Running Multiple Gauges off a single shunt

[Freddmc]

Is it possible to run more than one gauge (where each requires a shunt)off a single shunt providing they each require the same size shunt?

Regards

Fred

 

[FilterGuy]

I have never tried that, but it might work. The gauge is reading voltage across the shunt and nothing jumps out at me that says a 2nd gauge would impact the measurement.

I posted the following on a different thread.

A battery monitor is watching the voltage across a shunt hanging off the battery minus. A shunt is nothing more than a very low value resistor of a known value. Consequently, the monitor can use ohms law to calculate the current: Vs=I*R. ( Vs is the measured voltage across the shunt, I is the current and R is the known resistance). Note that in one direction the voltage will be measured as a positive value and in the other direction it is a negative value. This means the monitor knows if the current is going into the battery or coming out of the battery. By tracking the current in and out over time it knows the Ah SOC of the battery. Since the Monitor also has a line to the battery+, it can also calculate Watts and Watt Hours using Watts Law: P=I*Vb (P= Power in Watts, I=the calculated current and Vb = the measured battery voltage)

If you run two gauges, make sure the B+ line is seperate for each gauge. This line is drawing current *and* measuring voltage so doubling the current could impact the voltage measurment.

 

[John Frum]

should be easy to test

 

[BiduleOhm]

Given the shunt is an extremely low impedance source you can put 100 gauges if you want. But you need each gauge to have its own wires if you want to keep the same accuracy

 

[FilterGuy]

Given the shunt is an extremely low impedance source you can put 100 gauges if you want. But you need each gauge to have its own wires if you want to keep the same accuracy

The gauge should be extremely high impedance, so there should be very little current through the wires coming off either side of the shunt, consequently, the voltage drop across those lines will be extremely low. You could *probably* get away with sharing those lines, but why take the chance. Do what @BiduleOhm suggest and run separate lines.

 

[BiduleOhm]

The gauge should be extremely high impedance, so there should be very little current through the wires coming off either side of the shunt, consequently, the voltage drop across those lines will be extremely low. You could *probably* get away with sharing those lines, but why take the chance. Do what @BiduleOhm suggest and run separate lines.

Yes, exactly what I was thinking when writing my post Thin wire like the one on the gauges is very cheap so no point in sharing them.

 

[FilterGuy]

Since we are talking about shunts and gauges.... here is some info on the shunt that comes with the AiLi gauge that Will reviewed.

 

[FilterGuy]

The Battery + connection to the shunt is just for routing B+ to the gauge through the common cable. The B+ is not used on the shunt.

Also, I need a slightly longer cable between the shunt and the gauge. I will be using shielded 2 twisted pair to make the longer cable.
Twisted pair 1: B+ and B- power wires.
Twisted pair 2: B- and P- Sense wires.
It will also be a heavier gauge wire than the original cable. (The original is 26awg)

 

[FilterGuy]

Something I just realized, When I hook this up I need to put a small fuse where the B+ hooks to the battery. A short anywhere along those small wires will quickly turn them into smoke....and maybe fire.

 

[BiduleOhm]

The Battery + connection to the shunt is just for routing B+ to the gauge through the common cable. The B+ is not used on the shunt.

Also, I need a slightly longer cable between the shunt and the gauge. I will be using shielded 2 twisted pair to make the longer cable.
Twisted pair 1: B+ and B- power wires.
Twisted pair 2: B- and P- Sense wires.
It will also be a heavier gauge wire than the original cable. (The original is 26awg)

I don't see a problem with that, it should work nicely, but don't forget to connect the cable shield (on the shunt side only)

Something I just realized, When I hook this up I need to put a small fuse where the B+ hooks to the battery. A short anywhere along those small wires will quickly turn them into smoke....and maybe fire.

Very good idea.

 

[ghostwriter66]

The answer is YES ....

You just need to ensure that your meter settings isn't relying on the SHUNT being specifically tuned to THAT meter/monitor ... some are (like Chargery) -- some aren't .. But on some of our systems we have multiple monitors (bluetooth and hardwire) that are using the same shunt monitoring various things .....