Root cause insight into the common BMW blower motor resistorfailures

>> 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

On Sun, 24 Mar 2013 02:28:00 -0400, "Michael A. Terrell"
> wrote:

>
wrote:
>>
>> On Sat, 23 Mar 2013 22:27:41 -0400, "Michael A. Terrell"
>> > wrote:
>>
>> >
>> wrote:
>> >>
>> >> On Fri, 22 Mar 2013 04:31:00 +0000 (UTC), Bimmer Owner
>> >> > wrote:
>> >>
>> >> >On Thu, 21 Mar 2013 20:01:20 -0400, clare wrote:
>> >> >
>> >> >> Just put your ammeter into the heater blower fuse connector and you
>> >> >> get the current of the blower motor.
>> >> >
>> >> >That's an interesting idea.
>> >> > http://www3.picturepush.com/photo/a/...g/12475041.jpg
>> >> >
>> >> >The fuse for the blower motor is called the "infamous F76" for a reason.
>> >> > http://bimmerfest.com/forums/showthread.php?t=674612
>> >> >
>> >> >It's a 40 amp fuse under the glovebox but it's in a really inaccessible
>> >> >spot; however, it's right side up, so, the wires going INTO it are
>> >> >visible from the tips of your feet under the glove box.
>> >> >
>> >> >So that's a possibility; but you'd have to cut the wires.
>> >> > http://www5.picturepush.com/photo/a/...g/12475043.jpg
>> >> Why would you have to cut the wires????
>> >> Simply remove the fuse and connect the ammeter. You guys make your
>> >> lives so difficult
>> >
>> >
>> > Take a blown fuse and use it for a test connector with a cheap
>> >50-0-50A meter. Then you can just plug it in in place of the fuse to
>> >make the test. You won't even have to worry about the polarity. You
>> >can use a high current shunt, & a digital meter if you want more
>> >accuracy.
>> Or just get the special tester that is made to plug into the
>> fuseblock. Autel makes the MX101 and 201 (10 amp and 20 amp) units for
>> the lighter duty stuff.
>
>
> Is that cheaper than roll your own?
Definitely not, if you already have a multimeter - but it is easier
for the guys who can't figure out how to do it without butchering the
wiring harness.

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

wrote:
>
> On Sun, 24 Mar 2013 02:28:00 -0400, "Michael A. Terrell"
> > wrote:
>
> >
> wrote:
> >>
> >> On Sat, 23 Mar 2013 22:27:41 -0400, "Michael A. Terrell"
> >> > wrote:
> >>
> >> >
> >> wrote:
> >> >>
> >> >> On Fri, 22 Mar 2013 04:31:00 +0000 (UTC), Bimmer Owner
> >> >> > wrote:
> >> >>
> >> >> >On Thu, 21 Mar 2013 20:01:20 -0400, clare wrote:
> >> >> >
> >> >> >> Just put your ammeter into the heater blower fuse connector and you
> >> >> >> get the current of the blower motor.
> >> >> >
> >> >> >That's an interesting idea.
> >> >> > http://www3.picturepush.com/photo/a/...g/12475041.jpg
> >> >> >
> >> >> >The fuse for the blower motor is called the "infamous F76" for a reason.
> >> >> > http://bimmerfest.com/forums/showthread.php?t=674612
> >> >> >
> >> >> >It's a 40 amp fuse under the glovebox but it's in a really inaccessible
> >> >> >spot; however, it's right side up, so, the wires going INTO it are
> >> >> >visible from the tips of your feet under the glove box.
> >> >> >
> >> >> >So that's a possibility; but you'd have to cut the wires.
> >> >> > http://www5.picturepush.com/photo/a/...g/12475043.jpg
> >> >> Why would you have to cut the wires????
> >> >> Simply remove the fuse and connect the ammeter. You guys make your
> >> >> lives so difficult
> >> >
> >> >
> >> > Take a blown fuse and use it for a test connector with a cheap
> >> >50-0-50A meter. Then you can just plug it in in place of the fuse to
> >> >make the test. You won't even have to worry about the polarity. You
> >> >can use a high current shunt, & a digital meter if you want more
> >> >accuracy.
> >> Or just get the special tester that is made to plug into the
> >> fuseblock. Autel makes the MX101 and 201 (10 amp and 20 amp) units for
> >> the lighter duty stuff.
> >
> >
> > Is that cheaper than roll your own?
> Definitely not, if you already have a multimeter - but it is easier
> for the guys who can't figure out how to do it without butchering the
> wiring harness.


That type shouldn't be allowed to own any tools. They generally do
more damage than good. If they do get something to work, it rarely lasts
because they have no clue what because the problem.

I've seen too many vehicles that some idiot cut and patched back
together. One stepvan I bought years ago had a damaged harness and I
talked them down almost $1000 on the price. It was coming off lease
from a fleet, and they wanted to fix it themselves. i pointed out that
if they could repair it properly, it wouldn't be in that condition.
--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

Sometimes Friday is just the fifth Monday of the week.

Scott Dorsey wrote:
>
> Michael A. Terrell > wrote:
> >tm wrote:
> >>
> >>
> >> Are you sure it is not already a pulse width regulator? Those transistors
> >> look like they are TO-220 packages, not TO-3.
> >
> > I've seen 20W power resistors in TO-220 packages.
>
> It does indeed look like a TO-220 from the pin spacing (since there are no
> actual transistors in the photos, just spots from which they were removed).


All those photos only show one side. I full reverse engineering
should be done to draw a full schematic but I've never had my hands on
that module. It would probably take a couple of them, because ot the
potting.


> But if it had been a PWM device, there would have been some filtering in
> there, inductors and capacitors to keep the noise from getting into the
> power lines. Designing clean and quiet PWM controllers is not quite as
> trivial as some folks have made it out to be.

Have you looked at the National Semiconductor (Now part of T.I)
'Simple Switcher' series of controllers? Generally only one inductor
and a couple small electrolytics. A lot simpler than older designs, and
little noise because of the small footprint.


> >> PWM has been around longer than SMT parts.
> >>
> >> Maybe it is transients from the motor that are causing the failures.
>
> This is possible, if it is the transistors that are failing. I don't see
> any big protection diodes in there either.
>
> If it's a RoHS soldering issue, though, I would not be surprised.
> --scott
>
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."


--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

Sometimes Friday is just the fifth Monday of the week.

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

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

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