Question about inverter in solar setup

shamanjon

so I have spent a good majority of today googling and reading, trying to get a straight forward answer about whether or not I should ground my power inverter and how, I’m hoping someone here could give me some insight and point me in the right direction 
so right now I have a solar system set up in my van 
I have:
2 100w solar panels 
1 200 Ah deep cycle battery grounded to chassis
and a 1000 watt pure sine wave inverter 

everything is hooked up besides the inverter, please let me know what I’m doing wrong and what you’d recommend;
i plan to have the inverter about 10 feet away from my battery with 4 AWG welding cable 
(Not sure if that’s too far for cable size) 
with a 30 amp online fuse in between inverter and battery, 
now my big question... how to ground the inverter to make it “safer” 
the inverter I have is a mighty max 1000w pure sine wave inverter from Amazon, (seemed a little cheap but was within my budget) 
most other inverters I see have a ground lug somewhere on the frame of inverter, while the one I have does not, user manual it comes with shows a ground lug on it but it’s non existent in actual inverter, it also doesn’t say anything about grounding the inverter in the instuuctions
I read grounding the inverter to chassis could make it more dangerous in case of appliance short, could cause chassis to become hot? 
And then I’ve also read if you don’t ground it to chassis and there’s a short somewhere else the circuit won’t be completed and the frame of inverter will remain hot until someone touches it and gets shocked ? 
If anyone could clear things up for me it would be greatly appreciated 
thanks 
-Jon 

mcgivor

Welcome to the forum Jon

Let's start with what type of inverter it is you have, a pure sine wave or modified sine wave, also the voltage, assumption would be 12V nominal. Keeping the distance between the battery and inverter as short as possible is best, but understandably not always possible, with reference to chassis, is this a vehicle mounted system? 

shamanjon

It is a Mighty Max Pure sine wave inverter 1000w
and yes it is a 12v system.
and I have not yet mounted the inverter to the van, but I plan to, my only option is to mount it on my wooden cabinet 
-Jon 

mcgivor

If the intent is to only use the outlets provided on the inverter itself, it's generally not an issue to power consumer devices with a floating neutral. Vehicular applications are different to terrestrial installations where there is actually a ground/earth to reference to, a vehicle would in essence be a floating ground of sorts. The grounding of an output leg to the chassis could  provide a neutral but with modern vehicles with computer controled electronics I'm not sure this is the best approach. The manuals for cheaper inverters are pretty vague at best, one I use says not to ground an output leg to ground, it also goes on to say it has ground fault protection, but provides no ground bonding terminal, without which it couldn't provide ground fault detection. With this inverter I do ground one leg, feeding into a residual current circuit breaker and it works perfectly in ground fault, provided by the breaker, go figure..

The 4awg conductors are rated for a maximum of 60A,  at maximum power a 1000W inverter could approach 90A, the greater the distance the greater the voltage drop, if loads are less than maximum allowable it may be fine as the current ratings are very conservative, to get a better understanding, play around with a voltage drop calculator  https://www.calculator.net/voltage-drop-calculator.html remember to use DC amps, for every amp at 120V, the DC will be 10× higher, the 10:1 conversation ratio, with a 12V to 120V inverter. Hope you learn something with this, any questions, just ask. 

shamanjon

I appreciate the response, I only plan on using the inverter to charge a laptop, power drill, and occasionally use a coffee grinder, I tried messing with that calculator and with my minimal knowledge, I think the wire and distance might be okay, but maybe I should increase fuse size? Any input ? 

Now for the groundinf question, I’m still a bit confused about what I should do, I understand you’re saying I may be able to get away with having a floating neautral by not grounding it, as long as I don’t intend to max out the load, but I am trying to make it a safe as possible and completely eliminate any chance of shock, 
would it be a bad idea to run a wire from the metal frame of inverter to chassis of vehicle? 
Are their any pros and cons to doing that? Will it do anything at all? 
Thanks for any help 
-Jon

petertearai

Personally i would leave without bonding the case to the vehicle chassis .

shamanjon

petertearai said:

Personally i would leave without bonding the case to the vehicle chassis .

Any particular reason why? 
Pros/cons of doing it vs not doing it 
I have very minimal knowledge but from what I understand 
bonding the case to the chassis can only help? 

Estragon

Just a guess, but if the inverter is designed for portable use (just NEMA plugs, not terminals for hardwiring) it may be designed with an internal fuse/breaker to protect against shorts. 

As mentioned earlier, grounding vehicle equipment can get complicated.  In some wiring and fault condition combos, for example, you could have the vehicle chassis at high voltage with respect to actual ground.  Stay in the vehicle insulated by tires, all is good.  Step out into a puddle holding a metal door, could be bad.

Unless the unit is designed for hardwiring, not grounding to chassis may be simplest and best IMHO.

shamanjon

Estragon said:

Just a guess, but if the inverter is designed for portable use (just NEMA plugs, not terminals for hardwiring) it may be designed with an internal fuse/breaker to protect against shorts. 

As mentioned earlier, grounding vehicle equipment can get complicated.  In some wiring and fault condition combos, for example, you could have the vehicle chassis at high voltage with respect to actual ground.  Stay in the vehicle insulated by tires, all is good.  Step out into a puddle holding a metal door, could be bad.

Unless the unit is designed for hardwiring, not grounding to chassis may be simplest and best IMHO.

Well if I’m understanding you correctly the inverter is designed for hard wiring it has terminals on the back side of it to connect directly to the battery, and no other connections, no ground terminal, just two 3-prong outlets on the front of it 
I emailed the manufacturer about it since the instructions were of no help, just waiting on their response
I still have not installed it because I want to be sure I’m doing it right 

Estragon

No, the hardwiring I was referring to is the AC side.  It would have AC out terminals designed to be hardwired into an AC breaker panel.  With 3 prong AC outlets, its designed for portable use.

shamanjon

Estragon said:

No, the hardwiring I was referring to is the AC side.  It would have AC out terminals designed to be hardwired into an AC breaker panel.  With 3 prong AC outlets, its designed for portable use.

Okay thank you for the info 
I’ll probably give it a try on Monday when the rain clears up, I’ll keep you guys updated 
if anyone else has any input feel free to put it here 
I’m always looking to learn 
thanks again 
-Jon 

BB.

The chassis side of the inverter does need to be grounded (either through the mounting screws) and/or with a heavy cable from the chassis ground lug on the invert to your negative battery bank bus/battery lug, and/or to the chassis of the vehicle (vehicle chassis are frequently bad grounds--Newer vehicles may use glue/double stick tape for metal panels and rubber isolation mounts).

The chassis ground is to safety shunt short circuit current from the inverter chassis (something shorts inside to the case) and cause the fuse to blow.

The inverter manual should tell you the AWG of the wire used to connect&ground the inverter.

Note the AC output for a pure sine wave inverter (that is smaller than ~3,000 Watts or so) is generally floating (not neutral bonded to safety ground like normal house wiring).

There are very few appliances that will not work (well) with floating AC output. Some fluorescent lamps and spark ignition heaters (some fluorescent tube fixtures need grounding to reliably start; and some spark flame igniters for water heaters and stoves and space heaters need a grounded neutral for the "flame detect" to work properly).

Otherwise, floating output is fine. If you are using tools (or AC sound system, etc.) around water, you can install a GFI AC outlet (or use a GFI protected extension cord) to help prevent electrocution.

-Bill

shamanjon

BB. said:

The chassis side of the inverter does need to be grounded (either through the mounting screws) and/or with a heavy cable from the chassis ground lug on the invert to your negative battery bank bus/battery lug, and/or to the chassis of the vehicle (vehicle chassis are frequently bad grounds--Newer vehicles may use glue/double stick tape for metal panels and rubber isolation mounts).

The chassis ground is to safety shunt short circuit current from the inverter chassis (something shorts inside to the case) and cause the fuse to blow.

The inverter manual should tell you the AWG of the wire used to connect&ground the inverter.

Note the AC output for a pure sine wave inverter (that is smaller than ~3,000 Watts or so) is generally floating (not neutral bonded to safety ground like normal house wiring).

There are very few appliances that will not work (well) with floating AC output. Some fluorescent lamps and spark ignition heaters (some fluorescent tube fixtures need grounding to reliably start; and some spark flame igniters for water heaters and stoves and space heaters need a grounded neutral for the "flame detect" to work properly).

Otherwise, floating output is fine. If you are using tools (or AC sound system, etc.) around water, you can install a GFI AC outlet (or use a GFI protected extension cord) to help prevent electrocution.

-Bill

Thanks bill I appreciate the detailed response 
so what I have gathered from all of your guys input 
when I install my inverter 
I’m going to have it 8-10 ft away from battery with 4 AWG welding cable 
I’m going to upgrade my fuse from 30 to 80 amps and I’m going to bond the frame of the inverter to the chassis of the van through one of the mounting screws, I don’t have a negative bus bar but my vehicle is a 1992 dodge van and when it was gutted out I never noticed any rubber in between parts of the frame, I don’t ever plan to charge more than one laptop at a time, and just going to use a coffee grinder occasionally 
so I think should be fine with my situation
i don’t know if it necessary or not 
but I was also planning on adding a master cutoff switch between the battery and inverter and have it always set to off unless I planned to use inverter (reason for this is because I have been told inverters sometimes draw power even when off ? )
dont know how factual that is, but don’t think it could hurt 
anyways I appreciate all the feedback it’s been a Bunch of help
-jon

BB.

Depends on the inverter if they draw power when off... You need to look through the specifications.

For your usage, even a smaller inverter like 300 watts or so, would be a better choice. Lower self consumption (typically 6 Watts).

The MorningStar 300 Watt PSW 12 volt inverter is pretty nice. It has both a remote on/off switch, and a sleep mode (only turns on when >6 watt load is connected). Some of the newer inverters these days have remote displays and remote switches.

Your 200 AH battery -- A typical recommendation would be for a maximum of C/8 discharge rate (recommended for FLA type batteries):

• 200 AH * 1/8 discharge rate * 12 volts * 0.85 inverter eff = ~255 Watt recommended max continuous draw

Typically, larger inverters draw (waste) more current just being "on" with no loads (Tare Load of inverter).

And the "real switch" (or switched circuit breaker) ensures you will not take the battery dead if something is not "off" or is forgotten/left on.

-Bill

Tecnodave

I will add that a GFCI does need to be grounded. They work by sensing the balance of current between the hot side and the neutral side of the power line.  There is no way to test a GFCI that is not grounded and some will not reset if not grounded. The leakage will be through a fault or you. The standard here in California is that a vehicle with a mounted inverter does need to be grounded and a GFCI is required. All Motorhomes and travel trailers are equipped with GFCI's as standard factory Equiptment. This has been required for more than 20 years now. I would advise adding a GFCI external to the inverter and bonding (a NEC term) to the chassis. This ground bond cannot be smaller gauge wire  than the largest conductor. (wire size) used in the inverter system (again NEC). I think that your battery cables a bit too long and small in size. Also that inverter is a bit too big. IMHO. I'm thinking that your power needs are more like 300-500 watts. Smaller inverters usually are more efficient than larger ones. Most inverters are most efficient at 60-80% of full load capacity.  One worst case I have seen was a person using a Harbor Freight 12 volt 2500 watt inverter to run a 13 watt CFL. He thought he was only drawing only 13 watts off the battery. My DC ampclamp showed a whopping 230 watts!

david

Tecnodave

After reading that again let me clarify one point.  The Chassis bond is from the inverter frame to the Chassis. The GFCI  ground can be connected to the inverter crane at the same point as the chassis ground.

david

Tecnodave

Tecnodave said:

After reading that again let me clarify one point.  The Chassis bond is from the inverter frame to the Chassis. The GFCI  ground can be connected to the inverter frame at the same point as the chassis ground.

david

edited to correct my iPad's absolutely auto attempt at spell

Tecnodave

Not sure what just happened, my iPad locked up the keyboard and I could not finish that post
I complained about auto spell and I lost control of my keyboard......bad iPad. It just did it again!

david

BB.

I believe GFCI outlets are actually "approved" for use in ungrounded circuits (such as older homes that only have 2 wire outlets and no ground)...

https://ask-the-electrician.com/replacing-ungrounded-outlets-with-a-gfi/

How a GFI Outlet may be Installed In Place of  an Ungrounded Outlet

• Replacing Ungrounded 2-Prong Outlets with a GFCI Outlet
  • An old style non-grounded outlet may be replaced with a GFCI outlet and the Ground Fault protection circuitry and capabilities will still work.
  • When replacing a 2-wire outlet with a GFCI outlet the outlet  must be labeled indicating that there is no ground available. A label is provided with the GFCI outlet for this type of application.

• Replacing Ungrounded 2-Prong Outlets with a Standard 3-Prong Outlet
  • You may not replace a two prong ungrounded outlet with a standard 3-wire grounded outlet that has a ground prong unless there is a ground wire connection available.
  • Installing a standard 3-wire outlet that is  not grounded is not safe and is illegal  by electrical code standards and this is not an acceptable practice.
  • The danger is that there is no ground wire available, therefore there is no provision to interrupt the circuit in the event of a ground fault.
  • Ungrounded outlets may increase the risk of electrical shock potential.

The self test does not need to use a ground to simulate a "fault"... Just a ~5+ mAmp resistor from plug side of "Hot" to supply side of "Neutral" will do the self test and trip the GFCI (this is a guess on my part on how the self test works--And would work fine if there was no ground wire in the house wiring).

And the GFCI will detect the unbalanced current flow just fine without a ground connection (if the Hot and Neutral current flow are not "identical" within 0-5 millamps or so, the GFC is supposed to trip).

https://www.ecmweb.com/basics/how-gfcis-work

-Bill

Note: This is how I understand the GFCI subject... Not, in any way, an expert on GFCIs.

shamanjon

I appreciate all the info guys, trying my best to grasp what you guys are saying 
I also put the wrong cable size I actually have 4/0 AWG cables 
I plan to put the inverter 8-10 feet away from the battery, would you still say I should go with bigger wires ? 
Also, about the GFCI is this still necessary if I only plan to use the outlets on the inverter ? 
I’m not wiring the inverter to an AC breaker and using separate outlets 
I just wanted to be able to turn it on to charge a couple laptops every once in a while
i plan to ground the case to the chassis 
but as far as further grounding 
what would you guys recommend, is it necessary? 

BB.

4/0 cable, 10 feet (one way run), 11.5 minimum battery voltage, and current of:

• 1,000 Watts * 1/0.85 AC inverter eff * 1/10.5 volts inverter cutoff voltage = 112 amps (full rated power, ~2x for a few seconds of surge current at ~2,000 Watts)

Using a voltage drop calculator, we get:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.1608&voltage=11.5&phase=dc&noofconductor=1&distance=10&distanceunit=feet&amperes=112&x=75&y=19
Voltage drop: 0.11
Voltage drop percentage: 0.95%
Voltage at the end: 11.39

Which is "overkill" for your needs... It will work very well.

Or, you can use 4 AWG cable and:

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.8152&voltage=11.5&phase=dc&noofconductor=1&distance=10&distanceunit=feet&amperes=112&x=74&y=24
Voltage drop: 0.56
Voltage drop percentage: 4.84%
Voltage at the end: 10.94

Which is just about perfect... You want roughly 0.5 volt max drop for max continuous power, and 2x that current for short term search current (and ~1.0 volt drop).

Realistically, a C/5 discharge rate for a flooded cell lead acid battery, is about the maximum short term (minutes) of load. For example, your 200 AH @ 12 volt battery would "reliably" supply (roughly) a maximum of:

• 200 AH * 12 volts * 0.85 inverter eff * 1/5 hour discharge rate = 408 Watts output from your inverter+battery bank

If these are AGM or GEL batteries, they can support higher discharge rates (C/2 or some can do better than C/1 hour discharge rates).

-Bill

BB.

I, personally, would not worry about ground bonding the AC Neutral/White wire. It is not going to do anything (good or bad) for your needs.

Grounding the inverter case (bolting to the vehicle frame work and/or running a minimum of 6 AWG cable from chassis ground lug to a decent DC ground that returns back to your 200 AH battery, is a good protective measure to prevent the inverter's metal case from becoming "energized" (internal mechanical failure that crosses +12 volts or 120 VAC to the chassis metal inverter case--If properly grounded, the case will never become energized/hot if there is a failure and help prevent shock or fire--The chassis ground will trip/pop your overcurrent protective devices like a circuit breaker or fuse).

-Bill

shamanjon

Thank you bill you have been such a great help, I’m going to definitely bond the case to the chassis 
one last question, is there any way to test if the frame of the van that I bond the inverter case to is in fact connected to the 12v battery ground? 
I have my battery grounded to a piece of the metal floor, and where I plan to bond the inverter is a piece of the frame attached to the floor 
is there anyway to use a voltmeter or any other method to make sure they’re connected ? 

BRob

Jon, I'm not sure I'm completely following your last question about the frame, but I've put a lot of miles on full-size Dodge vans. The frame is unibody construction; there is no electrical isolation between the frame and body shell and is grounded to the starting battery negative.

I used an 800 watt size MSW inverter in mine for the past 19 years. I just ran a fused positive wire from the (dual-purpose marine starting) battery terminal to the inverter, and wired the negative post of the inverter to one of the seat pedestal bolts. Additional solid metal grounding can be found if you look under the van and pick an area of the floor that is also part of the frame rail flange.....just find some thick metal.

This is a maybe for you, but here's something to think about. If you can still return the Mighty Max to Amazon you might consider a $100 upgrade in inverter quality. As others have indicated, 1000w might be overkill for your needs. Consider a Xantrex PROwatt SW 600. Xantrex has been in the inverter business for many years and is now owned by Schneider, a big player in the electrical business. The Xantrex PROwatt SW already has a GFCI outlet which you could simply plug a power strip into and be sorted out as far as the AC side....the Mighty Max doesn't. It also has your USB output, a very quiet fan, and remote switching capabilities. There is also a comprehensive set of installation instructions aimed at mobile installs like yours, you can find that on line if you look at the manufacturer's site. 

Yes, the Xantrex inverter would be made in China, but it's going to have some solid engineering behind it, even if built for a price point. Sorry, but to me the Mighty Max looks like just a label stuck on a generic Chinese inverter.....who do you go to for tech support or real install answers? Might just be worth the extra money for the extra peace of mind in having a better quality unit when dealing with power electronics.

BB.

A simple/basic test is to connect a 12 volt lamp (anything from a brake light to a head light from +12 to chassis ground and see if the lamp lights. You can also get a simple test light from a hardware store (12 volts).

Using a typical DMM between +12 and chassis should show +12 volts battery voltage... However, DMM (digital multimeters) draw so little current that they do not really "stress" the connections (as little as 10 or 20 millionths of an amp). You want something that draws "substantial current" (like a lamp or other other 12 VDC load) and measure the resultant voltage.

In an engineering/electrician solution, we would use a load bank with ~100 Amps to "test" the connection--But that is more than most DIY folks would be expected to do.

-Bill

Tecnodave

Bill,

You are correct, a GFCI is legal in a 2 wire non grounded situation, I install them in older houses all the time. They do the test function from both the hot wire and the neutral wire to the ground wire. This test will work when you have a failed neutral connection. That is not uncommon here on the coast. The latest Leviton Smart GFCI will not reset on a 2 wire connection. I'm not sure why that is. 

I test GFCI's in a 2 wire situation with a 7 watt incandescent lamp with probes to the hot wire and neutral wire any convient connection. I probe sinks, plumbing connections, etc. This will also tell me if the plumbing is not grounded. I test both the cold water and the hot water plumbing to verify that they do have a ground wire, and a bonding strap between the cold and hot water lines at the water heater,as most water heaters have plastic isolaters at the tank connection to prevent current flow through the water heater. This method does not require you to pull the GFCI to test its operation. 

In some fail modes where the utility connection at the weatherhead the neutral connection is corroded and the ground rod is corroded there will be considerable voltage on the neutral wire which should be not more than a few volts at worst case. At one house in Monterey, facing the ocean I had 40-65 volts at the neutral in the main panel.  I pulled on the ground rod and 6 inches were left of it. The PG$E connection was of the crimped aluminum type with no insulation and right at roof line inches from the metal guttering. To PG&E's credit they were there in less that 20 minutes to correct their issue, and installed a new ground rod.

I do err sometimes but always on the safety side. I have retired from in house electrical work and only do main panels and agriculture. There is little industry here so I don't bother with that. Farmers don't ask how much, rather can you come out now!

david

Tecnodave

For some reason I cannot use the edit function. So I will correct the issue on the ground rod, PG&E repaired the neutral connection and Installed the new ground rod

BB  please let system maintainer know that wher I use the edit function my iPad locks up and I cannot edit???
       iPad. MC707LL/A.   Software. 9.3.5. (13G36).  (for debugging purpose)

BB.

Hi Dave,

I have opened a trouble ticket with Vanilla Software... I have told them they can contact you directly, if they wish.

Take care,
-Bill

Tecnodave

BB,

I just noticed a clue as to what happened, I had posted post #26.  was trying to edit out a mistake as I was editing then iPad would not respond to keyboard, when I lost  control post # 27 wasn't there   iPad does not totally lock up but does not respond to keyboard, To fix I log out and then log back in, keyboard control is regained unfinished edit is still there grayed  out a bit as in edit , directly below post #26  I post Correction, left the forum for a bit. I come back and see your message about the ticket and notice that user BRob had posted #27 which was duplicated as post #28. , I'm thinking that as the time was nearly the same BRob and I were posting at the same time......strange coincidence ,I lose keyboard and his post is posted twice???   
And yes Vanilla can contact me, no problem

thanks...david

BB.

Thank you David.

I have updated the trouble ticket.

-Bill

BRob

Apology, guys....I might have gunked up the system unintentionally. I made an initial posting, then tried to edit several small details. That may have caused the double....actually triple posting. I may not have been patient enough with the system. I deleted the extra postings as the intent had not changed. I've been reading this forum for a number of years in learning mode, but I'm not used to posting on forums. I hope I can still claim some newbie ignorance.