Hockey puck SCRs: why they need clamping force? / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Hockey puck SCRs: why they need clamping force?

1 2 next

Move Thread

LAN_403

Kizmo

Thu Apr 10 2008, 01:55PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

I just bought few 3.3kA (peak) rated SCRs for coilgun/ring launcher applications. These will need 3.5-4kN axial pressure. Why? I did some googling but i didn't found any good articles about this.

Dr. Shark

Thu Apr 10 2008, 02:15PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Nice pucks, do you have data on them? Action and risetime are probably the most important parameters to look at.

I am surprised Google did not turn up anything. Anyway, in these puck devices the silicon die is not physically connected to the terminals. The terminals have a thin gold coating which needs to be pressed on the die to give a good low resistance contact.

Kizmo

Thu Apr 10 2008, 02:18PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

It was that simple :)

Maybe i didn't use right search word or something. Is there greater idea behind this structure?

EDIT:

Here is datasheet. Brand new, never been used, from welding machine factory :)

Dr. Shark

Thu Apr 10 2008, 02:45PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Wow, impressive German made quality

The action integral is given with 50kAÂ²s, which is really not bad. The way to use this figure is to divide the energy in your capacitor bank by the total circuit resistance. For example if you have a 1kJ bank and 50mOhm circuit resistance, the action would come out as 20kAÂ²s which would be safely within spec.

dI/dt at 1600A / us is also quite impressive, I don't think you will ever be able to exceed this figure with an induction launcher.

I am not sure about the pressure thing, but I suppose that for proper heat sinking in continuous duty, you would need the pressure anyway. Maybe the manufacturers can safe some cost by not directly boding the die to metal.

HV Enthusiast

Thu Apr 10 2008, 02:53PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Dr. Shark wrote ...

Anyway, in these puck devices the silicon die is not physically connected to the terminals. The terminals have a thin gold coating which needs to be pressed on the die to give a good low resistance contact.

Actually, thats not correct Dr. Shark.

The reason is because the die / connections inside are not bonded to each other as in your standard semiconductor. The internal connections are only made when the package itself is compressed. Thus, if you don't compress the part, the part looks like an "open circuit."

[EDIT] - Oops. Actually, i reread your post and i misread it the first time. Yes, that basically does mean the same thing i just said, so you were correct.

rp181

Thu Apr 10 2008, 11:15PM

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

how would you go about putting 700 pounds of force? If using 2 plates and bolts, it would seem that the threads would come right off.

Dr. Shark

Fri Apr 11 2008, 11:14AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Think about it this way: If you jack up your car to change a tire, you are putting about 4000 pounds of force on the screw in the jack. Of course they use special ACME screws (I totally don't have a clue why they are called that), but we are only talking about a fraction of the force here. In fact I would be more worried about the plates bending (1/2" Aluminium should do though), than the threads stripping.

Bored Chemist

Sat Apr 12 2008, 12:43AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Re acme.
from wiki "The company name is ironic since the word acme is derived from Greek (Î±ÎºÎ¼Î®) meaning the peak, zenith or prime. Generally, products from the fictional Acme Corporation are very generic and tend to fail "

lpfthings

Sat Apr 12 2008, 01:33PM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Bored Chemist wrote ...

.....products from the fictional Acme Corporation are very generic and tend to fail "

Hopefully its ONLY the fictional corporation

Quantum Singularity

Mon Apr 14 2008, 04:45PM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

I've wondered about the puck thyristors too, at least wondering if there is an easy way to DIY rig em up that isnt costly or too heavy. I've always ended up limiting myself to the brick type thyristors, since they have a nice heavy duty bolt connection. But there does seem to often be some really powerful puck style ones on ebay.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob