2MC Capacitor & Lecky IGN

GDay Folks,

Most Commando owners will be aware that out of the factory the bike (MKIII 850 in my case) was fitted with a Lucas 2MC capacitor, designed to get the bike going if you've been daft enough to flatten the battery. My question is simply how can this function be maintained when most of us have electronic IGN? I fitted a certain British make of 'lecky IGN in favour of old Joe's points as I used to ride the bike to work in Central London. One day I was stupid enough to leave the IGN on after faffing about with keys, chains and padlocks and found the bike was dead as dead gets at the end of the day. Whilst even the 2MC capacitor may not have worked with points in this scenario, what do folk think about maintaining this function with electronic IGN. Is it still possible to start with a dead battery and 'lecky IGN? My experience says no but if any smart chap knows better, please get in touch!

crusadersports

Somehow I thought that the capacitor was provided to allow the bike to be used in competition without the battery, the cap providing a load to the charging system. I would expect that if you let the battery discharge to a low voltage the cap would at best be at the same voltage as the battery. Therefore, I think if your battery is discharged below that necessary to excite the electronic ignition, the cap won't either.

I have run my 850Mk2 with an original Boyer analogue EI on the 2MC several times. According to general advice from EI makers, this should be avoided but it still worked with no bad after effect. I've even started and run the bike with the battery fuse disconnected for several miles before I realised that the fuse was in my pocket! The 2MC works well when its in good order, but they deteriorate with age and can cause more difficulties than they are worth.

Mick

SteveMinning said:

Somehow I thought that the capacitor was provided to allow the bike to be used in competition without the battery, the cap providing a load to the charging system.

Click to expand...

The Commando 2MC is really intended as an emergency starting aid, rather than as a battery replacement for competition-which of course the 2MC can also be used for if necessary.

SteveMinning said:

I would expect that if you let the battery discharge to a low voltage the cap would at best be at the same voltage as the battery. Therefore, I think if your battery is discharged below that necessary to excite the electronic ignition, the cap won't either.

Click to expand...

If the battery has become completely discharged, then it should be temporarily disconnected-so the alternator output during kickstarting isn't drained by the discharged battery. Once the bike has been started the battery can be reconnected.

Ahhh. Makes perfect sense L.A.B. So, for an electronic ignition equipped bike with a dead battery you can disconnect the battery with the capacitor still in circuit and the cap will charge as you kick it until it reaches the voltage necessary to excite the ignition. Hmmm, never thought of it that way.

SteveMinning
The finer technicality of this capacitors function is as an efficiency "aid" to the alternator.
To define aid....only "during the kick" does it help to route "all" the energy to the ignition.
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.
Yes it is better than nothing, but putting a capacitor that is to large is also just as bad or worse than no capacitor at all.

Dave, Once the bike is up and running, the capacitor can fill in gaps produced by AC being converted to DC making a better quality DC for the bike?
“A tiny battery used to just fill in the low spots taking as much as it gives but making an over all better DC system based on an AC core?
Hard to test but easy to believe?

Not all that hard to test its effect on the ripply DC waveform if you have an oscilloscope handy.

I would have to respectfully disagree with dynodaves spin on the capacitor, this electrolytic capacitor does not discharge entirely unless the ignition drags all that power out of the capacitor.

Once there is sufficient power within the capacitor, from your kicking over the engine, the engine will probably start, soon as the engine spins again ( from the start or another kick over ), presto, more DC power. If the battery was left in the circuit whilst doing this, the battery would take all the charge, and it will take alot longer for you to charge the battery using the kick start method ( months I'd reckon ), rolling down a hill in first might get you going.

Electrolytic capacitors are generally used for smoothing out DC ripple, the rectifier ( Bridge type generally ), it turns AC in to DC, but the DC is not "smoothed out", the battery will do it as will the capacitor.

In the case of this 2MC capacitor, it usually help the battery smooth out the rippled DC. DC batteries do not like ripple, so having the capacitor inplace will be good for your batterys life.

For interest, the capacitor across the ignition points systems work pretty much in the fashion described above, they, when working, stop arcing across the points at in-opportune times, try running your bike with out the "condensor", the points will put on quite a light show and your bike will probably sound quite rough.

Nope - Dyno Dave is right. The current draw of most ignitions is on the order of amps. That will discharge the capacitor each time after the bike is kicked. That is why he says if the capacitor is too large it will not charge up fast enough with each kick.

This is with the battery disconnected for emergency start.

I fitted a Cap the size of a soup can to my Victor, if the battery is dead after dissconnecting it I leave the ignition off and kick the bike over with the compression release pulled in 4 or 5 times. When I turn the ignition on I have according to the voltage LED I have fitted about 30 secs to get the first kick in before the cap is discharged which is plenty.

kommando said:

When I turn the ignition on I have according to the voltage LED I have fitted about 30 secs to get the first kick in before the cap is discharged which is plenty.

Click to expand...

The Commando charge warning lamp and also the MKIII neutral lamp are an additional drain on the 2MC and will discharge it immediately whenever the ignition is switched on.

The Commando charge warning lamp and also the MKIII neutral lamp are an additional drain on the 2MC and will discharge it immediately whenever the ignition is switched on.

Click to expand...

As I said it was on a Victor and not a Commando and the Cap is a huge one at least 20 times the charge holding power in that application it works, if the Commando had a compression release it would still work as long as you have a voltage LED as it carries at least 20 times the charge. Being able to kick over without resistance is why it works.

kommando said:

As I said it was on a Victor and not a Commando and the Cap is a huge one at least 20 times the charge holding power in that application it works,

Click to expand...

Yes, I was aware of that, I was attempting to point out that with the standard 2MC unit and warning lamps on a Commando, "priming" the capacitor wouldn't work-as the warning lamp/s (and perhaps the EI) will discharge it in under a second as soon as the ignition is switched on.

I've had to test dead and no battery on points and Boyer. Battery fell/thrown completely out of Ms Peel one day on a joy ride only discovered when I shut off throttle to slow up and wave as farmer friend it stalled dead out and could not be kick started fast enough, so grabbed hold of farmer PU and to 25 mph then let go and got home as long as I keep the rpm up enough. If the alternator coils were arranged to the volt spike hit about time points triggered there would be no need of cap at all. Think and wire in Cap in power gird as just another battery. Blue can is not sized big enough to hold ignition charge and light a small light too or over come a really dead chemical battery.

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.

Click to expand...

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.

When I got my '69 back in '72, the battery was dead. I took it out and never bought a new one. It always started in 2 or 3 kicks with just the 2MC. However now it won't, I have to use a battery. Don't know if it's the cap or as I suspect the rotor has lost some magnetism after 42 years. I have recollections of the charging system getting weak around '80. I would suspect that the cap won't hold much of a charge for long (ms) if either of the points are closed or you have any lights on in the circuit (brake).

Dave
69S

DogT,

Most likely just replace the capacitor, the electrolytic capacitors dry out over time, particularly when on a motorcycle. I would suggest changing the capacitor when you change your battery ( every couple of years ).

Loss of magnetism should just increase the number of kicks required.


Check the resistance of the capacitor versus a new one and you'll soon see the difference, anything over two mega ohms is generally OK ( it may take a while for the reading on the mutlimeter to stabilise, it usually increases in value to a final figure, may take a minute or two - remember when the multimeter is testing the capacitor, the capacitor is being charged by the multimeter ).

Josh,
Yeah, when I first tried starting this thing, we tried for about a half day with the MC2 and gave up. We probably were stepping on the rear brake too. I even put a new (large computer) cap in it and it didn't make any diff. As soon as I put a battery on it, started up second kick, it didn't take much of a battery either, a 3AH gel cell will start it. I did check the MC2 and it seemed OK, but after 40 years I suppose it really isn't any good. I have some old boat anchor radios that have some old caps in them and some are still good, not many though. I'll stick the Fluke on it and see what it does. The ammeter does start charging at about 3K rpm.

Dave
69S

Thanks to all who replied!

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


crusadersports