Back2Basics: My Genset is 240V,. Does that matter for my Inverter selection?

Old_Skewler

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I am a little lost on the basics and need some help and clarification: I have a 12 kW Genset which outputs 240V. My understanding is that the electrical panel is wired in split phase format and balanced thru load distribution: some circuit breakers take one of the hot legs to neutral while the other breakers take the other hot leg to the neutral. This statement could not be 100% accurate but I can visualize what is happening. I think I understand the above concept despite not being able to explain it correctly.

But now here is my question: having the above setup, what does that mean when looking for an inverter? Is it relevant at all or it does not change the inverter specs to work with the generator? If it is relevant, what metric on the inverter should I be concerned in order to have:

1. the generator, which outputs 240V split phase, to connect to the inverter
2. the existing electrical panel wiring, which is wired as described above.

As I am trying to ask this question, I don't even really know what I am asking. I guess I am researching inverters for this application but I am not sure what my existing 12 kW Generator wired in split phase means to the possible inverter selection. If anything at all.

Could someone shed some light here?

Thanks in advance.
 

Hedges

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If your generator is 120/240V split-phase, you can use it with a 120V only inverter or a 120/240V inverter (or stacked 120V inverters that synchronize with each other.) Several brands will let you parallel for more watts.

You might run the generator occasionally for 240V loads, have inverter just put out 120V for smaller loads.

If you go with an AC coupled system (battery inverter and separate grid-tie PV inverters that controls), most of those are 240V.

You can also use a 120V/240V auto-transformer to transfer power from one leg to the other.
 

boondox

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You need to read the specs of your inverter and make sure it is capable of charging from split phase 240.

And be aware that many gensets that are designed for 240 will only be able to put out 1/2 the rated wattage at 120.
 

Old_Skewler

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If your generator is 120/240V split-phase, you can use it with a 120V only inverter or a 120/240V inverter
That is about how much I was able to retain from your reply, the rest was not clear enough to my level of knowledge.

Is there a preference in inverter type for a generator that is 120/240V split-phase? Is one better than the other or it literally does not matter which inverter I choose, as long as the inverter is 120V or 120/240V?
 

Old_Skewler

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You need to read the specs of your inverter and make sure it is capable of charging from split phase 240.

I do not have the inverter. All I have is the Generator 240V with split-phase service in the cabin. The question is exactly which inverter metric I should be paying attention to in order to match properly with my existing generator.
 

boondox

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Well, the reason you would hook a generator to an inverter is so that the inverter can use the generator to charge your batteries if there is not enough sun. So look into the charging specs of prospective inverters t make sure that it can use a 240, split phase input. I use magnum inverters and they support 240. Since you already have the generator, just make sure the inverter can use it.

EDIT: When looking through the inverter information, look for terms like "ac in hot 1 and ac in hot 2". I think that is how Magnum puts it.
 

boondox

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as long as the inverter is 120V or 120/240V?

I meant to add, yes it does matter. As I stated above, if you get a 120VAC input inverter your 12kW generator will only be able to put out a max of 6kW. In practical terms even less, say 5kW continuous. This is because you will only be using one side of the generator winding.
 

Old_Skewler

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Well, the reason you would hook a generator to an inverter is so that the inverter can use the generator to charge your batteries if there is not enough sun. So look into the charging specs of prospective inverters t make sure that it can use a 240, split phase input.
Thank you for clarifying these relationships.

Follow up question: my generator is currently wired to the service panel, 240V split phase service. When I add the inverter, which I will make sure to get an inverter which supports 240V, will I simply re-wire the generator directly to the new inverter and then from the inverter back to the existing split-phase electrical service? Is this what is about to happen?

In other words, I need to add the inverter between the existing generator and the existing electrical panel? Am I getting this correctly?


I use magnum inverters and they support 240. Since you already have the generator, just make sure the inverter can use it.

EDIT: When looking through the inverter information, look for terms like "ac in hot 1 and ac in hot 2". I think that is how Magnum puts it.
Thank you!

Would you recommend a Magnum inverter for my application?
 

Old_Skewler

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I meant to add, yes it does matter. As I stated above, if you get a 120VAC input inverter your 12kW generator will only be able to put out a max of 6kW. In practical terms even less, say 5kW continuous. This is because you will only be using one side of the generator winding.
Got it.

So it makes sense to get an inverter that can fully use the full power of the generator. And the full power of the generator only comes in 240V spit-phase.

So when I look at inverters, other than Magnum, I should be looking for the option for 240V input AC. Is that correct?
 

boondox

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Well, if you have a generator currently hooked up, I assume and hope that you have a transfer switch? How to hook it up will depend so we need more information.

I really like my Magnum inverters. I have two in parallel. If one craps out (been running for almost 10 years non stop) I can get by on the other. Magnum also makes really nice panels and boxes that make it really easy to do a clean, safe install. They are not the cheapest by any stretch though. I have a couple of nits with the control system. But overall, I can recommend Magnum.
 

boondox

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Got it.

So it makes sense to get an inverter that can fully use the full power of the generator. And the full power of the generator only comes in 240V spit-phase.

So when I look at inverters, other than Magnum, I should be looking for the option for 240V input AC. Is that correct?

Yes.
 

Old_Skewler

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Well, if you have a generator currently hooked up, I assume and hope that you have a transfer switch? How to hook it up will depend so we need more information.
This is what I currently have and how it operates:

- Kohler 14kW Generator, hooked to a 12V car battery, to power the gen electronics. A small solar panel to keep the small generator battery running. All of this in a shed 50 feet away from the cabin.
- The generator has a breaker on it, stays on when I am using the cabin (when I leave the cabin for long periods of time I turn off the breaker in the generator and set if to OFF mode).
- The generator has basically three modes of operation: OFF / AUTO / ON
- When I am home I try to leave it in AUTO mode, meaning I have a switch INSIDE the cabin that I can turn on to run the generator when needed.
- Sometimes the generator switch does not work, so I go outside and physically put it on ON mode. I'll ask for help with this another time.
- The generator is wired DIRECTLY to the electrical service panel inside the cabin: 240V in (3) wires comes in from the generator straight to electrical panel then multiple breakers in split phase - whatever is the correct language to describe this.
- From the electrical panel, it goes directly to the house circuitry.

I do not believe there is ANY transfer switches. To be honest, I am not sure where or what would be transferred, since I do not have any other source of power at the cabin.

Could you tell me if the above description of my existing electrical system makes sense? Please let me know if I missed anything and whether this is clear.


I really like my Magnum inverters.
It seems like you are not alone.
 

boondox

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Ah, so it sounds like you do not have mains power at the cabin? If so, then no transfer switch needed.

If that is so, then what you would do is disconnect the generator from the panel and connect it to the AC input of your inverter. When you need the generator, fire it up. The inverter will then charge the batteries and go into "pass through" mode. What pass through mode is that while you are running the generator, all AC loads will come from the generator, not the inverter. This is because the inverter cannot charge the batteries and invert at the same time, since it uses the same circuits to do so. It also means that you want to set your inverter to charge at a rate that leaves some generator capacity available to run whatever else you need to run while charging. If you overload the generator then the voltage and frequency will drop and the inverter will kick it off line.

Here is an example of that. I have a 7.5kW generator. Really I don't want to pull more than 6.5kW continuous as I want the genny to last a long time. I usually charge at 4kW so I have 3.5kW overhead. That way if I turn on the coffee pot or the water pump kicks on the generator can handle the load. On the odd occasion that I over load the genny, the system kicks it off line and goes back into inverter mode. A few minutes later it tries again and repeats until the genny can handle the load.
 

smoothJoey

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@Old_Skewler its unusual to have a 240 volt generator in North America that only has 3 wires.

Typically a 120/240VAC split phase capable generator would have 4 wires.
Hot1, Neutral, Hot2 and ground.
If yours does not have 4 wires I think we should get some more details about it.
The exact make and model will help.
Pictures of the connections at the generator are also good.
Finally a picture showing your distribution panel and how the generator is wired to it.

Now to explain 120/240VAC split phase.
In North American residential mains power is 3 wires from the power company transformer.
Those wires are Hot1, Neutral and Hot2.
Hot1 and Hot2 are connected to the ends of the transformer winding.
Neutral is connected to the center of the transformer winding.
Voltage between Hot1 and Hot2 is 240VAC.
Voltage between either of the Hots and Neutral is 120VAC.
I don't want to get into the weeds talking about ground yet but there should be one to your generator even there is not to the power company transformer.
I'll explain about ground in another post if you are really curious.

Looking forward to more info on your generator and how it is connected.
 

Old_Skewler

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Ah, so it sounds like you do not have mains power at the cabin? If so, then no transfer switch needed.
I thought so too.

If that is so, then what you would do is disconnect the generator from the panel and connect it to the AC input of your inverter.
Thank you, I thought that was the case but needed validation.

When you need the generator, fire it up.
Please clarify whether this could be automated. My hope (and dream) is that the inverter should be able to monitor the battery voltage and if it drops below a certain preset, it would send a signal to run the generator.

Am I tripping here or is this possible to achieve? I am hoping this is doable. The way you wrote it, it seems like a manual switch.

The inverter will then charge the batteries and go into "pass through" mode. What pass through mode is that while you are running the generator, all AC loads will come from the generator, not the inverter. This is because the inverter cannot charge the batteries and invert at the same time, since it uses the same circuits to do so.
Really? Is this true for every inverter OR just some? I was under the impression I should be able to fast charge the batteries when the generator runs and satisfy AC loads at the same time.

Could you please expand on what you said and whether is 100% applicable to all inverters or not? Or maybe I am not understanding what you meant to say. It sounds like you said that if the Generator is running, I can't charge the batteries and use AC power in the cabin?

It also means that you want to set your inverter to charge at a rate that leaves some generator capacity available to run whatever else you need to run while charging.
How is that achieved? How do I control the charge rate of the inverter?
 

boondox

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@Old_Skewler its unusual to have a 240 volt generator in North America that only has 3 wires.

Typically a 120/240VAC split phase capable generator would have 4 wires.
Hot1, Neutral, Hot2 and ground.
If yours does not have 4 wires I think we should get some more details about it.
The exact make and model will help.
Pictures of the connections at the generator are also good.
Finally a picture showing your distribution panel and how the generator is wired to it.

Now to explain 120/240VAC split phase.
In North American residential mains power is 3 wires from the power company transformer.


Looking forward to more info on your generator and how it is connected.
Good catch. We need to know more.
 

boondox

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I thought so too.


Thank you, I thought that was the case but needed validation.


Please clarify whether this could be automated. My hope (and dream) is that the inverter should be able to monitor the battery voltage and if it drops below a certain preset, it would send a signal to run the generator.

Am I tripping here or is this possible to achieve? I am hoping this is doable. The way you wrote it, it seems like a manual switch.


Really? Is this true for every inverter OR just some? I was under the impression I should be able to fast charge the batteries when the generator runs and satisfy AC loads at the same time.

Could you please expand on what you said and whether is 100% applicable to all inverters or not? Or maybe I am not understanding what you meant to say. It sounds like you said that if the Generator is running, I can't charge the batteries and use AC power in the cabin?


How is that achieved? How do I control the charge rate of the inverter?

Yes, you can have auto-start for the generator.

I can't speak for EVERY inverter. Pass through mode is common. It does NOT mean that you can't charge your batteries AND use AC in the cabin. It means that the AC will be coming from your generator and not the inverter. This means that the draw from charging and the loads running cannot exceed the capacity of the generator.
 

Hedges

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Consider diagram at end of this data sheet. Ignore utility grid and transfer switch, which you don't have.


Sunny Island will connect to generator, pass through AC to loads and charge battery (up to 56A AC input.)
(There are a few stupid inverter designs that can't charge batteries during pass through. But SMA and many others function well.)

Sunny Island has a relay it uses to auto-start the generator based on battery depth of discharge. At night, it will wait longer to avoid noise.
A dual Sunny Island plus Sunny Boy system would work well, but is not cheap. MSRP about $15k for two, 6kW Sunny Island and two, 6kW Sunny Boy. You can probably get it for half that price.
Some other brands have hybrids which perform all the desired functions for less money. They may not be as durable or able to start heavy motor loads.
 

Old_Skewler

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@Old_Skewler its unusual to have a 240 volt generator in North America that only has 3 wires.

Typically a 120/240VAC split phase capable generator would have 4 wires.
Hot1, Neutral, Hot2 and ground.
If yours does not have 4 wires I think we should get some more details about it.
The exact make and model will help.
Pictures of the connections at the generator are also good.
Finally a picture showing your distribution panel and how the generator is wired to it.
Brother, I thought I was understanding everything but now you threw a wrench and sent my head spinning!

I went to the basement and double-checked: you are correct, (4) wires come from the genset, (3) insulated (black, red, white) and an uninsulated copper wire. Picture attached as requested.

I didnt realize the uninsulated wire was actually a piece of the puzzle.

And for the record, the generator is a Kohler 14RESA
 

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