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Converting a cheap welder to a high-current battery charger
I modified a low-cost Kenstar 200A
IGBT inverter welder so that it can be
used as a welder or a battery charger.
An added switch and relay allows either of the two functions to be selected.
The circuit uses the common
UC3846 switchmode controller chip.
Its output voltage can be varied from
11-22V, with the typically ~14.4V
charging voltage for 12V lead-acid batteries well within this range.
Generic IGBT or Mosfet welders are
cheap to buy and usually easy to repair
or modify. If they fail, it is often the
auxiliary ±24V power supply module
that is faulty.
I bought my welder for $7 in a nonworking condition and repaired it for
a few dollars. For any engineer used
to working on mains-powered equipment, it is easy to modify it to charge a
car battery. The high-voltage side does
not have to be changed – only the lowvoltage control board.
I purchased a low-cost LED voltage/
current meter online to display the battery voltage and charging current (see
our article on these meters in the De-
cember 2020 and this issue on p102;
siliconchip.com.au/Series/306). It is
necessary to add a current shunt resistor to sense and display the charge
current; most meters come with the
shunt. Both are shown in my circuit
diagram.
The modifications for switching between charging and welding are as follows. I added a 12V regulator on the
+24V rail which generates a voltage to
switch the coil of the added relay via
the charge/weld switch.
I cut the connection between pins
The modifications marked on the welder – remember to be careful when
working on mains-powered equipment.
Radiating test antenna for AM radios
Most transistor radios, and many
later valve models, use ferrite rod antennas. While some of these provide
external antenna/Earth connections,
most don’t.
While it is possible to connect a
signal generator directly to sets that
do have antenna connections, proper
alignment demands the use of a ‘dummy’ antenna to mimic the capacitive
nature of the few metres of wire typically used.
This radiating antenna solves several problems. It will work with all sets
using ferrite rod or wire loop antenna
circuits, needs no electrical connections to the set being tested and, for
ferrite rod antennas, gives an actual
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Silicon Chip
sensitivity calibration in microvolts
per metre (µV/m).
The antenna uses an ordinary 200 x
9.5mm ferrite rod. The coil is seventeen turns of wire, 0.4-0.65mm diameter (22~26 B&S gauge), spaced over
100mm. The two resistors, 100W and
82W, are carbon types. The antenna can
sit in a simple non-metallic cradle of
timber or plastic.
Placed close to the set under test, it’s
possible to inject IF signals at a high
enough level for IF alignment, even for
the low-sensitivity Regency TR-1 with
its unusual intermediate frequency of
262kHz. This eliminates the difficulties of injecting to the converter base
in compact sets.
Australia's
Australia’s electronics magazine
For broadcast alignment, set the
radiating antenna 600mm from the
receiver’s antenna and parallel to it,
and align at the usual frequencies of
1610kHz for the oscillator trimmer,
600kHz for the local oscillator coil
and antenna and 1400kHz for the antenna trimmer.
Once you have completed alignment, you can easily determine your
set’s sensitivity for 50mW output. With
the radiating antenna 600mm from the
set’s antenna rod, divide the generator
output by 20 to get the field strength
at the receiver.
For example, a signal generator output of 20mV RMS gives a field strength
of 1mV/m at the receiver.
The radiating loop gives useful results on sets with frame antenna loops,
but the radiating loop must be aimed
perpendicularly at the frame antenna
for measurement results.
This design is based on information
in Mingay’s Electrical Weekly, October 18, 1963: Pye Caddy Transistor
Portable Receiver Service Data Sheet.
Ian Batty,
Rosebud, Vic. ($80)
siliconchip.com.au
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