Electronic constant current DC load

[MJLorton]

Hi Folks,

Here is the "final" prototype circuit that I'll be using for my first build.
I will use this as a test to see how well it works and do any troubleshooting / learning from here....

Electronic DC Load #5 - Final circuit before build:
http://www.youtube.com/watch?v=cvc0XsB7LMk

Link to Kibi's "Dave Jones' dummy load with added features" :
http://mjlorton.com/forum/index.php?topic=29.msg92#msg92

Dave Jones / EEVblog video with the original post and design by Dave Jones:
http://www.youtube.com/watch?v=8xX2SVcItOA

WHAT IS AN OP-AMP?:
http://talkingelectronics.com/projects/OP-AMP/OP-AMP-1.html

My components:

* Infineon MOSFET N-channel 200V 13.5A TO-220 - BUZ31L H (I will be using two of these in parallel)
* Vishay 534 Series Pot with 6.34mm shaft, 50K
* Vishay 534 Series Pot with 6.34mm shaft, 5K
* 1 x 10 k Ohm resistor
* 1 x 10 turn 10K trim pot
* Arcol HS50 Al house wirewound high power resistor,1R (1 ohm) 50W - HS50 1R J
* National Semiconductor Quad op amp,LM324N 1MHz DIP14
* 1uF Capacitor


Cheers,
Martin.

[markm6164]

Hi Martin

Thanks for the info. Below is my circuit on a breadboard inspired by you and your videos. For my op-amps i use a LM358 as its what i had kicking around and only contains 2 op-amps. Still need to get some 10 turn pots though. I also notice without the 1 ohm load resistor the adjustment isn't as nice as it is with it in the circuit.

Thanks again, Mark

[Kiriakos GR]

The ten turn pot it is a bit costly ;-)

Martin what is the specifications ?
Max Load in Ampere ?
Min & Max  input voltage ?

[jwrelectro]

Hi Martin,
This is the same post I put on your YouTube channel:

I completely  understand if you do not want to do this but I was hoping you might wait a couple of days before you start your final build. I have the same E-MOSFET that you have and have gotten most of my components to build the el-load. I will start a project tonight and looking over your diagram I think I have a few suggestions. Since I will include my reasoning I think it will take multiple posts to this thread. I will include pics and maybe a link to videos.

I have never built a circuit with a MOSFET but like you I like to experiment and learn new things.  Some of things I will try and address in the next couple of posts: LM324N, the 1 uF capacitor, adding build out resistors to the two FET gates to prevent problems with the phase margin, the 10k-ohm voltage divider, the 10 k opamp load resistor, and
current hogging.   

As I mentioned before I really like your attitude of exploration and your YouTube channel.   One negative of watching Dave Jones and your videos it is costing me money.  I order the TekPower TP4000ZC and it seems to work including connection to a PC via USB adapter.  John

[MJLorton]

Hi Martin

Thanks for the info. Below is my circuit on a breadboard inspired by you and your videos. For my op-amps i use a LM358 as its what i had kicking around and only contains 2 op-amps. Still need to get some 10 turn pots though. I also notice without the 1 ohm load resistor the adjustment isn't as nice as it is with it in the circuit.

Thanks again, Mark

Hi Mark,

Thanks for the great post. Interesting to hear your feedback about the adjustment without the 1 Ohm resister as well.

I look forward to following your progress.

Cheers,
Martin.

[MJLorton]

The ten turn pot it is a bit costly ;-)

Martin what is the specifications ?
Max Load in Ampere ?
Min & Max  input voltage ?

Hello Kiriakos,

The maximum load on mine will be limited to 2 amp. The FETs can handle 13.5 amp as long as the total power is within 90 watt.

The FETs are rated for 200 v but again as long as power is within 90 watt. Mine will operate from about 0.5 volt to 30 volt.

I plan to build another one that will do about 5-10 amp at 12-15 volt.

Cheers,
Martin.

[MJLorton]

Hi Martin,
This is the same post I put on your YouTube channel:

I completely  understand if you do not want to do this but I was hoping you might wait a couple of days before you start your final build. I have the same E-MOSFET that you have and have gotten most of my components to build the el-load. I will start a project tonight and looking over your diagram I think I have a few suggestions. Since I will include my reasoning I think it will take multiple posts to this thread. I will include pics and maybe a link to videos.

I have never built a circuit with a MOSFET but like you I like to experiment and learn new things.  Some of things I will try and address in the next couple of posts: LM324N, the 1 uF capacitor, adding build out resistors to the two FET gates to prevent problems with the phase margin, the 10k-ohm voltage divider, the 10 k opamp load resistor, and
current hogging.   

As I mentioned before I really like your attitude of exploration and your YouTube channel.   One negative of watching Dave Jones and your videos it is costing me money.  I order the TekPower TP4000ZC and it seems to work including connection to a PC via USB adapter.  John

Hi John,

Thanks for the post and I look forward to your input and seeing your progress. It will take at least a week before I have time to start my build.

I'm glad to hear the TekPower is working for you.

Thanks and cheers,
Martin.

[Kiriakos GR]

Hello Kiriakos,

I plan to build another one that will do about 5-10 amp at 12-15 volt.

Cheers,
Martin.

If you do one at 17A 12V it would be more worthwhile because it will have the potentials to stress those batteries found in the UPS power supply too.
Which usually are 7Ah or 17Ah.     

[MJLorton]

Hello Kiriakos,

I plan to build another one that will do about 5-10 amp at 12-15 volt.

Cheers,
Martin.

If you do one at 17A 12V it would be more worthwhile because it will have the potentials to stress those batteries found in the UPS power supply too.
Which usually are 7Ah or 17Ah.     

Yes...good point. I'll look at some FETs in the TO-3 package for that option.

[SeanB]

More FET's in parallel in a TO247 or TO220 package will be easier to assemble though, and will be easier to find a heatsink for. I have some massive power supplies for old minicomputers that use a massive heatsink with TO3 devices on it. I have drilled the layout a few times for TO3 devices, it is hard to do accurately.

[Kiriakos GR]

I have drilled the layout a few times for TO3 devices, it is hard to do accurately.

To do Work on aluminum is an art by it self, I am master to it, but you need and professional quality tools too.
Even the quality of the drill bits, and the rotation speed, is tremendously important factors.

http://hackedgadgets.com/2010/09/04/diy-resistors-decade-box/

[MJLorton]

More FET's in parallel in a TO247 or TO220 package will be easier to assemble though, and will be easier to find a heatsink for. I have some massive power supplies for old minicomputers that use a massive heatsink with TO3 devices on it. I have drilled the layout a few times for TO3 devices, it is hard to do accurately.

Thanks, valuable feedback....plus I have found that the TO3 packages are many times more expensive than the TO220 packages.

[MJLorton]

I have drilled the layout a few times for TO3 devices, it is hard to do accurately.

To do Work on aluminum is an art by it self, I am master to it, but you need and professional quality tools too.
Even the quality of the drill bits, and the rotation speed, is tremendously important factors.

http://hackedgadgets.com/2010/09/04/diy-resistors-decade-box/

Very nice project Kiriakos...I need to add it to my list of tools too!

Cheers,
Martin.

[jwrelectro]

Hi Martin,

Just an update on my el-load project.  I have been working on the design (Dave's and yours)  for the last couple of days and it is nearing completion.  It is Friday night here in California and I think I will be able to post most of the design information this weekend.  I am waiting on the chassis and a digital meter which should be here in a few days.  Basic features (that might change) are:  0 to 5 amps at 12 volts, digital readout of current with set feature and on-off output control, heatsink tunnel with fan, two E-MOSTFETs (the ones you selected) for load control, only need one quad opamp, and some other goodies.  I plan to put the control circuits on a PC board and the basic design can support much higher voltages and currents... given a lot more E-MOSFETs.

John

[wade]

Hi Everyone, I am new to the forum and an amateur at electronics (but I am a very experienced software engineer). I watched Dave's and Martin's DC load videos and decided to build one as well. I have it working successfully on a breadboard, although I still need to do some more in depth measurements with the scope across a broader range of voltages and current. I built my load circuit using the same op amp, mosfet and power resistor as Martin. I also used a 10-turn pot that is nearly identical as well. My original attempt powered the op amp at 12V but I ran a voltage divider and another voltage follower to drop the voltage to the pot and comparator up to 11V. The circuit did work but I did not have much granularity in the pot - less than one turn and I was over 1 amp! Yikes! Today I tweaked the circuit to be more like Martin's last video on the subject by building up an LM317 with a couple of resistors to give me a 6V supply to the load circuit. I also added a pair of 10K resistors to form a fixed voltage divider just before the comparator op amp and another 10K resistor to ground just before the mosfet's gate. Under this config, the 10-turn pot has a lot of fine-grained control, which is nice. I am only using one 50K, 10-turn pot, not the coarse and fine controls. I do not believe I need a fine control. I have only tested it up to 1.5 amps for a very short time since I'm on a breadboard and I don't want a meltdown - the mosfet gets hot fast as I near one amp of constant current. My load is connected to a separate bench top power supply much like Martin does in his videos. Pretty cool project! Thanks for all of the great information!