ncserenity avatar image
ncserenity asked

500 Amp Smart Shunt...

Do you have to run the smaller power supply cable directly to the battery terminal or can you hook it to any constant 12v terminal. Wasn't sure if this cable measures voltage of the battery bank or is just a simple power supply? Trying to avoid digging out a bunch of caulk to get the red wire outside the trailer....

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

1 Answer
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

It must be connected to the battery. It is used as power supply but also for measuring and calculation.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

grantj avatar image grantj commented ·

With respect, Mr. Lange - could you explain further on this design? If the supplied VBatt+ cable must only be connected to the battery positive to be measured, then one would assume that it's length (resistance) would be critical - yet, in the Smart Shunt installation manual, there is no mention or prohibition on extending this cable to reach the battery in question. If extending the VBatt+ cable is in fact NOT permitted, this would restrict the location of the Smart Shunt installation significantly, as the cable is relatively short.

My understanding of the shunt principle is that it is uses the voltage drop measured across the NEGATIVE connections to calculate current. How does the Smart Shunt measure anything through the VBatt+ wire?

It seems unlikely to me that connecting the VBatt+ wire to, for example, a battery switch post that is connected directly to the battery positive by perhaps a 1m length of 4/0 AWG cable, has any electrical effect at all on the function of the Smart Shunt.

0 Likes 0 ·
Matthias Lange - DE avatar image Matthias Lange - DE ♦ grantj commented ·

The current measurement is done on the negative across the shunt. The small red wire is for the voltage measurement and power supply for the electronics of the Shunt/BMV. The power consumption of the Shunt/BMV is very small (around 1mA) and therefore there is almost no voltage drop at that part.

0 Likes 0 ·
grantj avatar image grantj Matthias Lange - DE ♦ commented ·
Thank you for your quick response (especially given the time zone difference!) So, to clarify, would it be correct to say "The Vbatt+ wire should be connected to the positive post of the battery, OR, other suitable location near the battery that avoids any measurable voltage drop on the Vbatt+ connection to the Smart Shunt" ?

As a practical matter, installers are often faced with installation instructions that recommend (either by text or diagram) a DC power source directly to the battery post. While this may be theoretically optimal and eliminate potential issues if sourced elsewhere in the system, it is seldom practical, or in my experience, required. A properly fused and appropriately gauged connection point, near the battery, is often preferable and reduces the "rats nest" of wiring and multiple terminals at the battery posts.

0 Likes 0 ·
Matthias Lange - DE avatar image Matthias Lange - DE ♦ grantj commented ·
If you can ensure that the voltage drop to the point you want to connect the red wire is minimal it should be fine.

But the best would be to connect it as close as possible to the battery terminal.

A main battery fuse and/or a main switch should also be close to the battery.

Connecting the red wire after the main switch will reset the SOC reading of the shunt every time you switch the system off.

0 Likes 0 ·

Related Resources

Additional resources still need to be added for this topic