Morris Minor Owners Club

hI all,
Can any one out there tell me what the condenser does inside the dizzy thanks
phil

More or less, it acts as a capacitor across the points, thus preventing excessive sparking as the points open and close, thus minimising points wear.

If it goes 'open circuit' then the points will spark so much that they
will not function properly for long. If it goes 'short circuit' then you
will get no spark at all!

It stores up energy which is then released into the coil each time the points open - causing the HT pulse which fires the points. Weak condenser = weak spark. They are so inexpensive they should be replaced every few years as a matter of course.

bmcecosse wrote:It stores up energy which is then released into the coil each time the points open - causing the HT pulse which fires the points.

No, it does not work like that. As has been said, it's a device for stopping excessive sparking across the points (bit like a low pass filter) to make the points last a lot longer due to reduced burning and carbon deposits caused by wideband (non-supressed) sparking.

Weak condenser = weak spark.

Weak? Well, if it fails completely in the open circuit mode then the spark at the plug will be the same (for a while until the points burn), but if it starts to go short then it will reduce the spark intensity (at the plugs) as the PD at the coil LT will be reduced and so the HT will follow suit.

They are so inexpensive they should be replaced every few years as a matter of course.

That's a good idea for reliability and really when you change the points at service time, you should change the condenser too.

To be fair, the cost of getting *all* the service items for the minor is so cheap that I just replace the whole lot - apart from the HT leads - at every service. New distributor cap / rotor arm / plugs / points / condenser. Maybe that's why my services take so long

There have been many reports of faulty new parts such as distributor caps and rotor arms that I prefer to just carry spares and leave the working items well alone at service time.

I do what Kate does

Change all the bits (plugs, points, etc) then I have a set that I know worked.
I used to file the points flat (the main problem is that the pip upsets the gap = timing, and the correct spark), but it really isn't worth it with the cost of replacements.

I must confess to the awful feeling of "it won't start - I've just fitted new points" every time. It's easily cured - swopping the insultaing washer around.

Colin

Hello all,
I'm with Bmcecosse,
it is not just for spark suppression but alters the coil HT voltage.

Alec

Hi Alec,

Are you then saying that it performs the following function:

bmcecosse wrote:It stores up energy which is then released into the coil each time the points open - causing the HT pulse which fires the points.

Because if that were the case then the ignition would not work without it - which it does.

It could alter the PF (power factor) in the same way as the capacitor does in a fluorescent light, but surely it would have to be in parallel with the coil rather than in series with it (points open) or not connected at all (points closed)!

This is quite interesting though. Do you have any info on how it alters the HT voltage?

Hello Cam,

it affects the rate of collapse of the magnetic field in the coil. When the points open there is an induced voltage in both the secondary (HT) winding and the primary (LT) winding which, without the capacitor would try and discharge across the points causing a spark. This voltage charges the capacitor instead and assists in giving a higher HT voltage.

Bmc is not absolutely accurate, the capacitor does not cause the pulse but helps to boost it. The 'pulse' is generated by the collapse of the magnetic field when the points open and primary current flow ceases.

Alec

Alec, the 'sparking' is caused by a tiny gap appearing (as it opens) which is sufficient to breaks down the dielectric (air gap) between the two contacts. The capacitor (connected across this 'switch') allows the AC component to pass (the AC spark energy) and blocks the DC.

The maximum PD is between the +ve to the coil and the earth. Any voltage fed to the earth of the coil connection would effectively reduce the PD across the coil and hence the intensity of the HT voltage produced UNLESS it was at a lower potential than the earth (-voltage). The DC 'charging' of the capacitor would raise the PD with respect to earth and not lower it.

This type of system is used extensively to reduce 'spikes' and contact bounce effects. It reduces the 'noise' on breaking the contact. It does not introduce a spike!

Also, the physical size of the capacitor is small and unsuitable for DC charging in this way. It is however ideally sized for noise supression and spark reduction.

Very interesting but beyond my comprehension..........................

Hello Cam,

do you know what back EMF is generated in the primary circuit, because I don't. The capacitor, however, does affect the rate of collapse of the magnetic field. I wish I could remember more of the electro magnetic theory I did at college but that was a long time ago.

Alec

I stick by my - admittedly slightly simplified - description of what the capacitor does ! Of course it works with the impedance of the coil to create the powerful spark. Yes the engine will just about run without it - but very very poorly. AA man very cleverly 'rescued' my daughter's Mini (which had ground to a halt away from home) by simply strapping a radio suppressor on the outside of the dizzy connected to the main lead - and off the car went just like new ! I sorted it out with a proper new condenser when she got it home - but i awarded 10/10 to the AA !!