Ballast Resistor
From Holdenpaedia
Original submission by T Mar 20th 2007:
Back to the Engine Section
[edit] Ballast Resistors:
[edit] Ballast Resistance:
In Holdens that had breaker point ignition as standard, from EH up to HZ, UC and VB, the ballast resistance
was a length of pink wire with "Resistance - Do Not Cut" printed on it, that attached to the coil positive at one end and tapped into the ignition feed either at the bulkhead connector or at the ignition switch.
These cars did not use a separate Ballast Resistor. One advantage of incorporating the resistance into the wire is that the heat generated in the resistance is dissipated over a wide area. Ballast Resistors burn
out more frequently than the wire because of the high heat concentration around them.
[edit] Ballast Resistors and Duty Cycle:
Submitted by T on Tue, 20/03/2007 - 09:46.[edit] The Ignition Coil is Not a Pure Resistance:
difference because the duty cycle would remain at largely 50% (equal
on and off times).
Operation of Ballast Resistor.
Early type Ballast Resistor wire showing pink and yellow wires. Click to Enlargen. Photo by juicematic64.
[edit] Because the Ignition Coil is an Inductor:
Because the coil is an inductor it takes time for the primary coilcurrent to reach its peak.
[edit] The Coil and Ballast Resistor at Idle:
At idle the coil has time to reach a peak and sustain the peakmeaning that more current flows into the coil than needs to since the
coil only needs to saturate the coil former, then have the primary
current path broken. The resistor minimises heat buildup in the coil
by soaking up a percentage of the power.
[edit] The Direct Current Behaviour of an Inductor:
As you know, when an inductor (coil) is presented to a DC voltage source it initially behaves as an open circuit. As time passesit eventually becomes a short circuit.
[edit] The Direct Current Behaviour of a Capacitor:
This behaves as a short circuit initially and in time becomes an open circuit.[edit] The Effect on the Ballast Resistor with the Increase in RPM:
As the Engine RPM increases, the amount of time available for the coil primary to reach a maximum is reduced. After about 3,000 RPM a points coil starts to lose output because its buildup time is reduced.[edit] Dual Point Ignitions and Dwell Extension:
Dual point ignitions and electronic dwell extension sustain thecoil's output by making the coil "on" time as long as possible
and the "off" time as brief as possible. The increase in output
is achieved just by changing the duty cycle.
[edit] Ballast Resistor Heat:
The power reduction effect with the increase in RPM is exactly the same as if the on time were getting shorter the faster the engine revs because the coil primary is givenprogressively less time to react.
On another note, if the coil had 0 resistance and the points were
closed a typical ballast resistor might be expected to dissipate
( 3 amps x 12 volts = 36 watts ). You could fry more than one egg on that lot. A 2 watt resistor can give you 1st degree burn.
T
