question

larsthebear avatar image

Looking for an inverter that can be used in a permanent off-grid installation

Hi. I'm looking for a 12V inverter with modest (~500W) power output that can be used to power an off-grid cabin with an existing electrical installation. The installation has a distribution board powered by a generator; the earth-neutral bond is made at the board, and connected to a set of earth stakes. I want to replace the generator with a battery-powered inverter (or provide a way to choose between them using a transfer switch).

So I need an inverter that can operate with earth and neutral bonded, and which will not impress AC voltages on the battery side when operating. I understand that many modern, transformerless inverters have no galvanic isolation between the AC and DC sides, so grounding the neutral connection will cause AC voltages to appear on the battery wiring -- if it doesn't actually blow up the inverter.

The 'Phoenix' inverters seem to be suitable for my application, because the documentation states that there is complete isolation between the DC and AC circuits. But I thought I'd better check.

Thanks

Lars


Grounding
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2 Answers
Pat Davitt avatar image
Pat Davitt answered ·

Lars,

John is correct the Multiplus 800 sounds perfect for your needs. And, you are correct that there should only be one neutral/ground bond active at any time. To answer your question about "reworking" the Neutral/Ground bond:

The Multiplus assumes that any AC source (Generator/Shore Power) will provide a Neutral/Ground bond. When an AC source is not present (Inverter Mode), the Multiplus provides a neutral/ground bond through means of an automatic transfer switch. So what you need to do is:

1. Remove the bond from your distribution board.

2. Install a bond at your generator.

3. Wire the Multiplus exactly as described in the Operating/Installation Manual which can be found here:

https://www.victronenergy.com/upload/documents/Manual-MultiPlus--500VA-1200VA-EN-NL-FR-DE-ES-IT.pdf

Hope this helps,

Pat

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JohnC avatar image
JohnC answered ·

Lars, Victron made the 800VA Multiplus just for you. Internal MEN switching to/from the genny, 16A ac transfer switch, seamless transfer of power from the genny.

It's an inverter/charger, so will absolutely minimize genny run time. Note all the genny's power will 'passthrough' the Multi, and your existing N-E link will need 'reworking'.

The beauty? All seamless. Just start/stop the genny when you need. No light flickers, no switches, nothing else to do..

https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-inverter-charger--800VA-5kVA-EN.pdf

4 comments
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Hi JohnC. Thanks. Are you able to explain in detail what "reworking" means here? I think the existing N-E link would have to be moved upstream to the generator, so the inverter could connect its own link when the generator is offline (?) Are there any detailed wiring schematics? The manuals seem to be pretty vague about the whole subject of grounding.

Lars.

Ha, I was really hoping you wouldn't ask me that. Yeh, the 'reworking' would likely just mean removing your existing switchboard MEN link, and earthing the Multi frame to your existing ground stakes.

Then, does your genny have internal MEN, or does it not? Should you earth it too?

Maybe sometimes you might want to run a separate circuit off the genny?

I'm really unqualified, so I *won't* comment for that reason alone. Complex subject, especially with marine/mobile applications on shore power.

Look hard at that Multi though.. the rest will follow with your inherent awareness & attention. :)



Thanks. You modestly say you're "not qualified" but I wonder if anybody is? I suspect that the techologies in play here are so new that nobody really has a firm idea what best practices are. Issues of earthing and isolation seem to be the elephant in the sitting room of the marine/off-grid power world -- these issues are at the back of everybody's minds, but nobody seems to want to talk about them ;)

Yeh, I hear ya Lars. It's not new stuff at the level we're talking, perhaps more that this is a global forum and local regulations in countries differ. I'm perhaps carrying some baggage from an Australian forum which forbids ac wiring discussion if just a sniff of diy is detected.

And I've come across young fresh sparkies who've been taught that MEN switching is taboo. So I just stay out of it.. just me, nothing sinister. Even though my own system switches MEN.. :)

Earthing is related, but really a little different. It's just hard to tie it all down to a 'one size fits all' thing.