Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx> Hi DC,I've been thinking that your dimensions of the toroid must be for its radius. I assumed diameter and this would give a cross section of only 6.75 sq inches. This seems way too small for 1.9 volts per turn. If the dimension were indeed for its radius, you would have 13.5 sq inches and I think 1.9 volts per turn would be just fine.
I have only 6 sq inches of core so I have 245 turns on my toroid. With 280 volts on the ballast, Im only at about 1.1 volts per turn with a flux density of about 11K gauss at 25 amps (13K gauss at 35 amps). I currently have a 200 mil gap and measure 3.5 amps with 140 Vac across it. My theoretical current is 6.5 amps at 140Vac but that assumes the H field does not bulge out from the sides of the gap. This divergence seems to become more significant with wider gaps. Before I open up the gap anymore, I need to figure the effect charging the Cp has on the ballast. Certainly, if operated at resonance, XC on the primary would cancel XL in the ballast and current limit would be controlled by resistance only (doesnt sound good). So a lot of factors to figure in here.
Thankyou for your info and if you could confirm that you are compensating for the XC, things could make more sense.
Gerry R.
Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>No, we actually wire all of our units for 240 in and 240 out. We don't push the pig in any way except for the power level rating. Not a problem, but we just don't do it because our coils run typically 9/7 on a weekly basis.We run between .05 uF and 0.1 uF in most coils. Some, like Big Bruiser, we run with 0.3 uF primary capacitance. I try to set capacitance and tuning so most primaries work out at 4-7 turns.Dr. ResonanceHi DC, I presume your "standard variac" is 240Vac in and 0-280Vac out???Your standard C core is a gapped toroid with 7.5 inch outer diam and 4.5 inch inner diameter and 4.5 inch thick?? Would the cross section then be 1.5 x 4.5 inches??. What is the Cp your PIG is driving?? This should help me figure out what is going on.Thankyou, Gerry R.Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>I'm not sure, but we build a lot of these for our pigs and they limit current right at 30 Amps when used with a standard variac.We gap our cores at 100 mils using standard "C" cores measuring 7.5 inch x 4.5 x 4.5 inches and usually approx 125 turns on each unit.Dr. ResonanceHi D C, OK, then what am I missing???Isn't 120mh, 45 ohms reactance at 60 Hz??? and doesn't 45ohms limit the current to 5.3 amps at 240 Vac??? or are you assuming a secondary Cp that reflects back to the primary and cancels some of the 45 ohms reactance??? If so, what are your assumptions.Please tell me before I cut my gap too wide in the toroid ballast Im building.Gerry ROriginal poster: "D.C. Cox" <resonance@xxxxxxxxxx>No. 120 mH provides control with 30 Amps as the max amount that may be drawn.Dr. ResonanceHi Dr R,120mh is 45 ohms at 60Hz. At 240Vac, this would limit the current to 5.3amps or ~1.2KVA. Is this in error or Im I missing something??Gerry R