Root cause insight into the common BMW blower motor resistorfailures

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...0&d=1194115994

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

On 03/20/2013 08:08 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...0&d=1194115994
>
> 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
>

that looks like a linear semiconductor controller - an incredibly
antiquated concept for a modern car.

old resistor packs for fans were open wire that sat in the fan's air
stream for cooling. they were generally very reliable if their alloy
wasn't too susceptible to salt.

that unit looks like it still sits in the air stream with that honking
great heat sink and i estimate it's trying to dissipate >100W. that can
only mean it's a linear controller because a modern pwm device can
control high motor currents with very little heat dissipation <10W.

bottom line, a linear controller is always going to get hot and end up
frying itself over time. the only thing you can do is either replace it
with another unit that will ultimately meet the same fate, or undertake
a significant modification.

for the latter, you can try putting an even bigger heat sink on it - but
i doubt there's a lot extra room available. you can also "pwm" it. i
built a similar unit to deal with a linear controller over-heat issue on
my 89 civic.

<http://www.flickr.com/photos/38636024@N00/5068043855>
<http://arduino.cc/en/Tutorial/PWM>

depending on how much time you want to spend on a project like that, pwm
can control superbly and offers benefits like motor speed not being so
susceptible to supply voltage [engine idle voltage drop] etc.

the down side of pwm is that it can generate electrical noise. [poor
stereo installations can be particularly susceptible.] the ideal
solution is to implement pwm with "soft switching", but that's getting
quite advanced.


--
fact check required

On 03/20/2013 09:13 PM, jim beam wrote:
> On 03/20/2013 08:08 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...0&d=1194115994
>>
>>
>> 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
>>
>
> that looks like a linear semiconductor controller - an incredibly
> antiquated concept for a modern car.

well, you live and learn. apparently the reason they use a linear
controller is because it allows the fan to run near silently at low
speed. with pwm control the fluctuating magnetic fields in the motor
coils cause it to vibrate and make a humming noise at the pwm control
frequency.

that doesn't of course get around the fact that the unit in question
here is apparently badly under rated, but the above does at least
explain why it's used.


>
> old resistor packs for fans were open wire that sat in the fan's air
> stream for cooling. they were generally very reliable if their alloy
> wasn't too susceptible to salt.
>
> that unit looks like it still sits in the air stream with that honking
> great heat sink and i estimate it's trying to dissipate >100W. that can
> only mean it's a linear controller because a modern pwm device can
> control high motor currents with very little heat dissipation <10W.
>
> bottom line, a linear controller is always going to get hot and end up
> frying itself over time. the only thing you can do is either replace it
> with another unit that will ultimately meet the same fate, or undertake
> a significant modification.
>
> for the latter, you can try putting an even bigger heat sink on it - but
> i doubt there's a lot extra room available. you can also "pwm" it. i
> built a similar unit to deal with a linear controller over-heat issue on
> my 89 civic.
>
> <http://www.flickr.com/photos/38636024@N00/5068043855>
> <http://arduino.cc/en/Tutorial/PWM>
>
> depending on how much time you want to spend on a project like that, pwm
> can control superbly and offers benefits like motor speed not being so
> susceptible to supply voltage [engine idle voltage drop] etc.
>
> the down side of pwm is that it can generate electrical noise. [poor
> stereo installations can be particularly susceptible.] the ideal
> solution is to implement pwm with "soft switching", but that's getting
> quite advanced.
>
>


--
fact check required

>> that looks like a linear semiconductor controller - an incredibly
>> antiquated concept for a modern car.

>well, you live and learn. apparently the reason they use a linear
>controller is because it allows the fan to run near silently at low
>speed. with pwm control the fluctuating magnetic fields in the motor
>coils cause it to vibrate and make a humming noise at the pwm control
>frequency.

>that doesn't of course get around the fact that the unit in question
>here is apparently badly under rated, but the above does at least
>explain why it's used.

I see many Motor Speed Control Manufacturers upped their PWM
frequency to be between 16 K to 22 K to eliminate much of the noise.
Mikek

"amdx" > wrote in message
...
> >> that looks like a linear semiconductor controller - an incredibly
> >> antiquated concept for a modern car.
>
> >well, you live and learn. apparently the reason they use a linear
> >controller is because it allows the fan to run near silently at low
> >speed. with pwm control the fluctuating magnetic fields in the motor
> >coils cause it to vibrate and make a humming noise at the pwm control
> >frequency.
>
> >that doesn't of course get around the fact that the unit in question here
> >is apparently badly under rated, but the above does at least explain why
> >it's used.
>
> I see many Motor Speed Control Manufacturers upped their PWM frequency
> to be between 16 K to 22 K to eliminate much of the noise.
> Mikek

That would also make the LPF very much smaller.

Even going to 40 to 60 kHz makes the magnetics smaller. We still do not know
what is under the PCB for that unit.

tm

amdx wrote:

> >> that looks like a linear semiconductor controller - an incredibly
> >> antiquated concept for a modern car.
>
> >well, you live and learn. apparently the reason they use a linear
> >controller is because it allows the fan to run near silently at low
> >speed. with pwm control the fluctuating magnetic fields in the motor
> >coils cause it to vibrate and make a humming noise at the pwm control
> >frequency.
>
> >that doesn't of course get around the fact that the unit in question
> >here is apparently badly under rated, but the above does at least
> >explain why it's used.
>
> I see many Motor Speed Control Manufacturers upped their PWM frequency
> to be between 16 K to 22 K to eliminate much of the noise.
> Mikek
Sure, if you don't mind heating the motor up...

Jamie

On 03/24/2013 02:30 PM, Jamie wrote:
> amdx wrote:
>
>> >> that looks like a linear semiconductor controller - an incredibly
>> >> antiquated concept for a modern car.
>>
>> >well, you live and learn. apparently the reason they use a linear
>> >controller is because it allows the fan to run near silently at low
>> >speed. with pwm control the fluctuating magnetic fields in the
>> motor >coils cause it to vibrate and make a humming noise at the pwm
>> control >frequency.
>>
>> >that doesn't of course get around the fact that the unit in question
>> >here is apparently badly under rated, but the above does at least
>> >explain why it's used.
>>
>> I see many Motor Speed Control Manufacturers upped their PWM
>> frequency to be between 16 K to 22 K to eliminate much of the noise.
>> Mikek
> Sure, if you don't mind heating the motor up...
>
> Jamie
>

good point - how much? sure, big motor coils, big inductors -so how to
balance against pulse frequency for a bigger motor like a blower fan?


--
fact check required

On 03/24/2013 08:52 AM, amdx wrote:
> >> that looks like a linear semiconductor controller - an incredibly
> >> antiquated concept for a modern car.
>
> >well, you live and learn. apparently the reason they use a linear
> >controller is because it allows the fan to run near silently at low
> >speed. with pwm control the fluctuating magnetic fields in the motor
> >coils cause it to vibrate and make a humming noise at the pwm control
> >frequency.
>
> >that doesn't of course get around the fact that the unit in question
> >here is apparently badly under rated, but the above does at least
> >explain why it's used.
>
> I see many Motor Speed Control Manufacturers upped their PWM
> frequency to be between 16 K to 22 K to eliminate much of the noise.
> Mikek

interesting.


--
fact check required

In article >, jim beam > wrote:
>
>well, you live and learn. apparently the reason they use a linear
>controller is because it allows the fan to run near silently at low
>speed. with pwm control the fluctuating magnetic fields in the motor
>coils cause it to vibrate and make a humming noise at the pwm control
>frequency.

Yes, this is why you put an integrator stage after the pwm stage, so that
the motor sees nice filtered DC with very little of the PWM leftover.

Problem is that the integrator stage costs money and big electrolytics
tend to have limited life, so auto folks don't like doing that.

>that doesn't of course get around the fact that the unit in question
>here is apparently badly under rated, but the above does at least
>explain why it's used.

It's a cheap, reliable way of doing the job, if it's done right. It's clear
that it wasn't done right, but I'm still waiting to hear what was done wrong.
Given all the RoHS-related failures and the report that touching up solder
joints on the transistors fixes the problem, I am suspicious that it's a
soldering issue made worse by the extreme temperature cycling.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On 03/25/2013 06:59 AM, Scott Dorsey wrote:
> In article >, jim beam > wrote:
>>
>> well, you live and learn. apparently the reason they use a linear
>> controller is because it allows the fan to run near silently at low
>> speed. with pwm control the fluctuating magnetic fields in the motor
>> coils cause it to vibrate and make a humming noise at the pwm control
>> frequency.
>
> Yes, this is why you put an integrator stage after the pwm stage, so that
> the motor sees nice filtered DC with very little of the PWM leftover.
>
> Problem is that the integrator stage costs money and big electrolytics
> tend to have limited life, so auto folks don't like doing that.

you don't want to integrate the output, merely rub the shoulders off the
square waves to get the harmonics down. the whole point and benefit of
pwm is that you have full voltage full power available in each pulse.
that's how you can start and control a motor with high torque at low
rpm. if you integrate or smooth out the motor's supply, you effectively
lose that and the motor won't start or torque the same way or even at all.


>
>> that doesn't of course get around the fact that the unit in question
>> here is apparently badly under rated, but the above does at least
>> explain why it's used.
>
> It's a cheap, reliable way of doing the job, if it's done right.

in this day and age, that's no longer true. motor control is one of the
hot ticket items on the silicon fab agenda, and has been for some time.
there are some great pwm options out there, and for not a lot of money.


> It's clear
> that it wasn't done right, but I'm still waiting to hear what was done wrong.
> Given all the RoHS-related failures and the report that touching up solder
> joints on the transistors fixes the problem, I am suspicious that it's a
> soldering issue made worse by the extreme temperature cycling.

you definitely have a point there, but given the size and shape of that
heat sink, i don't think there's any way that silicon is getting
sufficient cooling, and is clearly way up against its ceiling. whether
that's accident or design is another matter, but the bottom line is that
it's an issue that spans multiple different module manufacturers across
multiple continents with different internal designs - that reduces the
probability of it being rohs and slaps it firmly into the vehicle
manufacturer's lap.


--
fact check required