I plan to switch my air conditioning from 120 volt to 240 volt. Therefore, I need to either use an autotransformer for my A/C units, or switch my generator to 240 volt. I am most likely to switch my generator to 240 volt. How do I deal with most/all of my 120 volt load being on one leg of the 240 volt? My inverter is 120 volt only. I know the 240 volt generator heads don't like a highly unbalanced load.
A simple rough diagram of my plans is attached. I have more 120 volt loads than shown.
Victron transformers can also be used to balance loads on a 240 ac source. Some other brands probably can as well.
One of my first thoughts was using a Victron Autotransformer directly after the generator to balance loads across the 240 volt legs. However, even though there is a 100 amp unit they have restrictions that probably make this not a great option, at least with the Victron unit. Outback Power has one, but limited to 25 amps.
The victron is 28a continuous and 32a peak imbalance. There is a 32a or a 100a model. What are the limitations you speak of? Several people have them installed exactly for the purpose you speak of. If you have questions or concerns that are not covered in the manual you might try the victron forum for some answers.
Do you have two 120 volt hot legs coming off your genny output now?
If yes, you have 240v available.
Unless they are both on the same phase
David
I would call Jason at Wirco most of Dick's generators had 2 -110 volt leads, I called Gary for you, but he couldn't remember if yours did or not
I already talked to Justin at Wrico maybe a month ago. At the time I was more focused on using an autotransformer to take the 120 and change it to 240 for the A/C units than changing the generator to 240. It has been suggested to change the generator to 240 volt instead.
Justin was surprised I am using 120 volt as he shipped the generator as 240 volt. I followed the instructions in the manual to convert to straight 120 volt. One of the things I had to do was to tie the two legs together at the 50 amp breaker in the genset. Since I had no 240 volt loads I wanted to only do 120 volt. I am running two legs out of the generator from the two pole breaker, but they are each sized for 50 amps. The double pole breaker will trip if I use too much power on one leg, but I only had that happen once. I have spread the loads across the two legs as much as possible.
The limitation with the Victron Autotransformer is how much current you can have on the neutral. Even the 100 amp model has the same limit as the smaller one.
Quote from: David Anderson on November 11, 2025, 05:19:20 PM
Do you have two 120 volt hot legs coming off your genny output now?
If yes, you have 240v available.
Unless they are both on the same phase
I have two 120 volt legs on the same phase. I followed the instructions in the Wrico manual to convert to 120 volt. It would be easy to go back to 240 volt.
Switch back to 240 volt then. You will still have 120 volt on each leg (phase) in your panel. Nothing changes. You still get 50 amps on each leg.
Buy a 2 pole breaker and you have 240v to power your new air conditioning.
David
I could have the generator converted to 240 volt in less than 30 minutes. The conversion of the generator to 240 volt is not my concern. It is basically removing a jumper across the 50 amp double pole breaker, and moving a wire to a different spot on the terminal strip. I would not have to change anything else in my electrical system to switch to 240 volt.
My concern is in my current electrical setup essentially all of my 120 volt load would be on one leg of 240 volt. There could be up to 40 amps of 120 volt on one leg. 240 generator heads don't like a highly unbalanced load. I am trying to figure out how to deal with the unbalanced 120 volt load, or maybe it doesn't matter as much as I think it does. If I do a Google search there are plenty of web sites that state an unbalanced load can cause the generator head to overload. I attached a rough diagram of what my new setup would look like to my original post.
We run our Onan with unbalanced loads. The built in circuit breakers will protect the generator head from overload. When unbalanced the unit vibrates a little more but has never been an issue beyond that.
Sure, the 50 amp breaker would trip if pulling too much from one leg, but it sounds like 40 amp on one leg and no load on the leg is not good for the head. (Absolutely possibly, but improbable, if the mini splits are not in use.)
What is the total KW of yours? Knowing that would make a difference in which way to go.
Bruce
The load balance deal is why so many of the higher end RV's use a inverter type generator, they don't care about balance loads
Arrange your loads on your breaker panel to balance between the two phases as close as you can.
I put ammeters on each phase of mine so I can see the loads while driving down the road. I'm usually within 10 amps from being equal.
I installed current transformers on each hot leg to show the amp flow on the ammeters. They are analog dial meters. They have worked for 20 years.
David
Here is a pic of my ammeters and current transformers. My genny output goes through the CT's first then to the disconnect.
This is the first time I've opened the CT box in 20 years.
David
Quote from: bs4104 on November 13, 2025, 02:12:38 PM
What is the total KW of yours? Knowing that would make a difference in which way to go.
12.5 KW
Quote from: David Anderson on November 14, 2025, 05:06:11 PM
Arrange your loads on your breaker panel to balance between the two phases as close as you can.
That is the issue here. If you refer to my proposed schematic I attached essentially all of my 120 volt loads pass through my 120 volt inverter. I can't split the loads and still have them go through the inverter.
What does the other 120v leg of your genny feed now?
All my plugs in my coach go through my inverter, but all my heavy loads, four electric heaters, electric water heater, 3 AC's are evenly split on the two legs. Only front AC can pass through inverter so I can run it off my alternator with genny off.
I can balance the phases by watching the ammeters.
One could balance the phases by calculating the loads from the mfg nameplate.
David
Right now, the generator is configured for 120 volt only so it has a jumper connecting the two legs togther to balance the load across the legs.
I just studied your diagram and realized that your set up is exactly like mine. All of my heavy loads are on the 240 V panel. They are closely balanced between phases. I do not run the generator unless I'm using heavy loads
If I'm not running the generator then I just use the inverter on the batteries or I am hooked up to shore power.
I do have an automatic transfer switch.
Quote from: belfert on November 16, 2025, 08:39:21 PM
Right now, the generator is configured for 120 volt only so it has a jumper connecting the two legs togther to balance the load across the legs.
Got it.
So do you have two 120 v wires (same phase) going to each lug in your breaker panel?
If so reconfigure so each output is now opposite phase to the other with 120 v output on each leg and 240v leg to leg. Wire big 120v loads on the first panel upstream the inverter that run off genny or shore power.
Besides my rooftop air conditioners, the only 120 volt loads not going through the inverter are my electric water heater, and a dedicated circuit with a single receptacle to plug in a large 120 volt load like an electric heater.
Nearly all of my 120 volt loads go through the inverter which means the generator is loaded unevenly. The loads have to go through the inverter if I want them to be powered when on battery.
You might think of a second tranfer switch too for some of your loads
new switch control by inverter/ gen out put
Bruce
I have a Victron Multiplus II 48/3000 inverter. One option is to get a second Multiplus II that matches, and then the pair can run in split phase mode. The Multiplus II 48/3000 has something like six different product numbers even though they are all called Multiplus II 48/3000. The product numbers have to match.
My Multiplus II is somewhere between two and three years old, but I don't think I can buy a matching inverter with the same product number anymore. I might have to buy two new inverters which will put me up into the $3,000 range. I simply don't have $3,000 to spend on this right now.
Quote from: belfert on November 17, 2025, 09:16:29 AM
Besides my rooftop air conditioners, the only 120 volt loads not going through the inverter are my electric water heater, and a dedicated circuit with a single receptacle to plug in a large 120 volt load like an electric heater.
Nearly all of my 120 volt loads go through the inverter which means the generator is loaded unevenly. The loads have to go through the inverter if I want them to be powered when on battery.
I wired my coach just like yours except I'm 240V. I'm never more than 10 amps out of balance when genny is running.
I recommend the ammeters so you can monitor loads in real time. 20 plus uneventful years of usage is quality testimony.
David
My proposed setup is always going to be out of balance when any 120 volt load is used because basically 100% of the 120 volt load would be coming off of one leg.
Quote from: belfert on November 17, 2025, 10:40:01 AM
My proposed setup is always going to be out of balance when any 120 volt load is used because basically 100% of the 120 volt load would be coming off of one leg.
That's true on my setup also. However most of my inverter loads are minimal or only on a short time ie, a hair dryer or microwave. You still need to balance your non inverter 120v loads on the 240v panel upstream the inverter panel as best you can. The 240v loads if any don't require balancing. They use both phases.
That's why the ammeters are important to me. If I'm more than 10 amps out of balance I can turn on a device to load up the low amp phase to bring them closer to balance.
I looked online and found these
https://www.bluesea.com/products/9630/AC_Ammeter_-_0_to_50A_with_Coil
I think I paid about $19 each when I installed them. They've gone up in price.
It's got the wiring diagram on the site so you can see how the current transformers are wired.
Quote from: belfert on November 17, 2025, 10:40:01 AM
My proposed setup is always going to be out of balance when any 120 volt load is used because basically 100% of the 120 volt load would be coming off of one leg.
You could get a standalone charger for your battery bank and put it on the other leg.
That way, any time you are running the generator the 120V loads are on one leg and the dedicated charger is on the other leg recharging your batteries. If that would exceed the C-rating of your battery bank you can turn the inverter charger down or off which would also decrease the load on the leg feeding your inverter and 120V loads.
Do you intend to have (or do you already have) 240v shore power?
I would start by checking with the generator mfg to see whether unbalanced loads are an actual problem. Just because some people on the internet think it is, doesn't make it so.
If the imbalance is unacceptable to them, or the vibration is "too much", I feel like the most complete solution is going to be something like:
- 240v shore power
- 240v autoselect transfer switch between shore power and 240v generator
- feeding the 240v panel
- Convert water heater to 240v and connect at this panel
- 120v Victron is then being fed by one leg only, as designed
- Try it out in this configuration to check for generator vibration (as noted by another post)
- If needed or desired, insert autotransformer just before the Victron, to spread that single-leg load over the dual legs of the 240v system
- Program Victron to limit the battery charge current in order to not exceed the 28amp imbalance limit on the autotransformer. This is one of the larger loads on your 120v system and the only (?) one that is run for longer than a minute or two. Microwave ovens and hair driers are large, but short term, for example.
This has the effect of making electric water heating a non-battery function. If that's a problem, I personally would attack it by introducing either a combo electric/propane water heater or something similar. I like having two methods of heat anyway, but that's just me. I may be overthinking this part; if it's a 120v water heater it's probably something like 14 amps, so if you leave it downstream of the inverter that just means you can't run the microwave at the same time, basically; this is a not uncommon limitation even in 30-amp 120v shore power setups.
Many other options exist. I would start by checking the assumptions.
Quote from: David Anderson on November 17, 2025, 11:01:20 AM
That's true on my setup also. However most of my inverter loads are minimal or only on a short time ie, a hair dryer or microwave. You still need to balance your non inverter 120v loads on the 240v panel upstream the inverter panel as best you can. The 240v loads if any don't require balancing. They use both phases.
The only 120 volt load that doesn't go through the inverter is the water heater. I have a 120 volt connection back to an enclosed trailer where I want the 120 volt lights to work on inverted, but I also have a roof top A/C on the trailer.
No way around it, when hamstrung with an inverter.
Accept that there will be some imbalance, switch it to 240 and reverse course if it causes trouble?
Or, leave it alone and get a step up transformer for that one load?
Transformers are relatively inexpensive, vs some of the other mentioned solutions?
happy coaching!
buswarrior