What does "Transformerless" mean on the Sol-Ark?

[DIYSolarShed]

I notice that my new Sol-Ark unit says it is a "transformerless" DC design. Can someone explain what that means?

I notice that using my Tri-Field EMF meter, it has very low magnetic fields. (Basically close to the background level of my house, unless I am within 1-2 feet of the unit. Background at my house seems to be .2 to .5 milligauss). I am not not of those EMF nutters, but I suppose it's always a good thing to have lower interference, right? Is that part of the Sol-Ark's transformerless design?

Also, just for my learning, I have heard some talk about "high frequency" transformers, and dirty electricity. Can someone explain those to me?

 

[RCinFLA]

It means it is a high frequency first stage inverter. No big heavy low frequency transformer.

Transformerless is not really transformerless. There are transformers just small ferrite high frequency transformers, not big heavy iron 50/60 Hz transformers.

High frequency inverter has a DC to DC boost first stage that takes battery voltage up to about 180-200 vdc. Second stage is PWM H-bridge output MOSFET's that creates the Sinewave PWM profile from the high voltage DC. Output is filtered to sinewave with a toroid L, C filter.

A low freq inverter has H-bridge PWM directly from battery lines feeding into a heavy low frequency transformer to boost AC voltage up to 120/240 vac. The low frequency transformer has secondary function to provide most of the PWM filtering to sinewave.

 

[RCinFLA]

There are true transformerless battery-less Grid Tie Inverters. They require the PV panels to be highly series stacked to provide 370 to 450 vdc that is PWM chopped and filtered to feed the grid directly.

Problem with these, besides dealing with lethal DC voltages, is they do not have the benefit of any transformer isolation between grid and panels.

 

[DIYSolarShed]

It means it is a high frequency first stage inverter. No big heavy low frequency transformer.

Is that generally a good or bad thing?

 

[RCinFLA]

Is that generally a good or bad thing?

Usually high frequency inverters do not have the surge current capability that a low freq inverter has.

They do weigh less.

 

[Steve_S]

Inversion Methods Explained: High Frequency vs Low Frequency | Magnum Dimensions (magnum-dimensions.com)

Technology brief: Top ten transformerless myths (eaton.com)

What are Transformerless Inverters - Synergy Files

 

[Shunt Czar]

The main thing the Eaton document states that only begins to make their arguments credible
is that there inverters won't allow DC out if an output device fails. Unfortunately they are
vague on how that is accomplished, that vagueness alone calls their method into question.

This kind of failure has burned houses down.