Multiplus II 48/8000 off grid generator sizing

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scraggs asked Oct 18, '21

Multiplus II 48/8000 off grid generator sizing

Hi everyone
I am trying to spec a generator for my planned offgrid setup which includes a multiplus II 48/8000 linked to a 930amp wet cell battery bank, I believe the recommended minimum for the 48/8000 works out somewhere around 11kva but my question is would that 11kva allow for any passthrough when the charger is running at full power, my rough calculations (which could be wrong) tells me there is a little kw spare but not a huge amount and obviously there are loses along the way.
With trying to keep fuel usage to a minimum I am looking to try optimise the generator size to fuel usage to the throughput I need and keep the charger going at it's best.

battery charging Generator

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Answer 1 · 2021-10-19T01:20:34Z

shaneyake answered · Oct 19, 2021 at 01:20 AM

You can tell the Multiplus-II what the maximum power it can draw from the AC-INPUT.
You can then use an 11kva generator, configure the Multiplus to 11kva.
You then turn on a bunch of loads, let's say 5kva. The multiplus will then use the remaining 6kva to charge the batteries. If your load goes up or down the multiplus will increase or decrease the charging rate to keep the generator at below 11kva. I would not use a generator smaller than 8kva with 8kva inverter as the transition to and from generator could overload a smaller genny.

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Answer 2 · 2022-03-17T06:42:09Z

wolfbarnsolar answered · Mar 17, 2022 at 06:42 AM

I would Like to Know if this Gen is Larger enough to charge a 48V 970amp hour battery bank a multiplus 5000va soon to upgrade to a 8000Va

Rated 9.3kVA prime, 10kVA standby, 50Hz, Single Phase, 240V

https://generatorpower.com.au/generator-products/yanmar-himoinsa-hyw-13-m5-canopy-diesel-generator/

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JohnC ♦ commented · Mar 17, 2022 at 07:44 AM

Hi @wolfbarnsolar

A Multiplus II 8kVA has a rated charge capacity of 110Amps, so into a battery at (say) 55V that's about 6000W. Gensets usually have a 'happy spot', but that's probably a fair choice.

Bear in mind though that the Multi can also supply loads at the same time, so to cover them as well might push you to a larger unit. It's always possible to limit the genset input and/or charge rate though, so that's not a problem for most people.

Into 970Ah, 110A is probably a fair design point too. And you'd likely need to hardwire it in.

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Answer 3 · 2022-03-17T08:32:47Z

wolfbarnsolar answered · Mar 17, 2022 at 08:32 AM

Thanks John

So I could limit the charge rate when I upgrade to 8000Va to say 50 amps as is set currently in my 5000Va & it would just take longer to charge & run less Appliances at the same time.

Just trying to balance requirements with availability & running/purchase costs

Next gen size up is 17KVA Overkill but don't want to under power stalling the system either

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JohnC ♦ commented · Mar 17, 2022 at 09:46 AM

@wolfbarnsolar

I find the best way is to limit the total genset input to the Multi. (That setting is in AC Amps). Let's say you find the gen comfortable at 7kW, power quality good and not overstressing it. The loads get priority, so what's left goes to charge. No need to limit charge deliberately. And the genset runs smoooth at constant load. With low loads you can have max charge, with high loads you get less charge. Make sense?

Take care overspeccing a diesel unit. Diesels run better and last longer with a decent load on them.

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wolfbarnsolar JohnC ♦ commented · Mar 17, 2022 at 10:18 PM

Makes a Lot of Sense

Thanks I appreciate the advice

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