Is there any difference in the function of the circuit if the capacitor has a shorter wire path to the coil or to the points?
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1\$\begingroup\$ The arcing occurs at the points, thus best to "at the points". \$\endgroup\$– analogsystemsrfCommented Mar 27, 2019 at 3:34
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1\$\begingroup\$ Welcome. The capacitor allows a short HV pulse to flow to the spark plugs based on the points opening, dumping the coils magnetic field. Closing the points charges up the coils magnetic field. Tach and dwell. \$\endgroup\$– user105652Commented Mar 27, 2019 at 3:40
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1\$\begingroup\$ The points capacitor was customarily fitted right at the distributor (or on some inside the distributor). So make the connection as close to the points as possible. \$\endgroup\$– Jack CreaseyCommented Mar 27, 2019 at 4:51
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2 Answers
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TL;DR put it in the distributor housing, next to the points, where there's space for it and it's designed to go.
At the lowish frequencies associated with the main purpose of the capacitor, suppressing an arc at the points, there should not be too much difference between putting it at the points or the coil. However, to minimise the stray inductance in series with the points which the capacitor cannot control, it's best to minimise the loop area enclosed by the change of path between the points closed and points open current path, this is the loop that comprises the stray inductance.
When you look at what it also does for you, suppressing radio interference, it's best to minimise the loop area enclosed by the change of path between the points closed and points open current path, this is the loop that will radiate RF.
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\$\begingroup\$ This is on an Onan B48G 20hp. from the OEM, the capacitor was mounted to the points assembly on the crack case. A previous owner replaced it and put the new one up at the coil. And returning the machine to operation I wasnt sure if it made a diff. Many thanks I'll put it back where it used to be \$\endgroup\$– JimCommented Mar 27, 2019 at 16:24
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Close to the points, generally it mounts on the same screws that hold the points and connects to the same terminal as wire from the points to the coil.
Briggs and Stratton went one better and integrated the capacitor with the terminal and the points contact, but they have since switched to all electronic ignition.
answered Mar 27, 2019 at 8:35
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\$\begingroup\$ This is on an Onan B48G 20hp. The OEM had similar as what you mention, the capacitor was mounted to the points assembly on the crack case. A previous owner replaced it and put the new one up at the coil. And returning the machine to operation I want sure if it made a diff. Many thanks \$\endgroup\$– JimCommented Mar 27, 2019 at 16:23