Capacitor

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ELLIS

ELLIS

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How long will the capacitor function for once you have a flat battery and turned on the ignition on a MK3 Commando.

ELLIS
 
Agreed that discharging of a capacitor is very fast...but that does not imply you cannot run the bike without a battery just using the capacitor. The Alt will provide sufficient power to handle consumption rate once engine is rotating at reasonable rpm. Cap just needs to hold charge for initial kicks to fire ignition as I understand it.
 
As long as you can give it several good stout kicks in a row, the capacitor will work indefinitely.

I had an original 1969 Lucas 2MC capacitor in my '69 Bonnie that ran without a battery for the 15 years I owned it.

"Shelf life" my butt!

(and I don't subscribe to "Lucas is crap" either, LOTS of practical experience proved otherwise)
...apart from the CONNECTORS, especially the female tubes that crack)
 
Those female ends do suck, but all the remaining Lucas parts do the job very well for me so I can't complain.... Including that old capacitor in question. Very natty looking these days too.
 
grandpaul said:
"Shelf life" my butt!
Click to expand...

Sorry buddy, but as an EE who designed power supplies for a living I can assure you that electrolytic capacitors get leaky with age. That said, I have a 13.86 volt 30 amp power supply that still has very low ripple after 45 years, so sometimes we get lucky.
 
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I guess I should go purchase that lotto ticket about now.... I count myself fortunate that God has smiled on me on this small matter.
 
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Thanks to everybody who replied to my post. I feel i have learned something more about my Commando now.

ELLIS
 
I don't know that as i have not tried it. Just bought a new capacitor, only £16. The old one i replaced was the original so 45 years old. Fitted it on the bike and went for a short ride to charge it up, unplugged the battery and it started first kick. (result)

ELLIS
 
ELLIS said:
I don't know that as i have not tried it. Just bought a new capacitor, only £16. The old one i replaced was the original so 45 years old. Fitted it on the bike and went for a short ride to charge it up, unplugged the battery and it started first kick. (result)

ELLIS
Click to expand...

The capacitor was charged the moment you connected it to the battery.

And it was discharged within milliseconds of closing the circuit to charge the ignition coil once the battery was disconnected.

With no battery the capacitor charges off the pulse produced as the alternator magnet passes the coil in the stator.
It discharges completely each time it charges the ignition coil - between the capacitor and the alternator you hopefully charge the coil with enough power to create a feeble spark large enough to start the engine.

There is no "kicking multiple times" to charge the capacitor, although it might help get a good mixture in the cylinder that is easy to light with a feeble spark.
 
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There's no need to "charge it up".

The stator puts out enough voltage (actually current) per winding to start the bike, at least on points, and all the capacitor needs to do is hold that voltage until the rotor's next magnet passes by the next winding. You might have to bump start if you have an electronic ignition.

You can think of a capacitor as a tiny rechargeable battery. It helps smooth out the voltage from the bridge rectifier or modern voltage regulator. It does that while starting and while running.

On a normally wired Norton, if you have a dead battery, you might not be able to start because the battery is holding the voltage down. You take the fuse out and the bike will start. Then you put the fuse back in with the bike running and the battery charges.
 
Here the testing procedure in the manual:
Capacitor
 
crusadersports said:
You have to wonder why they fitted a capacitor to the Mk 3, with its ignition and neutral warning lights?
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Although the neutral light is an additional but small drain on the system as Jim said, the electrical power to start the bike comes from the alternator.

The Mk3 has a more powerful (RM23) alternator so I'd guess there could be slightly more output at kickstarting speed but I couldn't say for certain.
 
L.A.B. said:
Although the neutral light is an additional but small drain on the system as Jim said, the electrical power to start the bike comes from the alternator.

The Mk3 has a more powerful (RM23) alternator so I'd guess there could be slightly more output at kickstarting speed but I couldn't say for certain.
Click to expand...
Since the coils draw amps and the neutral light draws milliamps, that bulb is not a concern.
 
True what marshg246 said on the dead battery.
Suffered once from a bad quality new one while on the road with a Mk2, disconnected it, and the bike started one kick on the capacitor only. Again and again.
Seems to me low / bad battery shows up when bike jitters / dies when you brake and/or put blinker on say at traffic lights, an extra 21 / 42 Watts kicks in.
Anyway, I am a Blue Can Fan!

Warning light bulbs on Mk3 are 1.2 Watt so perhaps a bit more than just milliamps?
 
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