Check my work! Wiring a changeover switch to bypass my inverter

[MrMike]

Hello!

I have an RV with a 1000w solar system using an EG4 3k 48v inverter and 2 100ah 48v EG4 Lifepower batteries. The RV gets rented out, so I want a safe way to bypass the inverter so the RV only uses shore power (renters shouldn't be responsible for the health and welfare of this solar system). Here's how I'm thinking of wiring in a manual changover switch to either use the inverter or bypass it completely for renters.



My concern is when the system is on POS 2, Shore power only. The manual changeover switches on the market don't have enough terminals to cutoff the ground wires - so the inverter ground both for AC in and AC out would be bonded back to the shore power ground. Since the hot/neutral are definitely switched off, there shouldn't be a problem with ground loops - but I'd like anyone with more experience with these EG4 inverters to have a look and check my assumptions.

Thanks!

 

[chrisski]

Does EG4 have an off
switch? Most inverters have a two wire jumper that a switch can be added for on off.

I’d also want something a curious renter can’t access.

I don’t know what the two AC attachments are for AC power. I’m assuming one is a grid input and the other a generator.

I

 

[MrMike]

The NEMA 30A plug at the bottom is the 30A shore power - the "To RV Loads" at the top goes to the RV breaker box. Does that answer your question? Also - this whole system is secure - renters cannot access it.

 

[chrisski]

So you want an interlock switch like shown on the top two breakers on the left side of the pic that can bypass the inverter all together?


The two circuit breakers can be off, but only one can be on at a time.

This is a more detailed block diagram of what it does.

Both those pics are from my Outback Radian. Not sure how different your EG4 is.

I do think you are pretty brave to rent out an RV with a solar build.

 

[MrMike]

Yeah that's the general idea, but I'm looking for guidance particular to the EG4 inverter and how it handles bonding those grounds to shore power. But instead of switching power inputs like you would for a house, I'm bypassing the inverter completely when I want the RV to only use shore power, not the inverter.

 

[brainbone]

My concern is when the system is on POS 2, Shore power only. The manual changeover switches on the market don't have enough terminals to cutoff the ground wires

Maybe a 3 position rotary switch would work?

Amazon.com

Amazon.com

 

[MrMike]

A three position rotary manual transfer switch is my plan - This one from Heschen. My question isn't about the switch, its about the bonding of the ground wires when the switch is in POS 2. Can anyone find an issue with that diagram?

 

[MrMike]

Maybe @EG4TechSolutionsTeam has some tips for me?

 

[pvgirl]

There's no reason to switch the ground, just connect them all together.

 

[brainbone]

Can anyone find an issue with that diagram?

I would ask EG4 directly, or the vendor you got it from if they provide support, but I don't really like the idea of neutral bond on the output of the EG4 if the EG4 were to be inadvertently turned on while operating in POS2. Seems wrong to me, but again, I'd really only trust EG4's opinion on the matter.

Edit: A 5 phase rotary switch should give you enough contacts to switch grounds as well, if you can find an enclosure that fits your space. (Don't switch those 63A rotary switches when under load.)

 

[MrMike]

It would be ideal if the system were completely idiot proof - since I'll likely be the idiot in question. Whether the EG4 is on or off, and the transfer switch is in POS 0, 1, or 2, should not damage the system, backfeed power to the grid, or risk a fire.

 

[brainbone]

This switch should give you enough contacts to switch grounds, then you don't need to worry about it:

Amazon.com

Just need to find an enclosure that fits it.

I know mobile use of the EG4 isn't technically supported (I believe in part because of the way it bonds neutral), so when seeking advice from EG4 or the reseller, probably shouldn't stress your use of it in a mobile application.

Edit:
What about just letting them use the inverter? Is there anything they really need to monitor? Possibly just set the EG4 to cut off at a higher state of charge along with a sticker on your A/C(s) and microwave explaining the limitations of running from battery only without being plugged into shore power?

 

[MrMike]

I think to do this right I'd need a six-phase, 24 terminal switch to support 3 conductors each for the AC in and AC out of the inverter, wouldn't I?

 

[brainbone]

You may be right, didn't take the time to scribble it out, just added one to the 4 phase you selected, though I'm guessing you weren't switching ground at all in that case. If so, this beast:

https://www.amazon.com/Universal-Changeover-Positions-Terminals-Generators/dp/B096VQSV2K

 

[Rocketman]

I don’t think you need to switch the grounds , just the blacks & whites. (The white wires will prevent the extra ground loop - if I am thinking about it correctly).

Maybe look at air conditioning relays - or something like that for 12v (or even a 12v to 24v converter) - three sets of 2-wire ones will give you the six needed wires.

Using a 24v on-off-on switch wire them for position 1 & #2 - with off being 120v moves nowhere in your system. (I don’t know the power draw of those relays - maybe too much).

Good Luck

 

[brainbone]

I don’t think you need to switch the grounds , just the blacks & whites

Ideally, you would always keep all grounds tied together, but I don't believe the EG4 has the option of disconnecting its neutral bond, which potentially could be an issue. Switching the ground isn't a great idea, but nor is having the EG4 neutral bonded at the same time as shore power, even if the neutral and hot is disconnected from the EG4.

In short, I don't see a great option for bypassing the EG4 in the case where it could inadvertently still be on, but fully isolating it may be the better one if bypassing is absolutely required and there's no way to float its neutral output? (I still think the easiest/safest solution is to just let the renters use the EG4.)

Edit: Doesn't the EG4 have what is effectively an integrated bypass mode? Why not just use that?

 

[MrMike]

The EG4 does have a simple on/off switch, but all that does is turn the inverter off - the EG4 will still charge batteries, but even if you have shore power plugged in no AC power will make it to the load (maybe there's a config setting to change that behavior?)

 

[brainbone]

Looks like there isn't a way to just shut off the inverter on the EG4 yet allow shore power to pass through. Not sure why charging the battery from AC would be a problem, but pretty sure there's a setting to charge only from solar, though I wouldn't do that. You could also set the low voltage cutoff to its maximum (~54v), basically disabling the inverter after very minimal use when not on shore power... though I'm still confused why letting the system just run is a problem? Are you afraid of them damaging the batteries somehow?

 

[MrMike]

The problems happen when the house batteries run into a low voltage situation - such as what would happen if you were camping off-grid and you had a couple of days of bad weather. Basically the system goes into an alarm state, beeping like mad to alert you of the problem, but I don't trust a renter to be able to deal with that properly. Best to bypass the inverter so the only AC power they can get is from shore power or a generator.

 

[brainbone]

Basically the system goes into an alarm state, beeping like mad to alert you of the problem

Skimming over the manual for the EG4 3000EHV-48, I think you can easily mute/disable the buzzer and set the auto restarts for overload and overtemp. Could use the dry contacts to light up a remote LED labeled "Battery empty. Please plug me in!" on low battery state, if you don't have a remote display for SOC already.