[TCML] Discharge capacitor wiring/CB safety note

[sparktron01@xxxxxxxxxxx]

HI Bamacoiler/Bert 

I agree with Bert, I have a capacitor bank based on 16 x 2400uF @ 450V arranged as 8 in series 
X 2 banks in parallel. They are buses together with aluminum plate (16 gauge), with anti-ox 
on all fasteners and electrical interfaces. At 3.6kV ~ 4kJ which would be quite sufficient to 
shrink a can. I haven't measured discharge currents (yet) but based on bulk resistance of 
AL bus bars and internal impedance of capacitors, peak current into a 0 ohm load is modeled 
at ~ 25kA. 

I have discharged into a Square D single pole 120/240V15A breaker as a reality check. At 3kV capacitor 
charge voltage remained constant when CB was open (CB was not breaking down). When closed 
and C discharged, CB successfully isolated power path 3 times; however, plasma was observed 
exiting near the load terminals of the CB and about 1.5kV remained on the capacitor bank! 
Square D QO series CB's have an maximum fault current interrupting rating of 10kA . 

Flame and plasma exiting anywhere around the CB case would have caused UL failure on CB at that 
current application level, so discharge current is probably significantly higher then 10kA. 

LIST SAFETY NOTICE: 
Molded case circuit breakers as used in residential applications are rated to interrupt fault 
currents <10kA ONLY ONCE! They may and can fail catastrophically with another short circuit 
application! The above test was performed to determine a gross magnitude of available 
discharge currents. Molded case POWER circuit breakers (bolt-in) generally are more robust 
and can withstand several (<10) fault applications without failure. Any fault current applied to a 
CB that is higher then the CB's withstand rating can result in a catastrophic failure or CB 
explosion. A good rule of thumb is if the CB has tripped, determine what caused the fault 
and correct; then replace the CB. A CB is cheaper then replacing your house! 

Regards 
Dave Sharpe, TCBOR/HEAS 
Chesterfield, VA. USA 

----- Original Message ----- 
From: "Bert Hickman" <bert.hickman@xxxxxxxxxx> 
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> 
Sent: Thursday, October 15, 2009 11:34:14 PM GMT -05:00 US/Canada Eastern 
Subject: Re: [TCML] Proper Energy Discharge Capacitors Wanted for trade/sale 

Hi Bamacoiler, 

Don't despair... For hobbyist use, you can use copper strip or aluminum 
flashing with bolts and star lock washers puncture the oxide film and 
get a gas-tight connection. Because of the higher frequency oscillatory 
discharge, skin depth is typically only 15-35 mils. Thick bus bars are 
actually overkill and are not necessary. 

Bert 

bamacoiler@xxxxxxxxx wrote: 
> Wanted: Proper energy discharge capacitor for coinshrinking/can 
> crushing/exploding. 
> I can trade 1 50kva 12470/480 2 eared pole pig with a 10kva 240/480 
+> stepup so it can be powered by 220. Or I can trade a # of 2.25µf 15kvdc 
> sangamo capacitors(30 total). Or i can buy it. It needs to be between 
> 9-20 kv, 50-300µf, in the 5-10kj range or higher. These requirements are 
> not concrete and suggestions will be entertained off list. The problem 
> I'm having is buying proper bus bars to connect the 30 caps I have is 
> going to be just as or more expensive as buying a proper energy 
> discharge cap and having it freighted to my house. Plus I really don't 
> know what the outcome will be inductance wise with 30 caps. Thanks in 
> advance. If it is the southeast I can make a long distance trip and 
> pickup/deliver. 
> Bamacoiler 
> 
> 
> ------------------------------------------------------------------------ 
> 
> _______________________________________________ 
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> Tesla@xxxxxxxxxx 
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