3.5 hp DC motor? Unless you already have this motor in your possession, that seems rather large for turning the rotary gap assembly of a <10 kVA SG coil. I believe my DC treadmill duty motor is rated up to 2.5 hp and it is PLENTY of motor for turning my 12” x 1/2” G-10 rotor with its (8) 3/8” dia. X 2” long tungsten flying electrodes. Each of the tungsten flying electrodes also have a 3/8” aluminum shaft collar on each side of the disc, so there is a total of 16 of those shaft collars that are being flung around, too. They help to secure the flying electrodes in place on the disc as well as assist in their cooling. I control the motor’s speed via a small panel mounted variac and a FWB rectifier to give infinite speed control of the ASYNCHRONOUS spark gap assembly.
My stationary electrodes are (2) ea. 1/2” dia. X 3” long solid tungsten rods that are each simply mounted in 1 1/4” brass square stock that is about 2” long, and is also mounted against a 1/8” thick x 4” diameter brass disc, to help dissipate the heat, and is mounted against a lexan frame housing.
I have found that this provides all of the quenching that I need and I run my coil at power levels that often exceed 15 kVA and can approach 20 kVA! From my experience, it seems that you can get to a point where you may actually over quench the gap when you start stacking multiple series spark gaps. I think someone has pointed out that each spark gap typically drops several hundred volts, so if you have a whole bunch of seriesed gaps, you’re gonna be losing some significant power in your gaps, too.
Finally, Gary is correct about the PVC deteriorating in the presence of the strong UV that is given off by the spark gap. It will turn a dingy yellowish-brown and loose it’s mechanical integrity and also become somewhat conductive. I ended up having to wrap the 2” PVC support pillars of my primary circuit assembly with aluminum duct tape to reflect away and protect their surfaces from the intense UV of the spark gap.
Hope this helps,
David
Sent from my iPhone
> On Jan 29, 2020, at 12:03 PM, Daniel Kunkel <dankunkel@xxxxxxxxx> wrote:
>
> Hello Tesla List!
> I am starting to work on my next spark gap for a 6-10 KVA magnifier. It
> seems the definitive spark gap design is that from Richard Hull/TCBOR using
> a rotary gap (to control timing only) combined with a multiple break series
> gap (to control quench only). Is there a better approach for gap design and
> construction?
>
> Currently my plan is to use a 3.5 HP DC motor to spin a G10 disk with
> tungsten electrodes and combine it with the PVC + copper tubes + fan series
> gap.
>
> Thanks,
> ~Dan
> Kansas City area
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