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d3v0311 asked

MultiPlus-II 12V 3kVA 2x120V recommended battery capacity

Putting together a system for my RV, looking at getting the MultiPlus-II 12V 2x120V. I Noticed in the manual it says recommended battery capacity to be 400ah to 1200ah. I understand that battery capacity will affect actual usable time when inverter is being used with things like TV, microwave, etc. Will having less than the recommend capacity affect anything or damage anything? Am im missing something? I just don't see why having 100ah or 200ah vs 400ah would affect anything other than usability time when using the inverter.

Multiplus-II
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klim8skeptic answered ·

I just don't see why having 100ah or 200ah vs 400ah would affect anything other than usability time when using the inverter.

It is related to how much current the inverter will draw from the battery to power a load.

The 3000Va inverter will draw 300a @ 12v to power a 3000Va load.

The 3000Va inverter is also rated to deliver 5500w for a few seconds (to start things like AC's) so will have a battery current draw approaching 600a.


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d3v0311 avatar image d3v0311 commented ·

Sorry for the confusion, im pretty new to this and still learning. So the inverter will draw 300amps normally?! or is that running 15 different things and the inverter being used to the max.


Lets take the air conditioner out of the equation, I understand those have massive draws. I will eventually upgrade to more batteries and probably solar. I am ok with not being able to run an air conditioner for the time being. I have on board generator if I need to run air conditioner. I want to start by being able to simply watch TV, and run a 110 fan overnight. wake up and run generator to recharge batteries. I just dont want to buy a smaller inverter, and then upgrade down the road. id rather just buy what ill need down the road now

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klim8skeptic avatar image klim8skeptic ♦ d3v0311 commented ·

So the inverter will draw 300amps normally?! or is that running 15 different things and the inverter being used to the max.

That is current at max output. Smaller loads = smaller dc input current.

I want to start by being able to simply watch TV, and run a 110 fan overnight.

No fridge? Laptop? Phone chargers? Other stuff?

A small TV (40w) and a box fan (40w) will draw about 8a per hour, and the inverter about 1.2a per hour. YMMV.

wake up and run generator to recharge batteries

Typically a 100Ah Lead Acid battery will have a 20a charge limit. Link~15 Charging above 20a results in accelerated battery aging/damage.

Lead batteries require complete charging regularly (a couple of times a week?). Charging lead batteries takes f o r e v e r . Running a generator to charge a battery at 20a (probably 300w gen input) co$t$ fuel. Charging a half discharged 100Ah lead battery will probably take 6 hours at 20a.

A larger lead battery bank makes more sense by utilizing more of the generators output.

Lithium batteries (100Ah drop ins) typically have a 50a charge/discharge limit (better ones even higher). Charging a half discharged lithium 100Ah battery at 50a can be done in 1 hour. Lithium batteries only need full charging a couple of times a month, and partial charging/discharging is not harmful.


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d3v0311 avatar image d3v0311 klim8skeptic ♦ commented ·
Fridge is dual and I would run off propane, laptop doesn't need to come along, Phones can charge from a separate portable battery bank i have that i use when we go to the beach, (one of those small portable ones) I don't plan on boondocking seriously until my system is more well equipped. We go to a motocross race every year in Pennsylvania that i always get a hotel and we drive over real early. would like to camp there for a night or two instead of pay for hotel. I understand my limits on actually being able to run things with a less than adequate capacity of batteries. My main focus is to make sure that by starting with only 100-200ah lithium batteries that i will not harm anything. with buying the inverter at $1500, then even the 100-200ah battery cost plus the other things i need just to get it hooked up. I want to be able to at least hook up the inverter to the system. but if i need to buy in pieces over time and hook it up all at once then i will. Just dont like the idea of buying myself stuff and watching it sit until i get the entire system...i get impatient lol. but if thats what needs to be done to not harm the inverter then i will. Even if i installed the inverter / charger and never even boondocked until i had 400ah+ batteries and just used the pass through and charger only feature that would be fine. just want to get it installed and all the wires and fuses and what not installed.
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