Root cause insight into the common BMW blower motor resistor failures

[Nate Nagel]

Sadly, I speak from experience, in both respects.

nate

[Bimmer Owner]

I 'think' (but I'm not sure) that these are the resistors in series:

[Bimmer Owner]

I'm still trying to figure out if there was only one or two:

[trader4]

If they are resistors, I've never seen any that look like that. Also, given that you want to thermally bond any components that generate major heat, why are they not heat sinked? With any power design I've seen, the key components, eg the transistors are directly bonded to the heat sink.

[tm]

The main points of his post, like the "two bridges that are .01 ohm resistors, that "balance" the motor don't concern you in the least?

Blind leading the blind =============================================

It is common to place low value resistors in the emitters to balance the current in two paralleled devices.

0.01 ohms would be very realistic in a 40 amp system.

As to blind, you exhibit that trait much better than anyone else involved with this thread. Asshole.

[tm]

/You said you tested the FSU alone. If so, how can you /say there is no PWM signal between the car and FSU?

/ the gates signals are continuous voltage only , this is the reason /why it heat so much its aluminium box... In fact there is no point on /the board where square signals are present. Can somebody check its own /FSU if it's the same ?

/Say what? 10 milliohms is .01 ohms. How could that /possibly balance the power to a motor in a 40 amp circuit?

Not to the motor idiot. To the transistors.

/Which makes no sense at all.

Certainly not to you.

/It seems they last at least a few years. Maybe it's like /gas. You buy it and you go so far. I think you're in way /over your head here;

But not yours?

[Michael A. Terrell]

I was never crazy about that style of heatsink.

[Michael A. Terrell]

You've never seen strips of nichrome in a space heater?

[Michael A. Terrell]

Two.

[Michael A. Terrell]

Be careful with so called information from those types of sites. Most of their information is badly translated, or just plain wrong. Tabao.com is a prime example of crap information. I have never found correct information there. Most is from chinese Ebay sellers who make things up about items they sell. They have no idea what it is, just that they can sell it on Ebay or Tabao.com.

thyristor-transistor electronic ignition unit with a long spark, ensuring the rapid start-ups at various operating conditions, allowed to increase battery life of up to nine years.

switch blades and is contactless.

designs. The controller can be used as a universal device is suitable not only for mounting on any car, but everywhere, where the generator rotor speed is variable (eg, wind power). Choose the appropriate control elements, it can be easily adapted to work with any voltage (up to 400V) and excitation current (tens of amperes).

[Jamie]

currents between the 2 MOSFET and balance the power also. The mesure of the DC voltage on those resistors can be used to evaluate the current of the blower and its worn state.

Resistors are used in the emitter path when combining two or more to the same circuit. This is needed to insure both transistors share in the load when it comes to biasing... Otherwise, you'll get one that favors beta and the other will sit back and snooze. Call it a ballast R if you wish.. These R values are generally low.

Jamie

[Jamie]

Yup, and I see the legs of the transistors (two). So those R's are in line with the emitters where they joint.

Most likely thermo stress cracks due to the potting restraint.

Jamie

[Jamie]

THey make power resistors in T0-220 style cases, for heat sink mounting however, I doubt those are that.

Jamie

[trader4]

No, because I'm not the one trying to reverse engineer an electronics module in a car, that contains among other things, an unknown 16 pin chip, without benefit of any of the necessary tools. You guys don't even know what the interface to the car is, whether it's analog or digital, etc. And you don't even have an oscilloscope to look at anything with.

Oh, BTW, if you're all so smart, how come I was the first one to find out for you that the 16 pin chip number you had is a vaild one for a real chip?

[Scott Dorsey]

Bosch has done the nichrome insert power resistor for many years; I know that they used them in the turn signal flasher in the late seventies when they first went electronic. They aren't really very good resistors but they are very cheap.

--scott

[Scott Dorsey]

Okay, there is a TO-220 package that is split open there, with the backplate on the right and the cover on the left. Can you chip off enough of the araldite from the cover to be able to read the numbers on it?

Or, could you get a good picture of the die which is left on the piece on the right? We might be able to identify it with a sharp photo of the die... although from what I can see from the fuzzy photo it does not look like a very happy die.

If it is actually a MOSFET it will look like this:

(That's a package that is a little bigger than the TO-220, but you can still see the channel down the middle of the FET and the overheating damage to the source.... the three leads have been torn off in the unpotting process though.)

--scott

[Bimmer Owner]

Other people have suggested this also.

Some say the potting is what is causing the stress cracks.

Re-insert without potting, is the "said to be" solution.

One question: If the FSU works without potting, what was the purpose of the potting?

[Bimmer Owner]

I will try this morning. (I was away on a trip for the past two days).

PS: Had to look up araldite:

[Bimmer Owner]

The red jumper was a hack added by one user to fix the solder cracks, I think.

[Bimmer Owner]

This implies two transistors (although I only found one).

I will dig through the mess again - but I think I was too fat thumbed when I cut it open, and may have destroyed the evidence.

I do have a second FSU (since two failed on me) though ... but I want to try to FIX that one (instead of destroying it).