How a Simple Contactor Can Improve Your Battery Backup

Modest hybrid inverters are sometimes oversold by salespeople or romanticised by customers. Their ability to back up your house in a blackout can be limited by capacity and wiring constraints.

If you have awkward house wiring and an older, smaller, cheaper hybrid, we may have an answer to get you backup throughout the house.

So You Bought A Battery System

Sungrow, GoodWe, Solax, Redback, Alpha, SoFar and many others offer what we call a series-connected lightweight hybrid inverter.

Properly installed they’ll offer free solar energy, lower bills and modest blackout protection for a modest price, though not all hybrids offer this without an optional “backup box” and extra wiring.

The key detail to remember is series means the essential circuits are connected to a dedicated port on the inverter.

The backup power runs through the inverter.

Usually one power circuit to run the fridge, internet and phone charger is all that they will cope with, plus your lights.

Where complaints arise, it’s because a small hybrid will only offer around 15 or 27 amps backup capacity (3 to 6kW at a surge).

You can’t run more than 27 amps through the inverter, so it’s a choke point even if the grid is available. A responsible electrician simply won’t hook up too many circuits.

Other makers offer parallel connected hybrids, which use a gateway or contactor to disconnect the grid at the main switchboard. So if you buy Fronius, SolarEdge, Sigen or Tesla, the information in this article doesn’t apply.

Introducing The Bypass Contactor

In your kitchen, the fridge is likely to be sharing a circuit with the kettle, toaster and microwave, but any two of these would overload a small hybrid.

The answer is to bypass the inverter while the grid is available and automatically connect the circuits you want if there’s an outage. For this we use an electrically operated switch, a relay or a contactor in electrical jargon.

Who Needs A Heart Bypass

Solar Quotes always insist that if you install a series hybrid, it must have a manual bypass switch. 

If the inverter has a heart attack, anyone can switch the fridge and lights back onto mains power.

In fact, if you buy a Sungrow they’re now a standard inclusion.

How Does A Contactor Help?

Firstly it can be installed instead of the bypass switch, simplifying things for the technologically challenged.

For those with sprawling 3-phase houses or homes supplied from a subcircuit downstream from the shed, running a separate backup circuit can be impractical or cost prohibitive. Using a contactor can physically connect more things to the backup circuit.

There is an obvious risk you will overload the inverter, causing it to trip off temporarily (or just give up and require a manual reset) but having some basic level of power available means maybe the electric roller door will work, the freezer will stay frozen and if you manage it carefully the lights will stay on too.

Document What You Want Backed Up

For most people, a lightweight grid hybrid system is a perfectly good way to offer some protection from mains outages, but they’re not as good as the grid.

However as an electrician I’ve had a few awkward conversations with people who’ve bought the hype so to speak, only to be disappointed with the reality of a cheap battery system. Early models were all relatively small but that didn’t stop salespeople and customers alike imagining big things for them.

I was once browbeaten by customers who insisted they have lights, fridge, freezer, plus CPAP breathing equipment in the bedroom, all backed up. It ended up with nearly half the house on a weedy little 3kW inverter.

While it coped when the grid was good, frankly it was a recipe for disaster during an outage. All I could do was warn the end users that if they were very careful it might work in a blackout.

Though the kettle was out of bounds, the lights and CPAP machine wouldn’t be on at the same time, and hopefully the fridge and freezer took turns.

New Models Are More Capable

These days there are a variety 8 and 10kW single phase machines that are pretty gutsy contenders. They’re marketed for and genuinely capable of “whole home” blackout protection with only a few exceptions.

There are also 3 phase hybrids available but to single out Sungrow as an example, the 10kW 3ph units are very limited compared to the newer 15/20/25kW models.

Back Up 3 Phases With One

It’s not unusual to have a large 3 phase solar power system and a single phase battery hybrid. For some premises it’s difficult to segregate the circuits you want backed up, however a good electrician can use a combination of contactors to both isolate 3 phase appliances and bridge the remaining single phase circuits together to the backup supply.

Solar Edge offers this option straight out of the box; however, any reasonable electrician can arrange it with off-the-shelf components.

A Prime Recommendation
If you want a truly resilient power supply, that needs no internet and lets you treat the grid with contempt, this article isn’t it. We’ll soon have an update of what a durable, heavy duty system looks like.

Electricians Make Magic, Not Miracles

If you consider a 400 watt fridge motor might pull 3000 watts at the instant it starts, a small hybrid may have no spare capacity to run your lights. While this contactor arrangement won’t improve the backup capacity of your inverter, it might make better use of your system without having to rewire the house or dig up the garden to run cables.

If you need some work done on your switchboard, click here and enter a few details. There’s room at the end to add some notes, request a site visit and get some quotes.

And don’t forget your hot water, it’s the cheapest battery you buy.

Original Source: https://www.solarquotes.com.au/blog/backup-whole-house-contactor/