3000 Watt Inverter Ground Fault

ordonez1221

Hello all,

I am looking for guidance troubleshooting AC installation issues that I am experiencing with a 12K BTU Mini Split AC in my build. Upon completing the installation of the outdoor unit on my first test run, the AC fan turned on momentarily then the inverter shut off with a Ground Fault light coming on. Immediately I thought it was a grounding issue so I researched how to test ground faults but I was not able to find any grounding problems in my system. I also looked for damaged wires to make sure there weren't any breaks and all the wires turned up clean. I checked the terminals on the AC for continuity and all good on that end as well. The breaker inside my distribution panel never tripped during my test run but just in case, I replaced the 20/20 amp tandem breaker to a standard single 20 amp breaker. I tried testing the AC again after each troubleshooting step but the inverter still shut off just after a couple of minutes with the same ground fault light on the inverter. The compressor in the outdoor unit of the mini split never gets to turn on, only the fan, I am thinking maybe the AC unit is too big for my battery bank but through my research I thought I had enough juice to power it. I also tried turning off all other breakers to make sure there wasn't any power going other appliances and tested again but same problem persists. I looked at my battery monitor with each test, and there wasnt a huge draw on the batteries when I tried turning on the AC. I'm assuming because the compressor doesn't even turn on, I wouldn't be able to see the real draw on the batteries. I have run a wall AC unit on this same system before without any issues, that unit was 9,000 BTU.

Here goes my disclaimer, I most definitely am not an expert in solar or any electrical for that matter. I was able to put together my battery bank and solar panels through research through and asking advice and recommendations from experts. Also, I will be adding shore power but I am holding off on getting the equipment until a later time. I am including a diagram of my set up with as much detail as I can put together to give a clear picture and below I have listed the main components with the wiring and fuse info in case it helps clarify further....

Solar Array
8 - 100W Renogy Compact Solar panels in parrallel/series connection (800 Watts of Solar)
Wire - 10AWG
Fuse - 50A
Shut off Switch

Solar Charge Controller
150v/85A MPPT Victron Charge Controller
Wire - 4AWG
Fuse - 100A

Battery Bank
8 - 100ah 12V Lead Acid Batteries connected in parallel ("800Ah" Battery Bank)
Wires - 4/0
Fuse - 400A
Shut off Switch

Inverter
3000W Renogy Pure Sine Inverter
Wire - 4/0
Fuse 400A

Distribution Panel
WFCO WF8930/WF-8950
Wire - 6/3 Connected to inverter
AC - 30A Main Breaker
DC - 6AWG
Fuse - 30A

Mini Split AC
Pioneer 12K 1 Ton Air Conditioner/Heat Pump for 110/120V
Wire - 12/3 Triplex Marine Wire
20A Tandem Breaker

All components and batteries run through separate positive and negative bus bars. My negative bus bar has a shunt with a battery monitor and is also grounded with a 4/0 AWG wire to the chassis of my rig.

My next move this weekend is to test the Mini Split with direct residential power to make sure it isnt defective but I am throwing this in here to see if there are any recommendations for what might be the problem and hopefully come to a solution. I really appreciate anyone taking the time to read this and I am hoping I can find a solution to move forward with finishing up my build.

It has been very difficult finding an electrician that would take on the trouble shoot on a non residential application. I am located in Florida, South Miami. If by chance anyone is near.

Thank You!

ordonez1221

Here is also a diagram of the connections to the mini split AC

mike95490

Can you try hooking up a couple of electric heaters or blow dryers, you want to monitor the DC volts at the inverter and see if the DC sags any from 0 load, 1200w, 2400 w
 My guess is as the compressor trys to start,  you get a voltage sag at the inverter DC bus, and that can trip the inverter offline.
Is there a test or bypass mode on the inverter ?
Can you un-ground the the 1 ton AC .and test again ?

As nice as your setup and wiring is, 12V is the wrong voltage to choose to power large inverters, because of DC bus voltage sag.  Also many parallel batteries is a problem for long battery life.
 see    http://www.smartgauge.co.uk/batt_con.html for explanation

ordonez1221

That looks like good information on battery connections. Always looking for ways to improve my set up. Thanks!

As for the draw on start up, I did not see a huge drop upon start up of the mini split before the inverter shuts off. I have ran high power appliances through the system that display a significant draw on the batteries without any issues. Things like heat guns, table saw and refrigerator. The inverter does not have a bypass or test mode from what i have seen in the manual. I have also reached out to the manufacturer for some guidance. I am not sure I will be getting a response from them anytime soon though. 

Dave Angelini

Just a comment.  That does not look like a code compliant installation. If you had home insurance it could be an issue with claim!

mike95490

Also, when you connect the batteries, place the terminal lug against the post, no washer in-between,  That gives solid contact, and saves 2 interfaces that have finite resistance,  x 8 and you have saved a lot.   With the thru-bolts, you put a lug on each side of the terminal.
  Do you have any venting provisions ?   As sealed batteries age, they can and will, pop their vents sometimes and you don't want to fill that cavity with hydrogen

ordonez1221

Hello again!

I have been really busy with work so I have not had a chance to update the results of trouble shooting this past weekend. I do appreciate the input everyone gave. 

I was able to run a 10AWG Wire from the 3000W Inverter directly to the chassis for ground. I tested turning on the mini split with my battery system after doing that but the inverter still shut off after a few seconds. I proceeded to run a line directly from residential 110/120V with a dedicated 20A breaker in the house and tested the mini split that way. The mini split ran without any issues. I ran it for a couple of hours to make sure there wasn't any other issues. It cooled the space without any problems. That tells me the mini split is not malfunctioning and the problem very likely has to do with the capacity of my inverter. 

I decided to connect and test the mini split one more time with my battery system after testing with residential power. I turned the mini split on and the inverter did not shut off this time. I ran the mini split for a few hours to monitor the power draw and the behavior of the inverter and batteries and take inventory of the added power power draw along with all the other appliances already connected to the system. The power draw is concurrent with the specs of the mini split and also the inverter was not suffering any drastic changes or elevated temperature. Once the mini split cools the area to the desired temperature, the power draw lowers significantly to the equivalent of running a small fan. I do not know exactly what is allowing the mini split to run on my system now after running it through residential but I am sure glad it is working without any signs of it damaging my system.

I did see mention of double checking the capacitor or adding an easy start to the mini split  to give the compressor a slow start and less of a power draw on the inverter. On that note I reached out to Micro-Air who manufactures the "Easy Start" that can be added to RV AC units or residential units. I furnished them with the details of my application and the issue I was experiencing and they replied with the following:

"An EasyStart is not required for mini-split systems as they already supply the low current starts....

Mini splits typically have their own built in inverter and Easy Start is not necessary."

They also asked for a diagram of the mini split's internal components to review further. I am still waiting on a response. As I mentioned before, I will be adding components to be able to run my appliances from shore power and even generator to alleviate the wear and tear on the batteries. 

I am interested to read on what you all think is allowing the mini split to run now. Thanks all in advance for your feedback.

RCinFLA

A true ground fault would be an immediate shutdown.

In the U.S., some mini-splits have only a simple rectifier-filter capacitor to convert AC to high voltage DC to run the three phase inverter for the mini-split compressor.,

In Europe and other countries, they have power factor regulations that require a PF correction circuit for the AC to DC rectifier.

The simple rectifier-filter has two potential issues when running on a battery powered AC inverter supply.

First is initial surge current to charge the filter capacitor,  Many units have a NTC (negative temp coefficient) thermistor.  When thermistor is cool it has higher resistance to limit capacitor charging surge current then when it heats up its resistance drops.  Sometimes there is a relay that bypasses thermistor after capacitor charges up.  My Samsung inverter refrig is done this way.,

Second issue is the simple rectifier-filter capacitor has a poor power factor, typically around 0.6, due to current being supplied only during the short sinewave AC voltage peaks.  This results in short, high current pulses from the AC input that may exceed the battery powered AC inverter peak current capability.

It may be possible to buy a power factor correction module for your unit.  This is a controlled DC-DC pre-boost circuit that spreads the current supplied to filter capacitor over the whole AC cycle.  They might only be available for 220v units which is the common AC line voltage in countries requiring PF correction.

You can buy one of these cheap (<$20) meter to check unit's power factor.  Available on Amazon, eBay, etc.