Hello Gareth,As Scott mentioned, the secondary is very small for such a high current supply. The h/d is ok.
But the turns of 1200 is not correct "if" 0.35mm is the "bare" wire diameter. If it is, more like 1050 turns for single build insulation or 950 turns for heavy build insulation. The wire size is small (roughly 29 AWG). This coil will be lossy (low Q). Performance can be greatly improved. The fix is to increase the wire size and fix the overall size for the 4 MOT current. I would recommend .05mm bare wire size (minimum). This size requires a longer secondary for 1200 turns. So, 685.8mm in length and 152.4mm diameter for a nice h/d ratio (4.5). This will also lower the frequency from 600kHz down to 230kHz. This will raise Q and will better handle your 4 MOT system.
You can still use your MOT pack with the small 75mm x 420mm coil, but you must greatly limit current (not voltage), otherwise your breakrate will be very high and very lossy (you may burn up the coil from driving it too hard if you don't limit current). Using a "fixed" MOT to limit may not be enough. The sphere top load is ok, but a sphere's use can be problematic if the sphere is too small. A toroid would greatly reduce top coil breakout and corona. Salt water caps work, but they are very lossy (corona losses). All these losses rob power from the coil and reduce spark length performance.
Looking back at my coil recommendations (above), I realize they are Scott's recommendations. We both arrived at the same coil size and likely in the same way. How cool is that!
Regards, Bart kingsandangels@xxxxxxxxxxx wrote:
Hey everyone, Bart Im building a secondary of 75mm diameter with .35mm wire I want it 1200 turns which will give me 420mm height which is more than 375mm (5:1 ratio) What do you think is best for performance,Can I go more than 5:1 ratio? Oh we also get polyuathane but in varnish for floors only,is that correct? Can fiberglass resin also do the trick? The spark length on my 4 mots dont look long and you supposed to use a rotary spark gap,can anyone help me with mots(Is it also necessary to disconnect the outer mots from the core to prevent arcing?) Bart whats your take on my secondary? Im going to take my secondary and my copper sphere to the UK and make more! Thanks again Gareth
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