2MC Capacitor & Lecky IGN

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crusadersports said:
So are folk suggesting a Commando should start on the 2MC capacitor even with a completely drained battery where a Pazon or Boyer is fitted?

I hear you that the capacitor does need renewing every few years. I just wondered if electronic igntion renderd it completley obsolete: ie: Is there actually any point in renewing it? I'm sure I'm not the first person to accidentally leave the IGN on.... Just the situation where a magneto was useful...

I presume you can isolate the battery by simply removing the fuse? Will the warning lights make that much difference? I presumed they'd just glow when you kicked it over... hopefully they wouldn't prevent the fires lighting quote]

It will work best with a Pazon. Its possible with a Boyer that is in good condition.

Genuine 2MC items are old stock. They have not been made in years, Even sitting on the shelf the insulation degrades.

Yes you isolate the battery by removing the fuse, but it doesn't make any difference better to leave it contributing some current.

Yes warning lights will draw current. They're a ridiculous appendage on a chrome headlamp shell. Disconnect them.


Mick
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If you are using the original capacitor it's prob best to replace it. I don't know what type they are, but if they are like the ones in vintage synthesizers from the 70's there is a chance they will explode. Better safe than sorry
 
Mick,

Just about any reasonable electronics shop will sell a suitable alternate, Jaycar, Dick Smith etc etc ( the value of the capacitor does not really matter, the bigger the value the more capacity, but more kicking will initially be required, the max voltage rating and polarity if applicable is important).

My bike is still in pieces, when it is back together, I will be using a 50 uF(micro farad), 400 volt capacitor, my diesel standby generator uses the same item, if the generators one dies I can grab the one off the bike to keep the house powered )
 
If dead battery is disconnected first my original 2MC will work with an analog Boyer. You have to kick it like you mean it though. Or it will bite back.

Probably I should try and rebuild the 2MC some nice weekend this summer. It's been a long hard life for an electrolytic cap. Always been there -- part of the greasy blob on the right of the battery box -- so I hate to just remove it. I like the chain oiler too!

With old radios we put new caps inside the old cans and seal them back up with JB Weld. So I want to try it out on my blue guinea pig.

Russ
 
Josh Cox said:
Once the kick (engine spin) is over, within milliseconds the cap is fully discharged. So there is NO storing of energy to be added to your second kick effort.
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If that is the case, why does it take multiple kicks before the bike can be started ?, the capacitor will only be discharged when the load required is equal or greater than that being held in the capacitor.

The capacitor does not automatically (without a load greater than current capacity) dischage within milliseconds, infact capacitors will hold power for quite some time, the internal resistance of the average capacitor is usually greater that 2 mega ohms, this is one thing you check with a multi meter when testing a capacitors functionality.
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It takes multiple kicks..... to get your leg in condition to finally kick it fast enough to actually make enough current to fire it up. The ignition is always on and the current is alway being drawn off like a fire hose dumping water out of a 5 gallon pail. Unless you are so lucky to have stopped exactically between points opening on a points system.
Even on a boyer, as soon as the first trigger turns on the drive transistor the flood gates are opened with surge of over 2 amps which will deplete the cap in very short order.
What do you think the TC of a 450uF @14v (if lucky) through a 4 ohm resistor(2 coils in series)...can you do electronics 101 math? = .00018 seconds and therefore 3 TC will deplete the cap to under 1.2 volts in .00054 seconds. You're a very fast kicker if you can beat that....I will not confuse this discussion with the inductive aspect of this equipment.
FWIW http://en.wikipedia.org/wiki/RC_time_constant

A cap does start to dicharge the instant the EXTERNAL load (which is the coils) is applied ... the INSTANT the points close or transistor is turned on.
The internal impedance of the cap is not the issue here as it relates to discharge through an EXTERNAL load.
Of course the power going back IN to the cap does helps keep the voltage up but the power is still being depleted very quickly.
 
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