Unpotting is fun, it's a nice change in the day to just sit down for a couple
hours with a dremel tool and a dental pick.
But I agree, building an aftermarket controller replacement would not be
a tremendously difficult thing to do, and it might be a highly profitable
"C'est un Nagra. C'est suisse, et tres, tres precis."
well, it cost me about $18 in parts to retrofit the linear dash light
dimmer on my civic with a pre-built arduino unit. a custom unit could
come in substantially less than that, if in sufficient quantity.
On Thu, 21 Mar 2013 09:47:31 -0400, Scott Dorsey wrote:
Here are pictures from the last half dozen who tried that approach:
Most who try to unpot fail, mainly due to damage caused to the
surface-mount circuit board during the initial mechanical degooping
Those deft few who avoid knocking off the surface-mount components
with the debriding chisel, are left with a badly bruised board,
where some have said they've resoldered solder cracks (see pics).
One problem with "put a bigger xtor" is that nobody on this planet
has produced a decent circuit diagram of the FSU.
Does anyone here have access to an FSU circuit diagram?
if people priced their time and ignored the damage in which attempts to
unpot invariably result, it's cheaper to just buy a new one.
you don't need it any more than you need the circuit diagram of a chip's
internals - all you need is its function parameters - which you pretty
much already have.
you might be able to pwm the unit itself thus pretty much removing the
heat component thereby prolonging its life [literally] exponentially.
On Thu, 21 Mar 2013 08:14:12 -0700, jim beam wrote:
To be clear, that's what 99.99999999% of the BMW owners do.
But that's not the point of this thread.
The point of this thread is to get a handle on WHY they are all
Specifically, how to figure that out is the question.
That isn't necessarily the case. For example,t hey could be correctly
designed, rated for the application, etc but have a manufacturing
defect in just one of the components.
A better questions is why BMW apparently doesn't give a damn
to do the failure analysis to find out what's wrong. I have a friend
who has an X5 and had this problem with the blower resistors.
Even worse, the only symptom was it was draining the battery
and it took a huge number of hours to track it down.
While you're all wondering about that problem, might as well
add the fancy aux radiator fan to the list. This car had that go
and now the replacement one has failed again. And the
symptom there is, again, it drains the battery even when the
car is off. That fan is a real POS. Instead of just a simple
fan motor, it's a fan that's variable speed, driven by a PWM
signal. So, instead of just a motor, that fan sitting in front
of the hot radiator has electronics in it. A real genius of a
design. And for what? Like the fan can't just be on or off?
Only reason I can think of is that they want to save a few
watts of power to try to get better fuel economy. And for
that their customers get to shell out $500 for a new fan
every few years.
On 03/21/2013 06:01 PM, email@example.com wrote:
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
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.
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)
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)?
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.
replace "roosters" with "cox" to reply.
Sheesh indeed. That heatsink is small. Sure, it will work for a
while, but it isn't designed for long life. Depending on forced air
cooling when the air is either heated or cooled is just plain stupid.
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
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