[time-nuts] Need help with transformer core

Bill Hawkins bill at iaxs.net
Sat Aug 30 00:30:23 EDT 2014


Corby,

Assuming that what you want to do is find a substitute for the F1152,
you should be aware that schematics don't give you enough information to
build one from scratch. The easiest thing to do is buy one from a
catalog of DC-DC converters with the appropriate voltages and power -
unless the frequency matters. Modern converters run at 100 KHz or more.

Assuming you have the converter but it doesn't work, if the windings
aren't burned or shorted and the core isn't cracked, the transformer
should be OK. If a winding is bad, it shouldn't be difficult to rewind
for a 20 KHz converter. There's a lot more turns at 60 Hz. You must use
the same wire size or the winding won't fit.

But if you have to get into the magnetics, as I did for 30 KVA frequency
changers in 1968, and also DC converters, here are a few design
considerations:
(This assumes a saturating core oscillator with little more than two
semiconductor switches for the oscillator and a bridge rectifier and
filter for the output.)

1. Cores have maximum operating frequencies depending on material; power
capacity depending on amount of core material; and a primary winding
depending on the input current and voltage, or voltage and power.

4. The core has an open area which will be filled with windings. The
size/gauge of the wire depends on the current carried. The number of
turns determines the inductance of the primary, which determines the
time that it will take for the core to saturate at a fixed supply
voltage, by V = L di/dt. The saturation time, times 2, is the period of
the oscillation. Note that i is not a function of output power, but is
determined by L and V. For a given L and V, the saturation time is
determined by the amount of core material. The current falls out of the
equations when you are looking for saturation time. To be precise, the
current discussed here is the magnetizing current. Total current
increases as the output draws current.

8. The open area in the core also has to accommodate the secondary. The
number of turns is determined by the input/output voltage ratio. The
wire size for the necessary current and the open core area determine the
number of turns that will fit, as does the thickness of the insulation.
Throw in the calculations required to minimize the weight for a given
power, and perhaps you begin to see why transformer design is as much
art as science.

Disclaimer: This is from memory, as my design books have been downsized
on the way to a senior living apartment.

Bill Hawkins


-----Original Message-----
From: cdelect at juno.com
Sent: Friday, August 29, 2014 5:12 PM

I'm trying to built a DC to DC from an existing schematic for a
frequency
standard I'm working on.

The transformer core is identified as an Indiana General F1152-1-6

The Dc to Dc is running at 22Khz and maybe 20 Watts.

Can't find any info that would allow me to decide on a proper
substitute.

Anybody out there have any data on this?

Thanks.

Corby



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