Root cause insight into the common BMW blower motor resistor failures

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On 03/25/2013 08:10 AM, Scott Dorsey wrote:


true, but you don't want to "integrate" the full power individual pulses down to a lower average otherwise it won't run or torque.

they whine pretty effectively at centihertz too.

they will surely complain if it doesn't run.
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On Mon, 25 Mar 2013 07:55:03 -0700, jim beam wrote:

What does ROHS mean?
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Bimmer Owner wrote:

'Reduction Of Hazardous Substances'
Crappy lead free solder that cracks with a lot less stress that leaded solder. Brought to electronics by European bureaucrats.
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On 03/25/2013 01:58 PM, Bimmer Owner wrote:

Restriction of Hazardous Substances; that is, no lead (among other things.)
http://en.wikipedia.org/wiki/Restriction_of_Hazardous_Substances_Directive
nate
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Følgende er skrevet af Nate Nagel:

causing hazards to the users of the equipment :-(
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That's why there are exemptions for the military and telecom industry, where it's actually important that stuff work properly.
What I find ironic is that the shorter lifespan of consumer gear caused by the RoHS manufacturing has actually increased the amount of electronics going into landfills, making worse the problem that it was intended to reduce. --scott
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On 03/28/2013 05:20 AM, Scott Dorsey wrote:

and yet, some say that there can be increased reliability.
<http://en.wikipedia.org/wiki/ROHS#Reliability_concerns_unfounded btw, if you want /real/ reliability, you wire wrap.
<http://en.wikipedia.org/wiki/Wire_wrap
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jim beam wrote:

Sure you do. That's why it's mostly been abandoned. It was bulky, and had horrible crosstalk unless you resorted to twisted pair signaling. It is crap at higher frequencies. If you want to go back to <5 MHz hardware, it's perfect.
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On 03/28/2013 06:37 PM, Michael A. Terrell wrote:

stop being so bent out of shape that you can't think straight old man - i didn't say it was better at any of those things. i said it was more reliable than solder. and it is.
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jim beam wrote:

Yawn..............................................................
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Blower motor drawing too much amperage taking it out. Change the blower motor anytime?
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On 03/21/2013 03:55 AM, the will wrote:

if it were an adequately designed unit, it should tolerate that and worse.

analyze the actual problem - don't just waste money replacing stuff. a $30 dvm will diagnose this for you, and you should already own one if you have any ambition to repair any modern vehicle.
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On Wed, 20 Mar 2013 23:17:36 -0700, jim beam wrote:

That's exactly what we've done - yet - we need help since nobody to date has figured out HOW to test an FSU that is fried. http://www.bimmerfest.com/forums/showthread.php?tg8534
Note: It appears to be an active component, but it probably does dissipate 100W.
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On 03/21/2013 08:57 AM, Bimmer Owner wrote:

it's like testing a dead light bulb.

it dissipates Vd x Im where Vd = voltage drop across the unit output, and Im = current drawn by motor. it will indeed get hotter when running the motor slower because of the greater voltage drop across the unit. that's why pwm is the better solution - the semiconductors are either fully on [minimal heat dissipation] or fully off [minimal heat dissipation]. the only time they get to dissipate heat is during switching which is a sub-millisecond event and a tiny percentage of the base time.
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On Thu, 21 Mar 2013 19:15:16 -0700, jim beam wrote:

Does pulse width modulation cause radio EMI?
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On 03/21/2013 07:39 PM, Bimmer Owner wrote:

it can if the radio isn't very noise resistant and the switching is "hard". you won't typically hear it on the fm bands, but you might on the am.
you can make a pwm unit "soft switch" and kill pretty much all of the electrical noise it would otherwise generate and incur only a very small heating penalty.
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It can if it's not properly filtered. And the reason why I think beam is correct about this being a linear control is that there is no filtration in there.
My guess is that the cost of proper filtering and shielding makes the pwm controller cost more than the linear controller in this case, which is probably why they went the linear route. --scott
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On 03/21/2013 08:10 PM, Scott Dorsey wrote:

it's the heat sink that's the dead give-away. a pwm controller heatsink would be 1/10th the capacity. or less.

i think the cost of that honking great heatsink significantly exceeds the cost of a couple of extra inductors and caps.
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On 03/21/2013 06:55 AM, the will wrote:

My thought as well. Have you measured current draw on a new blower motor and compared it to one that is installed in a car where the FSU has failed? that would tell you whether there's any merit to this idea or not.
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My inclination is to do exactly the same thing I do with the cooling system issues: blame German engineers who seem to believe that their climate is typical of the entire world.
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. --scott
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