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Thomas W

Mon Sept 15 2014, 03:50PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

Hello 4HV,

One of my running projects at the moment is a large HVHF transformer, i have a large core, U126/91/20-3C90

i have 2 U cores set up in UU formation, its really rather massive. However, i realised im gonna need some mega coilforms too. College has given me the goahead to use the mills / lathes when they are free.

My previous design was just a plan single layer HV bobbin with a primary winding inside it, however im thinking maybe going for segmented windings... Im hoping for somthing like:

14,000v - 0v - 14,000v
or
30,000v - 0v - 30,000v

Im planning on using Nylon 6 for the bobbin material. Just messing around on cad at the moment.

I plugged some numbers into a program i often use for transformers:
3PJAcvg

How does that sound?

Im thinking of using a CM300DY-24NF fullbridge, maybe a driver like this:

Planning to go at 70kHz just like Steve.

Also, if i must, i can submurge in oil, however i would rather not.

Does anyone have any input information on this idea, some design ideas, do/don't dos?

Thanks!
Tom

Ash Small

Mon Sept 15 2014, 04:17PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Why don't you design it to be submerged in oil and vacuum impregnated? I'm sure they will sort out a suitable vacuum pump.

This will mean you're not relying on the bobbin itself for primary insulation and is (in most people's opinion) far more professional.

It will give you more freedom in bobbin design, etc. and could still be modified/repaired/ improved later.

Thomas W

Mon Sept 15 2014, 04:43PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

Ash Small wrote ...

Why don't you design it to be submerged in oil and vacuum impregnated? I'm sure they will sort out a suitable vacuum pump.

This will mean you're not relying on the bobbin itself for primary insulation and is (in most people's opinion) far more professional.

It will give you more freedom in bobbin design, etc. and could still be modified/repaired/ improved later.

Because its a bit of a pain, as much as i could potentially get my hands on some oil, i would have to make a case for it etc, and find/ make some HV feedthroughs.

Ash Small

Mon Sept 15 2014, 05:38PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Thomas W wrote ...

Because its a bit of a pain, as much as i could potentially get my hands on some oil, i would have to make a case for it etc, and find/ make some HV feedthroughs.

You would need to sort out some form of enclosure anyway, and HV feedthroughs need only be copper bolts in most situations, and you could use boiled cooking oil, the cheap stuff.

It can also help with cooling. Those big ferrites can get pretty hot.

Thomas W

Mon Sept 15 2014, 05:47PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

Ash Small wrote ...

You would need to sort out some form of enclosure anyway, and HV feedthroughs need only be copper bolts in most situations, and you could use boiled cooking oil, the cheap stuff.

It can also help with cooling. Those big ferrites can get pretty hot.

Good point, maybe i shall oil-cool it. here is my bobbin i have came up with:

Im thinking of winding each segment to 2000v and tap it off, then i can change the tappings for whatever voltage or current i intend to use.
Going to use a load of these on each hole.

i have a 5mm space to wind the primary on inside the former.

With pins in:

Sulaiman

Mon Sept 15 2014, 06:26PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I would not put the pins in a straight line,
example, alternate layers in line, two rows 45 degrees apart
this would reduce the risk of flashover.

I can not really see the point of taps, more feed-throughs, more wires to arc between etc.
... vary the primary drive for different outputs.

If you use epoxy or similar there will be no way to repair or modify the transformer,
if you use oil in a plastic container cooling will not be as good as
if you use a metal container, but feed-through and general insulation problems will be worse.

Consider a plastic oil-filled enclosure with oil pipes to an external radiator?

Last but not least, is nylon a good choice for the former?
Melting temperature, dielectric loss .....
just random thoughts

Thomas W

Mon Sept 15 2014, 07:09PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

Sulaiman wrote ...

I would not put the pins in a straight line,
example, alternate layers in line, two rows 45 degrees apart
this would reduce the risk of flashover.

I can not really see the point of taps, more feed-throughs, more wires to arc between etc.
... vary the primary drive for different outputs.

If you use epoxy or similar there will be no way to repair or modify the transformer,
if you use oil in a plastic container cooling will not be as good as
if you use a metal container, but feed-through and general insulation problems will be worse.

Consider a plastic oil-filled enclosure with oil pipes to an external radiator?

just random thoughts

Hmm, im thinking of machining this out of either PVC or Polypropylene now, im trying to cut down on the plastic cost (currently around Â£30 per core with one of those 2 materials)

Im thinking that those taps shouldn't be a problem as there is only a maximum of 2000v between any 2 adjacent wire. It also cuts down the risk of breaking the 0.355mm wire.
I shall do a few more mockups, i want to order the material within the next 2 days to get it done in college asap. I also have to take it to my friend to be wound as well.

Case wise, i would like to either have it just in air. Or have it under oil in a metal container.

new design:

hen918

Mon Sept 15 2014, 07:13PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

I, like Sulaiman, think that nylon is a bad idea, it tends to melt! I've had some bad experiences with PVC going gooey and my nylon MOSFET fasteners also failed before my MOSFETs.
BTW, can you tell me what software that is? I'm designing a switched mode inverter and it would be a godsend!

Thanks,
Henry

Thomas W

Mon Sept 15 2014, 07:20PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

hen918 wrote ...

I, like Sulaiman, think that nylon is a bad idea, it tends to melt! I've had some bad experiences with PVC going gooey and my nylon MOSFET fasteners also failed before my MOSFETs.
BTW, can you tell me what software that is? I'm designing a switched mode inverter and it would be a godsend!

Thanks,
Henry

Im just using Solid Edge ST6 Educational version (to purchase the software costs around Â£3-5k)
As for the transformer software, it can be found somewhere on diysmps.com. shouldn't be too hard to find but you will need to make an account.

Problem is, i really can't afford to spend over Â£40 on the coilforms materials really.
im using this company for the plastics:

hen918

Mon Sept 15 2014, 07:30PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

I think the coil formers I bought from RS were made of some sort of thermosetting plastic although they did cost a fair bit and they're much smaller than the ones you need...

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