Scullcom Hobby Electronics #56 - Electronic DC Load Part 8 

Thanks Bryan for your kind comment, much appreciated. Regards, Louis

Hi Pete, That was quick. Must have come via a rocket :-) I would appreciate it if you could mark it as delivered on eBay for me. Regards, Louis

Thanks Pete, Not sure how long it takes to get the New Zealand. But let me know when it arrives. Regards, Louis

Hi Colin, Nice to hear you are progressing well with your DC Load. Regards, Louis

Thanks Bruce. Regards, Louis PS: I think I click on a wrong button :-)

Thanks Gérard.

Thanks. yes you could glue that pin to the PCB. Regards, Louis

Thanks Ivan. Regards, Louis

Hi Brain, Thanks for your comment. Yes agree you can have the keypad layout anyway you wish. Simply just print a different overlay and change the Arduino code to suit. Regards, Louis

Thanks Tony, the PCB is on its way to you. Regards, Louis

Thanks Wolfgang. Regards, Louis

Thanks Mark. Will see what we can do. Regards, Louis

Thanks Charles. I will let you know when I have the new batch of the DC Load PCB's. Regards, Louis

Thank You

Hi Charles, Just listed 10 available on eBay link below: www.ebay.co.uk/itm/292478375166 Regards, Louis

Thanks, it did take a while and I went through a few prototypes before finalizing the PCB. Regards, Louis

Thanks for your comment. Regards, Louis

Thank you.

I have just ordered a new batch of PCB's and should have then in 7 days. I will reserve one for you. Let me have your email address in Private Message section of You Tube. Regards, Louis

Hi Reb, Just listed 10 available on eBay link below: www.ebay.co.uk/itm/292478375166 Regards, Louis

Hi Louis, got one a minute ago, many Thanks! And thank you for doing this. I've learned a lot from your videos and projects.

Hi Louis, PCB just arrived to Germany. My Wife "Jamila" was wondering about the PCB :) Now I have to build it. Thank you, you're very kind!

Hi Dave, This issues seems to be cause by some grounding problems on the underside of the PCB. When the fan/fans turn on the extra current on the power lines is causing a very small voltage drop on some sections of the grounding/earth return lines on the PCB print. I am just working on an update video for this project in which I will address this issue and should be uploading the video soon and discuss some other improvements. Adding some additional grounding on the underside of the PCB solves this issue - I will demonstrate this in the video. I am preparing some additional documentation on implementing this extra rounding and will supply it as a download on my next video. Regards, Louis

Louis, Thank you so much for taking the time to consider this and to respond ...your responsiveness is so much better than some of the paid service providers that I use in business :-) I do appreciate it. I am looking forward to seeing a possible resolution ...my current (no pun intended) thinking is to have the fan turn on permanently at start-up, and allow the voltages to "settle" ...it does mean continuous noise and a quieter alternative would be great. Thank you!!

Thanks Ray.

Thanks Mick. PCB is on its way -;) Regards, Louis

Received Louis, many thanks. Looking forward. to building this.

I have just ordered a new batch of PCB's and should have then in 7 days. I will put them on eBay when they arrive. I have sent you an email to your gmail account. Regards, Louis

Thanks.

Thanks Rudy. Regards, Louis

Hi Rudy, Just listed 10 available on eBay link below: www.ebay.co.uk/itm/292478375166 Regards, Louis

Thanks for the tip on the bootloader. I did not realise the Uno bootloader was different to the Nano. Regards, Louis

Thanks Asger.

Thanks Lord.

Thanks.

PS in my simple electronics load I made few years ago, I used SUP57N20 n-mosfet from VISHAY, was able to dissipate about 200W at 12V at only one piece! I achieved it by soldering the mosfet directly to copper IHS salvaged from old CPU, and then attached it to old AMD CPU cooler, also used good quality MX-2 thermal paste. Swap that old crusty cooler with something modern that uses heat pipes, like thermaltake macho, get bigger piece of copper so you can solder like 10 mosfets, and I would expect it to handle like 600W.

I think I will make this, but I'll change mosfets to these I mentioned above and replace 20x4 screen with 3,2' graphical display with touch screen from nexion, it has built in STM32 uC doing all the hard work and communicates via I2C.

I have just ordered another batch of PCB's. Should have them in about 7 days time. Regards, Louis

Thanks for the reply! Such a schame that I don't really have the time and conditions to build this(moved to another country) :/

Thanks.

Glad you liked it ;-)

Hi Martin, If you send me a private message in You Tube with your email details I should be able to help. Regards, Louis

Thanks for the comment. In practice I have found it has little effect. You could if you wish un-bolt it from the heat sink and bend it towards the PCB. Regards, Louis

Thanks.

Scullcom Hobby Electronics continue what you're doing. So easy to learn from your videos.

Hi Charles, I have another batch of DC Load PCB's on order should have them in about 7 days. I see you ordered another pair of the DC Voltage Calibrator PCB's which I have just packed up ready for the post tomorrow. Regards, Louis

Hi Charles, Just listed 10 available on eBay link below: www.ebay.co.uk/itm/292478375166 Regards, Louis

Hi, Thanks for your comment. Yes this could be an option. However, the current design of the DC Load already ensures that there is no drive voltage supplied to the Power Mosfets so effectively it is already off at switch-on. But you could add a relay as a fail safe option if you wished. Regards, Louis

Sorry not sure exactly what you mean about "change your UI to in transient mode" Regards, Louis

Hi George, I have ordered some more DC Load PCB's. If you can send me a message with your email address in You Tube private messages I will reserve one for you and keep you updated. Regards, Louis

Thanks Cliff for the question. The body diode of a power mosfet does provide some form of protection. If your load was connected in reverse the mosfet body diode would conduct and you would have maximum current flowing through the mosfets for a short time unit the 5 amp fuse blows. Therefore the fuse should in theory protect the power mosfets. In some of my early experiments with this DC load I did test this option but I found on some occasions one of the 4 power mosfets failed. So as to prevent this I added the series dual power Schottky Diode (connected in parallel) - in this instance protection is provided without blowing the fuse as no current flows through the mosfets under reverse load conditions. I also noted that some commercial DC Loads also used a similar technique. I have not found the very small voltage drop across the diode to effect calibration. Regards, Louis

Thanks.

Hi Mike, When you bend it down its OK some 5mm of more from that USB connector. You could also leave it standing vertical if you wish but then it blocks access to the USB connector if you want to re-program the Nano. Regards, Louis

Hi Mancel, The only reason I changed the values of R39 and R43 was to improve the zero reading of the actual voltage and current readings on the LCD. If you find the original values work OK for you in Part 7 version then leave them as they are. If you find that the readings are not go to zero them make the change. Regards, Louis

Hi Phil, Thanks for your comments. I have looked at using the IRFP250NPBF for the 4 Power Mosets myself. However, as they are not Logic Level Mosfets they will require a higher gate/source drive voltage. To achieve this I have looked at replacing the U7 (Quad Ultra Low Voltage Offset OP Amp) AD8630 (which can only operate to a maximum of +6V Supply) with a AD8664 which can operate at a higher supply voltages, you could then feed it with the +12 supply. As the pin layout are identical to the it is a drop in replacement for the AD8630. If using my PCB you would then need to cut the track from pin 4 of U7 (+V pin) and then connect Pin 4 of U7 to +12V supply with a wire. This should then give you the required gate drive voltage for the IRFP250NPBF. I have not tested this option yet but I may give it a try. The IRFP250NPBF is a TO247 package compared to a TO-220 package of the BUK956R1-100E, which would need to be taken in to account. Regards, Louis

Thank you much, Louis! Really looking forward to build this project! Also one more thing. As I wanna implement 25A capability, voltage across R17 will be 25A*0.1R = 2.5V, not 0.5V as it is in your initial design. Should I change R6 and R14 dividing resistors (for example make R6 - 1k and leave R14+RV4 as they are - 909R + 200R) to achieve a voltage control range of 0-2.5V? Cheers! Phil

Hi, If you are looking to have a maximum of 25A then I would suggest using a lower value sense resistor for R17 would be better. If you replace R17 with say a 0.02ohm 10 watt 1% resistor then at 25A the voltage across it would be 0.5 volt. The change in voltage then fed via buffer U7D to the ADC (U6) wound need to be compensated for as you are now using a lower sense resistor, this could be done by setting the gain of channel 2 of the MCP3426 in software to a gain of 8 (instead of the current setting of x4) and also making some changes to the code where the calculation is made for the current reading on the LCD. With regards the resistor divider R6, R14 and RV4. Try changing R6 to say a 27K and R14 to a 1K and RV4 to a 1K preset, to ensure you have sufficient range. Regards, Louis

Man, Thank you! I'll definitely go this way ;) Regards, Phil

Hi did you finish this 5 years ago and is it still going strong please ??@@deathblowhere

Hi Martin, The aluminium front panel thickness I used was 2mm. However, you may also find that 1.5mm may be suitable as it will be well supported in the case surround. Regards, Louis

Interesting question ;-) I started electronics when I was in my teens as a hobby, a long time ago. I then studied at college for 6 years. But the simple answer to your question is if you are really interested in electronics and spend time understanding the basics and practice building electronics projects you will soon progress to making your own basic designs and move on from there - it is really down to you, the time it take varies from person to person. But the important thing is enjoy what you do. Regards, Louis

You don't have to be an engineer to do it :D. For beginners, make first a circuit that is a simple one, then going to complicated.

Hi Julius, The specification for the current version of the DC Load is: 4 Amp (maximum) 50 Volt (maximum) 120 watt (maximum) I have found that the Power limit of 120 watt may be increased by using a larger heat sink and two fans. I have had the unit currently operating reliably at 3 Amp at 30 Volt (90 watts) on its current heat sink and one fan (heat sink temperature monitored at between 50 to 60 °C when running for more than 10 minutes). I will be looking at ways to fix the small 8-9 mA leakage current while the load is off (on the current PCB version 9.2) and will cover this shortly in an update video on this project - basically the Current Null preset (RV3) can reduce the leakage current to zero but may effect the calibration slightly. Regards, Louis

Thanks. Yes I will reserve one for you. I should have a new batch later this week. Will send you one when they arrive and we can arrange payment by Paypal. I see you have just ordered the DC Voltage Calibrator PCB's - I have just pack them and will post them to you first thing tomorrow morning. Can you give me your email in the private message here in You Tube so I can contact you. Regards, Louis

Thank you for the quick response. About the private message -how to do that?

check out the following link: support.google.com/youtube/answer/57955?hl=en-GB In addition I did put an information sheet also with the DC Voltage Calibrator PCB's I am sending you which also has my email address on. Regards, Louis

Thank you for the link, working fine. Best Regards, Flemming Loua Cristiansen

Hi Peter, I have seen them available on eBay. But one alternative could be the STP80NF55-06 from ST Microelectronics but it maximum voltage rating is 55V (compared to the 100V of the BUK956R1-100E). I do mention alternatives in Part 5 of this project at 34.45 minutes. I have sent you another message about this with your PCB order. Regards, Louis

A guy on EEVblog used IRLB4030PbF (it's rated for 100v) you can see it here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-23oiVOILgtE.html

Yes there is some small leakage current which I zero in software for the LCD display. It is possible to remove this leakage down to 0mA but then I found it effects the current reading on the low current settings below 200 mA. This seems to be due to the DAC (U5) accuracy at the very low settings. I will have another look at that and see if there is a solution to overcome the DAC zero offset error and the DNL error. The current Null preset (RV3) can be adjusted to improve this error. At the moment the current settings are OK from about 100mA to 4 amp with only a very small error of a few mA. I will have another look at this later. Regards, Louis

Hi Sandi, I have already sent you an email following your request on my website www.scullcom.uk Regards, Louis

Thanks. Sorry you missed out on the first batch. I was very surprised how quick they all went. I have just ordered another quantity from my PCB manufacturer today and should have them in 7 days time. I will put them on eBay and give a new like in the comments below my video. If you want to send me your email address in the Private Message section of You Tube I will reserve one for you. Regards, Louis

Scullcom Hobby Electronics Hi Lois Could you reserve me a pcb please. Regards Steve Cooper

Hi Steve, Yes I will reserve one for you. I should have the new batch in 6 days time. If you are able to contact me in the Private Message option of RU-vid with your email address that would help. Regards, Louis

Hi Louis I have been trying to figure out how to send a pm but after 3 hours of trying to figure it out, I have given up so here is my email address. stevecooper474@gmail.com

Steve I have sent you an email. Regards, Louis

Hi Alan, Yes I was surprised how quick they went! If you send me a private message in You Tube with your email details I should be able to help. Regards, Louis

Thanks. The design as it stands allows currents up to 4 amp and load voltages up to about 50V so in theory the maximum power could be around 200 watt. Sofar I have tested it to about 120 watt and it was OK. At the higher wattage you need to ensure you have a large heat sink and a good quality fan cooling the heat sink. Regards, Louis

Hi David, Saw your request for a PCB on my website. I have ordered a new batch and should have them in about 6 days time. I have sent you an email with details. Regards, Louis

Thanks Flemming for your comment. That could be an interesting option for long transient times. Could be a future upgrade. Regards, Louis

Hi Bruce, I have just ordered a new batch of PCB's and should have them in about 5 days time. If you go to my website www.scullcom.uk and leave a message there then I will be able to contact you by email and arrange a PCB for you. Regards, Louis

For ADC or DACs is better to use stable and precise voltage reference if you want to have good accuracy.

@@alexeicebanu7987 I see, thanks!!

​@@EdwinFairchild but, but... you already knew that right? :)) your name was seemed familiar to me and then, i realised that I am already subscribed to your channel! :D Cheers!

@@alexeicebanu7987 I know enough to know I don't know much. 😔

Hi John, I have just seen your message on my website and sent you an email. I have just received a new batch of PCB's today. Regards, Louis

No you will not damage anything. They could get a little warm at very high current loads so it is just a precaution and good practice. Regards, Louis

thanks

Might be okay, firstly the IRLB4030 has very slightly higher Vgs characteristics, but should still be fine for 5V operation. The bigger problem is the safe DC operating area graph, for the BUK this stretches all the way from 10V/11A out to 100V/.7A, for the IRLB they cut it off at basically 10V/10A and it barely goes past that.

I assume that CV is constant voltage. Not practical. Think about it and I am sure that you will see. This is not a power supply. It is a load. A battery under test is simply what it is. The same is true for a power supply under test. I am not the most knowledgeable tech around and if I am wrong I hope that someone will enlighten me.

In Constant Voltage (CV) mode operation, the DC Load must attempt to sink enough current to maintain the set voltage. However, a DC load will have limitations on how much current it is able to sink. Therefore, CV mode would not really be practicable in this project without adding limitations which would then defeat the purpose of having a CV mode. I agree with Mancel's comment. Regards, Louis

Thanks a lot, now I undrestand you and agree with you and Mancel.

I have just ordered a new batch of PCB's and should have then in 7 days. If you send me your email address in the Private Message section of RU-vid I will email you when I have them and I could reserve one for you if you wish. I will also put them on eBay again. Regards, Louis

Scullcom Hobby Electronics ok thank you very much... How i can send a pm?

Hi Mirko, I will reserve a PCB for you. You will find details how to do it here: support.google.com/youtube/answer/57955?hl=en-GB Regards, Louis

Hi Mirko, Just listed 10 available on eBay link below: www.ebay.co.uk/itm/292478375166 Regards, Louis

Scullcom Hobby Electronics too late... Any chance for another batch?

The DC Load PCB dimensions are 137.5mm * 134mm. Regards, Louis

Thanks

I will be providing PCB files later. I have just ordered another batch of PCB and should have them in 7 days time. Regards, Louis

I have just ordered a new batch of PCB's and should have then in 7 days. If you send me your email address in the Private Message section of RU-vid I will email you when I have them and I could reserve one for you if you wish. I will also put them on eBay again. Regards, Louis

Hi, Just listed 10 available on eBay link below: www.ebay.co.uk/itm/292478375166 Regards, Louis

thank you

that link tells me the listing has ended.

haha. they all sold out already.. bugger. :) not to worry. thanks anyway

Hi Terje, I just got a new batch in today. I have reserved one for you. I have sent you an email about it. Regards, Louis

Are the PCB's going to be listed on ebay again soon? I am also wanting to make the DC load and would like to grab a PCB.

Hi, just listed 10 available on eBay link below: www.ebay.co.uk/itm/292478375166 Regards, Louis

Scullcom Hobby Electronics awesome thanks. I have ordered a couple, one for myself and when I mentioned it to two makes over here in Australia they said they would like to build one too so we are all set.

mmmm ;-) Regards, Louis

Yes I was very surprised to. I have ordered a new batch. I have sent you an email about them. Regards, Louis

Thanks Louise

Hi, I have a new batch of PCB's on order and should have them in 6 days time. Would you like me to reserve one for you. Regards, Louis

Scullcom Hobby Electronics hi Louis. Il keep an eye out on Ebay and purchase one if that’s easier? Many thanks. Steve

Hi, Steve, Just listed 10 available on eBay link below: www.ebay.co.uk/itm/292478375166 Regards, Louis