[Prev][Next][Index][Thread]

120 or 240 ???

So which is it? 120 volts or 240 volts to supply your coil
system? I make this open soapbox post because I see a few
new projects in the making (and on the drawing board) and I
thought I would point out the advantages of powering a coil
system with 240 volts over the more common 120 volts used on
smaller coils.

240 volts is preferred.

First we should look at 120 vs 240 in your neons. Neons,
especially neons without power factor correction, are really
juice hungry when you throw them on a coil. It is not uncommon 
for a bank of neons putting out 1.5 kVA to a Tesla tank to trip
the 30 amp breakers on a common household 120v circuit. You say:
"I'll use power factor correction and reduce the draw by 50%."

Fine, add up the power factor correction required for a neon
power supply of 1.5 kVA, and after the math is worked out you are
looking at around 150 microFarads. That's a lot of 440 volt rated
motor starting capacitors...

But if you work the math for power factor correction at 240
volts, you find the required capacitance for power factor
correction drops by 75%. It reduces to around 35-40 microFarads
of power factor correction required at 240 volts. This really
cuts the cost for these capacitors.

"How difficult is it",  you might ask, "to rig neons up to
operate on 240 volts?"

It's really very easy. Most of the coil systems that have been
discussed here are using multiple neon transformers ganged
together to get the required current output. It is certain that
the lower output neons (30 mA) are more commonly found. Simply
wire the primaries of two neons in series and throw the 240 volts
across two transformers at a time. This means no odd numbers of
neons in the bank, and all the transformers must be paired up to
a unit with matching output. As far as the wiring is concerned
this is the only change required. Secondaries are still wired in
parallel, phasing must still be tested (out of phase units are
simply corrected by reversing the primary connections), and
grounding, safety gaps, bypassing etc. all remains the same. 

This will have the effect of reducing your current draw at the
breaker box by over 75% (assuming previous operation at 120 volts
without power factor correction). A power supply that was
tripping 30 Amp breakers at 120 volts is now drawing a measly 7.5
Amperes at 240 volts, and only requires 35-40 microFarads of
power factor correction capacitance to achieve this. 

If you can't see the advantage yet, then let me add another tip
or two. The first is that most 240 volt lines are breaker
protected at 50 amps minimum, so your 1.5 kVA neon power supply
is at the bottom of these circuit current ratings. This means
there is really nowhere to go but up in power levels. The second
factor is that once you move up to 240 volts you will never look
back; power supply components with 240 volt ratings are more
durable and generally higher quality; 240 volt equipment is
usually better able to handle voltage and current overloads.
Lastly I should mention that if you switch to 240 while still
using neons, adding a "real" transformer (i.e. potential or pig)
is a breeze, all you need to do is add in the current limiting.

If you have ever tripped a breaker or dimmed the lights during
normal coil operation, or you are moving up to 1.5kVA (or above)
for the first time, consider adding that 240 volt line to your
coil power supply. Nothing gets a person frustrated faster than
having a coil system that will spit fire for five minutes before
warming up, and then having the breaker trip after 30 seconds... 

Richard Quick


... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12