# Re: HV & ballasts

```Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:

> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"

> You just gave me an idea!
> I've been thinking about how to build a "variable ballast

>inductor" that has discrete steps. The idea would be inductors

>switched with relays (ss or electromechanical)... I've always

>been stopped by the pain of building the set of inductors.

> What about using fluorescent ballasts just as that... series

>ballast inductors for a polepig type supply...

Well, rough numbers:
40 watt, 4 foot tube, means a ballast to handle
0.4A (roughly).  Anyone building 0.4A input coils?

A manyness in Parallel, probably a complex series
parallel mesh.  Need to design the switching control
to avoid overloading the inductors.  Need to find a
manyness of same value, to keep design simple.

> Especially, if you find some of the big ones used in factories

>for the high output 8 foot tubes

Rule of thumb: 10W per foot of tube.  So that's getting
on to 1A per ballast.  But.  Most such are 'rapid start'
single pit tubes, with internal resonant circuit to
make the spike.  I have this Sneaky Suspicion this would
make them Very Complicated (==unstable) to work with.
(and, sometimes, even with two pin lamps, electrically,
the tubes only use open tube and the rapid start
ballast.)

>(which are being replaced....)... We used to have a bunch at my

>former work which were 160W (I can't recall if it was 2 tubes at

>160 each (i.e. 320 W all told) or 2 80W tubes..).

>I think it will be 2x 80W.

> Say they are 320W ballasts...

My recollection ( I think good) is that the
WATTAGE rating is of the ASSEMBLY (lets skip VA
for a bit??), that is ballast plus lamp.  Lamps run
40-60VAC, IIR, with the remainder across the ballast.
I Dunno if they run two lamps in series, i think not:
stability problems).

If I'm doing this right in my head, easiest way to
figure it would be to work with the current: 80W
implies a bit under 0.8A at 120V (and some industrial
fluorescents are set up for 240 or 277, so know what's
being got....)  ANYway, work with the current is
easiest, i think.

> This means that they have to be able to take a continuous current

>of 3-4 Amps (120V fixtures).

I think otherwise.  cf above.  160W for the assembly,
means 2x 0.8A ballasts.  Measure one & be sure...

> I think the tubes probably have a voltage drop of 50-60 volts

>after start, so the ballast is dropping some 60 volts

Concur, unless a 240V or 277 (maybe even 480) ballast.

> and must

??
8)>>

> therefore have an impedance of around 10-30 ohms...

For the 0.8A case ('80W' tube (Yes.  The tube only
actually dissipates about 40W.  I believe they are
RATED the other way...)) I think more like 60V/0.8A=
70 ohmish???.

> I imagine that ballasts are available for the carting away...

> When they get marginal in start performance, they just get

> replaced (obviously, you don't want the ones that exploded,

>overheated, failed catastrophically, etc.)...

Certainly possible, but I'd check the numbers a bit.
And i have this image of a manyness in parallel.

best
dwp

```