Inverter / sub panel question

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themcp

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Aug 25, 2018
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6
Greetings,
I am in the process of doing a lithium battery / solar upgrade, and had a question about the methodology for wiring up the new inverter (3000W, in this case).

The original idea was going to be to move the circuits (and breakers) that I want available to be powered by the inverter to a sub panel, put the inverter behind a 30 amp breaker on one leg of the main, and run from the inverter's output to the new sub panel.  Looking at the panel itself though, I'm seeing something I wasn't expecting.

Here is a picture of my breaker box: https://photos.app.goo.gl/P7V179HhnRBNBaQX8

As you can see, the label says "Max branch circuit breaker size: 20 amp".  On the other side, it says "Maximum of 20 amp branch circuit breaker for outlet receptacles".  Is it possible that there is something specific about this panel that would disallow use of a 30 amp breaker, even if it were connected to my inverter / sub panel via 10 gauge wire?  Or is it more likely that the "20 amp max" is there to protect the existing wiring in the RV from someone sticking a 30 amp breaker in and doing something crazy with the circuit?

I would have thought there would be no issue with the original plan, but the label is giving me pause and making me wonder if this setup needs to be wired differently.  Thanks, I appreciate any insight...
 
Thanks very much, I was guessing that would be the case, but it's something I wanted to be 100% sure of before moving forward.  Thank you for the reassurance
 
The problem with putting a crossover switch ahead of the existing panel (to switch between shore power and inverter power, I assume) is that it will connect EVERYTHING on the main panel to the inverter.

There are some things you don't want on the inverter because they will waste power.  Things like the air conditioners, maybe the electric side of the refrigerator and water heater, definitely the existing converter (if it's powered by the inverter it will set up a power wasting current loop from the batteries, to the inverter, then the converter and back to the batteries).

The original plan of feeding the inverter's AC input from a 30 amp breaker and putting the circuits you want it to power in a new breaker box downstream from the inverter is a good one.

The statement says "Maximum Branch Current Rating 20 amps or 20 Amp 2 pole" which implies the box buss is capable of handling up to 40 amps of current per circuit breaker position.

I'd use a 30 amp full width breaker that takes up a full breaker position, like the one for the refrigerator, to ensure you don't overload the buss by adding on a second circuit at some point.
 
Yes, the new inverter both has a built in transfer switch and is a converter as well, so some of those breakers will likely end up being unnecessary anyway (I still need to make sure that the breakers labelled inverter / converter aren't driving something other than the inverter / converter... doubtful but who knows).  The plan will be to move everything I might want while boondocking to the sub panel, then use the breakers on the sub panel to control which circuits are energized while on battery power to cut unintended waste.

We have a residential fridge, so that circuit will be coming over.  I am going back and forth between moving one of the A/C units, so that would be available in a pinch if I needed to run it temporarily on battery power.  I'll be adding a generator soon, and it seems like it might be simpler to just leave the A/C circuits where they are and run the generator if I need an A/C.  I'm planning on staying in moderate weather, but it probably makes sense to have a way to cool things down if need be.  Battery would be more convenient, but having the converter, fridge and an A/C on the other side of the new 30 amp breaker... I don't want to be tripping that all the time when plugged in to shore power.  For what its worth, I'm starting with 400AH of lithium batteries and about 1000 watts of solar.  It's a 24V system so if I decide I need more battery capacity or panels, it should be relatively straightforward to add either.

Thanks for the comments, I really appreciate them.  Please feel free to offer any commentary or opinions on my plan... I've been doing a lot of learning, reading and talking with the company that is helping me design the system, but I'm still quite new to this.
 
Lou Schneider said:
The problem with putting a crossover switch ahead of the existing panel (to switch between shore power and inverter power, I assume) is that it will connect EVERYTHING on the main panel to the inverter.

There are some things you don't want on the inverter because they will waste power.  Things like the air conditioners, maybe the electric side of the refrigerator and water heater, definitely the existing converter (if it's powered by the inverter it will set up a power wasting current loop from the batteries, to the inverter, then the converter and back to the batteries).
Click to expand...

Most of the things you describe - the air conditioners, the water heater - couldn't run off the inverter if your life depended on it.  You are absolutely right about the current loop between the converter and the inverter.

Basically, you turn off the circuit breakers to the stuff you don't want to run when you are on the inverter.

My real world concern here is the problem of moving wires from one panel to the other.  How many circuits are moving? Will the wires all be long enough to reach the new panel?  Will you be trying to splice on extensions?  Shortening wires that are too long? Are you going to end up with a spaghetti-like mess of wires behind your wall?  Are you sure you won't end up starting a fire in the wall?  Or introducing a mysterious electrical gremlin that comes and goes every time you bounce down the road?  And if you don't plan correctly, and end up missing a circuit that you later realize should have been on the inverter?

This strikes me as a perfect example of a situation where the KISS principle needs to be followed.  You're trying to re-invent the wheel, here.
 
Optimistic Paranoid said:
Most of the things you describe - the air conditioners, the water heater - couldn't run off the inverter if your life depended on it.  You are absolutely right about the current loop between the converter and the inverter.

Basically, you turn off the circuit breakers to the stuff you don't want to run when you are on the inverter.

My real world concern here is the problem of moving wires from one panel to the other.  How many circuits are moving? Will the wires all be long enough to reach the new panel?  Will you be trying to splice on extensions?  Shortening wires that are too long? Are you going to end up with a spaghetti-like mess of wires behind your wall?  Are you sure you won't end up starting a fire in the wall?  Or introducing a mysterious electrical gremlin that comes and goes every time you bounce down the road?  And if you don't plan correctly, and end up missing a circuit that you later realize should have been on the inverter?

This strikes me as a perfect example of a situation where the KISS principle needs to be followed.  You're trying to re-invent the wheel, here.
Click to expand...
I agree with Optimistic completely. :))
 
Optimistic Paranoid said:
Most of the things you describe - the air conditioners, the water heater - couldn't run off the inverter if your life depended on it.  You are absolutely right about the current loop between the converter and the inverter.

Basically, you turn off the circuit breakers to the stuff you don't want to run when you are on the inverter.

My real world concern here is the problem of moving wires from one panel to the other.  How many circuits are moving? Will the wires all be long enough to reach the new panel?  Will you be trying to splice on extensions?  Shortening wires that are too long? Are you going to end up with a spaghetti-like mess of wires behind your wall?  Are you sure you won't end up starting a fire in the wall?  Or introducing a mysterious electrical gremlin that comes and goes every time you bounce down the road?  And if you don't plan correctly, and end up missing a circuit that you later realize should have been on the inverter?

This strikes me as a perfect example of a situation where the KISS principle needs to be followed.  You're trying to re-invent the wheel, here.
Click to expand...

This is interesting... I will look into the crossover switch option.  Cable lengths and that kind of thing aren't an issue in my situation, the breaker box happens to back right up to the front basement area where there is a ton of room (relatively speaking) to work, but your point is well taken and if there is a simpler way from an installation standpoint I am certainly interested in exploring it.  The fewer things I need to change, the better, and I'm perfectly fine with manually selecting breakers while on battery power, in fact I'd prefer to do it that way if I can.

Off the top of my head, I'm not sure how this would be wired... the inverter has one 120V AC in / out, and obviously the main panel is driven by two, one for each leg.  Even with a crossover switch, would it be possible to drive both legs of the main panel with the inverter?

Thank you for the suggestions...
 
You need 120V to the inverter.  Each leg in the main box is 120V.  Pick a leg, either leg, and feed the inverter.  You asking for real trouble if you attempt to use both legs for feed lines, and overcomplicating a simple job.

Run your 30A breaker from the main panel to the inverter, through the auto transfer switch, and to your sub panel.

Do not attempt to run A/C or water heater from the inverter.  They will drain your batteries very quickly!

Obviously, your existing converter becomes excess baggage, as does that circuit.

Note SeilerBird is a licensed electrician.  I am not.
 
Specifically, what make and model inverter are you talking about?  I'd want to look at the manual for it before I could comment further.
 
It's this one here: https://www.aimscorp.net/3000-Watt-Pure-Sine-Inverter-Charger-24-Volt.html

The manual is here: http://www.aimscorp.net/documents/PICOGLF10w-60w%20071618.pdf

Please don't feel obligated to look, but I would be interested to hear what you think.  My ideal setup would have been to put the inverter between my generator / shore power ATS and the main, and flip breakers to choose what is on when I switch to battery power.  The options I was given to do it that way seemed... less than ideal, but that doesn't mean a better way doesn't exist.  Thanks very much
 
I'm going to take a look at it as much for personal curiosity as a desire to be helpful.  But I must warn you that my personal experience is all with 15 and 30 amp service, I have no personal experience with 50 amp, so I don't know how helpful my comments might be.

Of course, a first step is to figure out which hot line each of the circuits draw their power from.  I was sort of under the impression that the second hot was there primarily to power the second air conditioner, but that may be totally off.  But hey, 50 amp coaches often come with built in inverters, so ther's got to be a way to do this.
 
OK, I've had a chance to look it over.  The manual shows three different AC wiring options:  option 1 is single phase, options 2 and 3 are split phase.  Unfortunately, the model inverter you have - you already bought it, right? - shows it only works with option 1, the single phase.  You would need one of the other models to support both phases of the 50 amp service.  So I guess it can only support one phase or the other.

The manual also shows it has automatic features to switch over if the shore voltage goes too low.  That makes me wonder if the inverter would try to power one side while the other side still got shore power?  I'm not sure whether you would blow up the inverter in that case.  If it was me, I would definitely go with the aftermarket manual switch rather than the built in automatic switch.

Maybe SeilerBird will look at the manual and weigh in . . .
 
Optimistic Paranoid said:
Maybe SeilerBird will look at the manual and weigh in . . .
Click to expand...
I am pretty weak on inverters. I was a residential wireman, I wired houses. I looked at the manual I don't like any of the three options. I think you should wait until Gary weighs in on this, he knows a lot more about it that I do. :(
 
themcp said:
Greetings,
I am in the process of doing a lithium battery / solar upgrade, and had a question about the methodology for wiring up the new inverter (3000W, in this case).

The original idea was going to be to move the circuits (and breakers) that I want available to be powered by the inverter to a sub panel, put the inverter behind a 30 amp breaker on one leg of the main, and run from the inverter's output to the new sub panel.  Looking at the panel itself though, I'm seeing something I wasn't expecting.

Here is a picture of my breaker box: https://photos.app.goo.gl/P7V179HhnRBNBaQX8

As you can see, the label says "Max branch circuit breaker size: 20 amp".  On the other side, it says "Maximum of 20 amp branch circuit breaker for outlet receptacles".  Is it possible that there is something specific about this panel that would disallow use of a 30 amp breaker, even if it were connected to my inverter / sub panel via 10 gauge wire?  Or is it more likely that the "20 amp max" is there to protect the existing wiring in the RV from someone sticking a 30 amp breaker in and doing something crazy with the circuit?

I would have thought there would be no issue with the original plan, but the label is giving me pause and making me wonder if this setup needs to be wired differently.  Thanks, I appreciate any insight...
Click to expand...



There are several ways you can do this,

1. split the panel and power those loads with a 120 V inverter/charger/transfer switch unit, lots of extra work..
2. fit a 240 split phase inverter/charger/transfer switch unit to the panel input, much easier..


I fitted a combined 120 V charger/inverter/transfer switch when I converted over to 48 Volts, it powers the whole TT.
my system is only 30 Amp single phase though.

The Aims will only do item 1 above. you will need a Victron Multiplus, Schneider or Magnum for 240V split phase.




I would concur:-

from SeilerBird, "What it is saying is that outlet receptacles should be 20 amp maximum. It is poorly worded."




 
I'm looking into the split phase 240 option now... that'd certainly be simpler.  With an inverter like that, I wonder what happens in the internal transfer switch when you're plugged into 30 amp service and getting 120V on the neutral instead of on both hots.

Thanks again, still researching...
 
With an inverter like that, I wonder what happens in the internal transfer switch when you're plugged into 30 amp service and getting 120V on the neutral instead of on both hots.
Click to expand...
Huh?  The neutral is neutral, whether 50A/240v or 30A/120v.  The voltage between a hot wire and the neutral is 120v in either case.
 
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