Root cause insight into the common BMW blower motor resistor failures

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

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.

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???

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.

Reply to
jim beam
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won't save the unit, just a frozen motor.

you can run the unit out of the fan housing - hold it in your hand and you'll soon find out if it's getting hot or not.

Reply to
jim beam

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.

Reply to
jim beam

what he said.

Reply to
jim beam

indeed.

Reply to
jim beam

Yeah, we know that.

*why* is it overheating?

But it may make the replacement last longer.

nate

Reply to
Nate Nagel

All the standard Elmos part numbers begin with an E.

My guess is that the number on the chip is 10901D and that the other two numbers are date and batch codes.

--scott

Reply to
Scott Dorsey

because it's linear, retard. if you don't know what they means, f*ck off until you find out.

putting facts in front you dumb ass all day long doesn't make you any smarter.

Reply to
jim beam

Does pulse width modulation cause radio EMI?

Reply to
Bimmer Owner

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.

Reply to
jim beam

so "because it's linear" it by nature overheats to the point of failure? Odd, I'm pretty sure that that controller worked initially on, well, all of the vehicles in which it was originally installed.

The question is, is it overheating to the point of failure because the designer cut things too fine (in which case designing a better part would be the right approach), or is it because there's another issue somewhere else *causing* a part that would otherwise have acceptable service life to fail (in which case replacing it with a stock replacement and fixing the underlying issue would be the most economical thing to do)?

IKYABWAI.

It would really be just like you to spend all day designing a more robust controller, building it, watching it too burn up, and then realize that the problem was something else, like a chronic problem with dry fan motor bushings, windings dragging on the case, something like that.

But sure, don't check the obvious stuff, just go into your long-winded sometimes technically correct and sometimes not babble, I know that anything I say won't stop you anyway.

nate

Reply to
Nate Nagel

Nothing wrong with linear motor control, it's just inefficient and produces a lot of heat. I used to work in a place with a 1.2 MW DC motor whose field coil voltage was controlled by a couple rooms full of cast-iron resistors. The resistance array lasted nearly 80 years before the whole facility was taken down.

As long as you keep within the safe operating area of the semiconductors, you're fine. If you exceed them, bad things happen. But we don't know if the semiconductors are failing on these things, or if it's just ordinary RoHS solder failures; the RoHS crap doesn't like thermal cycling so well.

--scott

Reply to
Scott Dorsey

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

Reply to
Scott Dorsey

right, but what's the point in using 140W to run a 60W motor? and /certainly/ not when the devices to do so are so cheap and abundant. i can see doing it back in the day when there weren't any other options, but today there are, and there have been for 20+ years.

right. but again, we're dealing with mba's here. as an engineer, you're going to design with reliability and a safety margin built in. as an mba, you're going to cut and keep cutting until it meets "business objectives".

very true. but at the end of the day, that's still heat. and a linear semiconductor controller is just stooopid when a wire coil will do the same job more reliably and at a fraction of the cost.

Reply to
jim beam

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.

Reply to
jim beam

That's an interesting idea.

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The fuse for the blower motor is called the "infamous F76" for a reason.
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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.

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Reply to
Bimmer Owner

Hmm, it did look like it had quite a heat sink. I had assumed it used PWM to change speed, which should not generate much heat but my assumption might be wrong (or my understanding of PWM...) A solid state design that gets hot on purpose seems like a poor design to me.

Reply to
Ashton Crusher

If you google for 10901D it comes back with hits to Chinese chip brokers that show it as an Elmos 16 pin surface mount chip. Which is consistent with what's in the picture of the failed module, it has 16 pins. But I could not find any data sheet on the part either.

Reply to
trader4

I found the same. The chip is listed here:

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But there is no datasheet there.

Reply to
Bimmer Owner

I found a Russian language description of it here:

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Reply to
Bimmer Owner

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