Panel to power off inverter. Will only work on shore, or generator now.

[Scari]

We have a 2003 Newmar Dutch star 3893. We just installed our solar system. 1580w of solar, 600ah lithium batteries and a Multiplus ii inverter. We also installed soft starts on our two dometic penguin air conditioners. We have 10/2 romex, line in and line out from the inverter to the panel on the left only. Our coach is wired to only run the panel on the right, (Which has the air conditioners) when hooked up to shore power, or running the generator. We were thinking of some sort of relay, or transfer switch to combine the panels. We don't want to double the power on the left panel, or to feed back power to the inverter. What would we need? How would we do this?

 

[mopat]

I believe those Dometic ACUs draw about 13 amps, not sure how long it will run on solar & battery.

Don't see your inverter output wiring or generator output wiring in photo but I guess you could wire in a

Progressive Dynamics PD52V 5200 Series Automatic Transfer Switch - 240 VAC, 50 Amp​

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[Scari]

Thanks for the suggestion. We figured about 6 hours on the air conditioners. We ran 8awg cable from the panels to the mppts, to limit line loss and to charge faster-in theory.
We have a transfer switch for the generator and shore power for the panel on the right. (Here's a picture of the wiring in the current transfer switch.)
We can't possibly be the only people who have an older rig and ran into this issue.

 

[rickst29]

Your current 50A input is 120/240V single phase, with two hot wires offering 120V versus the "netural wire" and 240V when connected in oppostion to each other. Each of those hot leads (the big wires, black and red) runs only ONE air conditioner. Does your Generator run both AC units (120/240V output), or only one "side"?

If your generator creates 120/240 "split phase", then your Victron must be the Multiplus-II "dual 120v" model (in order to handle this in a roughly correct way, attempting to run BOTH air conditioners from only the one Inverter. With the "dual-120v model", there is a 4-wire input terminal, with 3-wire outputs. Each output corresponds to ONE of the hot wires, red or black, 120/240V is being supplied by "the grid" (or by a generator capable of doing that). When the Victron finds no Voltage on the input wires, it activates the Inverter. The Inverter is only 120v, not 120/240v, but it will "bridge" the two outputs together.

Your right-side picture isn't implemented with that Victron model. It shows only a "one-sided" Victron connection, with a circuit breaker feeding the Victron (input side) from the big RED wire wired into the RED power supply lead.

In any case, the AC units would both need to moved from the current breakers fed by the "Grid" hot wires, and be connected to Victron 120V output legs instead. I don't know if your Victron is big enough to run both AC units, because you didn't state which model you have.

 

[rickst29]

13A of average draw from the Dometics is about 1600 watts each . (Momentary compressor start peak loads are MUCH higher, but possibly moderated by your "soft start" units). Your "1580 watts" of Solar won't do 1580 watts, unless they're mounted at an angle towards the sun AND you are measuring them on a wonderful June near 1 PM Daylight time. For midafternoon on a flat-mounted RV roof installation, you might actually get 700 watts or so. (That's pure SWAG, of course.) So your shortfall in running one air conditioner, which must come from the Inverter, is around 1000 watts. The Multiplus-ii inverters have excellent efficiency, input from the battery bank (to supply 1000 output watts) might be as low as 1100-1200 watts.

Is "600Ah" @ 12V, 24V, or 48V ? We need to convert that to watt hours as follows: 600Ah * 12.8 discharge volts = 7680 watt-hours. One AC unit (assisted by all of the Solar) needs around 1150 watts, so you could theoretically last about 6.7 hours (running the batteries from 100% full to totally dead). You won't get all of the solar for the whole 6+ hours, and you won't want to destroy the battery - reserving 40% of battery capacity for other things (and not running the battery too low) cuts that capacity to only 4600 watt-hours, so you're probably down to something less than 4 hours.

Since you want to run both AC units (if the Victron can do that) you will spend (maybe) 3200 watts. Solar contributes only the original 700 watts or so, leaving a shortage of 2500 watts. 4600 watt-hours divided by 2500 watts is barely 110 minutes, if the battery bank is "12V".
- - - -
But you can double that time if your battery bank is "24V", and double it again if your battery bank is "48V". A friend of mine runs his single AC unit all day long from a 16S "48v" battery bank of "304Ah" cells, with no problem.

 

[Scari]

We have 1580w of solar, 600ah lithium batteries and a Multiplus 2 inverter. Our 8kw generator runs both air conditioners.
Would moving the output legs to the inverter isolate it from the generator and shore power?
It is a 12v system. The soft starts take out about 75% of the starting wattage out of the air conditioners, so we don't get that, 'kick.'
We have battle born lithium batteries. You can run them down 100%, but the bms will kick in, I think, when the battery has 20% left.
We are going to see how far we get running both air conditioners. Depending on how long we get, we will run one air conditioner and use a fan to push the air down the rig. Our generator also charges the batteries, so if need be, we can run the generator for a few hours.
I think another transfer switch is the way to go. Transfer switch the transfer switch.
There are no instructions to installing solar. This has been an interesting learning experience. Hopefully, after we install the battery isolator, this panel issue will be the last thing we need for solar.

 

[Scari]

Just wanted to let everyone know what we ended up doing, in case someone else has an older rig with the same set up. We have the multiplus 2 and we weren't using it to it's potential. We ended up running 2 cables of heavy duty, stranded, 6/3 under the rig, because the transfer switch and multiplus are on different sides of the rig. We used din rails in combiner boxes to mush everything together. This way we used line 1 and 2 of the multiplus and the transfer switch, to get the multiplus to do it's job combining both the 30 amp panel and 50 amp panel. We now can have 50 amps of power available, instead of 30. The generator is charging the batteries and still running the panel when on. The BIM is also working now. It's also charging the batteries off the alternator and don't have to worry about incorrect voltage. Whew!
It's working beautifully. I have to add that we had to blow 2 additional holes in the transfer switch bay and the inverter bay for the cables. Running cables under the rig wasn't too bad. (Besides getting extremely dirty.) We found a cable run that we followed and used heavy duty zip ties to manage the cables.
I think for now, our hands-on solar education is finally over-until the next problem pops up.

 

[Zil]

You have a transfer switch for the shore / generator. You need a transfer switch for the inverter / (gen/shore). Even a manual switch would work. There are inverters that can grid tie. That is beyond my experience.