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larsthebear avatar image
larsthebear asked

Multiplus or Phoenix inverters -- what AC voltage appears on the DC terminals (if any)?

I'm surprised that manufacturers don't state these figures (so far as I can tell) since they are of substantial importance for electrical safety.

If I run a Phoenix or Multiplus inverter with the AC neutral and earth bonded, what AC voltage, relative to earth, appears on the DC battery terminals?

I would hope that the answer would be "none at all", and that I could safely earth one of the DC battery terminals if I needed to. However, I've experimented with a couple of inexpensive (not Victron) inverters, and they both energize the DC terminals with AC to some extent. They couple only be run with floating, not earthed, batteries.

The reason this is relevant to me is that I have a significant 12V installation for lighting, etc., that will run from the same batteries as the inverter. This is all wired to comply with standards that apply to extra-low voltage installations. If using an inverter impresses an AC voltage on the DC side of more that 25V RMS relative to earth, then it would all have to be rewired.

Thanks.

Lars.


MultiPlus Quattro Inverter ChargerPhoenix Invertersafetymen
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2 Answers
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wkirby answered ·

The MultiPlus step up transformer is a low frequency transformer type. The primary and secondary windings are separate. This makes the DC and AC sides galvanically isolated. If correctly wired you should have no AC content in the DC side.

Poor DC wiring will cause ripple on the DC side which may look like AC depending upon the AC load. However if this gets above a couple of hundred millivolts (I can't remember the exact figure) then the MultiPlus will present an error.

It makes me wonder just how badly those cheap inverters need to be designed in order to get 25VAC to appear on the DC side!

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larsthebear answered ·

Thank you -- this is exactly the answer I was hoping for. Do you (or anybody) happen to know whether the same applies to the Phoenix range?

I have in my trash can a cheap inverter that sets 120V RMS AC on its DC battery terminals if either of its AC terminals is ground-bonded. That's not just a leakage ripple -- it's an honest-to-goodness supply voltage. I suspect most inverters aren't that bad, but 25V RMS is the limit in my jurisdiction, and I don't think it's all that unusual to see that kind of voltage on an inverter's input terminals.

Lars.

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wkirby avatar image wkirby ♦♦ commented ·

The Phoenix inverters use the same topology. The larger ones (1200VA and up) have the Neural Earth bonded inside with a hard link (which is removable if required). The smaller ones (180VA - 1200VA and the VE.Direct ones) need to be bonded externally if required.
The MultiPlus range have a relay which creates the bond when the upstream supply (AC-IN) goes away. The relay's default action is to create the bond when the mains / generator supply is missing, but it can be programmed to remain open if your bond is somewhere else.

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larsthebear avatar image larsthebear wkirby ♦♦ commented ·

Thanks. That's exactly the information I needed.

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