Modular DummyLoad ~180W 20-40A

[Spikee]

Hello everybody!

I have been playing with the idea of making a modular dummy load for quite a while.

When the MightyLoad came up on hackaday a few weeks ago i got inspired again.


Picture of the MightyLoad from kaktus circuits
http://kaktuscircuits.blogspot.cz/2014/02/mightywatt-arduino-electronic-load.html


My design is focused on being modular. I designed the board in a way so you could use multiple modules / loads together with one host board.
The modules will be controlled via an Isolated I2C bus by the master (yet to design board).

I will use two IXTH75N10L2 mosfets on each module. These will be cooled by a Artic Freezer 7 pro rev 2 CPU cooler.

For control I will use the Cypress Psoc 4 series System on chip for:

• 12Bit Differential ADC
• 12Bit ADC to measure heatsink temp using TMP37
• 4-pin Fan control
• Current shunt monitor (INA225) gain settings (via GPIO)
• I2C-1 to control the external 12bit DAC
• I2C-2 to send and receive data over the isolated I2C bus
• Analog mux to digitally change the voltage measurement opamp's gain

http://www.cypress.com/?rID=53408
 
I am aiming for around 180-200W head dissipation and a max current of 20-40A.
The current shunt monitor chips will be the TI INA225 with PGA of 25/50/100/200 and probably a 2mOhm 4 terminal current shunt.

My design files so far:

Schematic:
https://dl.dropboxusercontent.com/u/100819959/MegaLoad/MegaLoadV0.1.PDF

ALTIUM:
https://dl.dropboxusercontent.com/u/100819959/MegaLoadV0.1.zip

PSOC:
Psoc Designer top sheet:
https://dl.dropboxusercontent.com/u/100819959/MegaLoad/PsocDesigner/TopDesign.cysch.pdf

Psoc Desinger Pinout:
https://dl.dropboxusercontent.com/u/100819959/MegaLoad/PsocDesigner/Screenshot%202014-03-27%2002.43.08.png

I know the schematic is kinda messy ... already 129 components 
I added a lot of caps / resistors that are probably not needed but for a first prototype I want to keep my options open.
Also I tried to make star points as much as possible (Vref and GND , 5V) but I'm not sure if that will be such a success.
Any feedback / questions are appreciated.

[tom66]

Am I misinterpeting the design? There is no analog regulation loop for the current - this is all done in software?

[Spikee]

U2 is an dual spdt analog switch,  CC:CV wich is controlled by the mcu determines how U2 is switched (CC or CV control loop).

U2 part number: TS5A23157DGSR

[BravoV]

CC:CV wich is controlled by the mcu determines how U2 is switched (CC or CV control loop).

Really curious how good the software handle the CV or CC loop ? 

How is it's transient response ?

[Spikee]

CC:CV wich is controlled by the mcu determines how U2 is switched (CC or CV control loop).

Really curious how good the software handle the CV or CC loop ? 

How is it's transient response ?

The control loop is still analog via the opamps. The dual analog switch state determines if you want to operate your circuit in cc or cv mode.
Because it is an analog control loop it should not be to bad of a transient response.

[tom66]

That's kind of a neat solution - for a constant-R or constant-W mode (which are done in software) which control loop will work better? I have a feeling constant current will, but I'm not certain.

[Spikee]

That's kind of a neat solution - for a constant-R or constant-W mode (which are done in software) which control loop will work better? I have a feeling constant current will, but I'm not certain.

I'm not yet sure , I will just try what the kaktus circuits guy did in his arduino code.

You can find the Arduino code here:
https://drive.google.com/folderview?id=0B7G3xJXZNLUpWElUZUFneFNENTg&usp=drive_web

[Spikee]

Update:
I made all the footprints and added 3d models to them.
The schematic should be pretty much done. I only need to add a decent external power socket.

This will be a 4 layer board (100x150 mm) which will be produced by OSHPARK.

Current layer stackup:

• Analog routing
• GND/AGND/DGND
• Voltage lines/planes layer
• Digital routing

http://i61.tinypic.com/o76rfr.jpg


http://i61.tinypic.com/2cohq89.jpg

I still have to determine where to place all the components. When placing the components I try as much as possible to keep al the analog and digital parts in their own "sections" on the pcb.

Current schematic [PDF] :
https://dl.dropboxusercontent.com/u/100819959/MegaLoadV0.2/MegaLoadV0.2.PDF

MegaLoad V0.2 Altium design files:
https://dl.dropboxusercontent.com/u/100819959/MegaLoadV0.2/MegaLoadV0.2.zip


Any feedback is appreciated 

[diyaudio]

Hello everybody!

I have been playing with the idea of making a modular dummy load for quite a while.

When the MightyLoad came up on hackaday a few weeks ago i got inspired again.


Picture of the MightyLoad from kaktus circuits
http://kaktuscircuits.blogspot.cz/2014/02/mightywatt-arduino-electronic-load.html


My design is focused on being modular. I designed the board in a way so you could use multiple modules / loads together with one host board.
The modules will be controlled via an Isolated I2C bus by the master (yet to design board).

I will use two IXTH75N10L2 mosfets on each module. These will be cooled by a Artic Freezer 7 pro rev 2 CPU cooler.

For control I will use the Cypress Psoc 4 series System on chip for:

• 12Bit Differential ADC
• 12Bit ADC to measure heatsink temp using TMP37
• 4-pin Fan control
• Current shunt monitor (INA225) gain settings (via GPIO)
• I2C-1 to control the external 12bit DAC
• I2C-2 to send and receive data over the isolated I2C bus
• Analog mux to digitally change the voltage measurement opamp's gain

http://www.cypress.com/?rID=53408
 
I am aiming for around 180-200W head dissipation and a max current of 20-40A.
The current shunt monitor chips will be the TI INA225 with PGA of 25/50/100/200 and probably a 2mOhm 4 terminal current shunt.

My design files so far:

Schematic:
https://dl.dropboxusercontent.com/u/100819959/MegaLoad/MegaLoadV0.1.PDF

ALTIUM:
https://dl.dropboxusercontent.com/u/100819959/MegaLoadV0.1.zip

PSOC:
Psoc Designer top sheet:
https://dl.dropboxusercontent.com/u/100819959/MegaLoad/PsocDesigner/TopDesign.cysch.pdf

Psoc Desinger Pinout:
https://dl.dropboxusercontent.com/u/100819959/MegaLoad/PsocDesigner/Screenshot%202014-03-27%2002.43.08.png

I know the schematic is kinda messy ... already 129 components 
I added a lot of caps / resistors that are probably not needed but for a first prototype I want to keep my options open.
Also I tried to make star points as much as possible (Vref and GND , 5V) but I'm not sure if that will be such a success.
Any feedback / questions are appreciated.

Hey man this looks like a great project, thanks

[Spikee]

It took a long time but the prototype if finally here. Uni was in the way =/





Schematic:

Features:
-Cypress Psoc 4
-Isolated I2C control bus
-12 bit dac
-12 bit (integrated) adc
-External Voltage reference
-Two IXYX 75 L2 mosfets
-Programmable gain
-TI INA225 for the current measurement
-Two shunt resistors

When my mouser order comes in i can finish assembling the circuit and start writing code.

There are definitely some bugs but that will be fixed in an later revision.

[Spikee]

The big one also fits:
Cooler Master Hyper Z600
It is around 0.1 deg C/W

[Spikee]

I got myself a psoc programmer Miniprog 3. I had lots of problems with using the kitprog from the psoc 4 pioneer kit.
The micro works now. Basic status led, fan pwm, TMP37 temp measurement works. I'm soldering and testing the other components as we speak.
Updates will follow shortly.

[eneuro]

I designed the board in a way so you could use multiple modules / loads together with one host board.

So, how many such modules will be needed to make 5kW dump load? 
I used I2C too, but slightly different aproach-Hall current sensor and critical tracks filled with additional copper wires, while I do not believe in thin PCB copper layers covered by mask which does not help disipate heat

Did anyone tried... spot weld TO220 mosfet tap to copper heat sink ?
It should improove heat transfer but I'm not sure if some kind of ESD will not destroy them during spot welding 

[miguelvp]

I got myself a psoc programmer Miniprog 3. I had lots of problems with using the kitprog from the psoc 4 pioneer kit.
The micro works now. Basic status led, fan pwm, TMP37 temp measurement works. I'm soldering and testing the other components as we speak.
Updates will follow shortly.

What kind of problems did you have with the kitprog?

Just wondering because someone at cypress released the 2.03 version of kitprog:
http://www.element14.com/community/thread/27067/l/psoc-5lp-programmer-firmware

I just rewired SWDIO and SWDCLK to the 5LP header P0_0 and P0_1 and got it working fine as a programmer:
http://www.element14.com/community/thread/27067?start=15&tstart=0



So far it works with all the PSoC 4's I've tried:
CY8C4245AX-483 (4200 that comes with the prototype board 42xx and same as in the pioneer)
CY8C4125AX-483 (4100 that comes with the prototype board 41xx)
CY8C4245PV-482 (4200 ssop 28 pin)



Next one in line is another 4200
CY8C445LQI-483 (4200 QFN) and I started to solder it deadbug style but then wife called dinner time so I stopped, I gotta get some kapton tape anyways because even if the wires are not touching the bottom pads, mishandling it it will produce shorts.



4 down, 36 more to go

[Spikee]

From what i can see you are dooing bootloading using the psoc 5 and transferring the hex file over uart.
I'm talking about a fresh micro with no bootloader on it. One of the problems that i have had is that i updated the kitprog firmware and then programmed a chip. But after one programming cycle the psoc 5lp (kitprog) goes back into its own bootloading mode.

I'm not sure what exactly is wrong but it gave me a whole lot of issues. I have programmed many boards before with the kitprog, but it has always been an hassle.

The miniprog just works and that is what i need.

[miguelvp]

I'm doing a fresh micro, the last two chips came unprogrammed.
I did modify the kitprog project so the built in 4200 in the pioneer doesn't have to be unpowered by removing the jumper. If you remove that jumper then the 5LP gets into bootloading mode.

I modified the kitprog project so that SWDIO uses pin 5LP0_0 and SWDCLK uses pin 5LP0_1, the internal 4200 is still powered but not present in the SWD chain. I end up with 5 wires same as the miniprog.
I use the /xres and 4VDD plus ground on that other header.

Only thing to be aware is to only upgrade the bootloader and bootloadable modules to 1.1 (comes with 1.0) and also the USBFS modules have to remain at 2.51 or 2.5 on the instances of the project. Upgrading those to the latest modules makes the kitprog not work.

So it's not just a hex programmer, I can use it as a full programmer/debugger and I can program and debug the external 4200s without adding a bootloader on them of course I can if I choose to, restore the bootloader on those prototype boards.

But since you already have a miniprog 3 I wouldn't bother much with this.

[ass20]

hi

nice electronic load
this is project finished?

[Spikee]

I made a V2 a long time ago:


And it is finished in terms of:
pcb's are here, board is assembled but No time has been put into programming it.
Maybe next year when I might have more time.

[Sjokolade]

I want one of these,keep us updated.

[Spikee]

Maybe I'll put a new board under the liteplacer pick and place next week and look at the code again. No promises

[electricar]

Hey Spikee,

I'm designing my own load right now. I really like your way of switching between CC and CV! Have you done any tests on this? How is it behaving (stable)?
You also wrote that there are still some bugs in the current version. Can you please list them?
Thank you very much in advance!