In reply to a message from Cannara sent Tue 19 Feb 2008:
I was referring to any electronic ignition system like CRANE.
Walter--
The original message included these comments:
Walter, that’s simply not true. The whole idea of a fancy ignition amplifier
is to control the energy stored in the coil during the dwell period and to
deliver it to spark by stopping the coil current faster and better than an old
points system, at all rpm. That’s in fact why these are called Constant
Energy ignitions.
Ok, sure, if any system says it requires a ballast because of static-on
conditions, fine. However, as soon as you introduce a resistor in series with
the coil, you waste a huge amount of power for spark.
If the energy stored in a coil is proportional to the current squared (I x I),
then max current determines max energy. Put in a resistor R, and it wastes
power proportional to the square of the current (I x I x R). That’s a lot!
So, good electronic ignitions, like ours (GMs), do their own coil-current
management under all conditions. I keep repeating and repeating, you’re
welcome to a PDF of Motorola’s!–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.
W. Schuster wrote:
In reply to a message from Cannara sent Tue 19 Feb 2008:
I was referring to any electronic ignition system like CRANE.
In reply to a message from Cannara sent Wed 20 Feb 2008:
So to sum up…
If the ignition system can have a ‘‘static on time’’ , ie the coil
can draw current with the ignition on and the engine stationary
(contact breaker and Opus ignition), or the higher current draw
from a ‘‘cold start’’ coil can overload the ignition (contact breaker
or Opus) then the resistor is best left in place.
If the ignition system does not have a ‘‘static on time’’ ( CE
systems as fitted standard to series 3 models) and the ignition amp
has current limiting circuitry (Motorola amp as fited to Lucas CE
system) then the use of a ballst resistor is, to quote Frank, ‘‘not
necessary - and may be counterproductive…’’.
The only things I can think of adding is has the current limiting
Motorola amp been used in the CE system from day one, and has the
amp been updated over the years to improve areas such as current
limiting or did they get it right first time ?
See below, Dave…–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.
sparx wrote:
In reply to a message from Cannara sent Wed 20 Feb 2008:
So to sum up…
If the ignition system can have a ‘‘static on time’’ , ie the coil
can draw current with the ignition on and the engine stationary
(contact breaker and Opus ignition), or the higher current draw
from a ‘‘cold start’’ coil can overload the ignition (contact breaker
or Opus) then the resistor is best left in place.
…Maybe, a coil/contact isn’t automatically going to overheat. Obviously at
high rpm, the coil/contact is experiencing almost continuous dwell time and
thus full current. A cheap coil, sitting on a hot engine may indeed be
overloaded then, and as you say.
If the ignition system does not have a ‘‘static on time’’ ( CE
systems as fitted standard to series 3 models) and the ignition amp
has current limiting circuitry (Motorola amp as fited to Lucas CE
system) then the use of a ballst resistor is, to quote Frank, ‘‘not
necessary - and may be counterproductive…’’.
…All resistors waste energy in proportion to the square of the current
through them – indeed very wasteful. That’s what they’re for – dissipating
unwanted energy, but “unwanted” in the designer’s sense, not nonsensically, as
in blindly adding a resistor to a good ignition system. There’s no “may be”
in such cases.
The only things I can think of adding is has the current limiting
Motorola amp been used in the CE system from day one, and has the
amp been updated over the years to improve areas such as current
limiting or did they get it right first time ?
…The GM module has this too! They all have to, because “constant energy”
means managing current during dwell. Coil energy, again, is directly
proportional to the current through it. These CE designs are old & tested in
millions of vehicles worldwide. Our discussion of how it works now is almost
archaeological.
;]