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poida
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Posted: 19 May 2019 at 9:49am | IP Logged Copy link to clipboard   Quote poida

hary wrote:
BenandAmber, This puts me in the darkness.

We use toroid transformer to avoid leakage and now you say we need to add leakage with the choke ?
On the other side, I can understand we want to smooth the high frequency issued from the board's MOSFET.
The point I don't understand is : Why the toroid transformer's primary doesn't smooth the high frequency itself as it is also a winding on a magnetic core ?

And the picture you show just before look like toroid also ???


The main toriod transformer usually has very small leakage inductance.
This results in their good efficiency when used "normally" as a step down power transformer.

I've already stated the output of the inverter board consists of nothing more than
zero volts (i.e. a short) and full DC supply voltage, backed up by as much capacitance as possible.
Pumping this into something of relatively low inductance will result in likely too large currents in the primary circuit.
Best build practice here on the forum has the primary winding consisting of the largest gauge copper wire, with the shortest length of this copper wire.
A short length of thick copper wire has little inductance.

I short while ago I posted on this very subject here and it's worth your time to read it, in my view.

The summary from the above link is that when we evenly space the windings of both the primary and secondary around the toroid, obtaining very even spacing between each turn, we end up minimising leakage inductance. It becomes too small and so huge current peaks will be present in the primary winding, including the MOSFET's Drain to Source current path.

And so the primary choke was born. We include a choke of about 50uH and built with a core that will not saturate much if at all even up to the maximum operating output levels of the inverter. The choke absorbs the DC voltage pulse, backed up by huge capacitance, converting this into a rising current in the primary circuit.
This also results in a changing magnetic field strength in the choke.
We build the choke to operate efficiently and so nearly all of the magnetic field energy is returned to current.
The choke acts as a shock absorber, taking the killer punch out of the huge current pulses of the PWM design.

I have examined the voltage across the primary winding terminals of my inverters and when I have a good enough choke installed, all I see is clean steps in the voltage.
If the choke is insufficient, I see spikes on the rising edges of these step changes.
The step changes of course are due to the PWM, switching in a pulse of DC supply, which the choke absorbs, converting it to the smooth and small voltage step presented to the primary winding. Have a look here when I examine the choke's effect

Often, this discussion leads to the question "how best to build a choke tester"

In your case, with the 1000W inverter board, the inductor Ben & Amber showed at the top of here will be easy to build and work fine. I use 6mm2 PVC insulated house Earth wire in mine. It's more flexible to work with.

Sometimes it's helpful to think of the necessary inductance as being 1/2 of a high power, low loss LC low pass filter. The filter's job is to remove the 23kHz PWM, and it's higher overtones completely, letting 50 or 60Hz through with minimal loss.
The capacitor is positioned across the AC output winding. The inductor is placed..
When you put it on the secondary, there appears a capacitance across the primary, multiplied by the turns ratio.





Edited by poida on 19 May 2019 at 9:54am


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Clockmanfr
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Posted: 19 May 2019 at 6:53pm | IP Logged Copy link to clipboard   Quote Clockmanfr

My Personal observations on my OzInverter builds.

This below is from the New second edition workshop manual of the 6kW OzInverter build process.

The new book is a complete and utter new re-write, with absolutely everything about everything, 92 pages and 242 colour photographs and block diagrams, its at the printers at this very moment.


Toroid ferrite Ecore choke. For further information see the technical chapter.
A = 65mm (2.56") (Length) B = 45mm (1.75")
C = 32.5mm (1.28") (Height) D = 22mm (0.87")
E = 20mm (0.79") F = 27mm (1.06") (Width)

“The ecore will drop your idle current and at the same time take an enormous amount of heat out of the transformer due to the new efficiency.... other wise it will absord hundreds or watts for nothing but heat you don't want. ………..oztules”

The ferrite Ecore is very important as it reduces inverter idle current use, ie, the inverter is not using excess power while awaiting use when running, like night time when the household is asleep. With this 6kW OzInverter the running, ilde, power use is down to 30 to 40 watts.
The ferrite core is commercially available as ‘E6527 Ferroxcube E65 E EE Ferrite Cores’ , I have found this size to be the most efficient and quite. I have experimented with bigger cores with 70mm2, but then the flexible cable needs to be wound really tight or the Ecore Choke sounds like a Banshee on speed. The cores comes in two half’s, but those internal edges are very sharp so I use a fine needle file to gently round the corners.


I have found this particular size hits a sweet spot. You could widen the core gap but then at high power other problems arise.





Edited by Clockmanfr on 19 May 2019 at 6:54pm
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hary
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Posted: 20 May 2019 at 3:09am | IP Logged Copy link to clipboard   Quote hary

Clockmanfr, you say :"E6527 Ferroxcube E65 E EE Ferrite Cores"

But is this the correct core for all kind of inverter ? The 6kW and the one I'm intending to make, so 200W continuous, 1000W surge ?

Plus haw do we source core like that ? what are the data we're looking for ?
From what I understood, the core modify the relative magnetic permeability compared to an air core inductance.

So we should source a core with a specific permeability, I guess...


Edited by hary on 20 May 2019 at 3:22am
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BenandAmber
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Posted: 20 May 2019 at 5:14am | IP Logged Copy link to clipboard   Quote BenandAmber

When you're new here sometimes it might be hard to know who to trust

These greats on here their word is as good as gold

They are very careful of what they say and will not lead you wrong

In my post poida the great literally showed me the exact one to get

And every step from beginning to end

that information is still there on my post

That little inverter from that post absolutely runs perfect and I beat the crap out of it everyday



Edited by BenandAmber on 20 May 2019 at 5:21am
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hary
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Posted: 20 May 2019 at 6:12am | IP Logged Copy link to clipboard   Quote hary

Hi benandAmber.

from this post Poida talks about 5000W inverter, then he says he put 100A on 6mm2 wire which is very high current /mm2 to me.
I'm very humble, I'm not saying he is wrong, I'm only wondering from my own background !
Or maybe, the 5000W he's talking about is in surge condition ?

And As I'm on 24V, I'd probably need bigger wire, so I don't know if I could fit the 6 turn of bigger wire on the core Poida gave the reference.
Plus, again, being on 24V, it will double the current and so the same core is going to saturate much faster. This is what I understood from my "Sunday reading", so I'm not sure I need the same core as you if you're running on 48V ?

So I was trying to understand this magnetic stuff. But it seems to be a big stuff, indeed !

I'll be missing this choke for the build !




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BenandAmber
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Posted: 20 May 2019 at 6:19am | IP Logged Copy link to clipboard   Quote BenandAmber

That sounds really good Harry

I videotaped my first startup

if you don't care can you videotape yours

I'm thinking about putting everybody's first start up into one video and uploading it on YouTube
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