Root cause insight into the common BMW blower motor resistor failures

Sure it can, if you're nothing more than a low grade grease monkey.

Your checks always bounce.

Reply to
Michael A. Terrell
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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.
Reply to
Michael A. Terrell

It should generate less heat at low speeds, if it is PWM.

Reply to
Michael A. Terrell

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.

Reply to
clare

I've seen 20W power resistors in TO-220 packages.

Reply to
Michael A. Terrell

Is that cheaper than roll your own?

Reply to
Michael A. Terrell

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).

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.

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

Reply to
Scott Dorsey

A few car manufacturers use resistor wire in the harness leading to the motor connection at the blower box.

This lowers the Q significantly giving you a voltage drop of course, but it also reduces electrical noise and helps suppress the wheeling voltages.

Blower motors in this case are normally designed to operate lets say

8 volts for example, for full RPM.

I learned this years ago when going through the pain of removing the blower in an air box of a Chrysler product, only to find there was nothing wrong with the motor. Symptoms led on to the fact there was since the output of the speed control circuit was alive and happy but no obvious connection to the motor. If I had unplugged it from the air box before pulling that all apart, I would of noticed it.

The problem was the resistor wire in the harness which had open at the crimp point, also in the harness.

Jamie

Reply to
Jamie

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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.

Reply to
jim beam

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

Reply to
amdx

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

Reply to
tm

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.

Reply to
clare

Sure, if you don't mind heating the motor up...

Jamie

Reply to
Jamie

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.

Reply to
Michael A. Terrell

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.

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.

Reply to
Michael A. Terrell

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.

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

Reply to
Scott Dorsey

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.

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.

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.

Reply to
jim beam

interesting.

Reply to
jim beam

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?

Reply to
jim beam

if it's just a two-layer board, maybe. assuming you get the specs on the chips of course. but you'll need more than two units and a whole lot of patience trying to reverse the schematic if it's 4 or more layers. and you still don't achieve anything more than having a broken light bulb in your hand.

what you need to do is get the operational capacities of the /working/ unit, and work with those. that the unit is a black box is completely irrelevant.

/and/ a smaller footprint. the "because" is entirely due to the soft switching they've achieved. soft switching is still "big science" - there are still phd's being written on how to implement and design, both with the types of semiconductor, and the circuits in which they're used.

Reply to
jim beam

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