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RE: Toploads that bite


I would like to reinforce the "do not discharge with a screwdriver" point. One
gentleman I know of was repairing a photographic flash (studio kind with the
umbrella reflector) and was operating the unit with the cover off. He bumped a
screwdriver and it fell across the contacts. The screwdriver exploded (pulse
discharge style). 

In addition to this, it is possible to trigger the coil by shorting the caps,
after all, this is what the spark gap is for. A screwdriver is a bit too short
for my liking.

Justin G 

-----Original Message----- 
From: Tesla List [<mailto:tesla-at-pupman-dot-com>mailto:tesla-at-pupman-dot-com] 
Sent: Tuesday, 15 February 2000 5:50 
To: tesla-at-pupman-dot-com 
Subject: Re: Toploads that bite 

Original Poster: "Megavolt Nick" <tesla-at-fieldfamily.prontoserve.co.uk> 

Hi Herwig, 
                my comments: 
> > > You might want to include a safety gap (with a series resistor) in 
> parallel to the cap.The series resistor is essential in order not to 
> exceed the maximum current of the cap in case of a flashover. 
> 
> Nick Field wrote: 
> 
> > Don't use a resistor - use a coil of 14guage wire - the resistor will 
> not handle the voltage or current unless you use a huge bank of 
> power resistors. 
> 
> Nick, 
> 
> - A coil having got several turns of course will limit the peak 
> current. Drawbacks are mounting space and the menace of 
> oscillations. In my system I've used 34 Ohms consisting of two 
> paralelled 68 Ohm/100 W resistors. They are long enough to 
> handle the voltage as well. 
That surprises me, assuming a 10kV supply your peak current through each 
resistor is more than 100A - not for very long but at that current level it 
doesn't have to be. As for the oscillations - that is what the tank circuit 
is there for. 
> 
> > I personally advocate discharge resistors (note I said 'discharge' not 
> > 'equalising') across all the caps 
> - Every single cap of the MMC has got its 10 MOhm bleeder of 
> course. 10 MOhm is much to high to act as an equalizing resistor. 
I didn't mean across each cap of the mmc, I meant across all standalone 
capacitors - In the mmc case that would mean across the whole lot. 

> 
> >  I would also say to people that they should *physically* connect 
> the buss bars with a clip lead while working on a tesla coil cap. 
> - I agree if the cap was discharged before. 
of course - and not with a screwdriver!!! 

Regards 
Nick Field 
> 
> Regards Herwig 
> 
> 
> 
>