"Bob La Londe" wrote in message news:sq21vq$1d3v$1...@gioia.aioe.org...
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The rectifier is an MDQ-100A, $12.99 on Amazon. I found the 78000uF cap at a
ham radio flea market. A BeesClover 100V/100A DC meter displays the output
voltage and current. I buy from Amazon to minimize exposure of my credit
card, not because they are a great parts source. Amazon is like Radio Shack,
wide variety, uncertain availability, questionable quality.
The welder transformer has substantial uncoupled self inductance that gives
it a constant-current output curve, enough that the ripple is only about 1V
p-p at 20A DC out. The down side is poor output voltage regulation, it
droops from 57V at no load to 30V at 30A, which is still enough to charge
24V batteries but makes it dangerous to leave unattended since the voltage
won't stop rising as the battery nears full charge.
If you want lab-quality voltage and current regulation from it, add a
DPS5020 digital regulator.
https://www.electronics-lab.com/ruideng-dps5020-50v-20a-power-supply-module-review/
Without the regulator the supply can deliver up to 70A long enough to test
circuit breakers etc before its 30A output breaker trips. I have a surface
mount breaker in my solar power system that's rated for 30A but actually
trips below 19. The supply's output current limitation is from overheating,
especially the Variac's brush which may be hard to replace. I had to make
one by milling and filing a motor brush. The welder transformer I used
begins to saturate at a little over 120V in. The no-load input current rose
to 5A at 138V in, so you may want to connect the Variac for 0-120V out
instead of 0-140V.
-jsw