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Travel Trailer Generator Backup Question

Hello, I just wanted to ask if this setup sounds correct for a backup with a generator. I have a travel trailer with a 1600W air conditioner (3900W Startup). I want to have a 2800W generator to back up in case of loss of shore power. I am looking at the Multiplus 3000W 12V to 120V, and a 60A MPPT to handle the 800W of solar into 2400W of lifepo4 battery. The generator has an autostart feature that works when it senses a closed loop. So, my idea was to have the inverter installed normally with AC coming in from a Automatic Transfer Switch. I would have a rely that would close when shore power is lost thereby closing the loop and starting the generator. The ATS would switch to generator power and send it to the multiplus. Does this sound workable?

My questions are about the battery charging. Since I will be charging from solar and the multiplus, is there a way for the units to communicate so as to not send too much current from both units together? Any other devices I should have besides the multiplus, solar controller, and ATS?

Thanks!

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Jeremy Albrecht avatar image
Jeremy Albrecht answered ·

You said “2400W of lifepo4 battery.” Did you mean 2400Ah?

If so, that’s a ton of battery. Your A/C will happily run off your Multiplus (mine is doing so in my Airstream at this moment as I hurtle down the freeway typing this (my wife is driving!). I’d set the generator start from a relay on the MP (or a Venus device) driven by low battery SOC combined with a loss of A/C input.

For additional details on my system, it’s 600W of solar feeding an MPPT150/85 into an MP12/3000/120-50. Battery bank is 6 105Ah Lion Energy LifePO4s. There’s also a Renogy 60A DC-DC charger hooked to the truck via 2AWG and Anderson Powerpole connectors to help with the AC load while on the move, but that’s not relevant to your situation.

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cappyjax avatar image cappyjax commented ·

That was a typo. I meant 2400Wh of battery. One 12V 200Ah battery.

I think I have decided to skip the generator idea and just go with all batteries. I am looking at getting some used Tesla modules. They have to be some of the cheapest Wh batteries on the market. I am going to buy two modules and get a BMS to work with them. That will give me 10.6kWh of storage. I can then add modules in the future. I think I have room for four stacked, so that would give me 21.2kWh. However, with the Multiplus, I believe only about 80% is useable. Still is plenty for a couple days of running the AC.

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David Blackwell avatar image
David Blackwell answered ·

Your wattage profile sounds similar to my Dometic Cool Cat 10.5k btu air conditioner on my Aliner popup. My surge load was about 5300 watts (0.5 seconds) and then about 1100 watts for the rest of the compression cycle.

Last year I was also struggling to come up with a way to power my A/C unit instead of lugging around 2 generators. After a lot research I found soft start capacitors made by www.microair.net.

There are several companies making similar devices but I liked the way their product creates a profile of the energy demanded by the compressor. Although it takes about a minute to ramp up, instead of 5-10 seconds, I can now run the system with one Honda 2000 generator.

If that's the primary criteria driving your system design, reducing the watts required, can make a big difference in the weight/money in creating a system that works for you. Best of luck in your project.

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cappyjax avatar image cappyjax commented ·

Thanks! I decided to skip the generator idea and just go with about 10K of lithium ion batteries. That, along with the solar, should give me around 8 hours of AC run time. Would I still need a soft start with the 3000W Multiplus?

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cappyjax avatar image cappyjax commented ·

Here is what I have laid out so far. Any advice would be appreciated.

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rv-setup.jpg (2.3 MiB)