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MultiPlus ii 12/3000 - System info, Shunt Size and Earthing Requirements


Please see attached drawing for my proposed system - I have already bought the Multiplus ii 12/3000 and 4 x Bosch L5013 Leisure batteries.

I have seen in the Victron wiring unlimited info that the 12/3000 may need a 1000a shunt, is that correct or will a 500A be sufficient? I was planning to buy a smartshunt.

Wiring to/from the inverter and battery bank interlinks are 2x50mm2 with 2 x 200A fuses to protect the inverter connection. Also a 300A on the negative side of the leisure battery bank to protect that from vehicle short. Are any other fuses required/too small or large/in the wrong places? Hopefully my drawing is clear enough!

Also I have read about it being undesirable to go from TT to IT in terms of earthing arrangement, do I just run the CU earthing to the vehicle ground which is also connected to the earth of the inverter? I presume the inverter deals with fault current by linking the neutral and earth internally when the shore power is disconnected?

Any advice relating to any of that is helpful, thank you in advance! Is a BatteryProtect a good item to add to the system also? Where would this go? is anything else worth adding? I want no displays internally, all off the phone if possible, to go in a 7m class A motorhome.


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Multiplus-IISmartShuntHelp
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2 Answers
kevgermany avatar image
kevgermany answered ·

Yes neutral and ground are connected automatically when no shore power.

No need to fuse negatives, better not to. Otherwise you may have positive still connected.

I don't see the need for a 1000A shunt in your system. What was the reason given?

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joe90k avatar image joe90k commented ·

Thanks, I had the negative fused to protect the battery bank from short to chassis, should I just omit this? Does the battery bank need any fusing?

The top of page 36 from the victron wiring unlimited guide says this:-

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JohnC answered ·

Hi @Joe90k

A 500A shunt will be fine, but not wired like you show in your pic, that's all wrong. I wouldn't worry with a Battery Protect, but I'd add a GX device like a Cerbo. Then use wifi rather than bluetooth, once you go there you'd never want to go back.

Take a look at the example schematics on the website. Indexed under the kit you're considering. Many are complex, but you can see what the pros do if you separate out the chaff. https://www.victronenergy.com/support-and-downloads/systems

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joe90k avatar image joe90k commented ·

Thank you for the system schematics, I had not seen that, the SmartShunt diagram is very helpful. Please can you elaborate on why the wiring is all wrong?

I don't have space for Lynx (I have also seen some others have issues running the 2x50mm2 in and out of it for the inverter and being forced to insulate the main terminal lugs with large heat shrink !! ) I plan to use two inline 200A mega fuse holders for the inverter to batteries, all thicker lines on the diagram including battery interlinks will be 2 x 50mm2 cabling. I plan to run a smaller 500A rated 4 way distribution block with fuses rated for the consumers they are protected. I can't see an issue, just that I haven't used everything Victron, all the components are rated correctly I believe, please correct me if I am wrong!

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JohnC avatar image JohnC ♦ joe90k commented ·
@Joe90k

In your pic the negative wires from the Multi bypass the shunt and go direct to the batteries. So the Multi won't get measured, either charging or consuming. I suspect you want to monitor the batteries, so you'd need to change that. ALL the -ve wires intended for the batts go through the shunt, including Ground (that's ok on your pic).

I didn't mention Lynx, and of course you can use other stuff in it's place. What I did suggest was a Cerbo GX, Victron's 'data hub'. That's another world.

Don't get too tied down with fuse sizes, etc. That will come, even with reading the manuals. What you really want to design is the end result, the part you see on your phone..

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joe90k avatar image joe90k JohnC ♦ commented ·

Thank you for pointing that out, I have revised the diagram. Apologies for my assumption. I now have only one larger ground cable with the shunt in between, the inverter would meet this at the 300A busbar, it would be connected so as no current from the inverter would travel through the bus bar - I am only concerned with fuse sizes etc as I am ordering the cabling and components to wire everything up. I am still unsure if a 500A shunt is adequate or if I should go for the 1000A the batteries are rated to 800 CCA each also.

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I have looked into the Cerbo, I now agree that is vital so I will order one. Thank you again. I have HDMI input on my Alpine headunit, I wonder if it will output a display on this. I also wonder if I still need the VE.Bus Smart Dongle with Cerbo or if I could return it as that would help to offset some of the cost of the Cerbo!

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JohnC avatar image JohnC ♦ joe90k commented ·
@Joe90k

The CCA is just a crank rating for your batts, not applicable here. If you reached >500A from the batts, the shunt just wouldn't measure it properly. And you'd blow your fuses. Should never happen.

You won't regret the Cerbo choice. 'Ethernet' cable will replace the need for the smart dongle. And wifi/ethernet is a big step up from bluetooth anyway. You'll need a VE.Direct cable for the Smartshunt > Cerbo, so grab one of those. Look at the Cerbo manual for all needed cables.

I can't say whether your existing kit is compatible, but the options are wide. The free VRM Portal and all the software will blow your mind.

I note too mention of 'Immersion' (water heater?). Take care, these can draw big power..

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joe90k avatar image joe90k JohnC ♦ commented ·

Thanks for your advice, the Cerbo certainly looks very good. Being able to return the BT dongle offsets the cost by £75 odd also. I will purchase the VE.Direct cable.


Page 36 of the Victron Wiring Unlimited Manuel that says a 500A shunt is not big enough for 12v 3000VA:-

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As you say the fuses for the inverter total 400A so I can't see it being an issue with 500A+ only being for very short bursts at most. I just don't want any issues down the line!

I mainly wanted the Multiplus ii for the pass through. This is due to the 230V 1KW immersion (Water heater) which will only be in use when connected to shore power and not via the inverter. However, the attraction was also the limit capabilities of the inverter in terms of shore power draw, where some camp sites have 6A or less before the on site breakers will trip. Hopefully I can control all of this through the Cerbo.


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