Scullcom Hobby Electronics #47 - Electronic DC Load Part 3

[@martinmilner2019]

I learn so much from your videos. I find the pace, thorough explanations, diagramming on the white board, and step by step discussion, a real inspiration for my projects. Thanks for taking the time to do these projects and for sharing them with us on KZbin.

[@scullcomhobbyelectronics1702]

Martin Milner Thanks for your kind comments, much appreciated. Regards, Louis

[@philipgautschi]

I really like your style of explaining. Speed and level of detail works perfectly fine for me! Thank you very much!

[@scullcomhobbyelectronics1702]

Thank you for your comment, much appreciated. Regards, Louis

[@mrfrog8502]

I'm loving your tutorials. I'm hooked up. So much better than EEV Blog who only started uC controlled power supply tutorial and never finished it. Keep up the good work and big thank you.

[@scullcomhobbyelectronics1702]

Thanks.

[@medvidekkrupicka1404]

Excellent! Those iterations from a rough design to polished one with all the bells and whistles are a great learning experience.

[@scullcomhobbyelectronics1702]

Thanks. I try to add a little electronics theory in my projects.

[@rodneyjaygarrett]

Very nice project. I truly learn from you each time. Your projects that you provide are highly relevant. Thanks so much for sharing your knowledge with us!

[@scullcomhobbyelectronics1702]

Thanks for your kind comment.

[@Hugatry]

Already awesome project keeps getting even better! Very nice improvements again.

[@scullcomhobbyelectronics1702]

Nice of you to say, thanks.

[@saneeshelectronica9293]

Very nice project

[@chaswinder]

What a fantastic project and video series! Thank you.

[@ufohunter3688]

I love this project. It keeps getting better with time... Like fine wine.. I will incorporate this design into my lab experimenter box project. With minor improvements; like replacing the 0.1 Ohm with a 0.01 Ohm and amplifying it 10 times to save on power loss and since I already have the resistor. Will mod the code to suit my 320x240 color graphics screen, since it will be sharing the screen with many other functionalities on my experimenter Box; i.e. scope, signal generator, etc.... Will send a picture when ready. Thanks again for all the time spent on this insanely useful project.

[@scullcomhobbyelectronics1702]

Thanks for your comments. Look forward to seeing your project when you have finished it. Regards, Louis

[@robbruno8246]

Thank you. You are so generous with your knowledge and time. Excellent work. I have made several of your projects and have gained much understanding of electronic principles and theories.

[@scullcomhobbyelectronics1702]

Rob Bruno Glad to hear you are finding my projects helpful. Regards, Louis

[@freshneyorg]

I don't think I've ever seen a set of how-to electronics videos as good as these. Amazing :)

[@pfabiszewski]

Very nice, kind of "good old school" way of thinking, explaining and processing! Nice job!

[@scullcomhobbyelectronics1702]

Paweł Fabiszewski Thanks Pawel. I use to teach electronics in the mid 1970's for about 8 years. Hence, I still tend to use my whiteboard :)

[@pfabiszewski]

Great that you are "giving back" what you know.

[@hexefx]

Having a knowledge is one thing, but being able to pass it to others in an easy comprehensible way is a true gift. You have it, Sir! Love your channel :)

[@scullcomhobbyelectronics1702]

Many thanks.

[@chamikashamoth7273]

This is best video i ever seen in you tub for dc load

[@MattBaker1965]

Great work. I get a project to work and move on to the next one. nothing is quite so well produced as your project. Good to see a polished load project.

[@scullcomhobbyelectronics1702]

Thanks.

[@tonybell1597]

Thoroughly absorbed with this project, thanks Louis, finished my own pcb layout (getting to know Kicad....) excellent project, really like the addition of keypad and mods to the software... Looking forward to the next one! Keep up the excellent work.....

[@scullcomhobbyelectronics1702]

Thanks Tony. I will try and cover some more in Part 4. Glad to hear you are getting the swing of KiCad. Regards, Louis

[@symik3]

I have already commented on one of your videos, but didnt have time to reply(now i finally finished my exams). Excellent programming and electronic design. You have plenty of knowledge. Just simply excellent work. I had time to watch the all 3 part in one piece finnaly and i am impressed. i will use your ideas partially or fully i dont know yet, but definetly goin to build this. I stuck with programming, because it was my main object to use only a single rotary encoder, but i am not a programmer and wont be soon. In the area of teaching you became one of my favourite ones.

[@symik3]

Slight addon, wouldnt it be simplier just to in a battery capacity testing mode u ask for an input what the cutoff voltage be and from there you can use any kind of batteries.

[@scullcomhobbyelectronics1702]

SYM!K3 Thanks for your kind comments. With regards your question I will have a look at providing an option for the user to enter their own voltage cut-off voltage.

[@symik3]

I watched a few other video of yours, impressive work. Good job!

[@Newsparklabs]

Another great video, thanks Louis!

[@scullcomhobbyelectronics1702]

Thanks.

[@qzorn4440]

this is so exciting viewing the evolution of the dc load project 😀while using ideas that are some what familiar to me 🙃 and this is all free 🤑a real home diy plan 🥰 thanks 💫🥠☕

[@christophernetherton9389]

You have put a lot of work into this. Thank you, it just keeps getting better.

[@scullcomhobbyelectronics1702]

Thanks Christopher.

[@agaelema]

Excellent project!

[@scullcomhobbyelectronics1702]

Thank you.

[@smartups1]

awesome improvements.and project now more nicer.

[@scullcomhobbyelectronics1702]

Thanks Asif.

[@javierpallalorden]

Excellent follow-up video, thanks.

[@scullcomhobbyelectronics1702]

Thanks Javier.

[@michaelhawthorne8696]

This is a nice project. Nice design too.

[@scullcomhobbyelectronics1702]

Michael Hawthorne Thanks Michael.

[@berniken6511]

Great project Louis I'm sure that its been a lot of work............................Berni

[@scullcomhobbyelectronics1702]

berni ken Thanks Berni. These projects do need some planning and work before I commit them to video for KZbin and as such it takes more time to put them together. As a result it may be a few weeks between my videos as I fit it in during my free time. Regards, Louis

[@FlyingShotsman]

You've made some great improvements to accuracy and resolution with these upgrades, but I'll reiterate my comment from the last episode about remote voltage sense since these improvements make it even more relevant. The accuracy of displayed and calculated values will depend in large part on the resistive losses in the test leads. If you look at the voltage readings during your demonstration in this video, you'll see what I mean. It starts at 5.194V, drops to 5.185V with a 1A load and to 5.178V at a 2A load. Just a few things that contribute to this error: resistance of test lead wire due to its cross sectional area, resistance of the connection from the test lead wire to its connectors, and resistance of the connection between the test lead connector and the device under test. All of these errors would be eliminated if you implement remote voltage sense. All it requires is a SPDT switch on the front panel, a bit of wire and another panel connector. Consider two common test cases. 1) Testing batteries. Calculated capacity will be increasingly erroneous as test current rises unless voltage is sampled *at the cell*. 2) Testing a power supply. You can't tell if observed voltage drop is because of test lead losses or sag in supply output. In both cases, remote sense solves the problem. Great work, Louis! I'm looking forward to part 4.

[@scullcomhobbyelectronics1702]

FlyingShotsman Thanks for your detailed comment. I agree voltage sensing would improve the accuracy, the main cause of error is due to the length and gauge of the connecting load leads. I will have a look at the possibility in adding sensing. There is also technique now that uses electronic sensing in place of sensing wires. I need to look in to this possibility. Regards, Louis

[@FlyingShotsman]

Hmm, I would be interested to see how that works. If you find details, could you add a link to the info in the next video description? Cheers!

[@isidoromaich7226]

I love this project, it's getting bigger and better. Congratulations. A nice feature could be if we can collect the data to make graphs in excel.

[@scullcomhobbyelectronics1702]

Isidoro Maich Thanks. Data logging be easy to add. I will have a look at it as we progress.

[@samhsavdr9647]

beatiful design box waiting....

[@scullcomhobbyelectronics1702]

Thanks.

[@GeorgeGraves]

I'm really loving your video series. Thanks for the great work!

[@scullcomhobbyelectronics1702]

Thanks George.

[@NaudioElectronics]

Great project! Watched all episodes A nice feature instead fixed battery curoff voltage for each battery type will be a custom mode - an option where you can select the cutoff voltage manual from the keyboard. This can be usefull if you discharge more than one cell connected in series for example. Niki

[@scullcomhobbyelectronics1702]

Thanks. Yes we could add a feature for the cut-off voltage to be entered by the user.

[@standishgeezer]

Brilliant stuff!

[@scullcomhobbyelectronics1702]

Thanks.

[@dumouchelclermont4982]

Really enjoy it. Thanks for your efforts...

[@scullcomhobbyelectronics1702]

Thanks.

[@audiotecnologia4084]

Is Very Good !! Thanks my Friends

[@scullcomhobbyelectronics1702]

Thanks.

[@avejst]

Wow, well done. thanks for your big work 😀👍

[@scullcomhobbyelectronics1702]

Thanks.

[@chillipaste386]

Your projects are top notch. Thank you for sharing your knowledge. Just a quick question on the MOSFET... can't one just parallel a few of them to spread the load? Might also make it possible to increase the power capability of the unit?

[@scullcomhobbyelectronics1702]

Chilli Paste I will be looking at paralleling Mosfets in Part 4 so as to increase the power rating.

[@andrewpilk]

This is a great project, I love watching how it is evolving. A useful addion perhaps would be a watt hour calculator for battery capacity? The battery test screen is already very full so you might have to alternate between displaying mAh and Wh.

[@scullcomhobbyelectronics1702]

Thanks for your comments. We could add a Wh option but at the moment the LCD display is full.

[@techrah]

7 years later, I feel like I'm late to the party. Thank you for this excellent series! I'm learning so much. I have a question on the UF5408 diode place in parallel with the 0.1 ohm sense resistor. According to a datasheet I found, this diode is an ultrafast RECOVERY rectifier diode and there are specs for the reverse recover time in nanoseconds. However, in this project, it's the forward voltage that counts when there is an over-voltage. So wouldn't a standard fast-switching diode be more appropriate? What about common diodes like 1N4007? Can those be used or are they not fast enough?

[@zepplinc20]

Good stuff, subscribed. I plan on building this.

[@scullcomhobbyelectronics1702]

Thanks. Good luck with your own build.

[@goowatch]

Hi. I congratulate you for your channel and for sharing your knowledge with the world. I would like to ask you please to enable the subtitles for your videos since although your speech is very clear sometimes it gives me difficulty to understand because English is not my native language. Thank you very much for your dedication.

[@scullcomhobbyelectronics1702]

goowatch Thanks for your comments. I will have to look in to the subtitles as I am not familiar with it.

[@milanmladenovic]

Great video. Thanks a lot. :)

[@scullcomhobbyelectronics1702]

Thank you.

[@kees-ft1yb]

Very nice project. I definitely want to built it too. Maybe we can ad a feature , like the battery capacity test, but then for big capacitors of 100.000 uF. In that case you discharge and measure the mAh from a starting treshold until you reach a cutoff voltage. Its just an idea.

[@scullcomhobbyelectronics1702]

Thanks for your comment, interesting suggestion.

[@makerKID5]

Another fantastic video! What would be the correct term for the "resistive keypad" implemented in most commercial products like remote controls for example? Where there are traces on the PCB and the silicone keypad makes contact with those traces when the button is pressed. I want to go for something fairly ambitious since I've been following the project from the beginning I want to put it in a nice case and add custom buttons for constant current etc. I already have a blank silicone button mat.

[@vehasmaa]

Thats silicone keybad technology has been arround ages... even cheap calculators use it... basically underside button that silicone cone has conductive material that shorts pcb traces when you press a key.

[@scullcomhobbyelectronics1702]

The "Resistive Keypad" is a Silicone rubber keypad. Good luck with your own project.

[@makerKID5]

So I had the right idea, great. Thanks guys.

[@TheRealRR4711]

Have you considered leaving the buffer op amp out and directly use the sigma delta ADC on the shunt?

[@scullcomhobbyelectronics1702]

I have found the ADC works better with the addition of the buffer. Also maintaining a high impedance across the current sense resistor improves accuracy of the reading. The ADC conversion accuracy can be affected by the input signal source impedance and may have an effect on the ADC internal sampling capacitor which would cause errors. The datasheet for this ADC does recommend using an OP Amp with a closed-loop output impedance of tens of ohms.

[@DoRC]

Very cool are you going to do an updated pcb with the changes as well?

[@scullcomhobbyelectronics1702]

Do R/C! Thanks. I may do an update PCB as we finalise this project. But I will try and maintain the current PCB for those who are already building it.

[@drulli1]

Great, the project is getting even more advanced. Your explanations are really excellent. Seeing your high quality engineering skills and ambition can I assume that you will make a final PCB version which integrates the new elements, changes, mods, etc? And, if you have a proposal which housing you would take that would help a lot Thanks!.

[@scullcomhobbyelectronics1702]

Axel Haar Thanks for your comments. I may provide an updated PCB layout when the project is finalised. As a number of people are already building this project I want to also maintain the original PCB for them as the follow this project.

[@DavidLeeMenefee]

You could take this to yet another level by adding a data logger option. Just saying, I'm sure you already thought of this. Thumbs up

[@scullcomhobbyelectronics1702]

ElectronicWizard Thanks for your comment. I have been looking at data logging. I am currently testing some alternative Mosfets and adding more in parallel to increase the power. As we progress I will look at adding data logging.

[@javierpallalorden]

Hi ElectronicWizard, nice idea and very easy to implement, just use the Arduino serial (Serial.begin, Serial.print) and a little program called TelemetryViewer_0.2.jar.

[@DavidLeeMenefee]

OK I'll give it a try. Thanks

[@javierpallalorden]

I want to make it wireless with a couple of HC-12 (SI4463) modules (one HC-12 and one HC-12-USB).

[@HauptwerkHardware]

Loving the development of this. I have learnt a lot and found it inspirational so a big thankyou. Question though; if we wanted to dramatically increase the power handling is it as simple as using a much higher wattage current sense resistor - say a folded length of suitable wire and adding more power FET's in parallel or are there other considerations. I have seen commercial products like the DynaLoad which can handle 1500W and wondered if that sort of power is achievable for the hobbiest?

[@scullcomhobbyelectronics1702]

To increase the power handling I will be adding additional Mosfets. I will try and cover this in part 4 of this project. The resistor would stay the same as it is now.

[@budude2]

Just a thought for part 4... Instead of a separate keypad and display - how about a touch panel display? There are quite a few on ebay pretty cheap (

[@Hasitier]

Brian Ullmark a nextion Display could be the Solution.

[@scullcomhobbyelectronics1702]

Brian Ullmark This may be an option for the future. I am currently looking at some other improvements first. Thanks.

[@budude2]

Certainly - looking forward to the additional vids on this - I am very interested in this project for sure!

[@IvoBallie]

Hi. Excellent project. Do you have a printable BOM for this project? I was thinking that if you use a 12 V DC wall wart supply you could eliminate the 12 V regulator. Regards Ivo

[@scullcomhobbyelectronics1702]

Hi Ivo, I did supply a link to a Parts List in part 2 of this project - link is below: www.scullcom.com/Electronic_Load_Parts_List.pdf The only other items to add to that are as follows: 4x4 Matrix Keypad (ensure you get one as shown, otherwise you would have to alter the addressing pins in the software for different Keypads) REF5040 (4.096V Ref. IC) 10uF 16V or 25V tantulum 1uf 16V or 25V tantulum 8 pin SOIC to DIL small adapter PCB (you will find these on eBay) R6 the 9.09K was replaced with a 9K 0.1% resistor (Mouser Part No: 71-PTF569K0000BYEK) R14 the 909ohm was replaced with a 1K 0.1% resistor (Mouser Part No: 71-PTF561K0000BYEB) R7 and R19 were changed from 1K to 10K 1% UF5408 diode 5amp quick blow fuse and fuse holder RV1, R10 and R12 were removed. I will try and update the Parts List in Part 4 of this project. You could use a 12V D.C. Supply if you wish and leave out the 12volt regulator. I initially added the 12 volt regulator IC to improve any noise or ripple on the supply line which may effect the DC load operation, but you could probably get away with leaving it out. Regards, Louis

[@MauroSedrani]

Great stuff!

[@scullcomhobbyelectronics1702]

Thanks.

[@Hasitier]

Thanks for the update and the improvements. My suggestion: if we already have a keypad why not using it to enter the values for discharge current and so on? I would prefer a solution wehre you could enter a value using the keypad and also change the value easy with the rotary encoder. I am on building a power supply which has those both input methodes simultainiously for entering voltage and current limits at the moment.

[@scullcomhobbyelectronics1702]

Michael Bernhardt Thanks for your comment. I have been looking at using the keypad to also enter the user input setting but also keep the rotary encoder. In that way the project would then provide the same option as a commercial DC Load. I just have to work out the software to achieve this. I will try and include this option as we progress with this project. Regards, Louis

[@cowasakiElectronics]

Is there a way of getting the pcb as a Gerber file to have made?

[@zaprodk]

Getting along nicely - well done! - I had a look at the schematic - i see there is an RTC, but not used in the code as of now, any plans what to use that for? Data logging maybe? I could see an SD-card option as being nifty!

[@scullcomhobbyelectronics1702]

The RTC is just used as a timer at the moment for the Battery test mode. Which is using a Arduino library I put together for this project. We may use additional feature of this RTC chip at a later date.

[@grahamwise5719]

the current measurement, measure at safe gain, if small signal select highest to give a better match of ADC bits on small values. Could the cuttoff voltage be adjustable when shown on the LCD for battery discharge. Alternative main FET part number suggestion. Thanks for the good detailed viseo as always

[@scullcomhobbyelectronics1702]

Thanks for the comments. You could alter the gain for different input ranges but I think is would over complicate this project. We could provide an option for the user to enter their own cut-off voltage. I will be looking at alternative Mosfets for this project.

[@First2ner]

On battery discharge you could add Wh reading, since you could want to know what Wh did battery had, I think that would be useful and possibility to set cutoff voltage from menu, you might want higher or lower cutoff voltage

[@scullcomhobbyelectronics1702]

Thanks for the comment. I am looking at further software upgrades as we progress. A separate menu screen to set battery voltage is one option I am looking at. We could add Wh reading for the battery, the reason it is not there at the moment is due to lack of space on LCD but this could be changed - see how we go with this project. Regards, Louis

[@CliveChamberlain946]

Wow! Finding that MOSFET (BUK956R1-100E) would be slim-chance-to-none.. Both NXP and Digi-Key say it's discontinued.. So I watched all 3 parts and it looks do-able, but what now? Is it possible some could list some actively stocked substitutes?

There are MOSFETs specifically designed to work in linear mode. www.ixyspower.com/images/literature/250V-600V_Linear_L2_TM.pdf But I`m not sure if it is a drop-in replacement.

[@zepplinc20]

Maybe PSMN4R3-100 PS,127

[@CliveChamberlain946]

Thanks zepplinc20, looks close enough (at first glance) and under $4 in Canada! Link: www.digikey.ca/products/en?keywords=568-8595-5-ND

[@philspargo9543]

Try the CSD18502KCS. I tested this MOSET at 50 Watts for 2 hours, the temp remained at about 40 C, using a heat sink similar to Louis's and a 80 MM fan.

[@CliveChamberlain946]

Phil - That's this one: www.digikey.ca/products/en?keywords=296-34940-5-ND I like the RDS (doesn't apply much in linear region), but the Vds is only 40V which is cutting it a bit too close to higher failure... The CSD18502KCS has less than half the gate capacitance and that's good, but it also could imply a smaller die area (259W vs 338w). For the extra power and Vds (and an extra 0.72 cents), the suggestion from zepplinc20 still looks like the way to go.

[@First2ner]

Now, one important question for you is: how is with actual current drift when current is flowing through sense resistor and heating it up? I expect that you can have "big" drift from that. Resistor heats up, changes resistance (up) and then you read to high, compensate current back down, but actual current is lower than set. Is that right? maybe a test for next video?

[@scullcomhobbyelectronics1702]

First2ner At higher currents the PCB print tracks can effect the reading. I am looking at taking the MOSFET, 0.1 ohm sense resistor, LM35 and heat sink away from the PCB in the final design and then wire the power components with heavy gauge wire.

[@javierpallalorden]

Hi Louis, I have a couple of MCP1541's lying around, they are not as (long-term) stable as the REF5040 but maybe they will do the job.

[@scullcomhobbyelectronics1702]

Javier Palla Lorden The MCP1541 should be fine although it may not be quite as accurate. However, the nice thing about it is it is available in a TO-92 3 pin package which would make it very easy to solder on to the main PCB with out the need for a small PCB.

[@marcelvanooststroom1733]

I'm not sure if I would use the keypad for my project. Are the tactile buttons still usable including the updates? Keep on going your style of explaining the project. I like it a lot.

[@scullcomhobbyelectronics1702]

If you decide to stay with tactile buttons instead of the keypad then you would simply need to ensure that the Arduino software allows that. All the new features will still work. However, if you want to be able to select different battery types then you would need to add more tactile buttons or simply stick with just the LiPo option. When I have more time I will look at providing the latest Arduino code for the tactile button only option if that helps. Regards, Louis

[@marcelvanooststroom1733]

Scullcom Hobby Electronics Maybe I'll wait to see the end result. I was wondering how to mount the keypad in/on the projectcase. Thank you for your suggestion Louis.

[@scullcomhobbyelectronics1702]

I will show you how I build it in a project case as we progress.

[@marcelvanooststroom1733]

I've seen your result in part 4. Looks very good. Better then I thought.

[@scullcomhobbyelectronics1702]

The keypad allows more functions to be added with upgrades in software.

[@christianmock1815]

Another fantastic project. Well done. Will someone make a kit of this?

[@scullcomhobbyelectronics1702]

Thanks. I am still working on this project so it may change a little.

Great project, congratulations from Poland! It would be great to see you monetizing your projects. Did you think about croudfunding and small production batches?

[@scullcomhobbyelectronics1702]

Thanks Piotr, I am doing this just for fun and to try and teach the hobbyist a little bit about electronics on the way, so I have not considered Monetising. Regards, Louis

[@mathieub3953]

What happens if I set in CP mode the power to max. 50W with an input voltage of 1V, I would get 50A. Does the system shut down too?

[@scullcomhobbyelectronics1702]

The unit has safety limits which are set in software so if it exceeds them it will automatically switch off the load. In the later versions of this project these limits can be user set as well.

[@ParthBhat]

As always I love watching your videos.. best detailed explanations and I always recommend them to my friends too. I will be building this project after my exams and with a nice case and everything. (ofcourse I'll give you the credits) , but 1. any plans to update the pcb design ? 2. can't we have all the dip package Ic's? 3. can we add the feature to set the values with keypad too? cheers! thanks for the video again :)

[@scullcomhobbyelectronics1702]

Hi Parth, I may have a go at an updated PCB when the project is finally completed. However, as a number of my subscribers are now building this project I have been adding addition small add-on PCB's to the main PCB for the upgrades, this means they can simply add to what they have already built. Both the Real Time Clock and the Voltage Reference for the DAC options were added on small additional PCB's which can simply be added (connected) to the main PCB. I am also working on another upgrade which will involve another small PCB which I will cover in Part 4 of this project. With regards the IC's on the main PCB they are only available in a SMD (SOIC) package. However, for the next add-on PCB which I will add in Part 4 of this project I have chosen 8 pin DIL IC's making it easier for the hobbyist to build. I am just finalising the next part of this project (Part 4) and hope to film it soon and then upload it to my You Tube channel. I am looking at the possibility of also having the keypad with an option to key in the set values. Regards, Louis

[@ParthBhat]

Scullcom Hobby Electronics thank you so much for the reply.. I'll be eagerly waiting for the 4th part. cheers Parth

[@dan3460]

As always a very interesting project. Thanks very much. I was looking at commercial electronic loads and my money is on your design, I'm always testing power supplies and is a pain to change resistors to change the loads on them. Many of the power supplies that I test have several voltages, so I'm planning to add to your design a couple of circuits to have 2 or 3 loads working on the same box. That part should not be that difficult to do. My question will be with the max amps for one of the loads. The power supplies that I have worked on have one supply, normally in the +/- 5 to +/- 15V range, that can handle 10 to 15 amps.Would putting 3 or 4 FETs in parallel handle the extra current? If so, do I need to design a circuit to balance all those FETs?I'm not using Arduino to program the MCU, so I will be writing my own software and I do understand that will be changes on the way that voltage and current are calculated.Thanks for your comments and thanks for the work you give to our community.Cheers,

[@scullcomhobbyelectronics1702]

dan3460 Thanks for your comments. I will be looking at adding Mosfets in parallel in Part 4 of this project to increase the power capability. I have just ordered a number of different Mosfets to test and hope to cover that also in the next part, so that we can use some alternative ones in our project.

[@MaddMart]

Maybe a stupid question but why doesn't 9.09k and 909r give a ratio of 10:1?

[@scullcomhobbyelectronics1702]

9.09K is 10 times larger than 909r. The total resistance would be 9.09K + 909r = 9.999K. Therefore if you divide 909r in to 9.999K you get 11. Therefore the ration is 11:1 and not 10:1. Hope I have explained it OK. Regards, Louis

[@MaddMart]

Ah! yes. I was dividing 9.09k by 909r getting 10. I have both of these resistors with 0.1% tol. but I'm having trouble getting 9k 0.1%. So would it be ok to use the 9.09k with a 1k giving a ratio of 10.09:1?

[@monvagen10]

Is it possible to get the hands on a BOM for this project?

[@scullcomhobbyelectronics1702]

Hi, In Part 4 of this project I give a zip file which contains a BOM (Parts List) and other details. I same download link is also below: www.scullcom.com/DC_Load_files_Part4.zip

[@biggrey54]

could you use a MAX6173 instead of the lm7805 and lm35

[@scullcomhobbyelectronics1702]

You could use the 4.096V version (MAX6174) for the reference. The Temperature pin is just for monitoring the die temperature of the IC and not intended for measuring the temperature of other objects. The REF5040 I use also as a Temperature monitor pin, but we do not use it in this project. These reference IC's could NOT be used to replace the LM7805 as they can only handle a maximum of about 30mA of current which would not be enough for this project.

[@johan-fredrikgrgaard2869]

Why not make an option for the number of cells on the discard program? Most RC cars, boats, planes and quadcopters use 2S to 8S. Testing one cell is for lab use, testing a battery pack is even useful for RC hobby (and you would not loose any of your functions). On my battery tester I use the AtMegas Eeprom to store the cutoff voltages and change them from a password protected setup menu. On the battery test menu you change the number of cells and then check that the voltage match the chemistry and the number of cells before discharge begins.LA7SJA

[@scullcomhobbyelectronics1702]

Thanks for your comment. We could add a feature for multiply cells.

[@smartups1]

very big thumbs up for this. Sir make a new project on MPPT charge controller or Arduino based buck boost converter which controls current and output voltage also.

[@scullcomhobbyelectronics1702]

Thanks for your comments and idea - may be for the future!

[@rohanventer2010]

Why use a tantalum capacitor instead of a ceramic capacitor? Tantalums caps' failed state tend to be short circuit.

[@scullcomhobbyelectronics1702]

Thanks for your comments. I used tantalum as I needed a 10uF and 1uF with a low ESR value, as the reference IC performs better with a low ESR capacitor. Also we are only operating at low voltages so the tantalums should be just fine. Although you may find a 1uF ceramic capacitor a 10uF would be more difficult.

[@TnInventor]

the 0,006A current that the arduino is reading with no load is the leakage current in the MOSFET diode , unless you use a relays do disconnect the voltage from the MOSFET it will always be there. in my opinion a software reset is not the solution