A 400W (1kW Peak) 100A Electronic Load Using Linear MOSFETs

[@loosrudi]

Very nice. To minimize the fan noise, put a gap between the heat sink and the fans. You can then shroud it to prevent the flow escaping out of the sides. The noise is actually the fan blades chopping the air on the heat sink fins. Anything more than 5mm should do the trick. I think you will be pleased by the result.

[@digitalradiohacker]

For those who want a bit of fun, there is DC. For those who want a challenge, there is AC. Need more problems in your life? Increase the frequency. Still not difficult enough? Turn up the wick right into the RF domain. Still falling asleep? Try aerodynamics.

[@SebastianScholle]

Those mosfets are serious! Some of the priciest one's I've seen used in a diy application, but they seem to be rated correctly for this purpose. Good component selection, I learned something new today!

[@TheDanyschannel]

Nice video! Used your circuit with smaller transistors with great results! Thanks for sharing!

[@KerryWongBlog]

You are welcome!

[@cryscrystiii7023]

Please try with FDL100N50F soldered/tinned on cooper sheet (thickness>3mm and surface>25cm2) before radiator mounting. I easily dissipate 600W for a long time with only one MOSFET for a maximum temperature near the capsule of 70C mount on 5Kg aluminum with Sanyo 9SG1212P1G03 120mm/50W.

[@OneBiOzZ]

Very nice, i have been meaning to make such a load to go along with my other loads for testing, its nice to know some good tested linear mosfets for the task personally i would have amplified the shunts anyway to prevent noise pickup on the input voltage or take it a step further and amplify the shunts for 100mV per amp, use a 10 turn pot and a voltage reference like a REF5010 with a panel voltmeter to monitor the current on the device while being contained and avoiding the use of a microcontroller but its a long term project in my mind also the temperature control is a nice touch!

[@KerryWongBlog]

Thanks Alyx. Yes, when I get a chance, I probably will make it MCU controlled so I don't have to rely on the voltage standard.

[@grerlab2777]

I tried with a water-cooling system and I was able to get 100A ... Thank you...

[@symik3]

Excellent job, what a good morning to wake up to this :D

[@KerryWongBlog]

Thanks!

[@johnconrad5487]

Hello Kerry, Remember I said that I had trouble getting down to a low input voltage? These are the test results of my Electronic load. I am working on the design, still a long way to go. i need to find a way to control the current over the full range of input from Vin = 60 V down to Vin = 1 V and 20 Amps down to 0.5 Amp (that's my spec for this) Vmax Vmax Vmin Vmin Vin 60 60 1 1 Iin 19.412 0.736 22.36 20.3 Pin 1164.72 44.16 22.36 20.3 Vinmax = 60 Volts the max input current is 19.4 (approx 20) Amps; and min is 0.736 (0.75) Amps; with 1 Volt input the max input current is 22.36 and min is 20.3 Amps.

[@KerryWongBlog]

If I read it correctly you were saying that when the input voltage goes down to 1V you could not control the current any more? If that's the case I'd take a look a look at the opamp output as it looks like it's still somehow driving the MOSFET?

[@johnconrad5487]

yeah. it is. i need much better control on this animal. i am still having trouble with it. buuuuttttt.... still persevering... LOL

[@cipher-1]

Did you find solution at low voltage? I am trying to do similar this E Load and use another Opams and at low voltage the Gate voltaje is around 12 volts but current is less than when I apply 5 volts.... for example with 5 volts is 12 ampere and with 2 or 1 volts the current go down to half

[@richardnanis]

Very interesting project! Did you do an accuracy test of shunts? It would be nice to have a display showing the actual amps, voltage (wattage, temperature e.g.) and it also would be nice to set these values to a predefined value. Also setting the resistance would be interesting. You would probably need a kind of Microcontroller/Arduino to do so - but that would be much more useful in my opinion. Also a possibility to log the values to some memory would be useful. O.k. i know - this would make the project much more complicate and i like also to keep it simple :-) One point i dont like too much in this built are these multi-flying cables and these cheap clamps for 100A - this is a weak point i would say. I prefer beefy copper cables and big copper connections that could be easily made by ordinary copper tubing (6mm, 8mm, 10mm, 12mm) with a drilled hole and a screw it gives you very good contact :-)

[@Graham1904]

Very and well done but if it were me, at least for the testing phase, I would have put an Arduino or PIC driven LCD display measuring the mV across both sides of the load and display it as amps. You could of course choose a 4-line display and indicate FET temperatures as well. Nice permanent feature as well....

[@SatyajitRoy2048]

Awesome testing. It would be nice of you if you could plan for a detailed tear down of that HP power supply. It should be fun and informative.

[@KerryWongBlog]

I doubt it is much different than other switching PSUs though.

[@stevebliss6056]

The IPW60R045CP also has great SOA, and can be used up to 400V at 1A

[@davestech6357]

I have built similar loads like this and have a arc lamp driver very similar. I really cringed when you touched the heat sink of the power supply. Many supplies have voltage on the heatsinks that can kick you or worse. Excellent idea of using the shunts instead of a resistor feedback setup.

[@KerryWongBlog]

I should have mentioned that I did check before hand that the heatsink of the open frame supply is isolated. But yes, in general you should not touch the heatsink of a live switching mode PS without checking.

[@johncoops6897]

Just a comment on an old post.... a Current Shunt *IS* a resistor. They are exactly the same thing.

[@ATauheed]

Can you explain how are you connecting the two grounds (control voltage and PSU). From the looks of it, two grounds are connected together. Wouldn't that mess up the isolation and ground reference and evidently result in the opamps and the MOSFET not working properly. I am a little confused on that part. Can you please explain because I was looking around to make a DIY E-load for a school project where we need to test a fuse that is expected to blow at 75-80 amps and your tutorial is exactly what we need. thank you!!!

[@jwong19]

Very nice approach.

[@meirmark778]

good work, check the feedback from the shunt to the gate of the mosfet with a scop, myb your circuit is oscillating .( the sound of the first power supply you tested.

[@KerryWongBlog]

Thanks. I'll take a look when I get a chance.

[@Shubham-po2tp]

@@KerryWongBlog Please tell me any channel who teaches Electronics from basic using practical s For m resistance to opamp and big circuit I am beginner

[@eligijuspranskunas3509]

i made with one transistor, for some reason burns R2 (resistor to the gate)

[@Kaxlon]

Back in the days before Class D were available for audio we often heard parts "sing" when we pressured the audio amp to the max. =) Great video!

[@MinecraftPianoPlayz]

Awesome, very interested in this type of thing. Great work!

[@markkennard69]

I have a large battery bank constructed from 18650 cells. I wish to present a 50A load when the cells go above 4.2v. Im good with the controls but want to know if mosfets are usable for the load at this low voltage. Primary use is for balancing a string of series cells for 12.6 or 25.2v . Currently I switch in wire wound resistors but the heat that's generated limits me to about 15A. Comments anyone ?

[@royrogers7644]

How about making a audio amplifier out of it?

[@oswaldocunha9455]

Nice job. Congratulation !

[@gerliansilvasilva8084]

Hello Kerry, I am wanting to build an adjustable electronic load capable of draining up to 250 Amperes, I initially build one using 32 IRFP260N mosfets but I believe they will not support for a long time, I am using 4 LM324 comparator based control module doing gate control of the mosfets, As a Shunt resistor each mosfet has a 0.10r 5W resistor, My question is, Is it possible to use 8 mosfets IXTK82N25P to obtain a good current drain? Each control module controls 4 mosfets and would it be necessary to change each Shunt resistor of 0.10r for a smaller value, for example, 0.05r? Would it be necessary to do this or would I have much more efficiency just changing the IRFP260N mosfets for the IXTK82N25P linear mosfets?

[@yaghiyahbrenner8902]

The challenge with electronic loads are the small signal stuff with 0.1% accuracy specs I am busy with one and its bloody tough ,its mostly the tempco and analog section that's the hard part with the various signaling paths depending on the range.

[@KerryWongBlog]

Indeed, in your case low tempco 4-wire sense resistor and low offset low drift R-R opamps would be a must.

[@ovalwingnut]

I like the way you think. GR8T infotainment. Thank you.

[@JaswanthiMukkamala]

what is the Aluminium heat sink blocks measurements to withstand for 1kw heat dissipating ?

[@bitelaserkhalif]

Ideal for psu testers

[@user-uy4ty9vt2x]

I also want to make a 1kw electronic load but I don't know the proper heat sink, where could I get that heat sink?

[@Yorumcu63]

Great video

[@thecombatengineer7069]

I watched this a year ago and came back to watch it again. I wonder if you still use this unit? Have you have experimented to ensure the two FETS are sharing the load equally? I bought a Fluke 335 and drive a similar unit based on this design, so MANY THANKS MATE!

[@KerryWongBlog]

Yes I have been using this load numerous times when testing power supplies and battery banks. The loads are shared pretty evenly by the readings of the shunt resistors.

[@jorgeldelapaz6961]

Great Tutorial. Is the DRAIN (tab) connected to the aluminum Panel, and if its do you insulate it from rest of Project?

[@HassanETECH]

this is pretty awesome. the only draw back is the bulky size and i know due to high power dissipation. well done 👍 and i subbed to your channel

[@KerryWongBlog]

Thanks!

[@waltschannel7465]

I jyst discovered your channel while looking for a circuit for an electronic load. Fantastic job! Where did you get the heavy duty shunts?

[@KerryWongBlog]

Thanks! You can get these shunts on eBay.

[@manuelmota9285]

💡💡💡💡💡 WONDERFUL TEST !!! 💡💡💡💡💡 Congratulations for the excelente work. Thank You for sharing. 👍 Kind regards from Portugal

[@KerryWongBlog]

Thanks Manuel!

[@ourchannel8215]

good job...👍👍👍

[@zaidhussain5206]

Really useful project , thank you so much

[@KerryWongBlog]

You are welcome!

[@sheep1ewe]

Just found Your channel, lot of great tips and info here, i subbed.

[@KerryWongBlog]

Thanks!

[@SteelBlueVision]

So I have a crapload of these critters (IXFZ520N075T2) and am wondering if I should try something similar to what you've built up there. Also, my largest power supply goes up to 200 amps at 12 V (needs to be powered by 240 V, which in the US means combining two 180 degree out of phase outlets into one 240 V)

[@ryebis]

Just came across this, thanks! Do you have recommendations for other (cheaper) mosfets that are designed for linear operation like the IXTK90N25L2 ?

[@oetken007]

Great device you build! But does these cheap clamps not giving really small contact points? I would clamp some solderwick between the surfaces to get a lower resistance.

[@rancid11999988]

Very nice!

[@zunriya]

Can i add more mosfet to increase its heat surface for reduced its heat sources density (more surface more easy to cool it down than small density heat ) ? On pararel

[@allthegearnoidea6752]

100Amps this is awesome

[@Mainstream818]

Very great project, will be building one soon to test my 24V battery pack. Question about the 19V op amp rail. Is this able to run with a rail to rail voltage of 5V like your previous 150W load? Or is this rail voltage needed because the Vgs of the linear fets are much higher? Thank you for your knowledge and project

[@cccyberfamilydk]

Great video. Thanks

[@donaldhenke2750]

i like that heah sink. where can i get that heat sink. please.

[@tablatronix]

Imma steal this! Looks good

[@andymouse]

Fascinating..cheers!

[@songkai1981]

Nice project, Kerry. Just a quick one, how did you connect MOS-FET's drain pin to the PSU wires? By the contact of screws on each copper plate? Thanks.

[@enffinity420]

I managed to dissipate 400W permanently with a single FDL100N50F MOSFET that can dissipate up to 2500W

[@davidkierzkowski]

Good video!

[@PelDaddy]

Nice job, Kerry. Now you just need to add a uC and a display to do the math as display the load for you. Thanks for sharing.

[@KerryWongBlog]

Thanks. I will probably do that some time in the future if I get around to it.

[@esdblog6100]

You are operating MOSFETs in saturation region. If they were BJTs than you would operate them in linear region.

[@johnconrad5487]

No. he operating the MOSFET in the linear region same as if it is a BJT

[@prabirdebnath5197]

Hi Kerry, Good Work. I am designing a 500watt DC load. The mosfet you are using are almost identical - I intend to use IXTN200N10L2 . Could you please share the schematic of your design

[@KerryWongBlog]

Thanks Prabir, the schematics are on my website linked in the description under the video.

[@prabirdebnath5197]

Hi Kerry, Is it necessary to add a reverse polarity diode at DUT end. What if the the DUT is connected reverse, I was wandering whether there is any weak link to destroy the mosfet if the DUT is connected in reverse by mistake.

[@KerryWongBlog]

The source-drain diode for this particular MOSFET is rated at 90A continuous and 360A pulse, so I don't think you'd need to worry about the MOSFETs.

[@davidgaleski5303]

thank you

[@KerryWongBlog]

You are welcome!

[@prabirdebnath5197]

Further, on thermal issue, if the mosfet is driven by PWM do you think there will be reduction in heat as the mosfet wont be ON continuously

[@KerryWongBlog]

Yes, if it's driven by PWM then the power dissipation would be equivalent to the average power dissipation.

[@prabirdebnath5197]

So any plans to incorporate a PWM controller in your circuit in the coming days

[@KerryWongBlog]

I don't have any immediate plan, but you could easily add a MOSFET that shunts the gate and source of the power MOSFET used for the electronic load and drive the shunting MOSFET with a PWM.

[@cheapmod]

Wear safety google when playing with mosfet. I have bad experience once which almost blown my left eyes

[@DanielsGameVault]

Hi it's me again LOL :)) Another question: what about the gate threshold voltage of the FETs ? It's 2v according to the datasheet, yet if you want to have, say 0.075v flowing (let's take the worst case, 100a scenario), can you attain that ? Does this threshold voltage represent the value at which the D-S path is at its lowest resistance ? If I have 0.075v on the gate, will I get 0.075v drain to source and through the resistors ? I read about it many times, but can't quite grasp it unless I try out myself. Cheers.

[@KerryWongBlog]

The threshold of Vgs doesn't really affect Ohmic region. When the this threshold is reached the MOSFET turns on fully and the resistance is largely dependent on Rdson. By increasing the Vgs beyond the threshold would further reduce Rdson although only slightly. The gate voltage has nothing to do with your Ids, you can reference each MOSFET's datasheet (Vds versus Ids curve for different Vgs) to see the approximately where the operation point is at for a given Vds and Ids.

[@johnconrad5487]

@ Daniel ...... you have to go to at least Vgs = 2 Volts which is the threshold voltage on the gate for the transistor to start conducting. 2V is what is in the data sheet for this FET. there are some that start conducting a lower than 2 Volts and some require a little more. 0.075V across the gate source will do nothing.

[@SanjaySharma-pw6ww]

👍 like the idea.

[@DanielsGameVault]

Question: I'm trying to achieve something similar, though for a much smaller load (like 10a max) and I've got those same shunts as you 50A at 75mV, but there's one thing I'm curious about: I see you've got 2 wires on each resistor (one on each side of the resistor). One is the feedback wire that goes to the - input of the op amp, but what about the other one ? The one on the "ground" side of the resistor. The page you linked to explains it's Kelvin sensing and I know what that means, but the second wire is not drawn in your schematic...I may be wrong, so please help me out :D Such a cool device and I need to build my own to stress-test TV power supplies (often they look well under no load but act up when the TV loads them). Cheers.

[@KerryWongBlog]

Hi Daniel, the other end of the wire on the resistor goes to the ground (as close as to op-amp's ground as possible). This is to eliminate ground loop and ensures the accuracy of the voltage measurements.

[@DanielsGameVault]

Ok, cool. Thanks for the reply :D YOU HAVE NO IDEA through how many textbooks and designs I went to figure out what that wire does, when all it does is grounding :)) Is it by any chance also going to SHDN pin 5 to disable the shutdown feature ?

[@KerryWongBlog]

correct, pin 5 of the opamp is also tied to ground.

[@DanielsGameVault]

Great, it's coming together slowly :D I'll be pestering you a bit more on this build, since I suck at math so thanks for putting up with me :)) Is the following statement correct ? To sink 100A with this thing, you'd need 0.075v flowing through the resistors, since 0.075v divided by 0.00075 ohms (two 0,0015 ohm resistors in parallel and yes, I like to use the "1" multiplier and write down the whole number, otherwise I screw up :)) ) equals 100. If so, the power dissipation would be 7w ? Cheers.

[@DanielsGameVault]

Correction: 7.5w

[@extoprak]

Hi, I believe I can do similar load with IGBT instead of MOSFET, what do you think? I have a couple of dual pack IGBT (half bridge). I also have some closed loop current transducer, maybe it is better to use them instead of the shunt?

[@KerryWongBlog]

Yes, you can use IGBTs as well. Usually though, IGBTs are mainly used for high voltage high current applications, and as a result it comes with rather high Vces which may not be suitable for your application, it all depends.

[@johnconrad5487]

what is the minimum voltage that the load will work at with max current? what is the max amperage?

[@KerryWongBlog]

It can work all the way down to 1v. Max current I tested was over 100A

[@johnconrad5487]

1V is pretty good. that MOSFET has low Rds. i dont want to spend $ on that MOSFET you are using so i am trying a different device. i am designing one using an IGBT (Vcesat is about 2 Volts) so it is difficult getting down to a low voltage. my minimum has been 2.5V at only a few amps. if i go higher in voltage i can load it with plenty of current but the trick is going down to low voltage and high current. anyway, thanks for answering my queries. not many people do that. :)

[@SebastianScholle]

NICE! But those mosfets are not cheap.

[@ufohunter3688]

Is there a reason you used such thin wires for current sense and thermistors? None of those readings are accurate if the wires are so thin!

[@KerryWongBlog]

No special reasons. Those are just the wires I had.

[@BikesBlades]

The wires used for sensing can be very fine, since they carry almost no current in this "Kelvin sense" connection scheme.

[@nbenci9005]

can be and need to be in order to mitigate external RF interference, thin and short as possible

[@stevebliss6056]

AOT290L a 100v mosfet with a nice SOA (100V @ 5Amps, and 60V @ 10Amps). Way cheaper (about US $3) than the IXYS (US $18). But I do agree, the IXYS is VERY NICE :)

[@schwarzarne]

You are not operating them in linear region. You really should get the nomenclature right. You operate them in saturation region. Switching happens in linear region.

[@KerryWongBlog]

Yes, I meant "Ohmic region" instead of linear region. Thanks for pointing that out.

[@BikesBlades]

The terminology is not very strict. Lots of people use "linear region" to describe the state where the MOSFET is not fully enhanced (working as a source- follower.)