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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Steve Conner wrote ...
Remember it's 350VA, not 350W :P
Well.. Steve, I believe it IS 350W. With no PFC caps the MOT draws ca. 2.5A, that's 570VA. With the right amount of caps so that I bring the current the lowest I can (all inductive/reactive current cancelled out), it draws 1.5A and that's 345W.
I guess it's right, it gets hot in a few minutes without any load lol.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Am I the only one who figures that jan used PFC caps? :p
And if he was running close to resonance, it would indeed be mostly W..
350W doesn't look like something the transformer would stand for long.
I'd expect current to be much lower with good PFC...
How big caps were you adding? You could try smaller steps and see if you can get the current lower. Still it is odd and I don't think you would need to truly resonate the transformer with PFC caps...
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hey guys, I need some help.. you probably know how I wired the MOTs, sec. in series and 2x2 microwave caps in series with output. I had problems with the arc sometimes extinguishing too soon- I found I need more inductance on the HV side to make the arc stable (I found this out by connecting a third MOT in series with HV output with shorted primary). The problem is that this third MOT is too smal and gets too hot.
My question: If I add a choke on the PRIMARY side of the MOTs, will it have the effect of increased inductance on the HV side too?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Steve Conner wrote ...
Yes, and the inductance "seen" at the secondary side will be the inductance that you put at the primary side, times the square of the turns ratio.
Thanks, that's good to know.. so now I need to make ca. 13mH choke.
I still have no idea about the air gap and core size... There will be maximum current through the choke a bit over 15A, how big core should I use and how big gap? I have a core from 300w xfmr, will this be enough for short runs (the MOTs overheat in a few mins anyway)?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Well, if it helps, I've made a couple of chokes like this.
A 230V MOT with the secondary removed and a 3mm air gap added had 32mH of inductance.
An old 100V line audio driver transformer (from a ~150w PA amp) rewound with about 50 turns of thick wire, and a few pieces of cereal packet as an airgap, had about 6mH.
For continuous running, a ballast ends up being about the same size as a transformer of the same kVA rating. It also needs roughly the same number of turns as a 230V transformer: the only big difference is that the ballast has an airgap and the transformer doesn't. A core without an airgap is useless as a ballast.
Richie Burnett once had some ballasts made by a transformer maker:
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Am I right if I say that when an inductor ungapped saturates at x volts per turn, will it saturate at x volts per turn too when gapped? Or will it be more?
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Inductor/ballast choke design
