Electronics > Power/Renewable Energy/EV's

My first invertor. Help me choose.

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Basic fixed requirements:  24V 220-240V off grid, pure sine.

Less fixed requirements:  Easily support at least 1kW output, without fuss or hassle.

Battery supply:  8S 1P 105Ah LiFePO4 24V pack.  Rated for 1-2C max discharge, 0.2C preferred.

I'm wrapping that in grace and taking.  1C 105A and rounding that to 100A at which I will be "breaker'ing"/fusing the battery.

So the invertor has 100A @24V MAX (at this upgrade level).  That is 2.4kW - losses.

Load side:
My aspirations on the load side are moderate multi-hour run times of ~100-250W.  And experimental short shots of 1kW.  ISLAND style.  ie.  a single 4 plug extension running off the invertor.  NEVER mixed with the grid phase. 

The inverter will be terminated on the AC side in a small consumer unit.  The house wide PE ground will be attached to all metal casings, including the solar MPPT controller and thus the battery -. 
Question!!!:  I am led to believe, if you want a proper AC circuit that will for example pass a plug tester, you are required to bond the invertor Neutral to the house PE.  This will prevent the NE fault.  It will also reference the neutral and earths to the same potential as the grid mains phase neutral.  Finally it will allow the ground fault protector to function correctly on the "off grid" extension.  Is this correct?  Are there any concerns with any potentials building between the neutrals and current flowing between the two?

Future proofing:
The final deciding factor for this system is the space on the garage roof for panels.  Due to shading of the sunlight on that roof there really only is room for 3 panels portrait or maybe at a push 2x2 landscape.  That ultimately limits this system to around 1000-1500W solar.
I currently have a 40A MPPT (EPEver Tracer4210AN) which supports up to 1000W with a 50% oversizing margin up to 1500W, but limited to 1000W battery charge.
I can add more solar controllers of course.  (I have another smaller MPPT, but it's common positive and I don't want to play "that" game with floating 41V DC systems at opposite polarity sitting beside each other.)
The battery can and will obviously continue to expand.  8S 1P will take a few months to build up enough disposable for another 8 cells, but that is the plan.  Maybe (finance dependant) go up to the 280Ah cells (£1000+ for 8).

That is mind, a 4kW invertor sounds like a good future proof.  However.  Regardless of how big the battery really gets, I feel it only prudent to keep it's current limit to 100A.  Not least because >100A = expensive hardware.  So a load greater than 2.4kW will require the step up to 48V and 16S.  I don't see that happening with this particularly system.  Given the panel power restrictions, keeping it as a 24V, 100A system seems safe and fair.

So... if I want 2.4kW I should aim for a GOOD 3kW inverter or a mediocre 4kW.

My eyes are on one of two invertors.

A Victron Pheonix 1kW 24V:  as an interim.  £450!

Less well branded:
An EPEver IP Plus 3000W:  £400 w/ shipping.

The MPPT is EPEver, which provides that "same eco-system" appeal.

Does this sound like a plan?  Any suggestions?  Dos, don'ts?

The "island" load.

This is where I have concerns.  Concerns around my understanding of some of the potential pit falls. 

One plan I have is to unplug a power extension "bus" in the office and connect it to the invertor.

The office has 2 mains buses.  24/7 and switched.  It is the switched bus I want to periodically run off the invertor.  The loads it runs include:

Umpteen DC bricks supplying 19V, 12V or 5V DC to appliances like PC Monitors, desktop speakers, a bunch of LED lights and the entirety of the electronics bench.

Obviously most of that stuff is floating.  The earth referenced stuff won't matter as the "island" phase will be referenced to the same earth.  None of the appliances have dual power.

The only concern would be the signal and DC power that goes between devices.  However, all of those signals and low voltage DC items will be floating and probably galvanically (save for a few Class Ys) isolated.

How much of a concern will those "class Y cap leakages" be for a dual phase system?  I assume this is a common thing on USA split phase 120/240V  systems, so it can't be that big an issue.  Maybe my unfounded concern would be that enough leakage current coming from the "island" phase leaks to the house earth and gets seen by the ground fault protector and causes potential (pun) "nuisance trips".  Thinking about this though.  The inverter circuit provides it's own perfectly adequate and low impedence neutral and earth path so, why would ground leakage current decide to go via some other applicance and onto the other circuit when it could just go via the sub ohm route via it's own power cord.

get a stock sinewave UPS, eg APC, these use 2..4x 12 V AGM or SLA battery in series for a 24 VDC inverter ( not invertor !) bus.

A 240 V UPS does exactly the desired function

Beware the duty cycle limit


Yeah.  My time with lead acids is over.  50% DoC?  300 cycles?  My 100Ah Marine lead acid which I decommissioned after running 365 days a year on a 50W panel and has charge my phone etc for about 3.5 years.  You would be lucky to get 3 amps out of it before it drops below 12V and not much more than 10Ah before it's below 11V

Even after I had it in service for 6 months, taking it off a solar panel controller fully charged... it struggled to start my 2 litre petrol car.  It's a honking great boat battery!

So.  Never lead acid again for cyclic purposes.

Likely you overcharged it. Lead acid doesn't like that but good lead acid chargers are rare. A traction battery (which is made for cycling) should last a long time if you don't let the charger apply too much voltage to it.


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