question

pizote avatar image

MultiPlus 12/2000 faulting on high load

Hello all, I have a MP 12/2000 which is faulting on A/C compressor starts. I have three DC inputs:

  • Two 170ah LiFePo batteries configured in parallel for 12v
  • 800w of solar through an MPPT controller
  • 165amp engine alternator

The issue happens when the A/C compressor turns on - during hot weather. The MP faults then comes back on. During cooler weather (80dF), the A/C compressor can turn on but you can hear the inverter struggling. I have installed a hard start capacitor on the A/C and have degreased the current draw by close to 45% - down to 34amps @ 120vac on start. Then it goes down and runs at 6-8amps.

To me it's obvious that I didn't take into account the starting amps on the compressor when I went with the 12/2000.

My question, is this: will the 12/3000 -really- be enough? Or will it struggle too at higher temps? At 104dF, the 12/3000 is rated at 2.2kw with surge being 4.4kw. The surge that I am getting on start is about 4kw. The idea is to run the A/C off the inverter using the engine alternator (I will be upgrading it to a 300amp one shortly) and it can be running for hours at a time.

TIA...

inverter current draw
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3 Answers
Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

I'd say the answer to this is "most likely".

We had a customer a couple of weeks ago with a similar setup (400Ah LiFePO4s, but otherwise very similar) whose Xantrex 3000VA inverter was faulting when his AC compressor started (also with a soft-start module installed). We bypassed his inverter and hooked his system up to our test bench MultiPlus 12/3000/120 and it did indeed run his setup with no problem, so I can definitely say that there's a very good chance that it will run yours.

I'd say a couple of uncertainties would be: the actual throughput of your lithiums (for example, Battle Born 100Ah drop-ins can put out an actual 100A, whereas the Victron 100Ah drop-in lithiums can only put out around 50A); whether or not your 360Ah of battery is quite enough to sustain that initial surge and then recover quickly enough to keep everything running smoothly; and, finally, your cabling... obviously you'll want to make certain that you've oversized all your cabling from the battery bank to the Multi to make sure that you're squeezing every last volt out of the system. When you're pushing a system like that, even if only for a few moments, a .75% voltage drop instead of a 1.3% voltage drop can be the difference between whether it works or not.

I'll also mention, just for the record, that a 300A alternator will certainly help you, but keep in mind that a 300A alternator is almost never putting out 300A... and indeed you don't want it to, because if you ran it at 300A all the time it would burn out within a day. I'd recommend looking into an alt-to-batt charger (Sterling has some great models like https://baymarinesupply.com/sterling-alternator-to-battery-charger-400-amp.html ) or a battery-to-battery charger (again, would recommend Sterling https://baymarinesupply.com/sterling-battery-to-battery-charger-12v-12v-120-amp-input.html )

...that's assuming you don't already have such a system in place to both protect your alternator from being overloaded as well as protect your lithiums from being over-charged.

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pizote avatar image
pizote answered ·

"most likely" ;)

Thank you Justin - I appreciate your response. I talked with Victron a few minutes ago and I got a qualified "it should work" as well.

Good info on the alternator and protection. I will look into solutions there. My understanding on the alternators is that they didn't run all the time anyway, that they kicked in when load was detected. But not all alternators are equal and better safe-then-sorry.

Thanks again...

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Tom avatar image
Tom answered ·

Before you purchase a 12/3000 Multiplus inverter you should first try to install a soft start compasitor on your fridge. Is this a RV fridge that may have a Danfoss compressor or a residential type fridge?

I use a Multiplus 24/3000 inverter and it runs my rooftop AC no problem even without a soft start.

Your battery cables may also need to be increased in size. What inverter and batteries are you using since you have not stated. As mentioned the batteries need to be capable of putting out the amps too.

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