Article about Lucas 2MC capacitor

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Hi guys , new to this forum having had several Nortons during my formative years, now the proud owner of a 1973 850 Roadster with 16,000m only.
After lots of research and tech info off ownes here in NZ, have fitted a Pazon Sure Fire, went to see Andy at Pazon as he lives 20 minutes from me, he states the same, that the cap is of good use if the battery is dead and you ned to kick some life into it. Other than the voltage check, is there anyway of checking '30 year old' unit by the resistance,(or lack of)acroos it?
Any of you guys have any feed back on RGM belt drives?
Great forum
Regards Mike
 
I'm rusty at this, but I believe you need a capacitor tester that measures the capacitance in microfarads; better testers can charge and load test the capacitor also.

I had a top-of-the-line tester when I was in the Air Conditioning business, did full range capacitor testing. It would allow you to substitude it's on-board array for the cap you where checking on whichever piece of equipment (motor, compressor, etc), AND it would let you "rock" a compressor back to life before giving up on it.
 
Connect a 12 V battery to the capacitor for a few seconds. Take the wires off. Let the MC2 sit overnight. Test the voltage with a digital VOM and there should still be good voltage on it. If not, it's leaky or shorted. If a digital VOM reads a short it's bad. You can also test the actual capacitance by measuring the discharge through a resistor. I forget the capacitance of the MC2, but T=RC and you can check the time it takes to discharge (67% I think) the capacitor and come up with the actual capacitance fairly easy. Look it up, commonly available information, I get tired of looking it up (lazy) because I can't remember.

Dave
69S
 
Ok thanks for that, i guess the charge with 12V and disconnect battery and measure the voltage over different time method would be the easiest in lieu of a microfarrad tester!!! and the last test method poasted by Dog T
I would still like to use one , just want to make sure it works.
Do you or any of your Norton contacts have some feed back on RGM priamary belt drives. looking at fitting one to a low miles '73 850 that is very straight.
Regards Mike
 
Brooking 850 said:
Ok thanks for that, i guess the charge with 12V and disconnect battery and measure the voltage over different time method would be the easiest in lieu of a microfarrad tester!!! and the last test method poasted by Dog T
I would still like to use one , just want to make sure it works.
Do you or any of your Norton contacts have some feed back on RGM priamary belt drives. looking at fitting one to a low miles '73 850 that is very straight.
Regards Mike
Click to expand...
There's nothing wrong with using the Cap for a 'battery'. I did it for many years after the original battery died. Trouble is if your rotor is not up to snuff, it won't produce enough juice to get it started, unless you have a large hill to coast down and forget the EI.

If you have a decent digital VOM (Fluke), it will have a MFD tester included, you may have a friend that has one, they are quite accurate.

Dave
69S
 
L.A.B. said:
illf8ed said:
I pulled the wires from the capacitor connections and checked the output....12.7v. It's been a week since the last ride, so means the capacitor is still good, right?
Click to expand...

It would be, if you had disconnected the 2MC a week ago?

Switching off the ignition doesn't disconnect the 2MC from the battery, whether the bike has been unused for a day, a week or a month makes no difference as the 2MC will remain fully charged until it is actually disconnected from the battery, (or the fuse is removed etc) only then will it begin to discharge which-if it's still good, could take several hours. The 2MC test procedure is in the factory manuals.
Click to expand...

OK thanks
 
L.A.B. said:
.. if it's still good, could take several hours..
Click to expand...

that's not good enough .
If discharged after 24 h , replace it .
A good one will hold 90 % of its charge for several weeks .
 
ludwig said:
L.A.B. said:
.. if it's still good, could take several hours..
Click to expand...

that's not good enough .
If discharged after 24 h , replace it .
A good one will hold 90 % of its charge for several weeks .
Click to expand...


Why would the 2MC need to hold a charge for several weeks. According to the manual test procedure the 2MC is serviceable if it registers not less than 9V after 5 minutes disconnection. Surely the important thing is that the 2MC does not leak a significant amount of battery current to earth/ground and thus drain the battery when the bike is not in use.
 
Functionally the cap only need to hold charge for length of time between a magnet passing an alternator coil and the next contact breaker to open. In this application the capacitor is exactly like an extra tiny fast charge discharge battery. I use way way bigger ones to store and release the amphere's needed on powerful base hits of stereo that no mere battery bank could deliver the spike peaks w/o lopping em off.

Tickier batteryless ignition charging systems are called magnetos.
 
L.A.B. said:
..Why would the 2MC need to hold a charge for several weeks..
Click to expand...

That's almost like saying that it is ok if an engine leaks 100cc of oil a week ..
If a capacitor discharges in a few hours , that is an indication that something is wrong .
Maybe a pinhole in the insulation foil ..
This can get rapidly worse . ( read the initial article ..)
I know , some live by the adagio " if it ain't broke , don't fix it " and only start thinking when they are stranded by the roadside ..
 
ludwig said:
L.A.B. said:
..Why would the 2MC need to hold a charge for several weeks..
Click to expand...

That's almost like saying that it is ok if an engine leaks 100cc of oil a week ..
Click to expand...

In oil terms I think it's probably nearer 10cc a year!

My Mk3's 2MC will stay charged for several hours but nowhere near as long as a week, however a test of battery current drain with the 2MC connected doesn't move the reading off zero on the milliamp scale-so where's the problem?
 
L.A.B. said:
ludwig said:
L.A.B. said:
..In oil terms I think it's probably nearer 10cc a year! ..
Click to expand...
Even 1 cc a year is unacceptable ..
Click to expand...

For you, perhaps?
Click to expand...

Yes , and for everyone who takes engineering seriously .
I t is presicely this "close enough" mentality that made the entire British automotive and motorcycle industry go belly up ..
 
ludwig said:
Yes , and for everyone who takes engineering seriously .
I t is presicely this "close enough" mentality that made the entire British automotive and motorcycle industry go belly up ..
Click to expand...

Well I'm not an engineer-just a happy amateur-so I wouldn't really know, however I think that I, and perhaps other mere mortals would be content to accept such a low rate of depletion (a zero reading) as being "within acceptable limits".
 
illf8ed said:
L.A.B. said:
illf8ed said:
I pulled the wires from the capacitor connections and checked the output....12.7v. It's been a week since the last ride, so means the capacitor is still good, right?
Click to expand...

It would be, if you had disconnected the 2MC a week ago?

Switching off the ignition doesn't disconnect the 2MC from the battery, whether the bike has been unused for a day, a week or a month makes no difference as the 2MC will remain fully charged until it is actually disconnected from the battery, (or the fuse is removed etc) only then will it begin to discharge which-if it's still good, could take several hours. The 2MC test procedure is in the factory manuals.
Click to expand...

OK thanks
Click to expand...

It's been 4 days now since I disconnected the 2MC blue can. It still has 12.4v output. At what point should I make the judgement as good or bad?
 
illf8ed said:
It's been 4 days now since I disconnected the 2MC blue can. It still has 12.4v output. At what point should I make the judgement as good or bad?
Click to expand...

According to the test data given in the factory workshop manuals you could have made that judgement 3 days 23 hours and 55 minutes ago. :wink:
 
L.A.B. said:
..According to the test data given in the factory workshop manuals you could have made that judgement 3 days 23 hours and 55 minutes ago. :wink:
Click to expand...
But then , going strictly by the factory workshop manuals will only allow you to reproduce the same POS that left the factory 40 years ago . This is 2011 and the bar is raised ..
 
It isn't really raising the bar when the amount of time the capacitor remains charged during a period of inactivity appears to have little or nothing to do with how efficiently the 2MC operates.

Re-read what hobot and dynodave said.

hobot said:
Functionally the cap only need to hold charge for length of time between a magnet passing an alternator coil and the next contact breaker to open. In this application the capacitor is exactly like an extra tiny fast charge discharge battery. I use way way bigger ones to store and release the amphere's needed on powerful base hits of stereo that no mere battery bank could deliver the spike peaks w/o lopping em off.
Click to expand...


dynodave said:
"In an RC circuit, the value of the time constant (in seconds) is equal to the product of the circuit resistance (in ohms) and the circuit capacitance (in farads)",
.0045f (4500Uf)x1.8ohms = .008sec to loose 66% of the 12V. Therefore only 4 V remaining.... after .024 sec the cap is effectly discharged
from the time you release the kill switch.... can you have the kick lever in full swing in 24 milliseconds ?????
Click to expand...
 
Because of this thread , and out of curiousity , I loaded up all the electrolitic capacitors I have lying around a few days ago ,
using a car battery and a test bulb ,ranging fron 4800 to 14000 Mf :

Article about Lucas 2MC capacitor


I just checked them , and ALL show at least 11Volts , except one of the 2MC 's .

If from 5 identical caps , from the same producer , one sjhows 11 volts after 5 days, and the other 0 after 1 hour , then I know something is wrong , and I won't use that cap for any aplication , even if some 40 year old factory manual says it is ok to do so .

I could bore you with some breakdown stories due to failing caps , but I won't

I believe the comparison with an oil leaking engine is valid .

By raisng the bar , I mean we don't have to accept the sloppy tolerances of the British industry of the sixties any more .
We all know where it brought them ..
 
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