Does anyone know how much power the Mulitplus-II consumes when running off batteries with a 25-watt load? In the spec sheet I see the zero-load power consumption numbers (eg 11w for the 48/3000/35-50) and the maximum efficiency number (eg 95%), but I can’t find any information on the efficiency curve vs power.
The reason for the question is that I’m designing a battery backup system for a load that is usually 25-watts, but rises up to around 1500w at times, and so am looking for a system with good efficiency at low loads.
-J
Have a read of this document. At 25W it suggests you will draw the idle current plus 25W, so 36W so about 67% efficient.
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Thanks! I didn’t know there were additional reference documents. Oh, I just saw it at: Victron - Downloads
The graphs in it explain a lot.
For the Multiplus-II 3000VA, it looks like, up until a load of about 400w, the heat loss is mostly just the background no-load draw of 11w.
Heat dissipation increases up to 461w at 3000w load. 461w is a fair amount of heat.
The best efficiency is in the roughly 250w - 1000w range. Which is another reason to overspec your inverter I suppose.
EDIT: I just noticed that doc is talking about power in watts, but their explanation talks about I^2R loss in wires, which makes it sound like at least some of the heat loss depends on apparent power (VA) rather than real power.
Josh