Capacitor query

[MrB]

Question for the learned:What is the purpose of the capacitor on the IP2 attached to the battery negative? Is it essential / desirable / probably redundant if the police equipment is stripped off?

[Richard Negus]

The capacitor was introduced to protect voltage-sensitive equipment from surges in the system. Strobe lamps, for example, take a lot of current and with the small battery capacity of the IP2, could cause significant voltage changes when switched on or off.Main item to be affected by surge was the Sparkrite ignition unit ; if you still have one of these, I suggest keeping the capacitor even though you don't have any police equipment. It also helps when you have to push-start (perish the thought) which is why a similar capacitor was fitted to most Commando's.Commanders, with double battery capacity, Boyer ignition and a more robust voltage regulator, don't seem to suffer.R.

[MrB]

Thanks for the advice Richard.

[rustynuts]

Perhaps you missed the saga of the Lucas MC2 capacitor (as fitted to Commandos) in a recent issue of the NOC Roadhoder magazine a couple of months ago. It always amuses me how so much myth and misunderstanding builds up arround all things electrical. There was not one fitted to my IP2 when I purchased it. I still have the Sparkite units fitted but have not yet observed any ill effects due to lack of capacitor. There are many variables in an electrical system such as battery capacity, contact resistances and component values which all change over the years due to ageing, corrosion etc, so there could be a fine line between running OK without one or not.As Richard says, if you have a modern regulator and ignition unit, a capacitor would be of no benefit (apart from in the push start scenario) as much more attention is paid to power conditioning in modern electronics due to the fact that digital systems can both emit and be susceptible to electrical noise often to a greater extent than old analogue systems.Keeping a capacitor in the system can do you no harm.....Unless it fails short circuit.....or unless you connect it in reverse polarity - in which case it is liable to go bang and shower you in nasty fluid and curly bits of paper!One thing to watch out for is that electrolytic capacitors lose their capacity as they age so will become less effective over time. They also become increasingly (electrically) leaky over time so could eventually drain your battery at an undesirable rate. Beware of 'new old stock' replacements as these will have aged at the same rate as ones in use.

[Richard Negus]

Harking back to Commando days (early '70s), there is another Lucas item which controls the ignition warning light. Ignition 'on', engine not running = light 'on' ; engine running + system charging = light 'off', just like a car ('just like a Golf', some might say). Lucas produced a thing slightly smaller than the MC2, mounted on a dangly spring under the tank, which sensed alternator a/c and switched the light off. Lucas, for obvious reasons, called this a SIMULATOR. Somehow this got translated by Norton Villiers staff into ASSIMULATOR, which means something entirely different, but is still used as the description in parts books and manuals even today.R.