Inverter sizing base on available current.

[Inq720]

I'm putting together my first system and would like to ask a basic Inverter question. I'm going to use the Overkill Solar 12V/120a BMS. It should be able to drive a 1500W inverter. Would there be any advantage to getting a 2000W or 3000W inverter? I know the BMS will trigger long before hitting those numbers... but I'm wondering are there any efficiencies or longevity advantages by driving the more capable inverter at a small fraction of its rating?

Thanks.

 

[Samsonite801]

There could be factors to consider like idle draw watts, and how much watts you need max... Larger inverter may be more capable to provide with surge to run motors and things like that, but too big 'for your needs' really depends on what matters to you.

My RV has a 2800w 12v Magnum inverter (which it came with), and I am going to install 2x 4s 12v LiFePO4 banks with 2x OverKill 120a BMS, but it does have a remote panel on it in the kitchen so I can turn it off easy when not using it so it doesn't idle draw all the time. I don't even know the idle draw rating on mine (since it's off when I don't use it), but I just thought I'd mention it as a factor, that larger may mean more idle draw.

What you mentioned about higher rating under lower duty cycle, means it will run cooler and may last longer, as it isn't getting hammered as hard as one running near peak continuous rating all the time.

 

[linkcat]

I'm putting together my first system and would like to ask a basic Inverter question. I'm going to use the Overkill Solar 12V/120a BMS. It should be able to drive a 1500W inverter. Would there be any advantage to getting a 2000W or 3000W inverter? I know the BMS will trigger long before hitting those numbers... but I'm wondering are there any efficiencies or longevity advantages by driving the more capable inverter at a small fraction of its rating?

Thanks.

I'm in the same position as you. I have 8 280ah cells (2s2p, 12v, 560ah) and the same BMS. Will wait here to other responses.

 

[snoobler]

10 year old solar needs battery bank upgrade

I have (2) magnum ms4448pae with an outback flex 80 with 18 panel solar array im needing to upgrade my battery bank (currently 2 banks of 8 - full river agm dc400-6) i dont have issue with building out batteries from raw cell but i wonder if the warranty exchange is worth the cost comparison...

diysolarforum.com

100% duty cycle at rated.

12*120 = 1440W sustained
24*100 = 2400W sustained

Manual indicates a programmable time delay between over-current and cut-off, presumably for surges.

@Samsonite801 gave good reasons, but to break it down simply, if a quality 1500W inverter meets your needs, there is no benefit to a 2000-3000W inverter. In fact, there will likely be an increased idle draw using more of your battery capacity just by being on and ready to supply AC power.

 

[Inq720]

Since I'm going to be very watchful of said system while in the boat, I'll use the remote switch and won't really have any idle time. Fridge, all marine electronics and lighting will be 12VDC... only use the inverter for temporary "luxury" items... blender, maybe inverter microwave... etc.

After the OP, I read through the 1500 GoWISE inverter reviews. Some review mentioned it stopped output lower than the 1500W even though the BMS was still delivering. In my noob, logical way, I was thinking the 2000W unit will give me a little more chance of the BMS being the "quitter" and thus getting closer to the 120 amps x 14.65 V = 1758 watts.

Not that I know I need that, but the Inverter Microwave is a big unknown for me also.
Note: I haven't purchased the inverter. I will once my group-buy LiFePO4 cells with Michael show up. Inverter is just two days away with Amazon.

 

[snoobler]

In that case, for convenience, many inverters have a power save mode that substantially cuts their idle current. They basically check for a load periodically and only fire up if something wants power. As I get older, I find myself less reliable as a system safeguard.

120A is a current limit, not a power limit, so it's likely voltage sag that's cutting off the inverter. 10.5V * 120A = 1260W - not the inverter's fault here. LFP shouldn't sag as much as FLA/AGM at 120A, so it should be less of a problem.

 

[Inq720]

Maybe, there'll be an after Christmas sale to make the decision for me.

 

[Fallingaway]

Anyone use portable a/c? I don’t have the instrument to measure it’s max startup current draw but the ac is rated at 890w 115v. My 1k inverter won’t handle it. Wandering if anyone uses a 2k watt or if I should just go with 3k inverter.

 

[baipin]

Anyone use portable a/c? I don’t have the instrument to measure it’s max startup current draw but the ac is rated at 890w 115v. My 1k inverter won’t handle it. Wandering if anyone uses a 2k watt or if I should just go with 3k inverter.

Do you have startup surge specs for the AC?

 

[snoobler]

Surge specs are typically 4-10X run.

 

[baipin]

What if he used some sort of soft starter? Do those really work?

 

[Fallingaway]

No I don’t and 4-10x is a huge variation. I know some of the clamp style meters can measure this current but I don’t have access to one or really want to buy it just for this. Is anyone powering their RV a/c with an inverter? It would atleast give me an idea

 

[baipin]

I have heard of mini-splits run on a 2000W. I imagine it might help to start those on a lower power setting, since they draw as low as 300W on lowest?

 

[chrisski]

I'd try contacting manufacturer tech support to find the inverter needed. Most have been real helpful within a few days when I've E-Mailed them. Quicker if there's a number listed.

You may get lucky and find someone here who has a portable AC, but I bet model makes a big difference.

If there is a soft start for the AC, that can cut that surge by a lot.

Part of that surge rating is quicker than a typical clamp meter could measure. When measuring my biggest draw, my 8 amp propane heater fan blower, I see that start up surge in my amp readings at 10 amps before it quickly settles to 8 amps on my Victron BMS-712 battery monitor, but by the time it takes its first reading, it's settled somewhat. To measure the initial surge is supposed to take some expensive equipment.

 

[Fallingaway]

I may try to contact them. Weird that never crossed my mind either. The soft starts I saw for a/c’s were 300$+. I’d rather put that toward a bigger inverter

 

[chrisski]

When you get an answer, just remember all inveters are not equal. Some entertaining videos of some catching on fire below rated watts. UL458 certification on an inverter means it’s good.

 

[snoobler]

I know for sure a 2000W/4000W surge high frequency PSW inverter will NOT run an RV A/C. My 5kW Victron will run it, the water heater and the microwave.

 

[Fallingaway]

Ya I was thinking I’m going to need atleast a 3000w and I’ve seen others complain about cheaper inverters not able to hit their advertised output before tripping. Speaking of that is there no agency that can punish Chinese manufacturers when they false label products!? They are still manufacturing and selling those 9600mah ultrafire 18650 on eBay among tons of other crap.

 

[snoobler]

I assume you have a metric crapton of batteries to run this A/C unit?

A 2-3kW low frequency inverter with a legit 2-3X surge for 20+ seconds will work like this one:

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It's a Sigineer, which is essentially an AIMS as Sigineer makes AIMS. The only downside to these is they have a higher idle draw and a lower efficiency. It will give a look of disdain at the A/C unit and say "dat all you got!!??" as it fires it up.

Anybody falling for Ultrafire at this point almost deserves it. The Chinese do what they want because we will continue supporting their economy, though we appear to draw the line at toxic baby formula and dog food.