Why do Betas have a ballast resistor?

[Thotos]

My understanding of ignition systems with a ballast resistor is that you have a 6 volt (or 9 volt) coil and the ballast resistor under normal running conditions reduces the battery's 12V to the correct voltage for the coil. But as battery voltage can drop during engine cranking, a relay is used to bypass the ballast resistor so the full available battery voltage is fed to the coil to ensure a strong enough spark to start the engine. Once the engine has started and the ignition key is released to its normal position, the ballast resistor comes back into play and provides the correct voltage for the coil. But not with the Beta! Or not with my Trevi at least! Power (12volts) are fed to the ballast resistor and the other end of the ballast feeds the coil + terminal. There's no other wires on the coil + terminal or the ballast resistor ends so there's no way the ballast resistor is bypassed during engine cranking. So why is it there?

[peteracs]

Hi

You are correct in the reasoning why they are there for starting, but I suspect that the ballast resistor may have been left in

a) To keep with the same part, though why there is no bypass is maybe just a price cutting exercise when batteries improved and with electronic ignition.

b) If the coil shorts then you have some safeguard against the wires burning out and potentially causing a fire under the bonnet. Also it limits the current drawn when you connect/disconnect the coil which is done via the elec ignition, presumably a transistor in it.

Peter

[thecolonel]

I expect it was a standard fitment at the time or they
had 1000s of 9 volt coils on the shelf.
The gamma uses the same parts, although on 1 of
mine I have a start boost button which bypasses the
resistor and sends 12 volts direct to the coil, my other
one utilizes a beta coil pack without the resistor.

Geoff

[Thotos]

Yes the Gamma uses the same setup but on my Gamma there are two wires on the 'low' side of the ballast resistor and that second wire effectively bypasses the ballast resistor during engine cranking.