[s-cars] individual fused coils

[brian hoeft]

Thanks listers, thank you Paul, I was unsure about that effect when
I was leaning toward a 3A marine tube style fuse like Manny suggests.. What
Bill points toward is nifty too and then has me thinking about how if hidden
well would also make for a nice&easy added security feature.

Thanks again for the added detailed explanation.

...Then life happens, and fused coils will have to wait.. Dislocated my
shoulder today, so soldering tomorrow will be more fun,, parts would be a
couple days away anyway and my friend that *was* going to be driving 6 hours
to VT Thursday has car issues so it looks like OE wiring is in my future for
tomorrow, so I can be the driver/car instead.. ah, it never ends

..brian




On 3/18/08, Paul Gailus <gailus at mindspring.com> wrote:
>
>  Well, I wasn't going to get into that much detail, but here goes:    ;-)
>
> The reason that the currents of the individual coils should be added is
> that the thermal time constant of even fast-acting ATO fuses is
> significantly longer than the period of the current pulses.
>
>  For example, looking at the following time curve of  ATO fuses the
> thermal time constant is about 1 second:
> http://www.littelfuse.co.kr/data/en/Time_Curve/257.tc.pdf
>
> Even at idle we'll have about 6 pulses/sec in each coil, and we'll
> have about 10x that at redline where the average current is highest. The
> fact that the individual current pulses are non-overlapping in time allows
> us to simply add the currents.  If they start to overlap then we'd have to
> do a root-mean-square (RMS) of all 5 current waveforms to get the correct
> power dissipation.
>
> -Paul
>
> -----Original Message-----
> From: Mike Sylvester
> Sent: Mar 18, 2008 7:52 AM
> To: Paul Gailus
> Cc: brian hoeft , liSt
> Subject: RE: [s-cars] individual fused coils
>
> I haven't done any evaluation of this so I don't know what value should be
> used, but I'm not sure about that last statement.
>
> Since none of the coils are drawing current at the same time I don't see
> why their individual currents would be additive.
>
>
> Mike
>
> www.urq20v.com
>
>
>
> -------- Original Message --------
> Subject: Re: [s-cars] individual fused coils
> From: Paul Gailus <gailus at mindspring.com>
> Date: Mon, March 17, 2008 8:39 pm
> To: brian hoeft <qweblog at gmail.com>,  liSt <s-car-list at audifans.com>
>
> Brian,
>
> I'd recommend using 5 amp individual fuses, although you could probably go
> as low as 3 amps and still be OK.
>
> The rating of this downstream fuse must be small enough that a short will
> blow this fuse but leave the existing 15A upstream fuse fully intact. This
> will depend on the "selectivity ratio" of the particular fuses that are
> used, but a 5A fuse should provide enough margin.
>
> The other more obvious constraint is that the 5 individual fuses each need
> to be at least 3A to support the same total average current as the existing
> 15A fuse.
>
> -Paul
>
>
> -----Original Message-----
> >From: brian hoeft <qweblog**@gmail.com<http://mail.google.com/mail/?ui=1&ik=89acdb3245&view=cv&search=cat&cat=VAG&th=118c226813045198&ww=976&cvap=12&qt=&zx=u7gxi0-olmyr6#118c226813045198_Compose>
> >
> >Sent: Mar 17, 2008 11:49 AM
> >To: liSt <s-car-list**@audifans.com<http://mail.google.com/mail/?ui=1&ik=89acdb3245&view=cv&search=cat&cat=VAG&th=118c226813045198&ww=976&cvap=12&qt=&zx=u7gxi0-olmyr6#118c226813045198_Compose>
> >
> >Subject: [s-cars] individual fused coils
> >
> >Hi list,
> >
> >After some personal debate I decided to purchase 5 OE coils for complete
> >replacement and want to go with individual fuses for them.
> >
> >I know a few of you have done it from searching archives but I didnt find
> an
> >amp rating mentioned. Hoping someone could chime in with that.
> >
> >Also, if anyone has pictures they could email, that would be a bonus.
> Even
> >the smallest fuse holders im finding are going to grab my eye in the end,
> >but I think its worth it.
> >
> >thanks, brian
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