and changes to the software. Regards, Louis

[@pirickyp]

I used op-amp ADA4522-4 instead AD8630 but I have to connect the op-amp V+ rail to 12V because voltage follower U7A cannot reach +5V on pin1 and between 4V to 5V behave strange. Many thanks for your project. It's well explained. I manage it, at version 1.

[@MaciekDrozd]

It is the best tutorial about DC load.

[@michaelnobibux2886]

Another outstanding project! Thank you so much !! Greetings from south America!!

[@agaelema]

Another very interesting project Louis. I think would be a good idea to use a differential measurement over the sensing resistor, this change will decrease the impact of the trace resistance, making the measurement more accurate.

[@scullcomhobbyelectronics1702]

Thanks for you comment and suggestion for this project. Regards, Louis

[@adilmalik7066]

excellent project! your projects are complete and amazing

[@scullcomhobbyelectronics1702]

Thanks.

[@voltlog]

nice project! I was wondering when you we're going to publish something on this subject :-)

[@scullcomhobbyelectronics1702]

Thanks. I thought this would be a nice project to tackle.

[@richardkelly4254]

Great Video, thank you for your efforts and importantly for sharing the design. I feel a construction project coming on... looking forward to part 2 Ric

[@scullcomhobbyelectronics1702]

Thanks Richard, working on Part 2 now with an update to the software.

[@tonybell1597]

Excellent project, thanks, love these tutorials, very clear and concise.... Would love to be able add some functionality for this to test batteries, and perhaps extract the data from the arduino to display graphs etc...... Loads of scope I reckon, looking forward to,part two! Time to dust off my pcb chemicals and and start making somethings!....

[@scullcomhobbyelectronics1702]

Thanks. I will be looking add additional features and updates in the other parts to this project.

[@NaudioElectronics]

Thanks for sharing with us this nice project. I have few ideas to improve it: 1. using 3 pin fan to control the speed will fix the nois from fan in most cases :) 2. Improve the LCD text arrangement. Right now one row is used for indicating on and off state of the current source. Imho better idea is to add external LED to indicate that. 3. Increasing the maximum voltage support :) Niki

[@scullcomhobbyelectronics1702]

Thanks Niki for your comments. The speed of the fan can be controlled with PWM. I may make some changes to the LCD text as we progress with this project. I also plan to increase the load voltage it can support. Regards, Louis

[@NaudioElectronics]

Thanks for your answer :) Yes, PWM control is better alternative. What you think about changing to 18bit for 0.1mA reading? :) Also a good example of good looking graphical display too lygte-info.dk/pic/USB%20meter/yzxStudio%20ZY1265/DSC_3919.jpg

[@scullcomhobbyelectronics1702]

Thanks for the comment. Your link did not work but had a look at the parent page with the images on. Link that works is: lygte-info.dk/review/usbMeter%20YZXStudio%20ZY1265%20UK.html

[@NaudioElectronics]

Yes. I mean similar parameter arrangement. What you think about 0.1mA resolution of the current measurement? :)

[@republicoftutorials6068]

Best ever electronic tutorial

[@marcelvanooststroom1733]

Another nice project to look forward to. This is a useful device. A very educating video. Thank you.

[@scullcomhobbyelectronics1702]

Thanks.

[@dalwindersingh9455]

wonderful explanation ,always waiting for new upload

[@scullcomhobbyelectronics1702]

Thanks.

[@dismayer666]

Voltage read will always be off. Changing opamp pot will not be accurate, because voltage drop on the probes will differ depending on current. What I recommend is using 4-wire measurement.

[@surgingcircuits6955]

Very glad to see this project. Think I will attempt to build your design project as well. Very good. Carry On!

[@scullcomhobbyelectronics1702]

Thanks, enjoy.

[@billfield8300]

Great project and as always, an excellent explanation. I look forward to the second part. Merry Christmas.

[@scullcomhobbyelectronics1702]

Thanks Bill. Merry Christmas.

[@isidoromaich7226]

This is great! an unexpected christmas gift, thank you!

[@scullcomhobbyelectronics1702]

Thanks. Merry Christmas.

[@johnnymotorboat8824]

Really excellent description and teaching methods.

[@scullcomhobbyelectronics1702]

Thanks David.

[@meltronix2194]

I have been following this tutorial from the beginning, this is a very interesting project and i really love your step by step approach of dealing with each problems, i am interested in the project and will like to purchase if it exist as a kit. thanks

[@scullcomhobbyelectronics1702]

Hi, Thanks for your comment. Sorry I do not supply kits as I simply do this as a hobby in my spare time. I can however help with the PCB. If you leave a comment on my website at www.scullcom.uk I will be able to contact you by email. Regards, Louis

[@medvidekkrupicka1404]

Maybe one should look into the mosfet's datasheet at its DC safe operating area and either parallel a couple of standard mosfets or buy a proper "linear" mosfet to preven the hot-spotting in the mosfet die and subsequent thermal runaway. Nevertheless, a nice project!

[@scullcomhobbyelectronics1702]

Thanks for your comment. I will be discussing the Mosfet type again in Part 2 as I have now made a change and replaced it with a different one with higher capacity as far as the DC safe operating area.

[@oldblokeh]

Yes, I was curious about the choice of a logic level switching mosfet, as the examples I have all seem to have a very small ohmic region.

[@MarkGarth]

Another excellent project and very well explained, as usual. Thanks and have a Merry Christmas and a Happy New Year.

[@scullcomhobbyelectronics1702]

Thanks Mark. Best wishes for 2017.

[@indikadeepal]

Very nice project.Thank you so much. Why not use the current feedback from U7D as the feedback of U7B? So instead of using the precision voltage divider to reduce the control voltage, you can feed the 0-5V from DAC to U7B directly.

[@nickpelov]

That's a nice one. However I'm not sure the trim procedure was correct. You said it's set to 1A, but did you really measure that with DMM before trimming? Also you said you pass 10V, but did you really measure the voltage near the pcb? Maybe it was measuring more accurate than you think, but there is burden voltage in the wires and connections. The wires didn't seam too thick. Another thing is that rail to rail opamps do not actually reach rails. That includes ground rail. That's probably the reason of not having zero when the load is off. I would suggest not calibrate at 0 V for the offset, but calibrate at 0.1V (measured with trusted DMM) - you get the offset from zero. And when you calibrate gain (at 10V) you can use very little current - like 10-20 mA to avoid voltage drops on the tracks and cables.

[@scullcomhobbyelectronics1702]

Thanks Nickolay for your comments. The cable I used from the power source need to be of higher gauge as at high currents there was a voltage drop due to the resistance of the leads - hence the difference as you say in voltage reading. I did use a DMM to check the accuracy of the current reading. I am just finalising Part 2 of this project and hope to upload it in the next few days.

[@brunofonseca9686]

This is awesome! I'm definitely translating this one and linking your video to my website.

[@scullcomhobbyelectronics1702]

Thanks Bruno.

[@superblondmale]

Thanks for this entertaining and interesting video. I am looking forward for part 2.

[@scullcomhobbyelectronics1702]

Working on Part 2 now.

[@MartijnvanBuul]

Out of curiousity: You use the same I2C bus for the ADCs, the DAC and the LCD. Is this wise? Those LCD backpacks use the LCD in 4-bit mode, which is rather chatty. Furthermore, after glancing at the the arduino source, you seem to be doing the LCD printing in the control loop. Together, this makes me a bit concerned about the update frequency of that control loop. For a accurate behaviour of the constant power and constant resistance modes, this loop probably should be as consistent as possible. Why not connect the LCD to a separate bus (wich will have to use bit-banging, but there are libraries available for that), and operate the control loop from an interrupt ?

[@medvidekkrupicka1404]

I do not think that the I2C speed will be a big deal here. The ADC is rather slow (15SPS@16bit, 60SPS@14bit), so this load is not supposed not be fast by any means. But who of us hackers really needs a fast load? A scope and a handful of good resistors are usually better choice for checking transients anyway. Nevertheless, some code optimization is always a good practice.

[@crocellian2972]

This is one of those always true, back-bench trolls. Why don't you build it with a half dozen low value resistor/scope probe points and see if your troll means anything? I built it with a different logic level MOSFET and a Due. Rock solid.

[@sparktechedm]

Very nice project and excelent class, thanks a lot for sharing

[@scullcomhobbyelectronics1702]

Thanks Erico, much appreciated. Regards, Louis

[@freddiemortos8519]

Very nice year-end project sir :). How I wished I can make one myself. Unfortunately I can't because I can't source out those SMD parts here in my place. 'Cause I'm living in a place very far from the city. Hats off to you sir. Again you make another quality project.

[@javierpallalorden]

Most parts are available from ebay ( that is why I would like to use the ADS1115, very cheap on ebay ). For the OP Amps I am not shure if they can be replaced by simple LM358's, but I think Louis will explain that part in part 2.

[@scullcomhobbyelectronics1702]

Thanks for your comments. You could build it also with standard though hole components. There is options to use other IC's.

[@scullcomhobbyelectronics1702]

Thanks Javier for you input on this. I will as you say discuss options in Part 2. Regards, Louis

[@kktech04]

What a phenomenal, video! I just found my new favorite channel !

[@Pops180]

I think you would need a gate resistor to achieve what you are trying to do. Since the comparator output would be a 0 to 5v pwm due to the hysteresis, you need to essentially create a lowpass filter with the aforementioned resistor and the intrinsic gate capacitance. This will allow you to apply a dc voltage to the gate at the levels you are looking for. Nevermind. I didn't see the full schematic

[@scullcomhobbyelectronics1702]

Hi Andrew, That's OK things are easily missed sometimes. If you check the other parts to this project you will see I also made further changes and updates. I have just finished designing a new single board double sided PCB for the final project and will do an update soon and make some PCB's available on eBay. Regards, Louis

[@nkp5845]

Another great project - now one of my New Year's resolution to build :)

[@scullcomhobbyelectronics1702]

Thank you. Have fun!

[@nkp5845]

You are a great teacher! Have you done any work with IGBTs? I saw it being used in a analogue DC load to handle very high currents.

[@vlsidesigning-veriloghdltu5954]

Would like to know the max power of this electronic load and whether its possible to increase the power to killowatt

[@vds0672]

Hello, I'm running through this project but it's more easy for me to use SMD resistors, caps & diodes. I then wonder why you are using polyester box caps and if I could substitute then with regulars SMD caps. Also, I wondered if 2N3904 BJT could not be used instead of the PN2222A as I assumed the amount of current going thought should be fairly low. Thank you so much for your time !

[@frankderks1150]

Hi, Looks like another nice project.It would be better to switch the load off automatically when changing between CC, CV and CP modes.This also gives the possibility to use one button to cycle between the modes and freeing up two buttons for other future functions.

[@scullcomhobbyelectronics1702]

I am made a number of changes in Part 2 which will be available soon.

[@breedj1]

Wouldn't it be better to have a direct feedback loop in the hardware for the CV, CR and CP modes. The response of the load is now depending on the speed of the controller. Any short transient might be missed by the controller and ruin your day. I'm curious because I was planning to design a load myself and wanted to use a analog voltage devider/multiplier like the AD633 to accomplice that.

[@BiddutMitra]

I am a software guy, it helps me a lot.

[@kevinbyrne4538]

I wonder whether the load current could have been measured using a current mirror instead of a resistor.

[@anjayv8347]

Another amazing project ! thank you! :)

[@scullcomhobbyelectronics1702]

Thanks Anjay.

[@fursino]

Dear Sir, for studying purposes I'd like to look at the schematic but the link provided is unfortunately not working. Will be possible to activate the link and have access to the schematic you are explaining in the video? thanks.

[@pcbreflux]

hi, as always great explaination and excellent video! but I don't get the first part with the MOSFET and the active curve. In my opinion the MOSFET in the dummy load is used with the opamp in some kind of 2.5MHz PWM (more time on the more current flows in a time portion, switching between rails i.e. 0V and 5V). And the usage of the mosfet (Id vs Vds) depends on the voltage of the load Vds+Vr17. so if the load exceed 1V (SDP36NF06L with Vgs 5V) you more in the saturated side? all other is perfect.

[@scullcomhobbyelectronics1702]

Hi, Thanks for your comments. Yes you have a good point about the Mosfet. I have found that with this particular Mosfet it can operate in the active region (some times also called the ohmic region) up to nearly 10 volts. Once you go to a much higher load voltage it will work similar to how you explain. So in essence at lower voltages it acts as a variable resistor whilst at higher load voltages it is pulsed. As I wanted to introduce the hobbyist to the active region of a Mosfet I decided to include that explanation in this project. It may be worth going in to more detail in part 2 of this project. Thanks again for your input, much appreciated. Regards, Louis

[@g1fsh]

thats a great project i will be having a go at building this. Thanks for the information and a merry Christmas to u

[@scullcomhobbyelectronics1702]

Thanks Gary. I am looking forward to progressing on with this project. Merry Christmas.

[@zdravkokreze1914]

Excellent video. I think max values 30V /5A is overkill for that mosfet.

[@scullcomhobbyelectronics1702]

Thanks. I agree - I will be looking at a different Mosfet for Part 2.

[@hansschroder4643]

Great stuff! You are very good in teaching!

[@recolaq]

As always, perfect explanation! . Looking forward on how this project will develop. Would be nice to test 18650's with it. Happy Christmas and a healthy 2017, thanks a LOT!

[@scullcomhobbyelectronics1702]

Thanks. I plan to try and add a battery capacity function as we progress with this project. All the best for 2017.

[@SuperBrainAK]

Wow 4 minutes in and I now understand those mosfet graphs

[@scullcomhobbyelectronics1702]

Nice to hear. Regards, Louis

[@bwack]

Nice design and well presented. I liked the white board simplification of the circuit. Giving it more clarity before introducing the real circuit. Can I ask what R16 and R17 are for ?`They are connected to the power mosfet gate and opamp input.

[@scullcomhobbyelectronics1702]

Thanks. R17 is the 0.1 ohm current sense resistor for monitoring the load current. R16 (10K) ensures the high input impedance of the OP Amp + input is maintained and remains similar to the OP Amp - input pin. Without the 10K resistor the OP Amp + input is simply connected to ground via R17 which is just 0.1 ohm. As the inputs of the OP Amp draw no current there is no voltage drop across R16.

[@tl2797]

Thank you, very interesting video! Can't wait for the part two! :)

[@scullcomhobbyelectronics1702]

Thanks.

[@endremurti]

If i want to load my smps which is usualy have 200volt dc output ,what could i change to your circuit?

[@leppie]

Why do you need a buffer after the divider from DAC to the opamp? I would think a buffer a before the divider would make more sense if you have some 'funny' impedance from the DAC. Edit: Makes sense with the resistor in the schematic, but not sure why you need that. (DAC needs output load?)

[@scullcomhobbyelectronics1702]

Thanks for your comments. We could move the buffer to be before the resistor divider so as to reduce the load effects on the DAC. I will have another look at this as we progress with the project. The reason I placed it after the resistor divider was to reduce the load effect on the input to the control OP Amp.

[@smartups1]

sir. make a battery balance project . li ion battery or lead acid battery .

[@TheKetsa]

that would be awesome.

[@petercalum9767]

Really good video. However, can this system (with modifications) be used for much higher voltage values for examble load for tubes. For example 500V 300 mA load.

[@unicusequipments4871]

One doubt about this video , 1. How to control the constant current and power through the software or hardware 2.Please explain the constant current and power circuit

[@scullcomhobbyelectronics1702]

Hi, The hardware provides both load voltage and load current monitoring which is fed back to the Arduino for control purposes. These are then used to control the drive voltage which drives the Mosfet so as to maintain it at the set current level required. Maintaining a Constant Power mode is achieved by monitoring the output load power which is just a simple calculation of multipying the actual load voltage with the actual load current to give the actual power. If you have a look at the software you will find all the calculations below the following header line: //-----------------------DAC Control Voltage for Mosfet--------------------- Regards, Louis

[@keyen3]

Good video as usual. Why did you choose a darlington pair instead of a mosfet for the fan?

[@scullcomhobbyelectronics1702]

Thanks David. The reason I choose a darlington transistor to control the fan is that I wanted also to control the speed of the fan with a Pulse Width Modulation (PWM) signal from the Arduino Nano. A darlington transistor has a huge gain so you can easily switch it on with a very small base current and it is easier to control over a wider range. You could have use a Mosfet but that would act more like a switch on/off in this situation and may not allow the full control from a PWM signal as a darlington transistor would. As we progress with this project I wanted to be able to vary fan speed dependent on temperature.

[@EwaldBurger]

Very nice explanation and design. Thanks for your time! Ewald

[@scullcomhobbyelectronics1702]

Thank you. Glad you enjoy.

[@hewking]

hi can you please give me an idea about the cost of this unit?

[@Casiyounadatube]

Very nice simple project. Can you show what are you connecting to the load to test it?

[@scullcomhobbyelectronics1702]

Thanks for you comment. I had it connected to a Bench LAB Power Supply - I will show it in Part 2.

[@k1mgy]

Brilliant project! I have an e-bay find on the bench that has similar features. Yours is at far less cost! One feature that you might consider is that of pulsing the load on/off and also a ramped (perhaps linear sweep) between two load limits with a variable time constant. These features would provide some realistic stress testing to a device under test. I am curious about a comment regarding using PWM on the mosfet. Perhaps for some devices under test, you might want to avoid pulsing and instead have a linear load. Would you comment? For testing LiPo cells you might also consider adding a minimum voltage at which the load cuts off, and as a comment mentions, logging. I'd like to reproduce your project but use an MSP430 with a 12 bit ADC. It also has built in DAC so will reduce external parts. I was curious about your choice of mosfet . Would you describe your thinking here? Thank you!

[@k1mgy]

Never mind on the ADC. I see that the unit you chose has better resolution than the MSP430. :) Perhaps needed for your 1mv and 1ma display..

[@sufzoli]

You can use MSP430i2xxx series with 24bit SD ADC, and consider to use the timer in PWM mode as DAC (if the 250sps is fast enough you can get 16 bit resolution)

[@scullcomhobbyelectronics1702]

Thanks for your comments. Yes a Pulse option could be added and have been thinking about that as a possible addition. At higher gate source voltages the Mosfet works in the saturation region (also sometimes this is referred to as the "linear region". With regards the Mosfet I will discuss this further in part 2.

[@Gooberslot]

What a good (day after) Christmas present! Did you use a microscope to solder that tiny sot23 part?

[@scullcomhobbyelectronics1702]

Thanks. I used a bench magnifier lamp when I soldered the SOT23 IC. I find this works OK if I use a fine tip soldering iron.