TC power factor issues
I did some work on my PT powered TC, and looked at the power factor.
I'm not a power factor expert, but anyhow, here are my observations
I now have this TC set up so I can easily change to LTR, reso, or STR
operation simply by adjusting the ballast L and the sync gap phase.
I'm using a 0.031uF cap, and two 1.5kVA potential transformers in
series, at 120bps sync. By connecting the PT primaries in parallel,
my present ballast capabilities, (up to about 40mH) gives me a good
In all cases, the power factor is best when the charging circuit is
adjusted for reso, or near reso operation. As the LTR and STR
realms are entered, the power factor gets worse. The farther one
moves from resonance...the worse the power factor becomes. This
makes perfect sense, although I hadn't really thought about it much
before. Using LTR, there's "too much" inductance, which naturally
ruins the power factor. Using STR, there's not enough, which ruins
the power factor. I'm using sync gaps for all this work, but I guess
that static gaps or non-sync rotaries wouldn't change the power
factor situation very much...I can't see why they should.
Using an LTR cap of double the reso-size, the power factor is
about 50 to 60%. In all cases I'm measuring the power factor by
comparing watts and volt-amps.
I do notice that certain sync firing phase settings can make the
power factor worse, but can't compensate for LTR or STR operation to
make it better by adjusting firing angle, etc.
A thought comes to mind: In a typical large coil, or other coil using
a non-shunted xfrmer.....since most folks don't use a wattmeter,
but rather a ammeter, they will be setting their systems for best
power factor automatically, by adjusting for best spark with minimum
input current. This will require that they use a ballast setting that
produces a near reso charging situation. There will only be a small
ballast setting "window" that will give efficient operation (good power
factor). (for electrical newbies, a poor power factor means there's a
lot of wasted reactive (apparent) power that does not go into the TC's
output, but heats up the input wires and variac, and adds to the
For LTR's we can just throw a cap across the TC input like we do
for NST's, to fix the power factor. But for STR's is there a simple
cure, other than adjusting the charging ballast closer to reso?