Root cause insight into the common BMW blower motor resistor failures

Page 8 of 14  
On 3/25/2013 10:56 PM, Bimmer Owner wrote:


Of all people, sears has one for less than $100 that does DC current
http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P
as i recall, i think harbor freights clamp meters are AC current only (like most are)
I am a fluke man too. Own at least 5 DVM's of various types. Big fan of the 70's series. Tough, last forever if you take care of them
bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bimmer Owner wrote on 03/21/2013 11:04 ET :

the FSR /fsu is a variable resistor that will control the fan speed; consequently at the lower speed of the fan the FSR will have the highest resistance > hence it will heat the most, and the bad thing: there is not enough air flow to cool it down (around 200W i suppose) newer replacement FSR units have more aluminium bars to increase the heat dissipation area. maybe the worst thing of all is that the FSR will eat up fuel for nothing (just to produce heat by electricity) something in the range of 100..200W and since the electricity is made with the efficiency of a gasoline engine (from 44MJ/kg), it is ~4times more expensive as the same electric load in the house
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 21 Mar 2013 15:22:42 +0000 (UTC), Bimmer Owner

If one replaces one of these perhaps it would be advisable to put a fuse in the blower motor lines (it sounds like those can be gotten to easily unlike the motor itself). If it's being blown by intermittent high current draws the fuse could protect the $100 FSU. Another option would be, at least for those who can live without the highest blower setting and who think excess current draw is the culprit, would be to put a power resistor in the blower motor line to limit the current a bit. On the cheap pedestrian cars I drive the whole speed control is just a trio of power resistors placed in the air flow to help cool them. If they burn out (which is rare) they can sometimes be fixed with a pop rivet.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 21 Mar 2013 15:03:45 -0700, Ashton Crusher wrote:

That's an interesting idea. The FSU supposedly consumes the most power when the blower motor is set to the LOW settings (simply because it has to dissipate the power as heat), so, we could prevent excess current by fusing... say with a 10A fuse, the blower motor (which is said to consume 5 to 6 A).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Are you sure it is not already a pulse width regulator? Those transistors look like they are TO-220 packages, not TO-3. PWM has been around longer than SMT parts.
Maybe it is transients from the motor that are causing the failures.
Another place you could measure the current is by putting an ammeter in place of the blower motor fuse.
tm
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
tm wrote:

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

--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Scott Dorsey wrote:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Scott Dorsey wrote:

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.

--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/25/2013 06:42 AM, Michael A. Terrell wrote:

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.

--
fact check required

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
jim beam wrote:

Yawn. I worked with 16 layer boards at a factory troubleshooting defective, new boards that cost over $8,000 to stuff. The internal routing of a simple low frequency board is irrelevant for drawing a schematic. You can X-ray a board or mill it one layer at a time if you want to duplicate the routing. All you need to do for bais reverse engineering is to trace each with an ohm meter by probing every pad and termination to identify the signal path and draw a schematic from your notes. I've done this with four layer boards for 30+ years. "Specs on the chips" makes things easier but knowing who made it, and how it's connected will tell you if it is a custom part or just house numbered.
There are industrial solvents to remove any potting compound, but they aren't cheap or easy to buy. Failure analysis is a specialty in electronics manufacturing. It is expensive but gives you the answers you need so you can design out the problems.
A jig to hold the module in a CNC machine would allow you to cut accurate holes down to the right points to see if the IC was bad, without unpotting a failed unit. Then a test fixture with 'Pogo Pins' would allow you to see what was bad. If there were enough bad units, it would be worth designing and programming a computerized fixture.
--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/26/2013 10:41 AM, Michael A. Terrell wrote:

fantastic. could you condescend to help these guys wit their project then? or are you just here to whang your donger around?

then you're a complete genius because other people find it hard/impossible.

yeah, a schematic doesn't exactly mean much if you don't even know what the components actually are. [see above]

expensive? you're not kidding. and failure analysis is a whole lot easier if you know what you're looking at in the first place.

yeah, if you know precisely where you're drilling, in three dimensions. and you have dil/soic [etc] type chips. anything bga or similar, and you're sol.
and you're not doing that with a black box and getting meaningful data out of it.

ok, but you're missing one simple thing - this is a bunch of guys with a dremel and a dental pick. money/time are limiting factors, even if there were logic to reverse engineering, which i don't think there is in this case.
--
fact check required

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
jim beam wrote:

No, I'm not like you. I have worked in Electronics for 52 years. I could draw the schematics, but I would need a handful of bad modules and the time to do it right. Just like the kU band microwave audio, video, and data terminal hardware I worked on that's in orbit aboard the ISS. It takes hands on effort to reverse engineer a design.
Bomarc has reverse engineered a lot of automotive modules:
<http://www.bomarc.org/basement/viewtopic.php?f=1&t=6&sid e707756ef37b24ff5aa633f1b4548a>
The one you want might be on their lists.
--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/26/2013 08:20 PM, Michael A. Terrell wrote:

so what you're saying is that you're just here to piss and moan because you know how to help, but won't.
and credentials don't work on usenet - they're completely uncheckable and many are bogus. what matters is whether you can walk the talk.
as for having stuff in orbit, i don't have anything, but two of my best friends do. the difference between them and you is that they're not jaded and they're actually helpful.

<http://www.bomarc.org/basement/viewtopic.php?f=1&t=6&sid e707756ef37b24ff5aa633f1b4548a>

that at least is vaguely useful, but you could have come up with that 20 posts ago.
--
fact check required

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
jim beam wrote:

Yawn. I don't have access to any defective modules. I don't know anyone at the local BMW dealership to ask for failed units and I'm not going to buy a new module to destroy for a whiny piss ant like you.

You can't even crawl.

Then tell them to reverse engineer it for you. Or can't they 'walk the talk', either?

And you couldn't so you piss and moan. I couldn't remember their name, since I hadn't seen one of their print ads for over 20 years. I looked them up, when I did.
--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/27/2013 09:45 AM, Michael A. Terrell wrote:

i don't know who you think you're talking to, but i have consistently advocated /not/ deconstructing this unit. it's not worth it when cost of replacement isn't that high or you can build an alternate controller that will be more reliable.

at least i can follow a thread without being a crotchety old fart.

i don't /want/ to reverse engineer it any more than i want to repair broken light bulbs. you were the one bragging about how easy it was. i said it wasn't. and when it comes down to walking the talk, you won't.

i guess we should be grateful...
--
fact check required

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
jim beam wrote:

Apparently I'm talking to a blowhard troll.

Ass. The first step in designing a replacement is to understand what it is supposed to do, and how the original performed that function.

Show us.

Send me some defective modules, or quit trolling.
--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/27/2013 09:33 PM, Michael A. Terrell wrote:

no???? really? are you /sure/ about that??? or doesn't sarcasm work for you???

no, you're doing that.

they're not my modules [again, you're not following the thread] and i wouldn't replace them - i'd pwm the motor instead.
--
fact check required

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
jim beam wrote:

Without knowing how to interface it to the vehicle. What a lame ass lying idiot. You demanded that I do the reverse engineering of said modules, but you run in circles like chained animal. Hopefully you don't change directions, before you choke yourself.

You wouldn't know a fact, even if it walked up and puked on your shoes.
--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/28/2013 06:46 PM, Michael A. Terrell wrote:

??? if it were my vehicle, i'd be able to find it out now, wouldn't i!!!

whatever you say dude, but the fact is, i've done it before and i'd do it again.

i didn't demand any such thing, i pointed out that if you did, since you were bragging about having done so much of it, you wouldn't be making everyone have to listen to you piss and moan. but here you still are, pissing and moaning since i guess it's so much easier, even for an expert like yourself.

--
fact check required

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.