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[SOLVED] High-power-capacitance-voltage-doubler topology

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Zak28

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Need help winding my own transformer

Im going to make a transformer for residential power, its going to step up voltage then be rectified for charging a capacitor.

Questions:
Is the current in the primary winding limited by and frequency (60hz) and inductance?
IIRC it should be because XL=jωfL and I=V/XL in my case its 177Vpeak.
If I want to set the current to 5amps then I=V/XL = 5amps=177/XL = XL = 35.4Ω ofcourse this isn't considering resistance per length of wire. Is this correct or will I trip a circuit breaker?
 

Re: Need help winding my own transformer

Hi,

You are thinking the wrong direction.
First you have to decide all your transformer's specifications.
Then go to one of the many transformer calculation tutorials.

If you still have problems then show your specifications, the tutorial you use and your calculations.

Klaus
 
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Re: Need help winding my own transformer

Usually I've found some amount of DC resistance in the primary. This is from measuring a few power transformers using my ordinary multimeter.

It is a low ohm value therefore it does not hamper efficiency too much. I suppose it is built in by manufacturers as a precaution, so as to limit current draw to a reasonable level in all situations, ranging from no load attached to the secondary, to a shorted secondary.

By the way, since you want DC output, you might consider an alternate method, namely to send house voltage through a capacitor-action voltage multiplier.
 
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Re: Need help winding my own transformer

Usually I've found some amount of DC resistance in the primary. This is from measuring a few power transformers using my ordinary multimeter.

It is a low ohm value therefore it does not hamper efficiency too much. I suppose it is built in by manufacturers as a precaution, so as to limit current draw to a reasonable level in all situations, ranging from no load attached to the secondary, to a shorted secondary.

By the way, since you want DC output, you might consider an alternate method, namely to send house voltage through a capacitor-action voltage multiplier.

Can I achieve 400v @ 400mA with cap multipliers?
 

Re: Need help winding my own transformer

Can I achieve 400v @ 400mA with cap multipliers?

Yes, the simplest arrangement uses 2 caps and 2 diodes. However you might want to construct gangs of capacitors since they have several hundred mA going back and forth through them, at 50 (or 60) times per second.
 
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Re: Need help winding my own transformer

Yes, the simplest arrangement uses 2 caps and 2 diodes. However you might want to construct gangs of capacitors since they have several hundred mA going back and forth through them, at 50 (or 60) times per second.

Would using large cap sizes play a key role in increasing output current? Also does anybody know of a good tutorial about winding your own transformer for use with residential power?
 

Re: Need help winding my own transformer

Referring to the initial post, current limiting by inductance doesn't occur with regular transformers, a special "high reactance" or "stray field" transformer design is required to achieve it, used e.g. in microwave oven or neon sign HV supply. It's probably easier to use an additional input choke for current limiting.
 
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Re: Need help winding my own transformer

Can I achieve 400v @ 400mA with cap multipliers?

Yes by adding a Villard stage, since a doubler can only give you 2 * 170 = 340V.

Supply is 120 VAC (peak 170V).

3 Villard stage voltage tripler 120VAC to 1k load 400VDC.png

The 1/2 ohm resistor is unnecessary. It portrays a certain amount of input resistance.
The inductor is optional. It has the effect of spreading the incoming bursts of supply current so that they are less severe.
 
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Re: Need help winding my own transformer

The topology is almost what I need (I need 500-520Vdc & as much amps as I can get). Is the circuit verbatim? Meaning I really hookup an inductor right into line power?

Also, whats the matter with my circuit - LTSPICE is not simulating it past 12.4%

Untitled.png

LTSPICE circuit:
View attachment multiplier.zip
 
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Re: Need help winding my own transformer

Your LTspice circuit reaches 500VDC at the load, at t=50mSec. It should reach a stable level if you command the simulation to portray 200mSec.

With a capacitor-action multiplier you get:
1) sudden severe bursts of incoming current.
2) power factor error due to current bursts coming before peaks of the voltage cycle.
An inductor is a simple solution to both situations. Ideally you wish to fashion a sine-shape Ampere curve. You get that by using a transformer but at greater expense.

Your output specs (hi V/ hi A) make your project the kind that needs a generous budget in the development phase. You can expect to replace several components during testing. My simulation merely illustrates a concept. You can expect to make a few design changes, as you encounter challenges. About the best you can hope to do, is convert 120VAC at 15A, to 500 VDC at 4 or 5 A.
 
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Re: Need help winding my own transformer

I doubt I will encounter design changes after circuit finalization. The most concerning thing to me is the capacitor turning into a very lethal bomb by exploding (my cap https://media.digikey.com/pdf/Data Sheets/United Chemi-Con PDFs/U36D Series.pdf) Im going to make the enclosure out of abs plastic and its going to be really thick and likely multiwalled with lots of slots to permit gasses to escape in the case of a catastrophic failure.

Now that I mentioned the capacitor I might as well point out this project is all about rapidly discharging the capacitor with the rotary mechanical mechanism which I designed into a 2.5mH 800w crossover inductor at 3x per second. Im hoping the cap will charge fast enough to discharge 3x per second because I already specced out 180rpm 6v motor. The next most concerning thing to me is putting harmonics onto the power grid and even perhaps damaging house hold equipment because of said harmonics, should I even be worried about this?
 

Re: Need help winding my own transformer

I'm missing the said transformer in the simulation circuit. Due to the even number of diodes, the circuit is drawing DC current from the source (either mains or transformer) which is basically bad. In case of a transformer, the DC current must be expected to cause saturation. Should be corrected.

As for the "rapid discharge" operation, there's well a possibility to exceed the capacitor ripple current rating. It's not completely clear which exact capacitor type is used. Is it 3 x 300 µF as in the simulation schematic? To estimate also the discharge waveform and related capacitor power dissipation, we must know the inductor characteristic, particularly series resistance and possible saturation characteristic if it's a bobbin core type.

- - - Updated - - -

Purpose of the device is described in this previous thread, I guess https://www.edaboard.com/showthread.php?t=359530
 
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Re: Need help winding my own transformer

If you need ~400VDC at max amps then you need 2 x 1kW or bigger 230:230 isolation transformers and a variac, rectify the output of the iso Tx's (with about 1000uF 450V electro on each, and put them in series. Run the two primaries off the variac (in parallel) - you should get ~ 400VDC at about 150 Vac on the variac.

Lots of energy avail at the o/p - so BE careful ...! lethal voltage and high energy - put bleed resistors on the electro's 100k 5 or 10W.
 
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Re: Need help winding my own transformer

Good capacitors are not cheap and niether will be the isolation transformer. The cap I choose for multipier stages is film, it should last a while the price point for ~300uF went up considerably and I am hoping to do a massive purchase from digikey so I would rather have what is in stock with them.
https://www.vishay.com/docs/26011/mkt1820.pdf
MKT1820722065

Also I changed the primary discharge cap which will dump energy into crossover inductor from that electrolytic to this far more reliable film cap.
https://www.cde.com/resources/catalogs/947C.pdf
947C601K801CCMS

- - - Updated - - -

I came to realise that 3 discharges per second is unfeasible because I rather have the device mobile, were as the weight of the appropriate hardware such as transformers will cause it to be so heavy that its transport will really be impractical. I just don't want to spend on bulky and very heavy hardware. But I do realise I will need 1 isolation transformer I hope that I will be able to get away with 500VA with a decent charge speed.
 

Re: Need help winding my own transformer

Also I changed the primary discharge cap which will dump energy into crossover inductor from that electrolytic to this far more reliable film cap.
There's no single "discharge cap" in the shown schematic in #9.

Anyway, an overall film capacitor circuit has no problems with AC current rating, if you use electrolytic capacitors, you can calculate Irms over a charge/discharge cycle and check against specification.

Irms = √(1/T*∫i²dt)

- - - Updated - - -

Strictly speaking, you don't need an isolation transformer. Just safe insulation of your circuit to avoid touching of the hazardous contact voltage.
 
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High power capacitive voltage doubler topology

Which capacitor voltage doubler topology is suited for exactly doubling an ac potential whilst yeilding high current to its load?
 

Re: High power capacitave voltage doubler topology

Your project sounds similar to charging an experimental railgun. The capacitors need to be robust, to fulfill demanding specifications for volts and Amperes. It is common to build banks of capacitors in parallel.

When you first apply power, you'l get severe startup surge through diodes and capacitors. It's a good idea to examine railgun circuits, to see how they get past certain hurdles.

If you want to draw 15A from house voltage, stepping it up 2 or 3 times, then a simulation reveals that Farad values from 1000 to 10,000 uF might be suitable. Where my simulations show one capacitor, a real-life circuit ought to consist of a bank of several capacitors.
 
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Re: High power capacitave voltage doubler topology

Your project sounds similar to charging an experimental railgun. The capacitors need to be robust, to fulfill demanding specifications for volts and Amperes. It is common to build banks of capacitors in parallel.

When you first apply power, you'l get severe startup surge through diodes and capacitors. It's a good idea to examine railgun circuits, to see how they get past certain hurdles.

If you want to draw 15A from house voltage, stepping it up 2 or 3 times, then a simulation reveals that Farad values from 1000 to 10,000 uF might be suitable. Where my simulations show one capacitor, a real-life circuit ought to consist of a bank of several capacitors.

Is my circuit legit?

View attachment doubler.zip
 

Re: High power capacitave voltage doubler topology

Asking too much to expect a screenshot of your simple circuit? It would also help to know that you posted a Ltspice schematic in the zip file.

doubler.PNG

The circuit has at least this problems:
- no input current limit
- closing the discharge switch (omitted in your schematic) also causes a huge current through C1 and D4 (depending on the instantaneous grid polarity), which is propagated to the grid.

A good chance to trip any MCB, if present in your distribution board.

Operating the discharge circuit connected to the grid longer than a second or so hardly confirms with any power quality regulations.
 
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Re: High power capacitave voltage doubler topology

Asking too much to expect a screenshot of your simple circuit? It would also help to know that you posted a Ltspice schematic in the zip file.
A good chance to trip any MCB, if present in your distribution board.

I deliberately ommited the switch in previous post because I thought it was unneeded. Here is the complete circuit.

I have no idea how to limit current from mains aside from adding seres resistance which is not realistic. How should I limit current?

Asking too much to expect a screenshot of your simple circuit?

I thought circuit was better than screenshot but here is a screenshot of circuit.
circuit22.png

circuit:
View attachment circuit.zip

Don't know what to do about diode propagating to grid.


Greatly appreciated.
 

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