bison
Well-Known Member
They are yapping about a new improved PMD on the place,go have a look.
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New re engineered flight system PMD
- Thread starter bison
- Start date
Woody35
Active Member
i saw that. intersting stuff
Brooklyn Tow
9 11 Never Forget
For the sake of all the BANNED members.....Whats the skinny?
bison
Well-Known Member
I let some one else link the tread in.
I don't know how to do that.
I don't know how to do that.
ak diesel driver
6.5 driver
supposedly the electronic noise that the transistors generate kill it and the new ones are supposed to stop that
Woody35
Active Member
mods feel free to delete this if this is against the rules.
Hey guys,
I recently had the privilege of helping the development process for a new PMD design. The company that I worked for is the same company that sells to dipaco, kieth, dorman, GM, and the rest of the smaller shops that supply PMD's, they're all the same.
The previous design as you all know had a lot of flaws. The new design is far superior. Contrary to popular belief, most of the failure issues were due to noise. Heat definitely helped this, but was not the root cause of the failure modes (especially run-away motor conditions). The main problems with the design of the PMD with the MJ15004 Transistors is that the transistor's collectors are common to their housing. This means that if they are mounted in the heat sink without the isolation pads, the heat sink cannot touch Vehicle ground or a short from (battery +) to ground will occur. This is why there is an isolation pad from the transistors to the heat sink and also as an extra safe guard, another isolation pad from the PMD heat sink to the remote heat sink (or pump) and anodizing on the PMD heat sink.
Because of this design, there is a lot of EMI generated on the heat sink from the high switching currents of the transistors. This creates noise in the whole system that otherwise would be mitigated if the heat sink were grounded. These high noise levels reduce the signal to noise ratio in the logic chips inside of the PMD.
The new design uses most of the same components, and is in the same housing, you wont be able to visually tell the difference without popping the lid off or bench testing it. The component grouping and the noise suppressing method is a lot better in the new design. The new design has passed multiple conditions that would otherwise have failed in the previous design.
I have played with, ripped apart, built hundreds of PMDs and did hundreds of miles of vehicle testing and I must say the new design is about as good as its going to get using those transistors. The overall design is a very challenging electrical problem, in most electrical systems you would suppress inductive noise (switching noise from the fuel solenoid), but in this scenario we are measuring the noise as a guarantee that the solenoid closed and sending this feed back signal back to the PCM so it knows how long the solenoid took to close.
I have been using this forum for some research and as an automotive enthusiast I know that if you are going to buy a new PMD you want the best one out there for your truck so I figured I'd let you guys know first.
thanks,
-hxtasy
and his responce to some questions
Originally Posted by Bison
Same loaf of bread in a diff bag will still be the same loaf.
What exactly would be different from the old style??
Why use the same PMD size and not going bigger and incorporate a remote mounted isolated heatsink to both tackle the heat and as you say noise.?
No it's a different loaf of bread in the same bag. To sell to GM, Dorman and et cetera so they can do OEM replacement it has to meet certain dimensions and performances.
The old design doesn't work correctly at certain frequencies, but you would not notice this in your truck because it is only under certain conditions that the PCM would send this signal (any frequnecy higher than 240 hz which is around 3krpm on the solenoid that is less than 50% duty cycle), You would be getting incorrect fuel timing with the old PMD. You can see this during a bench test and see that the new design does not have this problem. This is an indication that there is too much noise on the control signal of the IC inside of the PMD. this is evident in every PMD, the ones that fail are the ones that just have this noise problem worse.
Bigger is not better, a Standard MOSFET transistor you could get today could handle more current and have lower internal resistance (less heat), weigh less, and cost less than both of the BJT's in the current design. With the MOSFET though you would lose your feedback signal to the PCM.
I've already designed MOSFET PMD's and thought about using optical isolation to measure the reverse inductive kick, but it's just not going to be incorporated in production that is for older engines when company's already have the tooling made to bang out thousands of these PMD housings/parts a week; especially when the majority of the units out there work fine.
All the feedback circuitry does is tell you when your solenoid is going bad, it's really not worth having it in there because of all the electrical noise it creates but that is the specification that GM decided to have.
Hey guys,
I recently had the privilege of helping the development process for a new PMD design. The company that I worked for is the same company that sells to dipaco, kieth, dorman, GM, and the rest of the smaller shops that supply PMD's, they're all the same.
The previous design as you all know had a lot of flaws. The new design is far superior. Contrary to popular belief, most of the failure issues were due to noise. Heat definitely helped this, but was not the root cause of the failure modes (especially run-away motor conditions). The main problems with the design of the PMD with the MJ15004 Transistors is that the transistor's collectors are common to their housing. This means that if they are mounted in the heat sink without the isolation pads, the heat sink cannot touch Vehicle ground or a short from (battery +) to ground will occur. This is why there is an isolation pad from the transistors to the heat sink and also as an extra safe guard, another isolation pad from the PMD heat sink to the remote heat sink (or pump) and anodizing on the PMD heat sink.
Because of this design, there is a lot of EMI generated on the heat sink from the high switching currents of the transistors. This creates noise in the whole system that otherwise would be mitigated if the heat sink were grounded. These high noise levels reduce the signal to noise ratio in the logic chips inside of the PMD.
The new design uses most of the same components, and is in the same housing, you wont be able to visually tell the difference without popping the lid off or bench testing it. The component grouping and the noise suppressing method is a lot better in the new design. The new design has passed multiple conditions that would otherwise have failed in the previous design.
I have played with, ripped apart, built hundreds of PMDs and did hundreds of miles of vehicle testing and I must say the new design is about as good as its going to get using those transistors. The overall design is a very challenging electrical problem, in most electrical systems you would suppress inductive noise (switching noise from the fuel solenoid), but in this scenario we are measuring the noise as a guarantee that the solenoid closed and sending this feed back signal back to the PCM so it knows how long the solenoid took to close.
I have been using this forum for some research and as an automotive enthusiast I know that if you are going to buy a new PMD you want the best one out there for your truck so I figured I'd let you guys know first.
thanks,
-hxtasy
and his responce to some questions
Originally Posted by Bison
Same loaf of bread in a diff bag will still be the same loaf.
What exactly would be different from the old style??
Why use the same PMD size and not going bigger and incorporate a remote mounted isolated heatsink to both tackle the heat and as you say noise.?
No it's a different loaf of bread in the same bag. To sell to GM, Dorman and et cetera so they can do OEM replacement it has to meet certain dimensions and performances.
The old design doesn't work correctly at certain frequencies, but you would not notice this in your truck because it is only under certain conditions that the PCM would send this signal (any frequnecy higher than 240 hz which is around 3krpm on the solenoid that is less than 50% duty cycle), You would be getting incorrect fuel timing with the old PMD. You can see this during a bench test and see that the new design does not have this problem. This is an indication that there is too much noise on the control signal of the IC inside of the PMD. this is evident in every PMD, the ones that fail are the ones that just have this noise problem worse.
Bigger is not better, a Standard MOSFET transistor you could get today could handle more current and have lower internal resistance (less heat), weigh less, and cost less than both of the BJT's in the current design. With the MOSFET though you would lose your feedback signal to the PCM.
I've already designed MOSFET PMD's and thought about using optical isolation to measure the reverse inductive kick, but it's just not going to be incorporated in production that is for older engines when company's already have the tooling made to bang out thousands of these PMD housings/parts a week; especially when the majority of the units out there work fine.
All the feedback circuitry does is tell you when your solenoid is going bad, it's really not worth having it in there because of all the electrical noise it creates but that is the specification that GM decided to have.
ak diesel driver
6.5 driver
especially when the majority of the units out there work fine.
for a time
for a time
bison
Well-Known Member
You and i took these transistors apart.What did you find?
I found there is bugger all under that cover,a 3/16 or so tiny square plate stuck to the transistor base plate with two itty bitty thin tin(solder) strands running to the pins.
Wouldn't take much vibration or heat to melt these strands me thinks.Yet the 4 transistors i opened up looked all intact.
ak diesel driver
6.5 driver
mine acted like it was soldered to the plate. I couldn't find/see the thin strips your talking about
btfarm
America First!
Very interesting that the guy comes out of nowhere and has the long sought solution in hand.:skep:
ak diesel driver
6.5 driver
my thoughts too I actually sent an email to FS to see what they had to say
Crankme69
New Member
X3 I'm hoping though ... 
great white
Well-Known Member
Hey Simon, how did you get the potting compound off?
I popped the cover off a bad PMD and it's all a hardened epoxy like compound.
I've seen potting compound before, but not like this...
ak diesel driver
6.5 driver
I took a screwdriver and a hammer to mine. wasn't pretty but Simon thought I did a cleaner job than he did
ak diesel driver
6.5 driver
great white
Well-Known Member
You would think their distributors would hear news like this first. I hope its true that they are fixed because I won't buy another one until they have some history behind them again. i swore by FS at first, but when run away engines are cause by their part I don't want anything to do with it.
Got a link to the DP post?
Got a link to the DP post?
bison
Well-Known Member
Perhaps you pulled the pins out of the transistor when you pried them off,taking the strands with it!
I see if i still can find mine and take a pic.
i have a bit trouble understanding how these transistors are suppose to transfer heat to the base or the heat sink anyway.
There's an insulation pad between the transistors and the base and then originally a plastic cover over it on the outside and than an air pocket surrounding it completely.
The 2 pins are insulated from the base as are the 2 bolts holding it.
If anything else it looks like they realy tried to make them contain the heat instead!.?
btfarm
America First!
buddy
Active Member
The transistors have to be isolated from the sink, because the case of the transistor is the collector connection that sends power to the Fuel Solenoid.
They went overboard I think then also trying to isolate the sink by annodizing it and providing a non-conductive gasket. This made the PMD insulate all the EMI inside of itself. The sink is isolated, and we would do better to ground it.
Someone mentioned that Heath machines the plates flat, but do they also machine the PMD sink surface smooth? If so, I would guess that ditching the annodized coating and letting all the EMI disipate through the aluminum plate and out is part of his success.
I plan to sand the coating off the one on my truck and see how it goes. Been living 4 years now, see how much longer.
I think these components are not that susceptable to heat, so just keeping the sink cool can remove heat from the whole internals to make it happy enough.
They went overboard I think then also trying to isolate the sink by annodizing it and providing a non-conductive gasket. This made the PMD insulate all the EMI inside of itself. The sink is isolated, and we would do better to ground it.
Someone mentioned that Heath machines the plates flat, but do they also machine the PMD sink surface smooth? If so, I would guess that ditching the annodized coating and letting all the EMI disipate through the aluminum plate and out is part of his success.
I plan to sand the coating off the one on my truck and see how it goes. Been living 4 years now, see how much longer.
I think these components are not that susceptable to heat, so just keeping the sink cool can remove heat from the whole internals to make it happy enough.