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Murphy's friend

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Joined: 04/10/2019
Location: Australia
Posts: 671

Posted: 01:01pm 05 May 2021

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Seeing that there is an interesting discussion at another topic regarding inverter PCB layouts I thought I show how I now build mine.

The design is based on Wiseguy's schematic, basically a nano inverter running Poida's code with opto isolated drivers and a final totem pole stage.

The following pictures should explain better than words;

As you can see the heat sink fins face each other with the half bridge boards on each outside. The power tracks are alu 50x3mm flat bar and the capacitors are mounted on those. This allowed the use of 1oz PCB boards.

There is a fan underneath the heatsinks. I use an external fan controller rather than the nano for it.
The control board fits on a 100x100PCB and incorporates low voltage shut down.

The mosfets are on little carrier boards to make replacement easy. But the surprising robustness of this inverter design has made that so far unlikely. The inverter has a 6KW (2x3KW) double stack transformer and powers all of the house. Nothing I have tried has killed it yet, it just shuts down if I do something silly.

Here is what the whole assembly minus the covers looks:

I'll post a picture of the finished inverter in another topic later.

wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 1206

Posted: 02:08pm 05 May 2021

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What I want to know is how the hell you lifted it onto that table ! That is one very impressive iteration of my topology. Thanks for the vote of confidence by building it.

A couple of questions, what gate resistor value did you use ? How accurate is the output voltage control for various loads - what is the largest deviation from the setpoint (240V) ? What choke did you use - I cant make it out from the pictures.

I see that you have solid bars over the FETs & torqued down to hold the smoke in

Did you use separate isolated supplies for each of the 4 legs of the bridge ? What is the idling power ? How warm do your heatsinks get under serious load ?

What is the little sub board on the controller - is that a low pass filter ? Did you try it without the filter - if so what were the results. Do you hear the hum slowly and randomly change or is it rock solid?

The controller is simplicity - well done, the mechanics alas is a bit out of my league !

Sorry for all the questions - I get excited over stuff like this.
Edited 2021-05-06 00:15 by wiseguy

If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike

johnmc
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Joined: 21/01/2011
Location: Australia
Posts: 282

Posted: 10:58pm 05 May 2021

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Thanks for the pics
Most impressive

cheers john

johnmc

Warpspeed
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Joined: 09/08/2007
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Posted: 11:00pm 05 May 2021

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That is a true work of art.
I could look at that all day.
A very great deal there to learn from.

Cheers, �Tony.

Murphy's friend

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Joined: 04/10/2019
Location: Australia
Posts: 671

Posted: 08:33am 06 May 2021

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wiseguy said What I want to know is how the hell you lifted it onto that table ! That is one very impressive iteration of my topology. Thanks for the vote of confidence by building it.

I use a 1 ton chain hoist with webbing slings under the inverter to lift that ~75kg monster.
BTW, yours was a 'belts and braces' approach, I left some of the braces off to conserve PCB area and it seems to work.

A couple of questions, what gate resistor value did you use ? How accurate is the output voltage control for various loads - what is the largest deviation from the setpoint (240V) ? What choke did you use - I cant make it out from the pictures.

There is a 1R gate resistor on the driver board and another 1R at each mosfet.
Load control (not measured) is nothing to worry for me - it looks fine. Set point 235V, down to about 231V when I back charge ~2KW via GTI into the battery bank.
Choke picture below, its of a similar choke I have for a spare:

These chokes are wound on my lathe using multi layers of 2 parallel 1.8mm dia wire.

I see that you have solid bars over the FETs & torqued down to hold the smoke in

No, there is another reason. I use the heat sink for the drain current path so the top bars help secure mosfet clamping to the heat sink.

Did you use separate isolated supplies for each of the 4 legs of the bridge ? What is the idling power ? How warm do your heatsinks get under serious load ?

There are 4 isolated 15V DC/DC supplies. Idling power is 29W @ 55V DC. Fan comes on at 50 deg C but that happens very rarely on a very hot day if I run machinery for a long time. Usually inside inverter temp is around 10 deg above ambient.

What is the little sub board on the controller - is that a low pass filter ? Did you try it without the filter - if so what were the results. Do you hear the hum slowly and randomly change or is it rock solid?

Yes, its the low pass filter, have not tried without it. Inverter barely hums normally unless microwave or similar is used or high power back charging happens.

The controller is simplicity - well done, the mechanics alas is a bit out of my league !

I do like the mechanical part of building it

. Not being an electronics engineer, thanks for doing that side of the work for me.

Sorry for all the questions - I get excited over stuff like this.

Haxby

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Joined: 07/07/2008
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Posts: 423

Posted: 03:28am 07 May 2021

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Great work! Well done!

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