Avoid open neutrals!

[Hedges]

My reasoning for switching neutrals was based on having only the neutral come from the AIO to the sub panel when operating. Possibly not really needed. My neutral ground bond is at the main panel. The sub panel is not bonded.

When running on AOI, neutral is not bonded. A short from line to ground would not trip a breaker or crowbar output. If ground is isolated, chassis may float to a voltage that can shock but is low current. If ground goes to main panel, the other line would go to 240V and neutral to 120V. Protection of consumer from contacting neutral usually isn't as good. Ungrounded single phase appliances will AC couple (low current) to the voltage. Grounded devices with EMI filters, and surge arrestors, will experience excessive line to ground voltage.

You ought to ensure neutral is bonded to ground. Most simply, by not switching it.

 

[Mattb4]

When running on AOI, neutral is not bonded. A short from line to ground would not trip a breaker or crowbar output. If ground is isolated, chassis may float to a voltage that can shock but is low current. If ground goes to main panel, the other line would go to 240V and neutral to 120V. Protection of consumer from contacting neutral usually isn't as good. Ungrounded single phase appliances will AC couple (low current) to the voltage. Grounded devices with EMI filters, and surge arrestors, will experience excessive line to ground voltage.

You ought to ensure neutral is bonded to ground. Most simply, by not switching it.

Thanks I think I will change my setup to not switch neutral.

Edit: Wiring change completed.

 

[Zwy]

When running on AOI, neutral is not bonded.

I think the problem arises from removal of the bonding screw in the inverters.

I'm a firm believer in leaving the bonding screw in, N-G bond under inverter power would be provided by the inverter.

A short from line to ground would not trip a breaker or crowbar output.

It would if the bonding screw is present under inverter power.

If ground is isolated, chassis may float to a voltage that can shock but is low current. If ground goes to main panel, the other line would go to 240V and neutral to 120V. Protection of consumer from contacting neutral usually isn't as good. Ungrounded single phase appliances will AC couple (low current) to the voltage. Grounded devices with EMI filters, and surge arrestors, will experience excessive line to ground voltage.

You ought to ensure neutral is bonded to ground. Most simply, by not switching it.

It would depend on inverter model and whether it bonds N-G under inverter power. This is why I do not advocate removal of the bonding screw in inverters that bond N-G under inverter power. Members have been removing the screw in order to eliminate objectionable current between a pair of inverters, this creates a different problem as you describe where the source is no longer N-G bonded.

 

[Zwy]

I should have been paying more attention category.

I am in the process of setting up a AIO powering a sub panel with critical loads. I wanted to be able to switch the panel back to the mains if there was a problem with the AIO setup. So I wired up a manual transfer switch with both the positive and neutral being switched. Only one problem I forgot to actually connect the wire to the neutral from the main. Should have let the coffee this morning work a bit longer. So when I flipped the power on for a quick test I had open neutral conditions. This in itself would have been OK since I had thought I had off all loads but I did not. There was a surge protector power strip with a wall wart charger that I had neglected to unplug.

Bzap! I immediately flip the power back off and start to figure out what I had screwed up. The surge strip is toast although the wall wart appears OK.

Not the most brilliant thing I have done.

A single AIO? Split phase or 120V unit? And not 120V in pairs set for split phase? Was the bonding screw present?

This should have been open circuit and devices would not operate. Either you have a wiring issue in the circuits or something else is amiss. A single AIO that is 120V does not need the bonding screw removed when feeding a subpanel.

 

[Hedges]

True, if his AOI has neutral-ground bond, then he should switch the loads neutral as well as line from grid to AOI. Keep ground continuous.

If loads were fine on AOI, blew when switched to just L1/L2 but not N of grid, all we know is AOI produced split phase (or was that single phase to one leg, other leg off?). Need to determine whether it bonds neutral to ground.

The European 220V single-phase inverters were designed to wire to grid. I think a portable AOI, like a generator, may be floated. Need to check.

 

[Mattb4]

A single AIO? Split phase or 120V unit? And not 120V in pairs set for split phase? Was the bonding screw present?

This should have been open circuit and devices would not operate. Either you have a wiring issue in the circuits or something else is amiss. A single AIO that is 120V does not need the bonding screw removed when feeding a subpanel.

The AIO was not being used. (not even wired up yet) The power was from the main and because there was no neutral when the sub panel was energized the surge suppressor blew.

I have no idea if there is a neutral ground/bond in my AIO. I would expect not since it is a sub panel for pass through. Sadly there is no wiring diagram that comes with this Easun (iSolar) unit.

So Switch neutral or not? Seems it depends.

But you made some good points Zwy and Hedges and they did correspond to how I originally planned it out. Before I turn on the AIO I may just go back to switching neutral.

 

[Hedges]

Use an ohm meter to check between Neutral and Ground of the AOI.
If it may is bonded (with power off), then you know.

It is also possible it uses a relay to bond, but I think that would only be done if it has AC input and output (like a mobile inverter/charger). Since you used an external transfer switch, I assume it has no AC input.

 

[Mattb4]

Use an ohm meter to check between Neutral and Ground of the AOI.
If it may is bonded (with power off), then you know.

It is also possible it uses a relay to bond, but I think that would only be done if it has AC input and output (like a mobile inverter/charger). Since you used an external transfer switch, I assume it has no AC input.

Understand the first part of your post but the second part confuses me. These off grid hybrid AIO use AC power in and AC power pass through when not operating under inverter power. It is powered of a breaker from the main panel.

My manual transfer switch is to allow isolating the AIO from the system and being able to power the sub from the Main.

There is no ground neutral bond at AIO when tested with meter. Without ac being turned on.

 

[Hedges]

So the AOI does act like a UPS, feed grid power through to loads, disconnect and supply power from battery when grid goes down?
But it sounds like you are also using a transfer switch bypassing it externally. Redundant, but would allow AOI to be removed.

If AOI does pass grid through, and probably can also operate stand-alone, would be good to determine what it does with neutral.
Without any of your transfer switch or sub-panel connected, you could put a light bulb between AOI output "Line" and "ground". See if it is lit with grid power applied, with grid power turned off, with grid power (and neutral, and ground) disconnected.

A DMM is high impedance, may not register clearly with isolated connections. Often, shows 60V +/- for floating 120V. A light bulb draws enough current to show if there is a hard connection or not.

 

[Mattb4]

Good idea for the test of output. These devices can be a might confusing how they handle neutral & ground out under the various methods of operation.

It is a bit redundant to have the separate transfer switch but it will allow for a quick sub panel switch to main if I need to deal with a problem hybrid system. Sometimes I like to put time between finding a problem and adopting a solution.

 

[Hedges]

I use interlocked "generator" breakers for bypass.
Costs about $50 for the sheetmetal interlock, $50 for the extra breaker.
I've also bought panels with pair of interlocked breakers pre-installed, close to $200.

 

[Zwy]

The AIO was not being used. (not even wired up yet) The power was from the main and because there was no neutral when the sub panel was energized the surge suppressor blew.

Makes a little more sense.

I have no idea if there is a neutral ground/bond in my AIO. I would expect not since it is a sub panel for pass through. Sadly there is no wiring diagram that comes with this Easun (iSolar) unit.

Which model exactly? I would say most likely it will have N-G bond under inverter power. The reason is this is most likely produced by Voltronic.

So Switch neutral or not? Seems it depends.

But you made some good points Zwy and Hedges and they did correspond to how I originally planned it out. Before I turn on the AIO I may just go back to switching neutral.

This wasn't a case of switching neutral that caused the problem but rather a case of an open neutral with L1 and L2 hot.

 

[Mattb4]

I wired the AIO (MLV 3KW-U) in this morning. I ran a series of tests and the unit does indeed provide a N-G bond when running as an inverter. I used my circuit tester that plugs into a receptacle that has simple 3 lights that display correct polarity and if there is any open ground or neutral. Everything checks out. Using my DMM I get 118vAC out to the sub panel at 60HZ. 118vAC to neutral, 118vAC to ground and 0vAC from neutral to ground.

Everything looked good so I energized various circuits (like my computer and cellular internet device) and I am up and running.

Should be interesting as the sun gets up higher and I can witness more than a small charge current. it also will be interesting to when the batteries get low and the AC pass through occurs.

New systems always leave me anxious until enough proper operation is displayed.

 

[Hedges]

In that case, 3-pole bypass switching neutral is what you want, as a redundant disconnect allowing AOI to be removed.
Interlocked "generator" breaker wouldn't provide that.

Is this the inverter?

ENF Ltd.

Easun Power Technology Co., Ltd. Solar Inverter Series ISolar MLV-U. Detailed profile including pictures, certification details and manufacturer PDF

www.enfsolar.com

Battery lithium with BMS? Have you checked out high/low voltage settings of AOI, that they fit battery range and don't force disconnect?

 

[Mattb4]

That looks like my unit. I am presently running SLA batteries. 2 - 12vDC at 100ah in series for 24vDC. I am going through the settings. Preference is SBU. I raised the Batt to utility set point from 23v up to 24.2 volts since I do not want to run these batteries down greater than 50% . I selected FLA for battery type. My max charge current is 30 amp. My max AC charger current is 25a.

Thanks for your advice. Sorta went off topic from the open neutral, which was the topic of the Thread, and on to my AIO setup which seemed to confuse people that responded. Doing some searching around I see that there is many cases where open neutrals damaged equipment. Based on your explanation of how that could output 240vAC on just one hot leg. Must admit it was new to me.

 

[Hedges]

Voltage alone will be a poor indicator of SoC, because voltage drops at high current.
It also changes with temperature, and required charge voltage does, especially. Maybe if climate controlled that won't be a problem. Does AIO have battery temperature sensor and parameters for temperature coefficient?

Lead acid batteries are best off kept at float, and either shallow cycled or rarely deep cycled. Having grid available but cycling batteries means wearing them out, and they cost $0.50/kWh of cycle life. An AC powered battery charger which kicks in just below float voltage should let PV carry loads if available, otherwise the AIO acts as an on-line UPS.

Or does the AIO have a built-in charger, and can it do that?

I learned the open neutral thing as a kid, when I wired a branch from my mom's kitchen circuit to garage workbench, removing and reconnecting wire nuts with power on.

 

[Mattb4]

Voltage alone will be a poor indicator of SoC, because voltage drops at high current.
It also changes with temperature, and required charge voltage does, especially. Maybe if climate controlled that won't be a problem. Does AIO have battery temperature sensor and parameters for temperature coefficient?

Lead acid batteries are best off kept at float, and either shallow cycled or rarely deep cycled. Having grid available but cycling batteries means wearing them out, and they cost $0.50/kWh of cycle life. An AC powered battery charger which kicks in just below float voltage should let PV carry loads if available, otherwise the AIO acts as an on-line UPS.

Or does the AIO have a built-in charger, and can it do that?

I learned the open neutral thing as a kid, when I wired a branch from my mom's kitchen circuit to garage workbench, removing and reconnecting wire nuts with power on.

Oh no question that SOC of a battery under load it is hard to use voltage as a perfect indicator. However if you wait until the default low set point voltage of most of these devices you can seriously discharge your batteries. That is because the battery voltage plateaus for a long time before it drops off like a rock as battery goes low. Battery under load versus static voltages is always going to be a guessing game. My research indicates that a for a SLA 12 volt battery under load you should avoid dropping below 12.1v. Thus the 24.2 for the 2 in series.

The AIO does have a charger built in. It charges anytime the battery drops below the low set point and is operating in pass through. That is why with both solar and mains charging I needed to set the max charge current. LA batteries last longer if you avoid high rates of recharge.

There is no external cable to the battery for temp detection although it does have room temperature and inverter case temperature readouts.

There is software that installs to a computer for keeping track of all things. It connects via USB cable. I will be setting it up to run a simple Windows mini PC that is powered by a separate SCC inverter setup that I have. I already have software installed to the computer but I lack the USB to AIO cable.

 

[Hedges]

Maybe an external charger then. You want PV power used when available, but best to keep battery about 90% or 95% when grid is available rather than cycling it nightly. Otherwise, better to ignore PV power and use grid directly than cycle the battery, because battery costs maybe twice what grid power does.

The ideal setup has charger (whether PV or grid) able to put out enough power for most if not all loads, but throttles back as necessary so battery charge current remains at desired level. Does AIO have programmable battery charge current, so it harvests more from PV only if needed for inverter?

But depending on loads, just a separate battery charger to keep charging at night might keep it full enough.

 

[Mattb4]

My grid power is very much less expensive than running this solar inverter setup. It is more a hobby for me than trying to accomplish cost savings. My average gird bill is around $40/mo. That is powering everything.

If the Zombie apocalypse happens it might come in handy. Until then it is for fun.

 

[Mattb4]

It would be nice if these AIO's had a clock and time setting for when AC pass through would be utilized. Then I could turn it off for solar hours and on afterwards. Would not help necessarily for long periods of bad weather but you would not need to worry about loads depleting batteries overnight.