question

grayjp5 avatar image
grayjp5 asked

Smartshunt Lug Size

I am contemplating installing a Smartshunt 500A to monitor my house battery (and possibly running battery on the alternate channel). I've looked through the manual and it specifies that the 2 bolt terminals on the unit are M10 in size. This would correlate to a 3/8" lug. So why on earth would Victron make the studs this size? It is standard practice that positive terminals are sized at 3/8" and negative terminals are sized at 5/16". At least that is the case in the US. In wiring this I would start at a 5/16" (aka M8) terminal at the battery, step up to 3/8" (aka M10) on both Smartshunt terminals, then back down to 5/16" at the bus bar. This would require custom cables of course. Is this really the way that Victron designed this unit, or am I misinterpreting something?

battery chargingBMV Battery MonitorSmartShuntAGM Batteryterminals
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6 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

This is how the shunts are since ... forever(?). At least 15 years or more.

I don't see a problem there, we always make individual cables for the systems we install.

And I'm pretty sure that you can also buy cables with M8 on one end and M10 on the other end.

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seb71 avatar image
seb71 answered ·

Are you asking if the manual is correct about M10 bolts on SmartShunt 500A? It is.

This is designed for high currents (for a long time), so I don't see a problem of using larger bolts.

If you are DIY the busbars, you can bolt the negative one directly to the SmartShunt.

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grayjp5 avatar image
grayjp5 answered ·

I appreciate your response. But why add that complication? Was it just poorly engineered? Since either end separate from the shunt is 5/16" (as it should be) there would seem to be no reason at all for this (i.e. capacity). I haven't been able to find any M8 - M10 "jumper" cables available.. :-0

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hjohnson avatar image
hjohnson answered ·

Every 500 A shunt in my system is 3/8” lug sized (and yes, there are 4 shunts… I’m an instrumentation geek). Only two of those are from victron.

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It must stem from perhaps being spliced into the positive side or something, and now "that's just the way it's done" lemming mentality follows? Putting 3/8" lugs (as in the shunt) between multiple 5/16" lugs does nothing for anything (except for the manufacturers of custom cables). Similarly splicing a couple inches of 2/0 wire into a 20' stretch of 20 gauge, doesn't make it 2/0...
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trevor-bird avatar image
trevor-bird answered ·

I’m very happy M10 is used both ends. A 500 amp device needs bigger than M8. We have never done an installation with only one battery and always custom make the cables anyway.

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Pretty senseless to use M10 for these other connections since the battery terminal is M8. Don't you think?
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Not all battery terminals are the same. There are batteries with different size terminals: M6, M8, M10, etc.

Some SimpliPhi are M10.

Some Victron are M10.

Some BYD are M10.

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Not, not at all. The smartshunt carries the current for the entire system. A battery carries the current for one battery. If several batteries are paralleled the current capacity of the bank is much more than the current capacity of one battery. The size of the terminal on one battery is completely irrelevant when considering the size of the lug on a shunt. Very few ( in fact in my experience never) has the smartshunt simply been connected to one battery. Further to that, when making custom cables, the size of the lugs is simply a choice to be made, not a big deal.
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seb71 avatar image
seb71 answered ·

Also a M10 bolt is NOT the same as a 3/8 bolt. They are close in size, so can be used for the same lug (so same through-hole size), but do not try to screw a M10 bolt in a 3/8 nut.

And M8 is NOT 5/16".

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Yes, correct, the thread pitch is different on metric.
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