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steve9900 avatar image
steve9900 asked

longer bolt for BMV 712 shunt

I am installing a 712 shunt and will connect a negative 4/0 cable with lug from the Multiplus 3000 to the load side. For a few more smaller connections, I will add a busbar connected to the shunt with 4/0 cable. But I was told that it’s best if the Multiplus cable is connected directly to the shunt and not a busbar. With a 4/0 short cable to the busbar, that makes two 4/0 lugs connected to the shunt bolt, which is short and there is not a lot of thread to screw into the shunt. Enough to tighten but not very deep. I can buy a 20mm long M10 brass bolt to replace the bolt that came with the 712. Is that a good solution?

BMV Battery Monitor
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6 Answers
pstover avatar image
pstover answered ·

I'm installing a BMV 712 with 500A shunt now, and needed a longer shunt bolt on the non-battery side. The original bolt is 15mm long. I found what I think is a high quality equivalent that is 20mm long. The extra 5mm allows me to stack three lug rings plus the lock washer and flat washer, and still seat 5mm of bolt length into the shunt base. This is working for me, but it may not work for everyone since each lug ring needs to be offset (or flipped upside down) to seat flat together. Depending on your installation, there may not be enough room around the shunt to stack like this anyway.


Here's the link to the bolt I purchased. Cost with shipping was $11.92, so I paid more for shipping than the cost of the bolt.


https://www.mcmaster.com/93270A620



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Mark avatar image
Mark answered ·

Why not use the Victron Lynx busbar system, it is designed to have the multiplus mppt etc connected to it!.


https://www.victronenergy.com/dc-distribution-systems/lynx-distributor

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Mike Dorsett avatar image Mike Dorsett commented ·
money. I use some 400A busbar each side of the shunt to connect all cables to. The shunt bolts were replaced by stainless M10 x 20.
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steve9900 avatar image
steve9900 answered ·

I didn't know about it, but at $200, that's a bit more than the under $40 cost of my 250A busbar and a couple of cable lugs, which I've already purchased. Someone suggested I use a junction post, which is $10 and I can buy a longer brass bolt for about $3. I only need add two more negative cables beyond the multiplus.

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Mark avatar image
Mark answered ·

Yes you could purchase a longer brass bolt, however if you have many connections I recommend to use a busbar, rather than stacking multiple connections on the single joint.

Just beware of cheap brass bolts on eBay/from overseas as they may not be real brass - best to get one from a local engineering supplies (note that brass bolts are now getting a little harder to find).

In my own system I have 2 battery banks in parallel and to ensure identical resistance I made up my own adapter plate out of 1/2" brass plate - with 1x 10mm through hole and 2x M10 tapped holes, directly bolted to the shunt (see below).


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Mike Dorsett avatar image
Mike Dorsett answered ·

@mvader (Victron Energy)

I also find the bolts too short. I have a 500A shunt, and in trying to attach 400A busbar (25mm x 6.3mm thick) to the shunt, one bolt just caught, the other was just FLUSH with the busbar when the washer and spring washer are attached. It looks like no allowance has been made for lugs or busbar thickness. I'm going to have to find some stainless M10 bolts to cut to the correct length...

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Jeff Jensen avatar image
Jeff Jensen answered ·

Thank you @pstover for the link. My bolts got here today. Some pictures. The bolt with the lock washer is fully bottomed out in the shunt.20220830-103314.jpg


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