They are lower cost and lower waste . Commonly the
transistors are in a wasteful configuration and can easily be
switched to a single NPN configuration .
Cheap diodes can be added in many places to shut down
quickly , in case of hot spots in the circuitry .
They all can be adapted to wire feed , allowing dynamic
control of current to the wire .
i dont like company i bought the 518 welder from .
Simon K of Longevity-inc.com refuses to fix his web site .
Try phoning in ur order ..
518 has the full range of voltages to do all welding and
plasma . But you need to beef up the input capacitances
by 2000 microfarads . simply place these across the
existing caps , but place new caps so they get 310vdc .
and observing correct polarity .
Now you can plug into 110vac , and get full power .
Simon K , uneducated in electronics , said 110vac
option makes lower weld power . Its simply voltage sag
at the input caps . These caps droop too much as the
transistors feed the transformer .
on 110vac , if there is even a trace of hi OHMs , such
as a line cord less than #10 , the caps cant get the energy .
The old welders had transformers that were too
expensive to control their voltage . Today , a MJE13007
is about $0.15 and controls 1000 watts ,
But since they ARE businessmen , they install IGBTs
costing $25-40 ..
IGBTs get 10 times hotter for the same power .
My 518 has foot control , so i tossed the hvy box in the
trash , mounted the small "pots" in the torch , now i
do Stck , TIG with a control on the output .
Im welding thin , and i pull the trigger to strike the
AWS60111 at 100 amps ,
release it all the way , and i get
20 amps to the 1/8" 6011 .
BTW , the MOSFETs are vulerable in the half-bridge config ,
so , place them or MJE13007's in parallel at transformer
primary ( input ) ,, rearrange drive circuitry ...
Motorola clearly shows the half-bridge to be the only dangerous
config for Power MOSFETs . Its for the accidental diode
in all mosfets , but missing in bipolars ...
Harbor Fright has a $200 E-welder that uses the
industry std IGBT's . They simply waste more power,
need a bigger fan . I have 5 .
They use the 3525 current mode controllers , simply
shut off the surface mount NPN's , the chip drives ,
to get a better control of power transformer .
It has a huge Feritte transformer , it has a low Curie
temp , so if it gets warm , it may fail . It must get
direct air from a fan . Fortunetaly the huge copper
wires in it are heat sinks , arrange thesee wires
so fan pushes air over these bared wires .....
The output diodes are 8 in parallel , calculate a
small OHM resistor to place in series with each ,
maybe just use smaller wires . Calc it such that
at max power , they drop .05 volts .
This is enough to equalize the load on the 8 DIODES
so ya cant possible burn them . Another diode
could read the temp at each output diode .
Thermal shut down
13 years ago