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I have a small 200w solar power system consisting of a Victron 500VA inverter (900w peak) with a 100ah AGM battery.

I just purchased a 5000BTU/4 amp window unit that draws a peak of 430w according to my meter. I thought it would be luxurious to be able to run it for an hour or two during the heat of the day when the battery is full and the panels have nothing better to do.

The AC runs fine from an extension cord plugged into mains, but the millisecond I switch to inverter power, the LCDI at the end of the cord trips...why is that?

Is it because my inverter isn't grounded?

Could I overcome this by removing the LCDI?

Is removing the LCDI a terrible idea? (it will be used just inside of an RV with some ducting+venting)

Is my inverter just not strong enough? Just noticed a max continuous output could be as low as 350w at very high temps...but it doesn't even seem to get a chance to invert before the circuit is broken.

Thanks!

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    A rough rule is often that the inverter needs to be 4 times the size of the starting load, but there are so many other factors... – Solar Mike Sep 6 '19 at 17:04
  • Wait, did you say that your inverter isn't grounded? Or are you just wondering if that is somehow the problem? Also, how are you transferring power from the mains to the inverter? Can you start the AC on inverter power? – Dotes Sep 6 '19 at 17:14
  • What is the voltage--120 V or 240 V? – Jim Stewart Sep 6 '19 at 17:21
  • Wait. You can switch it? Live in a millisecond? How is your switch wired? That sounds like the crux. Why are you starting it on mains? If you have mains, why not just use it? – Harper - Reinstate Monica Sep 6 '19 at 18:01
  • What model of inverter do you have? Victron has a good reputation in the off-grid and multimode world from what I gather, and some of their multimode gear is quite capable, but there's also potential for weird stuff to happen here. Also, where are you on this planet? – ThreePhaseEel Sep 7 '19 at 0:49
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The LDCI or air conditioner microcontroller may be checking for proper grounding. You should have exactly one neutral-ground bond. When on shore power, that bond is on the shore-side so the RV should have no bond. When on inverter, that must come from inverter, and be removed when on shore.

Other than that, I suspect the inverter is much too small for the cheap A/C's startup surge, which the Kill-a-Watt is dramatically under-reporting.

Keep in mind a residential grade air conditioner will be quickly destroyed by the vibration of a moving vehicle.

Hacking out the LDCI may not be practicable. We have seen reports of the LDCI communicating with the onboard controller on the A/C, to the effect that the controller will refuse to start if it is unable to detect the LDCI. Emulating this may be challenging.

Keep in mind also that lead-acid batteries are a "lie". Using anywhere near their full claimed amp-hour capacity damages the battery - common wisdom is to only go down to 70-80% SOC in daily use (i.e. Only use 20-30% of the battery's capacity). Consider your battery to have 20-30AH.

Lithium batteries are also a lie, but a much smaller one :) as 60-70% of the battery's range can be used daily without deterioration or fire. Only allowing you to use part of the range (and giving you more battery to compensate) is how companies like Tesla and Apple get impressive reliability from their batteries.

Your A/C unit will draw 35 amps or so unassisted by the solar panels. So not even 1 hour of runtime. Watch your draws and SoC carefully.

Preventing solar gain is a great deal more valuable than running A/C. White paint, insulation, whole nine yards.

The Kill-a-Watt is not accurately reporting startup current of the A/C. It is not fast enough, as the peak startup current comes and goes faster than Kill-a-Watt's sampling rate. Cheap A/C units use simple motors (i.e. Not VFD soft-start drives) and startup current will be "locked rotor amperage" which is typically 5-10x running amperage.

So I suspect the inverter is "browning out" and this is tripping the LDCI.

You can fix that with a much larger inverter (with correspondingly-larger idling and conversion losses) or an air conditioner with a VFD on the motor, with soft-start as the least of its features, which will be a more pricey model. This will do nothing to rectify the vibration problem.

Another option is to go 12/24V A/C packs, but you would probably have to build this out of components intended for marine application, at nosebleed marine prices, but the vibration issue still might getcha.

Lastly, you might try a Thermo King style pack as used for standby power and HVAC on semi's. They can often work multi-mode, off onboard gen, battery or utility. Search for a rebuildable one in a junkyard.

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  • The Thermo King type stuff would be ideal for this, yes -- likely 12VDC/24VDC capable, and available in units designed for RV/bus/... service (as well as the big semitrailer ones) – ThreePhaseEel Sep 7 '19 at 23:42
  • Confirming that Thermo King makes an all battery HVAC unit for delivery vans (the B100) – ThreePhaseEel Sep 11 '19 at 1:40
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Upon further investigation it's just too high of a startup surge. Somewhere around 1800w according to my meter (which doesn't always catch the brief surge).

I'm not the only one having overload problems running a 5000 BTU A/C off inverter power - most are having issues with 1000-2000w inverter generators.

There are some devices on the market for this that may or may not help me.

"Hard start" capacitor: ~$10 5-2-1 Relay "Compressor Savers" ~$30 Micro-Air Easystart Microcontroller soft start ~$300

The microcontroller soft start seems like the highest chance of working but it's over 4x my AC cost - Maybe next summer!

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