Is there a device that chang the frequency of an AC current ?

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
Jack Puntawong
Posts: 150
Joined: Wed Aug 29, 2012 1:10 am
Real name: Kunakorn Puntawong
Location: Bangkok, Thailand
Contact:

Is there a device that chang the frequency of an AC current ?

Post by Jack Puntawong » Sat Nov 24, 2012 3:13 am

Hi,

Recently I have acquired a 15kw transformer

Input: 300v 30,000hz

Output: 66kv 230mA

I was wondering if there is a device which allow you to change the frequency of the AC circuit from 50hz to 30,000. If so, anyone who had any experience buying one or making one, please give me some advice.

Also, can I assume that multiple diode assembled in series will achieve the effect of a single high voltage diode ? I was planning to make a rectifier without big diodes as they are very hard to come by in Thailand.

Ex: 100 unit of 10v diode in series = 1 unit of 1000 volt

Thanks,

Jack Puntawong
Attachments
$(KGrHqR,!mIE9JBsBfNPBPW9KVTjFw~~60_57.JPG
$(KGrHqR,!mIE9JBsBfNPBPW9KVTjFw~~60_57.JPG (510.35 KiB) Viewed 3279 times
$(KGrHqJ,!qIE8WnQh994BPW9T6ZP+!~~60_57 (1).JPG
$(KGrHqJ,!qIE8WnQh994BPW9T6ZP+!~~60_57 (1).JPG (597.19 KiB) Viewed 3279 times

Tyler Christensen
Site Admin
Posts: 551
Joined: Tue Feb 24, 2009 2:08 am
Real name:

Re: Is there a device that chang the frequency of an AC current ?

Post by Tyler Christensen » Sat Nov 24, 2012 3:33 am

If you manage to actually find such a device, it will probably be very expensive (I've never seen a retail product that offers exactly this). You can gut one out of some other power supply and use it if you can figure out the control interfaces, but I've never heard of a complete product that does what you want.

There are lots of DIY projects as many fusor.net members, myself included, have built the inverter you're looking for.


As for series diodes, yes they do add up in voltage. Not necessarily exactly to rating * n though. I usually use 0.5n, so 100 10v diodes would be treated as 500v. They don't balance perfectly, especially at high frequencies.

User avatar
Chris Bradley
Posts: 2930
Joined: Fri May 02, 2008 11:05 am
Real name:

Re: Is there a device that chang the frequency of an AC current ?

Post by Chris Bradley » Sat Nov 24, 2012 10:23 am

Jack Puntawong wrote:
> I was wondering if there is a device which allow you to change the frequency of the AC circuit from 50hz to 30,000. If so, anyone who had any experience buying one or making one, please give me some advice.
Your uncle may be a bit of a comedian if he told you this is no problem.

But seriously, if he knows then he should be able to help. There are a number of examples of building the requisite circuit on the forum. It's not a problem in as much as 'it can be done', but is quite a project from scratch, especially from a starting point of minimal electronics knowledge. A knowledgeable local mentor would be a good idea if you are to proceed on this project.


PS.. rarely a problem so long as you use fast diodes, but be wary of putting too many diodes in a string. The trr add cumulatively and the total needs to be small enough for the application.

ed
Posts: 25
Joined: Fri Sep 21, 2012 11:29 pm
Real name:

Re: Is there a device that chang the frequency of an AC current ?

Post by ed » Sat Nov 24, 2012 6:48 pm

That's quite a versatile transformer with plenty of power capability. There are many ways to drive it, but if you are not savvy in electronic design, or have help from someone who is, then don't bother to start from scratch.

With adequate knowledge, you can use an existing swirching supply from other equipment and modify it to run the transformer to a reasonable power level. Even then, it would take quite a bit of design effort.

The closest match to the characteristics needed may be an "inverter" type microwave oven supply - these use a high frequency (>20 kHz) off-line inverter instead of the old-school line frequency transformer system. This makes it much smaller, lighter, and ultimately cheaper since so much less copper and iron are needed. That's also why your fairly small transformer is capable of 15 kW - to do that at line frequency, it would weigh over a hundred pounds.

The most "off-shelf" and simplest way to experiment with it would be to drive it from a high-powered audio amplifier - say 200W RMS and up. There is nothing magic about the 30 kHz input - it's what it takes to reach it's full voltage, so you can run it at lower frequency, say 18-20 kHz at less voltage, to get a maximum of around 40 kV instead, using the original output section design. What you want is to be above human hearing range - otherwise it will sound awful.

The first thing is to put the transformer primaries in parallel rather than series - that gets you to 150 V peak input rather than "300 VPK" for full rated voltage. If you can't find more info about this unit, you'll need to experiment later to see just what the real turns ratio is, and if they mean peak to peak, or peak voltage excursion in each direction. It makes a factor of two difference.

You must protect the amplifier from the reactive and non-linear load of the transformer and output system, so start with a series ballast resistance of a few ohms and fairly high power in the 100W range - a bunch of paralleled incandescent light bulbs would be a good start since it will serve as a resettable fuse. On the amplifier side, the peak voltage excursions should be clamped by transient voltage suppressors, to a value just above what the amplier can put out - it depends on the amplifier ratings.

This setup would allow you to experiment fairly easily at lower voltages up to about one-half of the ultimate capability. Once you have learned enough about the system, you can raise the voltage and try less ballast. Since most readily available and cheap audio amplifiers will be old stereo receivers, you can go to push-pull to effectively double the available drive voltage. The transformer and its ballast would be run between the two amplifier outputs, instead of from one of them to ground. This should be able to reach the desired 150 V range. Each output would of course need protection as mentioned above. The amplifier inputs would then need to be driven 180 degrees out of phase - easily accomplished at these frequencies by small audio or ferrite transformers. The phase shift through the amplifiers near the top of their frequency range will far from perfect, so that's another variable that will affect performance, and need to be studied. This is most likely the configuration that the transformer was designed for - look up "power conversion" AND "full-bridge" to learn more.

The ultimate voltage and power available will depend on the transformer primary inductance, the amplifier ratings, the ballast losses, and the output rectifiers. If the available amplifier voltage is insufficient, there are other ways to boost the primary drive voltage using readily available junk parts. The transformer will never provide anything near its rated power with this setup - probably a good thing - so it should be safe from damge no matter what happens to the rest of the system. The amplifiers are most at risk.

Also keep in mind that a significant amount of power will be needed just to excite the transformer itself - it's due to the magnetizing current in the primary inductance needed to establish the magnetic field in the core. It's mostly reactive, representing energy stored in the field, but it still must come from somewhere, and it must circulate in the system, where much of it will be converted to heat loss. That's one problem with using a large transformer at much lower power - the magnetizing current (or VA) is generally specified at some reasonable fraction of its full rating, so if used at far less, then it becomes a much more significant portion. There are ways to reduce the loss, once the basics are figured out, by making it resonant at the desired power frequency.

An audio range oscillator or function generator can supply the input signal with a sinewave drive at appropriate frequency and voltage. The amplifier volume control can be set to control the output level, while the generator level should be set such that at maximum volume, the output won't exceed any overall ratings.

Even this fairly simple system would take quite a bit of effort, but you would learn a lot, and how to improve and customize it to the application.

Ed

ed
Posts: 25
Joined: Fri Sep 21, 2012 11:29 pm
Real name:

Re: Is there a device that chang the frequency of an AC current ?

Post by ed » Sat Nov 24, 2012 7:21 pm

A couple more things occured to me.

First, I think that transformer will need to be potted or in an oil bath to reach its rated voltage reliably.

Second, I think that you should power it from audio and experiment first - even at low power - if you don't have access to high-powered amplifiers. You will need to determine a lot about the unit before deciding on which way to ultimately drive it. Experiments and measurements at low power will tell you what you need to know when scaling up later.

Ed

JohnCuthbert
Posts: 339
Joined: Mon Aug 19, 2002 8:30 pm
Real name:

Re: Is there a device that chang the frequency of an AC current ?

Post by JohnCuthbert » Sat Nov 24, 2012 7:51 pm

I wonder if the driver for an induction hob would power this sort of transformer.

Jack Puntawong
Posts: 150
Joined: Wed Aug 29, 2012 1:10 am
Real name: Kunakorn Puntawong
Location: Bangkok, Thailand
Contact:

Re: Is there a device that chang the frequency of an AC current ?

Post by Jack Puntawong » Thu Dec 13, 2012 1:50 pm

Thanks Ed!

Looks like, I will learn much more about the inverter system by creating this high voltage power supply. There's a lot of reading material ahead of me. Now that the transformer has arrived at my house. I will begin designing and experiment the system after I finished my winter exam~! I'll go find reading material so that I could understand the system thoroughly and proceed with safety. As you have mention, I have prepared some quantity of mineral oil for the transformer and diode to be submerge. Also, I will be having a mentor and will be experimenting at low voltage. Thanks again for your advice.

Jack Puntawong

User avatar
Rich Feldman
Posts: 1333
Joined: Mon Dec 21, 2009 11:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

Re: Is there a device that chang the frequency of an AC current ?

Post by Rich Feldman » Thu Dec 13, 2012 5:39 pm

Sounds good, Jack.

I have procured one of those transformers myself. Am planning to characterize it and develop the ancillary circuits. It'll be a learning experience for me, perhaps a bit less than for you. So let's compare notes.

You too, Ed B. I get to Menlo Park every week.

Watch for (or start) a new thread with a better-focused Subject line.

-Rich
[edit] here's a thread from August 2012 about the same part number: viewtopic.php?f=11&t=4881#p27719
All models are wrong; some models are useful. -- George Box

User avatar
Frank Sanns
Site Admin
Posts: 1721
Joined: Fri Jun 14, 2002 6:26 pm
Real name: Frank Sanns
Location: Pittsburgh, PA USA

Re: Is there a device that chang the frequency of an AC current ?

Post by Frank Sanns » Thu Dec 13, 2012 7:18 pm

This is a typical commercial drive for the better high voltage supplies. It reduces ripple and efficiencies can be >90%. They operate between around 30kHz and 70kHz and use either FETs or IGBTs for the switching supply. Find a schematic for a Glassman supply and you will have a complete schematic for what you are trying to do.

Frank Sanns

User avatar
Rich Feldman
Posts: 1333
Joined: Mon Dec 21, 2009 11:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

Re: Is there a device that change the frequency of an AC current ?

Post by Rich Feldman » Thu Dec 13, 2012 10:40 pm

From seller I got assembly drawings, transformer mfg. drawings (how often do you see the S and F ends of each winding identified?), and schematic of the whole HV potted assy including voltage doubler stack. Nothing about driving the primary, which is brought out in a pair of 8 or 10 AWG (IIRC) stranded hookup wires.

It would be fun to run it without having to mount or solder any inverter transistors. For example, graft it onto one of those $18 Kaiser 1.5-KW laser supplies that were discussed here a couple years ago, and have only recently dried up (?) on ebay. I just saw Carl W's usage reports on those.
Attachments
HFHV_trans.GIF
HFHV_trans.GIF (6.69 KiB) Viewed 3279 times
All models are wrong; some models are useful. -- George Box

Post Reply