Root cause insight into the common BMW blower motor resistorfailures

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).

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

>
>"Scott Dorsey" > wrote in message
...
>> Bimmer Owner > 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.

"Bimmer Owner" > wrote in message
...
> 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

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

On Mar 21, 5:58*pm, Ashton Crusher > wrote:
> On Thu, 21 Mar 2013 16:00:13 +0000 (UTC), 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.
>
> >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.

On Mar 21, 8:08*pm, wrote:
> On Thu, 21 Mar 2013 22:54:59 +0000 (UTC), Bimmer Owner
>
> > 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.

On Mar 20, 11:08*pm, Bimmer Owner > 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?
> *http://www.bimmerfest.com/forums/att...entid=126060&d...
>
> Also, does anyone have an idea HOW TO TEST a "repaired" FSU?
>
> The "blower motor resistor", which also goes by FSR (Final Stage Resistor)
> or by FSU (Final Stage Unit), is known to fry itself in almost every single
> E46 (3-series), E39 (5-series), and E38 (7-series) BMW.
> *http://www.bimmerfest.com/forums/sho...d.php?t=143393
>
> 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.
> *http://www.bimmerfest.com/forums/sho...d.php?t=528566
>
> That's fine for most people (although the DIY is a PITA) - but I ask
> this newsgroup whether anyone has any insight into WHAT is actually
> breaking - and - why?
> *http://www.bimmerfest.com/forums/sho...d.php?t=309399
>
> Here is the best (admittedly sketchy) wiring diagram we have so far:
> *http://www1.picturepush.com/photo/a/...g/12467819.png

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

On 03/21/2013 12:05 PM, Scott Dorsey wrote:
> In article >, jim beam > 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

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

On 03/21/2013 06:01 PM, wrote:
> On Mar 21, 5:58�pm, Ashton Crusher > wrote:
>> On Thu, 21 Mar 2013 16:00:13 +0000 (UTC), 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.
>>
>>> 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