[200q20v] Another fusible link question

Bernie Benz b.m.benz at prodigy.net
Fri Oct 12 10:56:41 EDT 2001

I'm pulling these figures out of the air as examples, don't design around
them!  You could calculate the locked armature current from the measured
voltage drop across two different value small omage, power resistors.

One must include the characteristics of a "slo blo" fuse into the design.
Audi didn't, that's why the fuse fatigues over time.


> From: Dave Haupt <quattrodave at yahoo.com>
> Date: Fri, 12 Oct 2001 09:16:12 -0700 (PDT)
> To: Bernie Benz <b.m.benz at prodigy.net>
> Subject: Re: [200q20v] Another fusible link question
> Ah, then 30A is the correct number.  0.2 ohms across
> 12V is 60A - won't blow the 70A fuse, but it will
> surely melt the 10 gauge wiring!  In fact, I'd bet the
> wiring has more than 0.2 ohms of series resistance.
> It's amazing how many people have written to me that
> the "standard" part is 80A or 70A.  Just seems like
> too much.  I don't have a way to measure DC currents
> that high, otherwise I would drive 12V directly into
> the motor and find out as a certainty how much current
> it draws.  The motor on mine is stiff, but I'm in the
> mode of minimal cost repairs prior to sale, but am
> perfectly willing to protect the next owner against
> such a meltdown.
> thanks!
> Dave
> --- Bernie Benz <b.m.benz at prodigy.net> wrote:
>> You're right, Dave.  The fuse need only handle the
>> steady-state motor
>> current, plus have the slow blow characteristics to
>> handle the starting
>> curent surge of maybe 70A.  A stalled or frozen
>> motor may have an internal
>> resistance of around 0.2 Ohm.
>> Bernie
>>> From: Dave Haupt <quattrodave at yahoo.com>
>>> Date: Thu, 11 Oct 2001 23:40:13 -0700 (PDT)
>>> To: 200q20v at audifans.com
>>> Subject: [200q20v] Another fusible link question
>>> OK, so I looked at it, looked at it again, read
>>> emails, wrote incorrectly to a few....sorry!
>>> The fusible link, as shipped by Carlsen, is,
>> indeed, a
>>> 30 amp link.  Has anybody actually measured the
>>> steady-state current consumption of the motor at
>> the
>>> various speeds?  I have to admit, even though
>> there
>>> are lots of references to 70 amps worth of fusible
>>> link, that smacks of downright dangerous
>> engineering -
>>> the wiring for the fan motor includes some fairly
>> long
>>> runs of 10 gauge wire, which would certainly catch
>>> fire at a steady 70 amps.
>>> So the current trouble is this: the fusible link
>>> fitment box came without screws.  I'm sure they
>> have
>>> to be some sort of brass metric screw.  Anybody
>> have
>>> an idea what size they are and where I can mail
>> order
>>> them without having to spend yet more of my
>> employer's
>>> long distance money during working hours?  Or
>> maybe an
>>> Audi PN, so I can try to get the local VW dealer
>> (I'm
>>> 120 miles from the nearest interested Audi dealer)
>> to
>>> get some for me?
>>> I guess I'll keep plugging away at this until it's
>>> done.  This repair started August 13th....
>>> TIA!
>>> Dave
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