These are kind of sloppy jobs. But it's clear there are two TO-3 devices there which have been removed in all of those photos.
Well, has anyone got docs on that mystery IC there? It's from Elmos Semiconductor, but it's not a standard Elmos part number on it, so it's almost certainly a custom, since it doesn't look like anything in their standard book.
--scott
I don't know the wiring diagram on that particular model, so I don't know where you would need to break in to measure just the current of the blower without anything else. But it does not seem terribly insurmountable, especially seeing that BMW is very good about breaking everything out into connectors all over.
Well, that's partly why I drive a 2002 and an E28, everything is much easier to get to.
You would expect that, indeed.
--scott
Just measure the battery current with and without the blower running.
Turn every thing else off.
QED
That's a pretty good idea.
Of course, it's impossible to turn everything off, as the computer won't go to sleep for 16 minutes after the car is shut and armed, but, still - with the blower consuming something like 5 or 6 amps, we should be able to measure at least that.
The problem, even with the car's additional electronics powered up, is HOW MUCH of a difference are we expecting between an older blower motor current draw and a new one?
Are we looking for a 1 amp difference, for example?
At a guess, one or both of the big power transistors that are inside the FSU are failing. If the failure is that the blower motor doesn't run at all, they are probably failing open. If the failure is either that the blower motor runs at maximum speed, or a fuse blows, then they are probably failing shorted. The blower motor probably draws more current as it ages, and it may eventually be exceeding the power-handling capability of the transistor(s). When the motor is switched off, it may also generate a bit of a voltage spike, which may be above the voltage rating of the transistor(s).
A possible solution is to replace the transistor(s) with ones with a higher power rating in the same package. Another approach is to improve the heat-sinking, maybe by adding metal to the existing fins. Or, cut off the existing fins, bolt it to a huge slab of metal, and relocate the entire thing away from the blower duct.
As a crutch, you could drop the voltage to the FSU a little bit. This would slow down the blower, but also might tend to keep the voltages and currents down to what the transistors can handle. You would need to know the maximum current you would expect the FSU to draw; this probably happens when the charging system voltage is at is maximum, the blower motor is stone cold, and you turn it from "off" to "max". Then, buy a big rectifier diode with a rating of a few amps more than that, and splice it in to the power wire to the FSU. This will drop the voltage by a volt or two all the time. Or, you could put a power resistor in line instead; this will cause a variable voltage drop depending on how much power the FSU and blower is drawing at the time.
Keep in mind that in the winter, keeping the windshield clear is a safety function, so don't drop the blower speed too much.
The tricky part depends on the nature of the control signal to the FSU. If it's a simple analog voltage, that is easy to generate on the bench with a potentiometer. If it's some kind of digital bus (CAN?), it is
*possible* to generate that on the bench, but it's probably easier to get the dashboard heater control out of a junked car and let it generate the signal.To load the FSU, you can either use a power resistor that draws about the same amount of current as the blower motor on "high" (a headlight lamp might qualify), or an actual blower motor. The resistor will be "better behaved" than a real motor.
For a power supply, it depends on how much current the blower motor needs. You can get relatively inexpensive 13.8-volt power supplies in ranges up to several amps, designed for running "12 V" equipment on the bench. Samlex is one manufacturer but there are others. If it needs more than 10 A or so, it's probably cheaper to just use a real car battery and charge it when it's not being used.
You should probably arrange it so that there is some air blowing on the FSU under test. If you are using a real blower motor, you can make a duct out of cardboard. If not, use something like a 12 V computer case fan to move a little air across the FSU.
It may also be interesting to have some kind of thermometer on the FSU case while it is under test.
A good way to figure out what the FSU is actually doing is to probe a working car with an oscilloscope. This will show you immediately how the FSU is controlling the blower motor speed, as well as what the control signal looks like. You can stick a straight pin *through* the wire insulation as a test point, and then seal up the hole with electrical tape or silicone sealant.
As has been mentioned, it would be also interesting to cut one of the blower wires and measure the current drawn by the blower motor. For extra credit, do this on a new car (or a newly-installed blower motor) and then compare to a blower motor in a car that has just had its FSU fail.
On one hand, you would like stuff not to break. On the other hand, spending $100 every two or three years on a car that starts around $36,000 new is maybe not out of the realm of possibility. (Perspective: that's one tire or 25 to 30 gallons of gas.)
These cars are apparently sold worldwide. If the FSUs sell for cheaper in a lower-cost country, enough to offset shipping and taxes, import a box full of them and make money. :)
Matt Roberds
The simple answer is that they are under-designed for the conditions under which they apparently are regularly subject to.
If one replaces one of these perhaps it would be advisable to put a fuse in the blower motor lines (it sounds like those can be gotten to easily unlike the motor itself). If it's being blown by intermittent high current draws the fuse could protect the $100 FSU. Another option would be, at least for those who can live without the highest blower setting and who think excess current draw is the culprit, would be to put a power resistor in the blower motor line to limit the current a bit. On the cheap pedestrian cars I drive the whole speed control is just a trio of power resistors placed in the air flow to help cool them. If they burn out (which is rare) they can sometimes be fixed with a pop rivet.
That's an interesting idea. The FSU supposedly consumes the most power when the blower motor is set to the LOW settings (simply because it has to dissipate the power as heat), so, we could prevent excess current by fusing... say with a 10A fuse, the blower motor (which is said to consume 5 to 6 A).
Actually, I was remiss in not stating that the blower motor generally fails by acting weirdly, often said to "have a mind of its own", and, most often by a parasitic current draw overnight that kills the battery.
i guess they call replacing a simple resistor with a bunch of transistors.... "progress"
i'd replace the module with a bunch of power resistors and maybe a PTC (self resetting) fuse
Mark
Mark
I don't know what a "TO-3" device is, but nobody removed anything in those photos other than the goop that covered the circuit board.
Focusing just on that Elmos Semiconductor AG IC from this thread:
That seems like an EXCELLENT idea, if we can put some kind of temperature indicator in the FSU tines, then we can observe what the temperature is in situ - which might tell us something about what is overheating these things (assuming heat is the culprit).
Just put your ammeter into the heater blower fuse connector and you get the current of the blower motor.
Are you sure it is not already a pulse width regulator? Those transistors look like they are TO-220 packages, not TO-3. PWM has been around longer than SMT parts.
Maybe it is transients from the motor that are causing the failures.
Another place you could measure the current is by putting an ammeter in place of the blower motor fuse.
tm
So the crafty germans are using a high tech solid state resistor instead of a PWM speed controller???
If I had one and it blew I think I'd be designing a PWM controller to take it's place. Need to find out what kind of signal the controller expects, but that shouldn't be too difficult.
That isn't necessarily the case. For example,t hey could be correctly designed, rated for the application, etc but have a manufacturing defect in just one of the components.
A better questions is why BMW apparently doesn't give a damn to do the failure analysis to find out what's wrong. I have a friend who has an X5 and had this problem with the blower resistors. Even worse, the only symptom was it was draining the battery and it took a huge number of hours to track it down.
While you're all wondering about that problem, might as well add the fancy aux radiator fan to the list. This car had that go and now the replacement one has failed again. And the symptom there is, again, it drains the battery even when the car is off. That fan is a real POS. Instead of just a simple fan motor, it's a fan that's variable speed, driven by a PWM signal. So, instead of just a motor, that fan sitting in front of the hot radiator has electronics in it. A real genius of a design. And for what? Like the fan can't just be on or off? Only reason I can think of is that they want to save a few watts of power to try to get better fuel economy. And for that their customers get to shell out $500 for a new fan every few years.
The dopes at BMW aren't any better at PWM's either. They use a PWM signal to control the aux fan on the radiator. You, know, the one that comes on if the cooling temp gets too high or the AC is on, etc. Apparently just a simple on/off motor wasn't good enough. So they made another one of their German electronic miracle gadgets that's part of the fan motor. That's right, electronics sitting right next to the hot radiator.....
On the TV show All in The Family, the meathead was arguing about Nixon and Watergate with Archie. Archie told the meathead that Nixon's mistake was when it involved electronics, ie bugging, taping, etc, that he should have used the Japanese, not Germans, ie Haldeman, Ehrlichman, etc. I think Archie was on to something.
I had a dodge caravan that fried its heater AC motor speed control resistor repeatedly....
the connector to the wiring harness detoriates from the high current and the voltage drop causes the connector to heat up and the entire assembly fails.
Oddly enough I repair roll laminators that apply plastic film to paper think menus:)
laminators experience similiar failures so I did the following.
Purchased a new resistor block, soldered wires on all the connectors putting a heavy wire on each one.... Put a pigtail on each one. Installed resistor block. Its screwerd to the fire wall.
Cut the plug assembly off the harness, stripped all wires, twisted them together and installed wire nuts on each one.
had the van for years with zero problems for this part:)
i'd rather repair light bulbs.
well, it cost me about $18 in parts to retrofit the linear dash light dimmer on my civic with a pre-built arduino unit. a custom unit could come in substantially less than that, if in sufficient quantity.
i already told you - it's overheating. semiconductors don't like heat.
knowing how the light bulb blew doesn't fix it.
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