Inverter drops immediately.

Welcome to the forum Chris,

Li Ion batteries have great surge/load current support with little voltage drop... And you can run at C/1 discharge rate (1 hour to discharge) where Flooded Cell Lead Acid batteries are "happier" at C/8 or possibly down to C/5 discharge rate.

A common first time inverter fault is trying to get the inverter powered up with automotive jumper cables... The cables and alligator clamps just do not carry the "high current" needed by the AC inverter--And frequently cannot reliably start even smaller AC inverters.

It sounds like none of this is your issue.

Question... You put a "new 150 Amp Fuse" in the holder, and try to start the inverter? And it blows the fuse?

If yes, then two possibilities (other than a bad inverter) that you should check.

First, make sure that the + and - Leads from battery bank to AC inverter's DC inputs are the correct polarity... A frequent method for the inverter to protect against reverse polarity is for the inverter to draw huge current (through a protection diode) and blow the input fuses/breakers.

A second possible issue... Is a mismatch between DC inverter bus voltage (say 24 or 48 VDC battery bus) and the inverter's input voltage of 12 VDC...

If you had 2x 12 volt batteries batteries wired in series for 24 VDC and a 12 VDC input AC inverter--That (and other wrong wiring) too could cause unhappiness with the inverter.

I am guessing you are looking at both a 12 VDC battery bus and a 12 VDC inverter.

Is that really a 150 Amp rated fuse? (I am sure it is--Just asking all the questions).

Longer term, you may want to look at a 150 Amp, or larger, Circuit Breaker to replace the fuse and fuse holder. Circuit Breakers are not that much more costly than a quality fuse and fuse holder, and they give you a handy On/Off Switch for servicing the system and turning off the AC inverter between trips (save draining batteries when parked during winter, etc.).

You may wish to visit what you expect from a 200 AH @ 12 volt Li Ion battery bank (current wise, and Amp*Hours for how long can run your loads on battery bank power), and what your actual AC loads are...

3,000 Watt (and 6,000 Watt surge?) AC inverters are not small--And draw a lot of current on a 12 volt battery bank. Typical math:

• 3,000 Watt AC load * 1/0.85 AC inverter eff * 1/10.5 battery cutoff voltage (for 12 volt bank+inverter) = 336 Amps max (and 2x that for 6,000 Watt surge)
• 150 Amp fuse * 0.85 inverter eff * 10.5 volt battery cutoff = 1,338.75 Watt AC load max for your system (and 2x that for a few seconds of surge current to start a motor, etc.)

For that size of AC inverter--Really need to look at 24 or even 48 VDC battery bus long term... It makes for much easier, and less expensive, cabling for your DC power system:

• 3,000 Watt AC load * 1/0.85 AC inverter eff * 1/21.0 battery cutoff voltage (for 24 volt bank+inverter) = 168 Amp max continuous current
• 3,000 Watt AC load * 1/0.85 AC inverter eff * 1/42.0 battery cutoff voltage (for 48 volt bank+inverter) = 84 Amp max continuous current
  

You may think you need to stay with 12 VDC because your RV is 12 volts (engine battery, a few lights, a fan, etc.)...

But 24 VDC is not a bad compromise for 24 VDC... You can get 12/24 VDC LED Lights, and 24 VDC to 12 VDC down converters if needed to run "native" 12 volt stuff...

If you are planning on running mostly AC power (also not bad for many electronics that have rechargeable batteries, LED TV/Monitor, laptop computer, etc.), 120 VAC for most loads can work well too... The "down side" of "large AC inverters" is they can take a fair amount of power just turned on (Tare Losses)--Something like 6 Watts for small inverters, 10-20-40+ Watts for some larger inverters.

If you decide that your present 3kWatt inverter is "bad"--Then instead of just replacing with another 12 volt inverter, you may want to explore these other options.

Take care,
-Bill