MultiPlus-II as UPS only, LFP battery Ah requirements and placement

DIY
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I’m looking to install a MultiPlus-II 48/3000/35 (GX) + 2.5 kWh LFP battery at home in New Zealand for use purely as an unattended “UPS” for a critical mains-powered stormwater pump. Obviously I’ll get an electrician to wire it up to the mains but I’m going to do as much of the engineering myself as I can to avoid surprises.

There is no solar setup and I just have a simple domestic 230V 60 A 1-ph service. The pump is on a 20 A circuit and currently has a diesel generator + ATS inline as a backup. The problem with a generator solution however is the number of starts required during a heavy rain event can deplete the 12V starter battery.

Power failures during rain are rare, perhaps happening only once every 5-10 years but I have to cover the possibility to avoid property damage.

The in-tank pump draws 1.25 kW over the 1 minute it typically runs when triggered, that being when the tank has filled, every 3 mm of rainfall.

The start-up current is measured at 23A (@ 230VAC) for 250mS.

In terms of energy I need about 2 kWh to cover 200mm of rain with a depth of discharge of 70-80%. 200 mm would be a significant rain event but I may be able to retain the generator + ATS upstream of the MultiPlus and trigger that if needed.

Questions:

  1. I would like to use a 48VDC system (instead of 24V) but I see there is a Victron ‘recommendation’ for 100 Ah minimum battery size?
    I’d like to use a 52 Ah. Is there any technical basis behind that recommendation?

  2. The MultiPlus and battery need to be outside on my patio but will be under cover next to the generator. I anticipate installing both in a standard electrical enclosure (with vents added) but one large enough is hard to find when taking into account the recommended 100mm clearance around the MultiPlus. If I use two enclosures how do I run the battery wires between them without using a ‘closed conduit’ as the install manual says not to do?

Thanks for any comments or suggestions.

-Paul

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The AH rating is for lead acid bank to be able to meet the discharge amps needed.

You can use a smaller lithium bank if it meets the noinla disharge current the inverter need for a full load ability of the inverter.

Use a larger gauge wire if enclosed in a conduit. The cabling is the open air rating that is all. Some countries the regulation is to enclose them, so there is a work around.
You do need to protect your cables from mechanical damage which is also regulation.

3

Thanks for those clarifications.