DIY DIY EKPM3 Active Cooling for LPFP

[fmorelli]

I have a backlog of stuff to post, and I've been remiss as I've not wanted to do write-ups until projects are done. But somehow I have a ton of projects that are 80% finished, and the last 80% of the work is in the 20%. Anyway, there are a few threads on active cooling. I decided to build several active cooling EKPM3 setups, to include one for @barry@3DM's 3DM Motorsport track E90 build, @NoQuarter (we work on projects together from time to time), and of course my Z4.

First off, for reference, there are a few threads floating around on the subject: here on Spoolstreet EKP Active Cooling, Cooling the EKP, and here's one on Bimmerfest EKP Fuel Module Overheating - CPU Fan Install. And there are other solutions, wiring Hobbs switch, etc. I suspect one can even run multiple EPK's with a little bit of tomfoolery but not sure I've seen anyone figure that out.

An alternative is the EOSpeed BPM4 controller - which redesigned to support higher lift pump demands for the N54/N55. It's $650-750 and people seem to have generally good results with this unit. Definitely the buy it and run with it solution.

For the Z4, the EKP is in the trunk - plenty of room.


On to the DIY: basically my approach is a couple-fold:

First off there is an IC that is in harm's way, which is basically the PWM control. You can the Infineon BTN7960 Data Sheet which I placed in the N54 resource section of Spoolstreet. This until would benefit from a properly fitted and installed heat sink.


Second, add active cooling. In my case I decided to use a high end, Taiwanese-made fan, which mounts to the stock EKP case, which is then also drilled to flow air over the heat sink.

I have yet to determine how I want to wire the fan for power - I'll post when I hit that. In the meantime, minus any connectors for car hookup, here's what I'm using:

• Heatsink kit (easier just to buy a variety pack): https://www.amazon.com/gp/product/B078KB7V5J/
• Arctic Alumina Thermal Adhesive (great stuff, been using it since overclocking days): http://www.arcticsilver.com/arctic_alumina_thermal_adhesive.htm
• Noctua NF-A4x20 FLX fan (note they have a 10mm tall fan if space is an issue): https://noctua.at/en/nf-a4x20-flx/specification

Next post I'll get into the DIY.

Filippo

 

[NoGuru]

I'll post my wiring when I get time. If there is a part that can be replaced to allow more current that anyone knows of, I could do, just need to know what part?

 

[NoQuarter]

Another copy of my note...

I have a pic somewhere of the resistor that I think is for the slew rate

Section 5.4.3 explains the resistor that is next to the chip on the EKP. Seems that resistor can be changed to allow more current at the expense of more emission interference.

 

[NoGuru]

Another copy of my note...

I have a pic somewhere of the resistor that I think is for the slew rate

Section 5.4.3 explains the resistor that is next to the chip on the EKP. Seems that resistor can be changed to allow more current at the expense of more emission interference.

A pic of the resister and a link to the upgraded part from Digi key and I will make these!!

 

[fmorelli]

So first on to the PWM IC and heat sink.

If you've not done this before, plenty of info on the web around how to apply a heat sink with adhesive heat paste. I won't cover that but instead just provide a variety of photos. On the heat sink, I needed to find one that fit, footprint-wise, then had to shorten its height to fit the inside of the case. Apply adhesive sparingly - it is conductive so you don't want it to squeeze out over the contacts. I used a bit of tape to help keep any adhesive from ending up in bad places. I remove circuit board to give a quick look, there is a heat transfer pad on the aluminum casing.

Filippo

 

[NoQuarter]

Should be this 6.8k resistor. Haven't worked out what to change it to yet.

 

[fmorelli]

Mounting the fan is pretty straightforward, once you figure out where to place the hole. I wanted it on the other side of the heatsink so air is drawn from the entrance holes, across the heatsink and then out. Photos do most of the talking. Note the 23mm inset marking on the case, before drilling. 1 3/8" Forstner bit fits perfectly.

The air entrance holes are trickier to do. Combination of drilling and cutting to maximize the air entrance area without screwing up the case. And adventurous person could design and 3D print a better cooling cover, and kit up a solution including wiring. Seems like a fair $100 item. I digress.

Filippo

 

[b4llistic]

EDIT: Thanks your finding and reading my post. Unfortunately, Spoolstreet is no longer a neutral platform where we can have honest discussions on subjects and products freely.
For this reason I have deleted all information I posted on the forums.

 

[NoGuru]

Oh great. A 3rd topic about this....

Oh great, even better, a post with no value added.

 

[NoQuarter]

Should be this 6.8k resistor. Haven't worked out what to change it to yet.

View attachment 40506

It seems all the minimum current ratings are already higher than needed so switching the mosfets faster likely won't help any further.

Looking this over i am not seeing why pulling a few more amps should be a problem nor why stock amps can be a problem.

Even the max temp ratings are really high.

Looks like the active cooling is the best medicine but it would be interesting to know why.

 

[S54ca]

The IC is not the main heat generation component on this PCBA, it is the mosfet underneath which is coupled to the heat sink via the heat transfer pad.

Not to say this method won’t work, but replacing the thermal pad with a higher thermal conductivity and /or cooling the heat sink will be more effective, and you may not need a fan.

 

[fmorelli]

The IC is not the main heat generation component on this PCBA, it is the mosfet underneath which is coupled to the heat sink via the heat transfer pad.

Not to say this method won’t work, but replacing the thermal pad with a higher thermal conductivity and /or cooling the heat sink will be more effective, and you may not need a fan.

Might you have a specific recommendation for a higher quality thermal pad? Or other way to increase thermal conductivity on that IC?

Filippo

 

[NoGuru]

The IC is not the main heat generation component on this PCBA, it is the mosfet underneath which is coupled to the heat sink via the heat transfer pad.

Not to say this method won’t work, but replacing the thermal pad with a higher thermal conductivity and /or cooling the heat sink will be more effective, and you may not need a fan.

Which Mosfet?

 

[NoGuru]

Is this the part in question? https://www.digikey.com/product-det...ies/BTN7960BAUMA1/BTN7960BAUMA1DKR-ND/2231303

 

[fmorelli]

The IC is not the main heat generation component on this PCBA, it is the mosfet underneath which is coupled to the heat sink via the heat transfer pad.

Not to say this method won’t work, but replacing the thermal pad with a higher thermal conductivity and /or cooling the heat sink will be more effective, and you may not need a fan.

Pardon my ignorance, but I'm not tracking. The heat transfer pad is mounted directly to the bottom of the circuit board. One can see the heat being generated as it cooks the the board. I inferred from your comment that mounting a heat sink to the IC was not helpful to dissipating the heat.

The photo below is directly under the aforementioned IC.

Filippo

 

[NoQuarter]

Looks like a hot spot to me

 

[NoQuarter]

Seems the chip specs say the amps and shutdown temp should be in spec but experience and that brown spot seem to say it could be the culprit

 

[S54ca]

Pardon my ignorance, but I'm not tracking. The heat transfer pad is mounted directly to the bottom of the circuit board. One can see the heat being generated as it cooks the the board. I inferred from your comment that mounting a heat sink to the IC was not helpful to dissipating the heat.

The photo below is directly under the aforementioned IC.

Filippo

I apologize, I was mistaken. I thought I remembered there being another MOSFET on the bottom of the PCBA.

Regardless, the main heat rejection path is still through the bottom of the device. If wiring up a fan is undesirable, replacing the pad with a higher conductivity one (or even better, gap filler) will still reduce the temperature of the chip, potentially to the point where overheating no longer occurs.

 

[fmorelli]

@S54ca thanks.

We don't know the thermal conductivity of the existing pad. Would there be a way to know? Values for materials seem to be all over the place, up to 6.0 w/mk common, some stuff claims 11-17w/mk and still somewhat affordable.

Filippo

 

[ajm8127]

I've been lurking on this forum for a while, but have been in the community for many years. I was on a different forum a few years back but it devolved into a mess and most people came here. I just took a break from forums for a while. I am also an electrical design engineer so I have some insight here.

From the back of the board you can clearly see where the heat is being generated. For it to get discolored like that it is getting pretty warm. The part in question is a motor driver and that is what is going to dissipate all of the power. Pretty obvious.

Your approach to slap a heatsink on the top of the package is logical, but the thermal resistance from the package die (the silicon die inside the part where the power is being dissipated) is much lower to the board than it is to the top of the package. The part has an exposed pad under it ("pin" 8 in the datasheet) specifically to help get the heat out. You can clearly see a lot of heat is being transferred to the board. That's one of the reasons there are so many vias in the board under the driver. You can see that copper pad on the underside has no connection electrically. It is there to help transfer heat.

I would focus on transferring the heat from the board to the aluminum plate. You can see the part is already designed to do that. Heat gets transferred to the board and then through the gap pad and into the plate where there is a raised area to ensure good contact and a recessed area to prevent interference with parts on the bottom of the board. I would change out that pad with the same thickness pad with a higher thermal conductivity (W/m*k) rating.

Check digikey.com, but watch the "Usage" column. Some of the newer graphite pads are designed to conduct heat in mainly one direction (through plane vs. in plane). Also, graphite is conductive so it would be a poor choice for a PCB. I would just exclude it from the "Type" column and then sort descending by "Thermal Conductivity". Pick one of the right size and thickness.

I would also attach a large heatsink to the aluminum plate and mount the EKP upside down. Orient the fins vertically so convection currents can form. You may or may not need a fan this this solution. Use some non threaded spacers to avoid crushing the plastic case. A new bottom section made from a piece of Al with heatsink fins milled in would be best, but putting a larger heatsink on the aluminum base is second best. Use some CPU thermal compound between the plate and the heatsink along with the new thermal pad between the board the the plate as mentioned above.

Old CPU coolers look like they would be just about the right size to mount on the plate, and they already come with 12V fans. You could attach one with screws to the EKP plate. You should be able to pick up 12V through terminal 30G, the power supply to the module. I think that is switched with the ignition.

I notice the BTN7960 is discontinued. I wonder if pin-for-pin compatible parts exist that have less loss and higher continuous current specs. Those big parts are easy to replace.

[EDIT] BTN8982 replaces BTN7960, is pin for pin compatible, has lower on state resistance and has higher current carrying capabilities. https://www.infineon.com/cms/en/search.html#!view=discontinued&term=BTN7960