High frequency 60kHz converter circuit (24VDC step up to 800VAC 500W)

[Enzy]

I wanted to build a circuit that can use 24vdc and converter to Ac @800v at about 60khz any wave form is acceptable, I was wonderin if anyone knew of any working circuits I could try out in a similar range.

 

[KlausST]

Hi,

No current, no power?

What about pushpull and a transformer?

Klaus

 

[Enzy]

I didnt ask about power because I know thats dependent on battery AH and transformer wattage alone with output FETs, but for now I would be working with about 500w, and to tell the truth in circuit designs like this I have only ever worked with push pull topology so I would work with that.

Transformer I have a e80 Core already.

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If it helps I could use a micro controller in the form of an arduino, Im not a experienced person with it though, I have done a few coding, I can make pwm signals but to vary frequency I havent yet done that or knw the limits to that chip but Its an idea that just came to me.

 

[KlausST]

Hi,

If you are familiar with push pull, then use it.
No need for regulation, no need for frequency adjust, no need for duty cycle adjust.

Klaus

 

[Enzy]

So could I use this circuit and adjust the frequency to 60khz?



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So by changing the capacitor connected to 6 and 2 I could get a higher value and by adjusting the 500k pot.

Then I would need a ferrite core? If so as I said I have a E80 core but how would would the turns be like for a 24v to 800v system?

 

[KlausST]

Hi,

Turn ON and turn OFF of the Mosfets will be slow, causing a lot of switching losses.
The transformer is 50% OFF, this additionally reduces efficiency. (25% OFF, 25% positive, 25% OFF, 25% negative). I don´t know if this is what you need.

VDD of the 4017 urgently needs a capacitor to GND.

I´d say this is a "minimal effort" circuit. Don´t expect much.

Klaus

 

[Enzy]

Hi,

Turn ON and turn OFF of the Mosfets will be slow, causing a lot of switching losses.
The transformer is 50% OFF, this additionally reduces efficiency. (25% OFF, 25% positive, 25% OFF, 25% negative). I don´t know if this is what you need.

VDD of the 4017 urgently needs a capacitor to GND.

I´d say this is a "minimal effort" circuit. Don´t expect much.

Klaus

Well that's why I'm here these types of circuits are all I'm used to, based on what your saying it can work but just not efficiently. I would still. Give it a try but would need to know how to wrap the transformer.

 

[FlapJack]

What frequency do you want the 800 VAC to be.

 

[Enzy]

60khz as mentioned, ill even start out @ 400v if thats easier.

So ill tone things down a bit and say I need 24v dc to 400v Ac @60Khz even 200w

 

[FlapJack]

Usually people want 60khz on primary side and 50 or 60 hz output. But if you want 800 vac at 60 Khz that is easier. But even so this is a tricky project. You want to use batterys for 24vdc so regulation will be poor. Does it matter if the 800 or 400 vac varies.

A E80 transformer core is nice and big, you need two pieces. Are you sure you know what you have? A picture with a ruler next to the core would help. Also if you know the ferrite type.

400 vac is very dangerous, 800 vac is scary, especially at 60khz. Personally i would not choose to work with that voltage unless i absolutely had to.

 

[BradtheRad]

This simulation gives an idea how to achieve your specs. The load receives modified sinewave, 500W average.

The primary loop has upwards of 50A during "On' time. The primary has a value around 100 uH (a few turns of wire). I tried to mimic a center-tapped primary. In any case the transformer specs need to create similar characteristics.

 

[Enzy]

the voltage can vary thats ok and so can the frequency, I bought the core from ebay a while back. yes 800v is scary Ill be ok tsting out @400v first though.

 

[Warpspeed]

I am developing something similar right now myself, but my requirement is +230v dc and -230v tightly regulated dc from a (minimum) 30v battery at around 1Kw.

Like everyone else I started out putting together a full bridge forward converter driving a rectifier with a choke input filter. It worked well at full load, but the main problem with it is that there was a minimum output load below which the output filter goes discontinuous and it all became very unhappy. I did mess with swinging chokes but it never worked as well as I really wanted.
My requirement requires it to sometimes run with zero load with minimal battery draw, and still have good output regulation and a very fast transient response to sudden step load changes.

So I am going to a discontinuous dc/dc boost converter. It should do everything right, no problem with going down to zero load, very fast transient response, and very simple magnetics requiring few turns of foil rather than high voltage litz windings with many turns.
Only disadvantage of it is very high peak currents and high ripple.
I plan to get over that by interleaving four 250 watt dc/dc converters.

Its an unusual solution, but its all pretty straightforward, and I expect it should work very well.
I am much more interested in how it behaves at low loads and zero load. It will hardly if ever see continuous full load rated power except for some sudden short surges.

 

[Enzy]

I have several projects that I am trying to take on myself, I try to read and teach myself but there is only so much one can learn in a given time and at times I think its good to ask for help.

when I have issues with audio I realize I can ask Audioguru for help here but other related topics seems experienced members arent that willing to help much I guess since its so easy in their eyes.

Im not wealthy like that most times I ask for help I ask because Its very time consuming and cost alot to be building and failing because what I read I dont always fully understand as we know electronics is complex and also sometimes there is wrong information or sometimes some of the info is missing from things you read that is critical to success.

I was wodering if its not legal to share schematics here since many of the time it would be nice to get aided with a drawing even if its just a link to a source.

 

[BradtheRad]

Hello BradtheRad, want to ask, what software did you use in setting up that circuit ?

This is Falstad's animated interactive simulator. Your computer needs Java installed to run the applet. Free to download and use at:

www.falstad.com/circuit

To allow a frequency of 60kHz, you need to reduce the timestep from its default 5 uSec.
Select Options >> Other Options.

Although Falstad's has a simple transformer model, it creates spikes at turn off (because I did not include a snubber network). You may also like to try LTSpice which is free and gets favorable recommendations by many here.

 

[FlapJack]

Here is some design information for the transformer, no small task to actually make one.

ee80 CORE
Ae 3.925 cm^2
2.22 inches winding area - 3mm (margins) x 2 = .236" = 1.984" winding area.

Design for 400 volts
24 vdc nominal input

Design transformer for push pull operation.
2 primarys, each operating at 30 KHz, giving 60 KHz output.


pri turns = Vpri^8 / 4 x freq x Flux x Ae

2,400,000,000 / 4 x 30,000Hz x 1200 gauss x 3.925 cm^2 = 4.25 turns

Use 4 turns, for each primary.


500 watts / .7 efficiency = 714 watts input.

714 watts input / 20 VDC low vdc = 36 amps. call it 40 amps.

Each primary has to supply 20 amps. 20 amp wire has to be thick and thick

wire works poorly at high frequency.

You only have 3 choices, magnet wire (easy to find, bad for high current), litz wire (hard to find, OK for high current), or copper foil (hard to find, hard to use, good for high current).

If you use magnet wire you have the high frequency problem. For 30 KHz 22 AWG is about right, good for around 1.3 amps per strand.

20 amps / 1.3 amps = 15.38 strands, call it 15. Laid out flat not twisted together.

22 awg heavy = .0276 in Dia. x 15 strands = .414 inches x 4 turns = 1.656" .

Lots of room for this winding but difficult to manage and spread out 15 strands across the 1.984" winding area. You will need about 6 hands.

If you can find copper foil .004" would be about right at 1.984" wide. .008" overkill but may be easier to find. .005" is available, and maybe others.

As you can see, high current windings are a problem. It is usually what you can scrounge up.

***

Secondary

Non regulated, just go with simple ratio.

4 pri x (400 vdc out / 24 vdc input) = 67 turns

I = P/E
500 W / 400 vdc = 1.25 A, at 60 KHz

25 AWG OK for 60 KHz good for .64A
.64A x 2 strands = 1.28A

25awg heavy = .0199 in Dia.

67 turns x 2 strands x .0199" dia = 2.667", and you only have 1.984 inches.

So you need two secondarys wired externally in series.

***

It is best if the primary and secondary windings cover the whole winding area for the best coupling and core utilization. In this case envyingly spaced out the windings across the winding area. At the end of each layer the exiting wire should have a piece of UL rated Sleeving/Shrink Tube. Each layer has to be protected from the next with a minimum of 3 wraps of Mylar tape. The tape extends fully into the margins.

You can wind
pri
sec
sec
pri

or

pri
sec
pri
sec

or

sec
pri
sec
pri

or

sec
pri
sec
pri

This is a tricky/difficult transformer to make and it is hard to know what winding method is best. Lets see what comments we can get from others and what materials you may have.

 

[FlapJack]

First i made a mistake above. The last

sec
pri
sec
pri

should have been.

sec
pri
pri
sec

With that said, if you use litz wire you can do a

sec
pri-pri
sec

and by dumb luck, there is a 20 amp litz wire on Ebay now.

"Type 2 Litz wire, 660/38 AWG, 30 feet, Equivalent to AWG #10 wire"

The primary layer would have both primary windings wound side by side. Because they are low voltage this will not be an insulation problem.

So secondary and 3 wraps of Mylar tape, both primary windings and 3 wraps of Mylar tape, then last secondary and at least 2 wraps of Mylar tape on exterior. Do not forget the Sleeving/Shrink Tube on every wire exiting the transformer, very important for the high voltages present.

Also i was optimistic in winding length. Before you start know how much room you have. Buying a bobbing will be almost impossible. You will have to make one by winding paper up into a tube and gluing some ends on. When you are finished then measure how much room you have left and how the wire will fit.

Do not give up your 3mm margins minimum on each end. This is vital to safety. Your Mylar tape will extend into the margins and touch the ends of the bobbin. The margin is designed to give a clearance between each layer to prevent the secondarys from shorting to the primarys.

 

[Enzy]

First i made a mistake above. The last

sec
pri
sec
pri

should have been.

sec
pri
pri
sec

With that said, if you use litz wire you can do a

sec
pri-pri
sec

and by dumb luck, there is a 20 amp litz wire on Ebay now.

"Type 2 Litz wire, 660/38 AWG, 30 feet, Equivalent to AWG #10 wire"

The primary layer would have both primary windings wound side by side. Because they are low voltage this will not be an insulation problem.

So secondary and 3 wraps of Mylar tape, both primary windings and 3 wraps of Mylar tape, then last secondary and at least 2 wraps of Mylar tape on exterior. Do not forget the Sleeving/Shrink Tube on every wire exiting the transformer, very important for the high voltages present.

Also i was optimistic in winding length. Before you start know how much room you have. Buying a bobbing will be almost impossible. You will have to make one by winding paper up into a tube and gluing some ends on. When you are finished then measure how much room you have left and how the wire will fit.

Do not give up your 3mm margins minimum on each end. This is vital to safety. Your Mylar tape will extend into the margins and touch the ends of the bobbin. The margin is designed to give a clearance between each layer to prevent the secondarys from shorting to the primarys.

Wow this sounds like very good information, I will need to buy some wire then because I only have copper wire 18 gauge.
And I will have to buy that tape also, I have never really wrapped transformers like this, I have only done a few microwave transformers in the past .

FOr the bobbin what about getting something like a soccet or a bolt of similar size as the middle of the core place a paper around the bolt, glue or tape it the start wrapping the LTz wire around it and after Im finished I should be able to silde the wrapping with the paper off the bolt and on to the core.

 

[FlapJack]

Well anything that works. Scroll down a little in this link and here is a simple method to make a bobbin, with good pictures.

https://ludens.cl/Electron/trafos/trafos.html

Else ware in this website he makes a bobbin by rolling up paper and using glue between the layers.

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Further thoughts. You can not start at this power level and voltage from scratch. You are going to be burning up components like pop corn trying to make it work.

Start with a small low power push pull project powered by 12vdc and try to make 30 volts at .5 amp. Now when you are burning up parts they will cost much less and you can use cheap magnet wire and you do not have to be worried about being electrocuted. Go for the 60 KHz you want. Work out the problems with making a bobbin and getting the proper phasing of transformer windings etc on the cheap system.

Each transformer core has an Ae value that you need as i showed in the formula, It will be easy to look up. Also for small cores use 1600 Gauss.

 

[Enzy]

Well so far I have made a couple inverters, been trying out designs on the Internet that don't work so well and do my own readings and made some modifications or big changes, so far I have been making 12/24v DC to 120/220v 50hz circuits so I dnt think I'll need to be scared so much of popping stuff. What I would ask is if I can use my same inverter circuit to get the 60 khz and then use the ferrite core on it. Because all I would need to do mod my circuit for 60khz.

But that's good advice once again and I'll take precautions as you recommend.