Tapping a shunt

[wmcunninghamii]

So I have a 500/50 shunt supporting a Xantrex batt monitor. Has worked fine for fourteen years,

About four years ago I purchased a Midnite Solar "Kid" SA charge controller. That unit has also worked very well.

Recently I purchased a small unit which attaches to the shunt and allows the Kid controller to monitor battery SOC and react appropriately in terms of charge voltages.

http://www.midnitesolar.com/productP...=5&sortOrder=9

Unfortunately the new device consists of a small CB with holes drilled to allow mounting directly to the shunt. I can mount the connections to the batt monitor to this device and basically use the shunt for both monitors..very cool.

But, the holes on the new device are not spaced properly to attach to the old shunt. It would be very easy to drill and tap another hole in the shunt post so the new device can be installed, but will doing so foul up the calibration of the shunt in any way. Electrically speaking the new hole distance from the old hole is utterly trivial, about 1/4 inch, but I know these things are designed to produce extremely low voltage drops in order to perform measurements so I wonder of my relocation of holes is going to impact these measurements.

Does anyone have any thoughts on this? A new shunt is going to cost $50. Not much but if I could drill/tap, the cost will be zero.

[timeout2]

the two ends are simply terminals. You should be able to drill and tap anywhere. In between the two terminals is the resistor (the actual shunt) Damage that and you will throw off the calibration.

[wmcunninghamii]

Originally Posted by timeout2

the two ends are simply terminals. You should be able to drill and tap anywhere. In between the two terminals is the resistor (the actual shunt) Damage that and you will throw off the calibration.

Ah, that is what I was hoping. I believe I can drill such that the resistor elements and their junction with the terminal are undisturbed. Thanks for the response.

[noelex 77]

You cannot drill or tap into the shunt material (the “wire”) that spans between the two large terminals. This is a calibrated resistance and removing material will effect the calibration.

You can drill or tap the two large posts without effecting the calibration, but this may slightly reduce the maximum current carrying capacity.

The Whiz Bang Jr is attached to the shunt by two bolts but these terminals only supply a very small current. You could mount the Whiz Bang Jr away from the shunt and use two small wires to connect these bolt holes to the shunt terminals. This will only work if the shunt you have has the same resistance as the Midnite shunt. This is 50mv / 500A

[wmcunninghamii]

Originally Posted by noelex 77

You cannot drill or tap into the shunt material (the “wire”) that spans between the two large terminals. This is a calibrated resistance and removing material will effect the calibration.

You can drill or tap the two large posts without effecting the calibration, but this may slightly reduce the maximum current carrying capacity.

The Whiz Bang Jr is attached to the shunt by two bolts but these terminals only supply a very small current. You could mount the Whiz Bang Jr away from the shunt and use two small wires to connect these bolt holes to the shunt terminals. This will only work if the shunt you have has the same resistance as the Midnite shunt. This is 50mv / 500A

Excellent info. i do have the correct shunt value but incorrect hole location. I considered the supplemental wire attachment but I really want to keep the install clean and do not want to risk any cal issues so will definitely stay away from the resistor array.