Raspberry PI Controlled DC Electronic Load

In this video I build a DC Load that's controlled by a raspberry pi. I've built dc loads before, but this time I decided to up the goal to supporting 100w (it actually handled 200w) using three mosfets instead of one. I drive it with a DAC and read back the actual state using an ADC. The CPU board is a raspberry pi, and I have a VFD, encoder, and some buttons for control. It also has a web UI. For more electronics projects, see www.smbaker.com/

[@Pops180]

The major temp difference is due to all three mosfets being driven by a single driver. Each mosfet is a little different in regards to their gate threshold voltage. I would treat each mosfet as a separate circuit ( individual drivers and current shunts)

[@cyclemoto8744]

Many thanks for your content. Based on most of the other KZbin contact your presentation stands out due to the fact that you actually verbally explain your process. Evidently this feature of yours (talking) is beyond the grasp of most of the other channels. Keep up the great work. Cheers from oz

[@TheRealSasquatch]

Nice solution - I esp. like the use of VFD.

[@nosafetyswitch9378]

Amazing job! Makes me feel very embarased about my ugly looking Arduino Load but it works so I dont complain and costed me almost nothing! Mine runs a single transistor and I wont push it for more than 50W but what I have done is i ve used a GPU cooler from an old graphics card and run the fan at 5-6v so it is not loud but the cooling is amazing, It also has 3 buttons but they dont look nearly as neat as your setup! Again great job!

[@BartdeBoisblanc]

I know why it is oscillating ,the LM324 can't handle the capacitive load of the MOSFET. You capacitor is dampening the oscillation by attenuating the frequency of oscillation through feedback. it is making the ac gain of you feedback loop less than 1.

[@tsusec]

When i do something with opamps, Rail-to-Rail opamps in my xp dont go to true zero output voltage, so if it is necessary to remove that offset @0V input, i make negative voltage generator, so negative pole of OP is below 0V ie. -2.5V.. By that you remove most(not all) problems.

[@prashkd7684]

I don't think this design will last long with you run it at full capacity. There is no current balancing between the mosfets so you never know which one is pulling more current

[@UpLateGeek]

I was just looking to buy a cheap electronic load from China, and while it would be fun to build one of these myself, it would definitely take a lot longer considering all the work involved, ordering parts and the board. Plus my 3D printer is out of action right now, so I'd have to get that working to print a case. Anyway, it was a nice little project. The VFD is cool, I always like seeing them in projects rather than a boring old LCD. Have you considered using a piece of transparent green acrylic or colour gel to give better contrast? I bought a big sheet of red colour gel from a photography place, which I use on my LED displays. It really makes the segments stand out.

[@smbakeryt]

I do have some orange filters (bought them to use to color the VFD I put on my Prusa 3D Printer) but have not put them into use yet. I do think it would be fun to color them. If you want a commercial load from China, the Kunken KP184 seems to be a popular one. I have a KP184 here as well, but I thought it would be fun to build my own, and the UI on the Kunken feels a bit like it was designed in the 1980s.

[@EasyOne]

good

[@ugetridofit]

you should try the INA219AID IC. This is what I used for mine and makes it real easy to measure volts and amps at same time.

[@ahmedelwan9129]

ads115 is really better then ina219 i am using both and ads115 has 16bit and better i know you need to add shunt and resistor but its ok i think

[@tablatronix]

VFD, niiice, raspi seems overkill but flexible for sure. Why the IO expanders ?

[@DaveMcAnulty]

Since your already sampling the current sense resistor's voltage with the PI why don't you just control the mosfets directly with a spare gpio pin?

[@bitsurfer0101]

What is the size of the new heatsink? Would you be able to post dimensions? Thanks for posting this video.

[@flemming2jacobsen911]

If you added a .01R-ish resistor in each source of the power FETs, would it not help balance the load on each?

[@RicardoPenders]

yes it would, I made a DC load myself and I'm using from an old amplifier those double 0.22 Ohm resistors in a ceramic package and I have the 2 source pins connected to that resistor which balances it quite nicely

[@bitsurfer0101]

How hot does your sense resistor get?

[@guillep2k]

Why do you need a unity gain OpAmp @ 2:30 to feed the next OpAmp? Unless you've actually meant to connect pin 2 of SV1 to its output, which would make more sense.

[@smbaker-3d-prints122]

This was a holdover from my original design that used a potentiometer, and I suppose it buffered the potentiometer. Even then I'm not sure it's necessary (may have come from the original EEVBlog video that I watched long ago). I am working on a respin of the board where I drop the unity gain stage as well as switch the dual op-amp out for a single op-amp that has an offset trimmer.

[@gnabla321]

What is the advantage to drive the gates through OpAmps? I have built an electronic load where the DAC is directly connected to the gate. Seems to work so far.

[@largepimping]

I believe that putting individual opamps on each gate makes the load sharing between the mosfets much more equal - much more than other options.

[@iyan1khz]

how does the cellphone camera to check temperature?

[@smbakeryt]

I'm using a "seek thermal" compact thermal imager that plugs into the phone.

[@sathyaprasad1411]

👏👏👏👌👌👌🤝

[@samhsavdr9647]

good day i want to convert irobot roomba battery to li ion battery. This is a very common issue. How can I do charge voltage ranges from 7 to 20v .. 3200ma - 14.4v 5200ma liion battery

[@zaprodk]

What on earth does this relate to this video? ...

[@cyclemoto8744]

further to my last comment, at this point in time 2 viewers disliked this video so let's assume those ungrateful people don't like the presenter to talk through the content. Either that or they're just idiots. Maybe my last point stands true regardless.