Inverter choice for an RV

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solarchain asked Oct 18, '19

Inverter choice for an RV

We have a small 19’ rv that we are converting to Solar/lithium. I am looking to find the most suitable Inverter for the upgrade. Here are some of the requirements..

1.] We would like to use two Leaf cells or two tesla Model S Batteries to create the battery bank

2.] We will only only have about 600 watts of solar that our rig can support as don’t want to be transporting any portable panels. When boon docking we calculate that over several days we will gradually draw down the batteries before needing the generator.

3.] The solar charge controller and the batteries are located together. About 15’ on the other side of the RV is the inverter which is housed near where the shore power comes in. There is 6ga wire to connect the inverter to the battery bank, so I would like to use 24v maybe even 48v so I don’t have to rewire

4.] for shore power we have a 30 amp connector near the inverter and are limited to a 2000 watt generator when boondocking. Otherwise we get a full 30 amp when connected to shore power. We need to be able to limit the charging from the generator as we don’t want to overload it when charging our batteries.

5.] The inverter needs to be able to draw from the batteries in cases where the generator is providing less than spikes for Air conditioner etc. , in our case we have about a 3k watt requirements in the RV max.

The inverter should be as small and light as possible I was thinking the Multiplus-II, but am not sure if the grid features would necessary, are there any other options I should consider?

Lithium Battery solar inverter current draw

2 |3000

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Murray van Graan answered · Oct 18, 2019 at 08:00 PM

How about a Quattro unit? You have two AC inputs on a Quattro, which you can separately program with different input current limits. So you could limit shore input say to 25A and the generator input to be below the 2kw generator limit. If you had a Multiplus, you would have to manually change the input current limit when switching from the one ac input to the other

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2 |3000

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solarchain commented · Oct 18, 2019 at 08:44 PM

Thank you for the response. the quattro looks good and will fit, as well this is about the same weight as the MultiplusII

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Answer 1 · 2019-10-19T22:50:28Z

Tom answered · Oct 19, 2019 at 10:50 PM

I am using a Multiplus 24/3000 70-50 110 VAC unit in my RV with two 5.3KW Tesla modules set up as a 24 volt system. I also have a BMS system installed. I do not think you can wire the leaf modules in a 24 volt battery that will work with a Multiplus. A 48 volt Multiplus or Quatro will play well with the Leaf but I have no idea where you are going to fit that battery in a 19 ft RV?. 600 watts of PV is not enough to charge a 8000-10000 watt battery (2 Teslas). Using a Quatro in a 19 ft RV seems like a waste of money to me when a $1500 3000 watt multiplus will do the job. You can possibly get by with one Tesla module and a Multiplus 24/2000 compact will do the job.

Yes I can power my rooftop 13500BTU AC with the Multiplus 24/3000 without issue(no need for a soft start) and with my 800watts of PV and 8kw of usable battery it will fun 6-10 hours. I can also fast charge my battery with my 30 amp Shore power or generator in about 5-8 hours at 50-70 amps.

Your other option to charge is using the alternator and a Smart Orion TR to get an extra 400 watts of charging power. Or the Buck Boost charger if you have a large size alternator that has extra power to do so.

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Answer 2 · 2019-10-20T20:51:09Z

solarchain answered · Oct 20, 2019 at 08:51 PM

Hi Tom, I appreciate your input. We are leaning toward using 2 Model C batteries which we have space for, is this what you used? .. With 600 watt solar we expect to run down the batteries but calculate that we will have about 5 days or so capacity while boondocking before this happens which is our target.

The wiring thickness with my existing cable may necessitate using 48 volt. This is because Airstream separates the Inverter from the Batteries and interconnects them using 6 gauge wire. It would be very hard to re-wire with heavier gauge wire. I do concur that a smaller inverter might be possible.

I have not decided on the BMS yet. I see some designers have opted for using relays vs. external BMS, my preference would be to use an external BMS as it would seem more flexible. Very curious as to the BMS unit that you ended up going with and how you found setting it up.

The boost charger is an interesting idea I will look into.

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Tom commented · Oct 20, 2019 at 10:43 PM

I am using two Tesla S 5.3hwatt 233 amp hour modules. From my research Tesla Model C modules can not be used. You need to match up the charge profile and operational range of the inverter charger with the battery module. The Multiplus 24/3000 or 48/3000 best matches the Tesla S module. I am using two Electrodacus SBMS0 one for each module for my fully automated BMS and it will work with all Victron Equipment for high and low voltage alert signals. The nice thing about the SBMS0 is it calculates SOC using two shunts on the positive cable, so there is no need to purchase the BVM712 as the functions are built into the SBMS0 and has a full color display and wifi as an option. I purchased two SBMS0 for less than $250USD.

My Multiplus 24/3000 is wired for 24 volts and operates in my full battery output of 19 VDC to 24.40VDC. The Tesla usable range is 18 VDC to 25.2 VDC, but to extend the life of each module I have it set up as listed. This provides me 8kw of power total but if I need more I can go as high as the full 10.6 kw. My Multiplus is mounted less than one meter from the battery modules so I can use 1/0 battery cables (55mm2) as recommended by Victron. Buy 600 amp welding cable as it is more flexible and besure to use a hydraulic lug crimper and do not solder the lugs.

The one issue with going to a 48 VDC system as you will need a solar array the will put out a minimum 60 volts and use a 48 volt MPPT which are more expensive. Also going 48 volts you can not install the Orion Smart TR battery to battery charger since they do not manufacture a 12/48 charger.

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