# Voltage aiding transformer.

Discussion in 'Electronic Basics' started by Terry, Oct 2, 2003.

1. ### TerryGuest

Anybody have any experience/advice concerning a proposed 'voltage
aiding' transformer set up.

Namely a 115 to 230 volt (1:2 step up with completely separate
primary and secondary windings; not an auto transformer).

Input 115 volts with secondary 230 volts 'added' to produce an
output of 345 volts to power three 347 volt commercial
fluorescent light fixtures. Each fixture equipped with two 60
watt 96 inch tubes, a total of six 60 watt tubes plus ballast
transformer inefficiencies and possible power factor.

My figuring says that the transformer will have to up voltage
from 115 to 230 and be capable of handling two thirds of the
total wattage (VA), approximately. Also that it's secondary
winding must be able to carry the total input current since that
will flow through both windings in the 'series voltage aiding'
configuration.

Several primary/secondary transformers available; one, typically
is rated 340 VA, 115 to 230 volts.
Also have an a centre tapped auto transformer 0-115-230 available
but haven't figured out a way to use that in a voltage aiding
situation; at least with a suitable and conventional zero
potential neutral connection to the fixtures, also it would
require 230 volts (which is available) and double pole switching
of that 230 volt input which would like to avoid.

Would anyone like to push a pencil around and recommend ideas or
problems? Any suggestions ranging from "Crazy idea" to practical
considerations welcomed. When weather gets wintry intend to 'test
bench' this idea and possibly build into workshop; I've got scads
of spare 96 inch light tubes, more than we'll ever need, a spare
347 volt ballast; the fixtures were free and will provide 24 feet
of lighting, ideal for our 44 foot long workshop along with other
spot lighting over specific items.

Thanks for any input. Terry.

2. ### John FieldsGuest

When you're finished it'll be an autotransformer, and here's how to do
it:

+--------+
| |
115HOT>--+-- || --+
o)||(
)||(
)||(o
NEUT>----+-- || -------->345HOT
|
+-------------->NEUT

3. ### John PopelishGuest

My figuring agrees.
The center tapped autotransformer is really a 120 to 120 transformer
with the primary and secondary connected in series, much like you want
ot do with a 120 to 240 volt transformer. The only ways to get 360
volts out of it is to connect it as you say, across half of a 230 volt
circuit boosting that to 240, and adding the other half of the 240 in
series. So you are correct that it would take a double pole switch to
operate it, but would allow a smaller transformer.

4. ### TerryGuest

John Popelish and John Fields replied, thanks both for confirming
my various configurations. Wanted to make sure I hadn't missed
something obvious.

For example John Popelish said;
Yes transformer, with 230 volt input to circuit, would handle
about one third of the wattage plus losses & PF etc. And would
need double pole switch to open both sides (legs) of the 230
volts input.

I'd like to have a two wire 115 volt input with conventional
(white wire in North America) unswitched neutral and a single
pole switch in the live 115 volt (black in North America) lead.
I'll probably use red or a other colour for the live 345 volt
output lead. Mounting the whole voltage step up arrangement in a
grounded/earthed metal box with warning sign and circuit
description on outside; cos the next person to work on it, even
if an electrician, won't be expecting 345 volts in a residential
situation! May even put say a 5 amp fuse in the input to the
transformer and/or wire it from an individual 115 volt 15 amp
breaker in the panel. Since the transformers I have are rated for
230 volts etc. and were likely factory tested to higher voltages
I don't expect insulation to frame/ground to be a problem even
though transformer/s old.

Many thanks for input and comments. Terry.