[928uk] Jump start

[Mike Dawe]

RE: [928uk] Jump startThank you Scott and John, I will continue to offer up
thanks that I have an early car,but must get round to installing a battery
isolation system.Mike (T reg)
  -----Original Message-----
  From: Walker, Scott [mailto:SWalker at ndsuk.com]
  Sent: 05 July 2004 13:49
  To: 'mike at dawe.com'; 928
  Subject: RE: [928uk] Jump start


  Mike - the wire thickness at the jump-start terminal under the bonnet is
not in question... that's why Porsche put it there!

  The issue with using it to jump-start the later cars (S4-on with
electronic fuel delivery control via the infamous "LH ECU") is that the
chipset within the fuel ECU is prone to 'destructive aging', and the 'jolt'
from a jump-start can quicken its demise!

  Your car has mechanical fuel injection so you don't have to worry about
this!

  However, on the charging front you need to heed what Smiffy has said about
your alternator. The problem here is that charging the battery via the
jump-start terminal (i.e. with battery still connected to the car - and
hence to the alternator) puts a high current through your electrical system
in the reverse direction to normal. Your alternator has a diode pack which
fights against this... and can overheat & die. Price up a new alternator &
see if you want to risk it!

  I would say don't connect a 4A-capable trickle charger to your jump-point.
Even the 1A you say it settles to is a fair current "in the wrong direction"
for your car's elec system. The battery maintainers/conditioners only put
out tiny currents in comparison - which is safe for the elec system.

  Scott '91 GT

  -----Original Message-----
  From: Mike Dawe [mailto:mike at dawe.com]

  In the interests of science and fellow listers,particularly early cars
  viz.928 (without much electronics),I have been charging and jump starting
  (from other batteries,'ware using cars) my 79 model through the
'terminals'
  under the bonnet.
  My 4 amp charger soon settles down to 1 amp or so. I have jump started it
at
  least one hundred times.....have I been lucky or was my local car
electrian
  correct when he took one look at the thickness of the wires involved and
  announced both charging and jump starting safe......this continues to
puzzle
  me! Mike (T reg)

  -----Original Message-----
  From: 928uk-bounces at 928.org.uk [mailto:928uk-bounces at 928.org.uk]On

  >
  > I have jump started by 928S a number of times using the terminal under
the
  > bonnet - without any problems.
  >
  > Regards
  > Andrew - 82S
  > >>>>>>>>>>>>
  The early cars don't have a problem in the same way as the S4 and later.
  It's the later LH ECUs that are fragile.

  John
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