Modified LM324 Based 150W 72V 10A Electronic Load [COMPLETED]

[tekguy]

so what pins on the 12v reg go to what points on the schematic then,just to clarifie ok,thanks.

[enut11]

@tekguy, I suggest you forget about the 7812 mod and use a regulated 15vDC/1A plugpack into the '12v AC input' socket on the PCB. Much easier to implement.
enut11

[Vovk_Z]

I have produced a label that now sits on top of the plastic enclosure and it shows the expected amps for each rotation of the 10-turn-pot.

I used an additional "0-I-II" switch and a multiturn potentiometer in my electronic load. Additional switch gives two ranges and '0' position ('No load'). That is much more convenient to have different ranges and an ability to turn off a load completely. Ranges in my load are '2 Amperes' and '15 Amperes'. So I have ability to work with high voltage (up to 250 VDC) low-current powers supplies, and with low-voltage high current power supplies. Load current is distributed across 4 TO-247 MOSFETs (IRFP450).

[enut11]

@Vovk_Z
I like the idea of a "0-I-II" switch and the ability to quickly disconnect/reconnect the load. By switching resistors above the helipot you still retain the 10-turn resolution.
enut11

[tekguy]

is there a mod to have this cut off automaticaly say at 3.5v for 18650 lion cells?

[enut11]

Not that I know of. Only if the cells have a BMS board. Most 18650 BMS cut power at about 3v. This one is rated at 5A.

[misa2]

This thread was very good source of information for my own build of DC load based on this kit. I’ll post my experience, maybe someone will find it useful.

I used enut11 modifications (R1 shunts, extra trim pot to limit current), and Kleinstein’s suggestion about snubber circit(4,7uF and 10R across terminals). Thank you guys.

I omitted bridge rectifier and got 12V 500mA wall mounted power supply. As it is non switching, I expected a bit higher voltage without load, but this one had 17V!. Under load it produces 15V, which this kit happily uses. Even 12V rated fan works without overheating. I considered using 7812, but opted not since everything works pretty stable as it is. When i find less powerful power supply I will ditch this one.

MOSFETs are STP9NK50Z, TO-220 devices which are specified for DC operation. They cost 1,5EUR a piece here in Serbia.

The box is locally produced plastic one. Dimensions are 138X120X55mm. Because of mounting points I had to drill the PCB. It looks ugly but it works.

The cooler is for Intel socket 478. I drilled 2,5mm blind holes into aluminium heatsink and used M3 self threading screws to fasten MOSFETs. Drill broke on the last one, so I had to mount it a bit lower. Fan is working nonstop, and this is not an issue for me.

I used M430 panel ammeter/voltmeter, which has interesting feature to display power instead of current for 1sec every 4secs. I tried old version that doesn’t display power, but the new ones was more convenient to use. There is a big gotcha with these panel meters: thin black wire must not be connected to GND terminal, as it is not the same ground as shunt. This leads to erroneous current display. Ultimately, I didn’t connect that wire at all.

In the works, device was tested up to 60V and up to 10A, which are limits of my lab power supply. In this MOSFET/heatsink/cooler configuration it can sink up to 100W continuously – I tested it for 30minutes. MOSFETS didn’t go to thermal runaway, but at this power level, rightmost MOSFET had 140 deg celsius case temperature. I wasn’t comfortable pushing them further. For brief periods of time (1 minute) I tested it up to 150W, which confirms that this kit has potential for more, if better cooling is provided.

For my use case (testing power of unknown transformers, stress test of PSU’s) this is very good kit.

[misa2]

Just relevant SOA for STP9K50Z.

[gevv]

Hello, single layer pcb DIY version.






Attention: If you make a reverse connection, the MOSFETs may malfunction. As a precaution, you can connect a high-power diode in series to the positive line.

Parameters of the original kit;

Input voltage: 0-15v/0-72V (according to mosfet type)

Load current: 0-10A/0-2A (according to mosfet type)

75NF75 75V 150W

Interchangeable with R18 16K-18K 10A, 20K 8A C9 22uF