Welding rectifier more details

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

================================= Having built a machine that used heat transfer fluid, I wouldn't choose it for a home project. That machine temperature-cycled GM HEI ignition modules between [above boiling] and [well below freezing] to confirm that they would withstand the thermal shocks of for example starting cold and immediately plowing snow in Alaska. The heatsinks were channels formed on a press brake from 1/4" copper plate with tubing for the fluid soldered into the inside corners using large amounts of 95/5 solder.

One heatsink is positive, the other negative, so the welding leads can connect directly to them, which saves fuss and expense of high current terminal blocks. If instead you choose four identical diodes they need to mount on four separate heatsinks of the same total size since each diode conducts half the time. I would enclose the heatsinks in air ducts made of GRP (FRP here) to confine the air flow within the fins and protect you when testing it with the external covers off.

An electrically isolated module like this might be a simpler solution if you have or can machine a flat enough contact surface on the heatsink. It's less work to build, more to test that it won't overheat and burn out.

I haven't mentioned methods that require special test equipment like high voltage insulation testers.

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

My Maxarc rectifier unit is air cooled and no fan either, the cooling of the heatsinks and inductor being by natural convection. I could ask my mate who has it at the moment to pull to cover and takes some pics if necessary.

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

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The forward drops are as much as 1.65V for these devices:

This 400A rectifier module is electrically insulated from the heatsink it mounts on, which can be grounded to simplify construction.

I can't make out its size, but those terminals don't look huge, and I'm thinking "Wow is that all that's needed?" (??!!!). Given the size of a welding cable for 400A ... Plus the amount of heat one assumes it would have to dissipate (a few percent of the input power?) If that allowed you to keyhole with a 6010 from a "tombstone" welding machine that would be amazing. Given the cost is rather affordable if it gave that outcome...

Jim - I'll post about welding conditions on s.e.j.w. Bit of science in there. covid19 lockdown restricting us quite a lot - not welded for months and getting by as construction site labourer.

I can't make out its size, but those terminals don't look huge, and I'm thinking "Wow is that all that's needed?" (??!!!). Given the size of a welding cable for 400A ... Plus the amount of heat one assumes it would have to dissipate (a few percent of the input power?) If that allowed you to keyhole with a 6010 from a "tombstone" welding machine that would be amazing. Given the cost is rather affordable if it gave that outcome...

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Using the closest match on an architect's scale the 110mm dimension measures

If you figure on 1.5V drop per diode the power loss is 1200W, or less if ITM(?) is the peak forward voltage. For a rough comparison my 1500W electric heater has a 13 Watt, 5" diameter fan that blows 7(?) MPH at the outer edge.