External transfer switch requirement for Multiplus2

Q&A and troubleshooting
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1

I have an issue with the
MultiPlus-II External Transfer Switch application document.
In section 3 Installation it states that the ac input wires to the multiplus 2 inverter chargers are only used for voltage measurement, so only need to connect the master unit of each phase with thin 1.5mm wire and leave the slave units disconnected.

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Surely it needs conductor of sufficient size to supply the energy for battery charging??
And if you don’t connect the slave units then their battery chargers won’t contribute to the overall battery charging effort!!

I am currently setting up a 20kVA system with lithium batteries. I was going to use 2 x 10kVA Multiplus 2 units, until I read this!

Now I’ve decided to use 2 x 10kVA Quattro units instead as they use their internal transfer relays.

2

With the external transfer switch firmware the internal relays are never closed → no current can follow there only the input electronic can measure the voltage.

The power from or into the MultiPlus is only flowing on the output.

2 Likes
3

Ok, thankyou, I think that makes sense to me now. The power for battery charging flows “into” the output terminals of the multplus units, just like it does when there is excess pv generated power from a grid tied inverter attached to the output used in an off-grid situation.