Connecting 24v inverter to 240 panel.

[laird.small]

Hi all, I'm new here to the forum so thanks in advance for any help. I'm putting a solar system on a small off-grid cabin. An all-in-one 24v 3000w inverter with 240 ac output. The cabin has a a 240v panel box with just two breakers...one for the house and one for the well pump (picture attached). Currently the panel has 2 black and one green wire coming from the generator hookup. I'm trying to figure out the best way to tie in the inverter since it only has 2 ac outputs...Line and Neutral. Not sure what to do about the ground. Do you just run a wire off the ground post of the inverter? Also, aren't the two existing black wires in the box both hot? Not sure if the Line/Neutral coming from the inverter are the same. Thanks for any advice.

 

[iamrich]

Is your cabin wired for 240v outlets and appliances? I don't know much about 240V, but it looks like your box has x2 120v lines feeding the breakers to get you to 240v and double pole breakers that may or may not be feeding 240v items.

 

[laird.small]

Is your cabin wired for 240v outlets and appliances? I don't know much about 240V, but it looks like your box has x2 120v lines feeding the breakers to get you to 240v and double pole breakers that may or may not be feeding 240v items.

Thanks iamrich. Good point. The outlets in the cabin are just normal 110 outlets. I know the two black wires into the panel are coming off of a 4 prong male 220 cord that plugs directly into a Generac. Are the 2 hots wires from the generator just 120v each?

 

[iamrich]

I don't know, but that is the way it looks to me. If that is the case, I don't think your panel is really wired for 240v. I wonder if each of the wires coming out of the breaker is just 120v. Can you put a multi meter on the output and see what the AC voltage is?

For your all in one, I don't know how you can convert 240v into this panel. What model did you end up with?

 

[laird.small]

The All-in-one is similar to yours (MPP LV2424?) but 3000watts and a 230 ac output. I'm heading over there tomorrow and will see if I can put a volt meter on the outputs. Thanks again, and I'll keep you posted.

 

[Hedges]

Couple of funny things I see:

From the generator, 2 black wires plus one green. Green goes to the neutral. Do you have 240V between the two blacks, 120V from each to the green?

I think I see a screw bonding neutral bar to box, so that is your single point of connection. That should be OK.

Only one ground wire going to ground busbar. That means either pump or the house has ground, not both. Both ought to get a ground wire.

There ought to be a ground rod also wired in.

It appears pump gets no neutral, house gets a neutral. That is OK.

Now, if you are going to have two sources (Generator & inverter) you can't connect their outputs together without risking damage to one.
Possible solutions:

1) Feed generator into AC input of all-in-one (assuming it has one), and feed all-in-one to box.
2) Add a transfer switch to choose between them.
3) Add two more breakers, with interlock so only one can be closed at a time. Use each to backfeed one of the sources to busbar.
4) Feed panel with a cord & plug. Plug it into selected source.

Your all-in-one is 240V only?
That has a chance of running the pump, if it can deliver enough current. 3000W might start a 1/2 HP pump.
It won't work for 120V loads in the house if it doesn't have a neutral. You need to add a transformer to turn it into split-phase.

 

[laird.small]

Thank you very much for taking to time to look at it. Much appreciated. Yes, the all-in-one is 240V output only. I thought the same thing...maybe just use it for the pump. Could I just tap into the two wires in the panel that go to the pump? (someone also suggested a step down transformer for the panel, but I'm not sure if that's a good idea).

I had also considered your other suggestion: to use the generator for the AC inputs on the inverter. So maybe I'll try that first. Do you have a transformer recommendation to run the 110 outlets in the house (from the box)?


Thanks again for the help!

 

[Hedges]

Could I just tap into the two wires in the panel that go to the pump?

You should still have a way to ensure the breaker panel isn't wired to the inverter. Some kind of a DPDT transfer switch, plug and cord, etc.
But I don't know if your inverter can start the pump. Induction motors draw a huge surge current, about 5x their nameplate current.

I had also considered one of your other suggestions: use the generator for the AC inputs on the inverter. So maybe I'll try that first. I guess my other question is how to bring the inverter ac outputs wires into the panel since I only have a Line and Neutral. There's a ground post on the bottom of the case but I'm not sure if I can use that. (I'll attach a picture). Maybe I need a step down transformer(?)

The inverter may have a "neutral" that is tied to chassis, and it may just have two isolated hots.
It is even possible its chassis is a midpoint between the two hots, i.e. a neutral. Some cheap 120V inverters are actual +/- 60V.
Check voltage to chassis and see what you've got.

Do you have a transformer recommendation to run the 110 outlets in the house (from the box)?

Depending on whether inverter outputs are isolated or have a connection to battery or chassis, different transformer types might be considered.
An isolation transformer, 240V in, 120/240V out (or two isolated 120V secondaries) is one approach.
A non-isolating 120/240V transformer (or a 120V to 120V isolation transformer wired as such) would be half the mass for same VA rating (because only half the power goes through magnetics, the other half is direct wired.)

You need to determine what wattage loads you want to run. And if any are motors requiring surge capability.
I mostly shop on eBay, look for something with suitable voltage windings and VA ratings. Toroid transformers tend to be more efficient.

 

[laird.small]

Thanks again for the info. I hooked a generator up to the panel today and you're right, the well pump is a pretty big load. The generator handled it fine, but you could definitely tell when it was turned on. Made me wonder if my solar system could run it. I'll take a look at some of the stuff you suggested on ebay and will check back with any questions. Wish I knew half as much as you do!

ps. I hooked up a voltmeter to all the wires in the panel while the generator was going. The far left and far right black wires (on the bus bars) are 240V together. Every other combination is 120V. That seems about right, doesn't it?