dl09
Full Member level 4
i am planning to build a ruhmkorff coil ruhmkorff coils use a quenching capacitor how do i determine the amount of capacitance of the capacitor to use? is there a way to calculate the amount of capacitance to use?
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I would argue the opposite. It helps to preserve the contacts although there is some additional loss as the capacitor is shorted out and discharges into the contacts. The coil is essentially a high ratio step-up transformer with a mechanically pulsed current in the primary winding. Resonance comes into play to some extent but in general, the faster you pulse the primary, the more output it will produce. An arc at the input could well increase the output rather than reduce it.
A good MOSFET driven with a square wave instead of the contacts will give much higher output.
Brian.
but according to wikipedia the quenching capacitor eliminates arcing across the switch contacts and the arcing across the switch contacts reduces voltage output
The voltage of the capacitor is also limited by the available energy.So you need a very high voltage capacitor.
Yes, with 50+ years of experience, much of that designing test equipment!may i ask if you are an engineer?
It does not eliminate arcing across the switch contacts; but it reduces.
Think in terms of the total energy: when the current collapses, a part of the energy may be stored into the capacitor (a significant part may be sent to the secondary coils). The stored energy in the capacitor will be fed into the coil when the contact is made again.
The problem is that when the contact is broken, the current must change very rapidly and the induced voltage must be very large (a singular process). So you need a very high voltage capacitor.
The ideal capacitor value will be determined by the LC time const matching the spring time const (for the make and break switch). Tricky to figure out but not impossible.
If you haven't got an oscilloscope or frequency counter, try using a mobile phone app that measures audio frequencies (there are many!) and let it hear the output of a nearby AM radio. The 'buzz' will be at contact operating frequency.any way to measure the spring time const at home?
An arc at the input could well increase the output rather than reduce it.
Brian.
I don't agree with you. Arcing between contacts means they are shorted by the arc for a while.