visual effect of capacitors


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KiwiJohn
Guru

Joined: 01/12/2005
Location: New Zealand
Posts: 691
Posted: 07:20am 02 Sep 2008      

Gordon, I doubt there is a truer statement than yours when you say placement of the capacitors in the circuit may be critical!

There are two aspects, I think, where capacitors could bring improvement. One is where the addition of capacitance brings the current phase into exact synchronisation with the voltage phase as presented to the rectifiers. I say this because if I understand correctly the diodes are actually not conducting between the point where the voltage is -0.6V and until it rises about +0.6V. Now this would not be much of an issue if there was no current flowing during that time but as in an inductive circuit current lags voltage I assume current is abruptly cut off when the diodes stop conducting and current is slow to get going again when the diodes turn on again. Presumably this is what causes the strange step shapes we see in the various current waveforms that have been posted.

Now the second aspect, which I fully admit may actually be the same, is that the current through the inductive coils will be slow to rise in reaction to the changing magnetic flux and I presume if there was capacitance to counter this inductive reactance the current would rise faster.

The watts we can get out of the alternator is the multiple of amps times volts and because this is alternating current we also have a 'power factor'. Power factor is always less than one except when current is in phase with voltage.

Presumably when we have a power factor of less than one we need more current to get the same watts and more current means more resitance (i.e. heat) losses.

Now, and I apologise for being so long winded, it appears what we really need to get from the addition of capacitors is a power factor of one in the AC part of our system.

I think someone with just a little more knowledge than me could find the inductance of the various coil configurations and could calculate the ideal size capacitors for a particular RPM.Edited by KiwiJohn 2008-09-03