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Forum Index : Electronics : Wiseguy New Inverter Build Nano R6

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wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 998
Posted: 05:42am 20 Apr 2024
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The Inverter code is nearing completion, the most recent version I received last night, I cannot fault its operation, but still testing.

The setup/calibration is realtively simple, the default values essentially would allow the inverter to run for a 48V system, when the code is loaded. However, for accuracy there are calibrations for Vcap & Vin, both calibrated in one step, then there is the calibration for AC output Voltage and current. Please be aware that the AC readouts whilst quite accurate for resistive loads should not be totally relied on for exact accuracy as they are essentially peak readings but calibrated as for RMS.

I recommend using a true RMS meter when calibrating the AC volts and amps. For stress free settings of AC Amps and over current trip at for instance 5kW loads, a 10T winding through the current sense transformer allows 1 A to look like 10A.

My method is to place a short length of 2.5mm enamelled wire through the current sense transformer, as the main current conductor from the inverter to the load. Now from the load side connect a 1mm enamelled wire and wind through the current sense transformer 9 more times and terminate the 3 wires onto a terminal block or similar.

Now a 500W load using the extra 9T will calibrate as for a 5kW load whilst only supplying a load of 2A instead of 20A.  Another method is to use a 240V to 6 or 12V transformer wired with a 0.5 - 1 ohm resistor in series to a 1mm enamelled 10T winding and using a Variac (yes its coming....) and AC amp-clamp meter, you can calibrate the inverter AC Amp meter and the over current trip point as required.

The display shows the applied input voltage (Vin), the actual Voltage of the main capacitor bank (Vcap) The 240V Mains output Voltage and Current, the % of PWM power drive 0.0 - 99.9% and heatsink and toroid temperatures and status of the 2 Fans.  There is a "mains up", 12V open drain FET output to switch a relay that automatically connects the mains to the load when the ramp up is complete.

The test mode of the control PCB will allow the inveters PWM/Opto drive to run despite low capacitor bank and input voltages.  This function is invaluable for initial testing or repair. Simply put the J11 link to test and apply 16V to the controller, the LCD reports "Test mode" the main capacitor bank can now be powered from a variable DC supply. A sinewave is generated on the toroids output from as low as 1VDC (about 7VAC from the mains). The drive waveforms & current consumption etc can be monitored as you advance the FET Power section voltage up to its normal voltage.

I had to temporarily stop work on the new Variac PCB testing, to concentrate on the software creation and testing of the main inverter which I (and probably Poida) underestimated the total amount of work required to beat it into shape.

Hopefully in the near future (a week if all goes well) I can tell you they are both finished and ready for manufacture, after we work out who wants what and how many.

I will post a picture soon of the actual display with the inverter working.
Edited 2024-04-20 17:49 by wiseguy
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 998
Posted: 03:35am 22 Apr 2024
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Here are some pictures, first is the inverter operating display.  Note the % of PWM on the 3d line is overwritten by fault/error messages if they occur. It is informative to note, if you multiply the Vin by the % ie 48.9 x 0.916 the answer is 44.79, that is the actual DC input voltage where my inverter drops out of AC regulation with no load. If you put 44.8V in it will be at 99%



Then some pictures of the small Nano interface PCB I made cause I like neat tidy stuff. The LCD board will be in its 3d revision when it is next ordered.
I will be supplying them for 50c ea with orders.  Bad news is you need to run a jumper wire from +5 to pin 15 and join pin16 to ground if you want the backlight to work, this is for the first 20 odd display boards shipped out, after that it will be the new Rev.



The astute readers will notice that the black wire is shown deftly plugged into the +5
pin, I just plugged it in for the picture, it wont work very well if you actually do this.....

 

The third revision (I start at Rev0 so board shows Rev2) is as pictured below, you will see there are two pads that can be solder bridged to enable the backlight.  In a typical room the black on green displays are quite readable with no backlight, but the blue displays really need one.  Some LCD modules do not use a current limiting resistor, and their LEDs are directly on pins 15 & 16.  So if you have one of those LCDs a suitable value SMD part (or through hole part - a bit fiddly!) can be soldered to the pads. Suggest starting with 470R and adjusting up or down as required.  Both the recent ones (Blue and Green) I bought from different Ali suppliers had the current limit resistors fitted as standard.



Although I show a plug in connector fitted to the display module it makes the interface board feel a little "wobbly" when plugged in, I think the interface PCB should be soldered direct to the display but spaced from the back of the LCD by at least 5 or 6mm.  The 3 pins for J1 can be soldered vertically - or as I have done, horizontally.

The board can be constructed using just the 2 x 15 rows of pins the Nano PCB's are supplied with and the little dual row header is not required to be soldered to the Nano if you buy them unassembled.  Not all pins of the Nano or LCD are required to be connected so by cutting 3 lots of 6 pins 2 of 3 pins and 1 each of 4 & 2 pins. Some of the Nano pins are not required but the spare connectors were used for good stable anchoring.
Edited 2024-04-22 13:58 by wiseguy
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
poida

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Joined: 02/02/2017
Location: Australia
Posts: 1389
Posted: 08:41am 22 Apr 2024
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this is looking nice, WG

The PWM % is very useful in sorting out how many turns you really need
for the primary.

Most times I build or comment on this, I suggest
a primary that will run at the required AC output at 80% PWM
This allows for some voltage drop from the battery, through the power bridge.
And it allows for some drop through the primary & choke(s).
My build always use far too small primary conductor copper area
'cos I am cheap/stupid but the inverter is built for low power for most of the time
and 10x low power for 5 or 10 minutes max. bursts. Let things get warm and let the fans
cool things down, plz.


If you build an inverter with good, thick primary cable and good thick battery cable
and 4 FETs x 4 or even 6 x 4 then you could get away with running at higher PWM %
This would be good, it means lower DC current (from battery and through FETs)
and lower PWM current in the primary and choke(s).
(lower DC current means better efficiency)

This PWM % will be a useful design tool for optimising the build.
wronger than a phone book full of wrong phone numbers
 
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