Barry says:
> The purpose of the ballast resistor is to drop the voltage from twelve
> to eight volts. (It also sounds like your coil is designed for eight volts
> - thus the warning sticker.)
> There is a way to determine whether your current coil is designed for
> eight or twelve volts by measuring its resistance, but I'm afraid I can't
> remember what range to expect for each coil type.
> Maybe someone else can help out.
The coil and ballast resistor would be in series, so each ohm of total
resistance drops an equal amount of voltage. This means that to get a
4 volt drop across the ballast resistor, you need to have the coil
be twice the resistance of the ballast resistor. To be sure, though,
you also need to know the "fully charged" current expected for your
coil; that is, the current intended to be flowing just before the points
open. For an electronic ignition system, of course, the term "points"
is figuratives figurative.
This current value times the resistance of the coil should be
just about equal to the expected voltage drop across the coil.
The coil resistance being exactly twice that of the ballast resistor
is a pretty good clue, though.
> Here is my version of your diagram. Note the change in where the ignition
>gets
> it power.
>
> -------- Black
> |Elec |----------------------------------------------|
> |Ign | |
> | | Red |-------------------| |
> | |-------------| ballast resistor |--| |
> -------- ^ |-------------------| | |
> | | |+ve | -ve
> | | ---------------
> | | | |
> | | | |
> Earth 12 Volts | |
> | Coil |
> | |
> | |
> | |
> ---------------
Note also that "this diagram is simplified" if the coil should get
12 volts during starts.
> -Barry Klawans
> barry@sybase.com
--
---
John R. Lupien
lupienj@hpwarq.hp.com
|