transformer and choke insulation

[KI4YAN]

Fixing to start winding the mod transformer for my transmitter; and am wondering about insulation values. I have a core large enough, I think...but I am not sure about using standard bobbins for winding.

Core is 750VA, E-I style, on EI200 laminations.

I intend to run about 2200V or so maximum plate supply voltage for both the modulators (push-pull 4-65A's) and the RF final (6155/QB3-300, a close cousin of the 4-125A)

As soon as my filter choke gets wound, I'll know the final voltage. The transformer puts out 2300VAC at 530mA, so choke input I *should* get  2070VDC after the filter. Filter caps are 115uF at 2300VDC, I have five of them. I have some EI150 laminations here too...a square stack will give me enough core for a 250VA power transformer.

How much choke do I need? Assuming my choke and mod transformer need similar insulation required, and I have some kapton tape with 7kV puncture voltage, it's 1/2" wide so it'll have to be overlapped and layered.

I have 27g wire to wind with, so 500mA sustained winding currents won't be a problem. I also have 24g wire, so slightly higher currents are also permittable.

I plan to make a card-stock bobbin, layered in two layers of Kapton tape, for the choke...is this getting in the ballpark for insulation value? That's 14kV of punch-through, plus the card stock.

Will this work for the mod transformer as well? I know it needs to be minimum of 2X plate supply, so 5kV insulation is the bare minimum I'd go with, but I'd rather know if I need 14kV or 21kV...

[KA2DZT]

At 2000 volts DC I think the 14KV insulation should be enough.  Most 2000 volt range xfmrs do not have insulation ratings that high.  Adding another layer of tape will use up more core space which you can't afford to do.

Fred

[KL7OF]

I applaud your efforts at transformer winding....If possible, please post some pictures of laminations and wire being wound....Thanks and good luck...Steve

[KI4YAN]

As I've said in a few other threads...transformer winding isn't hard. A few evening's work can produce a fairly complex transformer...just takes proper planning...same as any other project.

I've found a new source of plastic bobbins, someone who will sell to me onesies-twosies, so this will be even easier than usual.

The kapton tape is 7kV puncture voltage but it's only 0.004" thick.

I've got 24g wire, and a roll of 18g...but I don't know the insulation rating on the 18g...the 24g is rated for 2kV puncture voltage.

I decided against the EI200 laminations when i found out I can get EI175 bobbins, but not EI200...I have a big box of EI175 lams and figure I can work to a standard size (it's a big box...probably 2500-3000VA worth of laminations.)

I will insulate the choke to 14kV, and will shoot for a inductance of 5-10Hy. Putting my 115uf/2300VDC capacitors in series will net me 57.5uF of capacitance if I use two, or 115uF if I use four. I will have one more 115uF cap left to use for a spare, as they are paper-in-oil pulse rated types.