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[TCML] GE Protective Capacitors - Part # 9L18DCL101 or 18L0009WH

Hi all,

I was just wanting to pass on to the rest of the TCML big SG coilers the amazing suitability that I have found of some certain GE Dielektrol protective capacitors to be for coiling. These have been showing up on eBay fairly frequently as of late and are rated at 0.25 uFd @ 13,800 V(AC). 



This appears to be the best current 'deals' on these units at this time. The original units (now discontinued from production) were PN - 9L18DCL101 and the updated ones are PN - 18L0009WH. Due to a GREAT eBay "deal" on three of these last year, I decided to try a pair of these (the original 9L18DCL101 units) in series (for 0.125 uFd @ 27,600 VAC - but measured C is just over 0.13 uFd) as the main primary circuit capacitor for my ARSG driven, big pole pig coil. Once the primary coil was properly retuned for the larger C than my original measured 0.113 uFd Maxwell pulse cap unit, these worked quite beautifully in my coil! There appears to be no discernable heating above ambient temperature of thier guts, although the outer casing that is in closest proximity to the primary coil will get a bit warm after an extended run, obviously due to magnetic heating of the ferromagnetic outer casing, not losses of the internal dielectric system. I say this due to the fact that the discernable warmth of the outer casing completely disappears within a couple of minutes following shutdown. From previous experience, I have found that internal dielectric heating due to excessive dissipational losses that is felt on the outer casing of the capacitor unit takes a considerable amount of time to fade after shutdown. Depending upon the internal thermal mass of the capcitor, this cool down can literally take hours! Even though they are 'used', I figure that I am actually running them at a pretty 'low stress' level, pushing only an absolute maximum of 16.8 kVAC RMS (about 60% of their combined 100% duty cycle nameplate rating and usually notably less than this). 

It appears that these caps were designed to be used in combination with a distribution surge arrestor to protect the windings of LARGE motors (that run on a nominal input line voltage up to 13,800 volts!) from sharp line voltage peaks. From what I have been able to determine online, they are constructed with a PP based "Hazy Film" dielectric system and extended end foil connections and like most of their medium voltage PFC cousins, they have internal discharge resistors to safely bleed off any residual HV charge from the capacitor to the 'safe to handle' range within <10 minutes after the circuit is de-energized. This is a nice feauture in my opinion, as it 'defangs the snake' of hidden residual charge that can creep back up to 'bite you' even after the terminals are shorted out with a hot-stick, due to dielectric memory, yet their resistance level is still high enough that their extra load across the cap's terminal is totally inconsequential to the coil's performance within the milliseconds time frame of the charge/discharge cycling in a Tesla coil primary circuit.

All in all, these units appear to be constructed quite robustly, too, both from a mechanical as well as an electrical standpoint. So, if you happen to have spotted these particular caps and are apprehensive about taking the leap, I can personally attest from a coiling standpoint that "the water is fine". ;^)

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