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Large stud mount diode heatsink(s)

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Billybobjoe

Sat Mar 28 2009, 10:45PM

Registered Member #396 Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176

I'm looking for some heatsinks for some 250 amp stud diodes. Ebay seems lacking in large heatsinks that would easily work with diodes . . .

The diodes I need to cool will be used to rectify a 50-200 amp welding current and will be fan-cooled.

Anyone have anything or have any good sources?

Something like these would be ideal:

Surplus sales of Nebraska has some but $55 a piece is almost 3 times what I paid for the diodes themselves . . .

theju

Sat Mar 28 2009, 11:19PM

Registered Member #1445 Joined: Tue Apr 15 2008, 01:25PM
Location: Germany
Posts: 24

i have 6 diodes rated with 400V 320A continious current heatsink included

if you want those pn to me

Tribologist

Mon Mar 30 2009, 04:10AM

Registered Member #1879 Joined: Mon Dec 22 2008, 04:11AM
Location:
Posts: 40

Heatsinks for old PC's should do ok with that type of load. I use them for smaller RF amplifiers and for my tesla projects. I get mine at local computershows.

Ulf

Billybobjoe

Fri Apr 03 2009, 08:29PM

Registered Member #396 Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176

These will need to dissipate up to 200 watts each for a period of time.

The problem is that I cannot use the normal and common heatsink style pictured below because the diodes need to be threaded onto the assembly and the fins interfere with this. I don't have the ability to mill down the fins in a 40mm circle to make this possible.

Steve Conner

Sat Apr 04 2009, 11:33AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, put them on the side without the fins then! You just drill a hole through the heatsink, and tap it to take the thread on the diode stud.

If you need the studs isolated from each other, cut the heatsink in half.

Billybobjoe

Sat Apr 04 2009, 08:48PM

Registered Member #396 Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176

Steve McConner wrote ...

Well, put them on the side without the fins then!

I knew someone would say that! Steve, you make me angry because you know everything.

What I meant was the threads are not long enough to use a nut on the other side when the fins are left in place. I never thought of tapping it though . . . the thread size isn't listed in the datasheet but its around 19mm - pretty big to tap. Although I do have some smaller studs that I will need to mount soon and those will be much easier to drill and tap (9mm).

Luckily I found some heatsinks on eBay that have a recessed channel in the middle that should work great. I sure will have a good time cutting them in half with a hacksaw . . .

rp181

Sat Apr 04 2009, 10:08PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Aluminium is soft enough that you can tap it just by screwing it in a slightly smaller hole.

Andyman

Wed Apr 08 2009, 04:37PM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

You don't need to actually have a tap for the aluminum to thread the stud into it. Like RP said, just measure the outside diameter of the threads and drill a hole with a bit that is 2 or 3 sizes smaller, and chamfer the opening. Then just thread the stud into the hole.

Billybobjoe

Sat Apr 11 2009, 07:47PM

Registered Member #396 Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176

Thanks - I've tapped aluminum before - - - but the threads on themselves are aluminum as well - - - and I'd rather not turn them into paper weights by stripping the threads. I just got some heat sinks that should work without any tapping.

EDIT - Nevermind, as soon as I said that I took a look at them again. They are magnetic but sure to look like old, oxidized aluminum. Although you never know what some manufacturers might do . . .

I just got these on eBay:

Obviously they're meant for clamping a puck style diode/SCR. I didn't realize how freaking big they were - the sellers pictures didn't show much. They even came with an awesome insulated clamp that wasn't mentioned in the auction! Each side weighs 6lbs. (2.7kg). I'm not sure I could bring myself to cut one of these in half . . . does anyone have an SCR that needs heatsinking? I can't imagine many people here using an SCR continuously at such a high power that would warrant using such a massive heatsink . . .

Electroholic

Sun Apr 12 2009, 12:32AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

doubt any mfr in their right mind would make alu stud diodes.

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