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benkay asked

Multiplus tripping Isolation Transformer if Lithium Batteries Turned Off

Hi everyone,

I'm looking for some help with our marine system.

We have a galvanic isolation transformer (not Victron) on our shore-power feed. This then goes into a MultiPlus 48V 5KVA unit, which charges a Torqueedo lithium battery bank (48V consisting of 4 x 24V batteries in series, and paralleled) via a 48V bus-bar, which also feeds an Orion 48-24V DC-DC converter which keeps our 24V house bank topped up.

If the Torqueedo 48V bank is "ON" via its BMS, then we have no issues at all. Should shore-power be temporarily interrupted, the MultiPlus nicely turns back on, and resumes what it was doing.

However, if we leave the boat for an extended time, the advice is to turn OFF our 48V Lithium bank via its BMS, keeping them completely isolated, and just allowing the output of the MultiPlus to feed the bus-bar, and therefore the DC-DC converter keeps charge in our 24V house bank.

In this state, should shore power be temporarily interrupted, the MultiPlus does not start up nicely again. Instead we see the blue light on the digital multi control flash for a short while, then instead of the relay clunk, our galvanic isolation transformer trips out.

The only reliable way we've found to correct this situation, is to turn ON the lithium batteries via the BMS, then go and re-set the galvanic isolation transformer. After this, the MultiPlus will turn on properly and resume operation, then we can turn the Torqueedo batteries back OFF again without a problem.

The danger here is if that if we're away from the boat when shore-power fails temporarily, there is no longer any 48V supply to the main bus-bar, and therefore no maintenance charge to our house bank from the DC-DC converter, and those batteries could easily be killed by running completely flat.

Any clues as to why this might be happening, and how it could be corrected?

MultiPlus Quattro Inverter ChargerIsolation Tranformer
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1 Answer
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

That is normal, the Multi is not designed to run without a battery.
With no battery connected he tries to charge his capacitors from shore power (you transformer) and causes a very high inrush current.

I would recommend turn off the Multi too and use a normal battery charger connected to the AC input side of the Multi to maintain the house batteries if you on shore power.

(maybe use a small relay at the AC input side of the Multi to switch off the Orion in case you are at shore and Multi + Torqueedo is switched on)

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