Root cause insight into the common BMW blower motor resistor

[Scott Dorsey]

Bimmer Owner <dontaskfor@mymail.com> wrote:

On Thu, 21 Mar 2013 09:47:31 -0400, Scott Dorsey wrote:

I don't see why it is so hard to unpot one of these things and repair them
directly, especially if it's a semiconductor failure.
Put a bigger transistor in there.

Here are pictures from the last half dozen who tried that approach:
http://www2.picturepush.com/photo/a/12470740/img/12470740.jpg
http://www4.picturepush.com/photo/a/12470742/img/12470742.jpg
http://www2.picturepush.com/photo/a/12470745/img/12470745.jpg
http://www4.picturepush.com/photo/a/12470747/img/12470747.jpg
http://www5.picturepush.com/photo/a/12470748/img/12470748.jpg
http://www2.picturepush.com/photo/a/12470750/img/12470750.jpg

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.

One problem with "put a bigger xtor" is that nobody on this planet
has produced a decent circuit diagram of the FSU.

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

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

 

[Scott Dorsey]

Bimmer Owner <dontaskfor@mymail.com> wrote:

On Thu, 21 Mar 2013 11:45:54 -0400, Scott Dorsey wrote:

Static resistance doesn't tell you anything, but operating current
measured with a DMM would tell you a lot.

It 'can' be done, but would require a test jig inserted inline
as the FSU is deeply ensconced under the dash while the blower motor
is even more deeply so.

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.

I've never tested one, but I put a drop of turbine oil on the
motor bearings every five years or so.

While that preventive work might be prudent, the sheer effort
to remove the entire dash simply to access the blower motor
would be problematic.

Well, that's partly why I drive a 2002 and an E28, everything is much
easier to get to.

Still, if the problem is that the blower motor is merely using more
current as it gets older, why wouldn't a NEW FSU burn up within a
few weeks of insertion?

You would expect that, indeed.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

 

[tm]

"Scott Dorsey" <kludge@panix.com> wrote in message
news:kifmfo$7l$1@panix2.panix.com...

Bimmer Owner <dontaskfor@mymail.com> wrote:
On Thu, 21 Mar 2013 11:45:54 -0400, Scott Dorsey wrote:

Static resistance doesn't tell you anything, but operating current
measured with a DMM would tell you a lot.

It 'can' be done, but would require a test jig inserted inline
as the FSU is deeply ensconced under the dash while the blower motor
is even more deeply so.

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.

Just measure the battery current with and without the blower running.

Turn every thing else off.


QED

 

[Ashton Crusher]

On Thu, 21 Mar 2013 16:00:13 +0000 (UTC), Bimmer Owner
<dontaskfor@mymail.com> wrote:

On Thu, 21 Mar 2013 08:14:12 -0700, jim beam wrote:

it's cheaper to just buy a new one.

To be clear, that's what 99.99999999% of the BMW owners do.
But that's not the point of this thread.

The point of this thread is to get a handle on WHY they are all
failing.

Specifically, how to figure that out is the question.

The simple answer is that they are under-designed for the conditions
under which they apparently are regularly subject to.

 

[Ashton Crusher]

On Thu, 21 Mar 2013 15:22:42 +0000 (UTC), Bimmer Owner
<dontaskfor@mymail.com> wrote:

On Thu, 21 Mar 2013 03:55:47 -0700, the will wrote:

Blower motor drawing too much amperage taking it out.
Change the blower motor anytime?

This is an interesting approach, given that the vast majority of
bimmer owners do NOT replace the blower motor - they replace the FSU.

While the blower motor replacement procedure is a major PITA, one
'can' test the leads from the FSU harness connector pins #5 and #1
which are power and ground respectively to the blower motor.

Again, we don't have a circuit diagram, but it has been said that
the blower motor takes about 6 amps (variously, depending on the speed)
but it would take a test jig to test that in operation.

To my knowledge, nobody has created that test jig (although I know
of only one attempt, which failed):
http://www.bimmerfest.com/forums/showthread.php?t=678534&highlight=fsu

It's easy enough to test the resistance of the blower motor though,
and those results have come out at about 0.4 to 0.6 ohms.

It would be expensive to change a blower motor on a whim, so, how
would YOU suggest the blower motor be tested in situ?

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.

 

[Bimmer Owner]

On Thu, 21 Mar 2013 16:59:01 -0400, tm wrote:

Just measure the battery current with and without the blower running.
Turn every thing else off.

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?

 

Followups set to sci.electronics.repair .

In sci.electronics.repair Bimmer Owner <dontaskfor@mymail.com> wrote:

Does anyone have insight into what is the root cause (and repair) of
the FSU failure that plagues almost every 1997 to 2003 BMW?

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.

Also, does anyone have an idea HOW TO TEST a "repaired" FSU?

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.

The problem with replacing this ~$100 part is that the new replacement
FSU fries itself just as often as the old one did, so you end up
repeatedly replacing your fried FSU every few years or so.

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

 

[Bimmer Owner]

On Thu, 21 Mar 2013 15:03:45 -0700, Ashton Crusher wrote:

If it's being blown by intermittent high current draws the
fuse could protect the $100 FSU.

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).

 

[Bimmer Owner]

On Thu, 21 Mar 2013 21:56:49 +0000, mroberds wrote:

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.

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.

 

On Thu, 21 Mar 2013 16:59:01 -0400, "tm" <No_one_home@white-house.gov>
wrote:

"Scott Dorsey" <kludge@panix.com> wrote in message
news:kifmfo$7l$1@panix2.panix.com...
Bimmer Owner <dontaskfor@mymail.com> wrote:
On Thu, 21 Mar 2013 11:45:54 -0400, Scott Dorsey wrote:

Static resistance doesn't tell you anything, but operating current
measured with a DMM would tell you a lot.

It 'can' be done, but would require a test jig inserted inline
as the FSU is deeply ensconced under the dash while the blower motor
is even more deeply so.

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.


Just measure the battery current with and without the blower running.

Turn every thing else off.


QED
Just put your ammeter into the heater blower fuse connector and you

get the current of the blower motor.

 

[tm]

"Bimmer Owner" <dontaskfor@mymail.com> wrote in message
news:kig343$pdf$2@news.albasani.net...

On Thu, 21 Mar 2013 15:03:45 -0700, Ashton Crusher wrote:

If it's being blown by intermittent high current draws the
fuse could protect the $100 FSU.

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).

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

 

[Mark]

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.

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

 

[Bimmer Owner]

On Thu, 21 Mar 2013 15:16:46 -0400, Scott Dorsey wrote:

there are two TO-3 devices there which have been removed
in all of those photos.

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.

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

Focusing just on that Elmos Semiconductor AG IC from this thread:
http://www.bimmerfest.com/forums/showthread.php?t=309399
It looks like the PN is ELMOS, 10901D, 667A 1302A

It might be a generic or a special chip; I can't find it on the web:
http://www.elmos.com/produkte/automotive/motor-control/dc-motor-ics.html

 

On Thu, 21 Mar 2013 22:54:59 +0000 (UTC), Bimmer Owner
<dontaskfor@mymail.com> wrote:

On Thu, 21 Mar 2013 15:03:45 -0700, Ashton Crusher wrote:

If it's being blown by intermittent high current draws the
fuse could protect the $100 FSU.

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).
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.

 

[Bimmer Owner]

On Thu, 21 Mar 2013 21:56:49 +0000, mroberds wrote:

It may also be interesting to have some kind of thermometer
on the FSU case ...

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).

 

[trader4@optonline.net]

On Mar 21, 5:58 pm, Ashton Crusher <d...@moore.net> wrote:

On Thu, 21 Mar 2013 16:00:13 +0000 (UTC), Bimmer Owner

dontask...@mymail.com> wrote:
On Thu, 21 Mar 2013 08:14:12 -0700, jim beam wrote:

it's cheaper to just buy a new one.

To be clear, that's what 99.99999999% of the BMW owners do.
But that's not the point of this thread.

The point of this thread is to get a handle on WHY they are all
failing.

Specifically, how to figure that out is the question.

The simple answer is that they are under-designed for the conditions
under which they apparently are regularly subject to.

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.

 

[jim beam]

On 03/21/2013 12:05 PM, Scott Dorsey wrote:

In article <kif3r7$252$1@dont-email.me>, jim beam <me@privacy.net> wrote:

I don't see why it is so hard to unpot one of these things and repair them
directly, especially if it's a semiconductor failure. Put a bigger transistor
in there.

unpotting is a nightmare - it will take much less time to build your own
pwm controller. who knows, maybe you can switch the existing unit???!!!

Unpotting is fun, it's a nice change in the day to just sit down for a couple
hours with a dremel tool and a dental pick.

i'd rather repair light bulbs.

But I agree, building an aftermarket controller replacement would not be
a tremendously difficult thing to do, and it might be a highly profitable
one.

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.


--
fact check required

 

[jim beam]

On 03/21/2013 09:00 AM, Bimmer Owner wrote:

On Thu, 21 Mar 2013 08:14:12 -0700, jim beam wrote:

it's cheaper to just buy a new one.

To be clear, that's what 99.99999999% of the BMW owners do.
But that's not the point of this thread.

The point of this thread is to get a handle on WHY they are all
failing.

i already told you - it's overheating. semiconductors don't like heat.

Specifically, how to figure that out is the question.

knowing how the light bulb blew doesn't fix it.


--
fact check required

 

[trader4@optonline.net]

On Mar 21, 8:08 pm, cl...@snyder.on.ca wrote:

On Thu, 21 Mar 2013 22:54:59 +0000 (UTC), Bimmer Owner

dontask...@mymail.com> wrote:
On Thu, 21 Mar 2013 15:03:45 -0700, Ashton Crusher wrote:

If it's being blown by intermittent high current draws the
fuse could protect the $100 FSU.

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).

  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.

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.

 

[jim beam]

On 03/21/2013 06:01 PM, trader4@optonline.net wrote:

On Mar 21, 5:58�pm, Ashton Crusher <d...@moore.net> wrote:
On Thu, 21 Mar 2013 16:00:13 +0000 (UTC), Bimmer Owner

dontask...@mymail.com> wrote:
On Thu, 21 Mar 2013 08:14:12 -0700, jim beam wrote:

it's cheaper to just buy a new one.

To be clear, that's what 99.99999999% of the BMW owners do.
But that's not the point of this thread.

The point of this thread is to get a handle on WHY they are all
failing.

Specifically, how to figure that out is the question.

The simple answer is that they are under-designed for the conditions
under which they apparently are regularly subject to.

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.

but that's not going to apply to multiple different unit manufacturers,
over long periods of time.

A better questions is why BMW apparently doesn't give a damn
to do the failure analysis to find out what's wrong.

um, because it's a profit center? either they charge you $100 for a $6
unit, or you get fed up with the vehicle and buy a new one. that latter
is the psychology of their target market.

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?

indeed - a very good point. which begs the question, if they can pwm
the aux fan, wtf can't they do it with the blower fan???

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.

bmw are designed, root and branch, to be expensive to maintain and own
after the warranty period. they spend a lot of money on r&d to achieve
that. and even more on advertising to convince their target that the
extra cost is justified for membership of the "ultimate marketing
tagline" club.


--
fact check required