On Fri, 08 May 2020 10:23:51 +0100, Richard Smith
wrote:
"Richard Smith" wrote in message ...
Occasionally day-dream about how I could make a stand-alone rectifier.
Practical advice appreciated.
Less and less need now with inverters getting better and better.
But no inverter I have yet met will run a 6010 "keyholing".
Rich Smith
https://www.electronics-notes.com/ar...-rectifier.php
Start with the welder's maximum current, lets say 300A.
https://www.digikey.com/product-deta...0U60A-ND/80681
The 300UR is reverse polarity. You need two electrically isolated
heatsinks, the positive one for the two diodes whose threaded studs
are cathodes and the negative one for the two that are
anodes. Insulating the four diodes from a single grounded heatsink is
possible but liable to hidden short circuits and the diodes will run
hotter.
https://www.dummies.com/programming/...onents-diodes/
Large finned aluminium heatsinks are common cheap electrical scrap, if
you know where to look. You may have to experiment to find how large a
fan it needs.
The hardest part may be finding and fabricating heat-resistant
electrical insulation that will withstand rough handling. I'd try
unperforated FR4 unclad circuit board material rather than the temping
PVC pipe. The high current terminals can be brass bolts through the
insulation. I've found threaded copper starting motor terminals at a
Diesel electrical shop and lathe-turned them into the high current
studs I needed for a current measuring shunt.
The housing for it can be a welded cube of angle iron with flat sides,
if you don't have equipment to bend sheetmetal. Be sure that at least
one side can be closed without access to the interior, i.e. tapped
instead of clearance holes for the screws.
Calling Jim, and anyone else who can help.
Jim - you said separate the four rectifiers of a bridge rectifier into
two pairs - because of their polarity? If I understand you rightly?
That would mean a practical welding rectifier could have two metallic
heat-sink assemblies separated in a glass-fibre (GRP) frame
(insulating)?
Like the idea...
Should it be air-cooled or oil-cooled?
The one I used (probably 1960's or 1970's vintage) was air-cooled.
Regards,
Rich Smith
Air cooled should be fine. If you are using silicone diodes the frop
is only about 0.7 volts If you have a 135 amp welder that is only
just over 80 watts dissipation.a few hundred square inches of heat
sink fins can handle that with no problem - particularly with a fan. I
have a set of 600 amp diodes on a finned heatsink of 288 square
inches, more or less. They are a 3/4" stud mount with 3/8" bolt on
"buss bar" type terminals