• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

PMD and a heatsink

D

D2 Cat

Member
Messages
190
Reaction score
0
Location
south of Kansas City
My understanding is the PMD generates heat and without dissipating it early failure results. With the PMD in the original position the engine heat adds to the problem. So the solution is to relocate the PMD to a cooler place, and part of the solution is to include an aluminum heat dissipater.

So, when I look at a PMD the power transistors are counter sunk in the back of the housing a little bit. My understanding is the case of the transistors functions as an integral part of the transistor and should not contact another surface.(That's why they are countersunk) The transistors generate the excess heat.

The heat sink I have seen are a flap piece with the cooling fins on the opposite side of where the PMD is mounted. And the PMD is mounted with specific heat transferring substances.

My question is: Wouldn't it be much more effective if the heat sink had two open spaces to match the case of the two power transistors to allow the heat to escape to the open air? Not to contain it and transfer it to the aluminum to dissipate?

Just doesn't make sense to contain that heat.

If the PMD is located behind the license plate without a heat sink the hottest air passing it would be about 110 deg. in Kansas. Why does that even need a heat sink?
 
Well you could try it with no heat sink and get back to us! that would cost you the price of a PMD.

Or you could just go with us,, who have figured out that a heat sink, and getting it out of the engine bay is THE way to go. My truck has run in 100F temps for a few hours and when I stopped, I reached in the bumper area and touched the PMD and heat sink, only to find it at the same temp as the bumper itself.
It's not so much the heat the PMD makes on it's own that kills it, as it is the heatsoak, that occurs after you shutdown you engine, and it sit's in that hot valley with engine temp of 200F plus turbo and exhaust manifold temps slowly soaking in the PMD,,with out the cooling effect of the fuel running behind the unit to cool it from the IP.

So stop over thinking something that has been thought out and tested, and get yourself a heat sink, extenstion cable, and mount that bad boy in the bumper area and forget about lt!
 
Here's a thought: when you boil a pan of water, does the pan touch the stove or have an air space between the burner and the pan? (thinking electric stove here guys) So if the PMD is like the burner, it will heat the heat sink faster if touching it, than by convection. The PMD needs to get rid of it's heat and it's more efficient via the heat sink than via air cooling. Then when you stop, it's got 0 to minimal cooling from ambient air with no flow.
 
D2 Cat said:
My understanding is the PMD generates heat and without dissipating it early failure results. With the PMD in the original position the engine heat adds to the problem. So the solution is to relocate the PMD to a cooler place, and part of the solution is to include an aluminum heat dissipater.

So, when I look at a PMD the power transistors are counter sunk in the back of the housing a little bit. My understanding is the case of the transistors functions as an integral part of the transistor and should not contact another surface.(That's why they are countersunk) The transistors generate the excess heat.

The heat sink I have seen are a flap piece with the cooling fins on the opposite side of where the PMD is mounted. And the PMD is mounted with specific heat transferring substances.

My question is: Wouldn't it be much more effective if the heat sink had two open spaces to match the case of the two power transistors to allow the heat to escape to the open air? Not to contain it and transfer it to the aluminum to dissipate?

Just doesn't make sense to contain that heat.

If the PMD is located behind the license plate without a heat sink the hottest air passing it would be about 110 deg. in Kansas. Why does that even need a heat sink?
Click to expand...

Those are 2 500 Watt transistors. I believe without any form of cooling, Heatsync, or Diesel fuel Original spot on the IP, It starts to smoke within minutes.
 
Pruittx2 said:
WTF is that about? :icon_bs:
Click to expand...

Its about If you don't ask or try, you don't learn. At least he's asking 1st and not pulling my stunts of finding out after-the-fact that you've learned a lesson the hard way. "Hey, watch this!"

Good answers by the way. It is about heat transferance and protection of the FSD. As has been said, the contrurction of the things is to help disapate the heat from the PMD to the the large flat surface on the IP being cooled by the fuel running through it. Sealing the unit to the flat surface provides weather protection to the electonic components.

Heat soak being the real issue once the engine is off and fuel flow stops, the large flat surface has to be replaced for the heat to transfer to and provide protection to the FSD now that it is off the pump. A large surface like the lisence plate sized aluminum pieces or the finned heatsinks do just that. Metal is an excellent conductor of heat and the "outside" air passing over the surfaces helps dispate it at a faster rate. 120 degrees of AZ heat is nothing compared to the underhood temps.
Putting my hand on my FSD cooler (finned heat sink with fins in the air behind bumper) in the summer time is much more pleasant than putting my hand on the top of my hood while bending down to check the FSD):h.

Hope this helps.
 
D2 Cat said:
Why didn't Columbus fall off the edge of the earth?

Why do we have airplanes?

How did Roger Bannister ever run a 3;59 mile?
Click to expand...


No reason to risk falling off the edge of the planet if the territory has been explored before, I wasn't the 1st, I came to the 6.5 dirver failiure world with the same musings and ran some experiments to better understand it :

http://www.thetruckstop.us/forum/showthread.php?t=11442

Bill Heath put his solution into place when these 1st came out, BETA cmae out with the 1st finned solutions after that, DSG and others carry that solution, SSD copied it, (not effective IMO) as those were still underhood solutions.

Out of engine bay is where this driver module needs to be wnat to build you own sink design have at let us know how you make out with it, my 1st Heath driver is still installed going into year 7 soon, so far no others have reported that level of longevity that I recall.
 
The answer is the same to the question:

Why a CPU needs a heatsink? Why don't we put the CPU in the bumper of a truck without a heatsink?

PMD is a primitive form of CPU with 2 transistors while a CPU have millions.
 
You must log in or register to reply here.
Back
Top