User Lightning: Earth Grounding off grid power system & EV charger fails to charge w/o grounding

System

This discussion was created from comments split from: Earth Grounding Battery Bank.

Lightning

I have a 5Kw Aims 120VAC @ 80A rated Industrial Inverter with 2 150A Midnight Solar Charge Controllers, 6 400W Solar Panels and 10 LiFePO4 12VDC 100Ah battery bank.

This is a 12VDC system to 120VAC. I have an open ground problem that will not allow me to use my Level 1 EV 120VAC Charger.

I have a Fridge, Freezer, Laptop, LED House Lights, Clock Radio's, Lathes, Mills, Grinders, Miller TIG/MIG/ARC Welder, Drills, Saws, a MasterCool ASA51 Swamp Cooler, 2 120VAC 1 Ton 12K BTU Cool/Heat Pump Mini Splits, etc.

I have earth grounded the AC side of the Inverter, Main Electrical Panels at house and Detached Garage earth grounded at 5 earth ground points in the system. When I use a Multi Meter, I get 120VAC from Black + and Green -. But when I check the Common white + to Ground Green - I get 60VAC.

My Inverter has 2 GFCI 120VAC outlets on Inverter that when I test also have open ground too. Should I ground the battery bank to earth ground and the 12VDC side of the inverter to earth ground. I would like to use my Off Grid Solar System to recharge my EV too. Everything else runs just fine, just not the EV Charger. My EV Charger charges my EV using the Grid Utility Power. Any Suggestions would be greatly appreciated.

Lightning

(10) LiFePO4 100Ah batteries for a 1,000Ah Battery Bank Capacity.

BB.

Welcome to the forum "Lightning".

I have split off your questions to their own thread--That way we can better follow your discussions without confusing with the earlier posts.

Since this is a "grounding question"... A bit more information is needed. What exactly is the brand/model of AC inverter you are using (links to the product is fine too). The first question is this a TSW/PSW (true/pure sine wave) inverter or an MSW (Modified sine/square wave) inverter?

The issue here is that (most all) TSW/PSW AC inverters have an isolated output and you can ground the "neutral+ground bonded" power that we have with a standard North American 120 VAC (and 120/240 split Phase VAC) power system.

With MSW inverters (almost all), they do not have an "isolated" AC output and if you attempt to make a neutral+ground bond, and also have any sort of battery negative+ground bonding, it will "short out" the inverter and ruin it.

Just to be clear... Your home has both a 120/240 VAC utility power connection (guessing around Yucca Valley California--Southern Ca desert area). And you have a 5,000 Watt AC off grid system too.

The EV Level 1 charger works fine with utility power (you get 120 VAC between Line and Neutral & between Line and Ground; and near zero volts between Neutral and Ground).

And with your off grid AC power system, you get 120 VAC between Line and Neutral, and ~60 VAC between Neutral and Ground--Which is pretty typical for a "floating" 120 VAC output (no N+G bonding).

If your AC inverter is a PSW/TSW type, then N+G bonding (neutral tide to safety ground) is a common solution. And if the Level 1 charger has a three prong 120 VAC plug with N+G bonding check--This should fix the AC charging failure. Functionally, any 120 VAC load should work with "floating' Neutrals... But some devices check the voltage between N and G as a "safety check" and will shutdown until the N+G are bonded... Also switching/incorrect Line and Neutral wiring at the outlet (i.e., Line goes to "narrow blade" and Neutral goes to "wide blade) can cause a similar issue.

If you have a MSW type inverter--There are issues that make N+G bonding something to generally avoid (cannot have a true AC N+G bonding for almost all MSW inverters). And your EV Level 1 charger will not be "compatible" with MSW inverters.

A separate question is ground bonding the negative (typical) terminal on the battery bank (not directly related to 120 N+G bonding issue).

Your user name "Lightning"--Does this indicate that you have significant lightning issues around home? If yes, then ground bonding the negative terminal on the battery bank is a good idea. You want lightning to find the best way to earth through a (6 AWG cable minimum) to the earth ground rod)... Bring the green wire 120 VAC ground to the same ground rod (you want a "single point" tie between your DC and AC safety ground wiring.

If you have dry sandy/clay soil--"True earth grounding" can be an issue (dry sandy soil does not like to conduct electricy--And neither does solid granite). 

Also, having surge supressors on the Solar Panel DC wiring, DC battery bus wiring, and AC output/house wiring is not a bad idea either (nothing will prevent damage from a direct strike--But this stuff helps). The Midnite SPDs are really nice:

https://www.solar-electric.com/search/?q=surge+suppressors

Your thoughts/corrections?

-Bill

BB.

For a large battery bank + AC inverter system, I suggest a higher voltage battery bank:

• 1,800 Watts max for a 12 volt bank
• 3,600 Watts max for a 24 volt bank
• >3,600 Watts, use a 48 volt battery bank

A 5,000 Watt @ 12 AC inverter draws:

• 5,000 Watts * 1/0.85 AC inverter eff * 1/10.5 volts inverter battery cutoff = 560 Amps @ 12 volts for full 5 kWatt inverter loading

And if you have large surge loads (like a typical well pump), the surge can be 2x the rated continuous power/current ratings.

Also, with your solar charge controllers, they are rated for a maximum output current. Say 80 Amps (Midnite does have slightly different current ratings for 12/24/48 volt battery bus)--This is an example:

80 Amps * 12 VDC * 1/0.77 panel+controller deratings = 1,247 Watt max suggested solar array @ 12 VDC
80 Amps * 24 VDC * 1/0.77 panel+controller deratings = 2,494 Watt max suggested solar array @ 24 VDC
80 Amps * 48 VDC * 1/0.77 panel+controller deratings = 4,987 Watt max suggested solar array @ 48 VDC

For every doubling of DC battery bank voltage, the same controller will "manage" a 2x larger array (fewer solar charge controllers needed). And doubling battery bank voltage, the wiring will only need to pass 1/2 the current (Power = Voltage * Current... 2x voltage and 1/2 the current = same Watts).

-Bill

Lightning

Thanks Bill. To answer your questions, I have an Aims 5000W Industrial Power Inverter True Sine Wave (TSW) Model PWRIG50001212OS. I live in Joshua Tree, CA. I have SCE- (Southern California Edison) as my Grid Power supplier.

My 5Kw system is a stand alone (Not Grid Tied) off grid system. I have 120VAC/240VAC 100A Service Grid SCE Power, and my 120VAC 60A or 80A? independent solar power system. My system is a 5Kw True Sine Wave with (6) 400 Watt Solar Panels (2,400 Watts Total), and (10) 100 Amp Hour LiFePO4 Batteries (1,000 Ah @ 12 VDC). 

I am asking you this question directly to be sure I can do this. Can I ground both the Green wire (Ground) and the White wire (Neutral) to the Earth 5/8" x 8' length Ground Rod together?

I really would like to plug my 3 prong level 1 EV Charger into my system rather than the SCE Grid Power System to charge my 2014 Chevy Spark EV. 

BTW- I used Lightning as my Username here since it was my call sign when I was in the military. It is totally unrelated to Lightning Strikes. 

Photowhit

Lightning said:

I have earth grounded the AC side of the Inverter, Main Electrical Panels at house and Detached Garage earth grounded at 5 earth ground points in the system. 

I'm going to plead mostly ignorance here, Bill is much more knowledgable...
...but, Are all these points bound together? My understanding for dry areas...

Lightning said:

I am asking you this question directly to be sure I can do this. Can I ground both the Green wire (Ground) and the White wire (Neutral) to the Earth 5/8" x 8' length Ground Rod together?

I think routinely the would be bound in your main electrical panel. As I recall from my faulty mind. The commercial AIMs inverters are internal switching. So if it 'sees' a neutral ground bond it won't bond internally. Of course only bond them in one place!

Though I would think another load on the system would allow the EV charger to work properly. This is reaching for me, Bill will likely give you much better advice.

Lightning

Hi Photowhit! Thanks for the knowledge. In answer to your questions, I have five ground rods. One ground rod in the remote stand alone Solar Power Plant Building. One ground rod at the electrical main box at the detached garage. Two ground rods at the house- one ground rod at the electrical main, and one ground rod at the sub main transfer switch box that runs the MasterCool ASA 51 Swamp Cooler from either SCE grid power, or my solar power system.

All 120VAC wiring is thru underground 3/4" EMT conduit from the Solar Power Plant Building to the House and Detached Garage, and all main and sub main panels. The system should be ground bonded through the EMT metal conduit Right???

I even wired the house and garage in 3/4" EMT surface mount conduit with surface mount metal single duplex outlet boxes from the electrical main boxes back to the Solar Power Plant Building. 

Everything else connected to my off grid 5Kw 120VAC stand alone system runs perfectly with no problems. It is just that EV Charger that is the only problem I have!

I have another (4) 400 Watt Solar Panels. A 12Kw 220VAC TSW Inverter. MPPT Charge Controller LiFePO4 Batteries- 500Ah total. I am contemplating on building a 220VAC only system and purchasing (2) 220VAC Level 2 dedicated Hard Wired EV Chargers just for that EV I currently own, and I am waiting on a New 2023 Chevy Silverado EV Pickup next year. Then I will have 2 EV's to charge!  I surmise the (2) 220VAC Level 2 EV Chargers will be needed at some point. Maybe this new system will solve my EV Charger problem ??? 

Dave Angelini

Photowit is asking you if the grounding rods are interconnected? Not saying this is your problem but it can make some electronics misbehave, especially under large loads.

This kind of large loading is not ideal on 12V inverter electronics in warm places.

Photowhit

Dave Angelini said:

Photowit is asking you if the grounding rods are interconnected? Not saying this is your problem but it can make some electronics misbehave, especially under large loads.

I didn't know this could create a problem with large loads, thanks for the education!

Dave Angelini said:

This kind of large loading is not ideal on 12V inverter electronics in warm places.

Another excellent point!
12volt inverters, particularly inverters that never should be made, like a 12 volt 5000watt inverter. Are often spec'd with under sized connectors. Lets see, 5000 watts / 12 volts = 416 amps x 1.1 for inverter inefficiencies(losses in the inverter converting DC to AC) = 478 amps. NEC table for ampacity of wire;


Looks like it should be wired with 500-600kcmil wire, I wouldn't worry much about voltage drop at the battery, I'll use 500kcmil. 
The batteries should be fine, with little to no voltage drop, but across the line to the inverter could represent the charger seeing unstable voltage.

Here's a video of a guy crimping 500 kcmil wire;
https://youtu.be/UgAbpuCgJnM

BB.

To discuss the EV charger and the failure... It sounds like your 120 VAC neutral is not tied to safety ground--The Neutral and Green Wire safety ground are usually bonded together in the main breaker panel (in a standard 120/240 VAC home powered by the utility).

For your inverter, I looked at the manual and it did not have any information about grounding (other than possible grounding of the inverter's case--Depending on local code).

From my limited experience, it appears that 120 VAC power sources (generators, AC inverters) that are ~3,500 Watts or larger output, will have an internal AC Neutral to Ground bond. Depending on your installation--If for example you are connecting to an AC breaker panel, there would be a N+G bond inside the box (some have an optional neutral bonding screw to connect to box ground) and normally any AC supply (genset, AC inverter) would have its internal G+N.

With a volt meter and the AC inverter turned on, check the voltage from Line to Neutral (should be around 120 VAC). And check Ground to Neutral (should be near zero volts if N+G bonding, and anywhere from 10's to 120 VAC if no N+G bonding).

And/or you can (with the inverter off), disconnect any AC plugs/wiring from the unit and check the resistance between Neutral and Ground... Near zero homes, the inverter probably has an internal N+G bond. If you see very high resistance, then the inverter probably does not have an internal N+G bond.

In general, you only make an N+G bond one place in the home. If, for example, there is an N+G bond in the inverter output, and N+G in your main AC panel, then you have the Neutral and AC green wire safety ground in parallel. And that means that each carries part of your AC load current (not allowed by code).

The issues with (for example) two N+G bonds (in AC inverter and AC main panel), you have parallel current flow in N and G wiring (or metal conduit, etc.). You do not want 30+ amps flowing through the conduit and the metal fittings.

Another issue is (common with gensets that have GFI outlets)--If you take a N+G bonded genset, plug in a three prong plug into the GFI outlet, and then connect to the AC main panel (with N+G bonding)--It will generally trip the GFI protection in the genset (because of the parallel N and G conductor AC current flow).

Another secondary issue. With AC power, you need to have all the AC current going into and out of one hole in the sheet metal box (for example in the AC main panel 1/2 inch opening for the wiring). If you put the AC hot (line) into one hole, and the AC neutral into a second hole--The magnetic coupling between the two cables and the sheet metal will cause current to flow in the sheet metal and can cause the sheet metal to overheat from the circulating current.

Same issue if you have N+G bond in two or more locations and use Conduit as your safety ground... If you have 20 amps in the Neutral and 20 amps in the conduit--You can overheat the conduit and any metal j-boxes/breaker panels sheet metal.

Anyway--It sounds like your 120 VAC inverter/power system does not have an N+G bond and this is causing the EV Charger to fault.

Regarding grounding and ground rods... In general, for common building power systems, you want the safety grounds (and ground rods) to be interconnected with copper cables. You do not want (for example) the AC safety ground rod for the home/utility power to be connected to to one ground rod. And a separate ground rod for your solar power system. The two should use the same ground rod, or you should have a 6 AWG (suggested minimum AWG) cable from ground rod 1 to ground rod 2...

You need a copper wire to carry any fault current (say a short to ground in the solar power conduit) from the 120/240 VAC Utility power) will carry enough current to trip the breaker.

Two ground rods 3 feet apart are not going to carry enough current (through the earth) to trip a breaker for a shorted AC line--You will end up with an "energized" AC Home grounding and AC solar grounding (you could get a shock touching between the Home Ground/metal j-boxes and the Solar j-boxes).

And regarding even charging an EV from your solar system...

Your 12 volt system with a 5,000 Watt AC inverter--It is very difficult to have large enough copper wiring and battery bank to run near 5,000 Watts (560 Amps @ 12 volt battery bus).

And how much solar energy can you harvest with your solar system... 2,400 Watts of solar and say you have 6 hours of sun in a southern California desert on your array (sunny, non-winter). The harvest would be:

2,400 Watt array * 0.61 AC Lithium off grid system eff * 6 hours per day = 8,784 Watt*Hours per day

And if your EV car uses 400 WH per mile:

8,784 Watt*Hours per day / 400 WH per mile = 21.96 miles of EV harvest per day

For an EV pickup, especially if carrying a load or towing a trailer are going to use way more than 400 WH per mile...

From this review for a 320 mile range F-150 Ford pickup... A full size RV Trailer would drop the range down to 90 miles per charge...

https://www.motortrend.com/reviews/ford-f150-lightning-electric-truck-towing-test/

Is this a "useful" amount of electrical power from your existing solar power system per day (20 miles down to 5 miles per day for a trailer towing EV pickup??? worth of solar power per day)?

In general, I highly suggest to measure/estimate your Watt*Hours (or kWH) per day and then design the solar power system to power your needs....

-Bill

Lightning

Thank You - Thank You - Thank You Bill, my EV Charger works now! I took a #10 Green wire and run it from the Green Bus Bar (Ground) to the White Bus Bar (Neutral) in one place only at my house 120VAC Solar Main Box. I plugged my EV Charger into my house Solar 120VAC outlet and it works. And just for fun, I plugged my EV Charger in to my Detached Garage Solar Power Electric Main Box 120VAC outlet and it works too. Seems the Neutral to Ground in one place only is all it took to make the whole system work together. One little thing like that caused so much frustration! Thanks everyone! Great suggestions. Problem solved.

BB.

Very happy to read that this was your "simple" solution to the EV charger failure to charge.

Take care,
-Bill