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rogerdw
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Joined: 22/10/2019
Location: Australia
Posts: 950

Posted: 01:49am 29 Dec 2025

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Merry Christmas and Happy New Year to everyone.

I'm in a facebook group of people focused around using forklift batteries for solar and a handful are keen to build a WG Inverter and are making inroads.

Here are some questions that came up this morning. I numbered them to make reply reference a bit easier. Thanks.

"Can we talk voltage here for a bit, as there are a few slight unknowns here which are worth clarifying before commencing permanent windings.

1) Does the different control chip in the WG build require any adjustments to the transformer design?

I assume not, but I mention it because P18 par 2 of the book (see below) mentions different target voltages for PJ processors vs the 8010 chip.

2) How important to the WG build is the 15% voltage safety margin mentioned at the bottom of page 16? (see below)

3) There is a comment on page 27 that also influences the design: (words to the effect of) leaving out one primary turn will help out as the battery discharges and produces a lower voltage, by allowing for a higher step-up voltage vs the design.

4) Should we also target a slightly higher step up ratio to allow for battery voltage decline?

5) What about battery overcharge to say, 52V?

6) Finally, referring to Wiseguys' recent comments, is it better to target 240V or 230V output?

For reference, my understanding of the step up caculations is: we are aiming for 240V RMS AC output which is 339V peak AC, plus 15% safety allowance for 390V peak AC which is 8.1:1 step up from a 48V DC input."

These quotes are from Leslie Bryan's OzInverter book

P18 par 2

Quote "It is important to wind for a few more volts than we want, our saturation is further away ... so say 240 or 260v for a 220v system gives us leeway and lower magnetising current ...

... from there about 1:8 primary : secondary.. and we have a workable start point.... that’s how I tackle it.

Provide you have a crane close handy to hold the thing for you, it will be easy to wind.. big hole and plenty of room.

It will be important to map out the wire sectors in advance.. or it will all end upon one side……

"We want the primary to be about 30 to 32v for the PJ style processors, and 28 to 30v for the 8010 chips for a nominal 48v system." ‘Oztules’.

Page 16

Quote Oztule's explanation:

"So to make 240v AC from a DC source we need to handle the 340v part of the curve as well ...

... so our DC side needs to be .7071 of the expected AC wave generated in it or for 48v about 48 X .7 = 33v ...

... so we need at least as low as a 33v primary to get to the peaks needed to make the sine wave ...

.... now with losses in the switch, wiring, sags to cover high power surges etc, we need another 15% safety margin so we are reasonably assured of getting our 240vrms at all times."

Cheers, Roger

KeepIS

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Joined: 13/10/2014
Location: Australia
Posts: 1994

Posted: 04:37am 29 Dec 2025

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Merry Christmas Rodger, just a few quick thoughts.

Quote 1) Does the different control chip in the WG build require any adjustments to the transformer design?

Not really, the WG design will operate over a wide range of voltage inputs, only the Nano Setup parameters and the Toriod design need to be changed to match the desired system DC input/output voltage range.

Quote 2) How important to the WG build is the 15% voltage safety margin mentioned at the bottom of page 16? (see below)

This is a function of Toroid design and is the same for any Inverter controller, primarily as indicated in the info you posted, to keep the Toriod away from saturation and lower magnetising currents by winding the output to a voltage higher than required, in turn winding for a lower flux density of around "1 T" instead of commercial Toroid values of around 1.4 T.

IE: The Toroid must be able to produce (Example 240Vac) at the "lowest" DC input voltage that the batteries are expected to run at and not reach 99% PWM drive, and if wound correctly will have a lower Idle current at the nominal running DC voltage.

Quote 3) There is a comment on page 27 that also influences the design: (words to the effect of) leaving out one primary turn will help out as the battery discharges and produces a lower voltage, by allowing for a higher step-up voltage vs the design.

4) Should we also target a slightly higher step up ratio to allow for battery voltage decline?

3 and 4 are similar, if you find you cannot get 240Vac regulated output at the design DC input you chose, you can remove a Primary turn to help fix the problem.

All of this come back to making sure you don't hit 99% PWM with the low voltage input selected for the chosen AC output voltage, and allowing a little headroom.

Quote 5) What about battery overcharge to say, 52V?

Both Battery over-voltage cutoff and AC over-voltage cutoff are adjustable in the Nano Settings.

Quote 6) Finally, referring to Wiseguys' recent comments, is it better to target 240V or 230V output?

If running off grid, I personal like around 230 to 235Vac, if switching to the Grid in an emergency then a voltage closer to the "average" grid voltage at your location might be advantageous.

My Toroids regulate at 240Vac down to 40VDC, which is totally unnecessary with LiFePO4.

The older design controllers did not have a neat PWM indicator, instead you used a DSO to confirm drive, the WG inverter will only drive to 99%, at which point regulation stops and output sags if load increases.

Which translates to, you should not blow the Inverter if it runs out of drive due to a miscalculation, the TEST mode in the WG inverter can be used to safely test the Toroid and the main Inverter limits and settings on the bench with a small Current regulated supply and a small CAP bank.
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Edited 2025-12-29 19:08 by KeepIS

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