NEWS FLASH - December 2013
We are now selling magneto bearings, insulators, oil seals and armature shims from our on-line shop.

Brightspark Magnetos

NEW ... Take a look at some of the equipment we use in our workshop for magneto servicing and overhauls.

 

 

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FAQ sections:

FAQs about the EasyCap
FAQs about magneto condensers
FAQs about magnetism and remagnetising
FAQs about ATDs and timing
FAQs specific to Lucas magnetos
FAQs about magnetos generally

In this section:

Do I really need to disconnect the old condenser?
Is the EasyCap covered by a guarantee?
How can a capacitor so small do its job properly?
What is the capacitance of the EasyCap?
What is the voltage rating of the EasyCap?
What is the dV/dt rating of the EasyCap?
Over what temperature range can the EasyCap be used?
Is the EasyCap susceptible to high humidity and dampness?
What quality control is the EasyCap subjected to?
How long will an EasyCap last?
How can I check my EasyCap?
Can I make my own version of the EasyCap?

FAQs

What is the capacitance of the Brightspark EasyCap?

The C01, C02, C03 and C05 EasyCaps have a nominal capacitance of 150 nF (0.15 µF). For the C04 EasyCap, the figure is 136 nF. The C06 and C07 EasyCaps for Magnéto France magnetos have a capacitance of 220 nF (0.22 µF). The tolerance is ±10%.

The capacitors that we use have an "X7R" dielectric and their capacitance does vary with temperature, age and voltage.

Over the temperature range 0°C to 60°C, the capacitance can change +1% to -4% compared to room temperature.

Ageing is caused by realignment of the crystalline structure of the ceramic and is logarithmic. We do not have a figure from the capacitor manufacturer, but X7R dielectrics typically have an ageing rate of -1.5% to -4% per decade and the nominal capacitance is quoted for an age of 1,000 hours after the capacitor was last cooled through its Curie point -  something which happens when the capacitor is soldered to its circuit board. So, in the worst case, the capacitance will have decreased by 4% after 10,000 hours (about 14 months) and by a total of 8% after 100,000 hours (about 11 years) total. The capacitor can, however, be rejuvenated if desired by reheating it above its Curie point, for example by placing it in the oven at 150°C (300°F, gas mark 2) for half an hour.

When all is said and done, these variations with temperature and age are insignificant in a magneto application.

The capacitance of X7R ceramic capacitors is also said to change with applied DC voltage and applied AC voltage. We do not have any detailed data from the manufacturer for the capacitors we use, and we have not been able to find any published information about how X7R capacitances change in response to a complex waveform such as the low-tension voltage in a magneto. Suffice it to say, however, that if one compares the LT voltage waveforms on the oscilloscope using capacitors with a paper dielectric and with an X7R dielectric, there is nothing to choose between them. The following 'scope traces were obtained using a Lucas K1F magneto running at 1200 rpm. Capacitances of 100 nF were used, rather than our preferred 150 nF, because we did not have a 150 nF paper capacitor available at the time. (You can click on each picture to fill the screen and then click the back button in your browser to return.)

An

EasyCap alongside our experimental Evox-Rifa capacitor

LT voltage throughout the whole cycle
100 nF paper capacitor

Evox-Rifa PME271M610MR30


100 nF X7R ceramic capacitor

Murata GRM43DR72J104KW01L


LT voltage during the spark phase
100 nF paper capacitor

Evox-Rifa PME271M610MR30


100 nF X7R ceramic capacitor

Murata GRM43DR72J104KW01L


LT voltage at the beginning of the spark phase
100 nF paper capacitor

Evox-Rifa PME271M610MR30


100 nF X7R ceramic capacitor

Murata GRM43DR72J104KW01L

  Note that in some of these pictures of the beginning of the spark phase, the LT voltage rises slightly above zero for a period before the oscillation begins. In others it rises considerably and is then clamped back to zero. This is believed to be due to the capacitance (100 nF) being smaller than is desirable and an arc forming at the points as they begin to open and/or due to the contact breaker action being 'creaky'.
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