I’m not finished yet, but check my design for this small travel trailer electrical system overhaul so far and let me know if there’s anything that needs to be changed or added.
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A small revision.
Is one panel supposed to be connected the 75/10 and two to the 100/50? Or is the mix of different panels intentional on the one mppt?
What size battery cable are you using from the Multiplus to the bus bar?
I may not really use the 75/10 MPPT. I just already have it for controlling a single panel already on my trailer so I was thinking about using it for a ground deploy, but it wouldn’t go too far. The 3 panels in the diagram would all be on the one (new) MPPT controller.
I haven’t calculated the wire size from Multi to bus bar yet. It needs to power the DC loads (30A) and carry the solar current back to the batteries (50A). I may also add an Orion XS for alternator charging and bring them in through that bus bar so that would be another (<50A) current.
One question I have is the sensibility of using the Multi’s 2 DC posts like I am. I’m using them like a mini bus bar - one post is the 70mm2 (2/0 AWG) cable to the battery and the other goes to the bus bar. Any problem with that?
Hello,
the priciple is OK, just missing some additionnal circuit breaker with DC load.
I use the Smart protect in my case…
Perhaps some temperature control with addtionnal ventilation.
Did you consider using 24V storage instead of 12V ? (Could be somehow cost effective to swtich to 24V)
Xavier
No need to the manuals on the product page give the manual for install and these have recommended battery cable and fuse sizing.
The same is true for the mppts.
Take the time to look them up and revise your design.
I am a separate bus bar fan myself. It has many advantages over lug stacking.
I see where the manual specs the cable size from Multi to battery, but not from multi to bus bar (load, solar, etc.). Wouldn’t that depend on load and the amount of solar?
I’m using 6mm2 (10 AWG) for all solar cables per math (and per recommendation from Explorist.life).
I wouldn’t be stacking lugs. The Multi has two positive and two negative studs so each lug would have its own stud.
6mm2 is too small for a 50A MPPT controller. This will need a fuse of at least 60A with the correct headroom over max continuous current. This then means 6mm2 is too small, you need at least 10mm2.
You show a 430W panel in series with 2 x 200W panels in parallel. For this system to work efficiently, the Imp of the 430W panel needs to be approximately twice the Imp of one 200W panel. If this is not the case, the lower current will be limiting.
The 3000VA 12V Multiplus has a recommended minimum battery size of 400Ah but 300Ah of lithium may suffice. The recommended cable from battery to Multiplus is 2 x 50mm2 with a 400A fuse. This is from the Victron manual. This is sized based on ripple voltage not voltage drop per se. This would mean you do not have a spare terminal. Personally, I would not use the chassis for these return currents but would wire back to the shunt. Partly this may come from my experience being from steel hulled boats.
Thank you for all of the feedback!
I see my mistake. I was using 6mm2 for even the battery side of the MPPT controller. The current on the PV side should be fine for 6mm2 but on the battery side I need more. The MPPT will be installed near the battery so that should be an easy run.
I did balance the voltage of the 430W and the 2x200W. Should be good.
Thanks for pointing out the spec in the manual that the Multi wants 2x50mm2. Any idea why they call for the double cable run instead of a larger cable? Ampacity of a 70mm2 (105°C, free air) is 270°C. That’s awfully close to the peak load of the Multi. I’m tempted to use what I’ve got. Advice welcome.
The DC load in my diagram is the existing DC panel of my trailer. It has a battery fuse, branch fuses, and a reverse polarity fuse. I think that’s enough, but if I could use more, do let me know.
The ship has sailed on the 12/24V decision. I did consider. It was close. I am (mostly) happy I went with 12V 
The cable size is for ripple as pointed out previoulsy. The unit will alarm or shutdown if its too high 1.5 - 2.5V. You can measure ripple with an AC multimeter on the DC terminals. Load it up and see what you get. 2 x 50mm? They are european engineers, maybe 95mm2 was not good enough.
Ha. Full disclosure, I speak AWG by birth but I’m trying to turn a corner and use the more sensible system (mm2). I’m not yet used to it. I wondered if the lug of a 70 or 95 might be to large for the stud on the multi.
I am not sure what the daly BMS is capable of but the 5500w peak will blow that 300A fuse. If you install the ESS assistant you can set the max inverter power to 3600W to be safe.
Ah, right. Thanks. That fuse was supposed to be 400A. Thanks for the recommendation on checking out the Daly. You sent me on a big research mission to figure out BMS current limits. Daly does make a 300A BMS but it’s $200 and that puts the cost of a DIY battery with BMS over the packaged batteries I’m finding. I’m currently looking at the WattCycle 12V 280Ah for $480. Thanks too for the note about the ESS assistant. I need to go learn more about that.
I think they are pretty good. In Australia, they are $719 AUD. I have built some big 12V batteries the last one I did had 340AH cells and a JBD BMS from aliexpress and this battery box in the link below was about $550 AUD total. I don’t think you can go wrong with the Wattcycle but may lack access to the BMS settings and Bluetooth I am not sure.
On the Solar panels, the 430W and 200W x 2 are in series, in this case you balance current not voltage. Double check the specs. You balance voltage if they are parallel.
The 2 x 50mm2 is probably to make it easier to get the cable and lugs in.
Thank you. I need to rearrange those because I meant to put the two 200’s in series and then parallel those with the 430. New diagram coming soon.
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Hello - this looks great but I have two questions.
- On your Smart Shunt, shouldn’t you have all your DC loads running on the opposite side of your NEG terminal on your Shunt so that it can accurately represent your current usage?
- If this is a travel trailer (I have one with full Victron integration), you might consider adding a Victron smart DC-DC charger so you can take advantage of an additional 200W of charging from you tow vehicle while you go down the road. This is connected in to the 12v line coming from your 7-way plug and prevents your lithium batteries from pulling too much current from your tow vehicle as well, get the 'isolated" model for this application.
Overall, good setup. You will enjoy the system.
Brian
The SmartShunt has all the loads and chargers on the load negative connection, the chassis is being used as the negative path. It will work correctly. It may be better connecting the negative bus to the smartshunt rather than the chassis but that is not because of incorrectly reading SmartShunt.
Sorry for the delay. Here’s the updated diagram.
- main fuse is 400A instead of 300A.
- there’s an actual wire connecting the Multi and the battery (instead of going through ground)
- the solar panel configuration is fixed with the two 200W panels in series and then in parallel with the 430W
- added a DC-DC for alternator charging
- replaced the raw cells and BMS with a battery (currently looking at the WattCycle)
- still missing some wire sizes and lengths
You still have 6mm for the 100/50 it needs 10mm to the battery. The DC-DC charger will need a USB to ve direct cable which I think you already know but checking as its going to the USB. The DC DC charger will need 10-16mm cable.