Re: [TCML] Power Factor Correction

["Phillip Slawinski" <pslawinski@xxxxxxxxx>]

Maybe 10uF is too much to get close to the right value.  It seemed like 30uF
was the correct value but it wasn't.  I measured secondary current and that
had been reduced by 25%.  90mA vs 120.  I did get a value that gave me 120mA
on the secondary side but the current draw on the primary was the same as it
had been before.

I have the PFC caps wired in series with the hot line to the transformer.

On Tue, Jul 15, 2008 at 2:52 PM, Skip Malley <skip@xxxxxxxxxxxxxxx> wrote:

> Where are you connecting the PFC capacitors and what value are you using?
>  The PFC caps should connect to the 120VAC input connections of the
> transformer.  If connected properly, the capacitance makes absolutely no
> difference to the current in the transformer.
>
> For the trial and error method follow these steps:
> 1.  connect an amp meter between the variac and the NST input.
> 2.  Power on the system and measure the current at some voltage near the
> expected operating voltage.
> 3.  Connect a PFC capacitor smaller than the expected value and measure the
> current.  If the capacitance is lower than the correct value, the current
> should be a bit lower.
> 4.  Continue adding capacitors until the current starts to rise again.  The
> best value is the value that had the lowest current reading.
>
> The best way to select the best PFC capacitance would be to use a current
> transformer or current probe and an oscilloscope.
> Connect the current transformer output to one channel of the scope and
> connect a probe to the HOT wire of the AC.  If you were to connect a light
> bulb to a current transformer, you would find that the voltage and current
> waveforms are in phase with each other with their zero crossings at the same
> time.  If you connect an inductive load, you would find that the zero
> crossings are skewed from each other.  By following the basic procedure
> above, the correct value is when the zero crossings are together again.
>
> I have made a couple current transformer setups where the transformer is
> mounted in a basic square electrical box with a standard line cord, an
> outlet, and a BNC output connector to connect to a scope.  I have calibrated
> them to show one Volt AC per Amp of current.  Other input/output ratios are
> easily made.
>
> It is also very interesting watching the waveforms of various pieces of
> equipment.  It can be a fun toy.
>
> If anyone is interested, I could show some photos and give some plans.  For
> a nominal price, I could also make and calibrate some transformers.  I could
> even provide a complete setup as I have described.  I will post a couple
> photos later.  I have a few things to accomplish this afternoon before I can
> "play".
>
> Skip
>
> At 01:40 PM 7/15/2008, you wrote:
>
>  How do I know what direction to go with capacitance?  I'm running the NST
>> with my Jacobs ladder to find the right value.  So far I've only found the
>> wrong value, and the very wrong value.  Turns out if you get it wrong you
>> actually increase [dramatically] the amount of current being dumped into
>> the
>> NST.  I was running it and all the sudden the aspahlt I neglected to
>> remove
>> between the core and the HV windings bubbled up from the oil.  When I run
>> without the PFC caps I'm drawing about 15A, with the caps I was pulling
>> peak
>> currents of 35A!  If I'm increasing current does that mean my capacitance
>> is
>> too high or too low?
>>
>
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