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duswami avatar image
duswami asked

Breaker & Fuse sizing Multiplus II 48/3000 35

A bit new to this so apologies in advance.

Equipment:

MultiPlus II 48/3000 35 120v

SSCC MPPT 150/45

Lynx Dist

SmartShunt

4 x 12v 200ah lead acid bats (48v)

Solar array output 1480w 96v 20amp

So I thought I had fusing with the lynx distributor and breaker sizing for the Multiplus all figured out, but doubting myself again.

First, fuse sizing the battery, charge controller and inverter at the lynx distributor.... I figured if the inverter with power assist runs at the full 3000w off my 48v batteries it draws approx 62 Amps. So, I'm thinking 60+ amp fuse is correct for the battery, CC and inverter??? The inverter manual states that the max charging current is 35 Amps. Consequently, on the AC side, I have a 60amp breaker for both the AC IN and AC OUT in the service panel. But after reading endless posts I'm doubting myself. Anyone see anything off here?

Multiplus-IIMPPT ControllersSmartShuntBattery Protectfuses
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2 Answers
seb71 avatar image
seb71 answered ·

You size the fuses and MCBs to protect the wires (they should blow/trip before the wires get dangerously hot). And you size the wires to be able to safely carry the expected current on that wire.


So for example, if a wire can safelly carry let's say 75A, then it's fine to use a 60A fuse/MCB on that wire.

But the same 60A fuse/MCB is not OK if you use a thinner wire, which melts at 30A.

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duswami avatar image duswami commented ·

I understand that. I'm using 6/2 wire on AC connections to the service panel. Amp rating is borderline though, 55a. 60a breaker prob to big? My reasoning is prob wrong here, but the unit can't pull or push 60a either so I'd be safe, or not?

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seb71 avatar image seb71 duswami commented ·
Since for AC you are using the biggest wires that fit into those terminals (AWG 6 / 13mm2), I think you can go with the AC MCB sizes (or lower) indicated in the Multiplus manual.


Make sure the DC wires are properly protected (by fuses of correct size), too.


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duswami avatar image duswami commented ·
Thank you
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Alexandra avatar image
Alexandra answered ·

@Duswami

The battery cable DC fusing has size for the Multiplus 2 recommendation in the manual.

The fusing for the mppt also has a manual recommended size.

So you can check your answers there. ;)

For PV string fusing, the panel manufacturers often have a recommendation on their datasheets.

And for AC in it is watts ÷ volts = amps. But the breaker has a trip curve so will not trip exactly on its rating. 3000w ÷ 120v = 25A for the output. The input is often the max transfer rating of the inverter especially if you are planning ESS to be installed for feedback. Unless you are being limited in other ways, like limited shore connect for mobile application.

It is also best to check you local regulations as well though.

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duswami avatar image duswami commented ·
So 125a for battery and 60 amp for CC. I assume then that's 125a also for the inverter, correct?


Care to chime in on the AC breakers? :-D

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Alexandra avatar image Alexandra ♦ duswami commented ·
@Duswami

Your max transfer for the model is 50A. So you can go as high as that on input.

Output is more likely around 25A. (Watts ÷ Volts = amps) Unless you plan on having the full transfer ability used for loads?

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duswami avatar image duswami Alexandra ♦ commented ·

So, not 60a breaker, 50a? It won't nuisance trip?

Yes, shooting for the full transfer ability, so 30A would be undersized no?


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Alexandra avatar image Alexandra ♦ duswami commented ·
@Duswami

Hard one to answer @Seb71 has put it correctly. It depends on your wiring now.

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