Condensors

Moto Rumi technical problems or solutions
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Elie
Posts: 94
Joined: Mon Jul 01, 2019 11:02 pm

Condensors

Post by Elie » Wed Aug 05, 2020 9:47 pm

I am going to replace the ignition condensers there is a difference between a 6 volt and a 12 volt condenser, 12 volt is easy to get

UHJ200
Posts: 556
Joined: Mon Aug 17, 2009 1:37 pm

Re: Condensors

Post by UHJ200 » Thu Aug 06, 2020 11:12 am

My understanding is that the capacitor's function is to suppress points arcing and the resulting erosion.
I very much doubt that it matters much what the voltage rating is as long as it exceeds the voltage it "sees".
I do dimly remember long ago discussing this very capacitor business with an electronically knowledgeable friend, I seem to recall him saying that to be truly effective the capacity should be matched to the energy involved, (or sumfink like that . . .) As an added complication it would appear that most capacitors have a manufacturing tolerance of 20% so the chances of getting two, even from the same batch. the same is slim. I rather suspect this is one of those "suck it and see" situations.

A small aside, Lucas magnetos have a capacitor built within the armature, due to the materials they were made from are often the cause of magneto failure due to age. In defence of Lucas they did their best with what was available, the units were probably not expected to last more than 10 years and most are now well over 50. It is interesting to note that it has been very difficult to find a modern replacement that can stand the severe electrical and mechanical stresses involved so they didn't do too badly. I have to wonder if age is not a factor in this case too.
The accusation that Lucas were "the company that invented darkness", in this case at least, is not deserved!

Ian Skinner
Posts: 551
Joined: Mon Aug 24, 2009 12:36 pm
Location: South Wales UK

Re: Condensors

Post by Ian Skinner » Thu Aug 06, 2020 3:23 pm

Hi David

I know, not applicable to Rumi. However, I am also a fifties Triumph enthusiast. About six years ago, I had a Mag failure on my 1957 Tiger 100. Spent a fortune with one of the lorded experts to rebuild the thing. Lasted 15 miles, till the engine warmed up. So I thought, I've had enough of this. So, I mentioned my problem to a BSA enthusiast that I knew. He said "Give up and do no more than fit a 'Brightspark Easy Cap' to the Magneto', after cutting the feed to the existing condenser. Wow!! I've never looked back, peanut solution beats £400 every time!! For comprehensive details see http://brightsparkmagnetos.com/easycap/

Ian

UHJ200
Posts: 556
Joined: Mon Aug 17, 2009 1:37 pm

Re: Condensors

Post by UHJ200 » Thu Aug 06, 2020 4:12 pm

"Wot's dat?"
"A goldfish".
"Wot's a goldfish?"

At my age you should expect nuffink more! :oops: :lol:

I rather suspect that those 'Brightspark' gizmos don't do the same job as the cappy buried inside a Lucas armature.

Still, it got you going which is what counts. :)

I do have a NOS Lucas cappy and some of the modern replacements, I'd post pictures but 'tis beyond my capabilities. If curosity gets the better of you PM me.

Elie
Posts: 94
Joined: Mon Jul 01, 2019 11:02 pm

Re: Condensors

Post by Elie » Fri Aug 07, 2020 5:55 pm

have replaced the condensers but that doesn't make much difference still bad starting could an electronic ignition make the difference? I also have a difference in pre-ignition between the left and the right cylinder, left 1.60 and right 2.10 mm btdc ,

UHJ200
Posts: 556
Joined: Mon Aug 17, 2009 1:37 pm

Re: Condensors

Post by UHJ200 » Fri Aug 07, 2020 6:55 pm

Ah! That you can do something about. The easiest option is to replace the points with a new matched pair of points. To check find something that is the same diameter as the pivot pins in the stator plate. A twist drill shank would do, place both of the moving parts of the breakers on the temporary pivot and compare the breaker heals for similarity in profile.

The other choice is to remove material from the face of the heal of the breaker that is opening soonest in order that the cam has to rotate further before it starts to lift.

arthur lewthwaite
Posts: 677
Joined: Fri Dec 28, 2012 7:03 pm

Re: Condensors

Post by arthur lewthwaite » Fri Aug 07, 2020 7:35 pm

look up runtronic electronic ignition,fit one of them.also see article on hugs first forma had an electronic sign he didn't know about until recently.regards arthur.

Elie
Posts: 94
Joined: Mon Jul 01, 2019 11:02 pm

Re: Condensors

Post by Elie » Sat Aug 08, 2020 9:31 pm

uhj 200 thanks for the idea to work the foot of the contact points, is a job that has to be done with patience, but now I have a difference of 0.20 mm between the piston height and start with 1 stage, thanks

Elie
Posts: 94
Joined: Mon Jul 01, 2019 11:02 pm

Re: Condensors

Post by Elie » Tue Aug 18, 2020 6:42 pm

the 12 volt condensers work fine and cost only 10 euros

Lars
Posts: 306
Joined: Fri Nov 02, 2012 3:09 pm
Location: Sweden

Re: Condensors

Post by Lars » Fri Aug 21, 2020 5:27 pm

Yes, that is to be expected. Good to know.

A few words about condensers, to adress the question in this thread:
The people selling these condensers are not telling us anything useful when they say "6V or 12 V condenser". Makes no sense, really. A condenser is just a capacitor, and they are always defined first by the capacitance and secondly by the maximum rated voltage. The problem is that in the automotive and motorcycle world, manufacturers usually do not give you either value! They just tell you to use their spare part number.

Condensers in both 6V and 12V systems must be able to withstand several hundred volts, and should be rated at least 500V, or even 1000V. Higher is just better, but does not affect the function. The important value is the capacitance. Each manufacturer is said to have chosen the optimal capacitance value for their system, but In reality, they all end up with almost the same value, usually between 0.1 and 0.3 microfarad (100 to 300 nF). The value is not super critical. A 0.22 uF (microfarad) value for example, is very common, and will work in almost any system.

What a seller is indicating by saying "for 12V system" is that the capacitance is towards the high end of the range listed above. 12V systems usually require a bit larger capacitance due to the higher energy involved. So, if you find a "12 V capacitor" that fits, it should work just fine.

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