Root cause insight into the common BMW blower motor resistor failures

Googling for the Russian text, I find they appear to have the same problem with the same FSU over here:

switch blades and is contactless.

you don't need to know this stuff any more than you need to know the gas excitation voltage in a broken fluorescent tube. because you're not going to unpot the thing and replace the chip. because it's probably not the chip in the first place.

not trying to be rude - just trying to get you focused on the relevant stuff - that the two options are:

1. continue replacing the existing [under-rated, low tech] unit.
2. build and deploy a pwm unit instead.

#1 is really not /that/ expensive, particularly if you factor in time, even if it is part of the bmw marketing susceptibility tax.

#2 is a much better time investment - it certainly has a much better return than figuring out that the existing unit is not repairable later rather than sooner.

you don't want to try and use a 10/20A meter in the slot of a 40A fuse. you probably already know that, but just saying.

jim beam wrote on Fri, 22 Mar 2013 07:04:19 -0700:

I don't know how many bmws are out there, but let's say it's a million and then multiply that million by 100 dollars, and then let's see how much it is in terms of expense.

If it's just a typical DC motor with two leads, apply 12V and it should run full speed. You could also measure how many amps it draws when running. That is, IF it's just an ordinary motor.

It's kind of amazing the fuse is 40 amps, no? I mean a 1 hp motor draws ~1500W And this heater blower is 480W? Seems like a lot to me.....

in this thread it's been said it draws 6A running. x 12V, that's 72W.

but the reason you have 40A is you have very high current start-up transients. on a cold day with a gale blowing outside the car, and some snow in the system, you could be into the 30's without too much problem. so you need an amperage that will still blow in the event of short circuit, but which will tolerate the above.

Have you got a link to these "common problems" you keep posting about?

I think it's already been suggested, but if the car were my own vehicle, I'd be content with a multi-position switch for the blower motor.. this is a very reliable method.

A heavy duty switch and some over-rated power resistors would likely outlast many replacement OEM miracle-in-a-box modules.

The parts, wire, a cover for the hole where the original removed module was, and a Saturday afternoon would likely cover the cost investment.

I'm fairly certain that there are off-the-shelf variable speed modules that would be an adequate replacement for an automotive blower motor application.

In message , " snipped-for-privacy@optonline.net" writes

If by PWM you mean pulse width modulation, then it would allow for variable speed, but a DC motor is an inductive load and is not sensibly controlled by such a system unless there is something in the circuit to allow the peak voltage generated by the motor at pulse cut of to be shunted to earth.

That "something" could be as simple as a diode. PWM is commonly used to vary the power to a motor. BMW, for example, uses it on the aux fan motor of the X5. And I would suspect that it's also used for the blower motor because you wind up wasting a lot less power that way. And every little bit of power saved adds up and effects MPG.

!- Hide quoted text -

I don't have a link, but we had the blower resistor widget go on an X5 here. And the aux cooling fan motor has gone twice. There are plenty of threads online about many people having those problems. Oh, and don't forget the nice X5 feature where the cable that they use to hold up the windows snaps, sending the window crashing down inside the door, breaking it into a million pieces. Had that happen twice too, once while the car was just sitting in the driveway. Other time was driving down the highway.

Then there are their defective rubber parts. Like the boot on the intake manifold that cracks in just a few years. Or the CV joint boots. I've had lots of cars with CV boots and only on the X5 do they fail every 20K miles. I've seen Honda CRVs that went 200K miles with no failure.

In message , " snipped-for-privacy@optonline.net" writes

I agree with all you say.

that must have been interesting - what did that motor do?

that must have been a sight to see too.

shipped to china? or replaced by pwm controllers?

ancient news - controller designers and semiconductor manufacturers have been on top of this from day 1.

Hide quoted text -

serious question - why did you buy it?

In message , Bimmer Owner writes

Motors are not just a resistive load though.

PWM is the most common method of controlling the speed of DC motors - a flywheel diode is part of the "system" to handle the inductive kick-back. Virtually all battery operated variable speed power tools use PWM. So do virtually all electric bicycles with brush motors and the vast majority of electric forklifts.

In fact, just about any application of a brush type DC motor that requires reasonable speed control has switched to PWM control of some sort over the last 20 years, including power wheel chairs (except those using 3 phase brushless motors)