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2.5kJ Capacitor Bank (Complete, finally!)

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LAN_403

KLH

Mon Mar 09 2009, 05:45AM

Registered Member #1819 Joined: Thu Nov 20 2008, 04:05PM
Location:
Posts: 137

Very nice work. I never thought of using copper pipes as bus bars

; looks like I'll be using that for my coilgun.

The arrangement of your bus bars is good; in fact, that is the recommended arrangement for equal current distribution among all of the capacitors, as specified in a capacitor application note.

Keep up the good work! I can't wait to see how well this will perform.

rp181

Mon Mar 09 2009, 12:19PM

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

You make the diodes look so much better from when i mounted them... On those diodes, tighten them as much as you can, the toothed washers are more effective than.

Nice job

Steve Conner

Mon Mar 09 2009, 12:42PM

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

Am I the only one who can't see what earthly good diodes in series with the load will do?
By the physics of RLC circuits, the current doesn't reverse until after the capacitor voltage has reversed and got as far negative as it's going to. So your capacitors and anti-parallel diodes are already blown by this point.

Dennis Rogers

Mon Mar 09 2009, 01:48PM

Registered Member #1837 Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65

Just another point of concern is using pipe for bus bars. Copper pipe is made from recycled copper. The recycling process leaves way to much impurity to make new electrical conductors. This may show up when you have large amps moving. I'm not saying it's not worth a shot, just be careful.

aonomus

Mon Mar 09 2009, 05:22PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Well there are SCR's on both the +ve and -ve side of the capacitors, and the diodes increase the total standoff voltage. Once the capacitors discharge through a inductive load, the inductor causes the voltage reversal. If there are that many diodes to block voltage reversal (2 scrs in series and 1 'big' diode), should there be little reverse biasing of the capacitors?

The simulation said it would work at least....

KLH

Mon Mar 09 2009, 06:43PM

Registered Member #1819 Joined: Thu Nov 20 2008, 04:05PM
Location:
Posts: 137

aonomus wrote ...

Well there are SCR's on both the +ve and -ve side of the capacitors, and the diodes increase the total standoff voltage. Once the capacitors discharge through a inductive load, the inductor causes the voltage reversal. If there are that many diodes to block voltage reversal (2 scrs in series and 1 'big' diode), should there be little reverse biasing of the capacitors?

The simulation said it would work at least....

Steve McConner made an important point. Inductors, when charged with energy, are current sources. They will increase the voltage across themselves until there is an available current path (theoretically to infinity). This means the inductive load will automatically increase its voltage until it is enough to blow thorugh all of your SCRs and diodes. Then it will go to your capacitors and... the rest is self-explanatory (a.k.a. expensive). Instead, you should put the diodes in anti-parallel with the inductive load and place a resistor in series with the diode so that the voltage spike resulting from inductor peak current does not exceed the total reverse breakdown of your SCRs (V = I * R).

aonomus

Wed Jul 01 2009, 09:04PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

So I finally got some traction on this project again... yesterday I had the capacitor bank charger/control system panel laser-cut from a really heavy duty ABS case (1/4" thick, IP66 rated, it was not fun to cut). The capacitor bank charger was based off of Uzzors ZVS driver with a few tweaks mainly for voltage control and voltage reference. the only remaining building for the charger would be wiring up the relays to control the charger.

On the capacitor bank side, I have reconfigured the SCRs in parallel, but I still have to mount the diodes and then solder all the bus bars together.

Note: the slight amount of burning was due to the laser being set too high, but a little soap/water will clean that char right off.

aonomus

Sun Jul 05 2009, 01:00AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

First charging test video:

To do:
Mount back-emf diode
Mount discharge SCR and load (light bulbs)
Tidy up connectors for charging/control
Test with inductive loads

aonomus

Thu Jul 09 2009, 09:26PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

So over the last 2 days I've worked to get this project finished finally. All the bus bars are soldered, connections tightened, discharge load mounted and connected to SCR.

I had some fun doing low power tests, right up until I exploded some wire at 25% power.

Videos:
Testing at low power for can crushing and ring launching:

Slow motion of the last test that left my ears ringing:

aonomus

Mon Jul 13 2009, 12:44AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Full writeup is here:

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